Influence of season on birth weight and weaning age of indigenous Balami and imported Sudan Desert sheep in the Sahel region of Northeastern Nigeria

Data on birth weight and age at weaning for 1,092 (609 indigenous Balami and 483 imported Sudan Desert) sheep born from 1975 to 1979 in a Government farm near Maiduguri were analysed to study the influence of season on birth weight and age at weaning in sheep reared in the sahel region of Northeastern Nigeria. The suitability of the Sudan Desert for replacing or upgrading the indigenous Balami was considered.Season, breed, sex and type of birth significantly (P<0.001) influenced birth weight, age at weaning and the average daily gain from birth to weaning of lambs. Heaviest lambs were born during the rainy season-June–August. Birth weight was lowest during the dry hot season. Balami lambs were heavier at birth and were weaned earlier with greater average daily gain than the Sudan Desert (P<0.001). Ram lambs were heavier at birth and had greater daily gain than the ewes (P<0.001). Also single-born lambs were heavier at birth and were weaned earlier (P<0.001) than twins. Twining rate in Balami was almost double that in the Sudanese. Survival tended to be greater in Sudanese than in Balami. Birth, twining and survival rates were highest for the dry cold season-born lambs. The dry cold season seems the best lambing season here. In all, the local Balami proved far superior in almost all traits considered. The use of the Sudan Desert here is definitely not econmically justifiable or rational.     

湖羊出生类型与产活羔数表型及遗传参数估计

收集了26只湖羊种公羊115个女儿共计458窝产羔记录。统计分析表明,湖羊母羊胎产活羔数为1－5羔的比例分别为21．18％、49．78％、25．76％、3．06％和0．22％;公羊对母羊出生类型和产活羔数具有显著影响,胎次对母羊出生类型和产活羔数没有显著影响;母羊出生类型对其产活羔数没有显著影响;湖羊母羊出生类型与产活羔数的遗传力分别为0．251和0．097,它们之间的遗传、表型和环境相关分别为0．241、0．008和0．181,它们之间的协遗传力为0．038。这些参数表明：母羊出生类型与产活羔数是遗传联系不紧密的两个不同性状;根据母羊出生类型来早期选择产活羔数是无效的。     

Agonistic and proximity patterns in enclosed mouflon (Ovis gmelini) ewes in relation to age, reproductive status and kinship

Agonistic and proximity patterns of mouflon sheep (Ovis gmelini) were studied in a group of enclosed females during two lambing periods. A non-random linear-tending hierarchy almost stable over the 2-years was found. Age was correlated to social rank and to the distribution of agonistic acts by females. The rank of the yearling females was linked to the rank of their mothers. The age of the animal and the degree of relatedness with its congeners appeared as main determinants of the proximity patterns of ewes. Strong associations between closely related females (especially mothers and daughters), brought out the existence of a familial structure in mouflon. Otherwise, we found a strong inter-attraction between yearlings, which received a large number of aggressions from older females. That revealed peer grouping superimposed on familial structures. Age also seemed to influence ‘sociality’ of females, older females tending to associate less with conspecifics than younger ones.     

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.     

Effect of maternal nutrient restriction in early to mid gestation and thyrotrophin-releasing hormone on lamb survival following Caesarean section delivery near to term

We investigated the influence of restricted maternal nutrition between 28 and 77 days gestation on survival and thermoregulatory adaptation following Caesarean section delivery near to term. This study was designed to examine the hypothesis that adaptation after birth would be compromised in those lambs born to nutrient restricted ewes. We further hypothesised that this would be due in part to inadequate hypothalamic-pituitary-thyroidal function. Lambs born to nutrient restricted ewes were untreated (RU) or treated with thyrotrophin-releasing hormone (TRH; RT) immediately prior to umbilical cord clamping. Single bearing ewes consumed either 6.60 MJ x day(-1) (controls, n = 4) or 3.00 MJ x day(-1) (nutrient restricted, n = 15) from 28-77 days gestation, after which all ewes consumed 7.20 MJ x day(-1). All lambs born to control ewes commenced continuous breathing and began to shiver following Caesarean section delivery and survived to 6 h after birth. Only 4 out of 9 RU lambs established continuous breathing and survived to 6 h after birth compared with all RT lambs. Six hours after birth, RT lambs possessed perirenal brown adipose tissue with a higher thermogenic activity than 6 h old RU or control lambs. Lamb birth weight was similar in all groups. In conclusion, near-term lambs born to ewes nutrient restricted in early to mid gestation are at increased risk of death following Caesarean section delivery. Survival after birth can be significantly enhanced if TRH is administered to the lambs immediately before delivery.     

