Bicarbonate Supplementation As a Strategy to Mitigate Effects of Endophyte-Infected Tall Fescue on Replacement Heifer Development

Endophyte-infected tall fescue occupies most grazing lands in the Southeastern U.S., and is associated with poor growth and reproductive performance. Supplementing bicarbonate to cattle grazing endophyte-infected tall fescue was hypothesized to be a strategy to alleviate these negative performance outcomes. The objective of this study was to evaluate growth and reproductive characteristics of heifers consuming endophyte-infected tall fescue with or without sodium bicarbonate supplementation. Forty-eight heifers (8 mo; BW = 589 ± 53 kg) were blocked by BW and assigned to pens and treatments. Heifers were group-housed and fed individually using Calan gates. Treatments were arranged as a 2 x 2 factorial design with heifers receiving either high- or low-endophyte fescue seed with (E+B, E-B) or without (E+, E-) sodium bicarbonate supplementation. Heifers were fed a corn silage diet; seed and bicarbonate were supplemented at 1.5 kg/day and 0.25 kg/day, respectively. Heifer BW was recorded on sequential days at the start and end of the 84 d experiment and every 14 d. Feed intake and refusals were collected daily. The BW and DMI data were used to estimate ADG and G:F. Reproductive tract scores (RTS) were performed every 28 d via transrectal palpation and ultrasonography. Results were analyzed after the 2^nd ultrasound (56 d) and at the end of the experiment. At d 56, RTS (P = 0.005) was affected by the interaction of bicarbonate supplementation and fescue seed type and G:F (P = 0.061) and ADG (P = 0.058) tended to be affected. In general, RTS, G:F and ADG of all other treatments was improved compared with the E+ treatment. Neither factor affected DMI at d 56 (P > 0.10). By d 84, bicarbonate supplementation tended to decrease ADG (P = 0.051) and decreased G:F (P = 0.016); and infected fescue consumption tended to decrease DMI (P = 0.060). On d 56, bicarbonate showed promise as a strategy to ameliorate the negative effects of endophyte-infected fescue consumption; however, by the end of the study, no effects of fescue seed type on ADG or G:F were observed. Short-term bicarbonate supplementation appears to be a promising strategy to eliminate negative production responses associated with endophyte-infected fescue consumption; however, additional research is needed to fully understand why this benefit was not sustained over the full experimental period and how the strategy would translate to traditional pasture systems where animals can self-select a bicarbonate supplementation level.