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Effect of Breeding Protocols and Reproductive Tract Score on Reproductive Performance of Dairy Heifers and Economic Outcome of Breeding Programs¹

J. L. Stevenson^*, J. A. Rodrigues^*, F. A. Braga^*, S. Bitente^*, J. C. Dalton, J. E. P. Santos and R. C. Chebel^*,2,3

^* Caine Veterinary Teaching Center, and
Research and Extension Center, University of Idaho, Caldwell 83607
Veterinary Medicine Teaching and Research Center, University of California-Davis, Tulare 93274

² Corresponding author: rchebel{at}vmtrc.ucdavis.edu

The objectives of this study were to evaluate the effect of reproductive protocols and reproductive tract score on reproductive performance of dairy heifers and economic outcomes of breeding programs. Holstein heifers (n = 534), 13 ± 1 mo of age, were randomly assigned to 1 of 4 reproductive protocols. On the day of enrollment (d 0), heifers were palpated per rectum and received a score according to the maturity of their reproductive tract (1 = prepubertal; 2 = peripubertal; and 3 = puber-tal). Estrous detection-control heifers (CON, n = 146) received no treatment and were inseminated on detection of estrus for 28 d. Prostaglandin F₂-treated heifers (PGED, n = 137) received 1 injection of PGF₂ on d 0 and were inseminated on detection of estrus; heifers not in-seminated by d 14 received a second injection of PGF₂ and were observed for estrus and artificial insemination (AI) for an additional 14 d. Heifers enrolled in the estrous detection-timed AI (EDTAI, n = 140) treatment received a controlled internal drug-release (CIDR) insert on d 0, and 7 d later, the CIDR was removed and all heifers received an injection of PGF₂, heifers received AI on detection of estrus, and those not inseminated by 72 h after PGF₂ received an injection of GnRH concurrent with AI. Heifers in the GnRH-timed AI (GTAI, n = 111) treatment received 1 injection of GnRH on d 0, on d 6 heifers received a CIDR insert and injections of GnRH and PGF₂, on d 13 the CIDR was removed and heifers received an injection of PGF₂, and 48 h later all heifers received an injection of GnRH and AI. Pregnancy was diagnosed at 32 ± 3 and 62 ± 3 d after AI. Cost of reproductive protocols and their economic outcomes were calculated for a 28 d period beginning at enrollment. Heifers in the PGED treatment were inseminated at a faster rate than CON heifers. A smaller proportion of prepubertal and peripubertal heifers were inseminated within 14 d of enrollment compared with pubertal heifers. Pregnancy per AI of CON and PGED heifers was greater compared with EDTAI and GTAI heifers. Proportion of GTAI heifers pregnant at the end of the 28-d breeding program was or tended to be smaller compared with PGED and CON heifers, respectively. Heifers in the CON and PGED treatments had the smallest cost per pregnancy followed by heifers in the EDTAI and GTAI treatments, respectively. When different scenarios were evaluated, however, the mean cost per pregnancy was smallest for PGED heifers. Cost per pregnancy generated was greatest for prepubertal heifers, whereas pubertal heifers had the smallest cost per pregnancy generated. Treatment of dairy heifers with PGF₂ every 14 d until insemination and pregnancy results in the best economic outcomes, and screening heifers according to RTS may prove beneficial to identify heifers that may not be pubertal and would have compromised reproductive and economic performance in a breeding program.

Key Words: reproductive protocol • economic outcome • dairy heifer