The relationship of libido and serving capacity test scores in rams on conception rates and lambing percentage in the ewe

A procedure for assessing sexual activity (libido) and serving capacity (number of ejaculations) in individual rams is described. Libido and serving capacity was measured by this procedure in 10 Lincoln, 10 Suffolk, 2 Columbia, and 2 Polypay rams prior to the breeding season. Semen was evaluated, and the scrotal circumference measured. The rams were single-sire mated to 10-12 whiteface, crossbred ewes during a 35-day breeding season (September 26 - October 29). First-service conception rates, total conception rate, lambing percentage per ewe lambing, and lambing percentage per ewe exposed were calculated for each ram. The mean libido score for the 24 rams was 8.95 and the mean serving capacity score was 3.16. The 24 rams were classified as low serving capacity (<2 ejaculation), medium serving capacity (2-3 ejaculations), or high serving capacity (>3 ejaculations). There were no significant differences in either conception rate or lambing percentages between the 3 groups of rams. The first-service conception rate, total conception rate, lambing percentage per ewe lambing, and lambing percentage per ewe exposed were 74.8, 93.8, 148.6, and 139.4 percent, respectively, for the 24 rams. Libido and serving capacity tests in the rams, as used in this experiment, prior to the breeding season, were not successful in predicting fertility or prolificacy in ewes.     

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.     

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.     

Effects of Melatonin,Progestagens, and the Ram on Out-of-Season Reproduction in Swedish Landrace Finewool Sheep

One hundred twenty-one Swedish Landrace Finewool ewes were treated with progestagen sponges (P), teaser ram stimulation (R), or melatonin implants plus teaser ram stimulation (M) in preparation for breeding with whole rams in August. Blood progesterone analyses from ewes in the R and M groups gave no evidence of luteal activity before the introduction of teaser rams. There were no significant differences between treatments for pregnancy rate (~90%). The P group had the most compact lambing season, while median breeding dates for M and R groups were delayed by one cycle. In those groups, the introduction of breeding rams was later found to have been too late. M and R differed significantly for probable conception date but not for lambing dates. Circa 30% of M ewes did not have a short 6 day ovulation cycle after the first ovulation, which resulted in a less concentrated lambing season than the other methods. Although no significant differences in litter size were seen among the 3 treatments, M had the highest group average, 2.25. The ewes in this study were not in very deep anestrous in the middle of August. This supports the conclusion that treatment with exogenous hormones is not necessary to breed Swedish Landrace Finewool ewes successfully in late August/early September.     

Influence of classification levels of ram sexual activity on spring breeding ewes

Ram lambs (7–8 months old) and mature rams (19–20 months old) were used to evaluate the effect of classification levels of male sexual performance on reproductive performance of ewes during spring breeding. In Exp. 1, sexually active ram lambs with high (1.8±0.3; n=5) and low (0.9±0.2; n=5) sexual performance scores (HP and LP; mean±S.E.M.) were used in single sire breeding pens. Ewes (n=305) were stratified by age and assigned to 10 pens for 34 days starting in late March. For Exps. 2 and 3, two replicates were conducted for 2 years with sexually active mature rams in a single sire mating scheme. For Exp. 2, HP rams (n=5) averaged 3.6±0.2 ejaculations and LP rams (n=7) 1.8±0.2 ejaculations for sexual performance scores based on nine, 30 min serving capacity tests (SCT). Polypay ewes (n=152 to 153 per year) were stratified by age and assigned to pens each year for 34–38 days starting in late March for years 1 and 2. For Exp. 3, HP rams (n=6) averaged 3.7±0.1 ejaculations and LP rams (n=10) 2.3±0.1 ejaculations for sexual performance scores based on 18, 30 min SCT. Polypay ewes (n=229 in year 3 and n=244 in year 4) were stratified by age and assigned to pens each year for 34 days starting in late March. In Exp. 1, lambing rates for ewes bred to HP versus LP ram lambs did not differ (65.8 versus 53.0; P=0.20). Prolificacy tended (P=0.06) to be increased by 0.1 lambs in ewes bred by LP ram lambs. Total number of lambs born per ewe present at lambing, and lambing distribution were not altered by HP and LP ram lambs. In Exp. 2, lambing rates for fall-lambing ewes bred to mature HP or LP rams did not differ (58.1 versus 60.1; P=0.78). In Exp. 3, lambing rates for fall-lambing ewes bred to mature HP or LP rams did not differ (74.3 versus 69.0; P=0.35). There was no difference (P>0.10) between years for Exp. 2 or Exp. 3, and mature HP and LP rams did not affect the other reproductive variables monitored. Analyses of the combined data for Exps. 2 and 3 indicated only a year difference (P<0.001) in lambing rates and total lambs born. Present studies indicate that different sexual performance classifications for ram lambs and mature rams did not alter lambing rates or distribution of lambing of Polypays bred in late March to April. These results indicate that HP and LP, sexually active, Polypay rams and ram lambs with average to high quality semen can provide a source of rams for spring breeding Polypays in ambient conditions and that there was no advantage to using HP over sexually active LP ram lambs or rams.     

