Statistical evaluation of some environmental factors aff ecting the gross effi ciency of crude protein in high producing dairy cows

Some environmental factors affecting the gross effi ciency of crude protein (GECP) were studied using 2824 records of 501 lactating Holstein cows. Th e eff ects of some independent variables on the GECP were tested using a general linear model analysis. Th e GECP was signifi cantly aff ected by parity and pregnancy stage and linearly related to dry matter intake, milk yield, milk fat, protein and lactose percentages, protein and lactose yields, dietary levels of net energy for lactation (NEL), crude protein (CP), ruminally undegradable protein (RUP), and ether extract (EE). Quadratic relation to the GECP with dietary levels of NEL, CP, RUP, and EE were also signifi cant. Th is study showed that high producing animals, especially high protein yielding cows are more effi cient users of dietary CP. Dietary requirements of NEL, RUP, and EE to maximize the GECP were estimated as 1.61 Mcal/kg, 7.14%, and 5.42%, respectively. In comparison to NRC estimations, it seems that more NEL, less CP, and more RUP are needed to maximize the protein effi ciency of lactating dairy cows.

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