Asynchronous ovulation in mares: seasonal variations in frequency.

The mare's reproductive system is rarely capable of sustaining multiple pregnancies to term. Multiple pregnancies largely derive from multiple ovulations, most commonly double ovulations, hence, double ovulations are of significant concern to breeders/veterinarians. Double ovulations may be synchronous or asynchronous. Asynchrony of up to 96 hours may result in two embryonic vesicles of very different sizes, which are challenging to detect at early ultrasonic pregnancy detection. This study aims to (1) document the incidence of synchronous and asynchronous double ovulation and (2) determine whether this varies with month/season. 506 cycles from double ovulating mares were monitored at 8±1 hour intervals before expected ovulation until 96 hours post initial ovulation. Mares were grouped according to eight-hour ovulation intervals and month/season. When asynchrony was classed as greater than or equal to eight hours or greater than or equal to 24 hours apart, respectively, a significant (P<0.001) difference existed between the number of mares demonstrating asynchronous double ovulations (65.8 and 28.5 per cent) and synchronous double ovulations (34.2 and 71.5 per cent). Significantly (P<0.05), more asynchronous ovulations occurred in the seasonal transition periods. This study demonstrates that asynchronous double ovulation is common and emphasises the importance of closely monitoring mares, particularly at the extremes of the breeding season, for double ovulation up to or at 96 hours postinitial ovulation in order to minimise the chances of missing multiple pregnancy.

Factors affecting pre-ovulatory follicle diameter in the mare: the effect of mare age, season and presence of other ovulatory follicles (multiple ovulation).

The importance of elucidating factors affecting reproductive performance and efficiency is of paramount concern to the equine industry. Oocyte viability is known to be one of the determinants of reproductive success and evidence suggests that it may be linked to follicle size. The aims of this study were, therefore, to ascertain: i) the average diameter and range of pre-ovulatory follicles in Thoroughbred mares; ii) whether this is affected by either mare age, time within the breeding season, or the presence of multiple pre-ovulatory follicles (MO). One thousand, four hundred and ninety two Thoroughbred mares, aged 2-26 years, were examined with ultrasound to ascertain ovulation date to within 24h, and pre-ovulatory follicle(s) (F1) diameter. Mares were divided into groups according to age (7 groups, 2-4 yr, 5-7 yr, 8-10 yr, 11-13 yr, 14-16 yr, 17-19 yr, >19 yr), time within the season (16 half-month groups, from Feb 1(st) to Sept 30(th)), and pre-ovulatory follicles (single, {SO} or multiple {MO}). Overall average F1 diameter was 39.95 ± 4.84 mm (range 22-50 mm). Mare age had a significant (P < 0.001) negative effect on F1 diameter (largest F1 38.95 ± 5.61 mm, mares 2-4 yrs; smallest F1 33.30 ± 4.66 mm, mares >19 yrs) as did season (largest F1 44.20 ± 3.95 mm, Feb 1(st)-14(th); smallest F1 33.74 ± 4.87 mm, Aug 15(th)-31(st)) and the presence of more than one pre-ovulatory follicle (MO F1 35.45 ± 4.53 mm; SO F1 37.44 ± 4.84 mm). In conclusion older mares, bred towards the end of the breeding season, especially if MO were present, were more likely to ovulate from smaller follicles. If, as suggested, small pre-ovulatory follicle size is associated with low oocyte viability, then this may account, at least in part, for the poor fertility rates characteristic of older MO mares, bred later in the season and so justify increased monitoring and careful reproductive management of such mares.

Sexual behavior and ejaculate characteristics in Pêga donkeys (Equus asinus) mounting estrous horse mares (Equus caballus).

The objectives were to (i) characterize sexual behavior of donkey stallions (jacks; Equus asinus) during on-farm semen collection using estrous horse mares (mares; Equus caballus); (ii) compare behavior of young (less experienced) versus older (more experienced) jacks; (iii) determine whether semen suitable for artificial insemination (AI) could be collected using mares; and (iv) determine the suitability of using mares in field collection of semen from jacks. Six Pêga jacks (3.5 to 16 yr old), previously conditioned to breed mares, were used. Mount mares were confirmed in estrus by a teaser horse stallion (stallion) and a jack. Semen was collected with an artificial vagina, at intervals of 48 to 72h (180 collections). The mean+/-SD (young [3.5 yr] vs. old [14 to 16 yr]) were Flehmen response frequency, 7.4+/-5.8 (8.1+/-3.0 vs. 7.0+/-2.0); number of mounts without erection, 1.1+/-1.3 (2.1+/-1.4 vs. 1.2+/-0.4, P<0.05); latency from first exposure to mare to full erection on the ejaculatory mount, 18.3+/-17.7min (25.3+/-21.3 vs. 12.2+/-6.2, P<0.05); latency from erection to insertion, 5.1+/-3.5sec (5.3+/-3.8 vs. 4.8+/-3.2); and duration of copulation from insertion to dismount after ejaculation, 25.4+/-7.8sec (22.1+/-2.9 vs. 28.1+/-9.3). In all jacks, sexual behavior was generally normal, with the notable absence of open mouth behavior. Mare estrous behavior was markedly less intense than that in the presence of a stallion and usually absent. Semen characteristics were gel free volume, 47.3+/-28.7mL; gel volume, 71.8+/-54.8mL; total motility, 84.3+/-6.0%; progressive motility, 74.3+/-74.5%; sperm vigor, 3.9+/-0.5 (scale 1 to 5); sperm concentration, 253x10(6) cells/mL; and total number of sperm, 10.3x10(9) cells. Copulation duration was significantly correlated with gel free volume (r=0.9) and gel volume (r=0.7). We concluded that (i) the sexual behavior of jacks during semen collection using mares was similar to that reported for natural mating to jennies, (ii) precopulatory and copulatory behavior for the young (less experienced) jacks and older (more experienced) jacks were generally similar (except number of mounts without erection and latency to full erection); (iii) semen obtained using mares as stimulus and mount females was similar to that reported with estrous jennies; and (iv) semen collection from previously conditioned jacks, using estrous mares, was appropriate for field collection of semen.