M. Colazo

Effect of length of progesterone exposure during ovulatory wave development on pregnancy rate.

The objective was to determine the effects of the duration of progesterone exposure during the ovulatory wave on fertility (pregnancy rate) in beef cattle. We tested the hypothesis that short-progesterone exposure during the growing and early-static phase of the ovulatory follicle (analogous to the ovulatory wave of 3-wave cycles) is associated with higher fertility than a longer duration of exposure (analogous to the ovulatory wave of 2-wave cycles). Three to 5 days after ovulation, beef heifers (n = 172) and suckled beef cows (n = 193) were given an intravaginal progesterone-releasing device (CIDR) and 2.5 mg estradiol - 17β +50 mg progesterone im to induce a new follicular wave. Cattle were allocated to short- or long-progesterone exposure groups (for 3 and 6 d after wave emergence, respectively) after which prostaglandin F(2α) was administered and CIDR were removed. Forty-eight hours later, all cattle were given 12.5 mg pLH and artificially inseminated (AI) with frozen-thawed semen. The diameter of the two largest follicles and the corpus luteum were measured by transrectal ultrasonography at CIDR removal, insemination, and 36 h after insemination. Pregnancy diagnosis was done ultrasonically 38 and 65 d post-AI. There was no difference in pregnancy rates in short- vs long-progesterone exposure in heifers (53 vs 47%, P = 0.44) or cows (63 vs 58%, P = 0.51). However, the diameter of the ovulatory follicle at CIDR removal and AI was smaller in short- than in long-progesterone groups (P < 0.02), and larger in cows than in heifers (P < 0.006). In conclusion, short-progesterone exposure during the growing and early-static phase of the ovulatory follicle (similar to 3-wave cycles) was not associated with higher fertility than a longer progesterone exposure (similar to 2-wave cycles).

Effects of exogenous progesterone and cloprostenol on ovarian follicular development and first ovulation in prepubertal heifers.

The objective of this study was to determine the effects of progesterone and cloprostenol (a PGF(2alpha) analogue) on ovarian follicular development and ovulation in prepubertal heifers. In Experiment 1, crossbred Hereford heifers (Bos taurus; 10 to 12 mo old, 255 to 320 kg) were assigned randomly to three groups and given (1) an intravaginal progesterone-releasing insert (CIDR; P group, n=13); (2) a CIDR plus 500 microg cloprostenol im (PGF(2alpha) analogue) at CIDR removal (PPG group, n=11); or (3) no treatment (control group, n=14). The CIDR inserts were removed 5 d after follicular wave emergence. Progesterone-treated heifers (P and PPG groups) had a larger dominant follicle than that of the control group (P=0.01). The percentage ovulating was highest in the PPG group (8 of 11, 73%), intermediate in the P group (4 of 13, 31%), and lowest in the control group (1 of 14, 7%; P<0.02). In Experiment 2, 16 heifers (14 to 16 mo old, 300 to 330 kg) were designated to have follicular wave emergence synchronized with either a CIDR and 1mg estradiol benzoate im (EP group, n=8) on Day 0 (beginning of experiment) or by transvaginal ultrasound-guided ablation of all follicles >or=5mm on Day 3 (FA group, n=8). On Day 7, CIDRs were removed in the EP group, and all heifers received 500 microg cloprostenol im. Ovulation was detected in 6 of 8 heifers (75%) in both groups. In summary, the use of PGF(2alpha) with or without exogenous progesterone treatment increased the percentage ovulating in heifers close to spontaneous puberty.

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

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 500μg of cloprostenol (Estroplan; Vetoquinol NA Inc., Edmonton, AB, Canada) on Day 5, and 100μg 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.