Influence of social interaction between rams on their serving capacity

The experiment was designed to test the hypothesis that social interaction between rams influenced their serving capacity and modified their preference for ewes.The serving capacity and the preference for particular ewes was recorded on the first and seventh day of joining in 8 rams mated either individually or in pairs to 12 oestrous ewes. The serving capacity (mean number ejaculates/hour) was 50% lower in both dominant and submissive rams when working together compared with single-sire matings. However, when working together, 33% of the available ewes were served by the submissive ram and 12.5% were served by the dominant ram so that, in total, more ewes were served (total mean number ± SE of ewes served/ram when mated either individually or as a pair = 4.50 ± 0.89 and 5.50 ± 0.57, respectively). This resulted from a modification in ewe preference by the submissive ram.In the absence of competition, the same ewes were observed to be preferred by most rams. This ewe “attractiveness” was found not to be a permanent characteristic, as the preferred ewes at one oestrus were not necessarily those most preferred at a subsequent oestrus.     

The continuous presence of ewes in estrus in spring influences testicular volume,testicular echogenicity and testosterone concentration,but not LH pulsatility in rams

The continuous presence of active male small ruminants prevents seasonal anestrus in females, but evidence of the same mechanism operating from the females to the males is scarce. This study assessed the effects of the continuous presence of ewes in estrus in spring on ram sexual activity, testicular size and echogenicity, and LH and testosterone concentrations. On 1 March, 20 rams were assigned to two groups (n = 10 each): isolated (ISO) from other sheep, or stimulated (STI) by 12 ewes, which were separated from the rams by an openwork metal barrier, allowing contact between sexes. Each week, four ewes were induced into estrus by intravaginal sponges. Live weight, scrotal circumference, testicular width (TW) and length (TL) were recorded at the beginning and at the end of the experiment, and testicular volume (TV) was calculated; at the same time, testicular ultrasonography and color Doppler scanning were performed. Blood samples (March to May) were collected once per week for testosterone determinations, and at the end of the experiment, blood samples were collected for 6 h at 20-min intervals for LH analysis. Rams were exposed to four estrous ewes in a serving-capacity test. Scrotal circumference, TW and TL were higher in the STI than in the ISO rams (P < 0.05) in May, and TV was higher (P < 0.05) in the STI (391 ± 17 cm³) than in the ISO rams (354 ± 24 cm³). In ISO rams, the number of white pixels was higher (P < 0.01) in May (348 ± 74) than in March (94 ± 21) and differed significantly (P < 0.01) from that of the STI rams in May (160 ± 33). In ISO rams, the number of grey pixels was higher (P < 0.05) in May (107 ± 3) than it was in March (99 ± 1). Stimulated and ISO rams did not differ significantly in mean LH plasma concentrations (0.8 ± 0.5 v. 0.9 ± 0.4 ng/ml), LH pulses (2.1 ± 0.5 v. 2.2 ± 0.2) and amplitude (2.0 ± 0.4 v. 3.2 ± 0.7 ng/ml, respectively). Stimulated rams had significantly higher testosterone concentrations than ISO rams from April to the end of the experiment. Stimulated rams performed more (P < 0.05) mountings with intromission (3.0 ± 0.4) than did ISO rams (1.5 ± 0.5). In conclusion, after 3 months in the continuous presence of ewes in estrus in spring, rams had higher TV and some testicular echogenic parameters were modified than isolated rams. Although exposed rams also had higher levels of testosterone after 2 months in the presence of estrous ewes, their LH pulsatility at the end of the study was not modified.     

