Influence of folic acid on postprandial endothelial dysfunction. Sialorrhea, or excessive salivation, may be perceived as vomiting, but it could be related to eating too quickly, too much at once, or dry foods. Br J Nutr 3: These concerns should be discussed with your health care provider prior to any treatment so that you have proper informed consent and understand that there are no guarantees to healing. Cancer Res 53 Dev Med Child Neurol 42 3: Am J Clin Nutr 85 3:
Pregnancy The calcium content of the newborn infant is about 24 g mmol. Most of this calcium is laid down in the last trimester of pregnancy, during which the foetus retains about mg 6 mmol of calcium daily There is some evidence that pregnancy is associated with an increase in calcium absorption [associated with a rise in the plasma 1,25 OH 2 D level] For a maternal urinary calcium of mg 3 mmol and a maternal skin loss of 60 mg 1.
Even at optimal calcium absorption, the corresponding calcium intake would need to be mg A lactating woman produces about ml of milk daily, which represents about mg 7. If calcium absorption efficiency is maximal i. However, although it is known that bone is lost during lactation and restored after weaning 73,74 , early reports that this bone loss could be prevented by calcium supplementation 75 have not been confirmed in controlled studies The prevailing view now is that calcium absorption does not increase and may decrease during lactation.
It is increasingly thought that lactational bone loss is not a nutritional problem but may be due to parathyroid hormone-related peptide secreted by the breast 79 and therefore beyond the control of dietary calcium. In view of this uncertainty, we do not at present recommend any extra calcium allowance during lactation; any risk to adolescent mothers is covered by our general recommendation of mg for adolescents.
Upper limits Because of the inverse relationship between fractional calcium absorption and calcium intake Figure 15 , a calcium supplement of mg 2.
Urinary calcium also rises very slowly with intake slope of percent and the risk of kidney stones from dietary hypercalciuria must therefore be negligible. In fact, it has been suggested that dietary calcium may protect against renal calculi because it binds dietary oxalate and reduces oxalate excretion 80, Toxic effects of a high calcium intake have only been described when the calcium is given as the carbonate in very high doses; this toxicity is caused as much by the alkali as by the calcium and is due to precipitation of calcium salts in renal tissue milk-alkali syndrome However, in practice we recommend an upper limit on calcium intake of 3 g 75 mmol.
Comparisons with other recommendations Our recommendations in Table 31 can be compared with the current recommendations of Australia, the United Kingdom, the European Union, and the United States and Canada in Table Our recommendations for adults are very close to those of the United States and Canada but higher than those of the United Kingdom and Australia, which do not take into account insensible losses, and higher than those of the European Union, which assumed 30 percent absorption of dietary calcium.
The British and European values make no allowance for ageing or menopause. Recommendations for other high-risk groups are very similar in all five sets of recommendations except for the rather low allowance for infants by the United States and Canada. Nonetheless, and despite this broad measure of agreement, we have some misgivings about the application of these recommendations, all of which rely ultimately on data from developed nations, to developing countries where other dietary constituents - such as animal protein and sodium - and environmental factors may be very different.
We shall therefore in the next sections briefly review current knowledge about the prevalence of osteoporosis across racial national boundaries and its relevance to calcium requirement. Ethnic and environmental variations in the prevalence of osteoporosis Intakes of calcium have been known for many years to vary greatly from one country to another, as is clearly shown in FAO food balance sheets Table Until fairly recently, it was widely assumed that low calcium intakes had no injurious consequences.
At that time, osteoporosis was still regarded as a bone matrix disorder and the possibility that it could be caused by calcium deficiency was barely considered.
The paradigm has changed since then. Calcium deficiency is taken more seriously than it was and the apparent discrepancy between calcium intake and bone status across the world has attracted more attention. In general, recent investigations have sought for evidence of low bone density and high fracture incidence in countries where calcium intake is low; rickets has not been looked for, but the low calcium rickets recently reported from Nigeria 83 will no doubt attract attention.
This issue can be considered at several levels. The first level is genetic: Is there a genetic ethnic difference in the prevalence of osteoporosis between racial groups within a given society? The second level might be termed environmental-cultural e. Is there a difference in the prevalence of osteoporosis between national groups of similar ethnic composition?
The third level is environmental-geographical e. Is there a difference in the prevalence of osteoporosis between countries regardless of ethnic composition? At each of these levels, the prevalence of osteoporosis can in theory be determined in at least two ways - from the distribution of bone density within the population and from the prevalence of fractures, notably hip fractures.
In practice, hip fracture data or mortality from falls for elderly people which has been used as a surrogate [ 84 ] are more readily available than bone densitometry. Ethnicity Comparisons between racial groups within countries suggest substantial racial differences in the prevalence of osteoporosis.
It was later shown that hip fracture rates were lower in blacks than Caucasians in South Africa 86 and the United States These observations have been repeatedly confirmed 88,89 without being fully explained but appear to be genetic in origin because the difference in bone status between blacks and Caucasians in the United States is already apparent in childhood 90 and cannot be explained by differences in body size The difference in fracture rates between blacks and Caucasians cannot be explained by differences in hip axis length 91 ; it seems to be largely or wholly due to real differences in bone density.
Comparisons between Caucasians and Samoans in New Zealand 92 have also shown the latter to have the higher bone densities whereas the lower bone densities of Asians than Caucasians in New Zealand are largely accounted for by differences in body size In the United States, fracture rates are lower among Japanese than among Caucasians but may be accounted for by their shorter hip axis length 93 and their lower incidence of falls Bone density is generally lower in Asians than Caucasians within the United States 95 but this again is largely accounted for by differences in body size The conclusion must be that there are probably genetic factors influencing the prevalence of osteoporosis and fractures, but it is impossible to exclude the role of differences in diet and lifestyle between ethnic communities within a country.