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.     

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.     

Study of LH response to GnRH in the young male as a criterion of genetic merit for female reproduction in sheep

A high and a low response line in sheep were selected on the basis of the mean concentration of LH in 10-week-old Finn-Dorset ram lambs after an i.v. injection of 5 micrograms GnRH. After 8 male generations the mean LH response of the high line was more than 5-fold that of the low line and the heritability of the selected trait was estimated at 0.44 +/- 0.015. Highly significant line differences in mean LH response to GnRH were also found in males at 20 weeks of age and females at 10 and 20 weeks of age and the genetic correlations between the four LH response traits appear to be close to unity. Large line differences in the mean FSH response to GnRH were also found in both males and females at 10 and 20 weeks of age. Selection had little effect on the physical characteristics of lambs. High-response line ewes entering their first breeding season at about 7 months of age showed oestrus earlier in the season and had higher ovulation rates and numbers of lambs born per ewe lambing than did low-response line ewes. In the second breeding season, at about 19 months of age, the only line difference was a higher ovulation rate early in the breeding season in high-line ewes. It is suggested that these changes may be mediated by a more rapid response in high-line ewes to increased GnRH stimulation at puberty or at the beginning of the breeding season.     

Pinealectomy delays puberty in ewe lambs

Fifteen pinealectomized and 15 unoperated ewes were exposed to constant light for 3 weeks before and 10 weeks after lambing. Fourteen pinealectomized and 15 unoperated ewes were allowed to lamb outdoors. Five ewe lambs born in constant light to the 2 groups of dams were pinealectomized at 10 weeks of age. Ewes and lambs were then returned to the field. Puberty (determined by weekly progesterone analysis) was significantly delayed (P less than 0.05) in the pinealectomized ewe lambs. Median pubertal age in pineal-intact ewe lambs was 37 weeks compared to 49 weeks in pinealectomized lambs. Constant light during the first 10 weeks of life had no effect upon puberty onset nor did the pineal status of the dam. Control lambs entered seasonal anoestrus at the time pinealectomized ewe lambs were entering puberty. Pinealectomized lambs entered anoestrus at the same time as control lambs were beginning their second breeding season. These results confirm a key role of pineal-mediated hormonal signals in the control of puberty in the sheep.     

Pair association between lambs of different breeds born to Jacob and Dalesbred ewes after embryo transplantation

Seven pairs of lambs, each pair consisting of one Dalesbred and one Jacob lamb born to either a Dalesbred or a Jacob ewe following embryo transplant, were observed for 5 weeks in a field. The association of the lambs with their sibling and with other sheep in the field was recorded. The lambs were seen to be with their dam 53% of the time at 10 weeks and this fell to 42% in weeks 11 and 12. They spent more than twice the amount of time near to a sibling than with any other lamb (54% and 25%). When the ewes were removed from the field, the lambs bunched together and the association with siblings and with other lambs increased. There was no breed identity amongst the lambs, but the Jacob ewes mixed more with other Jacobs and Dalesbred ewes mixed more with other Dalesbreds. Comparisons were made with pairs of genetically related Jacob lambs. It is concluded that association between lambs born to the same ewe is the result of that birth and subsequent upbringing and not due to genetic inheritance.     

Behavioral patterns of domestic sheep and their relationship to coyote predation

Activity patterns between individuals in a large herd of domestic sheep (Ovis aries) were examined to determine whether or not behavioral characteristics predisposed certain individuals to coyote (Canis latrans) predation. Coyotes killed 73 of 958 lambs and 6 of 624 ewes between 24 April and 15 August 1975. Twenty ewes and 19 lambs died from non-predatory causes. Coyote-kills accounted for 79.3% of the lamb losses. The amount of time ewes spent at various activities differed significantly by age or genotype, but the behavior of ewes whose lambs were killed was remarkably similar to that of other ewes. Single lambs were more active and were killed proportionately more often than twins. Within litters in which one of the lambs was killed, the killed sibling tended to be more active. Coyotes killed proportionately more disabled lambs and lambs from disabled ewes than healthy lambs or lambs from healthy ewes. Reduced mobility of either a lamb or a ewe increased the probability of a lamb's being on the periphery of the bed-ground and, hence, the probability that it would be noticed and attacked by a coyote. Coyote predation on domestic sheep was related more to the chance of an animal's being on the periphery of the bed-ground than to the animal's behavioral characteristics.     

