Abstract #M280

# M280
Effect of RDP:RUP ratio and corn processing on lactation performance, milk quality and efficiency of nutrients utilization in lactating dairy cows.
C. M. M. R. Martins*1, D. C. M. Fonseca1, M. A. Arcari1, B. G. Alves1, K. C. Welter2, F. P. Rennó1, M. V. Santos1, 1Department of Animal Nutrition and Production, School of Veterinary Medicine and Animal Science, University of São Paulo, Pirassununga, São Paulo, Brazil, 2Department of Animal Sciecen, School of Animal Science and Food Engineering, University of São Paulo, Pirassununga, São Paulo, Brazil.

The study aimed to evaluate the effect of RDP:RUP ratio and corn processing on lactation performance and milk heat coagulation time (HCT) at 140°C. Twenty Holstein cows (8 fitted with ruminal cannulas) averaged 162 ± 70 DIM, 666 ± 68 kg of body weight and 36 ± 7.78 kg/d of milk yield, were distributed in a Latin Square design with 5 contemporary squares, 4 periods of 21 d and 4 treatments (factorial arrangement 2 × 2). Factor 1 was corn processing (ground through 2-mm screen [GC] or steam-flaked [SFC]), and factor 2 was RDP:RUP ratio (High: 11% of RDP and 5.3% of RUP or Low: 9.8% of RDP and 6.5% of RUP; DM basis; NRC, 2001). For diets with High RDP:RUP ratio, 103.4 g/kg of conventional soybean meal (SM) and 7.8 g/kg of urea were included. For diets with Low RDP:RUP ratio, 91.9 of SM, 2.8 of urea and 44.7 g/kg of heated SM (SOYPASS, Brazil) were included. There was a tendency of interaction (P = 0.06) between RDP:RUP ratio and corn processing on DMI. Cows fed GC with low RDP:RUP ratio had higher DMI than cows fed GC with high RDP:RUP ratio. No effect of RPD:RUP ratio was found when cows were fed SFC. Cows fed SFC had lower DMI (P = 0.007), and higher DM (P = 0.03) and starch total apparent digestibility (P = 0.02), and higher productive efficiency (P = 0.002) than cows fed GC. Rumen pH was not affected by diets. It was observed an interaction between treatments on MY (P = 0.04), HCT (P = 0.029) and milk lactose content (P = 0.04). Cows fed GC had reduced MY by 2.3 kg/d when the diet had high RDP:RUP ratio, than cows fed low RDP:RUP ratio. However, when cows were fed SFC, MY did not change according to the RDP:RUP ratio. Similar interaction results were found for HCT and lactose content. Cows fed low RDP:RUP ratio had higher fat-corrected milk, milk protein content, and efficiency of N utilization for milk protein yield. Thus, diets with GC and high RDP:RUP ratio reduces MY and milk quality. For SFC corn diets the RDP:RUP ratio does not affect the lactation performance. Overall, feeding cows with low RDP:RUP ratio results in higher efficiency of N utilization to milk protein yield.

Key Words: casein, dairy industry, milk stability