RESUMEN
Background: Considering the difference between the rate of multiple ovulation and ovarian activities of different breeds of ewes in different regions, especially out of seasonal breeding condition, finding efficient and effective protocols to induce multiple ovulation out of seasonal breeding would be much appreciated
Objectives: This study was conducted to determine fertility and multiple ovulation rates during summer and investigate the effect of supplementary feeding, and eCG injection prior to mating in the reproductive performance of Zel ewes
Methods: At the beginning of summer, 135 ewes in Savadkooh region [north of Iran] were randomly selected and divided into six groups. The estrus cycles of ewes, except in control groups, were synchronized using a vaginal sponge for 14 days. In groups 1 [n=22] and 2 [n=22] ewes were fed with supplementary feeding for 21 and 8 days, respectively, prior to mating. In Group 3 [n=26] ewes were fed with the same ration as Group 2 and were injected [IM] with 400 IU eCG at the time of sponge withdrawal. Ewes in Group 4 [n=23] just grazed on the pasture and injected with eCG as Group 3. In Group 5 [n=20] the estrus of ewes was synchronized as other groups, but they were not received any other treatment. Ewes in Group 6 [n=22, Control] received no treatment, and as the same Group 1 and 2 were mated with fertile rams for eight weeks. Experimental ewes were mated with fertile rams [1:8] 48 hrs after sponge removal for 96 hrs
Results: The findings showed that the fertility in group 3 was significantly more than group 2 and 5, but there was no significant difference between the others [p>0.05]. The prolificacy and fecundity were significantly higher in groups treated with eCG than the others [p<0.01], however there was no significant difference between groups 3 [with flashing] and 4 [without flashing]
Conclusions: It could be concluded that vaginal sponge and eCG treatment may improve the multiple lambing and reproductive performance of Zel ewes during summer, and supplementary feeding prior to mating, as described in this experiment, cannot make any significant improvement in multiple lambing
RESUMEN
Objectives: Evaluation of the effects of dexamethasone on estrous cycle length
Design: Clinical trial
Animals: A total of 12 Holstein heifers at 16 month of age, 340kgs mean body weight and the average estrous cycle length of 20 days were selected
Treatment: Dexamethasone [4mg, im, Colvasone, Placebo [4mg, im, injectable Water solution] and PGF2a . Procedurs: The estrous cycles of the heifers were synchronized with two injections of PGF2a fourteen days apart . Estrous period [day=0] was detected with observation of estrous behaviors and evaluation of grafian follicle and regressed corpus luteum with rectal pulpation.In the treatment group, dexamethasone was injected at 12h intervals on days 13 to 17 of the iduced estrous cycle in six synchronized heifers .Blood sample were collected on day 13 and 21 via coccygeal vein puncture. Presence of corpus luteum was evaluated with rectal pulpation, and estrous behaviors were detected with observation at mentioned period . In control group ; water solutiom was injected at 12h intervals on day 13 to 17 of the induced estrous cycle in six remained synchronized heifers and serum progesterone assay, rectal pulpation and estrous detecion were accomplished as the test group
Statistical analysis: Difference between serum progesterone levels on day 13 and day21 of estrous cycle were statistically analysed by student t- test and difference between the number of animals suffered from luteolysis on day 21 of estrous cycle were analysed by fisher exact [two tailed] test
Results: In the test group, corpus luteum regressed normally in 4 heifers [66.6%], showing behavioral estrous and serum progesterone levels less than 0.5ng/m1 . However, two treated animals [33.3%] did not show estrus on day 21 of the cycle, retaining their corpura lutea with the serum progesterone concentrations higher than 1 ng/ml, persisting high until day 27 of estrus in one, and day 34 in the other . All the heifers in the control group with high concentration of progesterone on day 13 of the cycle returned to estrus on day 21 [100%] and showied serum progestrone levels less than 0.5 ng/ml
Conclusion: Findings of present study shows that dexamethasone injection at diestrous could not significantly inhibit, the endogenous regression of corpus luteum in Holstein heifers, and/or the presence of new estrous cycle