Applied Animal Ethology, 11(1983/84) 341-358 Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands

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THE ROLE OF BEHAVIOR IN SHEEP PRODUCTION: A REVIEW OF RESEARCH

H.W. GONYOU

Department of Animal Science, University of Illinois, Urbana, IL 61801 (U.S.A.)

(Accepted for publication 3 August 1983)

ABSTRACT

Gonyou, H.W., 1984. The role of behavior in sheep production: a review of research. Appl, Anim. Ethol., 11: 341-358.

Sheep production systems vary throughout the world, but many of the limitations and problems of production are universal. The behavior of sheep may be a limiting factor in some situations, while in others behavior facilitates the operation. The allo- cation of spatial resources, grazing behavior and feeding behavior in confinement are important for sheep to maintain themselves and grow efficiently. As sheep are social animals, sexual and maternal behavior must be viewed in a group context to ensure the highest reproductive rate and offspring survival. A review of recent literature on sheep behavior illustrates how production systems and behavior are intertwined.

INTRODUCTION

For a production system to operate efficiently, it must take into ac- count both the limitations and potential of all of the components. In the case of livestock production, a sound understanding of the biology, inclu- ding the behavior, of the species involved is required. Much of the research on sheep behavior can be applied to reducing the limitations or problems experienced in certain phases of production. As sheep are raised in many diverse areas of the world, the problems and solutions encountered will also vary considerably. This does not reduce the importance of behavioral research in other geographical areas, as the basic information obtained may be useful in solving problems encountered locally.

The behavior of sheep has been the subject of several reviews, including those of Hulet et al. (1975), Squires (1975) and Arnold and Dudzinski (1978). The behavior of specific populations of wild (Geist, 1971) and feral (Grubb and Jewell, 1966) sheep have also been published. This review is intended to supplement the material covered in the previous reviews.

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SPATIAL BEHAVIOR

Under some management systems, sheep are frequently regrouped and moved to new pastures or ranges several times in their lifetimes. The ob- servations of Grubb and Jewel1 (1974) indicate that feral ewes establish definite home ranges and that mixing of groups of ewes does not occur. Female young remain on their dam’s home range. Inbreeding is minimized by the formation of separate ram groups which disperse over the entire area during the breeding season. Arnold and Pahl (1974) mixed flocks of sheep of similar breeding and found that a consistent random grouping did not exist until 12 days post-mixing. Winfield et al. (1981) reported that newly-mixed groups prefer associating with former group members, regardless of breed.

Well-established home ranges may interfere with attempts to improve the nutritional status of sheep. Lambs that were returned to their original pasture after several months of supplemental feeding established a new home range in a poor area, whereas lambs that had been separated for shorter periods returned to the home ranges of their dams (Hunter and Davies, 1963). When supplementary feed is provided in a pasture, it may not be utilized by sheep in a distant home range (Hunter and Milner, 1963).

In large paddocks, Arnold and Pahl (1967) observed that sub-grouping of flocks occurred when feed availability was low, and that Merinos tended to form larger sub-groups than did the other genotypes. The dispersal of sheep may be related to breed characteristics or physiological conditions which limit walking speed. Kilgour et al. (1975) reported that Cheviot sheep travelled more rapidly than did Perendale and Dorset X Romneys, and thus dispersed more quickly when entering a pasture. Squires et al. (1972) found that Border Leicester and Merinos walked quickly and would travel farther to obtain additional water each day than would slower-moving Dorset Horns, pregnant or lactating ewes. Range size and quality could be a limiting factor in selecting breeds or for seasonal usage.

Connolly et al. (1976) observed that predation was often prevented by defensive stamping or charging at coyotes by sheep. The presence of a ram prevented predation of ewes, but not of the lambs, in a small flock. Newly introduced sheep, single lambs and those with abnormal movements or dams with restricted mobility were frequently on the periphery of the flock, and this location was believed to result in their higher predation rate (Gluesing, 1978).

GRAZING BEHAVIOR

Grazing is the most common means of feeding sheep, but it usually includes a period when vegetation is of poor quality and/or becomes sparse. In those situations, it is important to know how sheep will selectively graze the plants and be aware of problems which might arise. As grazing

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systems vary greatly, it is important to determine breed differences which will be useful in selecting breeds or breed crosses for an area.