In vivo and in vitro fertilizing capacity of cryopreserved European mouflon [Ovis gmelini musimon] spermatozoa used to restore genetically rare and isolated populations

European mouflon sheep are an endangered species of ovidae residing primarily in the mountenous habitat of the islands of Sardinia and Corsica. The purpose of this study was to assess the fertilizing capacity of cryopreserved European mouflon spermatozoa after AI in synchronized mouflon and domestic ewes and after IVF in in vitro matured mouflon and domestic ewe oocytes collected by OPU technique. Domestic ram (Ovis aries) spermatozoa served as control. Semen was collected by artificial vagina from three mouflons and three domestic rams during the breeding season and was cryopreserved. At thawing, no significant differences in sperm viability were found between the wild and the domestic species (53.1 +/- 4.6% versus 56.0 +/- 4.7%) whereas the percentage of acrosome-intact sperm was lower in mouflon (55.5 +/- 4.6%) than in ram semen (62.7 +/- 3.1%; P < 0.05). Lambing rate did not differ between synchronized mouflon and domestic ewes (5/11 versus 8/12) after 150 and 156 days of pregnancy, respectively. After two OPU sessions, 87 and 132 oocytes were collected from three hyperstimulated mouflon and three domestic ewes. Cryopreserved/thawed semen was inseminated with an endoscope into the uterus of corresponding species during the non-breeding season. The oocytes were matured and fertilized in vitro; 61/73 mouflon and 81/101 domestic ewe oocytes were found to be fertilized. From these, we obtained 6/61 and 17/81 blastocysts. After vitrification and thawing, the hatching rate showed no significant difference between mouflon and sheep blastocysts (4/6 versus 14/17). In conclusion, our data showed that cryopreserved mouflon spermatozoa can be successfully used to carry out a genuine and complete program of genetic restoration in small and isolated groups of European mouflons.     

Estimates of early embryonic loss in ewes mated to rams selected for high and low prolificacy

Two closed lines of sheep selected for high and low prolificacy were established in 1969. Rams within each line were selected on the basis of their dams' lambing records. Foundation ewes were assigned at random to selected rams, and no ewe selection was practiced until replacement yearlings were selected for mating. Selection of the rams used to mate the foundation ewes resulted in more lambs born per 100 ewes exposed to the ram (P<.10) and more lambs born per 100 ewes lambing from the high line rams (P<.05).Seven rams from each line were then used to estimate fertilization rate and embryonic survival rate when mated to an unrelated group of ewes. There was no difference in ovulation rate or fertilization rate of ewes mated to low and high line rams. Percent eggs recovered per CL was 80 and 92 (P<.01) for low and high line rams, respectively. At 35 days 82 and 86% of the ewes were pregnant, and 84 and 93% of the CL were represented by embryos in the pregnant ewes mated to low and high lines, respectively. Estimated embryonic survival rates were 81 and 89% in ewes mated to low and high line rams, respectively.     

Inheritance of an ovine lysosomal storage disease associated with deficiencies of beta-galactosidase and alpha-neuraminidase

Prospective and retrospective genetic studies were performed on sheep with a recently described inherited lysosomal storage disease that involves a profound deficiency of beta-galactosidase and an associated deficiency of alpha-neuraminidase. Retrospective studies of the flock of sheep in which four affected lambs were born indicated little inbreeding but the presence of a common ram in both the maternal and paternal sides of the pedigrees. When unrelated rams were used in the flock in subsequent years, no affected lambs were born. The affected lambs' parents were phenotypically normal, so the disease was investigated as a putative autosomal recessive condition in prospective breedings of related sheep over two breeding seasons. For the third breeding season, heterozygous ewes were superovulated and bred to a heterozygous ram, and the resultant embryos were transferred to recipient ewes. Later in the same breeding season, the heterozygous ewes were re-bred naturally to the heterozygous ram. Lambs were identified as affected by the development of signs of ataxia, levels of beta-galactosidase that were less than 7% of the levels in controls by spectrofluorometric assay, or the histopathologic demonstration of vacuolization of neurons. Heterozygous sheep were identified by the production of affected offspring and/or by levels of beta-galactosidase in fibroblast cultures that were approximately 50% of control levels. The phenotypic ratio of affected sheep to normal sheep and the genotypic ratio of affected to heterozygous to normal sheep were consistent, by chi-square analysis, with an autosomal recessive trait. It was concluded that this ovine lysosomal storage disease is an autosomal recessive disease.     

