Mass- and density-dependent reproductive success and reproductive costs in a capital breeder

For capital breeders, mass may affect reproductive potential. Reproductive expenditure may reduce future reproductive potential, particularly when resources are scarce. To test the hypothesis that reproductive success and the costs of reproduction vary according to mass and population density, we analyzed 25 yr of data on bighorn ewes (Ovis canadensis). The number of adult females was first limited by yearly removals, then allowed to triple. We found no survival costs of reproduction for ewes aged 4-7 yr. For ewes aged 8-14 yr, survival was density dependent for barren ewes but not for ewes that weaned lambs. Failure to lamb was rare and negatively correlated with fertility the following year. At low population density, lactation had a negative effect on mass gain but had a limited reproductive cost. At high density, heavy ewes had higher reproductive success than light ewes, and the reproductive cost and somatic costs of reproduction increased. The cost of reproduction was greater for light than for heavy ewes. Survival of weaned lambs to 1 yr was affected by population density but not by maternal mass or previous reproductive success. In large mammals, manipulations of reproductive effort are problematic, but long-term monitoring of individual mass and reproductive success under varying conditions of resource availability can provide insights into the evolution of life histories.     

Do Reproductive Status and Lamb Gender Affect the Foraging Behavior of Bighorn Ewes?

In female ungulates lactation carries a high energetic cost and mothers often devote more care to sons than to daughters. The aims of this study were to determine whether lactating bighorn ewes have higher foraging time, bite rate or selectivity of forage than barren ewes and whether reproductive status affects migration patterns. Ewes with male lambs were predicted to spend more time foraging and to have a higher bite rate than ewes with female lambs. There were no differences in foraging behavior according to ewe reproductive status from April to August. In September-November lactating ewes had a higher bite rate and spent more time foraging than nonlactating ewes but lamb gender did not affect foraging behavior. Lactating ewes gained less weight than nonlactating ones until mid-August; from mid-August to late September mass gain was similar for both groups of ewes. Nonlactating ewes spent more time standing but reproductive status did not affect vigilance behavior or step rate while foraging. Ewes with lambs did not differ from nonlactating ewes in step rate. Pregnant ewes migrated earlier than barren ewes to alpine areas in spring. By so doing they abandoned areas with good quality forage presumably to give birth in areas safer from predation. All ewes spent most of the summer in the alpine range but nonlactating ewes returned to the winter range earlier than lactating ewes, probably to profit from the abundant forage there.     

Determinants and consequences of age of primiparity in bighorn ewes

Because variation in age of first reproduction can have major effects on individual fitness and population dynamics, it is important to understand what maintains that variability. Although early primiparity is assumed to be costly, it is sometimes associated with high lifetime reproductive success. We used a long‐term study on bighorn sheep Ovis canadensis to determine what variables affect age at first reproduction, investigate the impact of primiparity on body resources and quantify the reproductive performance of primiparous ewes. We then examined the consequences of delayed primiparity on adult body mass, longevity and lifetime reproductive success. Environmental conditions during early development, body mass as a yearling, genotype and maternal effects affected age of primiparity. Primiparous ewes lost more mass in winter and gained less mass in summer than multiparous ewes. Small yearling ewes that postponed reproduction attained similar adult mass than heavy yearling ewes who reproduced at a younger age. Early primiparity did not reduce longevity and was positively associated with lifetime reproductive success. Starting to reproduce as soon as possible appears to maximize fitness of females. When early life conditions are unfavorable, however, delayed primiparity allows greater body growth and likely maximizes survival. The combination of a conservative reproductive strategy and maternal effects on age of primiparity may partly delay population recovery following density‐dependent declines.     

Variation in the timing of the reproductive season among breeds of sheep in relation to differences in photoperiodic synchronization of an endogenous rhythm.

