PSXIV-2 A novel non-protein nitrogen source supports productivity in Holstein cows.

Abstract Non protein nitrogen (NPN) sources offer the alternative to traditional vegetal protein in ruminant diets. The objective of this study was to assess the effect of a novel NPN source consisting of a urea-biuret mixture (UB) on performance of high-producing dairy cows on corn-based rations. The study was conducted as a complete randomized design at East Tennessee Research and Teaching Center – Little River Animal and Environmental Unit in 2024. Forty-eight Holstein cows (parity 1, 2 and ≥ 3; 44 ± 7.8 kg milk/d) were stratified by parity, milk yield, and days in milk, and randomly allocated to 1) control (CTL), 2) urea-biuret level 1 (UB1), and 3) urea-biuret level 2 (UB2) dietary treatment for 12 weeks (n = 16 per treatment). The diets contained 131 g urea/cow/d for the CTL cows, 137 g UB /cow/d for the UB1 cows, and 237 g UB per/cow/d for the UB2 cows. The treatments were designed according to industry recommendations using NASEM (2021) model to be isoenergetic (1.80 Mcal/kg of NEl) and provide 17.0 % CP (CTL and UB1) and 18.0% CP (UB2). Dietary treatments included ingredients typically used in commercial operations in the Southeast such as corn silage, straw, corn grain, soybean meal, protected soybean meal, soybean hulls, rumen-protected fat, and a premix of minerals and vitamins. Treatments were fed twice daily to achieve ad libitum intake (5-10 % refusals) using an automatic feeding system. The dry matter concentration of forage ingredients was determined, and diets were adjusted weekly. Feed ingredients and diets were analyzed by a commercial laboratory. Milk samples were collected twice a week. The statistical analysis was performed using mixed models in SAS, and data collected before treatment initiation was included as a covariate. Individual cows were used as the experimental unit for all dependent variables. The model included the fixed effects of treatment, time, and parity and the random effect of cow. Data were analyzed as repeated measures in time and the most suitable covariance structure was chosen using the smallest AIC values. The dry matter intake was not affected by treatments. There was a treatment x parity interaction (P < 0.01), and milk yield increased in UB1 compared with CTL in parity ≥ 3 cows (P < 0.01). The milk fat concentration and yield increased in UB2 compared with CTL and UB1 (P < 0.01). Milk protein yield decreased in UB1 compared with CTL and UB2 (P < 0.01). Compared with CTL and UB1, UB2 increased MUN (P < 0.01). Results indicate that the novel NPN product supports the productivity of dairy cows fed corn-based diets.