Sheep will normally have two daily grazing periods, which are highly correlated with the times of sunrise and sunset (Dudzinski and Arnold, 1979). In winter, when days are short and pasture quality is low, grazing becomes continuous during the day. Very hot weather will disorganize grazing patterns so that no distinct peaks exist during the day (Bueno and Ruckebusch, 1979). In tropical conditions, a mid-afternoon peak of grazing is sometimes evident (Asiedu, 1978).

Sheep select material that is higher in digestibility than do cattle (Mul- holland et al., 1977; Jamieson and Hodgson, 1979). When green forage is abundant, sheep select a diet that is more digestible than the average plant material on offer, but when green forage is sparse, dead material of lower digestibility is included (Hamilton et al., 1973). When pastures have been heavily grazed, sheep will start grazing previously-avoided urina- tion sites. In some locations, this has led to facial eczema due to the presence of spores in the plant material (Keogh, 1975). Sheep also form preferences for plant species based on previous experience, and when transferred to a pasture containing a low proportion of a familiar species will search the pasture extensively (Gluesing and Balph, 1980).

Intake on pasture is related to breed and physiological state as well as to pasture availability. Arnold (1975) reported that Corriedales and Border Leicester X Merinos ate less per unit of live weight than did Merinos and Dorset Horns. Pregnant or lactating ewes ate more than dry ewes. Thin sheep ate more than fat sheep and recently shorn sheep increased intake if temperatures were low (Arnold and Birrell, 1977). When supplementary feed was provided to grazing sheep, there was little assertion of dominance by fighting but considerable variation in competitiveness. Some sheep did not attempt to obtain the additional grain when trough space was limited (Arnold and Maller, 1974).

Sheep are one of the more drought-resistant of our domestic animals, and in some areas are grazed without access to water. Non-watered ewes tend to rest more on hot days and graze more at night than do watered ewes (Clark and Jay, 1975). Brown and Lynch (1972) found that total grazing time did not differ between watered and non-watered sheep, but observed that non-watered sheep apparently licked dew off of the grass and wire fences during the morning grazing period.

FEEDING IN CONFINEMENT

Moving animals into confinement provides man with greater control over the environment, feed and feeding techniques. Forages and concen- trates may be fed in forms which could affect intake. Feed additives are easily incorporated into a diet and represent a potential for increasing palatability. In addition, the construction of the pen or feeder may affect the behavior of the sheep.

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The diurnal eating pattern present in grazing sheep was also evident in feedlot lambs (Shreffler and Hohenboken, 1980). Whether these rhythms are free-running is questionable, as sheep in continuous light exhibited no clear pattern by the fourth day (Hunsaker and Wolynetz, 1979). An unsuccessful attempt has been made to increase feeding and growth in feedlot lambs by providing additional light or disturbances at night (Hackett and Hillers, 1979). Feeding sheep three times a day, as opposed to feeding once or twice, did increase rumen ciliate populations (Senaud et al., 1977), and it may be advantageous to develop a method of increasing the frequency of feeding, particularly at night. It should be noted that there is consider- able variation in the time required for lambs to drink or eat a given quan- tity of feed (Zenchak et al., 1974).

Some research has been conducted to determine the effects of various odorous compounds on the palatability of feedstuffs. Arnold et al. (1980) found that some feeds were rejected primarily due to smell and some due to taste. In some cases consumption was reduced even if the sheep could neither smell nor taste the substance. Aosmia induced by bulbectomy resulted in sheep pausing during eating, but did not alter daily food intake or meal size (Baldwin et al., 1977). Feed preferences may vary among individual sheep, as Lobato and Pearce (1980a, b) could find no consistent factor useful in enticing sheep to use urea blocks. It is not surprising, there- fore, that Lobato and Beilharz (1979) did not find a relationship between dominance value and the use of molasses-urea blocks, although intake of other feedstuffs was greater in dominant animals.