Geography There are wide geographical variations in hip fracture incidence, which cannot be accounted for by ethnicity. In the United States, the age-adjusted incidence of hip fracture in Caucasian women aged 65 and over varied with geography but was high everywhere - ranging from to per per year Within Europe, the age-adjusted hip fracture rates ranged from to per women in one study and from to per in another study 97 in which the comparable rates were In another study age-adjusted hip fracture rates in women in 12 European countries ranged from 46 per per year in Poland to per in Sweden, with a marked gradient from south to north and from poor to rich.
In Chinese populations, the hip fracture rate is much lower in Beijing per than in Hong Kong per , where the standard of living is higher. Thus there are marked geographic variations in hip fracture rates within the same ethnic groups. Ethnicity, environment, and lifestyle The conclusion from the above is that there are probably ethnic differences in hip fracture rates within countries but also environmental differences within the same ethnic group which may complicate the story.
For international comparisons on a larger scale, it is impossible to separate genetic from environmental factors, but certain patterns emerge which are likely to have biological meaning. The most striking of these is the positive correlation between hip fracture rates and standard of living noted by Hegsted when he observed that osteoporosis was largely a disease of affluent Western cultures He based this conclusion on a previously published review of hip fracture rates in 10 countries , which strongly suggested a correlation between hip fracture rate and affluence.
Another review of 19 regions and racial groups confirmed this by showing a gradient of age- and sex-adjusted hip fracture rates from 31 per in South African Bantu to per in Norway. In the analysis of hip fracture rates in Beijing and Hong Kong referred to above , it was noted that the rates in both cities were much lower than in the United States. Many other publications point to the same conclusion - that hip fracture prevalence and by implication osteoporosis is related to affluence and, consequently, to animal protein intake, as Hegsted pointed out, but also and paradoxically to calcium intake.
The calcium paradox The paradox that hip fracture rates are higher in developed nations where calcium intake is high than in developing nations where calcium intake is low clearly calls for an explanation.
Hegsted was probably the first to note the close relation between calcium and protein intakes across the world which is also true within nations [ 63 ] and to hint at but dismiss the possibility that the adverse effect of protein might outweigh the positive effect of calcium on calcium balance. Only recently has fracture risk been shown to be a function of protein intake in American women There is also suggestive evidence that hip fracture rates as judged by mortality from falls in elderly people across the world are a function of protein intake, national income, and latitude The latter is particularly interesting in view of the strong evidence of vitamin D deficiency in hip fracture patients in the developed world and the successful prevention of such fractures with small doses of vitamin D and calcium , see Chapter 8.
It is therefore possible that hip fracture rates may be related to protein intake, vitamin D status, or both and that either of these factors could explain the calcium paradox. We shall therefore consider how these and other nutrients notably sodium affect calcium requirement. Nutritional factors affecting calcium requirements The calculations of calcium requirements proposed above were based on data from developed countries notably the United States and Norway and can only be applied with any confidence to nations and populations with similar dietary cultures.
Other dietary cultures may entail different calcium requirements and call for different recommendations. In particular, the removal or addition of any nutrient that affects calcium absorption or excretion must have an effect on calcium requirement. Two such nutrients are sodium and animal protein, both of which increase urinary calcium and must be presumed therefore to increase calcium requirement.
A third candidate is vitamin D because of its role in calcium homeostasis and calcium absorption. Sodium It has been known at least since that urinary calcium is related to urinary sodium and that sodium administration raises calcium excretion, presumably because sodium competes with calcium for reabsorption in the renal tubules.
However, these are approximations, which conceal the close dependence of urinary sodium on sodium intake and the weaker dependence of urinary calcium on calcium intake.
It is an empirical fact that urinary sodium and calcium are significantly related in normal and hypercalciuric subjects on freely chosen diets The slope of urinary calcium on sodium varies in published work from about 0.
The biological significance of this relationship is supported by the accelerated osteoporosis induced by feeding salt to rats on low-calcium diets and the effects of salt administration and salt restriction on markers of bone resorption in postmenopausal women , Because salt restriction lowers urinary calcium, it is likely also to lower calcium requirement and, conversely, salt feeding is likely to increase calcium requirement.
This is illustrated in Figure 18 , which shows that lowering sodium intake by mmol 2. However, the implications of this on calcium requirement across the world cannot be computed because information about sodium intakes is available from very few countries Protein The positive effect of dietary protein - particularly animal protein - on urinary calcium has also been known at least since the s One study found that 0.
A meta-analysis of 16 studies in adult humans on protein intakes up to g found that 1. A small but more focussed study showed a rise of 40 mg in urinary calcium when dietary animal protein was raised from 40 to 80 g i. This ratio of urinary calcium to dietary protein ratio 1mg to 1g is a representative value, which we have adopted. This means that a 40g reduction in animal protein intake from 60 to 20 g or from the developed to the developing world [ Table 30 ] would reduce calcium requirement by the same amount as a 2.
The effect of varying protein or sodium intake on theoretical calcium requirement. In a western-style diet, absorbed calcium matches urinary and skin calcium at an intake of mg as in Figure Reducing animal protein intakes by 40 g reduces the intercept value and requirement to mg.
