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Effects of Creep Feeding and Monensin on Reproductive Performance and Lactation of Beef Heifers

University of Illinois, Urbana 61801²

Abstract

A 2³ factorial arrangement of treatments was utilized to determine the effect of breed, creep feeding and monensin on subsequent reproductive performance and lactation of 32 primiparous heifers. One-half of each breed (Angus and Hereford) group had access to creep feed (2.67 Meal metabolizable energy/kg) while nursing their dams. Approximately 40 d before breeding through 120 d of lactation, all heifers were fed a suboptimal energy diet and 50% of each breed and creep group received 200 mg monensin/head daily. Estrus was synchronized with a progestogen. Volatile fatty acids (VFA) were determined periodically throughout the monensin-feeding portion of the .experiment. Twenty-four hour milk production, percentage butterfat and percentage solids-not-fat were determined at 60 and 120 d postpartum. Weaning weights (adjusted to 205 d and for age of dam) of the original heifers were heavier (P<.05) for those that were creep fed compared with those not creep fed (219 vs 202 kg). Monensin-supplemented females gained significantly more weight from the initiation of treatment to immediately postcalving and gave birth to heavier aalves (P<.05) even though they received comparable amounts of dietary energy as those that did not receive monensin. The energy stressed, monensin-supplemented first-calf heifers exhibited a shorter postpartum interval (P<.05) to first estrus than did those that did not receive monensin (55.7 vs 69.1 d, respectively). First-calf heifers that had been creep fed while nursing their dams had a lower (P<.05) daily milk yield at 120 d postpartum than those that did not have access to creep feed. No detrimental effects were observed due to long-term monensin supplementation.

¹ Div. of Anim. Sci., Univ. of Wyoming, Laramie 82070.

² Dept. of Anim. Sci.