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Two papers on this theme were organized. The first Wilson reviewed the implications of these developments on the animal feed industry and the second Gibson and Karges, USA considered the technicalities of co-product production in the context of optimization of their nutritional value.

The Non-ruminant Session commenced with a detailed review of the role of muscle glycogen on meat quality in pigs Oksbjerg, Denmark and continued with a paper on L-carnitine and its effect on prenatal muscle development and subsequent offspring performance in pigs Woodworth, USA. With increasing concern over possible human infection associated with the H5N1 avian influenza virus, it was thought very opportune to include a paper Connerton and Connerton, Nottingham on zoonoses which identified the principal agents and the likely danger arising from them.

Nutrition x genotype interactions and recent developments in genetics were discussed Hoste, Malton , followed by a comprehensive review of sow and boar nutrition in the light of the emergence of new genotypes Close. Processing of raw materials for piglet diets is invariably defined simply in terms of the name of the process which is inadequate, as described in a paper Doucet, White, Wiseman and Hill; Nottingham on physicochemical changes to starch structure during processing of raw materials and their implications for starch digestibility in newly-weaned piglets.

We would like to thank all speakers and session chairmen David Parker, Brian Cooke, Julian Wiseman, Tim Parr and Steve Jagger , together with members of the Programme Committee, for contributing to a very successful and innovative programme.

We would also like to acknowledge the efficient administration managed by Sue Golds , catering and support staff who ensure the smooth running of the conference. We look forward to renewing old acquaintances and making new friends. Garnsworthy J.

Both were closely associated with the Nottingham Feed Conference and made major contributions to the conference for many years. Bob Pickford was a driving force behind the first Nutrition Conference for Feed Manufacturers held in His vision was for an annual forum that would facilitate translation of scientific ideas into commercial practice. There can be no doubt that this objective was achieved. He continued to serve on the Programme Committee right up until the conference this year.

Des Cole joined the Programme Committee in and acted as Chairman from to His extensive travels and attendance at conferences abroad provided Des with a wealth of ideas that helped to shape the format of the Nottingham Conference. He was particularly keen to maintain the reputation of a social gathering as well as a scientific meeting.

Following his retirement from the University in , Des continued his contact with the Conference through his publishing activities with Nottingham University Press. Salter1, A. Lock2, P. Garnsworthy1 and D. Lapierre1, G. Raggio2, D. Ouellet1, R. Berthiaume1, S. Lemosquet3, L. Doepel4 and D. Thatcher1, Flavio T. Silvestre1, Todd R. Bilby1, Charles R. Staples1, Jose E. Santos2, Carlos A. Risco3 and Leslie A. Macmillan1, C.

Grainger2, M. Connerton and Ian F. Salter et al. LOCK2, P. It has evolved to meet the energy and essential nutrient requirements of offspring up to the point of weaning. However, with the development of agriculture, man has exploited the potential of milk and dairy products as foods that can be consumed throughout the lifespan. Through breeding programmes and development of management techniques, milk from ruminant species has become a major staple of the human diet.

It is the contribution to saturated fat intake that has caused concern to many human nutritionists. For many years it has been recognised that certain dietary saturated fatty acids have the potential to raise plasma cholesterol and thereby increase the risk of developing atherosclerotic cardiovascular disease CVD. As a result, a reduction in intake of full-fat dairy products has been central to public health dietary recommendations around the world. However, the discovery of potential health benefits of a number of bioactive fatty acids, including conjugated linoleic acid CLA , which is uniquely associated with ruminant meat and milk fat, has led to some reconsideration of the impact of dairy fat on human health.

Figure 1 shows that death rates from coronary heart disease CHD in both the United Kingdom and the United States have declined over the last 40 years, particularly in men.

However, they appear to be due to a combination of improved treatment of individuals and changes in risk factor levels within the whole population.

We may expect further significant reductions in CVD morbidity and mortality as the impact of increased use of highly effective cholesterol- lowering drugs Statins is fully realised Salter However, at the present time specific dietary recommendations still continue to reinforce the avoidance of dairy fat Litchtenstein et al.

Dietary recommendations aimed at reducing cholesterol have been central to the public health policies of most industrialized countries. As noted above, a reduction in intake of saturated fat has remained central to such policies. This was first demonstrated in the s, when international comparisons showed that countries with lowest intakes of saturated fat also had the lowest population plasma cholesterol concentrations and lowest prevalence of CVD Keys et al.

The influence of dietary fat composition on cholesterol concentrations was further established in a series of carefully controlled human feeding studies. From these experiments, equations were derived to predict the impact of changes in the amount and type of fat on plasma cholesterol Keys et al. Such findings on the effect of dietary fat on total plasma cholesterol led to generalized advice that population intakes of SFA with between carbon atoms lauric, myristic and palmitic acids should be reduced.

This inevitably affected dairy fat intake, which represents one of the main dietary sources of SFA. Figure 2 shows the dramatic changes in household consumption of liquid milk, indicating that since its introduction in the mid s the consumption of reduced-fat skimmed milk has overtaken consumption of full fat milk.

The reasons for this are not completely clear but they probably include a change in dietary sources of SFAs with more being associated with processed food and pre-prepared meals and the continuing decline in total energy expenditure leading to reduced energy intake.

