Effect of the presence of male and female flockmates on reproductive activity in ewes

Abstract

Four experiments were carried out to determine the effect of the presence of ewes and rams on the reproductive state of ewes. In Expt 1, the breeding season of ewes kept with a vasectomized ram ended later (April 18 \ m=+-\ 8 days; mean \ m=+-\ sem) than that of ewes isolated from rams (6 March \ m=+-\ 7 days; P < 0.01). In Expt 2, the end of the breeding season was later (5 May \ m=+-\ 6 days; P < 0.05) and the onset of the next breeding season earlier (29 September \ m=+-\ 2 days; P < 0.001) in ewes maintained with rams, compared with ewes isolated from rams (14 April \ m=+-\ 7 days and 1 November \ m=+-\ 2 days, respectively). There was no difference in the timing of, or variation in, reproductive transitions between ewes maintained either as individuals or in groups. In Expt 3, all ewes exposed to artificial short days from the date of the winter solstice and interrupted with 35 long days in spring resumed cyclicity (median date, 7 September; range, 59 days). Most ewes (seven of nine) exposed to short days from the date of the winter solstice and isolated from other ewes did not resume cyclicity in the following 11 months. In contrast, all ewes resumed cyclicity (median date, 19 October; range, 144 days) when exposed to short days but housed in social contact with other ewes that became reproductively active in early September; however, the onset of cyclicity was later than in ewes exposed to long days (P < 0.01). In Expt 4, the number of LH pulses per 6 h in ewes exposed to rams was higher (P < 0.001) Vandenbergh, 1976 and cattle, Izard and Vandenbergh, 1982). Exposure of ewes in late anoestrus to a ram normally results in a rapid increase in LH pulse frequency (Martin et al, 1980) and ovulation approximately 40 h later (Oldham et al, 1979). The effect of rams on the reproductive system of ewes is thought to be mediated by pheromones present in the wool and wax from the fleece of rams (Knight and Lynch, 1980 (Kennaway et al, 1987).In addition, less variability in the onset of the breeding season was reported when blinded ewes were exposed to sighted rams (Legan and Karsch, 1983) Ewes were housed by treatment; visual and physical contact between groups was prevented but the airspace was common.

Reproductive Response in Seasonally Anestrous Suffolk Ewes After a Treatment Combining Melatonin Feeding and the 'Male Effect'.

“…In this study, most Suffolk ewes that joined an intact ram 5 weeks onward after the beginning of melatonin feeding showed the estrous onset about 3 weeks after the beginning of the joining. Such response seen in ewes fed melatonin is similar to the reproductive response in Suffolk and its cross ewes that joined a ram without melatonin in early August during the late anestrous season [16,17]. In addition, intervals from the ram introduction to the incidence of estrus in Sub-groups A, B and C ewes fed melatonin and control ewes were similar to each other, although the incidence of estrus in the latter was significantly lower than the former.…”

New insights into the influence of breed and time of the year on the response of ewes to the ‘ram effect’

“…This result does not agree with the findings of Thimonier and Maulé on (1969) who, in the same breed, detected considerable levels of ovulatory activity in April to May. There are two possible explanations for this difference: (i) in our experiment, we used concentrations of progesterone to define anoestrus, whereas they used direct laparoscopic observation of ovulation and (ii) in our experiment, ewes were completely isolated from rams, whereas in their study rams were continuously present in the flock and used to detect spontaneous oestrus and the presence of rams may have modified the endogenous pattern of seasonality (O'Callaghan et al, 1994).…”

“…Indeed, the mixing of cyclic and anoestrous ewes can induce a synchronized ovulation in the anoestrous ewes, a phenomenon called the 'female effect'. This effect is well known and effective in goats (Restall et al, 1995), but it is more controversial in sheep (Nugent and Notter, 1990;O'Callaghan et al, 1994;Zarco et al, 1995). This effect, if real in sheep, could interfere with the response to the 'ram effect' and its effect would vary depending on the proportion of spontaneously ovulating females in the flock.…”

Melatonin treatment in spring and reproductive recovery in sheep with different body condition score and age

“…Kennaway et al (1987) found that when ewes that had an advanced breeding season following treatment with melatonin were maintained in physical contact with anoestrous ewes, the onset of reproductive activity occurred earlier in these ewes than in isolated controls. Also O'Callaghan et al (1994) reported that in housed ewes under controlled photoperiod, effects of oestrous ewes on flockmate anoestrous ewes were obtained, indicating that female-female social interactions can play a role in the timing of reproductive transitions in ewes. This fact is of considerable importance for farmers since the treatment of half of the flock could be sufficient to increase reproductive efficiency of the entire flock.…”