Photoperiod may regulate seasonal reproduction either by providing the primary driving force for the reproductive transitions or by synchronizing an endogenous reproductive rhythm. This study evaluated whether breed differences in timing of the reproductive seasons of Finnish Landrace (Finn) and Galway ewes are due to differences in photoperiodic drive of the reproductive transitions or to differences in photoperiodic synchronization of the endogenous rhythm of reproductive activity. The importance of decreasing photoperiod after the summer solstice in determining the onset and duration of the breeding season was tested by housing ewes from the summer solstice in either a simulated natural photoperiod or a fixed summer-solstice photoperiod (18 h light:6 h dark; summer-solstice hold). Onset of the breeding season within each breed did not differ between these photoperiodic treatments, but Galway ewes began and ended their breeding season earlier than Finn ewes. The duration of the breeding season was shorter in Galway ewes on summer-solstice hold than on simulated natural photoperiod; duration did not differ between photoperiodic treatments in Finn ewes. The requirement for increasing photoperiod after the winter solstice for initiation of anoestrus was tested by exposing ewes from the winter solstice to either a simulated natural photoperiod or a winter-solstice hold photoperiod (8.5 h light:15.5 h dark). Onset of anoestrus within each breed did not differ between these photoperiodic treatments, but the time of this transition differed between breeds. These observations suggest that genetic differences in timing of the breeding season in Galway and Finn ewes do not reflect differences in the extent to which photoperiod drives the reproductive transitions, because neither breed requires shortening days to enter the breeding season or lengthening days to end it at appropriate times. These findings are consistent with the hypothesis that photoperiod synchronizes an endogenous rhythm of reproductive activity in both breeds and that genetic differences in timing of the breeding season reflect differences in photoperiodic synchronization of this rhythm.     

Does seasonal reproductive state affect the neuroendocrine response of the ewe to a long-day pattern of melatonin?

This study examined whether or not the reproductive response of female sheep to photoperiod varies with seasonal reproductive state. The specific objective was to test the hypothesis that the reproductive response to a long-day pattern of melatonin varies with the reproductive state of the ewe. The response examined was the synchronization of reproductive neuroendocrine induction (rise in serum luteinizing hormone, or LH) following nocturnal infusion of melatonin into pinealectomized ewes for 35 consecutive nights. This infusion restored a pattern of circulating melatonin similar to that in pineal-intact ewes maintained in a long photoperiod (LD 16:8). The ewes had been pinealectomized and without melatonin replacement for 16-25 months prior to the study. They were in differing reproductive states at the start of the infusion, as their endogenous reproductive rhythm had become desynchronized among individuals and with respect to time of year. Noninfused pinealectomized ewes served as controls. Regardless of the reproductive state at the start of the 35-day infusion of the long-day pattern of melatonin, all treated ewes exhibited the same reproductive neuroendocrine response after the infusion was ended. This consisted of a synchronized rise in LH some 6-8 weeks after the infusion was terminated, the maintenance of a high level of serum LH for some 15 weeks, and a subsequent precipitous fall in LH to a very low level. These results provide evidence that a long-day pattern of melatonin can synchronize reproductive neuroendocrine induction in the ewe, regardless of reproductive condition, and thus do not support the hypothesis that this response differs with seasonal reproductive state.     

Melatonin and photorefractoriness: loss of response to the melatonin signal leads to seasonal reproductive transitions in the ewe

Experiments were conducted to examine whether the refractoriness of the Suffolk ewe to the reproductive effects of day length is associated with a deficit in the generation of the circadian rhythm of melatonin secretion or in the postpineal processing of this photoperiodic message. Using serum luteinizing hormone (LH) concentrations in ovariectomized ewes bearing constant-release estradiol implants as a marker of reproductive induction, ewes with intact pineal glands were found to become unresponsive to fixed artificial photoperiods that initially had been either inductive (short days) or inhibitory (long days). The loss of the photoperiodic response was not associated with notable changes in the 24-h secretory pattern of melatonin, which remained characteristically low throughout the day and rose at night. In pinealectomized ewes, nightly infusion of a stimulatory pattern of melatonin (simulating that seen on short days) initially provoked reproductive induction; this response then lessened over much the same time course that pineal intact ewes became refractory to short days. These results support the hypothesis that photorefractoriness reflects a deficit in the postpineal processing of the photoperiodic message. Further, in view of recent evidence that photorefractoriness normally leads to both onset and cessation of the breeding season in Suffolk ewes maintained outdoors, these findings suggest that the loss of response to the melatonin signal contributes to at least one of these reproductive transitions, the cessation of the breeding season, under natural environmental conditions.     

What photoperiodic signal is provided by a continuous-release melatonin implant?

