Fostering in sheep. IV. Use of restraint

Fostering an additional lamb on to a ewe with a single lamb of her own was attempted in Dorset, Corriedale and Merino ewes restrained by the neck in pens for up to 12 days. Fostering occurred more rapidly in Dorsets than in Merinos, and success rates tended to be higher in Dorsets (81%) than the other breeds (73% in Corriedales and 69% in Merinos). The use of screens at the level of the ewe's neck to limit her olfactory examination of the lambs was more successful than when full olfactory contact was allowed. The prevention of any close olfactory contact resulted in an intermediate rate of acceptance, even though acceptance was apparently based on olfaction, as shown by universal rejection of strange alien lambs. Acceptance tests done within a few minutes of release from restraint were found not to reflect accurately the final level of acceptance, since some lambs came to be accepted within a day of being released. Further acceptances, that developed several days after release into a flock of ewes and lambs, emphasize an important role of the lamb in maintaining contact with the ewe. With few exceptions, lambs accepted when released from the pens were still accepted after a week or so in the flock.Dorset ewes given one or two foster lambs in the absence of their own lamb accepted the fosters within 9 days.Restraint fostering had no apparent harmful effects on the ewes or lambs, but had the disadvantages of being laborious and of soiling the ewes' wool. It has the advantage of providing lambs with an assured milk supply, and could prove useful for ewes that have failed to accept lambs under other methods.     

Fostering in sheep. III. Facilitation by the use of odorants

Lambs were thoroughly anointed with various odoriferous substances to test the facilitatory effects on substitutive fostering on to multiparous Merino ewes held in individual pens. The ewes were first familiarised with an odorant by anointing their own lamb with it 24 h before a similarly anointed foster lamb was presented. The odorants were neatsfoot oil, wool wax, vegetable oil, butyric and propionic acids, mercaptoethanol, vanillin, methyl salicylate and eucalyptus oil. Acceptance of foster lambs was assessed over the next 48 h. Odorants were not applied to the ewes.All eight foster lambs treated with neatsfoot oil were accepted within 24 h; seven immediately. There were few immediate acceptances with the other odorants, but from two to five lambs out of groups of six were permanently fostered by 48 h. Only one foster lamb was accepted in the control group of 12 in which no odorant was used. Fostering was most successful with neatsfoot oil and wool wax, both substances that originated from ruminant skin.Fostering was less successful in tests that omitted pre-exposure of the ewes to their own lambs treated with neatsfoot oil, wool wax or vegetable oil.Toxicity problems were encountered with ethanol solutions of mercaptoethanol, methyl salicylate, eucalyptus oil and neatsfoot oil.     

Effects of sex, litter size and periconceptional ewe nutrition on the ewe–lamb bond

Undernutrition restricted to the time around conception in sheep alters endocrine and metabolic responses in the offspring. Studies in rats suggest that such an early insult can also alter the behaviour of the offspring. We studied the effects of mild maternal periconceptional undernutrition (10–15% body weight reduction) on the lamb's response to separation from and reunion with the mother, and on the ewe–lamb bond, evaluated as the preference for each other over an alien ewe/lamb in a test enclosure, at 24 h, 1 and 4 weeks of age. Lamb birth weight was not affected by maternal nutrition. Maternal periconceptional undernutrition did not affect the lambs’ responses to separation and reunion (number of vocalisations, times to leave pen and achieve proximity with ewes) or the bond between ewes and lambs (percentage of time spent near their own dam/lamb). However, there were effects of sex, litter size and time on lambs’ responses to separation and reunion and on the ewe–lamb bond. Female lambs vocalised more during separation (P ≤ 0.01) and left the holding pen faster than males (P ≤ 0.05), and twins vocalised more than singletons (P ≤ 0.05). The time to leave the holding pen, achieve proximity with the ewes and number of vocalisations decreased with increasing postnatal age of the lamb (all P ≤ 0.001). Ewes showed a stronger preference for the lamb at 24 h and 1 week than at 4 weeks postpartum (P ≤ 0.001), whereas lambs followed an opposite trend, showing a lower preference for the mother at 24 h and 1 week and increased preference at 4 weeks of age (P ≤ 0.001). We conclude that periconceptional undernutrition does not affect offspring response to separation from the mother or the bond between ewes and lambs, but that these behaviours are affected by sex and litter size for up to 4 weeks after birth.     