It could thus be argued that the continued policy of advocating a reduction in saturated fat intake has negatively influenced dairy fat consumption without having any real impact on the health of the nation. A typical fatty acid composition of bovine milk is shown in Figure 4. It is generally accepted that these particular SFAs have no effect on plasma cholesterol. Fatty acid composition of cows milk Data redrawn from Lock et al.

In fact, compared to effects of dietary carbohydrates, their overall effect was small and, in the case of lauric acid, may actually be beneficial. This analysis therefore raises questions about the value of removing SFA from the diet if they are replaced simply by energy from carbohydrate. Thus, rather than reducing total milk fat consumption it may be potentially more beneficial to alter milk fatty acid composition. The majority of these contain only cis-double bonds.

Trans fatty acids have been the subject of considerable interested in recent years and the meta-analysis of Mensink et al. However, there are several isomers of trans C fatty acid and, as discussed below, those found in dairy products may not have the same impact on CVD risk as those found in hydrogenated vegetable oils.

Furthermore, CLA isomers containing a mixture of cis and trans double bonds are found naturally only in ruminant meat and milk, and may have specific benefits to human health Bauman et al.

Regulation of milk fatty acid composition The fatty acids in milk are a combination of those made de novo in the mammary gland, those mobilized from other body tissue, primarily adipose tissue, and those derived from the diet. However, specific sources of milk fatty acids vary depending on a number of factors, particularly stage of lactation.

As can be seen in Figure 5, the major product of de novo fatty acid synthesis is palmitic acid, with lesser amounts of the shorter chain saturated fatty acids being released from the fatty acid synthase FAS reaction.

Fatty acid metabolism in the ruminant mammary gland elongase activity in the ruminant mammary gland means that there is essentially no conversion of palmitic acid to stearic acid. The stearic acid in milk thus originates from either adipose tissue or indirectly from the diet. Biohydrogenation of dietary PUFA largely n-6 linoleic acid and n-3 linolenic acid within the rumen leads to a relatively high concentration of stearic acid being absorbed from the small intestine Lock et al.

In addition, a variety of intermediates in the biohydrogenation process, often containing trans double bonds, exit the rumen to be absorbed from the intestine, and can be found in relatively low concentrations in milk Lock and Bauman ; Bauman and Lock The remainder of the oleic acid in milk represents that from the diet which has escaped biohydrogenation, and a further contribution from adipose tissue stores.

Thus, manipulating the nature or proportion of milk fatty acids derived from the diet or adipose tissue could have an impact on the overall fatty acid composition of milk fat.

Manipulating the fatty acid content of milk fat through diet Nutrition is the predominant environmental factor affecting milk fat and represents a practical tool to alter its yield and composition Lock and Shingfield, For example, a recent study involving 26 dietary treatments showed that dietary oil concentration influenced milk fatty acids more than any other factor; increasing oil decreased SFA, and increased MUFA, CLA and trans fatty acids TFA Garnsworthy, Manipulating the diet has been extensively explored as a potential way of increasing the PUFA content of milk.

As discussed previously, the extent of such changes is limited by biohydrogenation of a large proportion of unsaturated fatty acids in the rumen Lock et al.

As has been previously reported at the Nottingham Feed Conference, various methods are available to protect unsaturated fatty acids from biohydrogenation Garnsworthy, ; Ashes et al. However, the extent of protection provided by current technologies is limited, allowing for only small increases in PUFA accumulation in milk. In recent years there has been particular interest in trying to increase the concentration of n-3 PUFA in milk. This is a result of the widely held view that in many industrialized countries the relative concentration of dietary n-3 PUFA, compared to n-6 PUFA, is low and may have detrimental effects on human health Gebauer et al.

Many countries have made specific recommendations that n-3 PUFA intake should be increased. For example, Jones et al. Adding large amounts of fish oil to the diet of ruminants, however, has a major impact on rumen function, interfering with biohydrogenation of unsaturated fatty acids and leading to accumulation of large quantities of trans fatty acids, which are subsequently absorbed by the animal and incorporated into milk Loor et al.

This is often associated with a significant reduction in total milk fat concentration. A potentially more attractive alternative is to feed cows ALA, which can be converted to EPA and DHA through elongation and desaturation either in the tissues of the cow, or in the tissues of the consumer following consumption of ALA-enriched milk.

Unfortunately neither the dairy cow Petit et al. From a human nutrition standpoint, using milk as a vehicle for delivering PUFA can be criticized due to the relatively high concentration of SFA associated with milk. At a time when most dietary advice is still aimed at reducing SFA intake by avoiding full fat dairy products, promoting milk as a source of PUFA, when sources low in SFA are available, may be difficult.

Ideally any strategy for manipulating milk fatty acid composition should include reducing SFA content. Stearoyl Coenzyme A Desaturase as a target for manipulating milk fatty acid composition One of the primary influences on the fatty acid composition of milk is the relative contribution of de novo lipogenesis in the mammary gland compared to uptake of fatty acids from plasma either of dietary origin or released from adipose tissue.