Fertility in South Australian commercial Merino flocks: aspects of management

Wide variation in reproductive performance of commercial Merino flocks in south central Australia is the result of genetic and environmental influences that are both amenable to change through decisions of management. Relationships of reproductive traits (estrus, ovulation, fertility, fecundity, lamb survival, and lambs weaned) with variables that graziers can change or modify (strain of Merino, day or month of exposure of ewes to rams, ram effect or teasing, length of the mating period, ram percentage, days between weaning and next mating, stocking density and flock size at lambing, ewe liveweight, and condition) are reported in this paper, the third in a series. Small differences were observed between medium and strong-wool South Australian Merino strains for reproductive traits. Choosing the time of year that ewes are exposed to rams, between late spring to autumn, may result in reduced ovulation rate during early summer (December) giving a potentially smaller net reproductive efficiency (lambs weaned). The ram effect or teasing, used by about 50% of graziers to synchronise lambing, could be effectively employed to the end of January. The technique was not reproductively advantageous when compared with flocks that were not teased. The percentage of rams mated to ewes varied widely (approximately 1-3%) and did not alter flock fertility, suggesting that a substantial proportion of graziers could safely reduce the number of rams purchased. A positive relationship between incidence of estrus during the first 14 d of the cycle and the number of days from weaning to next mating and a negative relationship of returns to service with the same variable indicates that managers should consider increasing the time allowed for recovery of liveweight and body condition by adjusting age at weaning, length of the mating period, or both. Lamb survival was curvilinearly related to flock size and not stocking intensity, with the optimum size at about 400 ewes. The number of lambs weaned per 100 ewes exposed to rams increased by 1.0 kg(-1) increase in liveweight at mating. We concluded that the major factor controlling net reproductive efficiency is nutritional in origin through its effects on ewe liveweight and condition, and is a factor that can be largely manipulated through management.     

Threshold of plasma testosterone required for normal mating activity in male sheep

The finer control of mating activity by testosterone in male sheep was investigated using the castrated ram (wether) as an experimental model. Adult wethers that had been castrated before puberty were injected with graded doses of testosterone propionate (TP) and mating behavior was assessed in standardized libido trials at various times during treatment. Doses of 1 to 2 mg TP/day elicited mounting behavior in wethers but did not result in intromission or ejaculation. On the other hand, TP doses of 4 mg/day or greater stimulated the complete mating response which included intromission and the ejaculatory reflex. The threshold dose of TP required for complete mating activity (4 mg/day) produced plasma testosterone levels which were lower than those normally observed in intact rams. The results of this study indicate that the behavioral aspects (arousal mechanisms) of mating in rams have a lower testosterone threshold than intromission and ejaculation (consummatory mechanisms). Also, since complete mating activity was stimulated in wethers having relatively low plasma testosterone levels, this may explain why there is no apparent relationship between plasma testosterone and mating drive in intact rams.     

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.     

