Metabolizable protein systems in ruminant nutrition: A review

Abstract

Protein available to ruminants is supplied by both microbial and dietary sources. Metabolizable protein (MP) is the true protein which is absorbed by the intestine and supplied by both microbial protein and protein which escapes degradation in the rumen; the protein which is available to the animal for maintenance, growth, fetal growth during gestation, and milk production. Thus, the concept of balancing ruminant rations basing on only dietary crude protein (CP) content seems erroneous. In India, ruminant rations are still balanced for digestible CP and total digestible nutrients for protein and energy requirements, respectively. Traditional feed analysis methods such as proximate analysis and detergent analysis consider feed protein as a single unit and do not take into account of the degradation processes that occur in rumen and passage rates of feed fractions from rumen to intestine. Therefore, the protein requirement of ruminants should include not only the dietary protein source, but also the microbial CP from rumen. The MP systems consider both the factors, thus predict the protein availability more accurately and precisely. This system is aptly designed to represent the extent of protein degradation in the rumen and the synthesis of microbial protein as variable functions. Feed protein fractions, i.e., rumen degradable protein and rumen undegradable protein play vital roles in meeting protein requirements of rumen microbes and host animal, respectively. With the advent of sophisticated nutrition models such as Cornell net carbohydrate and protein system, National Research Council, Agricultural Research Council, Cornell Penn Miner Dairy and Amino Cow; ration formulation has moved from balancing diets from CP to MP, a concept that describes the protein requirements of ruminants at intestinal level, and which is available to animals for useful purposes.

Use of black soldier fly larvae (Hermetia illucens) to substitute soybean meal in ruminant diet: An in vitro rumen fermentation study

“…Despite CP contents of T3 and T4 were much higher in comparison to control (T1), their ammonia concentrations were similar. The balance between the ratio of degradable and undegradable protein in the rumen is a key for optimizing protein utilization in ruminant livestock [ 34 ]. It is apparent that mixing between SBM and BSF may provide a more balance between degradable and undegradable protein ratio rather than SBM only.…”

Determination of Energy and Protein Requirements of Sheep in Indonesia using a Meta-analytical Approach

“…This system is less accurate and current system has to be shifted to metabolizable protein (MP) system or its equivalent (NRC, 2007;Van Duinkerken et al, 2011;Das et al, 2014;Owens et al, 2014;Van Amburgh et al, 2015). The old CP system has a main disadvantage, i.e.…”

“…The old CP system has a main disadvantage, i.e. it does not differentiate between protein requirement of rumen microbes and protein requirement of the host animal (Das et al, 2014). The MP system, conversely, addresses both the need of N for rumen microbes and postruminal need of amino acids for maintenance and growth of the host ruminant (Owens et al, 2014).…”

“…By employing the MP system, basic goals in protein nutrition of ruminants can be achieved, i.e. (1) to meet rumen degradable protein (RDP) requirement of rumen microbes for maximum carbohydrate digestion and microbial protein synthesis, (2) to meet MP requirement of host animal for maintenance, growth, optimum health, and reproduction with minimum intake of rumen undegradable protein (RUP), and (3) to meet MP and amino acids requirements of the host animal for a desired production level with minimum dietary CP (Das et al, 2014). Even though MP system is preferable as compared to CP system, such application may be difficult due to limited data available like the case in Indonesia.…”

Effect of metabolizable protein intake on growth performance, carcass characteristics, and feeding behavior in finishing steers

“…In addition, N excretion in ruminants is not only related to N intake but also microbial efficiency that influences metabolizable protein (MP) supply ( Niu et al , 2016 ). MP is the true protein absorbed from the small intestine, supplied by microbial true protein, ruminally undegradable protein, and epithelial sloughed cells, which is available to the animal for maintenance, growth, and production ( Das et al , 2014 ).…”