Comparison of the pregnancy rates and costs per calf born after fixed-time artificial insemination or artificial insemination after estrus detection in Bos indicus heifers

摘要

This study compared pregnancy rates (PRs) and costs per calf born after fixed-time artificial insemination (FTAI) or AI after estrus detection (i.e., estrus detection and AI, EDAI), before and after a single PGF2α treatment in Bos indicus (Brahman-cross) heifers. On Day 0, the body weight, body condition score, and presence of a CL (46% of heifers) were determined. The heifers were then alternately allocated to one of two FTAI groups (FTAI-1, n=139) and (FTAI-2, n=141) and an EDAI group (n=273). Heifers in the FTAI groups received an intravaginal progesterone-releasing device (IPRD; 0.78g of progesterone) and 1mg of estradiol benzoate intramuscularly (im) on Day 0. Eight days later, the IPRD was removed and heifers received 500μg of PGF2α and 300IU of eCG im; 24hours later, they received 1mg estradiol benzoate im and were submitted to FTAI 30 to 34hours later (54 and 58hours after IPRD removal). Heifers in the FTAI-2 group started treatment 8days after those in the FTAI-1 group. Heifers in the EDAI group were inseminated approximately 12hours after the detection of estrus between Days 4 and 9 at which time the heifers that had not been detected in estrus received 500μg of PGF2α im and EDAI continued until Day 13. Heifers in the FTAI groups had a higher overall PR (proportion pregnant as per the entire group) than the EDAI group (34.6% vs. 23.2%; P=0.003), however, conception rate (PR of heifers submitted for AI) tended to favor the estrus detection group (34.6% vs. 44.1%; P=0.059). The cost per AI calf born was estimated to be $267.67 and $291.37 for the FTAI and EDAI groups, respectively. It was concluded that in Brahman heifers typical of those annually mated in northern Australia FTAI compared with EDAI increases the number of heifers pregnant and reduces the cost per calf born.