Reducing both sodium and protein reduces the intercept value to mg. How animal protein exerts its effect on calcium excretion is not fully understood. A rise in glomerular filtration rate in response to protein has been suggested as one factor but this is unlikely to be important in the steady state. The major mechanisms are thought to be the effect of the acid load contained in animal proteins and the complexing of calcium in the renal tubules by sulphate and phosphate ions released by protein metabolism , Urinary calcium is significantly related to urinary phosphate as well as to urinary sodium , particularly in subjects on restricted calcium intakes or in the fasting state, and most of the phosphorus in the urine of people on Western-style diets comes from animal protein in the diet Similar considerations apply to urinary sulphate but it is probably less important than the phosphate ion because the association constant for calcium sulphate is lower than that for calcium phosphate The empirical observation that each 1 g of protein results in 1 mg of calcium in the urine agrees very well with the phosphorus content of animal protein about 1 percent by weight and the observed relationship between calcium and phosphate in the urine Vitamin D One of the first observations made on vitamin D after it had been identified in was that it promoted calcium absorption It is now well established that vitamin D synthesised in the skin under the influence of sunlight is converted to 25OHD in the liver and then to 1,25 OH 2 D in the kidneys and that the latter metabolite controls calcium absorption 21 see Chapter 8.
However, plasma 25OHD closely reflects vitamin D nutritional status and because it is the substrate for the renal enzyme which produces 1,25 OH 2 D, it could have an indirect effect on calcium absorption.
This has been seen consistently in animal studies, and the high calcium absorption and high plasma 1, OH 2 D observed in Gambian mothers is consistent with this type of adaptation. However, increasing latitude may compromise vitamin D synthesis to the degree that 25OHD levels are no longer sufficient to sustain adequate 1, OH 2 D levels and efficient intestinal calcium absorption, although this theory remains unproved.
Regardless of the mechanism of compromised vitamin D homeostasis, the differences in calcium absorption efficiency have a major effect on theoretical calcium requirement, as illustrated in Figure 18 , which shows that an increase in calcium absorption of as little as 10 percent reduces the intercept of excreted and absorbed calcium and therefore calcium requirement from to mg.
The figure also shows the great increase in calcium requirement that must result from any impairment of calcium absorption. Implications The major reduction in theoretical calcium requirement which follows animal protein restriction has led us to attempt to show in Table 33 how the calcium allowances recommended in Table 31 could be modified to apply to nations where the animal protein intake per capita is around g rather than around the g in developed countries.
These hypothetical allowances take into account the need to protect children, in whom skeletal needs are much more important determinants of calcium requirement than are urinary losses and in whom calcium supplementation had a beneficial effect in the Gambia However, adjustment for animal protein intake has a major effect on the recommended calcium allowances for adults as the table shows.
It also brings the allowances nearer to what the actual calcium intakes are in many parts of the world. If sodium intakes were also lower in developing than developed nations or urinary sodium were reduced for other reasons such as increased sweat losses, the calcium requirement might be even lower, for example, mg Figure This would be reduced still further by any increase in calcium absorption, whether resulting from better vitamin D status because of increased sunlight exposure or for other reasons, as illustrated in Figure Because the increase in calcium absorption in the Gambia is much more than 10 percent , this is likely to have a major - although not at present calculable - effect on calcium requirement there.
However, the adjusted bone mineral density in Gambian women is reported to be some 20 percent lower in the spine but not in the forearm than in British women , which emphasises the need for more data from developing countries.
The effect of varying calcium absorptive efficiency on theoretical calcium requirement Note: At normal calcium absorption, the intercept of urinary plus skin calcium meets absorbed calcium at an intake of mg as in Figure A 10 percent reduction in calcium absorption raises the intercept and requirement to mg and a 10 percent increase in calcium absorption reduces it to mg.
Conclusions Calcium is an essential nutrient that plays a vital role in neuromuscular function, many enzyme-mediated processes, blood clotting, and providing rigidity to the skeleton by virtue of its phosphate salts. Its non-structural roles require the strict maintenance of ionised calcium concentration in tissue fluids at the expense of the skeleton if necessary and it is therefore the skeleton which is at risk if the supply of calcium falls short of requirement.
Calcium requirements are essentially determined by the relationship between absorptive efficiency and excretory rate - excretion being through the bowel, kidneys, skin, hair, and nails. In adults, the rate of calcium absorption from the gastrointestinal tract needs to match the rate of all losses from the body if the skeleton is to be preserved; in children and adolescents, an extra input is needed to cover the requirements of skeletal growth.
Compared with that of other minerals, calcium economy is relatively inefficient. On most intakes, only about percent of dietary calcium is effectively absorbed and obligatory calcium losses are relatively large. Absorbed calcium has to match these obligatory losses and the dietary intake has to be large enough to ensure this rate of absorption if skeletal damage is to be avoided.
The system is subject to considerable inter-individual variation in both calcium absorption and excretion for reasons that are not fully understood but which include vitamin D status, sodium and protein intake, age, and menopausal status in women.
Although it needs to be emphasised that calcium deficiency and negative calcium balance must sooner or later lead to osteoporosis, this does not mean that all osteoporosis can be attributed to calcium deficiency. On the contrary, there may be more osteoporosis in the world from other causes.
Nonetheless, it would probably be generally agreed that any form of osteoporosis must inevitably be aggravated by negative external calcium balance. Such negative balance - even for short periods - is prejudicial because it takes so much longer to rebuild bone than to destroy it. Bone that is lost, even during short periods of calcium deficiency, is only slowly replaced when adequate amounts of calcium become available.
In seeking to define advisable calcium intakes on the basis of physiologic studies and clinical observations, nutrition authorities have to rely largely on data from developed nations living at relatively high latitudes. Although it is now possible to formulate recommendations that are appropriate to different stages in the life cycle of the populations of these nations, extrapolation from these figures to other cultures and nutritional environments can only be tentative and must rely on what is known of nutritional and environmental effects on calcium absorption and excretion.
Nonetheless, we have made an attempt in this direction, knowing that our speculative calculations may be incorrect because of other variables not yet identified. No reference has been made in this account to the possible beneficial effects of calcium in the prevention or treatment of pre-eclampsia , colon cancer , or hypertension and no attempt has been made to use these conditions as endpoints on which to base calcium intakes.
