Environment and reproductive behaviour

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Animal Reproduction Science 42 ( 19%) I- 12

Environment and reproductive behaviour David R. Lindsay

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Faculty of Agriculture (Animal Science), The University of Western Australia. Nedlands, WA. 6907, Australia

Abstract Most domestic species produce in environments to which their genotypes have not adapted. The response of the animals to the environment in which they are kept is often an important determinant of reproductive productivity. This paper gives examples of how the interaction between the environment and the reproductive, maternal and general hehaviour of the animals can affect their reproductive physiology and ultimate reproductive success. Keywords: Environment; Behaviour; Reproduction; Adaptation

1. Introduction The reproductive behaviour of domestic animals has often interested reproductive physiologists, but has seldom stirred their passions in the way that more fashionable physiology and endocrinology has done. This is unfortunate, especially as the interac-

tions between the behaviour and the reproductive physiology of animals are among the most interesting and fruitful lines of research in domestic animals. The purpose of this paper is to illustrate how profoundly the behaviour of animals can affect all stages of the reproductive process and particularly how the animals’ responses to environmental variables can be manifested through changes in their behaviour. In most cases the representative animal will be the domestic sheep. In the days before the massive migration of animals around the world as part of an increasing international trade and modemising of animal husbandry, most animals were born and reared, and reproduced in the environment that their ancestors had experienced continuously for thousands of years. Reproduction and, particularly, reproductive behaviour under these circumstances was fine-tuned to producing maximum numbers of offspring most efficiently. A further consequence of development in a single environ’Tel.: 09 380 1512; fax: 09 380

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0378-4320/%/$15.OO 0 1996 Elsevier Science B.V. All rights reserved. PII SO378-4320(96)01527-S

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ment is that the reproductive behavioural patterns within animal populations were stable and showed relatively little variation. Now, large numbers of animals no longer breed in the environments that their ancestors experienced because breeders have sought genetic material for special characteristics from sources across the world. Behavioural patterns have become far more variable, differences in behaviour within species have become far more noticeable and behavioural patterns have become far less predictable. In many cases they are not necessarily the behavioural patterns that are conducive to the most efficient reproductive outcome. One of the great challenges of modem animal husbandry is to understand behavioural patterns and their significance and to match them as closely as possible to the environmental conditions to enhance productivity. In view of the importance of behavioural patterns in aiding animals to adapt to environmental influences it is not surprising that, in some of the behavioural traits that have been examined, the heritability is high (Murphy et al., 1994b).

2. Mating behaviour and the environment 2.1. Males A significant outcome of domestication and modem management of domestic animals compared with free ranging animals is the reduction in the ratio of males to females. Males are expected to mate with many more females than their wild ancestors did, but they are usually not obliged to establish their right to do so by combat and the establishment of a dominance hierarchy. There have been many attempts to reduce this low ratio even further in species such as sheep, goats and cattle. These attempts have been frustrated to a greater or lesser extent by our not understanding fully the enormous variability in sexual capacity and sexual motivation of males of seemingly similar size and physiological condition. These differences can often control the efficacy of both natural mating programs and the frequency and success of collection of semen in artificial insemination schemes. Why are there such big differences? It has clearly been established that androgens play only a permissive role and have little relationship with the differences in sexual motivation between animals (D’Occhio and Brooks, 1982). By contrast, the environment at rearing can affect the performance of males as adults (Orgeur and Signoret, 1984). Some of these effects are permanent and others more transient. It is also known that the social environment of animals and the conditions under which they are mating can affect how males work in herds and flocks (Tilbrook and Cameron, 1990). However, the literature contains many contradictions and we do not know enough to specify ideal conditions for eliciting optimum performance from males. The common practice of rearing rams in all-male groups has been reported to lead to low sexual motivation, homosexuality and impotence in a proportion of such animals. Many authors have suggested that exposing males to females during the rearing phase can improve their sexual capacity as adults (reviewed by Tilbrook and Cameron, 1990). Some have connected homosexual behaviour in individual rams during rearing with disinterest in ewes as adults (Zenchak et al., 1973; Zenchak and Anderson, 1980; Katz et al., 1988). Other authors, such as Price et al. (19881, remarked on the absence of