The effect of scrotal circumference, sperm motility and morphology in the ram on conception rates and lambing percentage in the ewe

Ten Suffolk and ten Lincoln yearling rams were examined for breeding soundness. Semen was evaluated, and the scrotal circumference measured. They were single-sire mated to ten to twelve, whiteface ewe lambs during a 45-day breeding season (October 15 - December 1). First-service conception rates, total conception rate, lambing percentage and lambing percentage per ewe exposed were calculated for each ram and breed. The mean scrotal circumference was 36.5 cm (range 31 - 41.5 cm). The breeding data was then compared for eleven rams with a scrotal circumference of less than 36.5 cm and nine rams greater than 36.5 cm. No direct relationship was demonstrated between scrotal circumference, sperm motility or morphology with fertility in the rams used in this experiment. However, there was a tendency for rams with a high first-service conception rate to have sired more lambs per ewe exposed. The mean first-service conception rate was 63.2% (range 44.4 - 80.0%). When rams with greater than 63.2% first-service conception rate were compared to those with less than 63.2%. the lambs born per ewe exposed were 1.04 and .89, respectively, a significant difference (P<.05). There were no significant differences (P<.05) in performance between the two groups when rams with a scrotal circumference less than 36.5 cm and greater than 36.5 cm were compared, nor were there any differences between scrotal circumference, sperm motility, and morphology when rams with total conception rates greater than 80% were compared to those with conception rates less than 80%.     

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.     

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.     

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.     

Heritability of ram mating success in multi-sire breeding situations

Multi-sire mating of a mob of ewes is commonly used in commercial sheep production systems. However, ram mating success (defined as the number of lambs sired by an individual) can vary between rams in the mating group. If this trait was repeatable and heritable, selection of rams capable of siring larger numbers of lambs could reduce the number of rams required for mating and ultimately lead to increased genetic gain. However, genetic correlations with other productive traits, such as growth and female fertility, could influence the potential for ram mating success to be used as a selection trait. In order to investigate this trait, parentage records (including accuracy of sire assignment) from 15 commercial ram breeding flocks of various breeds were utilised to examine the repeatability and heritability of ram mating success in multi-sire mating groups. In addition, genetic and phenotypic correlations with growth and female fertility traits were estimated using ASReml. The final model used for the ram mating success traits included age of the ram and mating group as fixed effects. Older rams (3+years old) had 15% to 20% greater mating success than younger rams (1 or 2 years of age). Increasing the stringency of the criteria for inclusion of both an individual lamb, based on accuracy of sire assignment, or a whole mating group, based on how many lambs had an assigned sire, increased repeatability and heritability estimates of the ram mating success traits examined. With the most stringent criteria employed, where assignment of sire accuracy was >0.95 and the total number of lambs in the progeny group that failed to have a sire assigned was<0.05, repeatability and heritability for log_e(number of lambs) was 0.40±0.09 and 0.26±0.12, respectively. For proportion of lambs sired, repeatability and heritability were both 0.30±0.09. The two ram mating traits (log_e(nlamb) and proportion) were highly correlated, both phenotypically and genetically (0.88±0.01 and 0.94±0.06, respectively). Both phenotypic and genetic correlations between ram mating success and growth and other female fertility traits were low and non-significant. In conclusion, there is scope to select rams capable of producing high numbers of progeny and thus increase selection pressure on rams to increase genetic gain.     

Age-dependent sexual selection in bighorn rams.

Although mating systems and sexual selection have been intensively studied in ungulate model systems, very few studies have combined genetic paternity analysis with individual phenotypic data over several breeding seasons. We used microsatellite paternity analysis to determine the parentage of 83 bighorn sheep (Ovis canadensis) born between 1995 and 2000 at Ram Mountain, Alberta, Canada. We could assign the paternity of 64 lambs at a high level of statistical confidence (95%). Within each season, the most successful ram sired an average of 35.5% of the lambs with assigned paternity, and a single ram sired 26.1% of all lambs over the six mating seasons. Although a few large-horned, mature (age 8+ years) rams had very high reproductive success, younger rams sired ca. 50% of the lambs. Mixed-effects models indicated that mating success increases as a nonlinear function of age, with horn length increasingly positive in correlation with mating success in older rams. These results indicate that young or small rams possibly achieve mating success through alternative mating tactics that are less dependent on body and weapon size, such as coursing and blocking. Sexual selection is therefore likely to have age-dependent effects on traits such as agility, body and horn size.     

