Short term, repeated exposure to rams during the transition into the breeding season improves the synchrony of mating in the breeding season

The ram effect is widely used in Mediterranean breeds of sheep but its use in temperate genotypes is restricted by breed seasonality. However, ewes from these highly seasonal genotypes are sensitive to stimulation by rams close to the onset of the natural breeding season. In this study we developed a pre-mating protocol of repeated, short-term exposure to rams (fence-line contact or vasectomised rams) beginning during late anoestrus and continuing into the breeding season. We hypothesised that this pre-mating protocol would synchronise the distribution of mating of North of England Mule ewes during the breeding season above that observed in ewes isolated from rams prior to mating. Ram-exposed ewes were given contact with rams (Experiment 1: fence-line; FR, n = 94 and Experiment 2: vasectomised rams; VR; n = 103) for 24 h on Days 0 (10 September), 17 and 34 of the experiment. Control ewes (Experiment 1; FC, n = 98 and Experiment 2; VC; n = 106) remained isolated from rams prior to mating. In Experiment 2, a subset of VR (n = 35) and VC ewes (n = 35) were blood sampled twice weekly to monitor their pre-mating progesterone profiles. At mating, harnessed entire rams were introduced, 17 or 16 days after the last ram exposure (Experiments 1 and 2) and raddle marks were recorded daily. The median time from ram introduction to mating was reduced in ewes given both fence-line and vasectomised ram contact (P < 0.001), leading to a more compact distribution of mating and lambing (At least P < 0.01). In the blood sampled VR ewes, there was a progressive decline in the number of days from ram exposure to the onset of dioestrus (at least P < 0.05). This observation indicates that the cycles in VR ewes became increasingly synchronised over the pre-mating period, a pattern not evident in VC ewes. In conclusion, repeated, short-term exposure of ewes to rams during the transition into the breeding season is an effective method of synchronising the distribution of mating during the breeding season.     

Male reproductive success in a promiscuous mammal: behavioural estimates compared with genetic paternity

Molecular techniques have enabled behavioural ecologists to reassess mating systems from a genetic perspective. Studies of paternity frequently reveal that mating behaviour does not always reflect parentage, and may bring to light alternative mating tactics. Here we present a comparison of behavioural and genetic measures of male reproductive success in a mammalian mating system in which both sexes are highly promiscuous. Rather than having a stable harem social structure, Soay rams (Ovis aries) on the island of Hirta, St Kilda, UK usually consort with individual oestrous ewes sequentially. Not all matings occur between consort pairs, however, and ewes have been seen to mate with up to 10 different rams on the same day. Using locus-specific polymorphism at five protein and 10 microsatellite DNA loci, we determined paternity for 236 lambs born into three cohorts, and compared paternity with estimates of mating success derived from more than one census of rutting behaviour. The correlation between the number of ewes with which each ram was witnessed in consort and the number of paternities assigned was positive and statistically significant, and rams that were observed in consort with a ewe were 18 times more likely to have sired her offspring than other candidate rams. However, most lambs (73%) were not sired by a ram seen in consort with the oestrous mother. Many juveniles, yearlings and some adult rams were rarely seen in consort with ewes, yet were assigned a significant number of paternities. These results suggest that mating tactics differ between age groups, and that alternative mating strategies among adults that do not involve forming consorts with many females also confer mating success. For these reasons, census-based observations of consort associations between individuals cannot be used to accurately estimate individual male reproductive success in this population.     

Survival and behaviour of castrated Soay sheep (Ovis aries) in a feral island population on Hirta, St. Kilda, Scotland

The free-living population of Soay sheep on the island of Hirta, St. Kilda, in the Outer Hebrides, has been intensively studied since 1959. The present study was initiated to throw light on the causes of the high mortality rate of adult rams in comparison to that of ewes. In 1978, 1979 and 1980, a total of 72 male lambs was castrated within a day or two of birth. The survival of these castrates has been much longer than that of the entire rams, marked as controls, and longer than that of ewes of the cohorts of the same years. The daily activity pattern of the castrates was similar to that of ewes rather than that of rams. In particular, during the rut the castrates spent most of the daylight hours grazing, in contrast to the rams who were continuously moving and involved in agonistic and sexual encounters. This study substantiates the earlier assertion that the costs in energy of reproduction are a major cause of mortality in temperate zone ungulates. The social organization of some castrates was similar to that of females in that they remained with the home-range group of ewes into which they were born, but other individuals resembled males in that these castrates clubbed together in their own groups. These patterns of behaviour persisted throughout life.     