Mother–young bonding in prolific D’man and Romanov sheep

The effect of prolificacy on mother–young mutual recognition is still largely unknown in sheep. The aim of the present study was to investigate the ability of prolific ewes to develop an exclusive bond with their neonate and to recognize each other from alien subjects. Observations were performed on 11 D’man and 16 Romanov ewes with, respectively, 19 and 37 of their lambs. Maternal selectivity was tested at 24 h postpartum during two consecutive periods of 3 min. All mothers accepted their own lambs at suckling, while 21 out of 27 (78%) rejected the alien, thus displaying mostly selective nursing. To assess mother–young recognition, a two-choice test was performed at 36 h postpartum. Ewes clearly preferred their own lambs to an alien lamb and behavioral differences were not found between mothers of small (singletons and twins) and large litters (triplets and quadruplets). Romanov ewes reached their own lambsmore rapidly and spent more time near them than D’man ewes. Lambs from small litters, in particular light lambs, clearly preferred their mothers to an alien dam; however, both light and heavy lambs in large litters did not discriminate between the two stimulus ewes. D’man lambs clearly preferred their mothers to an alien dam; in contrast, such a preference was not as clearly demonstrated in Romanov lambs.     

Maternal selectivity suppression through peripheral anosmia affects neither overall nursing frequency and duration, nor lactation performance in ewes

The effects of prepartum peripheral anosmia on nursing activity, milk production and growth of the lambs, were assessed by comparing intact (n=10) and anosmic (n=10) multiparous Columbia and Rambouillet ewes and their single lamb during the first 2 months of lactation. Intact mothers only nursed their own lamb (98%) while most of the nursing activity in anosmic mothers concerned alien lambs (78%). On the other hand, the total duration and the frequencies of nursing did not differ significantly between groups (P>0.05). Nevertheless, the total percentage of nursing of own lamb by anosmic mothers (22%) was higher than expected at random (10%). Milk production or lambs' weights did not differ between groups. We conclude that prepartum anosmia resulted in the failure of ewes to develop true selective nursing up to the 8th week of lactation, although some preferential mother-young relationship yet developed. On the other hand, it did not affect significantly overall nursing activity.     

A quantitative ethogram of behavior of yearling ewes during two hours post-parturition

A total of 2130 behaviors representing 24 behavioral categories were observed during the period from parturition to lamb nursing for seven ewe-lamb pairs. Both individual behaviors and behavioral sequences were counted. Ewes showed a high frequency of licking, especially directed at the head (41% of licks) and anterior body (30% of licks) of their lambs. Licking followed a specific, non-random pattern. Ewes licked from front to back of their lambs. Ewes licked their lamb's anterior body and head immediately before their lambs stood. When the lambs sought teats, ewes either presented their udder to their lamb which facilitated nursing, or moved away from the lamb which delayed nursing. This research identified behaviors and behavioral sequences that may be used in future studies seeking to select for improved maternal ability or to design improved lambing environments. Finally, this work may lead to the generation of hypotheses which may be tested in future work examining behaviors involved as causal factors in lamb survival.     

Relationship between male-male and male-female sexual behavior in 5-6-month-old male lambs

