ESTROUS SYNCHRONIZATION TO FIXED-TIME ARTIFICIAL INSEMINATION ASSOCIATED TO TEMPORARY OR DEFINITIVE EARLY WEANNING IN BEEF COWS

Abstract

The objective of this experiment was to determine the reproductive performance of suckled beef cows in programs of artificial insemination (AI) submitted to definitive early or temporary weaning (EW or TW) and estrous synchronization protocol to fixed-time artificial insemination (FTAI). Two-hundred and five Angus x Nelore cows body with condition score 2.6±0.4 and post-partum period between 54 and 122 days were used in the trial. After EW, one-hundred, fifty three cows were separated three groups according to the AI or FTAI protocol. A group of cows was artificial inseminated according estrous detection after 10 days of definitive weaning during a period of 30 days (EW-AI, n= 53). Estrous synchronization programs to FTAI were carried out in two groups in different moments after EW. In the group EW-FTAI (n= 50), cows were treated at the moment calves were removed while in EW-FTAI 10 (n= 50) the hormonal treatment began 10 days later.  The hormonal treatment consisted of an intravaginal implant containing 1,9g of Progesterone, for 8 days, and an injection of  Estradiol benzoate (EB), 2mg, im. When the dispositives were removed, 75mcg of Cloprostenol were injected, im, and after 24 hours, 1mg of EB, im. Cows were fixed-time artificial inseminated 52 to 56 hours after implants removal. In TW-FTAI group (n= 52), cows were treated with the same hormonal therapy, but a temporary weaning of 60 hours was done after the implant removal and the FTAI moment. The breeding season was 60 days in EW-FTAI and TW-FTAI groups, 50 days in EW-FTAI10 group and 30 days in EW-AI group. In a sample of 20% of cows ovaries were scanned by ultrasound and it was determined that 55% of the cows were in anestrous. Follicular diameters were determined at beginning of hormonal treatment and at FTAI moment in cows submitted to estrous synchronization (EW-FTAI= 10, EW-FTAI10= 10 and TW-FTAI= 10) by ultrasound. The means of follicular diameters were not different (P>0.05) between groups at Day 0 (7.0±3.1mm; 8.1±1.9mm e 6.5±1.7mm) and at Day 10 (9.8±1.4mm; 12.5±1.2mm e 11.8±2.8mm). The pregnancy rates at AI were 57, 48, 48 and 46% and at the end of the breeding season were 77, 88, 68 and 78%, EW-AI, EW-FTAI, EW-FTAI10 and TW-FTAI respectively, without significance (P>0.05). According to the this study, EW didn’t improve reproductive performance compared to TW associated to estrous synchronization programs to FTAI and 10 days of interval from EW and hormonal therapy didn’t increase fertility in FTAI.

Key words: Beef cows, early weaning, fixed-time artificial insemination.