Sheep breeding schemes utilising artificial insemination; large-scale simulation with a complex breeding goal

Alternative Norwegian sheep breeding schemes were evaluated by stochastic simulation of a breeding population with about 120 000 ewes, considering the gain for an aggregate genotype including nine traits and also the rate of inbreeding. The schemes were: a scheme where both young unproven rams (test rams) and proven rams (elite rams) are used in artificial insemination (AI scheme), a scheme with test rams in natural mating in ram circles and elite rams (from one and a half years of age) in AI across all flocks in the country (NMAI2 scheme), a scheme where, in addition to testing rams, the youngest elite rams (one and a half years of age) are also used in natural mating in ram circles, while older elite rams are used in AI (NMAI1 scheme), and a scheme, acting as a control, where both test and elite rams are used in natural mating (NM scheme). Within the NMAI- and AI-schemes, experimentation was performed for percent ewes inseminated to elite rams v. test rams (EM%), numbers of ewes inseminated per elite ram (EAIn), and numbers of ewes mated per test ram by natural service (TNMn) or by AI (TAIn), respectively. With a restriction on the rate of inbreeding (⩽0.8% per generation), the AI scheme gave similar gain to the NMAI2 scheme (and about 40% more than did the NM scheme). Less gain was generated by the NMAI1 scheme, but it was still considerably more than for the NM scheme (about 25%). In the AI scheme, relatively few ewes (200/300) should be inseminated to each test/elite ram, and a low EM% should be chosen (10%). In the NMAI schemes, TNMn should be relatively high (40 to 50), combined with average and somewhat larger than average EAIn (NMAI2: 700 ewes, NMAI1: 900 ewes), and EM% medium (30%).     

Male mate choice influences female promiscuity in Soay sheep

In most animal species, males are predicted to compete for reproductive opportunities, while females are expected to choose between potential mates. However, when males' rate of reproduction is constrained, or females vary widely in 'quality', male mate choice is also predicted to occur. Such conditions exist in the promiscuous mating system of feral Soay sheep on St Kilda, Scotland, where a highly synchronized mating season, intense sperm competition and limitations on sperm production constrain males' potential reproductive rate, and females vary substantially in their ability to produce successful offspring. We show that, consistent with predictions, competitive rams focus their mating activity and siring success towards heavier females with higher inclusive fitness. To our knowledge, this is the first time that male mate choice has been identified and shown to lead to assortative patterns of parentage in a natural mammalian system, and occurs despite fierce male-male competition for mates. An additional consequence of assortative mating in this population is that lighter females experience a series of unstable consorts with less adept rams, and hence are mated by a greater number of males during their oestrus. We have thus also identified a novel male-driven mechanism that generates variation in female promiscuity, which suggests that the high levels of female promiscuity in this system are not part of an adaptive female tactic to intensify post-copulatory competition between males.     

Sex differences in cortisol secretion after administration of an ACTH analogue in sheep during the breeding and non-breeding season