In each of the above conditions, epidemiologic data suggested an association with calcium intake, and experimentation with increased calcium intakes has now been tried. In each case the results have been disappointing, inconclusive, or negative and have stirred controversy Because there is no clear consensus about optimal calcium intake for prevention or treatment of these conditions and also no clear mechanistic ideas on how dietary calcium intakes affect them, it is not possible to allow for the effect of health outcomes in these areas on our calcium recommendations.
However, although the anecdotal information and positive effects of calcium observed in these three conditions cannot influence our recommendations, they do suggest that generous calcium allowances may confer other benefits besides protecting the skeleton.
Similarly, no reference has been made to the effects of physical activity, alcohol, smoking, or other known risk factors on bone status because the effects of these variables on calcium requirement are beyond the realm of simple calculation.
Future research Future research should: Handbook on Human Nutritional Requirements. Osteomalacia, osteoporosis and calcium deficiency. Effects of natural and artificial menopause on plasma and urinary calcium and phosphorus. Bone loss and biochemical indices of bone remodeling in surgically induced postmenopausal women. Age and menopause-related changes in indices of bone turnover. Pathophysiological mechanisms of estrogen effect on bone metabolism. Dose-response relationships in early postmenopausal women.
Osteomalacia and related disorders. Metabolic Bone and Stone Disease. Histomorphometric profile and vitamin D status in patients with femoral neck fracture. Recommended dietary intakes around the world.
Food and Nutrition Board, Institute of Medicine. Dietary reference intakes for calcium, phosphorus, magnesium, vitamin D, and fluoride. Reports of the Scientific Committee for Food Thirty-first series. Nutrient and energy intakes for the European Community.
Office for Official Publications of the European Communities. National Health and Medical Research Council. Recommended Dietary Intakes for use in Australia. Calcium, Phosphate and Magnesium Metabolism. Ionised calcium in body fluids. Calcium-receptor-regulated parathyroid and renal function. Current understanding of the molecular actions of vitamin D.
Regional patterns of bone loss and altered bone remodeling in response to calcium deprivation in laboratory rabbits. Food and Agriculture Organization of the United Nations. Effect of dietary calcium and age on jejunal calcium absorption in Humans studied by intestinal perfusion. Calcium absorption as a function of calcium intake. Absorption of calcium, phosphorus and magnesium.
Calcium and phosphate kinetics Calcium, Phosphate and Magnesium Metabolism. Secretion and excretion of calcium by the Human gastrointestinal tract. Calcium, phosphorus and magnesium requirement. Dietary requirements for calcium. Calcium in Human Biology.
Calcium, phosphorus, nitrogen, and potassium balance studies in the aged male. The effect of a high intake of calcium and phosphate in normal subjects and patients with chronic renal failure.
Calcium retained by young women before and after adding spinach to the diet. Calcium requirement and adaptation in adult men. The calcium requirements of older male subjects with special reference to the genesis of senile osteoporosis.
The calcium requirement of adult man and the utilisation of the calcium in milk and in calcium gluconate. Further experiments on the calcium requirement of adult man and the utilisation of the calcium in milk. Variability in the calcium metabolism and calcium requirements of adult Human subjects. Intestinal calcium absorption and serum vitamin D metabolites in normal subjects and osteoporotic patients. Relations between calcium intake, calcitriol, polymorphisms of the vitamin D receptor gene, and calcium absorption in premenopausal women.
Effect of variation in dietary calcium on plasma concentration and urinary excretion of calcium. Urinary calcium in perimenopausal women: Calcium metabolism evaluated by Ca 45 kinetics: Calcium metabolism in postmenopausal osteoporosis: The dietary requirements of calcium and its significance.
Actualites Scientifique et Industrielles No. Study of minimum calcium requirements by adult men. Menopausal changes in calcium balance performance. Calcium balance during Human growth: Biochemical variables in pre- and postmenopausal women: American Academy of Pediatrics Committee on Nutrition.
Calcium requirements in infancy and childhood. Calcium and fat absorption in neonatal period. Calcium-fatty acid absorption in term infants fed Human milk and prepared formulas simulating Human milk. Evidence for defective skeletal mineralisation in low birthweight infants: Effect of giving phosphate supplements to breast-fed babies on absorption and excretion of calcium, strontium, magnesium and phosphorus.
The estimation of calcium requirements: Calcium metabolism and calcium requirements during skeletal modeling and consolidation of bone mass. Calcium metabolism in girls: Food habits of adolescents. Nutritional concerns during adolescence. The effects of menopause and age in calcitropic hormones: Metabolic consequences of the menopause.
A cross-sectional, longitudinal, and intervention study on normal postmenopausal women. Calcium absorption in women: Calcium potentiates the effect of estrogen and calcitonin on bone mass: Calcium absorption in normal and osteoporotic postmenopausal women. Influence of age on effects of endogenous 1,dihydroxyvitamin D on calcium absorption in normal women. Intestinal calcium absorption in men with spinal osteoporosis. Calcium metabolism in normal Human pregnancy. The efficiency of intestinal calcium absorption is increased in late pregnancy but not in established lactation.
Elevated 1,dihydroxyvitamin D plasma levels in normal Human pregnancy and lactation. Bone turnover and density in healthy women during breastfeeding and after weaning. Effects of increased dietary calcium intake upon the calcium and status of lactating adolescent and adult women.
Calcium requirements of lactating Gambian mothers: The effect of calcium supplementation on bone density during lactation and after weaning. Women's dietary calcium requirements are not increased by pregnancy or lactation. Elevated parathyroid hormone-related peptide associated with lactation and bone density loss. Comparison of dietary calcium with supplemental calcium and other nutrients as factors affecting the risk for kidney stones in women.
A prospective study of dietary calcium and other nutrients and the risk of symptomatic kidney stones. This is the amount of time a ruminant spends consuming feed.
