Fertility following fixed-time AI in CIDR-treated beef heifers given GnRH or estradiol cypionate and fed diets supplemented with flax seed or sunflower seed

The objectives were to determine pregnancy rates following fixed-time AI (FTAI) in heifers: (1) given GnRH or estradiol cypionate (ECP) to synchronize follicular wave emergence and ovulation in a CIDR-based protocol; and (2) fed diets supplemented with flax or sunflower seeds. At two locations, Angus and crossbred Angus heifers (n=983) were examined ultrasonically to confirm reproductive maturity and randomly allocated to six synchronization groups in a 2×3 factorial design. On Day 0 (start of synchronization treatments), heifers received a CIDR and either 100μg GnRH i.m. (n=492) or 1mg ECP plus 50mg progesterone i.m. (n=491); in these groups, CIDR removal and PGF treatment were done concurrently on Days 7 and 8.5, respectively. Heifers were re-randomized to receive 0.5mg ECP i.m. at CIDR removal or 24h later (with FTAI 58–60h after CIDR removal in both groups), or 100μg GnRH i.m. concurrent with FTAI (52–54h after CIDR removal). The heifers were fed a barley silage-based diet for 50 days (from Day −25 to 25) supplemented with 1kg/heifer per day of flax seed (n=321), sunflower seed (n=324), or no oilseed (n=338). Pregnancy rate to FTAI (overall, 56.2%) was not affected by treatment at CIDR insertion (P=0.96) but was higher (P<0.005) in heifers given ECP 24h after CIDR removal (216/330, 65.4%) than in those given either ECP at CIDR removal (168/322, 52.1%) or GnRH at AI (169/331, 51.1%). Overall, there was no effect of diet on pregnancy rates (P=0.46). In summary, pregnancy rate to FTAI was not significantly affected by treatment at CIDR insertion to synchronize follicular wave emergence, but 0.5mg ECP 24h after CIDR removal (to synchronize ovulation) resulted in the highest pregnancy rate.