The aim of this study was to compare the response of cortisol in sheep of different sex and gonadal status to adrenal cortex stimulation by an ACTH analogue in the breeding and non-breeding season. Twenty-four adult Corriedale sheep were used in the non-breeding season, and 19 in the breeding season. Three weeks prior to the first trial (non-breeding season), six rams and six ewes were gonadectomised. In each trial, blood was obtained every 15min for 9h and the animals received 0.5mg of ACTH (Tetracosactid, Synacthen Depot i.m., after 1.5h of sampling. Sampling began at 10:00a.m. in the non-breeding season and at 9:00a.m. in the breeding season. Three main effects (sex, gonadal status and season) were evaluated, each with two levels (male and female, intact and gonadectomised, breeding and non-breeding season, respectively). In both seasons, the females showed higher cortisol levels after ACTH than males (P<0.001), though the difference seemed less marked in the non-breeding season. The cortisol response in the ewes was not affected by season. The rams, however, showed a lower response in the breeding season (P<0.03). Gonadectomy reduced the response in the ewes (P<0.001) but had no effect in the rams. Nevertheless, gonadectomy also eliminated the differences between the ewes and the rams, such that the intact rams had lower levels of cortisol compared to the intact females, with those of the gonadectomised animals of both sexes being intermediate between the gonad-intact groups. The results of this study confirm sex differences in ACTH induced cortisol secretion in intact sheep in vivo. Furthermore, by applying exogenous ACTH we have directly stimulated the adrenal cortex, indicating the existence of sex differences also at this level. The circulating gonadal steroids, which are responsible at least in part for the sex differences in the responses to stress, may influence cortisol secretion from the adrenal gland by direct action at the cortex.     

Ram novelty and the duration of ram exposure affects the distribution of mating in ewes exposed to rams during the transition into the breeding season

This study compared the affect of short-term and continuous exposure to rams during the transition between anoestrus and the breeding season on the distribution of mating and subsequent lambing. Further, within ewes continuously exposed to rams we investigated the effect of replacing these rams every 17 days with 'novel' rams. During August (late anoestrus, Northern Hemisphere), multiparous, North of England mule ewes were allocated to one of four groups: SVR ewes were exposed to vasectomised rams for 24h on Day 0 (short term; n=109), RVR ewes were exposed to vasectomised rams for 24h on Days 0, 17 and 34 (short term; n=113); PVR ewes were exposed to vasectomised rams on Day 0 and remained with the same rams for the duration of the pre-mating period (continuous; n=104); NVR ewes were continuously exposed to vasectomised rams from Day 0 with the rams replaced with 'novel' rams every 17 days (continuous; n=113). Blood samples were collected from a subset of ewes (n=22 per group) to monitor progesterone. On Day 50, harnessed, entire rams were introduced for mating and raddle marks recorded daily for the first 17 days. The median date of mating occurred 1 day earlier in NVR ewes than PVR ewes (P<0.05). A synchrony score calculated from the blood sampled ewes showed that the distribution of mating was more synchronised in PVR and NVR ewes than SVR and RVR ewes (P<0.001). PVR and NVR ewes had an earlier onset of cyclic activity than RVR ewes (P<0.01). However, only NVR ewes differed from SVR ewes in this variable (P<0.05). Within ewes lambing to first service, the median date of lambing of PVR, NVR and SVR ewes occurred at least 2 days earlier than RVR ewes (at least P<0.05). Further, PVR and NVR ewes had a more compact distribution of lambing than SVR and RVR ewes (P<0.05) and lambing was more compact in NVR ewes than PVR ewes (P<0.05). In conclusion, ewes in continuous contact with rams prior to mating had a more synchronised distribution of mating and lambing than ewes given only short-term exposure to rams. This distribution of mating in continuous ram exposed ewes can be further enhanced by periodic exposure to novel rams.     

Early pregnancy diagnosis in the ewe, based on milk progesterone levels.

Plasma and milk progesterone concentrations in pregnant sheep (18--22 days after mating) were similar, about 3.7 ng/ml whereas values in non-pregnant sheep were less than 1 ng/ml. Lambing results indicated identical accuracy for both methods (82 and 84% in 2 flocks). The accuracy was 92--100% for ewes diagnosed non-pregnant in the breeding season, but for ewes tested in the non-breeding season the diagnosis of non-pregnancy according to milk progesterone levels was only 50% accurate.     