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such a relationship. In any case, even when contact with females during rearing improved the proportion of normally active rams as adults it was not always successful in eliminating rams whose interest was directed solely at other rams (Price et al., 1988). In a detailed study of the rearing environment of young rams, Orgeur and Signoret (1984) distinguished two phases of development and learning. The first was termed ‘infancy’, when the animals were still with their mothers, and the second, ‘adolescence’, the period between weaning and puberty. In the period of ‘infancy’ there is a large amount of ‘sexual’ play in both sexes, much of it resembling male sexual behaviour. However, Orgeur and Signoret could not relate this behaviour strongly to subsequent adult behaviour and performance. However, during the ‘adolescent’ phase, males reared with females developed male behaviour patterns directed specifically at those females, and males that were denied this developmental phase by segregation showed abnormal and slowly developed male mating behaviour as adults. The social environment of animals during breeding can influence the efficiency with which males will breed. Tilbrook and Cameron (1990) believe that the stimulation provided to rams by ewes and the social interaction between rams mated to these ewes greatly affect the number of ewes that are successfully mated under field conditions. A technique often used in AI centres with bulls is to stimulate the bull by having him observe mounting behaviour by other males (Blockey, 1981). A similar stimulatory effect has been shown in goats (Price et al., 1984). The evidence for this ‘audience effect’ in sheep is far more equivocal (Blockey and Wilkins, 1984; Price, 1987; Katz et al., 1988). Lindsay et al. (1976) suggest that the stimulatory or inhibitory effect of an ‘audience’ may depend largely on the relative position of the observed and observer males in the dominance hierarchy. 2.2. Females Reproductive behaviour in females has developed around one major objectivesurvival. Their seasonal patterns, their mating patterns and their parturient and maternal behaviour are all directed towards achieving maximum success in the environment in which the animal evolved. In modem agriculture it is common for the behavioural patterns and the environment to be out of synchrony. For example, Martin et al. (1994) have shown that the strict seasonal patterns of northern hemisphere sheep are quite inappropriate for the feed supply resulting from a ‘Mediterranean’ climate in the southern hemisphere (Fig. 1). A great many of the husbandry practices in the animal’s adopted country are aimed at changing either behavioural patterns to suit the environment or, where possible, environmental conditions such as feed supply and shelter to suit the entrenched behavioural patterns. Australia has been particularly fortunate in that its major breed of sheep, the Merino, does not show the same degree of rigidity in its response to photoperiod as do many of the breeds that emanate from higher latitudes. The Merino still responds to photoperiodic cues and its natural (or spontaneous) breeding season is confined to late summerautumn (Oldham et al., 1990). However, the ‘male effect’ can induce Merino ewes to breed at any time in the rest of the year so it acts as an alternative to photoperiod as a cue to initiate breeding activity. The ‘male effect’ is among the most powerful and

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Mating Mediterranean

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Fig. 1. Schema of the annual cycles in photoperiod (line) and pasture availability (vertical bars) in temperate, and ‘meditenanean’ regions. The major reproductive events superimposed on these patterns reflect the timing of a strict ‘short-day breeder’, such as the Soay sheep (Lincoln and Short, 1980). Animals whose reproductive rhythms are in synchrony with the nutritional supply in one environment are poorly matched to the other. Modified after Martin et al. (1994).

