Year-round supplementation of direct-fed microbials to cow-calf pairs and its effects on maternal and offspring productive performance

On day 0 (94 ± 19 days prepartum), 296 Brangus beef cows (7 ± 3 years of age; <25% <i>Bos indicus</i>) were stratified by body weight (<b>BW</b>; 537 ± 56 kg) and body condition score (<b>BCS</b>; 5.46 ± 0.74) and randomly assigned to 1 of 26 bahiagrass pastures (11 to 12 cows and 8.1 to 9.6 ha per pasture). On day 0, treatments were randomly assigned to pastures (13 pastures per treatment) and consisted of free-choice access to a trace mineral supplement, either alone (<b>CON</b>) or combined (<b>BAC</b>) with 3 g per head daily of a <i>Bacillus</i>-based DFM supplement (Bovacillus; Novonesis, Lyngby, Denmark) from day 0 to 330 (weaning). At weaning, 48 steers and 64 heifers were selected (3 steers and 4 heifers per pasture; 16 pastures) for the post-weaning phase. Steers were assigned to preconditioning (day 350 to 398) and feedlot periods (day 399 to 609), whereas heifers were developed from day 350 until pregnancy diagnosis (day 615). Non-binary and binary data were analyzed using the MIXED and GLIMMIX procedure of SAS, respectively. supplement DM intake was greater (<i>P </i>≤ 0.03) for BAC vs. CON cow-calf pairs on days 42 to 48, 56 to 62, 168 to 174, and 266 to 272. Cow BCS at the end of the breeding season was greater (<i>P </i>= 0.01) for BAC vs. CON cows, whereas all cow reproductive data and prepartum plasma data did not differ (<i>P </i>≥ 0.13) between treatments. Serum immunoglobulin G concentrations at birth, preweaning average daily gain (<b>ADG</b>), and BW at weaning were greater (<i>P </i>≤ 0.05) for BAC vs. CON calves. Steer growth performance during preconditioning did not differ (<i>P </i>≥ 0.18) between treatments, but serum titers against infectious bovine rhinotracheitis and parainfluenza 3 viruses were greater (<i>P </i>= 0.05) for BAC vs. CON steers 19 days after first vaccination. Steer feedlot performance and carcass traits did not differ between treatments (<i>P </i>≥ 0.16), except for carcasses grading Low Choice or above, which were greater (<i>P </i>= 0.05) for BAC vs. CON steers. Despite the greater (<i>P </i>= 0.03) pre-breeding ADG of CON vs. BAC heifers, the percentage of mature BW at breeding, puberty status, and pregnancy percentages did not differ (<i>P </i>≥ 0.17) between treatments. Thus, year-round supplementation of <i>Bacillus</i>-based DFM via a mineral delivery method improved cow BCS during breeding and enhanced calf preweaning growth. Although no reproductive benefits were observed for cows and their heifers, DFM supplementation increased post-weaning immune response and carcass quality of steers.