Molecular analysis of a promiscuous, fluctuating mating system

The Soay sheep population of St. Kilda fluctuates widely in population size and sex ratio, so diat the level of male-male competition for mates varies from one rut to the next. In this paper we investigate variation in individual male breeding success in relation to age and population size at the rut, and its outcome in terms of lifetime breeding success. Since both sexes are promiscuous, and census-based behavioural data do not predict paternity, we conducted the whole analysis on breeding success derived by molecular techniques. We assumed that every male living in our study area during the rut (N= 68–294 in different years) was a candidate father for each subsequent lamb, and used the parentage inference software CERVUS 1.0, applied to up to 17 allozyme and microsatellite loci, to infer paternity at 95% and 80% confidence. Using 945 paternities assigned at 80% confidence, we show that juvenile rams (aged 7 months) and yearling rams (aged 19 months) regularly obtained paternities and that mean individual breeding success varied inversely with levels of competition in the rut for all age classes of ram. The proportion of young (juvenile and yearling) and adult rams gaining one or more paternities showed similar variation with population size, but the sibship size sired by young and adult breeders showed different patterns: adult rams sired larger sibships at low population size, while the size of sibships sired by young rams was small across all population sizes. Variable breeding success by young rams approximately halved the estimated coefficient of variation in lifetime breeding success of Soay rams.     

Seasonal differences in the effect of isolation and restraint stress on the luteinizing hormone response to gonadotropin-releasing hormone in hypothalamopituitary disconnected,gonadectomized rams and ewes

Stress responses are thought to act within the hypothalamopituitary unit to impair the reproductive system, and the sites of action may differ between sexes. The effect of isolation and restraint stress on pituitary responsiveness to GnRH in sheep was investigated, with emphasis on possible sex differences. Experiments were conducted during the breeding season and the nonbreeding season. In both experiments, 125 ng of GnRH was injected i.v. every 2 h into hypothalamopituitary disconnected, gonadectomized rams and ewes on 3 experimental days, with each day divided into two periods. During the second period on Day 2, isolation and restraint stress was imposed for 5.5 h. Plasma concentrations of LH and cortisol were measured in samples of blood collected from the jugular vein. In the second experiment (nonbreeding season), plasma concentrations of epinephrine, norepinephrine, 3,4-dihydroxyphenylalanine, and 3,4-dihydroxyphenylglycol were also measured. In both experiments, there was no effect of isolation and restraint stress on plasma concentrations of cortisol in either sex. During the breeding season, there was no effect of isolation and restraint stress on plasma concentrations of LH in either sex. During the nonbreeding season, the amplitude of the first LH pulse after the commencement of stress was significantly reduced (P < 0.05) in rams and ewes. In the second experiment, during stress there was a significant increase (P < 0.05) in plasma concentrations of epinephrine in rams and ewes and significantly higher (P < 0.05) basal concentrations of norepinephrine in ewes than in rams. These results suggest that in sheep stress reduces responsiveness of the pituitary gland to exogenous GnRH during the nonbreeding season but not during the breeding season, possibly because of mediators of the stress response other than those of the hypothalamus-pituitary-adrenal gland axis.     

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.     

Effects of sexual experience, season, and mating stimuli on endocrine concentrations in the adult ram.

Two behavioral trials were conducted to determine the endocrine response of cortisol (C), luteinizing hormone (LH), testosterone (T), prolactin (PRL), and growth hormone (GH) in adult rams during exposure to estrous ewes during the breeding and nonbreeding seasons. One-half of the rams in each season were sexually experienced (SE) and the remainder were sexually inexperienced (SI). All SE rams (100%) achieved at least one ejaculation, but only 33% (summer) and 67% (fall) SI rams achieved ejaculation. In the fall, mean C, T, and GH concentrations were elevated (P less than .001) compared to values measured in the summer, whereas LH and PRL levels were higher (P less than .01) in the summer. Overall levels of C, LH, T, and PRL were higher (P less than .05) in SE rams than in SI rams. Mean GH concentration was higher (P less than .10) in SI than in SE rams during restricted and complete access to estrous ewes. In general, LH, PRL, and GH responses were similar during restricted and complete access to females for both SE and SI rams. Cortisol levels were higher (P less than .06) during periods of mating and T levels were higher (P less than .001) during periods where activity was limited to courtship behavior (nasogenital investigation). Correlations of hormones to reproductive behaviors indicated that mounting and intromission were associated with elevations in C and PRL, whereas elevated LH and T tended to be associated with courtship behaviors. Correlations between GH and behaviors were inconsistent. However, there was an increased coincidence between time of female exposure and hormonal response that occurred in the fall; brief exposure to estrous ewes resulted in increases in concentrations of all hormones examined. The most consistent response was observed in sexually experienced rams during restricted access to females during the breeding season. These results provide new information on the effects of season and level of sexual experience upon hormonal and behavioral characteristics of the ram during mating activity.     

