8 EFFECT OF SUCKLING RESTRICTION AND eCG TREATMENT ON PREGNANCY RATES IN POSTPARTUM BOS INDICUS CROSSBRED COWS TREATED WITH PROGESTERONE VAGINAL DEVICES AND ESTRADIOL BENZOATE

Abstract

Previous studies have shown that the use of eCG given at the time of removal of a progesterone (P4) releasing device improved pregnancy rates to fixed-time AI (FTAI) in postpartum Bos indicus cows (Bo GA et al. 2004 Reprod. Fertil. Dev. 16, 127). Suckling restriction with the placement of nose tags in calves has also been shown to induce cyclicity and increase pregnancy rates in postpartum Bos indicus cows (Stahringer RC 2003 Taurus 18, 21–23). An experiment was designed to compare the effect of eCG treatment and restricted suckling on pregnancy rates in postpartum cows in fair to poor body condition score (BCS). A secondary objective was to evaluate the effect of restricted suckling on weaning weights. Lactating primiparous crossbred Bos indicus cows (n = 399), 60 to 90 days postpartum with a BCS 2.0 (1 to 5 scale), were randomly allocated to 1 of 4 treatment groups, in a 2 × 2 factorial design. On Day 0, all cows received a P4 intravaginal device (DIB, Syntex, Argentina) and 2 mg estradiol benzoate (EB) i.m. (Syntex). On Day 8, DIB devices were removed and all cows received 150 μg D(+)cloprostenol i.m. (Ciclase, Syntex) and were randomly divided to receive 400 IU eCG (Novormon, Syntex) or no treatment at the same time. On Day 9, all cows received 1 mg EB i.m. and were FTAI 52 to 56 h after DIB removal. Nose tags were placed in half of the calves from Day 0 to the time of FTAI, whereas the other half of the calves remained untreated. All cows were examined by ultrasonography 30 d after FTAI to determine pregnancy status. Pregnancy data were analyzed by logistic regression, and birth and weaning weights were analyzed by Student's t-test. Ovarian activity was estimated by rectal palpation on Day 0: there were 57/399 (14.3%) cows with a CL, 203/399 (50.8%) cows with palpable medium size follicles, and 139/399 (34.8%) cows with ovaries containing no detectable structures. There was no effect of ovarian status at the time of treatment (P = 0.52) or semen (P = 0.89) on pregnancy rates. Suckling restriction increased (P = 0.03) pregnancy rates (91/195, 46.6% and 81/204, 39.7% for cows not suckled or suckled during the treatment, respectively). However, there was no effect of eCG or eCG by weaning interaction (P = 0.82) on pregnancy rates (82/192, 42.7% and 90/207, 43.4% for cows treated or not treated with eCG, respectively). Although mean (±SEM) birth weights were not different (29.4 ± 0.4 vs. 29.1 ± 0.4; P = 0.6), weaning weights were significantly affected (P = 0.001) by the suckling restriction (190.1 ± 1.9 vs. 200.4 ± 2.1 for calves treated or not treated with the nose tags, respectively). Although restricting suckling, by placement of a nose tag from Day 0 to FTAI, may increase pregnancy rates in primiparous Bos indicus cows in fair to poor BCS, the adverse effect of this treatment on weaning weights of the calves has to be considered. Furthermore, eCG did not increase pregnancy rates in the present study, as it has been previously reported. Research was supported by Syntex S.A., Estancia El Mangrullo S.A., and Agencia Cordoba Ciencia S.E.