While generally applied to actual grazing on pasture, the definition can be widened to include time spent browsing, consuming stover etc. Grazing time is determined by the availability and nutritive value of feed and by the management system used Gammon and Roberts, ; Lambourne et al, There is often an inverse relationship between grazing time per day and the quantity and quality of feed available Butterworth, Feed-related concepts These concepts include: The digestibility of a feed determines the amount that is actually absorbed by an animal and therefore the availability of nutrients for growth, reproduction etc.
Apparent digestibility is estimated by subtracting nutrients contained in the faeces from nutrients contained in the dietary intake.
Therefore, it does not account for nutrients lost as methane gas or as metabolic waste products excreted in the faeces. True digestibility is estimated by correcting for the endogenous and microbial amount of a nutrient actually lost in the faeces.
The measurement of apparent digestibility is less complex than measuring true digestibility and, therefore, more suited to the requirements of diagnostic livestock systems research. The amount of energy in or the energy content of feed potentially utilisable by animals can be expressed in the form of gross energy GE , digestible energy DE , metabolisable energy ME or net energy NE for maintenance and production. The relationships between them are as follows: The difference between the dry-matter weight and the weight of the ash remaining is the DOM weight of the feed.
Net energy is the energy actually available for maintenance and production after all losses have been accounted for. It is the most precise estimate of a feed's energy value, but, because of the complexities involved, net energy is rarely measured. Digestible energy is commonly taken as an indicator of a feed's energy value because faecal losses are relatively easy to measure.
Metabolisable energy can be approximated by multiplying digestible energy by a factor of 0. Protein is the basic structural material from which all body tissues e. It is, therefore, essential for production and maintenance and cannot be replaced by other nutrients in the feed. Ruminants are able to synthesise protein from non-protein nitrogen sources e. The nitrogen content of a feed is, therefore, often used to estimate the amount of protein available to the ruminant, which is expressed as the crude protein CP content of a feed and calculated as: This fraction refers to the cell-wall content of feeds and consists of carbohydrates hemicellulose and cellulose and lignin.
Carbohydrates are partially available for digestion by rumen micro-organisms and represent a major source of energy for ruminants. The lignin component of the fibre fraction limits the digestibility of cell-wall carbohydrates. Crude fibre which is used in the Wende system of feed analysis is a poor estimate of cell-wall content because it does not recover lignin and hemicellulose. Instead, the detergent system of analysis described in Part D below should be used where feasible, although there are other methods for estimating total fibre Van Soest, Minerals are required for tissue growth and the regulation of body functions.
So far, 22 mineral elements have been shown to be essential to animal nutrition Little, Table 1. Vitamins are organic substances required by animals in very small amounts for the regulation of various body processes which ensure normal health and production. Under most conditions, the ruminant is able to synthesise most of its vitamin requirements. A which can be deficient in tropical pastures and crop residues. The synthesis of vitamin B12 requires Co which may also be deficient in these feeds.
The specific functions of the different minerals and vitamins are discussed in any text on ruminant nutrition. Purposes Diagnostic research on animal nutrition problems The nature of nutritional constraints Scope for improvement.
During the descriptive phase of livestock systems research, data obtained from informal surveys, secondary data sources and other diagnostic studies can be used to determine the need for further diagnostic research on animal nutrition issues. The following types of data will often be useful in this respect: Also, the vegetation characteristics of an area e.
Evidence of overgrazing on a wide scale will indicate nutrition problems, particularly during the dry season when feed quantity and nutritive value are lowest.
For instance, a high proportion of fortes in the diet can usually be taken as an indication that minerals, in particular phosphorus, may not be deficient. The nature of nutritional constraints If solutions are to be identified, the nature of nutritional problems must be clearly defined. Studying the relationships between nutrition on the one hand and performance, management and grazing conditions on the other hand, as well as other nutritional relationships, might be useful in this context.
Relationships between nutrition and animal performance. By using techniques such as linear regression analysis, the relative importance of the different factors affecting production performance can be compared simultaneously.
Table 2 shows how performance could be related to different variables of which nutrition is only one. Relationships determining the effects of animal nutrition on production performance. Dependent variable production performance Independent influencing variables 1.
Fertility rate Seasonal conditions, breed, parity, disease, type of birth, sex of progeny 3. Milk production DM intake, 10 breed, parity, weaning period, disease, lactation length 10 When making comparisons between animals of different size to determine the importance of nutrition as a constraint, DM intake should be expressed in relation to the liveweight and preferably the metabolic weight, i.
When comparing animals of different species, the preferred exponent is LW 0. Various indicators or measures e. Surrogate or substitute variables for feed availability or intake can be used, as well.
For instance, seasonal rainfall is often assumed to be an indicator of feed conditions while stocking rate has been used as a substitute for feed intake Abel et al, Relationships between nutrition and management. The link between management practices and animal nutrition is often pronounced and needs to be understood. Examples of the relationships which might be studied are: Dahl and Sandford, ; Sandford, Crop residues can, for instance, have an important bearing on animal nutrition Bayer and Otchere, , by providing energy to carry stock through the dry season when feed quantity and nutritive value from grazing are low.
The availability of energy from stover will, therefore, influence mortalities and birth rates Powell and Waters-Bayer, ; Reed and Goe, Figure 2 gives a schematic representation of some of the linkages which commonly affect both crop and livestock performance.
Diagrams of this kind are useful in that they force the researcher to think through the system and identify some of the important linkages which exist. From this information, it is often possible to identify the data needs of research more precisely. Example of negative linkages between crop and livestock production in a mixed farming system.
Relationships between nutrition and grazing conditions. These include the relationships between: Bayer and Otchere also suggest that grazing time affects calving and weaning percentages for cattle owned by pastoralists in the Nigerian subhumid zone. This includes the relationships between digestibility end feed quality, and between seasonal conditions rainfall and the nutritive value of feed consumed measured in terms of energy or crude protein content.