Effect of breed and age on sexual behaviour of rams

The objective of this study was to highlight the problems that arise during the reproduction between thin-tailed rams and fat-tailed ewes. At the same time, particular emphasis laid on the influence of sheep breed, sheep age, time after ram introduction and day of the ewe estrus cycle on ram and ewe sexual behaviour. Rams were subjected to sexual performance tests by being individually exposed to 12 ewes for 3 h daily, 19 consecutive days. The 16 rams of the experiment were separated according to their age (9 and 21 months old) and breed (Chios and Karagouniki), and the 96 ewes of Chios fat-tailed breed, were divided by age (9 and 21 months old). The main characteristics of courtship behaviour, like sniffing, nudging, flehmen response and following were recorded and studied in detail. Mature Chios rams, which were the only one with previous experience of Chios ewes, exhibited higher rates of sexual interest per ewe than the other rams (P < 0.05). On the other hand, rams sniffed and nudged more young than mature ewes (P < 0.05), probably due to the fact that young ewes did not express intense symptoms of estrus. Young rams exhibited substandard sexual interest towards mature ewes, when they first came in contact with them (P < 0.05). In general, Karagouniki thin-tailed rams exhibited reduced rates of mating behaviour when they courted with Chios fat-tailed ewes in comparison with Chios rams (P < 0.05). Moreover, as the time after ram introduction passed, the frequency and duration of sexual behaviour components decreased (P < 0.001). Finally, the effect of the day of the experiment was only significant in the case of sniffing, which increased during the first 2 days and then declined and stabilized (P < 0.01). As it was demonstrated, ram age and ram breed played a fundamental role in the exhibition of sexual interest elements.     

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.     

Effects of the presence of rams during pregnancy on lambing performance in ewes

Ewes of the Préalpes-du-Sud breed (n=112) were mated with fertile rams and were used to investigate the effect of the presence of vasectomized rams during pregnancy on reproductive outcomes. Ewes in the control group (n=56) were isolated from rams during the whole period of pregnancy, whereas those in the experimental group (n=56) were kept with vasectomized rams from day 10 post-mating until lambing. At day 10 post-mating, a series of blood samples was collected every 15 min for 8 h from five control ewes and five experimental ewes to determine their patterns of LH secretion. The introduction of the ram was associated with a rapid increase of pulsatile LH release. The lag between the introduction of the ram and the onset of the first episodic LH release was less than 15 min. The mean(±sem) number of LH pulses/4 h after the introduction of the ram (2.8±0.4) was significantly higher (P<0.01) than that observed/4 h before the introduction of the ram (1.4±0.2). Although more ewes were pregnant in the control group (87.5%) than in the ram-exposed group (82.1%), the difference was not significant. The presence of rams did not affect gestation length (145.8 days), overall lamb mortality (3.5%) or birth weights of single (3.96 kg), twin (3.24 kg) or triplet (2.59 kg) lambs. The proportion of ewes with multiple births in the control group (69.4%) was significantly greater (P<0.05) than that in the ram-exposed ewes (47.8%). The ewes in the control group had significantly more (P<0.01) twin lambs born alive (72.3%) than the ewes in the ram-exposed group (50.0%). In conclusion, the presence of vasectomized rams during early pregnancy affected the incidence of multiple births but did not affect pregnancy rate or gestation length. The altered fertility of ewes exposed to vasectomized rams may reflect changes in embryonic loss during early pregnancy.     

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.     

Detection of estrus and quality of semen produced by rams with deviated penises

Nine rams had their penises deviated and three others were vasectomized. Six additional intact rams served as controls. Three of the penis-deviated rams were raddled and placed in small flocks of ewes where they proved to be satisfactory detectors of estrus.Vasectomized and penis-deviated rams each were exposed to an estrous ewe for 5 minutes. The number of mounts (mean ± SE) for vasectomized rams was 4.8 ± .5 and for penis-deviated rams was 4.3 ± .5 (P>.05). When the rams had become experienced there were very few failures to mount at least once during the 5-minute period in any of the groups.Semen collection was facilitated in penis-deviated rams. There were no significant differences (P>.05) between penis-deviated and control rams with respect to volume of the ejaculate, or motility, concentration or presence of abnormal spermatozoa. Rams with deviated penises could be useful for detecting estrus and supplying spermatozoa for experimental study or use in artificial insemination.     

Stimulation of seasonally anovular merino ewes by rams. I. Time from introduction of the rams to the preovulatory LH surge and ovulation

Two experiments were performed on seasonally anovular Merino ewes to determine the intervals between time of introduction of rams, the preovulatory surge of LH and the first ovulation. Ovulation was determined by laparoscopy and LH was measured by solid phase radioimmunoassay. In Experiment 1 the interval between the introduction of rams and the beginning of the LH surge was 27 ± 4 h (mean ± S.E., range 6–52 h), and in Experiment 2 probit analysis shows that 50% of teased ewes ovulated within 41 h of being exposed to rams.     

