SEXUAL RESPONSE OF ANOVULATORY DORPER X PELIBUEY NULLIPAROUS AND MULTIPAROUS EWES EXPOSED TO MALES + ESTROGENIZED FEMALES

Abstract Text:

SUMMARY. The aim of this study was to deter­mine whether  the stimulus exerted by the presence of males + estrogenized females, promotes both estrus (EA) and ovulatory activity (OA) in anestrous ewes in northern Mexico, (26°N). The study was conducted in April during the natural sheep anestrous season at this latitude.  Sheep ewes (n=104) were isolated from males two months prior to the begin­ning of the experiment. All females were subjected to evaluation of ovu­latory activity by transrectal ultrasonography (Aloka SSD- 500) on days -21, -14 and -7, and all of them were classified as anovulatory.  In order to synchronize reproductive activity, each ewe was treated with an intravaginal sponge impregnated with fluorogestone acetate (FGA; Chronogest® CR; Intervet) on days -9 to -2. Thereafter, on day 0, 50 nulliparous and 54 multiparous females were randomly assigned to four experimental groups: two groups of nulliparous (Stimulated Nulliparous, SN; n=25, and Non Stimulated Nulliparous NSN; n=25) with similar body weight; 30±1.1 Kg and body condition; 2.9±0.1) and two groups of multiparous (Stimulated Multiparous, SM; n=24, and non stimulated multiparous; NSM n=30), with similar body weight; 42 ±1.0 kg and body condition 3.2± 0.1. Males and females were fed with rolled corn, sorghum, wheat and sorghum silage. On March 19 (day 0) each group of the stimulated fema­les (SN and SM) was exposed to two inactive males (3.0 ± 0.1 BCS; scale 1-4) and 5 estrogenized females, (2 mg estradiol cypionate IM every 3^rd day).  In the same way, each group of the non-stimulated females (NSN and NSM) was exposed to two inactive males and 5 non estrogenized females. Rams were alternated between groups, and remained in contact during 15 days. Experimental groups were placed at a distance of approximately 100 m from each other. 

EA was recorded twice daily (AM and PM) and OA by ultrasonographic scanning, observing the presence of corpora lutea, on d 16. EA and OA were compared using Chi² test (MYSTAT 12).   The percentage of multiparous ewes depicting estrus [SM (63); NSM (60)] was greater (P<0.05) regarding nulliparous [SN (0); NSN (16)]. The same was true with respect to ovulation, favoring (P<0.05) to the multiparous group [SM (75); NSM (57)] with respect to nulliparous [SN (4) and NSN (25)]. Therefore, multiparous ewes depicted a greater ability to respond to male effect than nulliparous, regardless the presence or not of estrogenized females.

Keywords: Ewes, sexual activity, female effect