Such relationships need to be adequately understood if problems are to be correctly identified. For instance, a positive correlation between digestible energy or dry-matter intake and liveweight gain is commonly observed Ademosun et al, ; Zemmelink et al, Figure 3. While this correlation may correctly imply that energy is a limiting factor in the diet, the availability of energy may itself be limited by some other factor e. Effective diagnosis thus depends on the identification of the primary limiting nutrient Little, Relationship between intake and liveweight gain in cattle, Mali, Lambourne et al Scope for improvement The scope for alleviating nutritional problems will depend very much on the characteristics of the system being studied.
In pastoral systems, where the range vegetation is the major source of feed, improvements in animal nutrition may be virtually impossible without first addressing issues related to land tenure communal grazing 11 and management e. While in mixed cropping systems, technologies which increase the quantity and nutritive value of stover fed to animals at the end of the cropping season might be applicable Powell It should be remembered that in livestock systems research, the solution to a particular problem may not always be technological.
For instance, it may be more important to correct particular aspects of policy before significant improvements in production can be achieved. Feasible technological solutions to improve animal nutrition may come through one or more of the following pathways: In mixed systems of production, livestock nutrition may be enhanced by improving the quantity and nutritive value of crop residues used by stock through: This involves changing livestock management strategies to match feed availability with livestock feed requirements.
For instance, Wagenaar et al and Wilson and Sayers have shown that change in the timing of births to match feed demands with feed supplies can have significant effects on conception rates and parturition number in sheep and goats. These involve ranching schemes which aim to improve the management of the range and raise productivity, principally through increasing in the amount of available forage.
The available evidence suggests, however, that such schemes have mostly been unsuccessful in Africa Danckwerts, ; Behnke, The redistribution of water points to better utilise grazing resources is another example of a pasture improvement strategy. Fodder banks are concentrated stands of forage, often legumes, sown either on natural grass or fallows to provide dry-season supplementary grazing Bayer, ; Mohamed-Saleem, ; Taylor-Powell and Ingawa, However, widespread adoption of forage legumes is constrained by competition for land with food crops, labour shortages during crop operations and lack of adapted species Reed and Goe, Among fodder trees, leucaena and sesbania have been shown to be suitable for animal feed supplementation by the ILCA alley farming programme in Nigeria Atta-Krah, Browse gardens and multipurpose trees have also been tried Reed and Soller, Types of data Animal data Feed data.
The objectives of data collection in this case are to Table 3: With some of these data e. It is recommended that, when such dab are required, the ARC standards should be used. Types of animal data used to diagnose animal nutrition problems.
Objective Types of data Production effects Liveweight gain, condition scores, traction power, milk production, wool production Amount of feed consumed Feed intake Composition of feed consumed Oesophageal or rumen fistula samples, faecal samples, grazing behaviour studies selection data Feed data The principle objective, in this case, is to determine the nutritive value of the feed consumed and digested by the animal.
This may also involve an assessment of sources of feed as yet unutilised but with the potential for introduction into the diet. In particular, data will be collected on digestibility, the energy value of feed dry matter, dry organic matter, digestible energy and metabolisable energy , and crude protein content When assessing the nutritive value of feed, differentiation on the basis of season or system of production which affect feed sources and feed availability will often tee useful.
Under certain circumstances see Part D below , data on the mineral content and fibre composition of a diet may be necessary. When determining mineral content, samples of the feed consumed and of blood or bone may be needed. Methods of data collection Effects of nutrition on animal production performance Composition of consumed feed Feed digestibility Nutritive value of feed. The discussion in Module 11 of different methods of data collection is generally applicable to all types of diagnostic research, and the user is encouraged to read it before embarking on studies of animal nutrition.
The emphasis here is on those methods which have been tested by ILCA staff. Following the format adopted in Part C of this module, these methods have been grouped into methods used to measure: Effects of nutrition on animal production performance The production performance of an animal often reflects its nutritional status. Liveweight and body condition, for instance, provide a measure of the nutritional response, integrated over weeks or months Lambourne et al, Studies which attempt to isolate the key factors influencing animal production performance may, therefore, be the first step in the diagnosis of animal nutrition problems see Part B above.
If nutrition is identified as the critical constraint to performance, further studies on specific aspects of nutrition related to the animal or the feed may be needed. The various methods used to assess animal production performance are discussed in Module 5, and the reader should refer to it if detailed diagnosis of production performance is envisaged.
For instance, there may be data available from range evaluation and animal production studies and farm management surveys, which specifically identify nutrition as the critical constraint to production.
Feed intake Intake, or the amount of feed an animal consumes, can be estimated by using either digestibility data or 'markers'.
When such data are available, intake can be estimated by multiplying the dry-matter weight of faeces by a digestibility factor. The factor is known as the feed: Digestibility and intake data can be derived from the indigestible components of a diet, known as 'markers'. Markers are classified as internal, if they are ordinarily present in the diet e. Synthetic organic substances such as beads, rubber and ribbon have also been used, since they can be easily separated from the feed.
Van Soest provides a detailed account of the various markers used to estimate intake and digestibility, and of their advantages and disadvantages. The term 'indicator' is sometimes used instead of 'marker' Dicko-Touré, , Church and Pond, ; Lambourne et al, The formula to estimate faecal output is: An animal is dosed with 50 g of chromic oxide per day to determine its daily faecal output.
The concentration proportion of marker in the dry-faeces sample is 5. The dry-matter weight of faeces excreted per day is g and 5. The proportion of the marker in the diet is 3. Calculate the DM intake of the animal. These can then be related to such variables as seasonal rainfall, stocking rate, management practices or plant composition to isolate its main determinants. Summary The normal procedures to estimate DM digestibility and intake are to: This requires the further estimation of faecal output either by total faecal collection or dosing with known quantities of, for instance, chromic oxide.