Sarcocystis Infection in Sheep from South-Western Norway

The occurrence of Sarcocystis infection and pathological changes were recorded in samples of the heart, diaphragm, and oesophagus from 198 healthy sheep representing 3 different age groups, obtained from an abattoir. The infection rate of S. gigantea (syn. S. tenella) was 18.2 %, and the distribution within groups was: ewes 30.0 %, yearlings 11.6 %, lambs nil. The infection rate of S. tenella (syn. S. ovicanis) was 65.1 %, and the corresponding distribution was: ewes 83.5 %, yearlings 74.4 %, and lambs 25.0 %. A third type of Sarcocystis sp. displaying thick wall was found in 3 samples. Focal interstitial infiltrates of mononuclear cells were demonstrated in 47.9 % of the hearts, in 19.6 % of the diaphragms and in 31.3 % of the oesophagi. The occurrence of Sarcocystis and the focal interstitial mononuclear cell infiltrates were positively correlated (P < 0.0001). Morphologically identical sporocysts typical of S. tenella were produced by dogs and foxes fed naturally infected sheep tissues. A cat fed S. gigantea macrocysts produced sporocysts characteristic for the species. Sarcocystis; pathology; life cycle; final hosts; sheep.     

Control of oestrus in ewe lambs and yearling ewes with medroxyprogesterone acetate and fluorogestone acetate

Two experiments were conducted in a large flock of Berrichon purebred and Romanov × Berrichon F₁ crossbred ewes. In experiment 1, 157 ewe lambs were placed in six groups according to season of mating and maternal breed. Within each group equal numbers of females were treated with either medroxyprogesterone acetate (MAP) or fluorogestone acetate (FGA)-impregnated sponges for 14 days; dosage of PMSG at the time of sponge removal was 500 and 300 I.U. respectively for pure and crossbred. In experiment 2, 111 dry yearling ewes of the Berrichon breed were involved, of which 35, 51 and 25 had either a short lambing to treatment interval (approximately 3 months), a long lambing to treatment interval (approximately 6 months), or were primiparous or nulliparous. They were also treated either with MAP or FGA.The conception rates were extremely high (overall near 86%) in ewe lambs and not significantly affected by seasons or breeds or treatments. Prolificacy and number of lambs per ewe mated were higher in the F₁ crossbred group than in pure Berrichon females (respectively 1.91 vs. 1.34 lambs/mated ewe). No significant difference between the two progestagens could be observed for any of the productivity criteria. Fertility was equally satisfactory in yearlings (overall near 85%) irrespective of the interval between lambing and mating. However, the fertility of the nulliparous ewes (those that failed to conceive as ewe lambs) was significantly lower (72%). The number of lambs per ewe mated was 1.78 in yearlings with a 6-month interval from lambing to mating but was not significantly different from the numbers recorded in the other two groups (1.37 and 1.36). As in experiment 1, there was no difference in the results obtained after either of the two progestagen treatments.In conclusion, progestagen treatment has been shown in both ewe lambs and yearlings to be a very effective means of increasing lamb production in large flocks. This was achieved in ewe lambs regardless of the season and, in dry yearling ewes, regardless of the interval from lambing to mating in the anoestrous season.     

Effects of the Booroola (FecB) genotypes on growth performance, ewe's productivity efficiency and litter size in Garole x Malpura sheep

The present study was conducted to evaluate the effects of FecB genotypes on body weight, average daily gain (ADG), ewe's productivity efficiency (EPE) and litter size in FecB introgressed GarolexMalpura (GM) crossbred sheep. A total of 235 GM lambs were selected randomly and screened for FecB mutation using forced RFLP-PCR. The majority (69.8%) of GM individuals were carriers (BB and B+) for the FecB mutation and frequency of the FecB allele was about 0.40. The FecB genotypes were significantly (P<0.01) associated with the lamb's body weights from birth to 12 months of age. The generation wise (F(1), F(2) and F(3)), lamb's body weight did not differ significantly at birth, 6 and 12 months of the age, while it differed significantly (P<0.05) at 3 and 9 months of age. The ADG1 (0-3 months) was significantly associated (P<0.05), but not the ADG2 (3-6 months) and ADG3 (6-12 months) between genotypes. Type of birth and sex significantly (P<0.01) affected the body weight from birth to 12 months of age; and body weight of single born lambs was significantly higher (P<0.01) than that of twins and triplets from birth to 12 months of age. Type of birth significantly (P<0.01) affected the ADG1, but had no significant effect on ADG2 and ADG3. Year of birth did not affect the birth and weaning weights, but it significantly affected (P<0.01) the body weight and ADG's after weaning ages. The EPE was affected significantly (P<0.01) by the FecB genotypes at birth, 3 and 12 months of age. The EPE of B+ and BB ewes were 7.86 kg (36.9%) and 2.32 kg (10.9%) higher as compared to ++ ewes at 12 months of age, respectively. The mean litter size of BB ewes (2.17+/-0.24) was significantly higher (P<0.01) than that of B+ ewes (1.73+/-0.04) and ++ ewes (1.03+/-0.23). The present study indicated that the body weight and ADG of carrier lambs (BB and B+) was comparatively lower than that of non-carriers (++), while EPE of B+ ewes was comparatively higher than that of BB and ++ ewes. Further, it is interesting to note that heterozygous and homozygous state of individuals increased 0.70 and 1.14 extra lambs as compared to non-carriers (++), respectively.     

