Impacts of conventional and high-oleic soybean oil supplementation on rumen microbiology, physiology, immunity, and growth of recently weaned Brangus steers.

The current experiment evaluated the effects of conventional (CSBO) and high-oleic soybean oils (HOSBO) on rumen microbiology, physiology, immunity, and growth of beef steers during a 56-day preconditioning period. Seventy-two Brangus steers (body weight [BW] = 248 ± 30.6 kg) were assigned to 1 of 3 treatments (4 pastures per treatment; 6 steers/pasture): (i) no oil (Control), (ii) CSBO, or (iii) HOSBO. Oils were supplemented at 0.06% BW/day mixed with soybean hulls, which were offered at 0.8% BW/day. Bermudagrass hay was provided ad libitum. Steers were vaccinated against respiratory diseases on day 0, and BW and blood samples were collected on days 0, 21, and 56, while rumen fluid was collected on days 0 and 56. The CSBO steers had lower rumen bacterial richness (P = 0.05) and a tendency toward lower Shannon indices (P = 0.10) than others at the phylum level. Furthermore, HOSBO steers had greater plasma oleic acid concentrations (P = 0.05) than other steers on days 21 and 56. The CSBO steers had greater plasma linoleic acid concentrations (P < 0.01) than HOSBO steers, which in turn had greater concentrations than Control steers on days 21 and 56. The HOSBO steers tended to have greater plasma α-linolenic acid concentrations (P = 0.08) than others on day 21. However, CSBO steers had greater plasma cortisol concentrations (P = 0.05) than Control steers and did not differ from HOSBO steers on day 21. In addition, CSBO steers tended to have greater serum alanine aminotransferase concentrations (P = 0.09) on day 56 than others. The CSBO steers had greater serum titers (P ≤ 0.05) against bovine viral diarrhea virus types 1 (BVDV-1) and 2 (BVDV-2) than others. Moreover, HOSBO steers had greater serum titers against bovine respiratory syncytial virus (BRSV; P = 0.03) on day 21 than others. Additionally, on day 56, HOSBO steers tended (P = 0.10) to have greater BW than CSBO steers, which in turn tended (P = 0.10) to have greater BW than Control steers. Thus, HOSBO and CSBO supplementation had a low effect on rumen microbiology but modified plasma fatty acid profiles, increasing linoleic acid with CSBO and oleic acid with HOSBO supplementation. These changes resulted in distinct immune responses, with CSBO enhancing responses to BVDV-1 and BVDV-2, and HOSBO enhancing responses to BRSV. Moreover, HOSBO was more effective than CSBO in supporting the growth of recently weaned Brangus steers.