As described above, newly synthesised fatty acids are saturated and mainly represent those believed to increase human plasma cholesterol lauric, myristic and palmitic acid. Although a small proportion of these can be converted to their monounsaturated derivatives through the action of SCD, they represent relatively poor substrates for this enzyme. A large proportion of the fatty acids entering the mammary gland from the circulation is stearic acid. This is the preferred substrate of SCD and approximately two-thirds is converted into oleic acid Shorten et al.

We have been specifically interested in the regulation of SCD in both adipose tissue and the mammary gland and the potential for manipulating SCD activity to alter fatty acid composition. The ratio of milk C to C is often used as an index of SCD activity because both fatty acids are exclusively synthesized de novo in the mammary gland.

Previous work has shown considerable variability in this ratio among individual animals leading us to suggest that there may be significant genetic variability among animals Lock and Garnsworthy, ; Lock et al. In a structured genetic study involving cows, the heritability of this ratio was approximately 0. Thus, cows could potentially be selected for high mammary expression of SCD.

However, whether this would have a significant impact on milk fatty acid composition remains to be established. However, as will be discussed below, increasing SCD activity may also have a significant impact on production of CLA in the mammary gland. Trans fatty acids in milk As discussed above, it has been suggested that trans fatty acids represent the most potent cholesterol raising component of the human diet. This had led to specific public health policies to reduce trans fatty acid intake and a number of countries, such as the USA, have recently introduced legislation requiring labelling of trans fatty acid content on all food products Lock et al.

The two primary sources of dietary TFA are partially hydrogenated vegetable oil and milk and meat products from ruminant animals. As already discussed, trans fatty acids in milk are products of incomplete biohydrogenation of PUFA by rumen microbes. Estimates for intakes of trans fatty acids, and their source, vary considerably from country to country. The recent requirements for labelling of trans fatty acid content of food has led to an increased interest in the relative effects of trans fatty acids of ruminant origin compared to those in PHVO.

In fact, the chemical nature of the trans fats in these two sources varies substantially Lock et al d. These are predominantly trans C with an even distribution of trans-9, trans, trans and trans isomers Figure 6; Craig-Schmidt, ; Emken, Distribution of trans fatty acids in ruminant fat and partially hydrogenated vegetable oils PHVO Redrawn from data in Lock et al.

The double bond position can significantly influence the metabolism and physiological effects of trans fatty acids, suggesting that differences in distribution between ruminant and industrial sources may be of significance in relation to human health effects.

Lock at al. Much of the evidence that trans fatty acids are associated with adverse changes in plasma lipoproteins and increased risk of CVD arises from large epidemiological studies that have not distinguished between ruminant and PHVO sources. Where such analysis is possible, it is usually trans fatty acids from PHVO that are associated with adverse effects, whereas those from ruminants have shown no association with CVD risk Lock et al.

Several studies have established that humans are capable of this conversion Salminen et al. As described below, RA has been associated with a range of potential health benefits including anti-atherogenic and anti-carcinogenic actions.

RA content of milk can be increased by manipulating the diet of the cow, and such increases are usually associated with even greater increases in VA content. Since VA can be converted to RA in the tissues of the consumer, this particular trans fatty acid may actually benefit human health. Much of this has focussed on the trans, cis 12 C isomer and its ability to reduce body fat deposition.

This isomer normally occurs in only small amounts in the human food chain and studies have focused on chemically produced supplements. The dramatic effects of this isomer that were initially reported in mice have failed to be reproduced in human studies. Of greater interest to the dairy industry is RA, which occurs naturally in ruminant milk.

As reported previously at the Nottingham Feed Conference, RA production can be increased by manipulating the diet of the cow Bauman et al. As indicated in Figure 7, the basis for such manipulation is altered activity of the rumen microbial population so that biohydrogenation of PUFA is incomplete and there is an accumulation of intermediates including VA and RA. Rumen Mammary Linolenic acid Linoleic acid Tissue cis -9, cis , cis cis -9, cis cis -9, trans , cis trans , cis cis -9, trans CLA cis -9, trans CLA trans trans Vaccenic acid Figure 7.

CLA production in the ruminant Adapted from Bauman et al. Ip et al. This was supported by a subsequent study in which feeding rats increasing amounts of pure VA resulted in a progressive increase in tissue concentrations of RA with a corresponding reduction in the number of premalignant mammary lesions, an early marker for mammary cancer Banni et al.

Lock et al. Therefore, epidemiological data remain inconclusive Bauman et al. Numerous investigations with animal models have also examined the effects of CLA isomers on atherosclerosis and related variables.

The majority of these studies have utilized synthetic sources of CLA to examine cholesterol metabolism, and results indicate that dietary CLA can suppress dietary- cholesterol-induced atherosclerosis and, in some incidences, alter plasma cholesterol concentrations see review by Bauman et al.

As with cancer studies, promising results from animal experiments are not always supported by human epidemiological studies. This is another example where promising animal responses are not always translated into equivalent human responses. Conclusions It is clear that in many countries, including the UK, several decades of nutritional advice aimed at reducing dietary saturated fat intake have dramatically reduced intake of full-fat dairy products.

However, these changes appear to have had little impact on total SFA consumption when expressed as a proportion of total energy intake. Despite this, CVD death rates have continued to decline. Although this has led to a limited availability of n-3 PUFA enriched milk to the consumer, the value of such milk can be challenged because of its relatively high SFA content.

