Reproduction in Domestic Animals

132 RJ Scaramuzzi and GB Martinmaintained in good body condition (BCS, 2.8) comparedwith ewes maintained in poor body condition(BCS, 2.3).More extensive data are available for two otherseasonal species, the horse and the goat. In a study justcompleted at the INRA laboratory at Nouzilly, Salazar-Ortiz and Guillaume studied the effect of nutrition onthe seasonal rhythm of ovarian activity in mares keptunder natural photoperiod (Salazar-Ortiz 2006). Thepattern of ovarian cyclicity over three consecutive yearswas determined from weekly blood progesterone measurementsin two groups of mares. One group was wellfed and the other group was received a diet calculated tokeep the mares thin but in good health. At the start ofthe experiment, the average body weight of the twogroups was approximately 300 kg. The well-fed maresgained approximately 20 kg in the first year after whichtheir mean live weight did not change for the remainderof the experiment. The restricted mares lost approximately65 kg in the first year and then their live weightalso stabilized for the remainder of the experiment. Thenutritional regime had a profound effect on the patternof ovarian cyclicity (Fig. 2) – the well-fed mares had amuch longer period of ovarian cyclicity and six of the 10mares had no period of winter anovulation in the 3-yearexperiment. This was in contrast with the restrictedgroup in which the winter period of anovulation waslonger and present in all the 10 mares.Zarazaga et al. (2005) studied the effect of nutritionon the seasonal pattern of sexual activity in femalePayoya goats kept under natural photoperiod over aperiod of 20 months. The does were maintained on twolevels of nutrition: a high group fed 1.5 times theircalculated maintenance requirements and a low groupfed to maintenance. The pattern of seasonality was thendetermined by daily monitoring for oestrus and forovulation using progesterone measured in blood twice aweek. The length of anoestrus was 32 days shorter indoes on the high diet and this difference was significantbecause of both a delayed entry into anoestrus and anearlier resumption of ovarian cyclicity at the end ofanoestrus.Although domestic Bos taurus cattle are non-seasonal,one study (Montgomery et al. 1985) reported an interactionbetween season and nutrition on the resumptionof ovarian cyclicity post-partum. In this study, an effectAnovulatory mares (%)100806040200Sum Aut Win Spr Sum Aut Win Spr Sum Aut Win Spr SumSeasonFig. 2. The weekly proportion of anovulatory mares over a 3-yearperiod. The data for the mares on a high plane of nutrition are shownby the solid line and that for the mares on a low plane of nutrition bythe dashed line. Redrawn from Salazar-Ortiz (2006)of the season of calving (winter versus spring at latitude45° south) was observed only under conditions of lownutrition. The same seems to apply to laboratory rats, inwhich undernutrition seems to be able to modulatereproductive responses to photoperiod through a pinealdependentpathway (Walker and Bethea 1977).What do all these observations tell us? Most importantly,that there is an interaction in which nutritionaffects the seasonal pattern of ovarian cyclicity in sheep,goats and horses; the variety of species suggests thatnutritional influences on patterns of seasonal reproductionare probably present in most, if not all, seasonalbreeding mammals, including non-seasonal species suchas beef cattle. However, the studies done to date withfemale animals do not shed any light on the mechanismsthat underlie this interaction or on how the interactioncan be usefully incorporated into systems of CGEanimal production.Socio-sexual Signalling and Ovarian FunctionThe ‘male effect’ is a well-studied phenomenon in sheepand goats and there are a number of excellent recentreviews of the subject (Martin et al. 2004b; Ungerfeldet al. 2004; Chemineau et al. 2006; Ungerfeld 2007). Insummary, sexually active males produce a pheromonethat stimulates the secretion of GnRH pulses and ovarianactivity and can induce anovulatory females to ovulate.Interactions between nutrition and socio-sexual signalsAs with photoperiod, socio-sexual signals are a majorfactor controlling ovulation in seasonal species and,because nutrition also has major influences onovulation, it also seems highly probable that nutritionwould influence the efficacy of the ‘male effect’ and thatthe site of the interaction is again the GnRH neuron inthe hypothalamus (Martin et al. 2004b; Blache et al.2007). When a group of female goats were dividedaccording to bodyweight, it was observed that theoestrus response to the ‘buck effect’ was reduced in thedoes with the lowest body weight compared with thosewith medium and heavy weights (Ve´liz et al. 2006).Similar findings have been reported for ewes (Lassouedand Khaldi 1990). Similarly, in beef cattle, the sociosexualinfluence of bulls can affect growth rate and theage of puberty in heifers (Roberson et al. 1991), andnutrition modifies the ability of bulls to reduce theduration of post-partum anoestrus (Monje et al. 1992;Stumpf et al. 1992).In a recent experiment, we have investigated theinteraction between nutrition and the ‘male effect’ inanoestrous female goats (De Santiago-Miramontes et al.2008). Two groups of 25 anoestrous female goats grazedvery poor quality natural vegetation from 09:00 to16:00 h daily. Overnight, they were housed in pens andone of the groups received a supplement (950 g lucernehay, 290 g rolled corn and 140 g soy bean per animaldaily) for 7 days before exposure to bucks. The proportionof does ovulating, the proportion in oestrus and theovulation rate at the first ovulation detected within5 days of exposure to males were all greater in supplementedthan in the control females (Fig. 3). The effect ofÓ 2008 The Authors. Journal compilation Ó 2008 Blackwell Verlag