spectacular of the interactions between behaviour and the reproductive physiology of the animal. Martin et al. (1986) have demonstrated that females respond almost instantly to the unaccustomed presence of a male by initiating the events that lead to ovulation. Sheep breeders have been able to capitalise on the ‘male effect’ by using ‘teaser’ rams or testosterone treated wethers (Fulkerson et al., 1981) to induce oestrous activity and then introducing entire rams just before the ewes have become receptive. This not only increases the efficiency of mating, but can provide a degree of synchrony at the time of mating and later at the time of lambing. Breeders of sheep that originate from higher latitudes do not have the opportunity to breed their< animals throughout the year, but the ‘male effect’ is still capable of advancing the breeding season by four to six weeks and farmers often use this where there is an economic incentive to do so. The commercial advantages of the ‘male effect’ have been explored thoroughly in the last decade or so, but the evolutionary significance of the ‘male effect’ has received less attention. Originally the effect was demonstrated in the sheep (Underwood et al., 19441, but it has since been found that a wide range of species exhibit the ‘male effect’ or variations of it; for example goats (Shelton, 19601, red deer (Iason and Guinness, 1985) and wild pigs (Delcroix and Mauget, 1990). Under natural conditions the ‘male effect’ appears to be yet another mechanism for survival, albeit a rather elaborate one (Lindsay, 1988). A common characteristic of the species in which this phenomenon has been recorded is that they are all animals that naturally congregate in flocks or herds and they are all animals in which males and

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females live in separate groups for some part of the year. Then, just before the breeding or rutting season, the sexes come together setting up precisely the conditions described for successful use of the ‘male effect’ in domestic animals; the two sexes meet suddenly after a relatively long period of separation. All members of the female herd or flock are thus stimulated simultaneously. Not only is their breeding season initiated in this way but breeding begins more or less synchronously. This in turn ensures that at the end of gestation the offspring are born about the same time and this makes them vulnerable to predators for only a short period. For this strategy to succeed the males must be capable of inseminating a large number of females in a short time (Short, 1980). In all of the species in which the ‘male effect’ has been recorded, the males have large testes and large reserves of spermatozoa, further supporting the hypothesis that synchrony and mass mating have a place in the natural seasonal breeding of at least some nondomesticated gregarious species. Attempts to harness this in the synchronised natural and artificial breeding of sheep have had some success but with less reliability than is normally required (Wilkins, 1989; Lindsay et al., 1992). However, by combining the ‘male effect’ with hormonal measures, more effective and, possibly, more economical treatments are likely to result. Males can affect not only the seasonality of the cycles in some animals, but in the sheep, at least, they can affect the oestrous period itself and the timing of ovulation in relation to behavioural oestrus. By restricting the access of ewes in oestrus to the physical presence of rams, Lindsay et al. (1975) prolonged the length of the period of receptivity to the male by around 50% and delayed the average time of ovulation by about 12 h. In programs of artificial insemination where the timing of insemination relative to the time of ovulation is crucial to success, such variation in response to the sheep’s social environment can be important. Restall (1961) obtained better results from an artificial insemination program when, after insemination, he returned the ewes to a flock of vasectomised rams instead of isolating them from further contact with males. Presumably the re-joined ewes had been induced to ovulate sooner after insemination than the isolated ewes.

3. Maternal behaviour and the environment Among the behavioural patterns that contribute to reproductive success, none is more important than maternal behaviour and the associated care and survival of the young, particularly under extensive conditions. Strategies that increase ovulation rates such as the introduction of the ‘Booroola’ genes into Merino sheep (Piper and Bindon, 1988) and the immunisation of females against a variety of steroids (Scaramuzzi et al., 1988) have given producers in the sheep industry the capacity to double or even treble reproductive potential. Unfortunately, in both of these cases the gains in potential at the time of ovulation have been counter-balanced by very large losses at or after parturition. The enhanced capacity for ovulation in these animals was not matched with an enhanced capacity to care for the lambs, and producers had very little information on which to base strategies to prevent high rates of mortality. Fortunately, recent work is beginning to demonstrate some theoretical bases on which such strategies might be developed.

