Rams' reproductive status during a controlled breeding period: effect of social dominance.

The aim of this study was to compare the variation in body weight, scrotal circumference (SC), and seminal quality during a breeding period in dominant and subordinate rams. Data were collected from 12 dyads of rams, each bred with 15 ewes for 7 weeks. Before joining, the dominance relationship between both rams from each dyad was determined. Body weight and SC were recorded weekly in the morning, and semen was collected by electroejaculation, determining the volume, sperm concentration, mass motility, and percentage of sperm with progressive motility. In addition, the total number of sperm and sperm with progressive motility ejaculated were calculated. Dominance had no direct effect or interaction with time on any of the variables analyzed. Body weight, seminal volume, sperm concentration, mass motility, percentage of sperm with progressive motility, and total ejaculated sperm varied with time (p < 0.05), and scrotal circumference and total ejaculated sperm with progressive motility tended to vary with time. In general, all indicators evaluated were affected in the first weeks, when most ewes were cycling, recovering as the breeding progressed. It was concluded that, at least under the conditions of this study, dominance position did not affect the profile of the reproductive variables evaluated, although all of them were affected during the breeding period.

Cloprostenol enhances sexual behaviour and semen quality in growing lambs more effectively than Dinoprost.

Analogues of PGF2α have been used in boars with positive results on sexual behaviour, but limited impact on semen quality. The objective of this study was to determine whether the administration of Dinoprost tromethamine or D-Cloprostenol enhances the sexual behaviour and semen quality of sexually inexperienced growing lambs during the onset of the breeding season. The study lasted 10 weeks, beginning during the non-breeding season, with 24 sexually inexperienced Katahdin lambs (5.1 ± 0.5 months old). Three groups of eight lambs each received: (1) vehicle treatment (group CON); (2) 10 mg of Dinoprost tromethamine (group DIN); or (3) 0.15 mg of Cloprostenol dextrogy (group CLOP). The treatments were all applied im 5 min before the tests of sexual behaviour, or 20 min before the collection of semen. Sexual behaviour was evaluated twice weekly in a pen test with a non-oestrous ewe, and semen was collected once weekly with an artificial vagina. The latency to begin courtship was significantly shorter in both groups that received analogues of PGF2α than in CON lambs. The number of ano-genital sniffs, flehmens and lateral approaches was greater in both treated groups than in CON lambs (p < .05). Lambs from DIN group mounted significantly more than CLOP and CON lambs, which did not differ. However, CLOP lambs showed significantly greater mating efficiency (i.e. ejaculations/total mounts) than CON lambs, which exhibited significantly greater mating efficiency that DIN lambs. Lambs treated with CLOP produced significantly more semen volume with more mass motility than those treated with DIN and CON (without differences between DIN and CON). Overall, we concluded that the administration of cloprostenol or dinoprost before sexual evaluation in young rams enhances their sexual behaviour. Cloprostenol had greater effects than dinoprost. The administration of cloprostenol before semen collection also triggered the ejaculation of a greater volume of semen, with greater mass motility. These results open interesting possibilities to study deeply the use of simple and cost-effective treatments to improve the reproductive results of young growing rams.

The use of oxytocin to cause cervical dilation for transcervical insemination in nulliparous goats: Improving pregnancy and kidding rates.

To evaluate the effect of oxytocin as a cervical dilator, a study was carried out on nulliparous goats inseminated transcervically at the beginning of the breeding season. One hundred sixteen nulliparous goats with a mean live weight of 33.4 ± 0.68 kg and an age of 13.7 ± 0.37 months were used. The goats were exposed to active bucks of proven fertility for a period of 14 d in order to induce oestrus. One week later, the Ovsynch protocol was applied, which consisted of the application of 20 mg of gonadorelin (Day Zero), 0.075 mg of cloprostenol (Day 7) and of a second dose of 20 mg of gonadorelin applied on Day 9. Artificial insemination (AI) was performed 16 hr later. Three treatments were evaluated: T1 = 50 IU saline, T2 = 25 IU oxytocin; T3 = 50 IU of oxytocin, intravenously applied 10-15 min before AI. The time required to inseminate each treated goat from groups T2 and T3 was 49.56 and 56.25 s, respectively, versus 85.78 s needed for the goats from group T1 (p < .0001). In the T1 group of goats, the insemination catheter was inserted 2.1 cm into the cervical canal and in goats from groups T2 and T3 it reached 3.41 and 3.77 cm into the cervical canal, respectively (p = .02). Pregnancy rates and prolificacy (kids/doe) were higher (p = .02) for groups T2 (82.93%; 1.16) and T3 (76.92%; 1.21) respectively than for control goats (61.11%; 0.69). In conclusion, the intravenous administration of oxytocin led to greater dilation and depth of cervical penetration, obtaining higher pregnancy rates and prolificacy.

