Considering ruminal interactions in energy and protein evaluation systems for ruminants in Denmark

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1 Considering ruminal interactions in energy and protein evaluation systems for ruminants in Denmark J. Madsen 1, T. Hvelplund 2, M. R. Weisbjerg 2,, I. K. Hindrichsen 1 and P. Lund 2 1 Department of Large Animal Sciences, Faculty of Life Sciences, University of Copenhagen, Groennegaardsvej 2, DK-1870 Frederiksberg C., Denmark 2 Department of Animal Health, Welfare and Nutrition, Research Centre Foulum, Faculty of Agricultural Sciences, University of Aarhus, DK Tjele, Denmark ABSTRACT The transformation of the feeds in the rumen by microbes is included in most protein evaluations systems introduced in the 1980 and 1990 s but it is only partly considered in present energy evaluation systems. The microbial transformation not only change the composition of the nutrients available for the absorption by the ruminant, but it also cause an interaction between the feeds leading to a non additive protein and energy value of the feeds. These non additive values are difficult to handle and may lead to different energy and protein evaluation systems for different groups of animals and different production systems. KEY WORDS: AAT, cattle, feed, PBV, Scandinavia, NorFor TM, INTRODUCTION The most important transformations of the feeds influencing the energy and protein values of the feeds for ruminants, happens in the rumen. Most of the energy is by the microbes transformed from carbohydrates to short chain fatty acids and most of the feed protein is transformed to microbial protein. The ruminant itself subsequently feeds on the microbes and the by products from the microbial metabolism. This transformation of the feeds in the rumen by microbes is included in most protein evaluations systems introduced in the 1980 and 1990 s but it is only partly considered in present energy evaluation systems. The microbial transformation not only change the composition of the nutrients available for the absorption by the ruminant, but it also cause an interaction between the feeds leading to non additive protein and energy values of the Corresponding author: jom@life.ku.dk

2 feeds. These non additive values are difficult to handle and may lead to different energy and protein evaluation systems for different groups of animals and different production systems. In practice, slightly misleading feed values given by inadequate feed evaluation systems, caused by ruminal interactions, are often corrected through the recommendations for feeding the livestock. In the Nordic countries a new feed evaluation system, NorFor, (energy and protein) is at present under development and being introduced for dairy cows (Gustafsson et al. 2005). Similar systems are being developed for young stock and beef production. However, at present most dairy cows and the young stock and beef cattle in Denmark are still fed according to the modified Scandinavian feed unit (Weisbjerg and Hvelplund, 1993) and digestible crude protein or the AAT-PBV system (Madsen, 1985, Madsen et al ) THE MODIFIED SCANDINAVIAN FEED UNIT The Scandinavian Feed unit (SFU) is based on net energy and traditionally estimated from digestible nutrients found in digestibility experiments with sheep fed at maintenance level and converted to net energy based on production experiments where the estimated energy content was converted to actual energy value after correction with a value number. The energy value used for the individual nutrients originates from the starch equivalent system introduced by Kellner (1905). After modifications where the energy value of protein was increased and changed from its value as substrate for fat deposition to its value for milk production the system was introduced in Denmark together with the other Scandinavian countries as the Scandinavian Feed Unit in In principle this system is still used in Denmark although different modifications have been introduced. To day the feed unit is calculated from organic matter digestibility estimated from in vitro digestibility either by using rumen fluid or enzymes for the digestion process. Organic matter digestibility is then converted to protein, fat and carbohydrate digestibilities by the procedure described by Weisbjerg and Hvelplund (1993) according to the principles outlined in Figure 1. The principle is that digestible amounts of crude protein and crude fat are estimated based on their concentration in the feed DM (Lucas principle), and subsequently digestible carbohydrates are estimated by difference.

