Prediction of rumen microbial N supply in bovines from dietary values of partitioning factor (PF), in vitro rate of gas production (k), neutral detergent fibre and crude protein: A brief systematic review of studies completed in Bengaluru (India)

Experiments which used crossbred cows and heifers, from peer review publications originating from the Karnataka Veterinary, Animal and Fisheries Sciences University (Bidar) and Veterinary College (Bengaluru) in India were used to determine if ruminal microbial N (MN) supply could be predicted based upon the partitioning factor (PF, mg in vitro true digested organic matter: ml gas) of the diets fed to the cattle, their rate of gas production in vitro (k, /h,) as well as the neutral detergent fibre (NDFom) and crude protein levels of the diets. The MN supply to the duodenum was quantified based on allantoin excretion in urine. The five published experiments included 15 treatment groups. Multiple correlation analysis showed that the quadratic component of diet NDFom (P=0.02) and the linear (P<0.01) and quadratic (P<0.01) components of diet k (i.e., r2 = 0.87) predicted supply of microbial N (MN) to the duodenum according to the equation: MN (g/kg ADOM) = −25.7 + (1402*k) − (10177.4*k2) − (0.0000163*NDFom2) [SEP = 0.81], where k is in unit/h and NDFom is g/kg DM. Residuals of predicted versus actual MN values showed equal distribution. Changes in predicted values of MN were judged to be consistent with our understanding of their function in the rumen, as well as quantitatively consistent with published values determined in vivo. Overall, according to the prediction equation, supply of MN increases with increasing low levels of NDFom in the diet, but is maximized at all dietary NDFom levels with a dietary in vitro rate of gas production of 0.065–0.070/h. Results support utilizing in vitro rate of gas production in diet formulation, but not PF, although research with higher production ruminants is warranted.