ENERGETIC EFFICIENCY OF MILK-PRODUCTION IN JERSEY COWS

Eighteen nitrogen and energy balances were carried out with Jersey cows from 3 to 19 weeks after 2nd parturition. Protein, fat and energy content in milk varied significantly between cows but the proportion between energy deposited in protein, fat and carbohydrates was fairly constant for all balances, on average 21, 58 and 21 % respectively. During the mobilization period, the cows oxidized body fat as an surplus energy source for milk production but there was no occurance of protein mobilization as in all balances the protein retention was positive. The efficiency of ME utilization for milk production was k(l) = 0.68, and the energetic efficiency of energy mobilization from body fat was k(r) = 0.76. The high value of k(l) was affiliated with the high fat production in milk and high utilization of ME for fat energy deposition, being k(lf) = 0.82. The partial efficiency of ME utilization for protein + carbohydrates energy deposition in milk was k(lpc) = 0.54, indicating a major difference between ME utilization for energy deposition in fat and other solids.