Dulphy and Demarquilly (1974) and Dulphy and Bechet (1976) found that eating time of chopped green forages decreased with the maturity of the plants while rumination increased. They speculated that intake was probably limited by the time required for rumination. Feeding the same forage as either hay, fresh grass or silage resulted in similar intakes and rumination times, but shorter eating times for silage (Dulphy, 1972). In contrast, Fujihara (1980) reported that both eating and rumination times were increased when fresh grass was fed compared to hay. Compari- sons between fresh, ensiled or dried forages are unlikely to yield consistent results as feeding patterns for each form are variable. Silage with a short chop length, whether imposed at ensiling or just prior to feeding, resulted in increased rumination and intake compared to long silage (Dulphy and Demarquilly, 1972; Deswysen et al., 1978). Variation in eating time may be due to the bulkiness of the feed, as Peterson et al. (1974) found little variation in consumption rate of different forages and forage forms when expressed as volume consumed per minute. The rumination requirement may regulate intake for a specific feed and form, but different forms may vary in either rumination requirement or stimulation.

As lambs are frequently fed in feedlots, and to some extent on slotted floors, the effect of pen size, animal density, feeder space and location of feeders requires investigation to determine what factors may limit feeding.

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Stoerger et al. (1979a, b) found no effect of pen-type, pen-size, or feeder- placement on feeding, but the range of conditions was limited. Further effort should be directed to this area.

A final area related to feeding behavior concerns the use of drugs. Elfaze- pam has been shown to increase feed consumption, and this effect may be due to an increase in eating rate (Wangness et al., 1977). It has also resulted in increased digestibility. Stimulation of dopamine receptors in the brain results in an increase in oral activities, but this has not been related to feed intake (Sharman and Stephen, 1974). Investigations along this line may be of value in reducing some oral vices, such as wool picking.

SEXUAL BEHAVIOR IN EWES

A general trend in the sheep industry has been to early breeding of fe- males, either to lamb as yearlings or at two years of age. Attempts to re- duce the length of the lambing season or to use artificial insemination have been directed at synchronization of estrus. As sheep are seasonal breeders, it is logical to attempt to expand the breeding season by earlier or later breeding. All of these areas of endeavor have involved behavioral studies of the ewe. The research has included interaction with rams or an emphasis on hormonal control.

One of the more detailed studies of estrous behavior was conducted by Edey et al. (1978). Using the descriptions of estrous behavior as report- ed by Banks (1964), the authors quantified the behavior of mature ewes and ewe lambs (less than one year of age) during the first and subsequent estrous cycles. The mean duration of estrus for lambs was only 18 h, com- pared to 29 h for mature ewes. The length of estrous cycles varied little, and ranged from 15 to 19 days. In 3 h of intensive observations during estrus, 19 of 20 mature ewes displayed the full gamut of estrous responses, including tail-fanning, head-turning, nuzzling and mutual reinforcement, while only 14 of 51 lambs were given this rating. In addition, 15 of the lambs would not stand firmly for service and some failed to be inseminated. Mature ewes displayed a great deal of interest in the rams and would follow them after being mated, but lambs wandered away from rams during court- ing and after mating. The deficiencies in the behavior of ewe lambs empha- size the need for active and dexterious rams in flocks comprised of young females.

While other workers have confirmed that ewe lambs have shorter estrous periods than do mature sheep (Badawy et al., 1973), Allison and Davis (1976b) compared slightly older ewes (two-tooths) to mature ewes and found the young ewes had shorter estrous periods (10.8 vs. 12.8 h). In one of the trials, the rams were tethered in order to investigate ram-seeking behavior in the estrous ewes. Tethering of the rams resulted in only 43% of the two-tooth ewes being mated compared to 73,% of the older ewes. In larger breeding paddocks, where the ram-seeking behavior of the ewe

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increases in importance, a lower proportion of ewes were mated. In a sub- sequent study in which two-tooths and mature ewes were in one flock, fewer two-tooths were mated (Allison, 1977). The differences between age groups became greater as the ewe to ram ratio increased. Blockey (1980) indicated that the age differences observed in these studies may in fact be a parity effect.

