Submitted to: Theriogenology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/5/2001
Publication Date: 7/1/2001
Citation: BURKE, J.M., RORIE, R.W., PIPER, E.L., JACKSON, W.G. 2001. REPRODUCTIVE RESPONSES TO GRAZING ENDOPHYTE-INFECTED TALL FESCUE IN POSTPARTUM BEEF COWS. THERIOGENOLOGY. 56:357-369. Interpretive Summary: Tall fescue toxicosis, a collection of disorders occurring when cattle graze tall fescue, may reduce reproductive performance in beef cattle leading to economic losses. The current study examined pregnancy rate and stage of pregnancy losses in cows grazing endophyte-free or infected tall fescue during summer months. Although there was some early pregnancy loss when environmental temperatures were high, there was no significant difference in pregnancy rate or other reproductive responses between the two groups of cows. There was greater pregnancy loss in Hereford compared with Angus or Angus x Hereford cows. This information is valuable to producers and extension agents implying that with proper management of cows and forage, cows may graze tall fescue during summer months without significant detrimental effects to pregnancy rate
Technical Abstract: The objective of this experiment was to determine effects of endophyte- free (E-; n = 20) or infected (E+; n = 30) tall fescue on reproductive responses in postpartum beef cows with calves. Three weeks before estrus synchronization, cow-calf pairs were introduced to pasture treatment. Cows were synchronized and bred by AI following detected estrus for a period of 6 d and then by natural service for 62 d. Bulls were rotated weekly to minimize effects of fescue toxicosis on male fertility. Fetal development was monitored weekly between 30 and 60 d of pregnancy and at weaning using transrectal ultrasound. Signs of fescue toxicosis existed in E+ grazed cows. Respiration rate and rectal temperature increased in E+ cows and serum concentrations of prolactin, total, body condition and adjusted weaning weight of calves were reduced compared to that of E- cows. Backfat estimated at the rump and rib using ultrasound was not different (E- vs E+). Differences were not detected for estrus detection rate, pregnancy rate to synchronized estrus, overall pregnancy rate 30 d postbreeding, overall pregnancy rate at 60 d postbreeding, or serum concentrations of progesterone on day of PGF injection. Pregnancy losses that occurred between 30 and 60 d gestation were 6.0 (E-) vs 15.0 (E+) +/- 8.0 percent (P>0.10) and occurred after environmental temperatures rose above 37.8 degrees C for three weeks. Total pregnancy losses that occurred by weaning were 5.5 (E-) vs 17.6 (E+) +/- 8.0 percent (P>0.10). Fescue toxicosis may provoke an increase in embryo losses between 30 and 60 d pregnancy.