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Over the last decade a number of key studies have enhanced our understanding of those things that determine maternal behaviour and the reasons why lambs survive or not. Until that time it was generally thought that controlling the nutrition of ewes in order for them to produce lambs within a pre-determined weight range was the best, and probably the only, tactic for ensuring adequate survival of the lambs. This strategy did not take into account the breed of the ewe or its lamb, its previous maternal experience, its own environment between birth and puberty, or any of the many other factors that influence maternal behaviour. Neither was it possible to devise nutritional programs that could account for ewes carrying litters varying in size from one to four lambs. Recommendations for feeding heavily pregnant ewes were usually confined to the type and amount of feed used without regard to simple problems such as how the animals might be fed so as not to disturb their maternal behavioural patterns. A major characteristic of maternal behaviour in sheep is that it develops extremely rapidly and there appears to be little or no transitional phase from the non-maternal to the maternal state. However, in the ewe, there are two close, but distinct facets. First she responds to the presence of new born lambs of any origin (responsiveness) and second, she develops a bonding between herself and individual lambs, usually her own (selectivity). These two distinctive behaviours interact with other factors like the ewe’s own maternal experience and her temperament, the weather, and nutrition (Poindron and Le Neindre, 1980). Ewes do not remain maternal unless a selective bond has been established between them and a lamb and this must happen within the first 12 h after birth (Poindron and Le Neindre, 1980). In fact, in ewes that are deprived of all contact with their lambs, loss of maternal behaviour can be detected as early as 4 h after parturition. Le Neindre and Poindron (1990) have demonstrated that the two most important factors controlling the onset of maternal behaviour are the presence of oestradiol and the mechanical stimulation of the vagina and cervix caused by the expulsion of the foetus. In fact, non-pregnant ewes, primed with oestradiol and subject to stimulation of the vagina for a few minutes have been induced to display maternal behaviour when placed with a new born lamb (Keveme et al., 1983). This unique combination of hormonal and mechanical stimulation affects many aspects of the ewe’s behaviour that are associated with her maternal responsiveness. It stimulates the desire to lick young animals and it generates an attraction for amniotic fluids (Poindron and L&y, 1988). The cervical stimulation releases oxytocin intra-cerebrally (Kendrick et al., 1988). The olfactory bulbs are recipients of some of this oxytocin and it is thought that this may be the medium by which the transient, but spectacular changes in olfactory activity may occur. Amniotic fluid which is normally repulsive to ewes becomes, by contrast, highly attractive and the new mother quickly learns to distinguish the lamb or lambs that she is about to rear by the sense of smell. In the case of a ewe giving birth to twins an hour or so apart, the mother may become selective towards the first born lamb and reject other lambs in the vicinity, but the birth of the second lamb and the stimulation that this generates re-establishes the cycle of responsiveness and selectivity, so the.second born lamb is accepted along with the first. In fact, Keveme et al. (1983) were able to stimulate artificially the v.agina of single-bearing, selective ewes an hour or two after parturition and thereby induce them to accept lambs from other ewes. These physiological mechanisms are usually moderated by the environmental factors

