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Effect of Synchronization Protocols on Follicular Development and Estradiol and Progesterone Concentrations of Dairy Heifers

J. L. Stevenson^*, J. C. Dalton, J. E. P. Santos, R. Sartori, A. Ahmadzadeh^# and R. C. Chebel^*,1,2

^* Caine Veterinary Teaching Center
Research and Extension Center, University of Idaho, Moscow 83844
School of Veterinary Medicine, University of California-Davis, Tulare 93274
Embrapa Recursos Genéticos e Biotecnológicos, Brasília, Distrito Federal, Brazil
^# Animal and Veterinary Science Department, University of Idaho, Moscow 83844

¹ Corresponding author: rchebel{at}vmtrc.ucdavis.edu

The objectives were to evaluate the effect of synchronization protocols on follicular development and estradiol 17-β (E₂) and progesterone (P₄) concentrations in dairy heifers. In experiment 1, 36 heifers were assigned to 1 of 6 synchronization protocols in a 3 x 2 factorial design: presynchronization with GnRH on study d –6 or –9 [study d 0 = initiation of the Cosynch + CIDR (controlled internal drug releasing insert containing P₄) protocol] or no presynchronization (control) and one injection of PGF₂ or not on study d 0. In experiment 2, 126 heifers were assigned to 1 of 4 synchronization protocols in a 2 x 2 factorial arrangement: presynchronization or not with GnRH on study d –6 and injection of PGF₂ or not on study d 0. In experiments 1 and 2, all heifers received a modified Cosynch protocol with CIDR for 7 d starting on study d 0. After the PGF₂ of the Cosynch and removal of the CIDR, heifers were detected in estrus and inseminated. Those not inseminated by study d 10 received an injection of GnRH and were timed-inseminated. Ovaries were scanned by ultrasound on d 0, 2, and 5, daily from d 7 to 14, and on d 16. Blood samples collected on d 0, 2, 7, 9, and 16 were analyzed for P₄, and the blood sample collected on d 9 was analyzed for E₂. Pregnancy was diagnosed at 28 and 40 ± 3 d after artificial insemination. In experiment 1, there was a tendency for the presynchronization protocol to affect the proportion of heifers ovulating in response to the first GnRH injection of the Cosynch + CIDR protocol. In experiment 2, a greater proportion of presynchronized heifers ovulated in response to the first GnRH injection. Although heifers receiving PGF₂ had larger ovulatory follicles on d 7 and before ovulation and shorter intervals to estrus and ovulation, these heifers tended to have decreased concentrations of E₂ during proestrus. Presynchronization of dairy heifers with GnRH increased ovulation in response to the first GnRH injection, and treatment of heifers with PGF₂ at initiation of the Cosynch + CIDR protocol increased the size of the ovulatory follicle and reduced the intervals to estrus and ovulation.

Key Words: heifer • ovulation synchronization • follicle growth