1692
Grain processing and fat supplementation on milk yield and milk composition of dairy cows grazing a tropical pasture
The objective of this experiment was to investigate the effects of grain processing and fat supplementation to early lactation dairy cows grazing a tropical pasture on milk production and composition. Forty early lactation cows (15 ± 4 DIM) were used in a randomized block design and subjected to the following treatments: a) fine ground corn without fat; b) fine ground corn + 400 g calcium salts of palm oil cow-1 d-1; c) steam-flaked corn without fat; d) steam-flaked corn + 400 g of calcium salts of palm oil cow-1 d-1. Treatment periods were 90 d in length and cows grazed paddocks of Pennisetum purpureum and received 9 kg cow-1 d-1 (DM) of concentrate twice daily. Milk yield was measured every 2 d and milk composition was analyzed every 6 d. Data were analyzed as repeated measures using a mixed model with block as random effect and grain processing, fat supplementation and grain processing × fat supplementation as fixed effects. The means were compared by Tukey test. Steam-flaked corn increased (P=0.001) milk yield compared with fine ground corn (23.9 vs. 22.2 kg/d) and supplementation with fat also increased (P=0.0001) milk production (24.7 vs. 21.3 kg/d). Milk fat content was reduced (P=0.01) in steam-flaked corn in comparison with fine ground corn diets (3.22 vs. 3.30%). There was a pronounced increased (P=0.0001) in milk protein content in steam-flaked corn compared with fine ground corn diets (3.41 vs. 3.15%). In addition, milk casein content was increased (P=0.0001; 2.47 vs. 2.33%) and milk urea nitrogen was decreased (P=0.002; 12.1 vs. 16.3 mg/dL) in steam-flaked diets indicating greater efficiency of N utilization in these treatments. Total solids content was reduced (P=0.05) by fat supplementation (12.19 vs. 12.05%), which is associated with the tendency of reduction in milk protein content (P= 0.10; 3.29 vs. 3.22%). Milk fat yield was unaffected by grain processing (P= 0.18; 0.75 vs. 0.77 kg/d for fine ground corn and steam-flaked corn, respectively), but fat supplementation increased (P=0.001) milk fat yield (0.80 vs. 0.71 kg/d). Steam-flaked corn increased (P=0.001) milk protein yield compared with fine ground corn (0.81 vs. 0.71 kg/d). In grazing dairy cows, steam-flaked corn increased milk yield and milk protein, and fat supplementation increased milk yield and milk fat yield, and when combined (steam-flaked corn + fat) allowed the greatest milk yield, milk fat yield and milk protein yield.
Keywords: palm oil, flaked corn, tropical pasture