The most recent threat to the dairy industry could be a global move toward labelling of the trans fatty acid content of foods. With a reduction in the use of PHVO, dairy fat will become the largest source of dietary trans fatty acids. However, growing evidence suggests VA, that the predominant isomer found in milk fat, may actually be beneficial rather than detrimental to human health. A major challenge is, however, to persuade legislators and the public to recognise this distinction.

The last decade has seen a proliferation in potential health claims attributed to CLA. Growing evidence suggests that RA, the major CLA isomer associated with dairy fat, continues to hold some promise as an anti- carcinogenic and possibly anti-atherogenic component of milk fat. Further human feeding trials are required to confirm these benefits.

References Adlof, R. Lipids Arterburn, L. Ashes, J. Wiseman , pp Nutrition and Cancer 41, Bauman, D. Journal of Dairy Science 83, In: P.

Fox and P. McSweeney Eds. Corl, B. Ip, C. Salter, A. In: K. Sejrsen, T. Hvelplund, and M. Nielsen Eds. Marcel Dekker Inc. Craig-Schmidt, M.

Sebedio and W. The Oily Press, Dundee, Scotland, pp. Emken, E. Feng, S. Garnsworthy, P. Nottingham University Press, Nottingham. Gebauer, S. Grummer, R. Hoare, J. Volume 5. HMSO London. Hulshof, K. European Journal of Clinical Nutrition 53, Journal of Nutrition Jones, D. Journal of Dairy Science Keys, A. Particular saturated fatty acids in the diet. Metabolism Acta Med Scand Suppl. Lichtenstein, A. Circulation Lock, A.

Livestock Production Science Proceedings of Cornell Nutrition Conference pp. Salter c Effect of butter enriched in conjugated linoleic acid CLA and vaccenic acid on plasma lipoproteins and tissue fatty acid composition in the cholesterol-fed hamster.

Australian Journal of Dairy Technology In: E. Kebreab, J. Mills, and D. Beever Eds. Loor J. Animal Feed Science and Technology Mensink, R. American Journal of Clinical Nutrition Petit, H. Unal, B. A and Capewell, S. Salminen, I. Journal of Nutritional Biochemistry 9: Proceedings of the Cornell Nutrition Conference What has and what might be achieved?

Shorten, P. Journal of Dairy Research Stender, S. Atherosclerosis supplements 7: Tricon, S. Tricon, S.

Turpeinen, A. American Journal of Clinical Investigation Lapierre et al. Introduction Over the last decade, there has been a renewed interest to increase the efficiency of transfer of the crude protein fed to the dairy cow into milk true protein. Such increased efficiency would help to reach two high-currency objectives: increase the competitiveness of dairy producers and dairy products in a global market, and limit the impact of livestock production on the environment.

Part of the excretion of nitrogen N , which is the protein not used by the animal, is recognized to contribute to N 2 O formation, a greenhouse gas, and to ammonia emission leading to the formation of fine particulate matters, largely responsible for the deterioration of the quality of air.

To increase efficiency, we need to improve the match between supply and requirements, and we need to refine our estimations of both. Big improvements have been achieved in recent decades to refine our assessment of protein supply to dairy cows: we moved from crude protein to degradable and undegradable protein.

These represent a combination of partial requirements for rumen microflora and for the cow itself. A last step was then achieved to determine the amount of protein ultimately available and used by the animal itself, the metabolizable protein MP.

To estimate MP available to dairy cows, complex rumen sub-models have been developed to combine rumen degradability of protein and energy, rate of passage, etc. These predictions yield not only the flow of MP, but also the flow of individual amino acids AA. In this chapter, we will limit our considerations to essential AA. Essential AA include histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine. This does not deny the importance of the non-essential AA.

The polypeptide chains constituting proteins contain both essential and non-essential AA, but the non-essential AA can be synthesized by the dairy cow. However, there is a sub-group within the non-essential AA for which synthesis is not sufficient to support high levels of production; these are called semi-essential. Arginine is the most typical AA of this group as de novo synthesis of arginine could represent up to 0.

Histidine could theoretically also be synthesized by the mammal, but its synthetic pathway has limited capacity and therefore endogenous synthesis is usually ignored. It has also been suggested that glutamine may be classified as semi-essential under certain circumstances, especially around calving Doepel et al.

Data are scarce on non-essential AA metabolism especially to quantify de novo synthesis and therefore having an accurate estimate of their true total supply to the dairy cow , so the discussion will be limited to the fate of essential AA. Why should we consider individual AA? At the tissue level, it is clear that the raw material used by cells to build proteins is free AA. Therefore, an estimation of requirements in terms of AA theoretically would cover exactly what is being used by the animal.

If the supply of protein always contain the same proportions of AA, and all AA had similar metabolic fate, then we would not need to partition supply and requirement of MP into individual AA. This is clearly not the case, as discussed below. This clearly indicates that MP cannot be considered as a homogenous entity and needs to be better defined in terms of its AA to really assess what is provided to the dairy cow.