To characterize male–male sexual behavior during lamb development, to relate it with lamb body and testicular growth, and with sexual behavior toward estrual ewes, 40 Milchschaf male lambs, weaned at 45 days of age, were kept with ewes that were nursing younger lambs. Experimental lambs were weighed and scrotal circumference was measured every 2 weeks. Male–male sexual behavior was observed during 1–2 h every 2 weeks after birth until 7 months of age. Observations were recorded more intensively (3–4 h on five different days) for 2 weeks (5–6 months of age) as male–male sexual behavior increased during that period. Both mounting and mounted lambs were identified. An individual mounting index (MI) was calculated. To study male–female sexual behavior, lambs were individually located with two estrual ewes, and during 5 min the number of ano-genital sniffing, lateral approaches, mounts, and mounts with ejaculation were recorded. From those data, a libido index was also calculated. Male–male mounts (n = 308) were observed. Courtship behavior was displayed in 25% of interactions; mounts were accepted in 72.1% of attempted mounts. Mounts without previous courtship were accepted more frequently than mounts with previous courtship (P = 0.002). Lamb weight and scrotal circumference were not different according to MI groups. Lambs that mounted more times estrual ewes (first tertile) had greater (P = 0.04) MI (0.61 ± 0.10) than lambs with medium (0.27 ± 0.09) and less (0.30 ± 0.10) MI. The regression between MI and heterosexual libido index was r = 0.33 (P < 0.05). In summary, intensive male–male sexual activity during a short period of male lamb development was observed. There was a positive relationship between sexual behavior of male lambs towards other male lambs and towards estrual ewes.     

Breed, litter and parity effects on placental weight and placentome number, and consequences for the neonatal behaviour of the lamb

Lamb survival is impaired in low birth weight lambs, and those that are slow to stand and suck. Many of the factors that influence lamb vigour, such as parity, litter size, and breed, may exert their effects, at least partially, before birth by influencing placenta development. Our hypothesis was that retarded lamb behavioural development was due to differences in placentation in these animals. Data were collected from Blackface and Suffolk lambs in the first 2 h after birth and placentas were collected when delivered. Suffolk lambs, which were behaviourally slower and had lower rectal temperatures than Blackface lambs, were associated with larger but less efficient placentas (placental efficiency defined as foetal weight supported per g placenta) with fewer foetal cotyledons than Blackface placentas. Triplet lambs were significantly slower than twin or single lambs to suck and had lower rectal temperatures. Although placenta efficiency increased with litter size, placenta and cotyledon weight, and cotyledon number increased with twinning but not thereafter. It seemed likely that triplet lambs suffered some placental insufficiency in comparison to other litter sizes. Lambs born to first parity mothers were slower to stand and reach the udder than lambs of more experienced ewes, and first parity ewes also had smaller and less efficient placentas although cotyledon number was not affected. Male lambs tended to be slower than female lambs for most behaviours, although rectal temperatures were not affected. The sire of the lamb also influenced lamb behaviour and rectal temperature. Both lamb sex and lamb sire influenced the average weight of placental cotyledons, thus some of the sire effect on the behaviour and birth weight of his progeny might be mediated through placental development. Lamb neonatal vigour was correlated with placental efficiency suggesting that lamb behaviour immediately after birth is related to placental development and function.     

Ewe and lamb contact at lambing is influenced by both shelter type and birth number

A significant number of lambs born each year in Australia die within 72 h of birth. Periods of high wind, combined with rain and low temperatures can lead to marked increases in the mortality level. Under these climatic conditions mortality levels may be reduced with the provision of shelter. This study used contact loggers to compare interactions between ewes with twin lambs across two shelter types (Hessian and shrubs), while also comparing ewes with single and twin lambs in a single shelter type (Hessian). The contact loggers record the time of the initial contact (within approximately 4 to 5 m) between collared animals and the duration of each contact. Contact levels between ewes immediately after lambing were only 10% of the initial levels (1 h/day). For single-born lambs, lambs averaged 11 h contact per day with their mother, while for twinborn lambs, each lamb averaged 9.25 h/day with its mother and 14.7 h/day with its sibling. The level of contact between ewes and each of their offspring in the Hessian was 24% lower (P < 0.05) for ewes with twin lambs than with singles. For ewes with twin lambs the level of contact was 17% lower (P < 0.05) in the Hessian shelter compared with shrub shelter. We conclude that shelter type and birth number can affect the level of contact between ewes and their offspring.     

