ESTRUS DETECTION TECHNIQUES AND INSEMINATION STRATEGIES IN BOS-INDICUS HEIFERS SYNCHRONIZED WITH NORGESTOMET-ESTRADIOL

Oestrus was synchronised in 57 Bos indicus heifers using norgestometoe stradiol and pregnant mare serum gonadotrophin, Oestrus was detected b y observations made at six-hourly intervals, using oestrogen-treated a nd chin-ball harnessed steers, heatmount detectors, tail-paint and vis ual observation. Heifers were inseminated once at either a fixed time of 49.2 +/- 0.4 h (mean +/- SE; n = 29) after implant removal or 12.6 +/- 1.5 h (n = 28) after oestrus was detected. The mean (+/-SE) time t o the onset of oestrus was 47.1 +/- 1.9 h, while 90% of heifers record ed in oestrus were detected within 66 h of implant removal. Heatmount detectors were significantly more efficient at detecting oestrus than chin-ball harnessed steers, tail paint or visual observation (P < 0.00 1), A higher pregnancy rate was obtained in heifers inseminated after oestrus detection compared with heifers inseminated at a fixed-time (5 7.1 vs 34.5%; P = 0.043) and a higher pregnancy rate was obtained in h eifers classified as easy to inseminate compared with heifers classifi ed as difficult to inseminate (57.8 vs 0%, P < 0.001), We conclude tha t heatmount detectors are an efficient means of detecting oestrus in s ynchronised B indicus heifers and that pregnancy rates can be increase d when insemination follows oestrus detection compared with a fixed-ti me insemination regimen.