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Effect of dietary RDP / RUP ratio and starch processing on dry matter intake, milk yield and milk heat stability of dairy cows

Cristian Marlon de Magalhães Rodrigues Martins ; Danielle de Cassia Martins da Fonseca ; Gabriel Caixeta Ferreira ; Marcos André Arcari ; Bruna Gomes Alves ; Katiéli Caroline Welter  ; Francisco Palma Rennó ; Marcos Veiga dos Santos
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The term milk stability refers to the relative ability of milk proteins to resist industrial heat processing (milk heat stability) or the reaction with ethanol (milk ethanol stability) without undergoing coagulation. The present study aimed to evaluate the effect of RDP / RUP ratio and starch processing on dry matter intake (DMI), milk yield (MY) and milk heat coagulation time (HCT) at 140? C. At the beginning of the trial, 20 Holstein cows averaged 162 ? 70 days in milk, 666 ? 68 kg of body weight, 3.15 ? 0.48 of body condition score and 31.82 ? 7.78 kg/d of milk yield, and were distributed in a Latin Square design with 5 contemporary square, 4 periods of 21 d and 4 treatments (factorial arrangement 2 x 2). Factor 1 was corn starch processing (ground - 4 mm or steam flacked); Factor 2 was RDP / RUP ratio (High: 11% of RDP and 5.3% of RUP; Low: 9.8% of RDP and 6.5% of RUP; estimated on dry matter basis by NRC, 2001). Cows fed steam flacked corn had lower DMI (DMI = 23.3 kg/d; P = 0.007) than cows fed ground corn (DMI = 24.4 kg/d). Additionally, there was a tendency (P = 0.06) of interaction effect between RDP / RUP ratio and starch processing on DMI, as when cows were fed ground corn with low RDP / RUP ratio (DMI = 25.1 kg/d) tended to increase DMI by 1.3 kg/d when compared with high RDP / RUP ratio (DMI = 23.8 kg/d). Similarly, it was observed an interaction effect on MY (P = 0.042) and on HCT (P = 0.029). When cows were fed ground corn, there was a reduction of MY by 2.3 kg/d and in HCT by 4.8 min using high RDP / RUP ratio, than when cows were fed low RDP / RUP ratio (MY = 34.6 vs 36.9 kg/d and HCT = 14.4 vs 19.2 min, respectively). However, when cows were fed steam flacked corn, MY and HCT did not change with RDP / RUP ratio (MY = 36.1 vs 36.5 kg/d and HCT = 16.6 vs 14.47 min; for high or low RDP / RUP ratio, respectively). In conclusion, diets with ground corn with high RDP / RUP ratio reduces the MY, as well as HCT probably due changes in both quantity and quality of amino acid absorbed and supplied to milk protein synthesis in the mammary gland.