Conditioning ewes and lambs to increase consumption of spotted knapweed

Spotted knapweed (Centaurea maculosa Lam.) is an invasive plant that alters species composition and grazing value of rangelands in the northwestern United States. The spread of invasive plants may be reduced by using livestock as a biological control. We determined if mature ewes and their lambs (n = 34 ewe/lamb pairs) consume more spotted knapweed when ewes and/or lambs are conditioned to fresh-cut spotted knapweed. Ewe/lamb pairs were randomly assigned to one of four conditioning treatments: ewes and lambs not conditioned to spotted knapweed (N), conditioned ewes with non-conditioned lambs (E), non-conditioned ewes with conditioned lambs (L), or conditioned ewes and lambs (both—B). Then, ewes and lambs were observed together for 5 days (Trial 1); 11 days later, lambs were observed for 4 days without their mothers (Trial 2). During conditioning, intake by conditioned and non-conditioned ewes and lambs varied over time (as-fed basis, treatment by day interaction; ewes P = 0.03; lambs P = 0.05). Overall, non-conditioned lambs (N, E) consumed more than conditioned lambs (L, B; P = 0.02). In Trial 1, N ewes consumed similar amounts of spotted knapweed and bromegrass (Bromus inermis Leyss.) as the E, L, and B ewes (P = 0.67). E ewes spent more time eating spotted knapweed than L ewes (P = 0.001), and E ewe/lamb pairs consumed more spotted knapweed than L ewe/lamb pairs (P = 0.02). In Trial 2, N lambs consumed less spotted knapweed than E, L, and B lambs (P = 0.06). L lambs consumed more than E lambs (P = 0.007). Conditioning ewes, lambs, or ewes and lambs did not increase time spent eating spotted knapweed when both grazed together in a drylot, but conditioned lambs, without their mothers present, consumed more spotted knapweed 11 days later than non-conditioned lambs. Conditioning lambs only in a group setting with their peers may have the greatest potential to enhance consumption of spotted knapweed, because of social facilitation and the predilection for young animals to try novel feeds.     

A Hereditary Skin Defect in Sheep

Some years ago a lamb with abnormal skin was received at the State veterinary research station for small ruminants (SVRS), Stavanger, from a farm in Ryfylke. The lamb had apparently been normal at birth, but by normal activity and contact with its mother, extensive wounds developed, with large, loose skin areas. The lamb’s condition had deteriorated so much that it was killed when it was two days old. Two ewes sired by the same ram had given birth to similar lambs the same year, while some years earlier, lambs with the same defect had been born by other ewes in the flock.     

Reproductive costs of sons and daughters in Rocky Mountain bighorn sheep

Differential maternal investment theory predicts that in sexuallydimorphic and polygynous species mothers should invest morein sons than in daughters. We tested the hypothesis that bighornewes that raise sons incur greater reproductive costs than ewesthat raise daughters. Although ewe mass gain during lactationand subsequent winter body mass loss were independent of lambsex, lambs born the year following the weaning of a son hadlower survival than lambs born after a daughter. The effectsof lamb sex on subsequent reproductive success of ewes becamemore evident at high population density. Lamb sex did not affectmaternal survival. Population density, weather, and ewe agedid not alter the relationship between lamb sex and subsequentreproductive success of the ewe. The year after weaning a son,ewes were more likely to have a daughter than a son, while ewesthat had previously weaned a daughter had similar numbers ofsons and daughters. Our results show that for bighorn sheepewes, sons have a greater life-history cost than daughters,suggesting a differential maternal investment in the sexes.     

The effects of pasture availability for twin- and triplet-bearing ewes in mid and late pregnancy on ewe and lamb behaviour 12 to 24 h after birth