The purpose of this study was to evaluate whether the insertion of a continuous-release melatonin implant into ewes provides a short-day photoperiodic signal or acts as a functional pinealectomy (provides no specific photoperiodic signal but renders ewes incapable of responding to changes in photoperiod). Ewes primed with 60 long days (18L:6D) during the spring were moved to intermediate day length (13L:11D) for 66 days and then given one of five treatments: 1) short-day control, second drop in photoperiod to 8L:16D; 2) intermediate-photoperiod control, kept on 13L:11D; 3) pinealectomy and kept on 13L:11D; 4) melatonin implant and kept on 13L:11D; 5) melatonin implant and moved to 8L:16D. Mean number of estrous cycles per group and total duration of reproductive activity were determined. Ewes in all groups began to exhibit estrous cycles after the initial reduction in photoperiod. The number of estrous cycles and duration of reproductive activity differed among groups. The number of estrous cycles and duration of reproductive activity was extended in ewes receiving the second drop in photoperiod compared to that of the intermediate-photoperiod controls. Pinealectomized ewes had a number of estrous cycles and duration of reproductive activity similar to those of ewes maintained on the intermediate photoperiod. Melatonin implants increased the number of estrous cycles and prolonged reproductive activity in ewes maintained on the intermediate photoperiod; melatonin implants did not prevent the extension of reproductive activity in ewes receiving the second photoperiodic drop to the short daylength.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of insulin on feed intake and reproductive performance of well-nourished nulliparous ewes

Eighty-four nulliparous ewes were used to examine the effect of short-term insulin treatment on feed intake and reproductive performance. Following estrus synchronization, ewes were observed for estrus (= Day 0) and were penned individually beginning on Day 7. Ewes were fed twice daily and feed intake was recorded. On Days 9 through 13, ewes were treated s.c. with 1 IU/kg BW insulin (n = 44) or an equivalent volume of saline (n = 40). On Day 14, ewes were placed with fertile rams and number of ewes in estrus (bred) was recorded. Thirty days post-breeding, ewes were checked for pregnancy via ultrasonography. Feed intake and percentage of ewes in estrus did not differ between saline- and insulin-treated ewes. Similarly, neither pregnancy rate (69 +/- 8.7% vs. 80 +/- 8.1%, respectively) nor lambing rate (61 +/- 8.9% vs. 78 +/- 8.4%, respectively) differed between treatments. The number of lambs born per ewe was, however influenced by a breed-group effect (P < 0.0002). Romanov ewes had more (P < 0.001) lambs than the other breed groups in the study. Therefore, treating well-nourished, nulliparous ewe lambs with insulin did not increase reproductive efficiency, possibly because the ewes were already at a maximal nutritional and/or reproductive state.     

Prenatal programming of reproductive neuroendocrine function: the effect of prenatal androgens on the development of estrogen positive feedback and ovarian cycles in the ewe

Exposure of the female ovine fetus to male hormones during a sensitive window of in utero life causes disruption to reproductive function. In some animals, androgen exposure completely abolishes reproductive cycles, but in others, cycles are progressively lost with age. The present study tested two predictions: that noncycling, androgenized animals are unable to respond to estrogen with a preovulatory-like surge of LH (estrogen positive feedback), and that the androgenized animals that exhibit a progressive loss of cycles also show a progressive loss of estrogen positive feedback. Androgenized ewes were generated by injection of their mothers with testosterone propionate twice per week from Day 30 to Day 90 of pregnancy (term, 147 days). Control ewes received no injections. Whether ewes could exhibit estrogen positive feedback was tested on five occasions before puberty (30 wk) and once during the anestrous period. All control animals had repeated reproductive cycles in both the first and second breeding season, and all showed robust LH surges during test periods. Despite the fact that 64% of androgenized animals showed reproductive cycles, estrogen positive feedback could be demonstrated in only 6.1% of trials. Subsequent experiments revealed that the lack of response to estrogen in androgenized animals was not because of pituitary insensitivity to GnRH, a requirement for higher concentrations of estrogen, or a surge that was delayed relative to the time of estrogen administration. The mechanisms by which some androgenized ewes can produce normal reproductive cycles in the apparent absence of estrogen positive feedback are currently unknown.     

