Ninety-six yearling Hereford heifers (mean = 232 +/- 3 kg) were stratified on the basis of weight and then allotted randomly within weight groups into 16 pens of six each. Treatments were Hei-Gro (deviced or nondeviced; HG), Synovex-H (implanted or nonimplanted) and location in the feedlot relative to steers (isolated or nonisolated) imposed in a 2 x 2 x 2 factorial design with two replicates. During the growing phase, estrous activity was monitored by weekly rectal palpation of the reproductive tract of three heifers from each pen. Incidence of standing estrus, as determined by daily visual observation, was recorded for the first 21 d of the finishing phase. Heifers implanted with Synovex showed higher (p less than .05) average daily gains and final shrunk weights than nonimplanted heifers during the growing phase. Synovex also resulted in increased (P less than .05) weight gain during the finishing phase and produced heavier (P less than .05) hot carcass weights. HG did not significantly (p less than .05) affect any performance traits reported. Synovex or HG treatments had no effect on estrous activity of the heifers. Location significantly (P = .05) affected estrous activity during the finishing phase. HG caused reproductive tract scarring and infection (P less than .01). Heifers treated with the HG + Synovex combination had more severe (P less than .05) infection than those treated with HG alone. Heifers not isolated from steers had larger (P less than .05) ovaries than isolated heifers, although no difference (P less than .05) was found in ovarian weight.

Negative impacts of endophyte-infected Lolium arundinaceum (Darbyshire) (tall fescue) are responsible for over $2 billion in losses to livestock producers annually. While the influence of endophyte-infected tall fescue has been studied for decades, mitigation methods have not been clearly elucidated. Isoflavones found in Trifolium pretense (red clover) have been the subject of recent research regarding tall fescue toxicosis mitigation. Therefore, the aim of this study was to determine the effect of ergovaline and red clover isoflavones on rumen microbial populations, fiber degradation, and volatile fatty acids (VFA) in an in vitro system. Using a dose of 1.10 mg × L−1, endophyte-infected or endophyte-free tall fescue seed was added to ANKOM fiber bags with or without 2.19 mg of isoflavones in the form of a control, powder, or pulverized tablet, resulting in a 2 × 3 factorial arrangements of treatments. Measurements of pH, VFA, bacterial taxa, as well as the disappearance of neutral detergent fiber (aNDF), acid detergent fiber (ADF), and crude protein (CP) were taken after 48 h of incubation. aNDF disappearance values were significantly altered by seed type (P = 0.003) and isoflavone treatment (P = 0.005), and ADF disappearance values were significantly different in a seed x isoflavone treatment interaction (P ≤ 0.05). A seed x isoflavone treatment interaction was also observed with respect to CP disappearance (P ≤ 0.05). Seventeen bacterial taxa were significantly altered by seed x isoflavone treatment interaction groups (P ≤ 0.05), six bacterial taxa were increased by isoflavones (P ≤ 0.05), and eleven bacterial taxa were altered by seed type (P ≤ 0.05). Due to the beneficial effect of isoflavones on tall fescue seed fiber degradation, these compounds may be viable options for mitigating fescue toxicosis. Further research should be conducted to determine physiological implications as well as microbiological changes in vivo.