This experiment was conducted to evaluate the effect of offering ewes two different feeding levels, during mid and late pregnancy, on ewe and lamb behaviour 12 to 24 h after birth. Romney ewes, bearing twin (n = 80) or triplet foetuses (n = 56), were allocated to a pasture sward height of 2 or 4 cm between 70 and 107 days of pregnancy. In late pregnancy (day 107 to 147), half of the ewes were reallocated the alternate sward height, which produced four treatments: 2-2, 2-4, 4-2 and 4-4. Ewes were weighed on days 65, 92, 107 and 130 of pregnancy and lamb live weights were recorded 12 to 24 h after birth. Twelve to 24 h after birth the maternal behaviour score (MBS) of the ewes were determined, whilst their lambs were tagged. After the lambs were released, the behaviour of each ewe and her lambs was observed for 5 min. Ewe treatment and litter size had no effect on ewe MBS. However, as MBS increased (ewes stayed closer to lambs during tagging), ewes bleated less in a high-pitch and were quicker to make contact with their lamb. During the observation period, ewes in the 4-4 treatment had a greater percentage of their bleats in a low pitch (P < 0.05) than ewes in the 2-2 and 4-2 treatment (61.3% v. 41.3% and 38.8% low bleats, respectively) and more lambs born to 4-4 ewes (95%) bleated than lambs born to 2-2 ewes (84%; P < 0.05). However, lambs born to ewes in the 2-2 treatment bleated earlier than lambs in all other treatments (P < 0.05). Lambs born to 4-4 ewes were less likely (P < 0.05) to move towards their dam in order to make contact than lambs born to 2-2 or 4-2 ewes (3.1% v. 16.9% and 16.7%, respectively). These findings suggest that under the conditions of the present study, ewe nutrition had little effect on maternal behaviour. However, lambs born to ewes offered 2 cm pasture sward heights during mid and/or late pregnancy (2-2, 2-4 and 4-2 treatments) displayed behaviour that demonstrated greater 'need' whereas lambs born to ewes offered 4 cm during mid and late pregnancy sought less attention from their dam.     

Mob size of single-bearing or twin-bearing Merino ewes at lambing may not influence lamb survival when feed-on-offer is high

Limited research has suggested that higher lambing densities increase interference from foreign ewes at lambing which disrupts the ewe-lamb bond and compromises lamb survival. This may be particularly evident in mobs of twin-bearing ewes compared to single-bearing ewes because a greater number of lambs are born per day. Therefore, we hypothesised that; (i) decreasing the mob size of ewes at lambing has a greater impact on the survival of twin-born lambs than single-born lambs; (ii) the relationship between mob size and lamb survival can be explained by differences in the rate of interaction with foreign ewes and lambs at lambing; and (iii) ewes will utilise a limited area of the paddock at lambing and thus lambing density will be defined by the distribution of ewes in the paddock rather than the paddock area. Merino ewes were allocated into a 2×2 factorial combination of ewe pregnancy status (single- or twin-bearing) and mob size (high (n=130 ewes) or low (n=50 ewes)) on day 140 from the start of joining. Each treatment had two replicates excepting the low mob size for twins which had a third replicate. Ewes lambed at a stocking rate of 11 ewes/ha. Feed-on-offer during lambing exceeded 2400 kg dry matter (DM)/ha. Ewe-lamb behaviour was observed and dead lambs were autopsied over 11 days during the peak of lambing. The distribution of ewes in each paddock was recorded every 2 h during daylight hours by counting the number of ewes occupying 2500 m² grids. The proportion of ewes and their newborn progeny which interacted with foreign ewes at lambing did not differ between the high and low mob sizes for single- (24.9% v. 20.8%) or twin-bearing ewes (14.3% v. 19.6%; P=0.74). Similarly, interaction with foreign lambs did not differ between the high and low mob sizes for single- (14.5% v. 25.2%) and twin-bearing ewes (34.5% v. 26.4%; P=0.44). The distribution of ewes within the paddock did not differ between treatments (P=0.95). On average, single-bearing ewes which lambed at the high and low mob sizes occupied 34% and 36% of the paddock during daylight hours, and the corresponding values for twin-bearing ewes were 40% and 43%. Survival of twin-born lambs was lower than single-born lambs (75.3% v. 87.9%; P<0.01), however, lamb survival was not influenced by mob size regardless of birth type. These results suggest that higher mob sizes may not compromise lamb survival when feed-on-offer during lambing exceeds 2400 kg DM/ha.     

