Heat-treated whole cottonseed: effect of dietary protein concentration on the performance and amino acid utilization by the mammary gland of dairy cows

The effects of replacing whole cottonseed by heated whole cottonseed at two levels of crude protein on amino acid (XA) utilization by the bovine mamma ry gland mere investigated. Four Israeli Holstein cows were used in a 4 x 4 Latin square design with 2 x 2 factorial arrangements. Diets were formulat ed to contain two levels of crude protein (CP)I normal (160 g CP/kg dry mat ter) and low (140 g CP/kg dr!: matter), and two levels of rumen undegradabl e protein (UDP), high (380 g UDP/kg CP) and lon (350 g UDP/kg CP). Whole co ttonseed was quantitatively substituted by heated whole cottonseed to formu late the high UDP diets. Intakes of dry matter and organic matter were simi lar for all treatment and averaged 15.9 and 14.4 kg/d respectively. Yields of milk and its constituents were similar for all treatments. Milk yield av eraged 23.1 kg/d and this contained (per kg) 32.3 g CP, 25.4 g total casein and 47.5 g lactose. The milk fat content was lon-er in the cows given the high UDP diets, averaging 34.6 g/kg compared with 38.9 g/kg in the cows fed on the diets with low UDP. Plasma AA concentrations were similar for all t reatments apart from Leu and Ile, which were higher in the cows given the h igh CP diets: 152 and 103 mu M compared with 183.8 and 131.5 mu M for the l on CP diets. ?;ret extraction and balance of essential BA across the half u dder suggested that essential AA were supplied in amounts sufficient to mee t milk protein requirements for all treatments. The surplus BA supplied as a result of feeding the high dietary CP were probably catabolized via an en hanced oxidative pathway, possibly in the liver, presumably as a passive re sponse to their disposal.