Nursing behaviour of bighorn sheep: correlates of ewe age,parasitism, lamb age,birthdate and sex

The nursing behaviour of marked bighorn ewes, Ovis canadensis, and their lambs was observed in Alberta, Canada, for 2 years. Suckle duration decreased as lambs grew older. Nursing behaviour in midlactation was correlated with maternal condition; young ewes, ewes with high faecal counts of lungworm (Protostrongylus spp.) larvae, and ewes whose lambs were born late allowed shorter suckles and were less likely to nuzzle their lamb's rump during a suckle. Sons did not appear to receive more milk than daughters. Suckle duration in mid-lactation was correlated with survival for female lambs but not for males. Lambs born late were disadvantaged, probably because nutritious forage was accessible to their mothers only in early lactation.     

The effect of prenatal photoperiodic history on the postnatal endocrine status of female lambs

Postnatal photoperiodic experience plays a pivotal role in determining the timing of ovarian activity in female lambs. This study examines whether a photoperiodic history gained while in utero is able to influence this timing.Pregnant Soay ewes were maintained in either long days (n = 7, 18 h light : 6 h dark; group PLD) or short days (n = 12, y h light : 18 h dark; group PSD) from 25 days of gestation. At birth, female lambs (n = 8 per group) were transferred to long days for 10 weeks, and then placed under short days until the end of the experiment at 38 weeks of age. Blood samples were collected from lambs on the day of birth and three times weekly for the duration of the study and the resulting plasma assayed for progesterone and prolactin.Although both gestational photoperiods produced, at best, abbreviated periods of ovarian activity, lambs born to ewes which experienced long days during gestation (group PLD) exhibited elevated plasma progesterone concentrations significantly earlier (P < 0.05) than lambs born to ewes exposed to short days during gestation (group PSD) (mean ± SEM, 193 ± 17 versus 244 ± 14 days for PLD and PSD groups, respectively. Plasma prolactin concentrations in newborn lambs born between late December and early April were not affected by the ambient photoperiod, but reflected the artificial daylength experienced by their mothers during gestation. Lambs born to ewes maintained under long days during gestation (group PLD) had significantly higher prolactin concentrations on the day of birth than lambs born to ewes maintained under short days during gestation (group PSD) (45 ± 5.4 ng/ml versus 7 ± 3.7 ng/ml respectively, P < 0.001). The mean birth weight, rate of live weight gain and live body weight of lambs at the end of the experiment did not vary significantly between treatment groups. These results suggest that the ovine foetus is sensitive to photoperiodic information prior to birth, and develops a photoperiodic history which, under the present experimental conditions, modulates the subsequent endocrine status of the neonatal lamb.     

Effects of social status, age, and season on androgen and cortisol levels in wild male golden lion tamarins (Leontopithecus rosalia)

This study examines factors affecting androgen and cortisol levels in wild, male golden lion tamarins (Leontopithecus rosalia). Golden lion tamarins are a cooperatively breeding species in which groups often contain two potentially breeding males. Brothers frequently emigrate together and develop a clear dominance hierarchy, but interactions between them are primarily affiliative. Duos in which the males are not related are less stable. In addition, reproductive skew theory predicts that dominant males will be less likely to share reproduction with related subordinates. As such, we predicted that both androgens and cortisol would be higher in subordinate males unrelated to the dominant male. We also predicted that androgens in breeding males would be higher during the mating season than the birth/infant care season, as per Wingfield's "challenge hypothesis" (1990). Fecal samples were collected from 24 males in 14 social groups and assayed by enzyme immunoassay. Androgen levels were higher in breeding males during the mating season, thus supporting the challenge hypothesis. However, while subordinate males unrelated to the dominant male had significantly lower androgens than any other group, cortisol levels were not correspondingly higher. These results suggest that unrelated subordinate males show measurable reproductive suppression and may use strategies such as infantilization to avert aggression from dominant males.