Lysine and methionine content proportion of essential AA of feed ingredients, bacteria and milk. Concentration of lysine and methionine proportion of essential AA in duodenal protein from studies used by NRC to develop equations predicting duodenal AA flow. Once it is recognized that the proportion of AA in duodenal digesta can vary widely, the first challenge becomes to predict adequately the supply of individual AA.

Models use different approaches to estimate flow of individual AA available to the dairy cow, either assigning an AA composition to each duodenal fraction, RUP, microbial protein e. Estimated duodenal flow combined with a digestibility factor estimates the amount of AA available to the animal.

As discussed later, not all of the duodenal flow represents a net input of AA to the dairy cow. In dairy cows, up to 0. At the entrance to the duodenum, endogenous proteins comprise mainly mucoproteins, saliva, sloughed epithelial cells and enzyme secretions into the abomasum Tamminga et al.

This endogenous fraction constitutes a recycling of AA previously absorbed from the small intestine, returned to the gut tissue via arterial circulation and used to build proteins that are returned into the lumen of the gut prior to the duodenum. As such, they do not represent a net input of AA for the animal, but are just a form of recycling.

In summary, the proportion of essential AA in duodenal protein will vary greatly, depending mainly on source of RUP and its degradability in the rumen. The splanchnic tissues comprising the portal-drained viscera gut, spleen, pancreas and associated mesenteric fat plus the liver have been extensively studied because of their high metabolic activity.

In dairy cows, despite the fact that these tissues contribute less than 0. Net utilisation of essential AA across the gut Measurement of net utilisation of essential AA across the gut is not an easy task. In other tissues, AA are only supplied from the blood source and can be more easily quantified.

However, net supply of AA to the gut also requires quantification of AA digested from the lumen of the small intestine. More recent data in sheep MacRae et al. However, this ratio does not really represent what is being lost through passage across the gut. As discussed above, part of the small intestinal disappearance is not a net supply. Endogenous proteins secreted prior to the duodenum have been made from AA provided by arterial supply and their digestion and absorption do not contribute to net supply.

Therefore, without any net utilisation of AA by the gut tissue, portal absorption will always be less than apparent disappearance from the small intestine. True losses of AA across the gut will be through oxidation and those endogenous secretions that are not reabsorbed and therefore secreted in the faeces.

There are limited data in ruminants on endogenous protein secretions and gut oxidation; both processes being challenging to measure directly. However, recent studies reported oxidation across the portal-drained viscera of leucine in dairy cows Lapierre at al. Phenylalanine was also observed not to be oxidized across the gut in dairy cows Reynolds et al. In dairy cows, indirect measurements comparing estimated flow of digested AA and measured portal absorption have suggested substantial losses of branched- chained AA isoleucine, leucine and valine , probably via oxidation, and of threonine, most likely due to its high concentration in endogenous secretions Lapierre et al.

A more complete review of AA utilisation by the portal- drained viscera across farm species is in Lobley and Lapierre An additional loss of AA through gut metabolism is endogenous secretions that are not reabsorbed and are excreted in the faeces. Quantification of these losses is also challenging and there is no general agreement between predictive systems as to what they are and on which basis they should be calculated dry matter intake, body weight, or protein intake.

Recent work has shown that they can represent up to 0. More work is needed to elucidate the true loss of AA through this metabolic fate in high yielding dairy cows. Overall, despite the fact that exact amounts and regulatory mechanisms are still unknown, there is enough evidence to suggest significant net utilisation of some essential AA by gut tissues, mainly through oxidation and losses of endogenous proteins in the faeces, at a rate that differs among AA.

From a database of studies where N transfers across the splanchnic tissues had been studied 22 treatments , the liver removed 0. We have to be very cautious in the interpretation of this number before we apply it to all AA; a ratio of 0. This removal encompasses all AA, essential and non-essential. The liver removes AA for a number of purposes.

Among other functions, the liver plays the important role of avoiding hyperaminoacidaemia and therefore extracts excess AA through urea synthesis, uses AA for synthesis of proteins some of which are then exported to the plasma and also uses some AA, mainly non-essential, for synthesis of glucose. These different roles of the liver already suggest variable and different hepatic removal of different AA. To better estimate the fate of individual AA across the liver, another database was used, in which net splanchnic flux of individual AA had been measured 14 treatments; Lapierre et al.

Two groups of essential AA were quite distinctive in their behaviour across the splanchnic tissues and related well with the groups described by Mepham according to their metabolism across the mammary gland. Amino acids from Group 1, for which mammary uptake is approximately equal to secretion in milk protein, are substantially removed by the liver, and post-liver supply is approximately equal to mammary uptake. Histidine, methionine, phenylalanine, and tryptophan are included in this group.

On average, hepatic removal relative to net portal absorption varied from 0. In contrast, AA from Group 2, already identified as those for which mammary uptake exceeds milk output, are, on a net basis, barely removed by the liver, and post-liver supply is higher than mammary uptake.

Group 2 consists of the branched-chain AA isoleucine, leucine and valine and lysine. Therefore, despite the fact that the liver is the major site of ureagenesis, not all of the excess essential AA is, on a net basis, extracted by the liver. They can be deaminated elsewhere in the body and the N returned to the liver through shuttles like alanine or glutamine prior to excretion of the N as urea. The distribution of enzymes responsible for AA catabolism is directly linked with the two groups described above.