The estrous cycles of ewes are affected by the presence of rams. An- estrous ewes begin cycling earlier (Watson and Radford, 1960), and the sexual season may be prolonged (Riches and Watson, 1954) by the intro- duction of rams. In tropical sheep, which cycle the entire year, introduction of rams resulted in approximately 25% of the ewes displaying estrus the following day (Ngere and Dzakuma, 1975). Exposure to intact rams for only 48 h resulted in a similar increase in the proportion of ewes cycling, as did exposure to vasectomized rams for 17 days when compared to non- exposed ewes (Knight, 1980). Using short exposure techniques, one ram could be moved between several groups of ewes. Knight and Lynch (1980) applied urine, wool and wax collected from rams to ewes to determine if these substances could induce ovulation in ewes. The percent of ewes ovulating within 5 days in the wax and wool treatment did not differ from the ewes exposed to intact rams. Although a higher percent of ewes sprayed with urine ovulated than of those sprayed with water, the difference was not significant. The results strongly suggest a pheromone in the ram-derived substances, but the treatments, including introduction of strange rams, do not preclude a reaction to short-term stress as the cause of ovulation.

In research on the physiological control of estrus, behavior of the ewes is often the criterion used to determine the effectiveness of treatments. Both estradiol and progesterone must be present to induce normal estrus (Karsch et al., 1980). Cox et al. (1976) were able to prevent estrus by immunizing the ewes to estrogens. Frequently, these studies use standing to be mounted as the major criteria for estrus. More detailed analysis has indicated that differences in estrous behavior may exist between treatments even if standing does occur. Comparison of the last estrous cycle before anestrus with previous cycles indicates that the duration is shorter, and this may be related to decreased LH levels (Rawlings et al., 1977). Adams (1978) treated ovariectomized ewes with various levels of estradiol benzoate to induce estrous behavior. Squatting by the ewes and flehmen displays by the rams were not associated with the estrogen treatments. Looking over the shoulder at rams was evident in ewes on relatively low levels of estrogen, while active soliciting by the ewe, standing for mounting, and a higher frequency of mountings occurred with higher treatment levels. Tail-fanning and kicking by ewes were also associated with high levels of estrogen. Estrous behavior has been observed in intact ewes which did not ovulate when the pastures contained estrogenic clovers (Firth et al., 1977). Thus, the level of estrogen required for display of some estrous behaviors may not be sufficient to induce an LH surge and ovulation.

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Synchronization of estrus can be an important management tool, but it is also important that proper estrous behavior be induced. Parrott and Baldwin (1978) used progesterone, 5_dihydroprogesterone, corticosterone and desoxycorticosterone prior to estrogen to determine which compound was most effective in initiating estrous behavior. Proceptivity was not increased with any of the treatments. Receptivity was improved with 5- dihydroprogesterone or desoxycorticosterone. Thus, a progesterone meta- bolite, not progesterone, may be most important in initiating estrous behav- ior. In another experiment, normally-cycling ewes and ewes synchronized with progesterone were observed before and during estrus (Tomkins and Bryant, 1974). Prior to e&us, the males nudged the synchronized group more frequently, while the females displayed more squatting than the controls. During estrus, the normal group displayed more active soliciting of the male, flehmen was more common in the males with the normal ewes, and squatting was more common in the treated ewes. As in the case of young vs. mature ewes, detailed analysis of the behavior of the ewes whose estrus is synchronized may prove useful in determining the cause of any infertility.

MALE SEXUAL BEHAVIOR

The sexual behavior of domestic rams has been reported by Banks (1964) and that of feral Soay rams by Grubb (197413). Grubb described in detail the behavior he termed “blocking”, which involved pushing the side of another ram. Although not very aggressive, blocking was apparently used by rams to establish dominance when strangers were encountered. Smith (1975) reported that depriving rams of smell and hearing had no affect on sexual behavior, while blindfolded rams were limited in mounting abili- ty. Other researchers emphasize factors which affect sexual performance in libido tests or in the field. These involve such factors as genetics, season, physiology, social factors and number of ewes per ram.

Breed and season interact in the mating behavior of rams, with Merino and Dorset maintaining libido during summer while Border Leicester are more seasonal (Lindsay and Ellsmore, 1968). Merinos mature later than Finnish Landrace rams, and are not effective breeders in their first breeding season (Land and Sales, 1977). There are strain differences within Merinos, with rams from high-fecundity flocks being more sexually active (Fowler, 1977). The rams of a more primitive breed, the Soay sheep, are definitely seasonal and influenced by photoperiod. However, testosterone injections will induce mating behavior even when the photoperiod is long (Lincoln and Davidson, 1977). In contrast, D’Occhio and Brooks (1976) found that intact rams had sufficient circulating levels of testosterone to display mating behavior, and only wethers responded to injections. Thus, a mini- mum level of circulating testosterone may be required that is less than would be found in most rams. Mattner and Braden (1975) also found that

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hormonal treatments of testosterone did not affect libido in rams, but they reported that poor nutrition caused a decline in libido within 5 weeks.