A note on ram preference by oestrous ewes: Influence of rams’ age and sexual performance

Ewes in oestrus, besides being receptive to rams, develop an active search for them. We performed two experiments to determine if oestrous ewes prefer: (1) high or low sexual-performance rams, and (2) 2-year-old or aged (>8-years-old) rams. In the first experiment, the preference of ewes for rams with high or low sexual performances was compared in 16 tests. In the second experiment, 17 tests were performed comparing ewes’ preference for aged rams (>8-years-old) or young rams (2-years-old). In each test, two rams were tied at equal distances from the point of entrance of the ewe, with a maximum mobility for each ram of 2 m. The first approach to a ram, the quantity of approaches toward each ram (less than one body length), and the total time that the ewe remained near each ram were registered during 5 min. Oestrous ewes did not display any preference according to sexual performance of rams, but spent significantly more time (P = 0.02), and did it in more tests (P = 0.025), with young than with aged rams. Ewes also tended to approach first (P = 0.07), and more times in more tests (P = 0.06), to young than to aged rams. We conclude that ram's sexual performance seems not to influence oestrous ewes preference, and that ewes’ prefer young (2-years-old) rather than aged rams (>8-years-old).     

Influence of suckling status and type of birth on serum hormone profiles and return to estrus in early-postpartum spring-lambing ewes

Twenty-three mature, spring-lambing, fine-wool ewes of Debouillet × Rambouillet breeding were allotted at parturition to one of four treatments which were arranged in a 2 × 2 factorial design with groups representing number of lambs born (i.e., one or two) and suckling intensity (i.e., lambs were weaned at 2 d of age or lambs remained with dams). Beginning at 0900 h on Day 2, 9, 16, 23, and 30 post partum (PP), jugular blood samples were collected from each dam at hourly intervals for the ensuing 6 h. Additional jugular blood samples were collected daily (Days 2 through 30). Animals were observed twice daily for signs of estrus using vasectomized rams. Interval from parturition to estrus (mean ± SEM) was similar (P > 0.15) in ewes nursing their offspring (117 ± 6 d) and those that had their lambs removed (124 ± 6 d). Dams producing single lambs returned to estrus in 126 ± 5 d compared with 116 ± 5 d (P > 0.15) for ewes producing twins. Serum luteinizing hormone and progesterone were low (< 1.7 and 0.5 ng/ml, respectively) in all ewes during the first 30 d PP. Serum insulin did not differ (P > 0.10) between suckled dams and those that had their lambs removed, but ewes giving birth to single offspring had higher (P < 0.05) insulin levels on Days 16 and 30 PP (543 ± 73 and 578 ± 57 pg/ml, respectively) than did dams producing twin lambs (324 ± 73 and 361 ± 57 pg/ml, respectively). Serum growth hormone (GH) did not differ (P > 0.40) between suckling intensity groups on Day 2 PP; however, by Days 16, 23, and 30, ewes in the suckled group had more (P < 0.05) GH than did those producing single offspring (5.4 and 3.6 ± 0.4 ng/ml, respectively). Early removal of lambs in spring-lambing ewes did not shorten the interval from parturition to estrus.     

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.     

Fertility studies in young and mature merino ewes 1. Cervical mucus production

The production of cervical mucus was determined at six-hour intervals during oestrus in young (1 (1 2 ) years old) and mature (3 to 7 years old) Merino ewes. The length of the cervix and the length of the cervical epithelium was also measured in similar ewes. Total weight of mucus secreted as well as secretion rate per unit of time was greater in mature ewes than young ewes. Production was maximal during the first six hours of oestrus and declined considerably after 12 hours in young and 18 hours in mature ewes. The cervix was significantly shorter in young ewes while the length of the cervical epithelium was not significantly different in young and mature. It was concluded that lower mucus production in young ewes is not related to lower mucus output per unit area.     

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.     