Reproductive behaviour in survival: a comparison between wild and domestic sheep

The recorded behaviour of wild species of Ovis at the beginning of the breeding season supports the proposal that mating is synchronized by the 'ram effect', a phenomenon already described in domestic sheep. Animals separate into exclusive male flocks, and flocks of females and young animals for most of the year. They reunite just before the rutting season. At lambing there appear to be behavioural mechanisms that ensure that ewes lamb in close proximity to one another. It is hypothesized that these behavioural characteristics of wild sheep help protect the newborn and that much of the reproductive and maternal behaviour of domestic sheep may be traced to comparable behaviour in wild species.     

Clinical evaluation of reproductive ability of rams

Clinical evaluation of reproductive ability of rams is an integral part of sheep health management programs. The majority of problems adversely affecting the reproductive ability of rams can be easily detected with clinical evaluation. The procedure is easy to perform, has a small cost and does not require specialized support from a veterinary laboratory. As a management procedure, the method should be applied two months before the breeding season, in order to detect problems, which would adversely affect the reproductive ability of rams. It should also be performed when selecting ram-lambs as replacement sires in a flock; their first evaluation should be performed at weaning, followed by another two examinations: two to four months later and before the first mating season of these rams. The method should also be performed before the purchase of any ram as sire in a flock. Regular monitoring of reproductive ability of rams in a flock contributes to early diagnosis of disorders. As a diagnostic procedure, the method should be performed during the investigation of reproductive problems within a flock. During the evaluation of reproductive ability of rams, various clinical findings can be detected and their importance can vary. In general, rams should be in good condition and have healthy genitalia, normal libido and the ability to mate the ewes. Clinical evaluation of rams is performed in the following stages: (a) history-taking, (b) evaluation of the ratio “ewe:ram” in the flock, (c) general clinical examination, (d) clinical examination of the genitalia, (e) ultrasonographic examination of the genitalia and (f) evaluation of libido. Veterinary advice is important, in order to incorporate the clinical evaluation of reproductive ability of rams into the health management of sheep flocks.     

Effect of breeding season on fertility of sheep following estrus synchronization and fixed-time artificial insemination under field conditions in semi-arid tropical region

Accelerated lambing system is heavily reliant on reproductive technologies meant to enable off the season breeding in sheep. Therefore, the present study was programmed to assess the effect of breeding season (BS) on fertility of sheep following estrus synchronization (ES) and fixed time artificial insemination (FTAI). A total of 248 and 365 ewes were synchronized and inseminated during the BS (Febuary–March and July–September) and non-breeding season (NBS) respectively, during 2012–14. Synchronization of estrus was done by AVIKESIL-S, intra-vaginal progesterone sponges kept in situ in vagina for 12 days. 200 IU eCG was administered intramuscularly on 12th day after sponge withdrawal. FTAI was performed twice in ewes exhibiting signs of estrus at 48 and 56h after sponge removal, using liquid chilled semen of Patanwadi/Malpura rams containing 100 million sperm. Breeding season had no significant (p<0.05) effect on estrus synchronization. The estrous responses during the BS and NBS were 84.68% and 83.29% respectively. The lambing percentage during BS was 66.67%, which is significantly (p<0.05) higher than the lambing percentage of NBS (57.57%). Although, the lambing percentage in NBS maneuvered ewes were lower than the BS ewes but still the technology can be used to offset the effect of anestrus and to augment production in sheep.     

