18 DO TEMPORARY CALF REMOVAL AND/OR EQUINE CHORIONIC GONADOTROPIN ADMINISTRATION INCREASE PREGNANCY RATES IN LACTATING NELORE COWS TREATED WITH A PROGESTERONE-RELEASE INTRAVAGINAL DEVICE?

Abstract

Reports indicate that either temporary calf removal or equine chorionic gonadotropin administration can increase the efficiency (pregnancy rate) of hormonal treatments with progestins during postpartum anestrus. This experiment evaluated effects of TCR and/or eCG administration in a protocol with progesterone that is frequently used for fixed-time artificial insemination (FTAI) in cows during postpartum anestrus. The protocols were tested at three farms in lactating Nelore cows (40 to 70 days post-partum, n = 361) with body condition scores from 2.5 to 3.0 (0- to 5-point scale). At a random stage of the estrous cycle (Day 0), animals received a basic PEPE (progesterone-estrogen-prostaglandin-estrogen) protocol with insertion of an intravaginal device with 1.0 g progesterone (DIB^®, Syntex, Buenos Aires, Argentina) and an i.m. injection of 2.5 mg of estradiol benzoate (EB, Estrogin^®, Farmavet, São Paulo, Brazil). Eight days later (Day 8) cows were treated i.m. with 150 mg D-cloprostenol (PGF2Ã Prolise^®, ARSA S.R.L., Buenos Aires, Argentina), and the DIB was removed. Twenty-four hours after DIB removal, cows received 1.0 mg EB i.m. and 30 to 36 h later all animals were FTAIed without estrus detection. Cows were allocated randomly to four groups: PEPE, PEPE/TCR, PEPE/eCG, and PEPE/TCR/eCG. In Group PEPE/TCR, calves were removed temporarily for 54 h (from DIB removal until FTAI). In Group PEPE/eCG, animals received PEPE treatment plus one dose i.m. of 300 UI eCG (Novormon^®, Syntex) following PGF2Ã administration (Day 8). In Group PEPE/TCR/eCG, animals were treated as in protocol PEPE/TCR plus eCG on D8. All animals were examined by ultrasonography (Aloka SSD 500, 7.5 MHz probe) 10 days before and at the beginning of hormonal treatment in order to detect anestrous cows (absence of corpus lutcum in both exams). Pregnancy diagnosis was performed by ultrasonography 30 days after FTAI. The data were analyzed by logistic regression. The following variables were considered in the model and did not affect pregnancy rates: farms, inseminators, and semen (sire). A total of 75% of the animals were in anestrus (absence of CL) and the pregnancy rates were similar (P > 0.05) among the four groups: PEPE (43/85 = 50.6%), PEPE/TCR (42/98 = 42.9%), PEPE/eCG (41/88 = 46%), and PEPE/TCR/eCG (39/90 = 43.3%). The results indicate that in Nelore cows, in postpartum anestrus and good body condition, TCR and/or eCG administration do not improve the efficiency (pregnancy rate) of the PEPE protocol.

This work was supported by FAPESP. V.G.P. and A.F.S. received fellowships from CNPq, Brazil.