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- Title
Comparison of controlled internal drug release insert-based protocols to synchronize estrus in prepubertal and estrous-cycling beef heifers.
- Authors
Leitman, N. R.; Busch, D. C.; Wilson, D. J.; Mallory, D. A.; Ellersieck, M. R.; Smith, M. F.; Patterson, D. J.
- Abstract
The objective of the experiment was to examine the necessity of adding a GnRH injection to a 14-d controlled internal drug release (CIDR)-based protocol for synchronization of estrus in beef heifers that were prepubertal or estrous-cycling at the initiation of treatment. The hypothesis tested was that the addi- tion of GnRH in a CIDR-based estrus synchronization protocol would increase the synchrony of estrus after PGF2α (PC). Beef heifers (n = 285) were assigned to 1 of 2 treatments within reproductive tract scores (2 or 3 = prepubertal; 4 or 5 = estrous-cycling) by age and BW. Heifers assigned to CIDR Select received a CIDR insert (1.38 g of progesterone) from d 0 to 14 followed by GnRH (100 μg, intramuscularly) on d 23 and PG (25 mg intramuscularly) on d 30. Heifers assigned to CIDR-PG received a CIDR insert from d 0 to 14 and PG on d 30. Heifers were fitted with a HeatWatch estrus detection system transmitter at the time of PG administration for continuous estrus detection during the synchronized period (0 to 144 h after PC); AT was performed 12 h after estrus onset. Estrous response did not differ (P = 0.43) between treatments (94% CIDR Select, 98% CIDR-PG). Mean interval to estrus after PG was 7 h shorter (P = 0.01) and variance for interval to estrus was reduced (P < 0.01) among CIDR-PG- treated compared with CIDR Select-treated heifers. Conception rate to AT tended (P = 0.09) to be greater for CIDR-PG heifers (67%) compared with CIDR Select heifers (58%), and AT pregnancy rate was greater (P = 0.05) for CIDR-PG heifers (66%) compared with CIDR Select heifers (55%). Final pregnancy rate at the end of the breeding season was similar for the 2 treat- ments (81% for both; P = 0.94). We conclude that the administration of GnRH 9 d after CIDR removal in the CIDR Select protocol is not required to facilitate an improvement in the synchrony of estrus in beef heifers.
- Subjects
ESTRUS; MAMMAL reproduction; OVULATION; SEX (Biology); HEIFERS; OBSTETRICS; SYNCHRONIZATION; PREGNANCY; PHYSIOLOGY; REPRODUCTION
- Publication
Journal of Animal Science, 2009, Vol 87, Issue 12, p3976
- ISSN
0021-8812
- Publication type
Article
- DOI
10.2527/jas.2009-2250