Effect of the nutritional environment and reproductive investment on herbivore-parasite interactions in grazing environments

Parasitism is a serious challenge to herbivore health and fitness.To avoid parasites, herbivores avoid grazing near feces, creatinga mosaic of contaminated tall avoided areas (tussocks) and noncontaminatedshort grazed areas (gaps). The mosaic represents a nutritionversus parasitism trade-off in that feces-contaminated tussocksare localized concentrations of both forage resources and parasites.Here, we use a grazing experiment with a natural tussock–gapmosaic to determine how the nutritional environment and reproductiveeffort affect sheep grazing decisions when faced with this trade-off.There were 3 animal treatments (Barren ewes, ewes suckling asingle lamb, and ewes suckling twin lambs) and 2 environmenttreatments (low and high nitrogen). Sward selection and grazingbehavior were measured using focal observations on grazing ewes.Sheep showed an overall strong and significant avoidance oftussocks across all treatments. However, there was a reductionin the avoidance of tussocks by ewes on the low-nitrogen (low-N)plots. Ewes suckling twins showed a reduced avoidance of tussockscompared with barren ewes. Lactating ewes in low-N environmentsfurther reduced their avoidance of tussocks. Ewes with twins,which are at greatest risk from parasites, had the greatestcontact with feces and thus parasites, especially in low-N environments.We conclude that twin-bearing ewes accept the increased riskof parasitism in order to gain the nutrients required to supportincreased reproductive effort, thus increasing their investmentin current offspring at the cost of increased risk of parasitismand thus future potential reproductive attempts.     

Effect of immunization on reproducvive performance, embryo quality and progesterone in Rasa Aragonesa ewes actively immunized against androstenedione or passively immunized against testosterone

A total of 217 Rasa Aragonesa ewes were used to test two immunization treatments: 1.Active immunization against androstenedione: ewes immunized in previous matings (androstenedione, reimmunized; AR groups, n=58) or not (first immunization; AF groups n=64) were boosted either 2 or 4 wk before mating. 2.Passive immunization against testosterone: antisera were injected either at sponge withdrawal (zero time; T0 group, n=21) or 1 wk previously (Tl group, n=22). We used 52 ewes as controls (C group). Half of each group was used either to record reproductive performance or to embryo viability assessment. Prolificacy was significantly increased in ewes which reached a moderate antibody level, independently of the treatment. Fertility was lower in AR ewes that attained a high antibody titre (P<0.01). The percentage of viable embryos recovered was lower in AF ewes (P<0.01), and in ewes whose testosterone antibody titre was high (P<0.05), compared to C group. It was proven that similar or lower antibody levels were more harmful for ewes from AF and Tl than for ewes from AR or T0 groups. The proportion of nonfertilized recovered ova was not significant. Progesterone levels were notably increased in AR ewes (P<0.001) independently of ovulation rate and were positively correlated to antibody titre at mating (P<0.01) but these events were not observed in T ewes. These findings indicate that after androgen immunoneutralization, only those ewes having antibody titres within a limited range at mating had improved reproductive performance. Further research is needed in order to understand the role that progesterone plays in immunized ewes.     

Synchronization of the circannual reproductive rhythm of the ewe by discrete photoperiodic signals

Although many species display endogenous circannual rhythms of biological activity that are synchronized by day length, the specific photoperiodic requirements for synchronizing such rhythms are not established for any species. We tested the hypothesis that the circannual reproductive rhythm of sheep can be synchronized by exposure to just one or two discrete blocks of photoperiodic information each year. Ewes were pinealectomized to prevent their ability to transduce photoperiodic information into altered reproductive neuroendocrine activity. During the 53/4 yr following pinealectomy, specific photoperiodic signals were restored for discrete periods of time via replacement of 24-h patterns of melatonin, the pineal hormone that transmits photic information to the reproductive neuroendocrine axis. The ewes were kept in a 12-mo photoycycle that alternated between short (8L:16D) and long (16L:8D) days every 6 mo and that was 6 mo out of phase with the geophysical year. Pineal-intact control ewes exhibited synchronous annual reproductive cycles. Noninfused pinealectomized control ewes did not exhibit synchronous cycles. Pinealectomized ewes infused with alternating 70-day blocks of short- and long-day patterns of melatonin every 6 mo for the first 21/2 yr of the experiment exhibited synchronous annual reproductive cycles that were 6 mo out of phase with those of ewes maintained outdoors. This synchrony persisted when the frequency of the melatonin treatment was reduced to just one 70-day block of a long-day pattern of melatonin each 365 days. Cycle period was 368 +/- 3 days; standard deviation of the date of onset of reproductive induction averaged only 3 days. Our study provides the first direct evidence that a single block of photoperiodic information a year can synchronize a circannual rhythm.     