For Group 1 AA, degradative enzymes are predominantly restricted to the liver; for Group 2 AA, the enzymes responsible for catabolism are widely distributed across tissues, including liver, muscle, fat, gut and mammary gland Lobley and Lapierre, For AA of Group 2 isoleucine, leucine, valine and lysine , uptake usually exceeds output.

These observations have been made in connection with splanchnic measurements Berthiaume et al. It should be stated here that mammary uptake of non-essential AA except arginine is usually not sufficient to support the amount of non-essential AA used to make milk protein, i.

Effectively, it has been shown that N from lysine taken up by the mammary gland in excess of milk protein was used for synthesis of non-essential AA within the mammary gland Lapierre et al.

Figure 3 summarizes the fate of two AA representative of Group 1 methionine and Group 2 lysine across the splanchnic tissues and the mammary gland Lapierre et al. Overall, it is clear that metabolism of AA varies among AA and between tissues.

Therefore we need to refine our definition of supply and requirement to the AA level and not just their aggregate, the proteins. Such an approach has been proven to be beneficial in monogastrics, in terms of animal performance, production cost and reducing the impact of livestock on the environment.

Portal absorption 1. Net flux of two essential AA representative of Group 1 methionine and Group 2 lysine in dairy cows, relative to portal absorption. As both the proportional contribution to duodenal flow and the metabolic fate across the gut, the liver and the mammary gland vary markedly among essential AA, it appears necessary to consider individual AA in dairy nutrition.

However, it is not enough to determine adequately the supply of MP or individual AA. The NRC applies a fixed conversion factor of 0. Therefore, these models estimate a fixed return of increased protein supply into milk protein until requirements are reached, after which the response is zero.

These efficiency factors are unlikely to be fixed across protein intakes if energy is sufficient ; few biological systems work in a linear fashion with a zero response once a threshold is reached. To help solve this issue, a study was performed to measure net tissue AA metabolism at different protein intakes in dairy cows Raggio et al.

Second, post-liver supply of essential AA was sufficient for milk protein yield, which suggests that utilisation of body protein i. As shown in Figure 4, removal of AA methionine as an example of Group 1 and lysine as an example of Group 2 increased at a proportional rate higher than increased portal absorption. This increased removal occurred across the liver for Group 1 and across the mammary gland and peripheral tissues for Group 2, resulting in a decreased efficiency at higher protein intake.

For lysine, the ratio of milk protein output to portal absorption averaged 0. If estimated requirements for maintenance are removed to obtain efficiency for lactation, efficiencies of lactation are 0. Clearly, at lower protein supply, the animal has the capacity to reduce AA catabolism. Indeed, in dairy cows, increased MP supply increased oxidation of leucine across the gut, the liver Lapierre et al. It has also been observed that mammary uptake of AA from Group 2 in excess of the needs for AA output into milk protein increased as protein supply increased e.

Guinard and Rulquin, , Raggio et al. This indirectly suggests increased catabolism of these AA in the mammary gland, although this excess of uptake of AA from Group 2 relative to milk output is not essential to maintain milk protein output Bequette et al.

Studies measuring directly the fate of AA across tissues have shown that the dairy cow has the possibility to decrease catabolism of AA as supply is reduced. This decrease is observed whether the site of catabolism of essential AA is the liver or other tissues, including the gut and the mammary gland. Net flux of two essential AA representative of Group 1 a- methionine and Group 2 b- lysine in dairy cows at two protein feeding levels.

In an effort to predict efficiency in relation to supply, a database 59 trials was built by compiling all published reports where AA had been infused post-ruminally Doepel et al. Linear and non-linear models were tested to relate milk AA-protein output to AA supply with just the control treatment relying on a predictive model to estimate digestible AA.

A segmented-linear model fixed efficiency followed by zero response when requirements are met - Figure 5a and a logistic model Figure 5b were similar in their reliability Doepel et al. These estimates were close to the efficiencies estimated in the study of Raggio et al.

From estimation of the optimum supply for individual AA Doepel et al. Despite the fact that this theoretical calculation has many limitations, especially as AA were usually infused in groups rather than individually in most of the studies, the requirements estimated with this approach were identical to those obtained previously by Schwab et al.

Segment-linear a and logistic b models of lysine in milk protein as a function of lysine supply. Efficiency of utilisation of AA for lactation after discounting maintenance requirements from total AA supply.

Linear Logistic model model Proportion of optimum supply AA fixed 0. This should help to improve prediction of milk protein output with alterations in protein supply.

However, this approach maintains a fixed efficiency for utilization of absorbed AA towards maintenance functions. Such a situation, with variable efficiency of utilization of AA for production and fixed efficiency for maintenance, is somewhat artificial, as removal of each AA across the different tissues will be a single function. Therefore, the animal will not change efficiency of utilisation for one metabolic function and not for the other.

In a near future, we may need to rethink our estimation of maintenance requirements in line with a new approach for the efficiency of lactation. Because post-liver supply of Group 1 AA equals milk protein output, it becomes tempting to suggest that the liver has the role of regulator and only what passes through the liver can be used by the mammary gland. However, we have to remember that these are static net measurements. If the liver removes a high proportion of what is absorbed, total inflow to the liver is much higher than absorption alone.