The presence of cycling females may have an effect on mature rams. Illius et al. (1976) found that when mature rams were kept in close con- tact with females, the rams had larger testes and higher levels of testos- terone than did rams that were kept separate from females. In addition, when the rams were tested with ewes, it was found that the rams kept in close proximity to ewes had more ejaculations than the isolated group. Bryant (1975) examined the effect of early social environment on the sexual behavior of lambs and found no difference in the behavior of rams raised in isolation and those that were raised in a group. Social interactions among the males in a flock may be important in determining sexual behav- ior. Lindsay et al. (1976) found that subordinate rams were inhibited in terms of mounting and ejaculating when dominant rams were present in adjacent pens. Dominant rams performed equally well with or without an audience of subordinate animals. Bourke (1967) and Hulet et al. (1962) found that in multi-sire breeding flocks, the dominant ram always mounted more often than the subordinate rams. The difference between dominant and subordinate rams decreased when more females were present or when the ewes were more dispersed. However, Shreffler and Hohenboken (1974) found that while dominance was clearly expressed in terms of aggression among their rams, there were no differences in the number of mounts that were made. The conflicting results may have been due to the small (5 rams) unique social group in which individual differences were evident. In addition, the rams were all young, while those of Hulet et al. (1962) were of varying maturity.

The number of ewes serviced and impregnated is the ultimate measure of sexual performance in rams. Allison (1975) reported that three rams could be joined with up to 630 ewes and not significantly reduce the percent of ewes mated and not returning in a l7-day breeding season. However, ewes were less likely to be bred by more than one ram when the ewe to ram ratio was high. When two-tooth ewes were included in the flock, barren- ness increased when a ewe to ram ratio of only 300 to 3 was used (Allison and Davis, 1976a). This could be accounted for by the shorter period of estrus and poor sexual behavior in the younger ewes, as previously discussed.

The number of ewes a ram could service would be valuable information when it came time to set up breeding flocks. Attempts have been made to develop serving capacity or libido tests that would correlate well with field observations. Mattner et al. (1971) evaluated rams by placing them in a pen with five estrous ewes or in a field with a small flock. The performance of rams in these situations was highly correlated with the performance when placed in a regular breeding pasture. Cahill et al. (1975) also tested rams and then exposed them in pairs to ewes in a breeding pasture. Pairs of rams of low libido score did not differ from the high libido pairs in mounts, services, estrous detection or proportion of ewes impregnated.

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Kilgour (1980) found that high service capacity rams had an advantage in servicing ewes during the initial estrous periods. When mating of a ram to 200 ewes was restricted to only 17 days, medium or low service capacity rams impregnated only two-thirds of the number of ewes that high capacity rams did.

Synchronization of ewes results in a large number of ewes being in estrus at one time and the ewe to ram ratio must be decreased. Short-term en- durance of the ram becomes more important in this situation. Synnot et al. (1981) observed that rams exposed to 8 estrous ewes formed prefer- ences and never mated with more than 5 in one day. Jennings (1976) re- ported that when rams were exposed to 12 synchronized ewes, the majority of the matings took place in the first 6 h, and that ram preferences resulted in some ewes not being mated. Ram preferences may have been due to competition between ewes for the ram’s attention. Jennings (1977) reported that 60% of the mating in a synchronized flock occurred within 12 h after rams were introduced and that harem formation was evident, but only lasted for 1 h. Even in this situation, when estrous ewes were in abundance, one ram of each mating pair always dominated the other ram and mated and mounted more ewes than did the subordinate ram. Theorizing that rams may tire after being exposed to synchronized ewes, Bryant and Tom- kins (1976) joined rams with ewes at either 24 h after progesterone with- drawal when only 3 of 22 ewes were in estrus, or at 48 h after withdrawal when 19 of 22 ewes were in estrus. Rams were removed at 72 h post-proges- terone withdrawal. Although rams joined at 48 h served each female less frequently, they mated a higher percentage of the females when they were first released and a greater percentage of the serviced ewes lambed. The total number of lambs born did not differ between treatments.

