Effect of day of the estrous cycle at the initiation of a timed artificial insemination protocol on reproductive responses in dairy heifers

• Published in: Journal of animal science Vol. 78; no. 6; pp. 1568 - 1576
• Main Authors: Moreira, F, de la Sota, R. L, Diaz, T, Thatcher, W. W
• Format: Journal Article
• Language: English
• Published: Savoy, IL Am Soc Animal Sci 01.06.2000; American Society of Animal Science
• Subjects: Animal productions; Animals; Biological and medical sciences; Buserelin - pharmacology; Cattle - physiology; Dairying - methods; Dinoprost - pharmacology; Estrus - physiology; Estrus Synchronization; Female; Fertility Agents, Female - pharmacology; Fundamental and applied biological sciences. Psychology; Insemination, Artificial - methods; Insemination, Artificial - veterinary; Ovarian Follicle - physiology; Pregnancy; Progesterone - blood; Terrestrial animal productions; Time Factors; Vertebrates; Agonist; Farming animal; Bovine; Primiparity; Gonadotropin RH; Ox; Experimental study; Sexual reproduction; Synchronization; Ovulation; Prostaglandin F2α; Time dependence; Vertebrata; Mammalia; Artificial insemination; Heifer; Artiodactyla; Estrous cycle; Ungulata
• ISSN: 0021-8812; 1525-3163; 0021-8812
• DOI: 10.2527/2000.7861568x

Our objectives were to identify stages of the estrous cycle at which initiation of a timed artificial insemination (Ovsynch/TAI) protocol may reduce pregnancy rates and to monitor ovarian follicle dynamics and corpus luteum development after initiation of the Ovsynch/TAI protocol at different stages of the cycle. Cycling Holstein heifers (n = 24) were injected twice with prostaglandin F2alpha to induce estrus and were scanned by ovarian ultrasonography to determine the day of ovulation (d 0). Heifers were assigned to initiate the Ovsynch/TAI protocol at d 2 (n = 5), 5 (n = 5), 10 (n = 4), 15 (n = 5), or 18 (n = 5) of the cycle. The Ovsynch/TAI was initiated with an injection of gonadotropin-releasing hormone agonist followed 7 d later with an injection of prostaglandin F2alpha. At 36 h after injection of prostaglandin F2alpha, heifers were injected with gonadotropin-releasing hormone agonist and inseminated 16 h later. Heifers were scanned daily during the Ovsynch/TAI protocol and every other day after insemination until 16 d later. Blood samples were collected daily starting at the 1st day heifers were scanned and continued until 16 d after insemination. Initiation of the Ovsynch/TAI protocol at d 15 of the estrous cycle caused heifers to ovulate prior to insemination. A shortened return to estrus (< 16 d) was caused by ovulation failure to the second gonadotropin-releasing hormone injection, by incomplete regression of the corpus luteum, and by short life-span of the induced corpus luteum. Day of the cycle in which the Ovsynch/TAI protocol is initiated affects dynamics of follicular development, plasma progesterone profiles, and occurrence of premature ovulation. Size of the pre-ovulatory follicle was associated positively with subsequent progesterone concentrations following insemination.