Effects of retention of fetal membranes on subsequent reproductive performance of dairy ewes

Seventy-one pairs of ewes with or without retention of fetal membranes in the previous lambing season, were included in a cohort study of 25 flocks in southern Greece; in 27 pairs regulation of the breeding cycle was applied, whilst in the other 44 pairs natural mating took place. The following measures of reproductive performance were calculated: cycling rate, mating rate, return-to-estrus rate, abortion rate, lambing rate, total lambs born per ewe, liveborn lambs per ewe, stillbirth rate, lamb-bodyweight per ewe; furthermore, the incidence risk of retention of fetal membranes during the lambing examined in this study was also calculated. No statistically significant differences were observed in the reproductive performance among ewes that had or had not retained their fetal membranes during the previous lambing, whether the breeding cycle was regulated or not. The incidence risk of retention of fetal membranes among ewes that had not retained its placenta in the previous lambing was 1.6%, whilst that among ewes that had retained its placenta in the previous lactation was 0%. It is concluded that retention of fetal membranes did not appear to adversely affect subsequent reproductive performance of ewes.     

The influence of earlier mating experience of ewes on their subsequent mating behaviour and reproductive performance

The animals used in the experiment consisted of 411 aged (parous), and 171 maiden ewes (18 months old) and 17 rams. In total 357 observations were made during mating (272 on parous and 85 on maiden ewes). The average mating time for the parous ewes was 58.26 s, and for the maidens 97.0 s. The difference was highly significant (P < 0.01). Mean numbers of mounts per ejaculation for parous and maiden ewes were 2.17 and 2.53 respectively. The difference was highly significant (P < 0.01) and was caused, among other factors, by the reluctant standing attitude of maiden ewes. The results confirm that difficulties exist in the serving fo maiden ewes.The reproduction indices were calculated on the basis of service during the first oestrus in the mating season. The pregnancy rate was 56.45% for older ewes and 54.04% for maidens, the difference being not significant. The lambing rate was 113.3% and 110.3% for parous and maiden ewes respectively, the difference being statistically insignificant. The absence of divergence of reproduction indices between the two groups suggests that the difficulty in serving maiden ewes is due to their lack of reproductive experience which does not influence their reproductive capacity.     

Circannual cycles of luteinizing hormone and prolactin secretion in ewes during prolonged exposure to a fixed photoperiod: evidence for an endogenous reproductive rhythm

Circulating patterns of luteinizing hormone (LH) and prolactin (PRL) were monitored for 5 yr in ewes maintained either outdoors in natural conditions or indoors in a fixed, short photoperiod (8L:16D). The ewes were ovariectomized and each was treated with a Silastic implant containing estradiol to provide a fixed negative feedback signal to the reproductive neuroendocrine axis. Serum concentrations of LH and PRL were subjected to a statistical algorithm developed for the purpose of detecting hormone cycles. In ewes maintained outdoors, serum concentrations of both hormones underwent high amplitude cycles with a period no different from 365 days. Among ewes maintained in the fixed photoperiod, unambiguous cycles of LH and PRL persisted through the 5 yr of exposure to short days. Period of these cycles differed from 365 days. Further, the LH cycles became desynchronized among ewes housed together and desynchronized with respect to the LH cycles in ewes kept outdoors. These findings document the existence of an endogenous circannual rhythm of reproductive neuroendocrine function in ewes.     

