Effect of bypass protein on yield and composition of milk in cross bred cows

Abstract

Experiments were carried out to evaluate common feeds and fodders based on their rumen degradability rates and to assess the effect of varying bypass protein levels in concentrate mixtures on rumen fermentation profile and yield and composition of milk in Jersey crossbred cows. The dry matter and nitrogen disappearance rates in respect of nine concentrate feed ingredients and five green roughages commonly used in cattle rations, were determined using nylon bag technique in rumen fistulated crossbred cows. The effective protein degradability rates for groundnut cake, gingelly cake, cotton seed cake, coconut cake, yellow maize, jowar, wheat bran, rice bran, tapioca flour, green maize (Zea mays), green jowar (Sorghum bicolor) and guinea (Panicum maximum), para (Brachiariamutica) and napier grass (Pennisetumpurpureum) were found to be 66.17, 78.89, 27.72, 19.93, 22.64, 47.96,74.16, 60.59, 68.83, 56.93, 58.80, and 35.74, 45.39 and 36.68 per cent respectively at a rumen outflow rate of 0.05 per hour. Among the four oil cakes, gingelly cake and groundnut cake were more degradable in the rumen, whereas, cotton seed cake and coconut cake were comparatively insoluble and more resistant to degradation and thereby better sources of bypass protein for ruminants. The results on degradability measurements with respect to energy feeds revealed that yellow maize contained the least amounts of both soluble and degradable nitrogen as compared to jowar, wheat bran, rice bran and tapioca flour. Wheat bran was found to have higher contents of both rapidly soluble and potentially degradable protein as compared to rice bran. Among the different green fodders tested for protein degradability measurements, cereal fodders like maize and jowar were found more soluble and degradable as compared to different grasses. The effect of three varying ratios (high, medium and low) of Rumen Degradable Protein (RDP) to Undergradable Dietary Protein (UDP) of 37:63, 52:48 and 70:30 in isonitrogenous and isocaloric concentrate mixtures on rumen fermentation profile was studied using rumen fistulated Jersey crossbred cows. Rumen pH and ammonia nitrogen concentrations were found to be lower with concentrate mixture containing a higher UDP level of 63.38 per cent when compared with those having medium and low UDP levels of 47.55 and 29.75 per cent respectively at all post feeding intervals. Total volatile fatty acid concentrations as well as the concentration of individual fatty acids viz., acetate, propoionate and butyrate were also found higher in animals fed on concentrate mixture with the highest UDP level. The effect of the three UDP/bypass protein levels in isonitrogenous and isocaloric concentrate mixtures on milk yield and milk composition was studied using eighteen medium producing Jersey crossbred cows in their early lactation period for 100 days starting from 5th day post partum. The food consumption of the animals was found to increase with increasing UDP levels in concentrate mixtures, the percentage dry matter intake of animals calculated over the entire period of experiment being 3.70, 3.38 and 3.14 respectively for groups fed on concentrate mixtures of high, medium and low bypass protein levels. While animals maintained on the concentrate mixture with the higher UDP level of 63.38 per cent recorded a total gain of 10.83 kg over a period of 100 days, those fed concentrate mixtures with UDP levels of 47.55 and 29.75 per cent respectively lost body weights to the extent of 3.33 and 5.83 kg over the same period of the experiment. The average daily milk yields were found to be 10.11, 7.18 and 6.32 kg respectively for groups fed on concentrate mixtures with high, medium and low UDP levels. The results on milk composition as influenced by varying UDP levels in concentrate mixtures revealed that while milk fat percentage was not altered with degradability changes both milk protein and total solids were found to increase corresponding to increase in UDP levels. The feed conversion efficiency of milk production as well as persistency of milk production was also found to be higher UDP levels over the entire period of the experiment. The income over feed cost per cow per day, calculated over the experimental period of 100 days were found to be Rs. 44.54, 29.91 and 25.28 with the three concentrate mixtures of high, medium and low UDP levels respectively. The overall results clearly revealed that in medium producing Jersey crossbred cows on a grass based diet, a UDP level of 63.38 per cent may be considered optimum in a concentrate mixture with 20 per cent CP and 70 per cent TDN for higher production and better economic efficiency in their early part of lactation.