MATERNAL AND NEONATAL BEHAVIOR

Behavior of both the ewe and lamb during the period surrounding par- turition is critical, as failure to form a mother-offspring bond can result in poor growth or death. In addition, the newborn enters a frequently hostile environment and any protection provided by the mother is im- portant. Research has emphasized the behavior at birth, formation of the bond, identification and sheltering behavior. It is in this area that compari- sons of wild, feral and domestic sheep are most frequently made.

Prior to lambing, ewes frequently exhibit isolation-seeking, maternal interest in lambs, and lip-licking. Holmes (1976) indicated that behavioral signs were first evident from 15 days to 4 h prior to parturition. Geist (1971) reported that mountain sheep separated from the flock 2 weeks prior to giving birth and moved to isolated cliff terrain. This appears to be an extreme, as feral ewes separated from the flock but stayed within the home range (Grubb, 1974a). Although 45% of domestic ewes isolated themselves, they remained close to the flock (Arnold and Morgan, 1975).

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Alexander et al. (1979) indicated that ewes tended to lamb away from the main concentration of ewes. Gonyou and Stookey (1981) reported that the use of cubicles designed to provide isolation in the lambing area increased during the 12 h prior to parturition.

Choice of a lambing site may often involve shelter-seeking as opposed to isolation. Although neither Geist (1971) nor Grubb (1974a) felt that sheltering was of great concern to the ewes, a series of Australian reports indicate that shelter belts are effective in determining lambing sites. The shelter usually consisted of poorly palatable grass hedges located in several regions of the paddock. Use of the sheltered areas was greatest at night, and recently-shorn ewes used them to a greater extent than unshorn ewes (Lynch and Alexander, 1976). Hedges were extensively used when distances between shelters were 80 m (Lynch and Alexander, 1977) or even 240 m (Alexander et al., 1979). In these trials, the ewes would also shelter when they were not giving birth. In fact, perhaps due to a desire for isolation, ewes would sometimes move away from the hedges to give birth. Provision of the windbreaks resulted in increased survival in single lambs (10%) and twins (32%) (Alexander et al., 1980). Sheltering was only increased in shorn ewes if the ewes were exposed to the windbreaks within 4 weeks of shearing (Lynch and Alexander, 1980).

Interest in newborn lambs is evident in some ewes, and although usu- ally restricted to the 3 h prior to parturition, may begin earlier (Arnold and Morgan, 1975). This may be associated with an attraction to birth fluids, as 73% of ewes remained where birth fluids were first spilled. Pre- parturient maternal interest has been implicated in lamb-stealing (Winfield, 1970; Welch and Kilgour, 1972), but is considered to be a minor problem in Finn sheep (Holmes, 1976).

The behavior of the ewes and lambs at birth has been described by Collias (1956), Smith (1965), Poindron and Le Neindre (1975) and Bareham (1976, 1977). Vocalization by the ewe and lamb are common, and licking is usually directed at the head until the lamb stands and then at its back and tail areas. Licking decreases rapidly, from 75% of the time during the first 15 min to only 10% of the time 4 h later (Bareham, 1976). Ewes will follow a rag soaked in their birth fluids but not one soaked in water (Collias, 1956) or another ewe’s fluids (Smith, 1965). Some ewes will not notice their second or third lamb while licking the first (Smith, 1965), and Atroshi and Osterberg (1979) reported that licking decreased for lambs later in the birth order. Desertion of lambs can be a serious problem, par- ticularly with younger ewes (Shelley, 1970). Grubb (1974a) reported that only 30% of the yearling Soay ewes that produced lambs evidenced any maternal interest. Kilgour et al. (1976) reported that ewes in hill country would leave behind weak lambs or those that rolled away from the birth site. Loss of one of a pair of twins is more frequent than loss of a single lamb (Grubb, 1974a; Stevens et al., 1982).

