Delaying induction of ovulation and timed artificial insemination in a Double-Ovsynch protocol increased expression of estrus and altered first-service reproductive outcomes of lactating dairy cows

• Published in: Journal of dairy science 2025-01, Vol.108 (1), p.1103-1124
• Main Authors: Laplacette, A.L., Rial, C., Sitko, E., Perez, M.M., Tompkins, S., Stangaferro, M.L., Thomas, M.J., Giordano, J.O.
• Format: Article
• Language: English
• Subjects: Animals; automated detection of estrus; Cattle; delayed induction of ovulation; Estrus; Estrus Synchronization - methods; Female; fertility; Gonadotropin-Releasing Hormone - pharmacology; Insemination, Artificial - veterinary; Lactation; Ovulation - drug effects; Ovulation Induction - methods; Ovulation Induction - veterinary; Pregnancy; Progesterone - blood; timed artificial insemination
• ISSN: 0022-0302; 1525-3198; 1525-3198
• DOI: 10.3168/jds.2024-24994

The list of standard abbreviations for JDS is available at adsa.org/jds-abbreviations-24. Nonstandard abbreviations are available in the Notes. The objective of this randomized controlled experiment was to evaluate the effect of delaying induction of ovulation and timed artificial insemination (TAI) on expression of estrus before AI and first-service reproductive outcomes. A secondary objective was to evaluate the effects of delaying induction of ovulation in a Double-Ovsynch protocol on ovarian function. Lactating Holstein cows (n = 4,672) from 2 commercial dairy farms fitted with sensors for automated detection of estrus were synchronized with a Double-Ovsynch protocol up to the first PGF2α (PGF-L) of the Breeding-Ovsynch portion of the protocol (Pre-Ovsynch: GnRH, 7 d later PGF2α, 3 d later GnRH, 7 d later Breeding-Ovsynch: GnRH, 7 d later PGF2α, 1 d later PGF2α). At PGF-L, cows blocked by parity (primiparous vs. multiparous) and semen used for first service (sex-sorted dairy vs. conventional beef) were randomly assigned to the G56 (n = 2,338) or G80 (n = 2,334) treatments. Cows in G56 had 56 h whereas cows in G80 had 80 h from PGF-L to induction of ovulation with the last GnRH (GnRH2) before AI. For both treatments, TAI occurred ∼16 h after GnRH2. All cows with automated estrus alerts between PGF-L and TAI were inseminated at detected estrus (AIE) without GnRH. Ovarian function and responses to synchronization were monitored based on circulating concentrations of progesterone and examination of the ovaries by ultrasonography. Data for binary outcomes were analyzed by logistic and continuous outcomes with lineal regression. More cows in G80 received AIE and had estrus before AI. Overall, pregnancies per AI (P/AI) did not differ for the G80 and G56 treatments. Cows in G80 that received TAI and had no estrus had fewer P/AI than cows with estrus that received AIE or TAI in G80, and fewer P/AI than cows AIE and cows that received TAI and had or did not have estrus in the G56 treatment. No differences were observed between treatments or for cows with and without estrus for pregnancy loss. Unlike some minor differences between treatments for concentrations of progesterone at GnRH2, the most notable differences in ovarian function were for cows in both treatments with or without estrus that received TAI. Cows with estrus, were more likely to have follicles >16 mm, had larger follicles before ovulation, and had a greater ovulation risk after AI. Likewise, withi