The proportion of total inflow i. Thus, mammary gland anabolism and capture of AA would also affect gut and liver removal. What are the signals bridging mammary, gut and hepatic metabolism? In the fed situation, milk protein output of Group 1 AA is directly related to post-liver supply; in this case, hepatic removal is highly correlated with concentrations portal or arterial , portal-arterial difference or liver influx Hanigan et al.

However, when AA are infused into a jugular vein, the relation between hepatic removal and portal-arterial difference is totally lost and removal is then linked only with concentration or inflow Berthiaume et al. In addition, the mechanism regulating extraction of Group 2 AA across the mammary gland in excess of requirements for milk protein synthesis is unknown.

It is not clear if this is just an obligate mechanism due to the location of degradative enzymes for these AA to remove them when they are in excess, or if this excess uptake has some underlying purpose.

A recent study where milk protein production was enhanced with protein casein showed that mammary uptake of Group 2 AA is enhanced to support increased milk protein production more than uptake of non-essential AA, whereas propionate supply increased uptake of non-essential AA. Hormonal cross-talking probably drives this coordination Berthiaume et al.

Conclusion In conclusion, the biology beyond the rumen clearly indicates why we need to consider individual AA. The proportion of AA in duodenal protein flow and their metabolic fate across the gut, the liver and the mammary gland vary greatly among individual AA.

In addition, decreased efficiency of transfer of absorbed AA into milk protein with increased protein supply, supported by empirical observations, is directly related to increased extraction of AA for non-productive purposes across different tissues.

We still need to determine the key factors regulating how efficiency of transfer of absorbed AA into milk protein increases with decreased supply and vice-versa to improve prediction of milk output. The real challenge for nutritionists will be to determine to which level of total MP, and with which balance of individual AA supply, this optimal efficiency can be achieved, i.

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Animal Production, 80, Huntington, G. Reproduction Nutrition Development, 30, Edited by R. Jarrige and J. Eurotext, Paris, France. Lapierre, H. Journal of Dairy Science, 85, Edited by W. Animal Science, 80, Lobley, G. Dennison, N. British Journal of Nutrition, 89, Macrae, J. Journal of Animal Science, 75, Meijer, G. In Proceedings of the Seventh Symposium on protein metabolism and nutrition, pp. Edited by A. Nunes, A. Portugal, J. Costa and J. Estacoa Zootechnica National, Santerm, Portugal.

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Wright, T. Journal of Dairy Science, 81, Thatcher et al. However, it is evident that many of the cows presented for service are anovulatory and are not in a state to achieve optimal fertility. Pregnancy loss was highest Consequently, minimizing losses of BCS after calving and improving cyclicity early postpartum are expected to increase PR and enhance embryonic survival.

The challenge is to manage body condition in healthy cows, with an inherent high dry matter intake, so that they have sufficient energy stores at parturition to meet the demands of ensuing negative energy status without a predisposition to fatty livers and metabolic disturbances and have sufficient body condition at the beginning of the breeding period such that they are cycling and able to sustain a pregnancy. The focus of this chapter is to identify those physiological windows during the periparturient and postpartum periods that appear to be amenable to nutritional management that may improve subsequent fertility during the insemination period.

A better understanding of calving-related factors that predispose cows to PM would aid in the prevention, diagnosis, and treatment of this condition. A prospective longitudinal study was conducted with a cow dairy farm in north Florida between August 1, and April 15, to evaluate the effect of calving status, parity, and season on the incidence of postpartum PM in lactating dairy cows, and the role of rectal temperature as a predictor of this condition Benzaquen, Risco, Archbald, Melendez, Thatcher and Thatcher, The farm employed a postpartum health monitoring program.

Cows with an abnormal calving status Ac were those with dystocia, retained foetal membranes with or without dystocia, or twins at calving. Daily rectal temperature RT of all cows was taken between and h from days 3 to 13 post partum, and a health examination was performed by the on-farm veterinarian. Cows that appeared sick depressed, eyes tented, etc.

Cows diagnosed with septic metritis were treated with systemic antibiotics, anti-inflammatory agents, calcium, and energy supplements. The environmental thermal heat index THI was calculated using the daily ambient temperature and percent relative humidity recorded at the closest weather station. A total of parturitions were evaluated.

Cows with Nc had a lower incidence of PM compared to cows with an Ac status 13 vs. A season by parity interaction was detected. During the cool season, primiparous cows had the highest incidence of PM The reasons for the parity difference are speculative; perhaps foetal stunting during the hot season in Florida reduced the incidence of dystocia, whereas larger calves born in the winter season increased occurrence of dystocia and subsequent PM in primiparous heifers.

In cows with PM and fever at diagnosis, the RT started to increase between 72 to 48 h before the diagnosis of PM and continued to increase to a maximum RT of However, for cows with PM and no fever at diagnosis, no daily incremental increases of RT before the diagnosis of PM were detected; however, the RT on day 0 Cows without PM had a stable RT during the first 13 days postpartum mean of All cows were examined for clinical endometritis between 20 and 30 days postpartum.

The criterion used to diagnose clinical endometritis was one of the following conditions associated or not with each other: cervical diameter greater than 6. A higher incidence of clinical endometritis was detected for those cows diagnosed with PM A vivid example is the repeat breeder cow that appears to be clinically normal regarding the reproductive tract but has repeated normal cycles and fails to conceive.