When facilities for laboratory analysis are not available or are inadequate, intake should be calculated on the basis of digestibility.
Simple methods to estimate digestibility are given in the text which follows. Composition of consumed feed There are various methods used to determine what the animal is eating.
Those discussed here are: The botanical composition of feed consumed by an animal can be determined by using a surgical fistula inserted into an animal's oesophagus. The food eaten passes into a collection bag attached to the neck, and samples are taken directly from the bag after allowing the animals to graze for not more than two hours before re-inserting the fistula plug.
The oesophageal fistula method provides an accurate indication of the botanical composition of the feed consumed. An illustration of this type of approach is given by McLean et al However, because of salivary contamination of the samples, accurate direct estimates of the chemical composition of feed eaten are restricted to nitrogen, neutral detergent solubles, calcium, magnesium, sulphur and copper Little, ; Dietary phosphorus concentrations can be estimated accurately only from oesophageal extrusa labelled with radioactive P Little et al, It also tends to be time-consuming and costly, and farmers are unlikely to cooperate when their own stock is involved.
Nevertheless, ILCA research workers have used the method in the field. In Kenya, for instance, oesophageal fistulae were fitted to cows which had been purchased from Maasai pastoralists and herded with farmers herds during three seasons in several locations Semenye, a, b. The data obtained on feed composition were then complemented by studies on grazing behaviour of the type discussed below.
Material collected with the fistula method can be used in the determination of digestibility by in vitro estimation procedures see page This method is applicable to both cattle and smallstock and allows direct sampling of the contents of the rumen by means of a cannula surgically inserted into the rumen. It involves physically emptying the contents of the rumen by hand before the animal goes to graze and then taking samples from the freshly ingested material two to three hours after the animal started grazing.
It is therefore more likely to be applicable to on-farmlon-range experiments described in Section 2. Direct observation of grazing habits. The content of food consumed by grazing animals can be guesstimated by following selected animals in a herd or flock at distances which are close enough to observe what is being eaten.
Each selected animal is observed at regular intervals. Two field examples demonstrate the principles. De Leeuw and Chara used the technique to compare goat and sheep browse preferences in mixed Maasai flocks in Kenya. Observations were carried out during the dry season with randomly selected animals being followed for periods of one to two hours by one or two observers who were familiar with the local flora.
Because the animals were familiar with humans, observations could be made at distances of m. The aim was to obtain an equal number of 'hits' for sheep and goat - a 'hit' occurring each time a particular plant species was eaten.
Hits per plant species were then summed and compared with the total number to determine the proportion of each plant eaten. These figures were then used to derive an index of preference or selection. Between and hits were collected for both sheep and goats in each sample flock. Nyerges observed the grazing habits of sheep, by following each for a period of 20 minutes measured by stop watch.
Animals were followed at distances of m and the shrub and ground species consumed including ground litter during the observation period were recorded. Direct observation can also be applied to other studies of animal grazing behaviour, e. These variables can then be related to such parameters as intake, digestibility, stocking rate and distance to water, to isolate the more important determinants of grazing behaviour Lambourne et al, , pp.
A modification of the direct-observation method was used by Dicko-Touré in Mali to determine the composition of feed consumed. Selected animals were followed for a period of one minute, and distance walked as well as the number of mouthful taken during this period were recorded. A sample of forage was then collected by hand from the area grazed during the one-minute observation period. The size of the sample taken was in proportion to the observed number of mouthfuls one hand-grab for every five mouthful.
Similar measurements were made for each selected animal every 45 minutes throughout the day in order to obtain comprehensive data on feeding habits and feed composition. Lambourne et al argued that, for most purposes, such rapid-survey techniques provide sufficient detail on diet composition. They are low-cost, require minimal supervision and can be completed in a relatively short time.
Observers should, preferably, have a good knowledge of local flora, but it is more important for them to be observant. If hand samples are collected to mimic grazing habits, these can be analysed at a later stage by someone who is thoroughly familiar with the flora.
Data on diet composition can be complemented by opinions obtained from herdsmen in the area. Their knowledge about species differences in terms of selectivity and palatability is often very precise. Pasture analysis before and after grazing. The 'before' and 'after' method involves the demarcation of quadrats in a paddock before and after animals are released into an area for grazing Figure 4.
Adjacent to each fenced quadrat is an equally sized area, with similar vegetation characteristics. The biomass and vegetation composition of the two 'paired' areas are measured using one of the techniques described in Module 6 and animals are then released into the area to graze t'Mannetje, Schematic representation of the pasture analysis method. After a prescribed period e.
The method will give reasonable estimates provided that the two areas are not highly variable in terms of species composition. When vegetation is highly variable, the number of paired samples required must be increased, making measurement more time-consuming. Faecal samples have been used for microscopic analysis of the plant part they contain, to provide an indication of the vegetation consumed by an animal Stewart, However, as an indicator of dietary composition such samples tend to be unreliable since the indigestible portion of the diet may bear little relationship to the portion actually consumed.
The faeces may, for instance, contain high proportions of woody ligneous material consumed during browsing. This does not necessarily mean that the diet also contains similar proportions of this component. Feed digestibility The methods used to assess digestibility are based on: Of these, only the first three are relevant to the diagnostic phase of livestock systems research. The in vivo method is more applicable to on-station research and involves intensive laboratory work and careful supervision.
The use of markers. When it is impossible or inconvenient to measure total feed intake or to collect total faeces, markers can be used to determine intake see pages as well as digestibility.