Distance recognition in ewes and lambs kept permanently indoors or at pasture

We tested the ability of Merino and Merino × Romanov ewes and lambs to recognise each other at a distance when given the choice between an alien partner and their own. Two groups of animals were studied. In the first group, multiparous ewes and their lambs were housed permanently indoors at a stocking-rate of 1 ewe/2 m². In the second group, ewes and lambs were run permanently outside in a paddock at a stocking rate of 1 ewe/500 m². Of animals living outside, 87% of ewes recognised their own lamb (100% of multiparous dams versus 84% of primiparous ones, P = 0.02). This differed significantly from a random choice. By contrast, the proportion of correct choices by ewes living inside (all multiparous) was significantly lower (64%) and did not differ from a random choice at the 5% level. Lambs reared outside recognised their dam in 95% of cases, versus 72% in lambs reared indoors (P = 0.01). Both frequencies differed significantly from a choice at random. It is concluded that the environmental conditions in which ewes and lambs are maintained can influence their ability to select their partners at a distance with the help of auditory and visual cues.     

The effects of ablation of the olfactory bulbs on parturition and maternal behaviour in Soay sheep

Eight pregnant Soay ewes were made anosmic by ablation of the olfactory bulbs before their lambs were born. They were observed during parturition and in the following few days. Four out of five ewes seen during parturition did not show pre-natal lip licking which is normally seen in Soays. Four ewes did not lick their lambs properly after birth, and in six there was a lack of specific response to their own lambs, so that strange lambs were often fed. Post-mortem examination showed that olfactory tracts were absent in all except one of the ewes examined. It is suggested that the importance of olfaction in maternal care is concerned with identification of the lamb at close quarters and in forming the ewe-lamb relationship.     

Evaluation of ewe vaccination as a tool for increasing bighorn lamb survival following pasteurellosis epizootics

We conducted field and laboratory experiments to evaluate whether treating pregnant bighorn ewes with a combination of an experimental Pasteurella trehalosi and Mannheimia haemolytica (formerly P. haemolytica) vaccine and a commercially-available bovine P. multocida and M. haemolytica vaccine would increase lamb survival following a pneumonia epidemic. Three free-ranging bighorn herds affected by pasteurellosis outbreaks between November 1995 and June 1996 were included in the field experiment. Post-epidemic lamb survival was low in all three herds in 1996, with November lamb:ewe ratios of < or = 8:100. In March 1997, thirty-six ewes (12/herd) were captured and radiocollared. Half of the ewes captured in each herd were randomly selected to receive both vaccines; the other half were injected with 0.9% saline solution as controls. Lambs born to radiocollared ewes were observed two or more times per week and were considered to have survived if they were alive in October 1997, about 6 mo after birth. Lamb survival differed among herds (range 22% to 100%), and survival of lambs born to vaccinated ewes was lower (P = 0.08) than survival of lambs born to unvaccinated ewes. Bronchopneumonia (pasteurellosis) was the dominant cause of mortality among lambs examined. We concurrently evaluated vaccine effects on survival of lambs born to seven captive ewes removed from the wild during the 1995-96 epidemic. Antibody titers were high in captive ewes prior to vaccination, and vaccines failed to enhance antibody titers in treated captive ewes. None of the captive-born lambs survived. These data suggest that, using existing technology, vaccinating bighorn ewes following pneumonia epidemics has little chance of increasing neonatal survival and population recovery.     

Behavioural development in the neonatal lamb: effect of maternal and birth-related factors

The survival of the neonate relies on the integrated expression of appropriate behaviours from both the mother and young. In precocious species, like the sheep, the speed with which the lamb stands and seeks the udder is related to lamb survival. In this study the effects of birth difficulty, lamb birth weight, ewe loss or gain in backfat from conception to delivery, ewe parity, litter size, and lamb sex on neonatal lamb behavioural development were investigated in over 500 lambs of two breeds (Scottish Blackface and Suffolk). Lambs that required assistance to be delivered were significantly slower to perform all neonatal behaviours than unassisted lambs (P<0.001), and were less active over the first 3 days after delivery (P<0.05). There were no effects of lamb birthweight that were not accounted for by the increased likelihood of requiring assistance in heavier birth weight lambs. Ewes that mobilised less body fat during their pregnancy produced lambs that stood and sucked quickly (P<0.001), and were more active over the first 3 days of life. Lambs born to first parity ewes were slower to stand and suck than lambs born to experienced ewes (P<0.001). There was an improvement in time taken by lambs to stand, seek the udder and to suck with each increase in ewe parity. Litter size had an additional retarding influence on the behaviour of multiple-born lambs that could not be accounted for by birthweight. In the Suffolk breed male lambs were slower to stand and suck than female lambs, this effect was not seen in Blackface lambs. These data demonstrate that lambs that require assistance at birth, even if they survive the birth process, lambs born to ewes that lose a lot of condition over pregnancy or first parity ewes, triplet lambs and, at least in some breeds, male lambs are slower to progress through the sequence of neonatal behaviours. These lambs are, therefore, at greater risk of not surviving to weaning.     