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operating around the time of parturition. Alexander (1984) reviewed the factors that bring about the death of lambs under extensive conditions and concluded that inclement weather was the main cause, together with poor nutrition of the ewe during the period leading up to parturition. Certainly, if a lamb is cold and does not have sufficient food reserves it is likely to perish, but, until recently, there has been surprisingly little work on the effect of weather and nutrition on the behaviour of the animals and the possibility that favourable behaviour might improve the chances of survival of lambs under adverse conditions. We now know that the successful bonding of the ewe and her lamb or lambs and the behaviour that creates and maintains this bond strongly influence the survival of lambs. Inclement weather and poor nutrition may still be the ultimate cause of death in many lambs, but the predisposing cause is, in many cases, the failure to establish a powerful bond. Under extensive conditions, separation of the mother and at least one of her offspring is always a possibility. Where strong bonds are formed the likelihood of a separation is lower, lambs are able to take every opportunity to suck, predation of isolated lambs is reduced and the young animals receive at least the same protection as their mother might seek in the case of bad weather. Murphy et al. (1994a) have recognised the importance of studying twins and multiple born lambs when considering the factors associated with survival. Losses of twins are usually much higher than losses in single born animals and the development and maintenance of a strong bond between a mother and twin lambs is more difficult than between a mother and a single lamb. This becomes an even more important consideration when reproductive rates are raised by the induction of more twins in flocks of sheep. A behavioural characteristic of the Australian Merino sheep that has to be improved if high lambing percentages are to be expected from this breed is its inability to care for both members of a twin pair (Alexander et al., 1984). Certainly this attribute differs between breeds of ewes in both extensive conditions (Alexander et al., 1984) and intensive conditions (Poindron et al., 1984). This suggests that rearing capacity is heritable, but within the Merino breed at least, the few estimates that have been made have been disappointingly low (Piper et al., 1982; Haughey, 1984). Murphy et al. (1994a) have shown that conditions that induce a strong bond between the ewe and her offspring result in very high rates of survival even under extensive conditions. The principal, predisposing factor that leads to a strong bond formation is the continuous presence of the ewe with her lambs immediately after birth. As the ewe is attracted to the odour of amniotic fluids at this time she normally remains at the birth site on which these fluids have been shed. In fact, Stevens et al. (1983) and Alexander et al. (1984) have suggested that the amount of time the ewe spends on the birth site is strongly related to the incidence of separation between the ewe and her lambs. Simply removing the ewe and her lambs from the birth site within 30 min of the birth of the second lamb results in a significant increase in lamb mortality (Putu et al., 1988). Later, Murphy et al. (1994a) showed that the birth site itself had no specific role except as an identifiable focus for the ewe. They removed ewes from the birth site, but penned them together for 6 h on another site and found that the subsequent survival rates of lambs was high and equivalent to that of groups that had been penned on the birth site itself (Fig. 2). It is interesting that most of the losses in the study by Murphy et al. (1994a) were due to predation and their results show clearly that the groups that remain together

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Averagetime spent on birthsite

(hours)

Fig. 2. The relationship between the time spent at the birth site and the level of mortality in merino lambs. Modified from Murphy et al. (1994a). Data were derived from: Stevens et al. (1982) (2.5 h); Murphy et al. (1994.a) (3.5 h); Putu et al. (1988) (4.5 h); Futu et al. (1988) and Murphy et al. (1994a) (6.0 h, penned).

in the first 6 h after parturition were less susceptible to predation. In addition, of 16 twin-born lambs lost to predators between 48 h and 7 days after birth, 14 were individual lambs from sets of twins and in only one case were both lambs taken. The bond between the ewe and her two lambs was not strong enough for the ewe to protect the lamb from predators. This suggests that there is a qualitative component to the bonding process and poorly bonded groups allow twins to become separated while strongly bonded groups do not. The environmental circumstances that lead to poor bonding are those that result in animals leaving the birth site prematurely. These include shortage of feed, high temperatures that induce the dam to seek water or unnecessary disturbance of the animals from any source. Until recently it has also been assumed that responsibility for establishing a strong maternal bond lies entirely with the ewe. Nowak (1989) showed that this is not the case and the lamb itself plays an important part in establishing the conditions for its subsequent survival. Nowak (1989) showed that the new born lamb stimulates the ewe which at this stage is highly responsive. Stimulation from lambs is not necessarily in the form of their locomotor activity, but particularly in their vocal activity. Nowak found a strong correlation between the ability of 12-h-old Merino lambs to recognise their own mothers and the frequency of their bleatings recorded soon after birth. He found that the more the lamb bleated the more time it spent with its mother when tested in a two-choice situation. Further analysis showed that bleating by the lamb was almost invariably followed by a bleating response by the mother and this continual stimulus-response behaviour was the mechanism by which the bond was consolidated (Lindsay et al., 1990). Later, Murphy and Lindsay (1996a) attempted to control the stimulatory activity of the young lamb in an experiment in which, immediately after birth, three groups of lambs were either tranquillised, stimulated with noradrenaline or left as control. The behavioural characteristics of both the ewes and lambs and the survival of the lambs were then studied. There was no evidence that the noradrenaline stimulated either locomotor or vocal activity in lambs, but the tranquilliser completely sedated