Reproductive potential and endocrinological responses of sheep kept under controlled lighting. II. Pituitary and gonadal responses of ewes and rams to a six-monthly light cycle

Forty entire ewes of mixed breeds were kept in environmentally-controlled rooms with a 6-monthly light cycle. Six mature spayed Border Leicester × Merino ewes and four mature intact Poll Dorset rams were kept under the same conditions.Over a period of 2 years (four light cycles) estimates were made of ovarian, testicular and pituitary activity in response to the artificial light regime. Non-pregnant ewes were bled twice weekly: peripheral plasma progesterone levels > 1 ng/ml were taken as indicative of ovarian activity. Testicular activity was estimated by weekly tests for peripheral plasma testosterone and scrotal sac volume. Pituitary activity was estimated monthly by the response to the injection (i.v.) of 75 μg gonadotrophin releasing hormone (GnRH) to rams and of 18.75, 37.5 or 75 μg to ewes, using peripheral plasma luteinising hormone (LH) estimations from the time of GnRH injection.Data for ovarian and testicular measurements were classed into categories according to week and for pituitary response to month of the light cycle.Cubic regression analyses were conducted on the percentage of ewes with progesterone levels > 1 ng/ml and on ram testosterone and scrotal measurements.Despite the irregularity of the curve for the light cycle, the ovarian and testicular responses of rams and ewes followed an alternating curve with peaks and troughs of activity separated by approximately 13 weeks in the 26-week cycle. The peak of ovarian activity occurred during the long daylength period which followed a 22-week period of decreasing daylength and was preceded by 1 month by peak ram testosterone and scrotal sac volume.The pattern of pituitary response was related to that of the actual light cycle and the data were subjected to time-lag regression. This econometrical technique revealed that there was a delay in pituitary response to daylength changes of 2 months for rams, and between 2 and 3 months for the spayed ewes. The peak pituitary response to the GnRH test occurred one month earlier for rams than for the spayed ewes, and coincided with the corresponding troughs of gonadal activity of each sex.The results showed that the breeding season of sheep can be compressed into 6 months and that the pattern of pituitary response follows the daylength pattern more closely than do measurements of gonadal activity. Peak reproductive activity in rams, as measured by pituitary and gonadal activity, precedes that of ewes by approximately 1 month.     

Strategies for rapid rebreeding of lactating ewes in the spring

Rapid rebreeding of winter- and spring-lambing ewes is essential if ewes are to lamb more than once per year, but fertility of lactating ewes is often low and early weaning of lambs may be undesirable in forage-based production systems. Selection to improve fertility in spring matings has been successful and led to development of ewes with a reduced seasonal anestrus. Potential for rapid rebreeding of lactating out-of-season breeding (OOS) ewes was tested in three studies. In Experiment 1, effects of short-term lamb removal on rebreeding was evaluated over 2 years using 71 January-lambing OOS ewes. At an average of 63 days postpartum, 36 ewes had lambs removed for 72 h, and all ewes were joined with rams. Circulating progesterone levels indicated that 74% of ewes ovulated before lamb separation; 91% of ewes mated within 5 weeks of ram exposure, 85% were diagnosed as pregnant and 75% lambed. The average interval between lambings was 225 days. In contrast to results observed in cattle, none of the measured variables was affected by lamb separation (P>0.20). Experiment 2 compared rebreeding performance of 24 OOS and 23 St. Croix ewes that lambed in January and averaged 60 days postpartum at ram introduction. More OOS ewes ovulated, mated and became pregnant during the first 21 days of ram exposure (83.3%, 58.3%, and 41.7%, respectively; P<0.001) compared with St. Croix ewes (26.1%, 0%, and 0%, respectively). After 39 days of ram exposure, pregnancy rates still favored OOS ewes (66.7% v. 39.1%; P=0.06), but the percentage of ewes that lambed did not differ (P>0.20) between OOS (47.8%) and St. Croix ewes (34.8%). In the third study, 34 March-lambing OOS ewes were exposed to rams on May 3 at an average of 40 days postpartum to characterize their reproductive performance. After 39 days of ram exposure, 52.9±8.7% of the ewes had mated, and 38.2±8.5% were diagnosed as pregnant. However, only 20.6±7.0% of the ewes produced viable lambs, suggesting a high level of uterine insufficiency. Spring fertility of lactating OOS ewes in these studies was one of the highest reported in the literature and indicated that selection for fertility in spring mating would improve reproductive performance in accelerated lambing programs. However, exposure of lactating OOS ewes to rams at 30 to 50 days postpartum was associated with high prenatal lamb mortality.     

