Trace mineral source affects ruminal bacterial diversity and performance of grazing bos indicus nellore cattle during...

The objective of this study was to evaluate the effects of different trace mineral sources on rumen fermentation parameters and bacterial diversity, liver concentration of Cu and Zn, and performance of grazing Bos indicus Nellore cattle during the dry-to-rainy transition season. In Exp. 1, eight Nellore steers [body weight (BW) = 541 ± 18 kg, and 32 ± 1 mo. old] fitted with ruminal cannula were randomly assigned to eight paddocks in a completely randomized design. In Exp. 2, a total of 120 Nellore bulls (BW = 341 ± 45.9 kg and age = 20 ± 1 mo) were blocked by initial BW and distributed into 12 paddocks (6 paddocks/treatment). Each animal or paddock were supplemented with a protein supplement (5 g/kg of BW daily) containing (1) 40 mg of Cu/kg of supplement from the Cu sulfate source and 148 mg of Zn/kg of supplement from the Zn oxide source (ITM; n = 4), or (2) 40 mg of Cu/kg of supplement and 148 mg of Zn/kg of supplement from hydroxychloride sources (HTM; n = 4; IntelliBond CII, IntelliBond Z, Selko, Indianapolis, IN). The 101-d experiment included an 11-d adaptation period followed by three 30-d periods. Ruminal fluid was sampled at 0, 6, 12, and 18 h post-supplementation on d 24, 52, and 84 (Exp. 1). Body weight was recorded at the start, after adaptation, and every 30 d following a 16-h feed and water withdrawal (Exp. 2). In Exp. 1, no treatment effects were observed (P ≥ 0.13) for total short-chain fatty acid (SCFA) concentration and molar proportion of acetate, propionate, isobutyrate, butyrate, valerate, Ac: Pr ratio, ruminal pH, and N-NH3 concentration. The rumen microbiology analysis revealed that the phylum SR1 was affected by the treatments, with higher abundance in HTM (P = 0.03) than in ITM steers. At the genus level, 13 genera were affected (P ≤ 0.05) by treatments. Animals fed HTM had increased (P ≤ 0.05) ruminal abundance of taxa commonly associated with the fiber and starch and soluble carbohydrate degraders group, whereas steers receiving ITM had higher abundance of Fibrobacter, Butyrivibrio 2, Ruminiclostridium 5, and the Archaea genus Methanobrevibacter. In Exp. 2, HTM bulls had greater BW after 60 d (P ≤ 0.03) of the experiment, with greater ADG between days 30 and 60 (P < 0.03). These results demonstrate that HTM might serve as an effective source of Cu and Zn for grazing Nellore cattle and was associated with improved growth performance during the dry-to-rainy transition, along with concurrent shifts in ruminal microbial diversity.