Protein nutrition of dairy cows fed high fat diets

Abstract

Two experiments were conducted to determine the value of specific protein supplements in lactating dairy cows fed high fat diets. Experiment 1, six feedstuffs (wheat silage, corn, soybean meal, soybean hulls, whole cotton seed, and poultry protein meal) and a protein blend (fish meal and dry distillers grains) were evaluated for ruminal dry matter and crude protein degradation kinetics. Duplicate nylon bags were incubated for 0, 2, 4, 8, 16, 24, 48, and 72 h in two Holstein steers fitted with ruminal cannulae, fed at 3.5 X maintenance. Degradation constants for most of these feeds, except wheat silage, compared closely to values listed in the dairy NRC (4 X maintenance). An NRC value for pet food grade poultry protein meal is not available. Our results indicate that its CP kd is 2.45 %/h and its RUP is 58.49 %. In situ intestinal protein digestibility was obtained for six ruminally incubated feed ingredients (wheat silage, corn, soybean meal, whole cotton seed, and poultry protein meal) and a protein blend (fish meal and dry distillers grains). Quadruplicate nylon bags were introduced into the duodenum of two Hereford steers fitted with permanent cannulae. Six nylon bags were introduced per day with an interval of 15 min between bags. Digestibility values were higher for soybean meal. Poultry protein meal digestibility was lower than soybean meal but higher than the other feeds. Experiment 2, twenty-four high producing Holstein lactating dairy cows were used in a completely randomized design to determine the utilization of pet food grade poultry protein meal as a protein supplement in rations that were relatively high in both fat and fiber. Cows in early lactation ranging between 35 and 126 DIM, were distributed into six groups based on their level of milk production. The basal diet contained approximately 55% wheat silage and 6.5% fat. Treatments varied due to protein supplementation and were described as: 1) positive control-soybean meal (SBM), plus a ruminally undegraded protein (RUP) blend of fish meal (FM), blood meal (BM), and dry distillers grains (DDG); 2) negative control-SBM; 3) PPM-50%, 50% pet food grade poultry protein meal (PPM) substituted for the RUP blend in treatment 1; and 4) PPM-100%, 100% substitution PPM for RUP blend in treatment 1. Cattle were fed behind Calan gates, a common diet for two weeks and treatment diets for 12 wks afterwards. Intake (DMI) was lowest with the positive control diet and fat corrected milk production was higher in the 100% PPM diet. Fat corrected milk, milk fat, fiber digestibility and body weight loss were all lower in cattle fed the negative control. The most interesting response of practical value is the increase in DE concentrations of diets supplemented with RUP sources. This corresponded with an increase in diet NE content. Effect that is complemented with higher fiber and OM digestibilities that appears to be the main responsible for the increased DE. Back fat change detected from ultrasonography was greater in cattle fed the negative control diet. Insulin and blood urea nitrogen (BUN) were influenced by treatment especially during the first 4 weeks. These results indicate that PPM is an economic alternative for more expensive animal based sources of RUP.