The concept of a critical period during which ewes and lambs must

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form a bond is widely accepted in the literature. The duration of this period and the means of attachment are less clear. Smith et al. (1966) found that ewes separated from their lambs at birth would accept them up to 8 h afterwards. Ewes would not accept alien lambs if they had extensively licked their own lambs first. If an alien and a ewe’s own lamb were presented at the same time, both would be accepted. Poindron et al. (1980) also found that contact with her own lamb for 30 min resulted in a ewe rejecting alien newborn and older lambs which were frequently accepted if the ewe had not contacted her own lamb. A ewe would accept an alien newborn if it were placed with her at the time of the birth of her own second lamb. Ewes were more likely to accept a newborn lamb, even 12 h after giving birth, than a lamb that was 12 h old. The importance of olfaction in es- tablishing specific attachment was demonstrated by Baldwin and Shillito (1974) when bulbectomized sheep displayed little licking of their lambs and were non-specific in terms of the lambs allowed to suckle. Tomlinson et al. (1982) reported that tranquilization of the ewe increased acceptance of alien lambs.

Maternal behavior during the critical period can be modified by hormonal treatments. Multiparous ewes can be induced to display maternal behavior by injections of estradiol, progesterone and hydrocortisone (Le Neindre et al., 1979). The induction of parturition by estradiol benzoate resulted in an extension of the critical period compared to normal or dexamethasone- induced parturitions (Poindron et al., 1979). This may be related to high levels of estrogen and prolactin in the blood for 24 h after giving birth.

Although attachment and recognition of lambs at birth appears to be due to odor and newborn characteristics (perhaps birth fluids), the sensory mechanisms involved in recognition could change as lambs become mature. Lambs apparently rely more heavily on auditory cues to identify their dams as they get older (Arnold et al., 1975). Morgan et al. (1975) con- cluded that ewes recognized older lambs primarily by sight, then hearing, and finally by smell. Alexander and Shillito (1977a) concluded that vision and audition were important in identifying a lamb over a short distance, while olfaction was useful only when contact was possible. The odors of the head and tail region of the lambs were equally effective for recogni- tion when contact was possible (Alexander, 1978). Although producers frequently attempt to mask the odor of an alien lamb in order to facilitate fostering, ewes are able to distinguish their own lambs among several an- ointed with similar odoriferous compounds (Alexander and Stevens, 1982). In the test used, however, the criterion was selection of one’s own lamb over aliens and not that of acceptance of an alien, as would be the case in practice.

In order to investigate visual recognition, Alexander and Shillito (197713) blackened Merino lambs on various parts of their bodies. Ewes were most able to recognize the lambs if they were not blackened in the head area, indicating that visual cues from the head are most important. Ewes were

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also able to distinguish between different colors of artificially colored lambs, and would approach those of the same color as their own lamb (Alexander and Shillito, 1978). Although the sheep used were Merino, color or shade differences in lambs may be of practical consequence in other breeds or crossbreds which have differently colored lambs.

Lambs and ewes remain close together during the first few weeks after birth (Morgan and Arnold, 1974). Large distances (25 m) between ewes and lambs were only observed when ewes were grazing, and often involved play by lambs. Suckling is usually initiated by the lamb and terminated by the ewe (Stapleton et al., 1980). Twins suckle less frequently than do singles (Stapleton et al., 1980), and triplets suckle less than twins (Hess et al., 1974). Arnold et al. (1979) observed that ewe and lamb behavior indicative of weaning began to appear when milk production declined to less than 1000 ml per day. Ewes on a high protein diet continued to nurse lambs up to 140 days of age, while ewes on a low protein diet had already weaned most of their lambs.

CONCLUSION

Sheep have been the subject of a large proportion of the recent publi- cations in applied ethology (Alexander, 1982). This research has been directed to most aspects of sheep production and will ultimately influence management methods. Further research will no doubt serve to elucidate behavioral mechanisms and the practical results of applying our knowledge to production.

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Adams, N.R., 1978. Sexual behaviour responses of the ovariectomized ewe to oestradiol benzoate, and their persistent reduction after exposure to phyto-oestrogens. J. Re- prod. Fertil., 53 : 203-208.

Alexander, G., 1978. Odour, and the recognition of lambs by Merino ewes. Appl. Anim. Ethol., 4: 153-158.

Alexander, G., 1982. “Applied Animal Ethology”: Survey of the first twenty-five issues. Appl. Anim. Ethol., 8: 391-399.

Alexander, G. and Shillito, E.E., 1977a. The importance of odour, appearance and voice in maternal recognition of the young in Merino sheep (Ouis aries). Appl. Anim. Ethol., 3: 127-135.

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