Protein imbalance in dairy rations affects N balance and milk N efficiency (MNE) resulting in extra N excretion to the environment. The objective of this study was to investigate the changes in N balance, milk production, and plasma metabolites of lactating buffaloes in response to different dietary crude protein (CP) supplies. Six multiparous Nili Ravi buffaloes in mid-lactation were used in this experiment in a 3 × 3 Latin square design. The treatments were diets with 9.26, 10.0, and 11.4% of CP on DM basis. All the diets were iso-caloric (2.05 Mcal metabolizable energy/kg of DM), whereas oat silage was mixed with the respective concentrate and offered once daily as total mixed ration. Milk fat content and yields of actual milk, 4% fat corrected milk, milk fat, protein, and lactose increased by 3.97, 9.63, 11.8, 6.23, and 6.57%, respectively. Milk protein content tended to increase linearly with increasing dietary CP levels. Milk N secreted as g/d increased, while as percent of N intake decreased. The resulting decrease in MNE (13.7%) was 3.45 greater than the increase in milk yield observed by increasing dietary CP from 9.26 to 11.4% of DM. Total manure N increased linearly in terms of g/d and tended to increase as percent of N excreted. Excretion rate of N also increased linearly by 32%. In conclusion, milk yield, milk fat, protein, and lactose yields increased; however, decreased MNE indicates relatively greater N losses as observed by increased N excretion rate when CP level increased from 9.26 to 11.4% in the diet of lactating buffaloes.
Keywords: Milk nitrogen efficiency; Milk yield; Nili Ravi buffalo; Nitrogen balance.
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