HEAT-TREATED WHOLE COTTONSEED VERSUS MAIZE GLUTEN MEAL AS A RUMEN UNDEGRADABLE PROTEIN-SUPPLEMENT FOR LACTATING DAIRY-COWS

The effect of heat treatment on the nutritive value of rumen undegrada ble protein (UDP) fraction of whole cottonseed (WCS) was studied in th is experiment. Forty two multiparous Israeli Holstein cows were used i n a multiple double 3 X 3 Latin square design. Milk production average d 38+/-4.1 kg at the beginning of the experiment. Three different diet s were formulated to contain 160 g/kg crude protein (CP), 365 g/kg neu tral-detergent fibre (NDF) on a dry matter (DM) basis, 7.24 MJ net ene rgy for lactation (NEL)/kg DM and 170 g/kg WCS. 30% of dietary CP was of cotton origin. Diets were (1) whole cottonseed (WCS), (2) heated wh ole cottonseed (HWCS) and (3) whole cotton seeds plus 3.1% maize glute n meal (WCS + MG). Diets with HWCS and WCS + MG contained 60 g UDP/kg DM compared with 54 g UDP/kg DM in the WCS treatment. Heat treatment d ecreased ruminal CP degradability of WCS by 22% and ruminal organic ma tter (OM) degradability by 5%. Intakes of DM, OM and CP were similar a cross diets. Higher apparent total tract digestibilities of DM and OM were determined in HWCS and WCS + MG diets (0.62 and 0.64 and 0.63 and 0.65, respectively) compared to WCS diet (0.59 and 0.62, respectively ). Higher ruminal propionate proportion was determined in diets contai ning WCS and WCS + MG over the sampling hours. A higher ruminal ratio of acetate:propionate was measured in the diet containing HWCS. Ammoni a N concentration was similar in all treatments, however, blood urea N concentration was the lowest at 3 and 6 h after feeding in the HWCS d iet compared to the other diets. Milk yield and composition were simil ar for all treatments and averaged 34.2+/-0.45 kg/d with 34.2 g fat/kg , 30.1 g CP/kg and 47 g lactose/kg. It was suggested that inclusion of HWCS in diets for high-yielding dairy cows decreased the endogenous c atabolism of amino acids. In this study the effect of heat treatment o n WCS on the performance of cows was not apparent because the cows con sumed surplus of dietary CP. (C) 1998 Elsevier Science B.V.