1241 Accuracy and precision of diets for high-producing dairy cows and their impacts on production and milk composition

The goal of this study was evaluate associated feeding management and nutritional accuracy with milk production and composition on commercial herds. Twenty high-producing dairy farms from Campos Gerais county, Paraná State, Southern Brazil, were visited for 3 consecutive days in the 2015 fall season. Feeding management and TMR preparation related variables, and the physical and chemical characteristics of the offered diets and orts were collected. Production performance and milk composition from the high-production group of cows were obtained from regular milk testing, performed on average 1 ± 5d before or after the data collection period. Pearson correlations were estimated among the management and diet variables with production, milk composition, and feed sorting estimates. Using the Penn State Particle Separator, the offered diets had on average 14.9, 41.8, 32.8, and 10.5% (DM) of long, medium, short, and fine particles, respectively. Long particles showed a daily refusal rate of 9.0%, whereas short and medium particles were preferentially consumed at 1.1 and 1.7%, respectively. A high proportion of long particles in the forage (78.2% of haylage and hay) was associated with reduction in milk fat % (%MF) (r = −0.50; P < 0.05), and an increased proportion of cows with fat:protein ratio lower than 1 (FPR < 1) (r = 0.50; P < 0.05). Errors associated with loading an excess of concentrate ingredients in the TMR wagon were negatively associated with %MF (r = −0.52; P = 0.05) and milk production (r = −0.47; P < 0.05). By comparing the formulated diet with the one delivered to the cows, we noted, on a DM basis, a decrease in CP (−3.1%), fat (−7.0%), and ash contents (−10.5%), and an increase in NDF (+10.3%). The accuracy observed between formulated and delivered diets was not associated with the performance of the cows. However, daily variation of the DM content of the diet was associated with a greater proportion of cows with FPR < 1, and reduced FPR (r = 0.40; P = 0.09 and r = −0.43; P = 0.07, respectively). Low homogeneity (across 3 d) of the % of long particles in the diet was associated with greater selection against these particles (r = −0.64; P < 0.05), which showed a curvilinear association with %MF. These results demonstrated that the addition of more concentrate ingredients than expected, as well as the inconsistent intake of different particle sizes throughout the day, had a negative impact on milk production and composition of the studied herds.

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