LAUSR

Abstract This study evaluated the effects of different maternal supplement type and supplement fortification with methionine hydroxy analogue (MHA) on pre- and postpartum physiological responses of Bos indicus-influenced beef cows and preweaning growth of their calves. On d 0, 160 multiparous Brangus beef cows were stratified by body weight and body condition score (BCS) and randomly allocated into 1 of 16 bahiagrass pastures (10 cows and 8 ha/pasture). Pastures were randomly assigned to treatments in a 2 × 2 factorial arrangement distributed in a complete randomized design with four replicates (4 pastures/treatment). Treatments consisted of (dry matter basis): 0.35 kg/cow/wk of trace mineral and vitamin supplement (MIN) or MIN mixed into 7.5 kg/cow/wk of sugarcane molasses-based supplement (MOL), with or without MHA fortification (105 g/cow/wk; MFP, Novus International Inc., Romance, AR), and were provided from d 0 to 70 (47 ± 2.7 d prepartum until 23 ± 2.7 d postpartum). The respective weekly supplement amount assigned to each treatment was divided by 2 and offered every Monday and Thursday. On d 70, all cow-calf pairs were combined into 1 of 8 groups and managed similarly until calf weaning on d 295. Cows were exposed to natural breeding from d 104 to 189. Effects of supplement type × methionine fortification were not detected for any variable analyzed in the study, except for supplement disappearance, which was reduced at greater magnitude when MHA was added into MIN vs. MOL supplements. Plasma concentrations of glucose increased on d 70 whereas plasma non-esterified fatty acids decreased on d 70 for MOL vs. MIN cows. Cows offered MOL supplementation maintained BCS from d 0 to 70, whereas MIN cows lost BCS from d 0 to 70, leading to greater BCS at the start of the breeding season for MOL vs. MIN cows. Reproductive performance did not differ between MOL and MIN cows, except for calving date which occurred 8 d sooner for MOL vs. MIN cows. Pre-weaning calf body weight increased for calves born from MOL vs. MIN cows. Except for plasma glucose concentrations on d 70, supplement fortification with MHA did not impact any cow and calf variables analyzed herein, regardless of supplement type. Therefore, pre- and post-partum maternal supplementation of energy and protein, but not methionine hydroxy analogue, enhanced maternal physiological response and BCS at calving and start of the breeding season, and offspring pre-weaning growth compared to no energy and protein supplementation.