Reproductive activity of Pelibuey and Suffolk ewes at 19 degrees north latitude

Under photoperiod regulated conditions, some Pelibuey ewes appear to express estrous cycles continuously throughout the year. Ovulatory activity of Suffolk ewes has not being determined at 19 degrees N. The aim of the present study was to describe the annual reproductive cycle of Pelibuey and Suffolk ewes under natural conditions at 19 degrees N. Ten adult ewes of each breed were maintained under natural environmental conditions, on a constant plane of nutrition and isolated from rams. The ovulatory activity of both breeds was monitored over 2 years (2003 and 2004) by quantifying progesterone concentrations in blood samples taken twice a week. For both breeds, the proportion of ovulating ewes per month and year was analyzed by chi(2). The duration of anestrus was compared between breeds and years by analysis of variance. Correlation of ambient temperature and weight changes with the ovulatory activity was evaluated by regression procedure. Ovulatory activity was different (P<0.05) between breeds from February to July. Pelibuey sheep (60%, 6 of 10) ovulated continuously during the entire study; one animal was eliminated in the second year, due to ovarian follicular cysts and three ewes had anestrous periods from 65+/-46 to 70+/-36 days. Suffolk ewes displayed reproductive seasonality similar to that observed in sheep of the same breed in latitudes greater than 35 degrees . Within breed, reproductive behavior of sheep was similar between years, with the only difference (P<0.05) observed in February for Pelibuey and in July for Suffolk relative to other months. Ambient temperature was not correlated with ovulatory activity. The body weight of Pelibuey ewes was constant during the entire study and was not correlated with ovulatory activity. There was, however, an increase on the body weight of Suffolk ewes, but this variation was not related to ovulatory activity. These findings lead to the conclusion that at 19 degrees N, a high proportion of Pelibuey ewes is capable of ovulating throughout the year, whereas Suffolk ewes undergo seasonal anestrous periods similar to those observed in individuals of the same breed at latitudes greater than 35 degrees . Identification of continuous ovulatory Pelibuey ewes may be the first step for developing a selection program against seasonality to increase lambing frequency.     

The influence of haemoglobin types on reproduction and production in Hungarian Merino sheep

Fewer Hb A and AB lambs were born than expected in the investigated Hungarian Merino population but the factors responsible for these differences could not be identified. The Hb A and AB breeding ewes were not inferior to their B type herd mates with respect to average daily weight gain (when lambs), reproductive performance (prolificacy) and survival rate. Their reproductive performance was, in some cases, even better than that of the ewes with other haemoglobin types. The haemoglobin types cannot be used as markers when selecting for higher prolificacy.     

Consistency of temperament in bighorn ewes and correlates with behaviour and life history

Individual differences in temperament may affect how animals react to novel situations, avoid predation, invest in reproduction and behave in a variety of social contexts. Little information is available, however, about individual differences in temperament for wild animals. For bighorn sheep, Ovis canadensis, ewes captured as part of a long-term study, we compared behaviour during handling to behaviour in the field and reproductive history. We considered 'bold' ewes those that were frequently trapped during the summer, and assigned to each ewe a docility index based on her behaviour during handling. Measurements of temperament for the same individual at different captures were highly consistent. Temperament was not affected by reproductive status or age, nor was it related to body mass. Correlations between behaviour at the trap and in the field were weak and mostly nonsignificant, suggesting that temperament is domain specific rather than domain general. Bold ewes tended to start reproducing earlier and have higher weaning success than shy ewes. Variability in temperamental traits in the study population could be maintained by life-history trade-offs and by yearly changes in selective pressures. Copyright 2000 The Association for the Study of Animal Behaviour.     

Postpartum uterine and ovarian changes, and estrous behavior from lactation effects in normal and hormone treated ewes.

The influence of (1) lactation and (2) three different hormone treatments were measured in fall lambing ewes. By day 67 postpartum, considering lactation effect, 89% of nonlactating and 33 % of lactating ewes showed estrous behavior (P<0.05). Nonlactating control ewes ovulated significantly sooner postpartum than ewes in other treatment groups. Both nonlactating and lactating ewes ovulated prior to demonstrating estrus. In the hormone treatments those containing estrogen tended to have earlier estrus which is assumed to reflect a direct effect. Uterine involution in all animals was generally complete by day 24. No apparent treatment differences in uterine epithelial cells, gland number and size, edema, or interstitial hemorrhage were noted during the 67-day postpartum period studied. Data from this study indicate that the reproductive tract appears acceptable for rebreeding several weeks before the ewes show behavioral estrus.     

Social cues can play a role in timing onset of the breeding season of the ewe

Female Suffolk sheep were pinealectomized around the vernal equinox to eliminate the major environmental input to the reproductive system (photoperiod) and then either isolated from, or maintained with, pineal-intact gonad-intact sheep. The ewes were ovariectomized and treated with constant-release oestradiol implants and reproductive state was monitored by measuring serum LH concentrations. Pinealectomized ewes that were isolated from the normal flock showed a 2 1/2-month delay in onset of the seasonal rise in LH values compared with that of pineal-intact controls (18 November vs 5 September). On the other hand, pinealectomized ewes that were maintained with the flock showed an onset of the seasonal rise in LH that was not delayed. These results suggest a timekeeping role for social cues for timing onset of the breeding season in an animal that normally relies on photoperiodic signals for temporal regulation of the seasonal reproductive cycle.