Evaluation of three synchrony programs for pasture-based dairy heifers

The objective was to evaluate the efficacy and economic benefits of three synchrony programs in 1137 heifers from 10 pasture-based dairy herds. Heifers were randomly assigned to one of three treatments within each herd on Day −13 (Day 0 = start of the breeding program). They were treated with: (1) PGF2α on Days −13 and −2, with AI after detection of estrus between Days 0 and 3 (Double PG); (2) GnRH, PGF2α, and GnRH on Days −9, −2, and 0, respectively, with placement of an intravaginal progesterone (P4)-releasing device between Days −9 and −2, and set time AI on Day 1 (GPG + P4); or (3) same as the GPG + P4 group but with the set time AI on Day 0 (Cosynch + P4). Plasma P4 concentrations were determined on Days −20 and −13 to determine pubertal status. The Cosynch + P4 treatment had a higher (P < 0.05) conception rate to AI (57% vs. 47% vs. 48% for Cosynch + P4, GPG + P4, and Double PG, respectively), 21-day in-calf rate (76% vs. 72% vs. 63% for Cosynch + P4, GPG + P4, and Double PG), and a shorter median interval from the start of the breeding program to conception (0, 14, and 19 days for Cosynch + P4, GPG + P4, and Double PG). Heifers that had reached puberty before breeding, compared with those that had not, had higher (P < 0.05) in-calf rates to AI (53% vs. 47%) at 21 days (74% vs. 64%) and at 42 days (91% vs. 84%). Pubertal status was associated with herd, breed, age, and body condition score at the start of mating (P < 0.05). A partial budget model demonstrated that, compared with the Double PG program, there was an economic benefit from the Cosynch + P4 (mean, NZ$25.73; 95% confidence interval, 2.99-50.69), but not the GPG + P4 program (mean, NZ$−0.65; 95% confidence interval, −21.87 to 21.58). We concluded that the Cosynch + P4 program resulted in the highest fertility and economic benefit of the three programs evaluated, and that reproductive response was affected by pubertal status.