Nutrient utilization and metabolism by lactating dairy cows fed high-forage diets with protein supplements

Abstract Text: Due to the increasing cost of soybean meal and concerns of excess N being excreted into the environment, new protein supplements have been developed. Two products that have shown potential in increasing N utilization efficiency are slow release urea (SRU; Optigen, Alltech, Nicholasville, KY) and ruminal escape protein derived from yeast (YMP; DEMP, Alltech). The objective of this study was to assess the effects of feeding these 2 supplements in high-forage (54% of total dietary DM) dairy diets on nutrient utilization, feed efficiency, lactational performance of dairy cows, and their impacts on income-over feed costs (IOFC). Twelve multiparous dairy cows were used in a triple 4 × 4 Latin square design with one square consisting of ruminally cannulated cows. Treatments included: 1) control, 2) SRU-supplemented TMR (SRUT), 3) YMP-supplemented TMR (YMPT), and 4) SRU and YMP-supplemented TMR (SYT). The control consisted only of a mixture of soybean meal and canola meal (SBMCM) in a 50:50 ratio. The SRU and the YMP were supplemented at 0.49% and 1.15% DM, respectively. The experiment consisted of 4 periods lasting 28 d each (21 d of adaptation and 7 d of sampling). Cows fed YMPT and SYT had decreased DMI, and all supplemented treatments had lower CP intake compared to those fed the control. Milk yield tended (P = 0.08) to have the greatest increase in YMPT compared with the control (41.1 vs. 39.7 kg/d) as well as a tendency for increased milk fat (P = 0.10) and protein yields (P = 0.07). Feed efficiencies were improved in all diets with protein supplementation at 10-16% (P < 0.04). Cows fed with protein supplements partitioned less energy toward BW gain, but tended (P = 0.08) to partition more energy toward milk production. Efficiency of use of feed N to milk N increased by feeding SRUT and YMPT, and milk N to manure N ratio increased in YMPT. Cows fed SRUT or YMPT tended (P < 0.10) to improve IOFC. Overall results from this experiment indicate that replacing SBMCM with SRU and YMP in high-forage dairy diets can be a good approach to enhance farm profitability through improved nutrient utilization efficiencies by lactating dairy cows.

Keywords: dairy profitability, high-forage dairy diet, protein supplement