Use of two different dietary energy and protein contents to define nutritive requirements of lactating buffalo cows

Two total mixed rations, differing in energy and protein concentrations (diet A: 6.1 MJ/kg DM of NE(l), 112.5 g/kg DM of metabolizable protein, MP, and 101.7 g of protein digestible at the intestinal level, PDI, vs. diet B: 6.4 MJ, 95.1 g of MP, 78.9 g of PDI) were administered ad libitum for 1 year to two groups of 12 buffaloes in which the partial monthly turnover of animals allowed the lactation stage to be maintained close to 160 days. The diets were formulated to obtain, with a daily intake of about 15.5 kg of DM, a balanced energy supply but an excess of protein (diet A); the opposite occurred with diet B. The average dry matter intake recorded during the trial was 14.5 kg for diet A and 15.0 kg for diet B. Milk production was similar for both groups (7.94 kg vs. 7.95 kg). The diet with a higher protein concentration brought about a significant increase in protein, casein and non-protein nitrogen contents in the milk. A significant increase in milk fat percentage was observed when the animals were fed the diet with a higher energy concentration. The serum urea concentration (8.62 mm/l) of buffaloes fed diet A was outside the physiological range for lactating buffaloes. The energy and protein conversion efficiencies for milk production were more favourable when their supplies were balanced: 3.58 MJ of NE(l)/kg of FPCM for diet A; 2.50 g of MP or 2.07 g of PDI/g of protein milk for diet B. Moreover, when the requirements were satisfied, greater energy or protein supplies failed to induce significant changes in milk yield and quality. Finally, regarding the great differences between estimated MP requirements and those recorded during the trial, the authors suggest that the equations used in the CPM-Dairy software, formulated for dairy cows, are not applicable in buffaloes.