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Synchronization of ovulation for fixed-time insemination in heifers
Theriogenology
412
SYNCHRONIZATION OF OVULATION FOR FIXED-TIME INSEMINATION IN HEWERS M.F. Martinez, 1 J.P. Kastelic, 2 G.P Adams, 1 R.B. Cook 2 and R.J. Mapletoft 1 1WCVM, University of Saskatchewan, Saskatoon, SK, S7N 5B4, Canada 2Agriculture and Agri-Food Canada, Research Centre, Lethbridge, AB, T 1J 4B 1, Canada Two experiments compared methods of synchronizing follicular wave emergence and ovulation for fixed-time artificial insemination (AI) in progestagen-treated cattle. In Experiment I, 122 crossbred beef heifers were fed 0.5 mg/head/day melengestrol acetate (MGA, Upjohn Co, Orangeville, ON) from Days 0 to 6 and were given 500 gg i.m. cloprostenol (PGF; Estrumate, Schering-Plough Animal Health, Pointe-Claire, PQ) on Day 7. On Day 0, half the heifers were treated intramuscularly (i.m.) with 2 mg estradiol benzoate (EB; Sigma Chemical Co, St. Louis, MO) and 50 mg progesterone (P4; Sigma) and half received 100 gg gonadorelin (GnRH; Cystorelin, Merial Can Inc, Victoriaville, PQ); groups were further subdivided to either receive 1 mg EB 24 h after PGF and AI 28 h later or 100 gg GnRH 36 h after PGF and AI 14 h later (2x2 factorial design). Although pregnancy rates were disappointingly low, chi-square analysis revealed no significant differences among groups (EB/EB - 37%; EB/GnRH - 33%; GnRH/EB - 32%; and GnRH/GnRH - 42%) Experiment 1I was designed to compare progestagens and methods of synchronizing estrus and ovulation i n a fixed-time AI program. At random stages of the estrous cycle, Angus-cross heifers (n = 503) were placed in 2 synchronization groups and 3 treatment groups in a 2x3 factorial design. On Day 0, heifers received CIDR-B devices (Vetrepharm Canada Inc, London, ON; n = 257) or were started on 0.5 rag/head/day MGA (n=246) and then given i.m. injections of either 2 mg EB and 50 mg P4, 100 gg GnRH or 12.5 mg pLH (Lutropin-V, Vetrepharm Canada Inc). The last feeding of MGA was given on Day 6, and on Day 7 CIDR-B devices were removed and all heifers received PGF. Consistent with their treatment on Day 0, heifers were given either 1 mg EB 24 h after PGF and inseminated 28 h later or 100 gg GnRH or 12.5 mg pLH 48 h after PGF and concurrently inseminated. Heifers were exposed to bulls for 17 d, starting approximately 20 d after AI. Ultrasonic pregnancy diagnosis was done approximately 30 d after AI and again 25 d after bulls were removed. Estrus rate differed (P < 0.01), but there was no significant difference in pregnancy rates among groups (P > 0.3; Table 1). Table 1. Pregnancy rates to a single, timed insemination in CIDR-B- or MGA-treated beef heifers in which ovulation was synchronized with GnRH, pLH or estradiol benzoate (EB). CIDR-B
No. heifers Estrus rate (%) Conception to AI (%) Conception to bull (%)* Total pregnancy rate (%) abc
MGA
GnRH
pLH
EB
GnRH
pLH
EB
103 66 a 65 67 88
102 61 a 56 62 83
52 92 b 62 70 88
101 36 c 52 70 85
97 33 c 56 63 84
48 92 b 60 74 90
Percentages with different superscripts are different (P<0.01). * Heifers not conceiving to AI.
Overall, results suggest that the oral progestagen (MGA) and the intravaginal device (CIDR-B) are equally efficacious and that in combination with GnRH, pLH or EB, either can be effectively used to synchronize estms and ovulation for fixed-time artificial insemination.
412
SYNCHRONIZATION OF OVULATION FOR FIXED-TIME INSEMINATION IN HEWERS M.F. Martinez, 1 J.P. Kastelic, 2 G.P Adams, 1 R.B. Cook 2 and R.J. Mapletoft 1 1WCVM, University of Saskatchewan, Saskatoon, SK, S7N 5B4, Canada 2Agriculture and Agri-Food Canada, Research Centre, Lethbridge, AB, T 1J 4B 1, Canada Two experiments compared methods of synchronizing follicular wave emergence and ovulation for fixed-time artificial insemination (AI) in progestagen-treated cattle. In Experiment I, 122 crossbred beef heifers were fed 0.5 mg/head/day melengestrol acetate (MGA, Upjohn Co, Orangeville, ON) from Days 0 to 6 and were given 500 gg i.m. cloprostenol (PGF; Estrumate, Schering-Plough Animal Health, Pointe-Claire, PQ) on Day 7. On Day 0, half the heifers were treated intramuscularly (i.m.) with 2 mg estradiol benzoate (EB; Sigma Chemical Co, St. Louis, MO) and 50 mg progesterone (P4; Sigma) and half received 100 gg gonadorelin (GnRH; Cystorelin, Merial Can Inc, Victoriaville, PQ); groups were further subdivided to either receive 1 mg EB 24 h after PGF and AI 28 h later or 100 gg GnRH 36 h after PGF and AI 14 h later (2x2 factorial design). Although pregnancy rates were disappointingly low, chi-square analysis revealed no significant differences among groups (EB/EB - 37%; EB/GnRH - 33%; GnRH/EB - 32%; and GnRH/GnRH - 42%) Experiment 1I was designed to compare progestagens and methods of synchronizing estrus and ovulation i n a fixed-time AI program. At random stages of the estrous cycle, Angus-cross heifers (n = 503) were placed in 2 synchronization groups and 3 treatment groups in a 2x3 factorial design. On Day 0, heifers received CIDR-B devices (Vetrepharm Canada Inc, London, ON; n = 257) or were started on 0.5 rag/head/day MGA (n=246) and then given i.m. injections of either 2 mg EB and 50 mg P4, 100 gg GnRH or 12.5 mg pLH (Lutropin-V, Vetrepharm Canada Inc). The last feeding of MGA was given on Day 6, and on Day 7 CIDR-B devices were removed and all heifers received PGF. Consistent with their treatment on Day 0, heifers were given either 1 mg EB 24 h after PGF and inseminated 28 h later or 100 gg GnRH or 12.5 mg pLH 48 h after PGF and concurrently inseminated. Heifers were exposed to bulls for 17 d, starting approximately 20 d after AI. Ultrasonic pregnancy diagnosis was done approximately 30 d after AI and again 25 d after bulls were removed. Estrus rate differed (P < 0.01), but there was no significant difference in pregnancy rates among groups (P > 0.3; Table 1). Table 1. Pregnancy rates to a single, timed insemination in CIDR-B- or MGA-treated beef heifers in which ovulation was synchronized with GnRH, pLH or estradiol benzoate (EB). CIDR-B
No. heifers Estrus rate (%) Conception to AI (%) Conception to bull (%)* Total pregnancy rate (%) abc
MGA
GnRH
pLH
EB
GnRH
pLH
EB
103 66 a 65 67 88
102 61 a 56 62 83
52 92 b 62 70 88
101 36 c 52 70 85
97 33 c 56 63 84
48 92 b 60 74 90
Percentages with different superscripts are different (P<0.01). * Heifers not conceiving to AI.
Overall, results suggest that the oral progestagen (MGA) and the intravaginal device (CIDR-B) are equally efficacious and that in combination with GnRH, pLH or EB, either can be effectively used to synchronize estms and ovulation for fixed-time artificial insemination.