The formula used to calculate apparent digestibility 16 is: Calculate the apparent digestibility of the feed. To obtain data for the analysis based on markers, follow this procedure: There are two obvious sources of error in such a methodology. First, lignin may be partly digestible and is thus not always a reliable indicator marker. Second, the feed samples taken will often be not truly representative of actual intake, particularly when pasture is highly variable, and where the choice of samples is entirely dependent on the enumerator judgement.
There are various methods available to sample faecal output in the field, including: This method is practical in a range context. Schneider and Flatt, However, Dicko-Touré, , p.
She argued that the costs of using indicators to estimate faecal output would, in fact, have been more expensive since this method would have involved sending samples to another country at a cost that is at least 10 times higher than the cost actually incurred by using the bag-collection method. Thus, the methods adopted in any diagnostic study to sample faecal output should be tailored to the particular circumstances of the study, bearing in mind the financial and manpower resources of the research team.
The use of faecal indices. The methods using faecal indices to estimate digestibility are based on established regression relationships between faecal indices and the digestibility of dry or organic matter Van Soest, The general model for these relationships is: The two variables merely happen to go together i. The estimation of digestibility via faecal indices involves the following steps: The main advantages of this method are that it is relatively low-cost and results can be obtained fairly quickly.
Its chief disadvantage is that it is site-specific, and the derived parameters and relations In vitro analysis of consumed feed. When digestibility is analysed by in vitro methods, samples of feed ingested are subjected to artificial tests which simulate digestibility under controlled conditions.
The more commonly applied methods involve the use of rumen fluids, chemical fermenters and nylon bags see Church and Pond, Rumen fluids are extracted from rumen-fistulated animals and used in combination with buffers to simulate the action of saliva. The Tilley-Terry method, which is widely used, involves an additional stage in which the feed is further digested with acid pepsin for another 48 hours. The residual represents the indigestible portion of the feed.
Chemical fermenters added to the feed have been used to predict digestibility. The method is also used to study rumen function and the metabolism of certain compounds, e.
The advantage of the two methods is that the analysis is not expensive if laboratory facilities are available and that it can be performed fairly quickly. The methods can also be used to assess the digestibility of grab samples of grass or of cut samples of stover and straws taken after crop harvesting. These are inserted into the rumen of test animals and removed after a prescribed period. The loss of material from the bag as a result of fermentation is then calculated. The method is more applicable to on-station research, but it can be used together with the rumen cannula method to determine intake.
Nutritive value of feed This part of the module focuses on the methods and techniques used in estimating the supply of different nutrients to animals in particular situations or systems, in relation to their need for these nutrients. It starts with a general section on estimating the main feed components. It then goes straight to fibre analysis because of the difficulties involved in estimating feed values in very fibrous diets.
Finally, it looks at some of the techniques in use for the physical sampling, from stands of different kinds of feed, for laboratory analysis. Methods to estimate feed components The feed value of a source of feed can be assessed on the basis of its energy value, crude protein content and mineral content, using methods specifically designed to estimate these components of feed.
The energy yield of a source of feed such as natural pasture can be estimated from its dry-matter weight per unit area.
Module 6 discusses the various methods used to estimate biomass or dry-matter weight under rangeland conditions. Many of these methods rely on the use of predictive equations based on the relationship between biomass and the vegetation characteristics e. Samples can be taken to establish similar predictive relationships for the estimation of dry-matter weight of crop residues. Powell , for instance, used grain yield to predict total stover dry-matter weight and stalk and leaf dry-matter weights for millet and sorghum.
The relationships, which were based on data obtained from randomly chosen sites in Kaduna State, Nigeria, were highly significant Figure 5. Van Raay and de Leeuw adopted a similar procedure to determine the DM weight of crop residues in Katsina, Nigeria. They established predictive relationships on the basis of stalk and stand density, plant height and plant edibility subjectively estimated.
Relationships between sorghum and millet grain yields and stover dry-matter DM yields. Having obtained an estimate of dry-matter yield, an estimate of digestibility is then required before the desired approximation of the energy yield can be calculated. The fibrous portions of a feed must, therefore, be considered before more accurate estimates of nutritive value can be made. Feeds with a high biomass per unit area are often low in energy since they also contain a high proportion of indigestible fibrous matter.
Methods of fibre analysis have been devised to separate those portions of fibre which can be utilised by the ruminant from those which are essentially indigestible. Fibre analysis is thus particularly important in the assessment of the nutritive value of these feeds. For the purposes of illustration, however, the following average relationships can be used: Let us calculate the feed energy requirements of a kg liveweight ox for maintenance, foraging and production, and compare these with the availability of energy to that animal from its feed supply.
The maintenance fasting metabolism requirement is determined as follows: Km tends to lie in the range 0. We can call this 'foraging'.
The energy requirement for foraging Ef are given by the formula: To gain weight, an animal needs between 12 and 27 MJ of ME per kg liveweight, depending on the percentage that fat constitutes in the meat accumulated. We can now compare supply and requirements of feed energy per ox for the 90 days of the dry season as follows: The standard laboratory method for the estimation of crude protein is the Kjeldahl method which is described in most texts on animal nutrition e.
McDonald et al, ; Church and Pond, The analysis is used to determine the crude protein content of a sample of grass or stover, and the results can then be used to establish predictive regression equations similar to those illustrated in Figure 5. When estimating the crude protein content of browse plants and crop residues, it should be borne in mind that the presence of certain phenolics tannins in these feeds can affect the availability of nitrogen to the ruminant.
This is particularly true of feeds high in insoluble polyphenolics, for which the calculated crude protein content may overestimate the amount of nitrogen which can actually be synthesised into protein e.
Woodward and Reed, Analysis should only be attempted if mineral deficiencies are clearly evident. Even then, if other nutrients such as energy or crude protein are more limiting as is likely to be the case on African rangelands , the mineral constraint should be dealt with only after the primary deficiencies have been rectified Little,