Administration of a single dose of a PGF2α analogue (dinoprost) before sexual tests did not improve ram's sexual behaviour.

The aim of this study was to determine if a single administration of dinoprost tromethamine before each test enhances sexual behaviour in inexperienced rams, and if the possible effect is maintained after the rams gain sexual experience. The study was conducted in northeaster Mexico during autumn (breeding season). The study was performed with 26 Saint Croix rams (16.1 ± 1.1 months old). Rams were allocated to two treatments, which were subjected to 15 tests with 2 restrained non-oestrous ewes. While rams from one group (group DIN) received a single dose of dinoprost (10 mg im, Lutalyse, Zoetis) immediately before the test, the other rams remained untreated (group CON). Sexual behaviours were recorded during 5 min. The data were analysed with a mixed model that included the treatment, number of test and their interaction as main effects, and the individual as a random effect. DIN rams displayed less ano-genital sniffings (6.6 ± 0.8 vs 9.7 ± 0.8, P = 0.007), matings (0.11 ± 0.05 vs 0.29 ± 0.05, P = 0.03), and had a lower mating/total mounts ratio (0.05 ± 0.03 vs 0.16 ± 0.03, P = 0.006) than CON rams. There were no other treatment effects, but there were significant effects of time and interactions between treatment and time in all the behaviours. Overall, administration of a single dose of dinoprost before testing did not have positive effects in the development of rams' sexual behaviour, and even, might have negative effects. However, it should be considered that in this study only one prostaglandin analogue, one dose of this analogue, administered immediately before the tests was used, so more studies involving other analogues, doses, and/or regimes of administration should be done.

Seasonality in Saint Croix male lamb reproductive development in northern Mexico.

The aim of this study was to determine the influence of the season of birth on the body weight, testicular size, testosterone concentrations, semen output and sexual behaviour in Saint Croix male lambs. Thirty-three lambs were born in spring (n = 10), summer (Sum; n = 12) or autumn (n = 11). Body weight and the scrotal circumference were weekly recorded; semen was also weekly collected by electroejaculation; and sexual behaviour towards oestrous ewes was weekly evaluated. Data were recorded from 15 to 33 weeks of age. The reproductive development of Saint Croix male lambs differed according to the period in which they were born. More lambs born in spring than in summer and autumn achieved puberty during this study and were also more precocious in semen production and displayed sexual behaviour earlier. Lambs born in summer delayed their semen production; however, season-related negative effects were less pronounced at the end of the study than in autumn born lambs born. In conclusion, despite the apparently low seasonality of the breed, Saint Croix male lambs showed in this study a seasonal pattern in their reproductive development at least until they achieve the puberty.

Influence of eCG and breed on the number of oocytes collected and the production of in vitro embryos of young goats during the reproductive season.

The objective of this study was to determine the effect of breed and equine chorionic gonadotropin (eCG) on ovarian response and in vitro embryo production from young goats. Thirty-one (12 Alpine, 10 Nubian, and 9 Saanen) were randomly assigned into three treatments of eCG (T1, 0 IU; T2, 500 IU; and T3, 1000 IU). Alpine goats showed the highest amount and largest size of follicles (P = 0.003). The effect of eCG dose 24 h post application was significant (P < 0.05), and was superior in goats undergoing T2. The aspiration rate of cumulus-oocyte complexes (COC) was 34% (P > 0.05), except for percentage of denuded oocytes, which obtained the highest number (P = 0.003) in the Saanen goats. The same difference was found (P = 0.02) in oocytes grade III in T2 and T3, with 42.5 and 37.9% respectively. In vitro embryo production was 80.0% of IVF/cleavage in the Alpine goats (P = 0.003). Embryo production was the greatest for T2 (69.2%; P = 0.004). T3 goats had higher percentage of morula stage (66.6%; P = 0.030). It is concluded that the application of eCG has a significant effect on the ovarian status, and quality and quantity of embryos with a differential response depending on the breed.