A proportion of repeat breeder cows have distinct alterations in spatial endometrial architecture characterized by walled-off and occluded uterine glands, degeneration of the glandular epithelium, thickening of the underlying stroma, and infiltration of either eosinophils or lymphocytes or both Cupps, It was hypothesized that this localized condition was a carry over from prior inflammatory responses to metritis and endometritis in the early postpartum period.

Recent findings indicate that repeat breeder cows have an abnormal pattern of epidermal growth factor EGF concentrations in endometrial tissue during the oestrous cycle and that treatment involving exposure to oestradiol may restore a normal secretory pattern and fertility Katagiri and Takahashi, Perhaps the physiological status of lactation and high production has associated homeorhetic regulatory effects that alter the local inflammatory status within the uterus.

Perhaps the anti-inflammatory effects of long chain n-3 polyunsaturated fatty acids, administered via the diet, may have a therapeutic role during the breeding period. The incidence of diseases and disorders can be high during this time period and have a negative impact on reproductive performance. Reduction in adaptive and innate immunity at parturition increases the risk of health disorders such as RFM, metritis, and mastitis.

Selenium has long been associated with immunity. The state of Florida, USA is in a selenium deficient area, and lactating dairy cows are exposed to a seasonal period of heat stress that affects reproductive performance and health. We have conducted an experiment to evaluate a supplemental source of organic selenium on reproductive and immune responses by dairy cows Silvestre, Silvestre, Santos, Risco, Staples and Thatcher, ; Silvestre, Silvestre, Crawford, Santos, Staples, and Thatcher, Objectives were to evaluate effects of organic Se on PR at the first and second postpartum AI services, uterine health, and milk yield during the summer heat stress period.

Rectal temperature was recorded each morning for 10 days postpartum dpp. Vaginoscopies were performed at 5 and 10 dpp. All cows were resynchronized for a second service with Ovsynch at 20 to 23 days after first service. An ultrasound pregnancy diagnosis was conducted at 27 to 30 days after first TAI. Strategic blood sampling determined anovulatory status at Ovsynch and ovulatory response after TAI to first service.

Plasma Se increased in SY-fed cows 0. Milk yield These low pregnancy rates and high embryonic losses are typical of cows managed during the summer heat stress period of Florida.

The benefit of SY on second service pregnancy rate is intriguing. We hypothesize that cows of the SY group were better able to re-establish an embryo-trophic environment at second service following either early or late embryonic losses.

Vaginoscopy discharge scores at 5 and 10 dpp were better for the SY group; namely, Innate immunity i. Samples were collected from a subsample of 36 cows at dpp and 40 cows at 0, 7, 14, 21 and 37 dpp and analyzed for neutrophil function. Adaptive immunity ability to induce an antibody response was monitored with anti-IgG to Ovalbumin Ovalb following vaccination with Ovalb antigen 1 mg [i. Serum samples were collected on days of immunization and at 21 and 42 dpp.

Percentage of gated neutrophils that phagocytized E. It is clear that neutrophil function is suppressed in multiparous cows at the time of parturition and it is not restored until between 7 to 14 days postpartum Figure 1. Coli 65 60 55 50 45 40 35 30 25 20 15 0 7 14 21 37 Days relative to parturition Control Sel-Plex Figure 2. Organic Se improved phagocytosis and killing activity of neutrophils in both multiparous and primiparous cows Figures 1 and 2.

However, the primiparous cows seemed to be more responsive in that SY stimulated neutrophil function throughout 0 to 21 dpp whereas, SY stimulation in multiparous cows was evident on only the day of parturition. In most of our postpartum experiments, we detect distinct differences between primiparous and multiparous cows for a multiplicity of physiological and biochemical responses.

Although Anti-IgG to Ovalb concentration did not differ between dietary groups for primiparous cows 1. Thus our measurement of adaptive immunity was improved in multiparous dairy cows in response to SY but not in primiparous cows. It is clear that dietary fat effects are not simply due to energy, but that specific nutraceutical effects probably are manifested whereby certain fatty acids interact as substrates for specific enzymes e.

These specific long-chain polyunsaturated fatty acids produce eicosonaoid products of the prostaglandin series PGF1, PGF2 and PGF3, respectively, as well as various thromboxanes, leukotrienes, lipoxins, hydroperoxy- eicosatetraenoic acids and hydroxyeicosatetraenoic acids HETE that regulate inflammation and immunity.

Clearly, the early postpartum period represents a time when the immune system is suppressed severely and there are major inflammatory processes underway in association with regression of the uterus and reabsorption of uterine tissues.

Several of the eicosonaoids exert pro- inflammatory actions e. Consequently, feeding fatty acids e. Later on in the postpartum period, it may be reasonable to feed fatty acids e.

The study was designed to be carried out in the summer heat stress period of Florida. Blood samples were collected thrice weekly from calving until 10 weeks after parturition. An Ovsynch program was begun between 5 and 10 days of the cycle on 62 dpp with AI occurring at 72 dpp. Orthogonal contrasts tested for treatments were 1 vs.

Mean milk production was