Effect of undegradable protein supply on testicular size, spermiogram parameters and sexual behavior of mature Assaf rams

Eighteen mature Assaf rams were used to study the effect of undegradable protein (UDP) supply on testicular size, sperm production and quality, testosterone secretion and reproductive behavior. Animals were allocated to three groups of six animals each and fed during 10 weeks with different diets which were designed to supply approximately 0.5MJ of metabolisable energy (ME)/kg LBW(0.75) and 9g of effective rumen degradable protein (ERDP)/MJ of fermentable ME to all animals and to induce differences in rumen UDP intake (0.97, 1.72 and 3.08g of UDP/kg LBW(0.75) for LP, MP and HP diets, respectively). Neither plasma testosterone concentration nor reproductive behavior parameters (number of services, number of mounts without ejaculation and reaction time to first mount) were affected (P > 0.05) by protein intake. Nevertheless, there were significant (P < 0.05) differences between diets in both testicular size and sperm production. Scrotal circumference was lower in LP compared to MP and HP groups, no significant differences being observed between these latter two groups at any time. In relation to sperm production, the lowest and the highest values were always observed in LP and HP groups, respectively. MP group showed intermediate values, significantly different from those of LP and HP groups on Week 5 and only from those of LP group on Week 9. The present results provide a better understanding of the effect of protein nutrition and suggest that UDP should be supplied to Assaf rams during the mating season to improve their reproductive performance.     

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.     

Effect of rumen degradable bolus containing melatonin or progestagen pessary plus pregnant mare serum gonadotropin on estrus response and lambing rate in ewes

Two practical regimens designed to induce estrus and ovulation in ewes in late anestrus were compared. Forty ewes were given a soluble glass rumen bolus containing 150 mg melatonin on July 9 and were joined with two vasectomized rams on July 23 and with three fertile rams on August 6. A second group of 40 ewes was treated with an intravaginal progestagen pessary (60mg medroxy-progesterone acetate) on July 23. Following pessary removal after 12 d, ewes were given 750 IU of pregnant mare serum gonadotropin (PMSG). Five fertile rams were joined with these ewes 48 h after progestagen removal. Melatonin concentrations were determined in single blood samples collected in early afternoon of July 21. Mating dates, lambing dates and litter sizes were recorded. Date of mating was significantly later in ewes treated with melatonin compared with those treated with progestagen plus PMSG (P<0.0001). All ewes given melatonin were mated within 4 wk, and those on progestagen plus PMSG treatment within one day of fertile ram introduction. Thirty-four ewes (85%) allocated to melatonin treatment and 36 (90%) allocated to progestagen plus PMSG treatment lambed (P>0.05). Mean (+/-SEM) lambing date was later in melatonin-treated ewes (January 17+/-1.2 d) compared to those given progestagen plus PMSG (December 30+/-0.6 d; P<0.0001). Mean litter size was lower in melatonin-treated ewes (1.5+/-0.1) compared with those given progestagen plus PMSG (2.0+/-0.1; P<0.001). Plasma melatonin concentrations indicated that 9 of 40 ewes treated with melatonin had circulating melatonin concentrations of less than 16 pg/ml. It is concluded that under conditions that existed in this experiment, treatment with progestagen plus PMSG in late anestrus resulted in more synchronous mating and lambing and a higher litter size than that following administration of a soluble glass rumen-degradable bolus containing melatonin.     

Effects of sexual stimulation on the sexual performance of rams

The sexual performance of bulls and male goats is improved if they are allowed to view the hetero-sexual behavior of other males as a prelude to mating. The purpose of the following study was to determine whether sexual stimulation enhances the sexual performance of rams. In Experiment 1, 11 sexually experienced ram lambs ( 9 months of age) and 18 sexually experienced yearling and 2-year-old rams were individually exposed to 4 unrestrained, hormone-induced estrous ewes for 60 min after viewing the courtship and mounting behaviors of a male conspecific for 20 min (two tests) and in the absence of stimulator animals (two tests). In contrast to the results with bulls and bucks, the rams were hardly influenced by the sexual stimulation treatment. Latencies for first mount and first ejaculation were shorter for sexually stimulated ram lambs; otherwise, treatment differences were negligible.

A similar follow-up experiment was administered to 12 mature rams using restrained females in the sexual performance tests. Again, treatment differences were minor.

It was concluded that sexual stimulation does not functionally enhance the sexual performance of rams. Species differences in response to sexual stimulation are discussed in terms of female sexual behaviors that may result in a selective (competitive) advantage to males that are stimulated to locate and mate with females early in the estrous period.     