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lambs for the first half hour of their life after which they recovered rapidly and appeared to be as active as control lambs. However, the subsequent survival of the tranquillised lambs was significantly poorer than that of the control or the ‘stimulated’ lambs, indicating that the lack of activity on the part of the lamb in the first 30-60 min had had a permanent adverse response on the development of the bond. These results place a new perspective on the management of sheep for survival of lambs. It has long been known that there is an optimum range of birth weights for any breed of lamb that gives the best chance of survival compared with lambs below or above that birth weight. The birth weight itself is a crude measure of the lamb’s physiological state, but if, as is likely, it is correlated with factors such as bleating activity and locomotor activity, then the effect of birth weight on survival is more easily explained. Based on this hypothesis, current research is seeking to improve the development of the maternal-offspring bond by improving the activity of lambs without necessarily changing their birth weight (Murphy and Lindsay, 1996b). Selecting ewes for ‘good’ maternal behaviour is very difficult under almost all conditions because it requires 24 h day - ’ observation at the time of lambing. For that reason, indirect selection criteria have been sought for many years. Alexander et al. (1984) suggested that the emotivity, or the reaction of an animal to an external stimulus, might be a possible indirect selection criterion for the capacity of an animal to rear its offspring successfully. Putu (1990) devised an ‘open field’ system for measuring the emotivity and reactivity to the presence of a human and related the results to the subsequent lambing performance of these ewes. He found that those animals with the lowest score for emotivity were the most successful at rearing their lambs. In other words, temperament appeared to be related to maternal ability. Murphy et al. (1994b) began divergent selection for emotivity to develop two lines of sheep, one very quiet and unresponsive in strange surroundings and the other extremely nervous and reactive to new stimuli. They subsequently found that the survival rate of lambs born to ewes in these two lines was significantly different. Eighty-three percent of the losses in 4 consecutive years that were not attributable to stillbirths or accidents at birth were in the group of ewes that were classified as highly emotive. In these experiments selection for temperament was done at weaning in a relatively simple test so that it may be possible to select indirectly for maternal behaviour, even before the animal reaches puberty.

4. Conclusion Research into reproduction of domestic animals has resulted in major gains in productivity (Lindsay, 1995) but these gains have been characterised by small advances on a number of fronts rather than spectacular leaps in one area alone. Future progress will probably follow the same pattern and will be based on a growing understanding of the reproductive processes in the whole organism. Studies in reproductive behaviour have already contributed significantly to this, but our challenge is to understand better how behaviour and physiology interact to allow us to give our animals the best opportunity to produce and reproduce in environments to which they are not always well suited.