Continuous exposure to sexually active rams extends estrous activity in ewes in spring

Sexual activity in sheep is under photoperiodic control, which is the main environmental factor responsible for the seasonality of reproduction. However, other natural environmental factors such as presence of conspecifics can slightly influence the timing of onset and offset of the breeding season. In goats, we have found that the continuous presence of bucks that were rendered sexually active out of season by previous exposure to long days, prevented goats from displaying seasonal anestrus, which suggests that the relative contribution of photoperiod in controlling seasonal anestrus should be reevaluated in small ruminant species. The aim of this study was to assess whether the presence of sexually active rams that had been stimulated by artificial photoperiod and melatonin implants, reduces seasonal anestrus in sheep, by prolonging ovulatory activity in spring. Ewes were assigned to one of two groups (n = 16 and 15), which were housed in two separate barns, and kept in contact, either with the treated or the control rams between March and July. Vasectomized rams were either exposed to 2 months of long days followed by the insertion of three subcutaneous melatonin implants (treated rams, n = 8), or exposed to natural light conditions (control rams, n = 2). Estrus was monitored daily, and weekly plasma progesterone analyses indicated ovulatory activity. Ewes that were exposed to treated rams exhibited a higher proportion of monthly estrus than ewes exposed to the control rams (P < 0.05). Thirteen of 15 ewes (one ewe was not considered because of the presence of persistent CL) exposed to stimulated rams exhibited estrous behavior in a cyclic manner. In contrast, all ewes exposed to control rams stopped estrous activity for a period of time during the study, such that this group exhibited a significantly longer anestrous season (mean ± standard error of the mean 89 ± 9 days) than did the ewes housed with treated rams (26 ± 10 days; P < 0.0001). Among 15 ewes housed with treated rams, 13 of them exhibited continuous ovulatory activity between March and July, whereas one stopped in June and two in July. All ewes kept with control rams stopped ovulating for some time; consequently, those ewes had a longer anovulation period than did the group exposed to treated rams (3 ± 3 vs. 18 ± 7 days, respectively; P < 0.05). In conclusion, continuous exposure to sexually activated rams induced by artificial photoperiod and melatonin implants in spring extended the ovarian activity of ewes in spring, which results in an increase in estrous expression.     

An automated method for the evaluation of ram libido in real mating conditions

We investigated if sexual behaviour of rams can be assessed with an electronic Alpha-Detector (AD) which automatically records mounts of mating rams. To evaluate the rams’ libido (i.e. all sexual activities), we used six intact and six vasectomised rams in pen tests in three different seasons (late spring, autumn and early spring). The pen tests consisted of 30-min visual observations of each ram placed in a group of six Merino ewes (three ewes in oestrus and three ewes not in oestrus). In the pen tests, sexual behaviour was recorded and divided into two categories: pre-copulatory and copulatory. For validation purposes, during the pen tests the 12 rams were equipped with the AD and the number of times the 18 oestrous ewes were mounted were counted over a period of 3 days. Of the 1191 mounts visually identified in the six 30-min sessions, 1026 were recorded automatically by the AD (i.e. 94%). The paddock test is an automated method consisting of the same rams wearing an AD and placed in a flock of ~250 Merino ewes on two occasions (late spring (spring 1) and early spring of the following year (spring 2)), their copulatory activities were automatically recorded over a 5-day period. The results of the pen tests in the three seasons revealed no difference between the two types of rams (breeding v. detecting rams). Based on live observations high correlations (r=+0.81, P<0.003 for breeding and r=+0.76, P<0.02 for detecting rams) were found between pre-copulatory and copulatory behaviours. The libido of the two types of rams measured in pen tests showed high repeatability across the three seasons (83 and 75%, P<0.05 for copulatory and pre-copulatory behaviours, respectively). When measured automatically in paddock tests over two consecutive springs, even higher repeatability was observed in both breeding (94%; P<0.01) and detecting rams (97%; P<0.004) in the number of mounts. In addition, high correlations (+0.89<r<+0.94) between copulatory behaviours, as measured by live observations, and those measured by the AD were obtained. The automatic measurement of ram libido in paddock tests appears to be more reliable than pen tests and far less time consuming. We therefore recommend this automated method to estimate the libido of rams. In addition, this method can be used at any season of the year provided that ewes in oestrus are present in the flock.     

