Reproduction in Domestic Animals

Nutritional Interactions and Reproduction 1332.01.610080OvulatingOestrusOvulation rate1.20.8Response (%)60400.420Fig. 3. The ovulation rate(mean ± SEM; n = 25), interval(mean ± SEM days) from theintroduction of bucks to the onsetof oestrus, and the proportions ofdoes ovulating, showing oestrusand having short cycles at the firstovulation following buckintroduction in does that wereeither given nutritional supplementationor not given nutritionalsupplementation for 7 days beforethe introduction of sexually activebucks. All between-treatmentcomparisons are significant. Datataken from De Santiago-Miramontes et al. (2008)Interval to oestrus (days)0.08.06.04.02.00.0Does with short cycles (%)0100806040200Control Supplemented Control Supplementedsupplementation did not persist and the proportion ofdoes in oestrus was not different if ovulation occurredafter 5 days (Fig. 4) and neither was the ovulation rate(De Santiago-Miramontes et al. 2008). We concludedthat short-term feed supplementation before the ‘maleeffect’ can increase the proportion of females respondingand their ovulation rate. However, the stimulatory effectof supplementation did not persist and was not observedat the subsequent ovulation. The increase in ovulationrate suggests that the supplement promoted the growthof a greater number of ovulatory follicles or reduced therate of atresia among the existing cohort of follicles.Somewhat surprisingly, supplementation also increasedthe proportion of does showing short cycles after thefirst male-induced ovulation and this response wasassociated with a reduced interval from the introductionof bucks to oestrus (Fig. 3). The effect of nutritionalsupplementation on the proportion of short cyclesinduced by the male effect could be due to the fact thatDoes in oestrus (%)6050403020100a0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15Time relative to the introduction of bucks (days)Fig. 4. The daily proportion of does showing oestrus for 15 days afterthe introduction of sexually active bucks on day 0 and following anutritional supplementation for 7 days before the introduction of thebucks. The data for the supplemented group are shown by the dashedline and for the non-supplemented (control) group by the solid line; theletter ‘a’ = p < 0.05 compared with the control group at the sametime. Redrawn from De Santiago-Miramontes et al. (2008)more of supplemented does ovulated over the first5 days compared with the non-supplemented doesbecause most does responding in the first 5 days havea short cycle (Chemineau et al. 2006; Delgadillo et al.2006). These findings are consistent with the suggestionthat a shorter delay from male introduction to the firstovulation is associated with an increased proportion ofshort cycles (Pearce et al. 1985). The nutritional supplementappears to have accelerated the follicular phaseinduced by the ‘buck effect’ and the shorter period offollicular development (Fig. 4) leads to either a nonfunctionalCL or, perhaps, to uterine entrainment for anearly luteolytic signal.Somewhat similar findings have been reported forewes. In one study, Nottle et al. (1997b) reported thatsupplementation of Merino ewes daily with 500 g lupingrain from Days 12 to 26 after the introduction of ramssignificantly increased the ovulation rate from 1.26 to1.46 at the second ovulation following ram introduction.Working with lactating Sarda ewes, Molle et al. (1995)also observed an increase in ovulation rate followingsupplementation starting 2 weeks before the ‘ram effect’,but only with a supplement of soya bean meal and notwith whole corn grain. In a later study, Molle et al.(1997) reported that short-term supplementation foronly 7 days before the introduction of rams increasedovulation rate from 1.36 to 1.66 but, in this case,the difference was not significant, possibly because of thegroup size of 15 ewes per treatment was too small. Theseoutcomes contrast with those from a factorial study with390 Merino ewes (Fisher et al. 1993) – there were nosignificant effects of short-term supplementation withlupin grain on the proportion of the flock responding,ovulation rate or the frequency of short cycles in ewesstimulated with the ‘ram effect’. This outcome wasindependent of the previous nutritional history of theewes, although the percentage of ewes ovulating washigher in ewes in good condition than in ewes in poorÓ 2008 The Authors. Journal compilation Ó 2008 Blackwell Verlag