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References Alexander, GA., 1984. Constraints to lamb survival. In: D.R. Lindsay and D.T. Pearce (Editors), Reproduction in Sheep. Australian Wool Corporation and Australian Academy of Science, Canberra, pp. 199-209. Alexander, G., Kilgour, R., Stevens, D. and Bradley, L.R., 1984. The effect of experience on twin care in New Zealand Romney sheep. Appl. Anim. Behav. Sci., 12: 363-372. Blockey, M.A. deB., 1981. Modification of a serving capacity test for beef bulls. Pasture mating. Appl. Anim. Ethol., 7: 321-336. Blockey, M.A. deB. and Wilkins, J.F., 1984. Field application of the ram serving capacity test. In: D.R. Lindsay and D.T. Pearce (Editors), Reproduction in Sheep. Australian Wool Corporation and Australian Academy of Science, Canberra, pp. 53-58. D’Gcchio, M.J. and Brooks, D.E., 1982. Threshold of plasma testosterone required for normal mating activity in male sheep. Honn. Behav., 16: 383-394. Delcroix, Iand Mauget, R., 1990. Existence of synchronisation of reproduction at the level of the social group of the European wild boar @us scrofn). J. Reprod. Fertil., 89: 613-617. Fulkerson, W.J., Adams, N.R. and Gherardi, P.B., 1981. Ability of castrate male sheep treated with oestrogen of testosterone to induce and detect oestrus in ewes. Appl. Anim. Ethel., 11: 57-66. Haughey, KG., 1984. Can rearing ability be improved by selection? In: D.R. Lindsay and D.T. Pearce (Editors), Reproduction in Sheep. Australian Wool Corporation and Australian Academy of Science, Canberra, pp. 210-212. Iason, G.R. and Guinness, F.E., 1985. Synchrony of oestrus and conception in red deer (Ceruus elaphus L.). Anim. Behav., 33: 1169-I 174. Katz, L.S., Price, E.O., Wailach, S.J.R. and Zenchak, J.J., 1988. Sexual performance of rams reared with or without females after weaning. J. Anim. Sci., 66: 1166- 1173. Kendrick, K.M., Keveme, E.B., Chapman, C. and Baldwin, B.A., 1988. Intracranial dialysis measurement of oxytocin, monoamine and uric acid release from the olfactory bulb and substantia nigra of sheep during parturition, suckling, separation from lambs and eating. Brain Res., 439: l-10. Keveme, E.B., L&y, F., Poindron, P. and Lindsay, D.R., 1983. Seasonal breeding: nature’s contraceptive. Vaginal stimulation: an important determinant of maternal bonding in sheep. Science, 219: 81-83. Le Neindre, P. and Poindron, P., 1990. Physiological and sensory basis of the mother young relationship in sheep. In: C.M. Oldham, G.B. Martin and I.W. Purvis (Editors), Reproductive Physiology of Merino Sheep. Concepts and Consequences, University of Western Australia, Perth, pp. 179-190. Lincoln, G.A. and Short, R.V., 1980. Rec. hog. Harm. Res., 36: l-52. Lindsay, D.R., 1988. Reproductive behaviour in survival: a comparison between wild and domestic sheep. Aust. J. Biol. Sci., 41: 97-102. Lindsay, D.R., 1995. Changing patterns of livestock production in Australia. Proc. Aust Sot. Reprod. Biol., 27: 94. Lindsay, D.R., Cogni6, Y., Pelletier, J. and Signoret, J.-P., 1975. Influence of the presence of rams on the timing of ovulation and discharge of LH in ewes. Physiol. Behav., 15: 423-426. Lindsay, D.R., Dunsmore, D.G., Williams, J.D. and Syme, G.J., 1976. Audience effects on the mating behaviour of rams. Anim. Behav., 24: 818-821. Lindsay, D.R., Nowak, R., Punt, LG. and McNeil& D.M., 1990. Behavioural interactions between the ewe and her young at parturition: a vital step for the lamb. In: C.M. Oldham, G.B. Martin and I.W. Purvis (Editors), Reproductive Physiology of Merino Sheep. Concepts and Consequences, University of Western Australia, Perth, pp. 191-206. Lindsay, D.R., Wilkins, J.F. and Oldham, C.M., 1992. Overcoming constraints: the mm effect. hoc. Aust. Sot. Anim. Prod., 19: 208-210. Martin, G.B., Oldham, C.M., Cogni6, Y. and Pearce, D.T., 1986. The physiological responses of anovulatory ewes to the introduction of rams-a review. Livest. Prod. Sci., 15: 219-247. Martin, G.B., Walkden-Brown, SW., Boukhliq, R., Tjondronegoro, S., Miller, D.W., Fisher, J.S., Hiitxel, M.J., Restall, B.J. and Adams, N.R., 1994. Non-photoperiodic inputs into seasonal breeding in male ruminants. In: K.G. Davey, R.E. Peter and S.S. Tobe (Editors), Perspectives in Comparative Endocrinology. National Research Council of Canada, Ottawa, pp. 574-585.

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