The ovarian and hormonal response of the ewe to stimulation by the ram early in the breeding season

The introduction of Dorset rams to Romney ewes at the beginning of the breeding season (February 14 to March 1) stimulated 39% to 70% of the non-cycling ewes to ovulate. Most of the ewes that ovulated did so within 65 to 72 hours of ram introduction. The ovulations were preceded by LH peaks, the mean onset of which was 35.0±4.8 (SE) hours after ram introduction. The mean oestradiol-17β concentration per ewe ranged from 0.3 to 14.9 pg/ml plasma and there were large fluctuations among the samples collected every 3 hours. All ewes, irrespective of treatment, had similar mean concentrations of oestradiol-17β and ovarian follicular activity, and there were no changes in oestradiol-17β concentration that could be attributed to the presence of the rams.     

Ewe effect: endocrine and testicular changes in experienced adult and inexperienced young Corriedale rams used for the ram effect

Changes in LH, FSH, and testosterone concentrations, testicular firmness and resilience, and scrotal circumference were monitored in 16 Corriedale rams (8 experienced adult and 8 inexperienced young) for 20 days during which they were used to stimulate ewes. The experiment was conducted during November (mid-non-breeding season). Increases (P<0.05) were observed in LH and testosterone concentrations and in testicular firmness and resilience during the first 4 days when rams were in permanent contact with estrual ewes. During the following 13 days, when rams were in contact with non-estrual ewes (i.e. initially estrual ewes were no longer in estrus), LH and testosterone concentrations decreased. When initially anestrous ewes exhibited estrus 17 to 20 days later, concentrations of testosterone increased. Testicular firmness and resilience remained high throughout the period. We conclude that: (1) rams used to stimulate anestrous ewes show an increase in LH and testosterone concentrations beginning at 12 h after joining, and greater concentrations are maintained while estrual ewes and mating are allowed; and (2) estrous and mating activity are probably the most important stimuli for the increase in hormone concentrations.     

Ovulation rate in ewes after single oral glucogenic dosage during a ram-induced follicular phase

A 2-factor factorial array with three replicates (N = 280) was used to simultaneously assess the effects on ovulation rate of two alternative doses of medroxy-progesterone acetate (MPA) (10 or 60 mg), applied during a 6-day priming period, and the effect of a single dosage of a glucogenic formulation, administered immediately before ram exposure to groups of adult seasonally anovular Corriedale ewes. The glucogenic formulation contained 1,2,3-propanetriol (glycerol; 70% $\text{v}\text{v}$), 1,2-propanediol (propylene glycol; 20% $\text{v}\text{v}$) and distilled water (10% $\text{v}\text{v}$). At sponge withdrawal, a single oral dose of 100 ml of this formulation or the same volume of distilled water was administered to treated and control groups, respectively, and ewes were immediately exposed to rams and hormonally-induced oestrous ewes. Data from an ancillary experiment (n = 10) showed significantly (P < 0.005) above normal plasma glucose levels in treated animals at 3 and 6 h after dosage. A significant interaction (P = 0.0006) between MPA priming doses and glucogenic supplementation was detected. Supplemented ewes, among those exposed to the lower dose of MPA, exhibited a higher (P = 0.0098) mean ovulation rate (1.56 ± 0.076) than ewes that did not receive glucogenic treatment (1.31 ± 0.060). In contrast, ovulation rate was significantly decreased (P = 0.021) from 1.30 ± 0.058 to 1.13 ± 0.042 after glucogenic treatment in ewes that were primed with sponges containing 60 mg of MPA. Ewes exposed to 60 mg of MPA were marked by the rams at a significantly later (P < 0.00001) mean time (54.8 ± 1.44 h) than ewes receiving 10 mg sponges (43.6 ± 1.08 h). These results reveal the potential for modifying ovulation rate through short-term glucogenic manipulations, at least during the compressed follicular phase typical of ram-induced ovulations.     

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%).     

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.