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Effects of two levels of starch and monensin on performance of mid-lactation dairy cows.

P. Piantoni



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Effects of two levels of starch and monensin on performance of mid-lactation dairy cows.
P. Piantoni*, M. A. Messman, B. D. Strang, C. J. Canale, G. F. Schroeder. Cargill Animal Nutrition Innovation Center Elk River, MN.

Sixty Holstein cows (149 � 17.4 DIM; 37.4 � 5.7 kg/d milk yield) were used in a randomized block design experiment with a 2 � 2 factorial arrangement of treatments to evaluate the effects of dietary starch (20.1 and 26.7% of diet DM; LS and HS, respectively) and monensin levels (275 and 550 mg/d; LM and HM, respectively) on lactation performance. After a 2-wk covariate period, cows were assigned to 1 of 4 treatments: LSLM, LSHM, HSLM, and HSHM. Treatment diets were fed for 13 wks. Data were analyzed using the GLIMMIX procedure of SAS with fixed effects of starch, monensin, parity, week, and interactions between main effects and parity and week, the random effects of cow and block, and specific covariates. There were no interactions among starch and monensin levels and time for yields of milk, 3.5% FCM, or milk components. However, LSHM decreased DMI compared with the other diets, particularly after 5 wks on treatment (interaction P < 0.01). Overall, LS decreased DMI compared with HS (22.9 vs. 24.1 kg/d; P = 0.01), and the difference between treatments became larger overtime (interaction P = 0.09). LS did not affect 3.5% FCM overall but tended to decrease it toward the end of the treatment period (interaction P = 0.13). Therefore, LS increased feed efficiency overall compared with HS (1.57 vs. 1.51; P = 0.04), but especially when LS maintained 3.5% FCM yield (interaction P = 0.03). Starch level showed a tendency to interact with parity for BW, indicating that HS increased BW in primiparous but not multiparous cows (P = 0.15). Compared with LM, HM slightly increased DMI and yields of 3.5% FCM and milk protein and fat in multiparous cows but decreased them in primiparous (all interactions P < 0.10). HM decreased milk fat content regardless of starch level (3.34 vs. 3.18%; P = 0.05). In summary, results indicate that the interaction between starch and monensin levels affected DMI and feed efficiency, but not yields of milk and milk components, and that lower starch diets increased feed efficiency by decreasing intake and maintaining 3.5% FCM yield. In addition, a higher dose of monensin did not provide additional benefits in mid-lactation dairy cows.

Keywords: energy partitioning, feed efficiency, starch.