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ABSTRACT: The 6-d timed artificial insemination protocol has been designed to advance luteolysis after the first administration of GnRH so that the preovulatory follicular diameter at second GnRH is reduced and thereby pregnancy outcome may be improved. To achieve an earlier and complete luteolysis (5 to 6 d after the first GnRH treatment), an extra PGF(2α) treatment must be administered to cows 24 h after the initial PGF(2α) treatment. Although the use of 2 PGF(2α) treatments increases labor costs resulting from the increased handling of cows, no alternative and efficient protocol with a single PGF(2α) treatment has been found to date. The objective of this study was to compare the effect of a modified 6-d synchronization protocol on the luteolytic response and final preovulatory follicle diameter. The study followed a crossover design: 14 nonlactating dairy cows were included in 2 treatment doses. All cows received a presynchronization treatment consisting of 2 administrations of a PGF(2α) analog (PGF) 14 d apart followed by treatment with GnRH 11 d later. After the first GnRH administration, one treatment consisted of 150 μg of d-cloprostenol 5 and 6 d later (split dose) and the other treatment consisted of 375 μg of d-cloprostenol as a single dose 6 d after the first GnRH (single large dose). All cows were then treated with a second GnRH 8 d after the first. The luteolytic response to treatment was evaluated by blood progesterone concentration and CL area regression -1 to 3 d relative to the last PGF treatment obtained by ELISA and ultrasonography, respectively. Fewer cows of the split dose tended to have complete luteolysis 3 d after the last PGF treatment compared with the cows of the single large dose (35.7 and 64.3%, respectively). The final preovulatory diameter of the dominant follicle was similar in cows from the split dose and single large dose (13.7 ± 0.3 and 13.1 ± 0.5 mm, respectively). Our results support the modification of the 6-d synchronization protocol by administering a single high dose of PGF 6 d after GnRH (with the subsequent reduction in labor resulting from reduced handling of animals) without detrimental effects on the luteolytic response of dairy cows and preovulatory diameter of the dominant follicle compared with the original protocol. However, this modification of the 6-d synchronization protocol should be tested in a large field study involving fertility data with lactating cows before its use can be recommended.
Journal of Dairy Science 01/2013; · 2.56 Impact Factor
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ABSTRACT: Luteolysis is a key event in cattle reproduction. A standard dose of exogenous PGF(2α) will induce full luteolysis in the majority of cows with a matured corpus luteum (CL). However, this will not occur in cows with a CL <5d old. To date, it is not known whether a larger dose will have a more potent luteolytic effect in cows during early diestrus. The objective of this study was to characterize the effect of 2 doses of d-cloprostenol (150 and 300 μg) on the progesterone concentration, luteal diameter, and ovulation rate in nonlactating dairy cattle 96 to 132 h postovulation. Twenty nonlactating dairy cows were included in the study. Each cow received 2 treatments of d-cloprostenol in 2 consecutive cycles: a standard dose of 150 μg and a double dose of 300 μg. The cows were allocated randomly to 1 of 4 groups (5 cows in each group) according to the age of the CL at the time of treatment: 96, 108, 120, and 132 h. The exact time of ovulation was known within 12h, because of twice per day ultrasound examination. The CL diameter and progesterone concentration were measured before treatment (d 0) and 2 and 4d after treatment. Within each CL age group, the effect of d-cloprostenol dose on luteolysis was determined. More cows treated with double dose tended to have full luteolysis compared with the standard dose (8/10 vs. 4/10, respectively). This effect was only apparent in cows with CL of 120 and 132 h but not in earlier CL. The interval from treatment to ovulation was shorter (3.3 ± 0.1d) in cows treated with a double dose than in cows treated with the standard dose (4.5 ± 0.4d).
Journal of Dairy Science 08/2012; 95(8):4389-95. · 2.56 Impact Factor
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ABSTRACT: A single treatment with PGF2α is assumed to have no luteolytic effect on cows with corpora lutea < 5 days old. The objective of this study was to determine the effect of a single high dose of PGF2α administered to dairy cattle on the morphology and function of the early CL. The study followed a crossover design with a treatment cycle in which 50 mg of dinoprost were administered 3.5 days postovulation and a control untreated cycle. Ultrasound examination and blood samples were performed during the two consecutive cycles. Corpus luteum (CL) diameter, progesterone concentration, and follicular dynamics characteristics were compared between control and treated cycles. Two of nine cows (22%) developed full luteolysis. The remaining seven cows (78%) had partial luteolysis with a decrease (P < 0.05) in progesterone concentration and CL diameter for two and 12 days post-treatment, respectively. The interovulatory interval of treated cycles (19.7 ± 2.4 days) was not different (P > 0.05) from that of controls (23.8 ± 0.9 days). The transient reduction in progesterone of cows with partial luteolysis had no effect on the proportion of cows with two or three follicular waves, follicle growth rate, or preovulatory diameter (P > 0.05). Two cows developed ovarian cystic degeneration during the PGF2α-induced cycle. In conclusion, the treatment of cows with a high dose of PGF2α 3.5 days postovulation induced some degree of luteolysis in all treated cows. This resulted in partial luteolysis in 78% of treated animals and in full luteolysis in the remaining 22%.
Theriogenology 08/2011; 76(9):1736-43. · 1.96 Impact Factor
