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 x 3 factorial design. On Day 0 (start of synchronization treatments), heifers received a CIDR and either 100 mug GnRH i.m. (n = 492) or 1 mg ECP plus 50 mg 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 0.5 mg ECP i.m. at CIDR removal or 24 h later (with FTAI 58-60 h after CIDR removal in both groups), or 100 mug GnRH i.m. concurrent with FrAI (52-54 h after CIDR removal). The heifers were fed a barley silage-based diet for 50 days (from Day -25 to 25) supplemented with 1 kg/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 24 h 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 FrAI was not significantly affected by treatment at CIDR insertion to synchronize follicular wave emergence, but 0.5 mg ECP 24 h after CIDR removal (to synchronize ovulation) resulted in the highest pregnancy rate. (C) 2003 Elsevier B.V All rights reserved.