Non-genetic sources of variation of milk production and reproduction and interactions between both classes of traits in Sicilo-Sarde dairy sheep

This work aimed to study the sources of variation in productive and reproductive traits of the dairy Sicilo-Sarde ewes and to further investigate the interaction between both classes of traits. After edits, a database containing 5935 lactation records collected during 6 successive years in eight dairy flocks in the North of Tunisia was used. Total milked milk (TMM) in the milking-only period was retained as productive trait. The interval from the start of the mating period to the subsequent lambing (IML) and the lambing status (LS) were designed as reproductive traits. Sicilo-Sarde ewes had an average TMM of 60.93 l (±44.12) during 132.8 days (±46.6) after a suckling period of 100.4 days (±24.9). Average IML was 165.7 days. In a first step, the major factors influencing milk production and reproductive traits were determined. The significant sources of variation identified for TMM were: flock, month of lambing, year of lambing, parity, suckling length, litter size and milking-only length. Flock×month of the start of the mating period, parity, year of mating and litter size were identified as significant factors of variation for IML, while flock×month of the start of the mating period, parity and year of mating were identified as significant sources of variation for LS. In a second step, variance components were estimated using a three traits threshold mixed model, which combined LS as categorical trait and TMM and IML as continuous traits. Repeatability estimates were 0.21 (±0.03) for TMM, 0.09 (±0.02) for IML, and 0.10 (±0.05) for LS. Moreover, TMM and IML were found to be favorably associated for the flock× year of lambing effect (−0.45±0.18) but unfavorably associated for the animal effect (0.20±0.09).     

Ram effect: adult rams induce a greater reproductive response in anestrous ewes than yearling rams

The introduction of rams to previously isolated anestrous ewes ensures induction of ovulation and estrus in part of the flock, and allows for the potential to conceive. However, there is little known about the desirable characteristics of the rams used to induce these behavioral and physiological responses. Adult rams may be more effective than young rams in induction of these responses. The primary aim of the present study was to compare the response in ewes stimulated by adult or yearling rams. During the non-breeding season, two groups of 121 ewes were stimulated with adult (AR) or yearling (YR) rams. When adult rams were used, significantly more ewes had ovulations (78.5 compared with 61.1%) and came into estrus (47.9 compared with 35.5%). There were more corpora lutea per ewe exposed to rams (0.95+/-0.59 compared with 0.65+/-0.51) and per ewe that had ovulations (1.18+/-0.41 compared with 1.06+/-0.25) and a greater conception rate (58.6 compared with 20.9%) as a result. Subsequently, to determine what signals led to the greater response to adult rams, the courtship behavior of adult and yearling rams toward anestrous ewes was compared in 46 pen tests. There were no significant differences in the frequency of any of the recorded courtship behaviors (anogenital sniffing: 21.9+/-3.4 versus 25.7+/-3.2; lateral approaches: 7.1+/-1.5 compared with 9.9+/-2.9; flehmen: 2.1+/-0.4 compared with 2.2+/-0.4; mount attempts: 0.1+/-0.1 compared with 0.1+/-0.1, for AR and YR, respectively), latency to the onset of courtship behavior (13.1+/-7.0 compared with 17.3+/-6.2s) or the time engaged in courtship behavior (173.1+/-24.6 compared with 199.0+/-26.5s). The difference in the signals produced by adult and yearling rams skin glands was assessed by stimulating ewes with masks containing wool from adult (n=45) or yearling (n=48) rams. More ewes had ovulations (24/45 compared with 11/48) and came into estrus (21/45 compared with 10/48) when wool from adult rams was used. As in Experiment 1, pregnancy and conception rates were greater when adult rams were used, another trial was designed to determine if there were differences in mating and mounting frequency between adult and yearling rams. Seven adult and six yearling rams were subjected to three pen tests each with three estrual ewes. Adult rams mounted more (21.7+/-4.5 compared with 9.8+/-0.7) and tended to ejaculate more frequently (2.9+/-0.5 compared with 1.8+/-0.4) than yearling rams. It is concluded that adult rams induce a greater reproductive response in anestrous ewes than yearling rams, inducing a greater ovulation percentage and estrous response in ewes, resulting in greater ovulation numbers, pregnancy and conception rates. This greater stimulation is, in part, explained by differences in the signals provided in the wool (presumably odors) produced by adult rams. The lesser percentage of pregnancies obtained when yearling rams are used may be explained by differences in mounting behaviors and ejaculation frequency.