3 SFU per kg DM = x digestible energy (MJ/kg DM) x crude fibre (kg/kg DM) Digestible energy (MJ/kg DM) is estimated as follows: Digestible energy (MJ/kg DM) = x digestible crude protein (kg/kg DM) x digestible crude fat (kg/kg DM) x digestible carbohydrates (kg/kg DM) x sugar (kg/kg DM) where Digestible crude protein (kg/kg DM) = (0.93 x % crude protein in DM - 3)/100 Digestible crude fat (kg/kg DM) = (0.96 x % crude fat in DM - 1)/100 Digestible carbohydrates (kg/kg DM) = (digestibility of organic matter /100) x (100 - % crude ash in DM)/100 - digestible crude protein - digestible crude fat The correction for sugar is made only for feeds where the sugar content exceeds 20% of the DM content. Figure 1. Estimation of content of Scandinavian Feed Units (SFU) in feedstuffs THE AAT-PBV PROTEIN EVALUATION SYSTEM The protein evaluation system introduced together with the Scandinavian Feed Unit in 1926 was based on digestible pure protein and in 1961 changed to digestible crude protein based on the knowledge that ruminants could utilize non protein nitrogen in their microbial metabolism in the rumen. Improved knowledge on protein metabolism in the gastro-intestinal tract of ruminants, especially quantification of protein degradation and microbial protein synthesis, led to development of the AAT-PBV protein evaluation. This system was introduced in 1985 and subsequently applied in the Nordic countries. In the AAT-PBV protein evaluation system the feed is evaluated both with respect to its ability to supply the ruminant with amino acids originating from rumen undegraded feed protein and from microbial protein, and its ability to supply the rumen microbes with N originating from rumen degradable protein and with energy from fermentable organic matter (carbohydrates) for microbial protein synthesis.

4 Calculation of AAT and PBV requires information on several parameters related to the protein value of a feed (Madsen et al., 1995) and the calculation is outlined in Figure 2. Several factors are kept as constants in the system, but factors like protein degradation in the rumen and intestinal digestibility of undegraded protein are variables and are in the system estimated with the nylon bag technique (Hvelplund and Weisbjerg, 2000) and the mobile nylon bag technique (Hvelplund et al., 1992), respectively. The protein evaluation system also allows calculation of the contribution with individual amino acids based on the same principles as used for AAT as outlined above. This is based on knowledge of amino acid composition of feed and microbial protein and using the same factors for individual amino acids as applied for calculation of AAT (Hvelplund and Madsen, 1989). AAT (g/kg DM) = A x (1 - B/100) x C x D/100 + (E x F x G) PBV (g/kg DM) = (A x B/100) - (E x F/H) where A = crude protein (g/kg DM) B = effective rumen degradability of protein (% of N). C = proportion of amino acids in rumen undegraded protein [constant: 0.85 for concentrates and 0.65 for roughages] D = intestinal digestibility of rumen undegraded protein (%) E = synthesis of microbial amino acids (g/kg digestible carbohydrates) [constant = 125] F = digestible carbohydrates (kg/kg DM). G = digestibility of microbial amino acids. [constant = 0.85] H = proportion of amino acids in microbial protein. [constant = 0.70] Figure 2. Estimation of content of AAT and PBV in feedstuffs For the ruminant categories that are not considered to have a high requirement for absorbed amino acids in relation to the energy requirement it is likely that the content of digestible crude protein is as good as any other measurement for the protein value of the feed as the protein value in such a situation is describing how well the rumen microbes are supplied with nitrogen. In addition the rumen microbes may have a requirement for degradable pure protein, but this is not described in any system yet. NORFOR TM CONSIDERING RUMINAL INTERACTION

