Submitted to: American Society of Animal Science Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: April 21, 2004
Publication Date: July 24, 2004
Citation: Burke, J.M., Brauer, D.K., Looper, M.L. 2004. Calving rate and production responses of long-term exposure to endophyte-infected tall fescue. American Society of Animal Science Annual Meeting. 82(Supplement 1):90. Technical Abstract: The objective was to examine the effect of two or more continuous years of exposure to endophyte-infected (EI) tall fescue on pregnancy and calving rates and calf growth in cow-calf pairs. In 1999 and 2000, Angus and Angus x Hereford cows were randomly assigned to graze 16 ha endophyte-free (EF; n = 20) or 24 ha EI (n = 30) starting in April. From spring 2000 until fall 2003 cows were continuously exposed to each forage. Heifers were bred in April and cows were bred in May for a 90 and 60 day breeding period, respectively. Cows were removed or culled from treatments if they did not conceive or lost a pregnancy or calf. Cows grazing EI fescue were supplemented with approximately 48 kg/cow of corn/SBM during the winter so that body condition scores were similar between EF and EI cows by time bred. By the time the calves were weaned in early October, pregnancy rate, determined by transrectal ultrasound, and calving rate was similar between pasture groups and length of time on pasture. Calving interval tended to be reduced in cows grazing EI fescue the first year (374.0 ± 4.8 < 386.2 ± 4.4 d; forage x exposure; P < 0.06). Percent of cows culled or that died between forage treatments was similar. Despite supplemental feeding of EI cows over winter, body weight (forage x exposure x days postpartum, P < 0.03) and condition scores (1 = emaciated, 9 = obese; forage x exposure x days postpartum, P < 0.001) were greater in cows grazing EF fescue. Body weight and condition was greater in cows exposed for 3 to 5 years in both forage groups compared to those exposed to forage for 1 or 2 years. Birth weights of calves born to cows exposed to 2 years compared with 1 or 3 to 5 years of EI fescue were reduced (forage x exposure, P < 0.008). However, by weaning, the 205 day adjusted weaning weight was similar among exposure groups and greater in EF compared with EI calves (224.3 ± 3.8 > 199.7 ± 2.4 kg; P < 0.001). In summary, number of years of exposure to EI tall fescue did not greatly impact cow-calf performance.