Physiological limits to further improvement in the efficiency of oestrous synchronization in goats

Abstract

The variability between animals in the timing of oestrus after administration of a synchronization treatment seems to explain the low rate of fertility in goats inseminated at a predetermined time after progesterone withdrawal. Two experiments were performed during the breeding season to test whether the variation was due to the exogenous hormone regime or to the endogenous physiology of the animals. Twenty-one goats were given a synchronization treatment consisting of a vaginal sponge impregnated with 45 mg of fluorogestone acetate (FGA) for 11 days associated with intramuscular injection of 400 I.U. of equine chorionic gonadotrophin (eCG) and 50 microg of cloprostenol 48 h before sponge removal. Progesterone concentrations were measured during the subsequent cycle and the patterns were modelled to allow precise determination of the onset of luteolysis. Oestrus and the luteinizing hormone (LH) surge began 33.0+/-6.8 h and 76.0+/-33.0 h after sponge withdrawal, v. 43.4+/-5.7 h and 90.0+/-36.0 h after natural luteolysis. For both observations, the between-goat variability was larger during the natural than during the synchronized oestrus (P < 0.05). The duration of the oestrous cycle was independent of the number of corpora lutea (CL), whereas the duration of luteal phase was shorter in goats with 2-3 CL (16.4+/-0.9 day than in those with 1 CL: 17.7+/-1.3 day; P < 0.05). In the second experiment, 20 goats were ovariectomized and given a vaginal sponge as described above. Sixteen h after sponge removal, they were injected with 50 microg of oestradiol benzoate (ODB). This treatment was repeated with the second sponge being inserted 1-2 days after observation of oestrus. Oestrus and LH surge were observed: 32.8+/-6 8 h v. 27.8+/-7.8 h after the first ODB injection, and 36.6+/-7.3 h v. 34.3+/-4.8 h after the second ODB injection. No relationship was observed between data of the two experiments. In both cases, the variability in the occurrence of oestrus and LH surge was of the same order as observed in the first experiment. This study shows that the timing of oestrus and LH surge is less variable after progestagen treatment than during a natural oestrous cycle. Moreover, a significant proportion of variability is inherent in the delays following the oestradiol peak, suggesting that further improvement in the synchronizing capacity of treatment based on progestagen administration is unlikely.

Four years of induction/synchronization of estrus in dairy goats: effect on the evolution of eCG binding rate in relation with the parameters of reproduction

“…We confirmed the variability of the onset of estrus in dairy goats after synchronization with a progestagen/eCG treatment already described in other studies [2,4,13,19,22]. The variability of the onset of estrus and LH peak increased significantly with the repetition of treatments (Tabs.…”

“…Finally, we also suggest that the management of reproduction could introduce some genetic variability between the herds: AI was regularly used in H1 with subsequent introduction of new genotypes while H2 was in-bred. So, this herd effect could constitute a part of the endogenous physiology of the animals suggested by Freitas et al [13] to explain this phenomenon.…”

“…I, II). Freitas et al [13] showed that the timing of estrus and LH surge was less variable after a progestagen treatment than during a natural estrous cycle. Numerous factors are known to influence the time of occurrence of estrus: breed, age, season, type of synchronizing treatment, dose and time of eCG injections, presence of a male as well as body condition [1,[10][11][12].…”

Time of ovulation in nulliparous and multiparous goats

“…Onset of oestrus to LH peak and LH peak to ovulation intervals The onset of oestrus to LH peak interval observed in oestrus synchronized with prostaglandins (12.8 6 1.1 h) was similar to that observed by Freitas et al (1997a) in oestrus synchronized with FGA (12.0 6 4.4 h). In both studies, no differences were found between induced and natural oestrus regarding the onset of oestrus to LH peak interval.…”

Improving the Reproductive Efficiency, Pregnancy Diagnosis and Monitoring the Resumption of Luteal Activity in Indigenous Damascus Goats

“…Synchronization of oestrus is important in the improvement of reproductive efficiencies and management processes (Al‐Merestani et al 1999). Two types of intravaginal sponges are being used for oestrous synchronization of does, namely medroxyprogesterone acetate (MAP) (Menegatos et al 1995) and flugestone acetate (FGA) (Freitas et al 1997). Pregnant mare serum gonadotrophin (PMSG) was injected with the sponge treatment to improve fecundity (Baril et al 1998).…”