5 NORFOR TM is an example of the upcoming models which integrates new knowledge with respect to chemical composition of feeds, digestion processes in the gastro intestinal tract, the synthesis of microbial organic compounds in the rumen and large intestine, the interaction between the different feed components and the effect of feeding level. Moreover the system integrates the feed values and the requirements of the cows in one model. The overall picture of the system is illustrated in Figure 3. Input Feeds (Chemical and physical) Anim als (Yield, breed, weight, etc.) Structure (Chewing time) D igestion and interm ediate m etabolism Nutrient supply to the anim al Feed intake (Filling value) O utput M inim um cost ration + a lot of inform ation about for exam ple the content of energy, AATp, PBVp, rum en passage rates, microbiel efficiency Figure 3. The elements in NORFOR TM Compared to the proximate analysis used to characterise feeds the new system works with a more detailed fractionation of the feed and the different feed fractions are further characterized not only by their concentration but also the rate of degradation in the rumen. Based on the characteristics of the individual feed components the model then calculate the outcome of nutrients supplied to the animal based on the prediction of nutrient metabolism along the gastrointestinal tract. Passage rate and fermentation rate are the determining factors and these factors are then influenced by other factors where the structure of the feed, the content of sugar and starch in the diet and the feeding level are the most important factors. This means that the individual feeds cannot be characterized by their energy and protein value as the interactions predicted are related to the characteristics of the diet. However, two standard feed values calculated at a feeding level of 8 and 20 kg dry matter intake are tabulated for energy and protein values. The energy value is expressed as net energy lactation (NEL) and the protein values as amino acids absorbed in the small intestine (AAT p ) and the protein balance in the rumen (PBV p ).

6 DISCUSSION AND CONCLUSIONS When the SFU system was introduced in the beginning of last century there was only limited knowledge concerning rumen fermentation and the importance of this organ for metabolism of feed was consequently not included in the system. Improved knowledge on the importance of rumen metabolism is reflected in the protein evaluation systems formulated in many countries during the end of last century. Further attempts to improve utilization of the new knowledge have lead to development of several computer models for modelling either the gastro intestinal tract or the whole animal. The energy and protein evaluation systems in use in Denmark is at present in a state of change from the traditional systems where individual feeds were characterized by fixed values for energy and protein to a system based on a mechanistic model where the energy and protein values of the diet are predicted based on modelling of the nutrient output of the diet and thereby vary according to ration composition and feed intake level. However, only dairy cows are covered by the model at present. Finally, it is recommended that more focus is put on the requirements of the rumen microbes to optimize their symbiosis with the ruminant animals in different situations. REFERENCES Gustafsson, A. H., Volden, H., Mehlqvist, M., Larsen, M, Gudmunsson, G., Aaes, O NorFor TM the new Nordic feed evaluation system for cattle. The 56 Annual meeting of European Association for Animal production. Uppsala, Sweden. June pp. Hvelplund, T., Madsen, J Prediction of individual amino acid passage to the small intestine of dairy cows from characteristics of the feed. Acta Agr. Scand Hvelplund, T., Weisbjerg, M.R., Andersen, L.S., Estimation of the true digestibility of rumen undegraded protein in the small intestine of ruminants by the mobile bag technique. Acta Agric. Scand., sect. A, Anim. Sci Hvelplund, T. Weisbjerg, M.R., In situ techniques for the estimation of protein degradability and post rumen availability. In: D.I. Givens, E. Oven, R.F.E. Axford & H.M. Omed (eds). Forage evaluation in ruminant nutrition. CABI Publishing Kellner, O Die Ernährung der Landwirtschaftlichen Nutztiere. 1. Ausg. (1905), 1924, P. Parey, Berlin. Madsen, J The basis for the proposed Nordic protein evaluation system for ruminants. The AAT-PBV-system. Acta Agr. Scand. Suppl. 25, Madsen, J., Hvelplund, T., Weisbjerg, M.R., Bertilsson, J., Spörndly, R., Olsson, I., Harstad, O.M., Volden, H., Tuori, M., Varvikko, T., Huhtanen, R., Olafsson, B.L., The AAT-PBV protein evaluation system for ruminants. A revision. Norwegian J. Agric. Sci. Suppl. No. 19, Weisbjerg, M.R., Hvelplund, T., Bestemmelse af nettoenergiindhold (FE k ) i råvarer og kraftfoderblandinger. Forskningsrapport nr. 3, Statens Husdyrbrugsforsøg. 39 pp.