Reproductive performance of ewes exposed to vasectomized rams before breeding and forced exercise before lambing

Twenty days before a regular fall breeding season, 93 mature Rambouillet ewes were randomly allotted to one of two groups to examine the response of cycling females exposed to sterile rams. Six vasectomized rams were joined with 46 ewes during the 20-day period while 47 ewes remained separate from the rams. All ewes were judged to have been cycling either by paint marks from rams on treated animals or by the cyclic nature of progesterone (sampled at four-day intervals) profiles in control ewes. After removal of sterile males, fertile Debouillet rams remained with the ewes during a 34-day breeding season. Approximately six weeks before beginning the lambing season, one-half the females in each sterile ram treatment group were forced to walk 0.8 km per day to examine the influence of exercise on subsequent reproductive performance. Presence of sterile males did not alter (P>0.10) lambing rate, average lambing date or percentage of ewes lambing during thirds of the lambing season suggesting that prebreeding exposure of cycling ewes to vasectomized rams does not enhance lambing rate or shorten the lambing season. Forced exercise resulted in increased daily feed consumption which was reflected in heavier (P<0.05) lamb birth weights. Percentage of ewes experiencing either dystocia or pregnancy toxemia was similar (P>0.20) in exercised and unexercised animals. Moderate exercise during late gestation may increase lamb birth weight without increasing lambing difficulty.     

The influence of breeding intensity on above- and below-average sexual performance rams in single- and multiple-sire breeding environments

Two studies were conducted to evaluate the relationship between serving capacity scores and breeding performance of rams. The first study was conducted to determine whether rams with above or below mean serving capacity scores could perform equally in greater and lesser breeding intensity, single-sire mating schemes. The second study was conducted to determine whether rams with above and below mean serving capacity scores could perform equally well when only one or two ewes were in estrus daily in a multiple-sire breeding scheme (two rams/pen). Rams (n=68) were ranked according to average number of ejaculations recorded in serving capacity tests. Sixteen rams with the greatest scores (above-average) and 16 rams with least scores (below-average) were identified for breeding. Half of above-average and half of below-average rams were used in the two studies. For study 1, each ram was individually introduced to 23 estrus-synchronized ewes for 9 d to simulate high breeding intensity. Rams were given a 5-d rest before they were individually introduced to 23-24 naturally cyclic ewes for 17 d (low breeding intensity). For study 2, 16 rams were paired across ram types, and each pair competed for 20 ewes for 18 d (8 pens). For study 1, ewe fertility (ewes lambing/ewes present at lambing) and number of lambs born were greater (P<0.001) for above-average (0.67+/-0.03 and 27.6+/-1.2, respectively) than for below-average rams (0.39+/-0.07 and 15.3+/-2.7) with greater breeding intensity. Ewe fertility and lambs born did not differ for above-average (0.91+/-0.03 and 37.8+/-1.9, respectively) and below-average rams (0.86+/-0.03 and 39.0+/-1.9) with less breeding intensity. For study 2, number of ewes lambing (99+/-8.0 compared with 72+/-13.6; P=0.12) and number of lambs sired (149+/-18.5 compared with 101+/-22.8; P=0.14) did not differ between above- and below-average rams, respectively, in direct competition. Sexual classifications based on serving capacity tests are related to breeding performance of rams in certain breeding environments. When breeding intensity is greater, above-average rams impregnate more ewes and sire more lambs than below-average rams. When only a small number of ewes are in estrus daily, below-average rams for serving capacity scores perform as well as above-average rams in multiple-sire and single-sire breeding environments. We suggest that above-average rams should be used to reduce number of rams required when breeding intensity is greater.     

Intrasexual Competition and Mate Choice in Rocky Mountain Bighorn Sheep

Rocky Mountain bighorn (Ovis canadensis canadensis) rams employed three distinct mating tactics. When tending, rams defended single estrous ewes. In coursing, rams forced copulations with defended ewes, and, in blocking, rams sequestered ewes from more dominant rams. Ewes utilized a traditional area when tended, attempted to escape to this area when blocked, and resisted coursing ram attempts to force copulations. Between-year variation in the dispersion of estrous ewes about the tending area strongly influenced the consort and probably mating success of dominant rams. Thus, ewe spatial predictability during estrus — achieved by clustering in tended estrus and resisting blocking rams — appears to be an important mechanism of mate choice in this species. Ewes apparently did not gain material or risk-related benefits by mating dominant rams. That such males provide ewes with “good genes” is an attractive remaining possibility.