Social rank affects reproductive development in male lambs

Under field conditions, dominant rams may prevent mating by other rams, thereby depressing flock fertility. However, little is known about the effects of social rank on prepuberal reproductive development in male lambs. The objective of this experiment was to determine if social rank of lambs is related to body weight, scrotal circumference, testosterone concentrations, semen production and courtship behavior until 38 weeks of age. An additional aim was to characterize male-male sexual behavior and to determine if this behavior was related to social rank. Body weight, scrotal circumference and testosterone serum concentrations were measured weekly in 13 male lambs. In addition, semen was obtained by electroejaculation, and sexual behavior towards non-estrous ewes was registered every 2 weeks. Male-male mounts were also recorded weekly. Individual social rank success indexes were determined using the food competition test when lambs were 3 and 6 months old. The five rams with greater (GR) and the five with lesser (LR) success indexes were used in the experiment. Body weight and scrotal circumference increases were greater in GR than in LR lambs. Testosterone concentrations increased with age, but were not related to social rank. Semen characteristics matured earlier in GR than in LR lambs. Most courtship and mating behaviors (lateral approaches, flehmen, ejaculations and ejaculations/total mounts) increased with age, but no effect of social rank was observed. The number of ano-genital sniffing and mount attempts increased with age and was greater in GR than LR. The total number of male-male mounts in which each lamb took part was positively related with the success index (r=0.48; P=0.05), and tended to be related with the number of times each lamb was mounted (r=0.42; P=0.06). No relation was observed between the number of times each lamb mounted and the social rank success index. We observed that GR lambs mature earlier than LR lambs, which is reflected by a greater increase of their body weight and scrotal circumference. Semen production and male-female sexual behavior also occurred earlier in high-ranked than in low-ranked lambs. It remains to be determined if low-ranked lambs can achieve similar development than high-ranked lambs over longer time intervals, or if their maximum developmental capacity is lower than the maximum obtained by high-ranked lambs.     

From birth to colostrum: early steps leading to lamb survival

New-born lambs have limited energy reserves and need a rapid access to colostrum to maintain homeothermy and survive. In addition to energy, colostrum provides immunoglobulins which ensure passive systemic immunity. Therefore, getting early access to the udder is essential for the neonate. The results from the literature reviewed here highlight the importance of the birth site as the location where the mutual bonding between the mother and her young takes place. Attraction to birth fluids by the periparturient ewe leads to intense licking of the lamb. Grooming not only dries, cleans and stimulates the newborn it also facilitates bonding through learning of its individual odour. Ewes having twins should ideally stay on the birth site for at least six hours in order to establish a strong bond with both lambs and favour lambs survival. However, primiparous ewes or ewes having high levels of emotivity are more likely to exhibit poor maternal behaviour. In addition, difficult parturition and weather conditions have an indirect effect on the behaviour of the mother and are other major causes of lamb death. On the lamb's side, rapid access to the udder and early suckling are extremely important. Delayed lactation or insufficient colostrum yield may be fatal especially since suckling has strong rewarding properties in the establishment of a preference for the mother, which in turn increases lamb survival. Insufficient access to the udder in mothers leaving the birth site too soon after parturition, especially in twin-bearing ewes, could also partly account for the high incidence of loss of mother-young contact and subsequent death in such lambs. Strategies to improve neonatal survival should be aimed at maximising lamb vigour, colostrum production, and mutual mother-young bonding through adequate feeding in late pregnancy and selection on behaviour.