9 EVALUATION OF A MODIFIED GnRH-BASED TIMED ARTIFICIAL INSEMINATION PROTOCOL ASSOCIATED WITH ESTRUS DETECTION IN CYCLIC BEEF HEIFERS INSEMINATED WITH SEX-SELECTED SEMEN

Abstract

This study compared pregnancy per TAI (P/TAI) between sex-selected and conventional semen in cyclic beef heifers subjected to the modified (without initial GnRH) 5-day Co-synch protocol and evaluated the usefulness of an oestrus detection (ED) to identify heifers that were most likely to conceive. Heifers (n = 1034; 13 to 15 months of age) at three locations were scanned by ultrasonography to determine cyclicity (presence of corpus luteum) and reproductive tract normalcy. Cyclic heifers (n = 940) received a 1.38-g progesterone-releasing device (CIDR; Zoetis Animal Health, Florham Park, NJ, USA) on Day 0, CIDR removal and 500 μg of cloprostenol (Estroplan; Vetoquinol NA Inc., Edmonton, AB, Canada) on Day 5, and 100 μg of GnRH (Fertiline; Vetoquinol NA Inc.) along with TAI on Day 8 (72 ± 1 h after CIDR removal). On Day 5, heifers received ED patches (EstrotectTM; Estrotect Inc.) that were scored from 0 to 3, based on colour change between initial application and Day 8; 0 = unchanged, 1 = ≤50% colour change, 2 = >50% colour change, 3 = missing. Heifers were assigned by ear-tag number to be inseminated with frozen–thawed sex-selected or conventional semen from either of two sires available commercially. Pregnancy diagnosis was performed by transrectal ultrasonography 28 (herd A) or 48 (herds B and C) days after TAI. Data were analysed using the PROC GLIMMIX in SAS (SAS Institute Inc., Cary, NC, USA), with herd included as a random effect. The CIDR retention rate was 98%; P/TAI in heifers that lost the CIDR was 21%. Pregnancy per TAI [% (no.)] did not differ (P > 0.05) between sires [58.4 (426) v. 58.0 (414) for sires A and B, respectively], but it was higher (P < 0.01) for conventional semen [63.7 (422) v. 52.6 (418)]. An interaction between sire and type of semen (P = 0.07) revealed that sex-selected semen from bull B had the lowest P/TAI [49.3 (203)]. Overall, heifers with an ED patch scored 2 had greater (P < 0.01) P/TAI [64.8 (526)] than those scored 0 [42.9 (170)] or 1 [46.8 (79)]. Heifers with a missing ED patch had intermediate P/TAI [58.5 (65)]. However, the effect of ED patch scoring on P/TAI depended on type of semen. In heifers inseminated with conventional semen, PTAI was significantly lower (P < 0.01) in those with an ED patch scored 0 [49.4(87)] compared to those with a patch scored 2 [69.6 (270)]. In heifers inseminated with sex-selected semen, P/TAI was significantly lower (P < 0.05) in those with an ED patch scored 0 [36.1(83)] or 1 [37.2 (43)] compared with those scored 2 [59.8 (256)] or 3 [58.3 (36)]. In summary, P/TAI was greater in heifers inseminated with conventional semen. However, the P/TAI obtained with the modified GnRH-based TAI protocol in cyclic heifers inseminated with sex-selected semen was encouraging. In addition, the Estrotect oestrus detection patches were considered useful to identify animals for TAI with sex-selected semen and could be used to increase the adoption of this technology in beef herds. This study was supported by Alberta Agriculture and Forestry, Vetoquinol NA Inc., Estrotect Inc. and collaborative beef producers.