Environmental factors and ram influence litter size, birth, and weaning weight in Saint Croix hair sheep under semi-arid conditions in Mexico.

This study was conducted to evaluate the effects of season, year of lambing, parity, and the effect of ram on litter size, birth, and weaning weight through 8 years. Data of 4078 lambs sired by 21 rams and 1072 ewes were analyzed by a lineal model. There was a significant effect (P < 0.05) of lambing number on litter size and birth weight, but not on weaning weight (P > 0.05). For litter size, the lowest numbers were obtained on the first lambing ewes (1.21 ± 0.03) and the highest ones inewes starting from the fourth lambing (1.69 ± 0.04). Lowest body weights were found in lambs born from first lambing ewes (3.01 ± 0.1 kg) and the highest ones in lambs born from the second (3.14 ± 0.1) to the fifth (3.15 ± 0.2) lambing ewes. The lambing breeding season had a significant effect on weaning weight: the highest weaning weights were recorded in lambs born in spring (12.70 ± 0.20 kg) and the lowest ones in those born in summer (11.93 ± 0.20 kg). Lambing year had a significant effect (P < 0.05) on litter size and weaning weight, since the values of both traits improved through the years. Effect of ram was significant (P < 0.05) for each of the traits considered: there were differences up to one lamb per litter, also differences up to 1.5 kg for birth weight and up to 6.5 kg for weaning weight among rams. In conclusion, these results indicate that environmental conditions are important source of variation in litter size, birth, and weaning weight in hair sheep under semi-arid climate.

Systematic review of hormonal strategies to improve fertility in rams.

Reviewing the current state of knowledge on reproductive performance and productive traits in rams has many advantages. First, the compilation of this information will serve as a literature resource for scientists conducting research around the world and will contribute to the understanding of the data collected and interpreted by researchers on the different hormonal strategies used to improve reproductive performance in rams. Second, it will allow scientists to identify current knowledge gaps and set future research priorities in ram reproduction. Rams play an important role in the global flock economy, but their reproductive analysis has been limited in the use of hormonal technologies to increase the productivity of sheep flocks. In this review, we cite the most important works on six hormones that, in one way or another, modify the hypothalamus-pituitary-gonadal axis, at different doses, in and out of the reproductive season, breeds, application methods, among other factors. The overall aim is to increase the reproductive efficiency of rams in different scenarios and, in some cases, of other species due to the lack of limited information on rams.

Selenium Injection in Dam Rabbits During Gestation Has Important Effects on Progeny Productive Performance.

Micromineral elements have a fundamental participation in the processes of organogenesis and fetal development. The objective of this study was to assess the effect of selenium (Se) injection in pregnant female rabbits, during organogenesis or rapid fetal growth, on the productive performance of their progeny. An experiment was carried out with 30 New Zealand female rabbits, with an average age of 6 months. At the end of mating (day 0), using a randomized complete design, the female rabbits were distributed into three experimental groups, which were assigned to the following treatments: Control, female rabbits were injected intramuscularly (IM) with 0.5 ml of saline on days 13 and 23 of gestation; Early administration, female rabbits that were injected IM with Se (0.10 mg/kg BW) on day 13 of gestation (organogenesis) and 0.5 ml of saline on day 23 of gestation; and Late administration, female rabbits that were injected IM with 0.5 ml of saline on day 13 of gestation and Se (0.10 mg/kg BW) on day 23 of gestation (rapid fetal growth). No differences were found on kindling performance of dams and pre-weaning growth of rabbit offspring. However, an injection of Se to pregnant rabbits affected the growth and development of their progeny, with the treatment leading to changes in the yield of some carcass traits (forelimb weight and forelimb muscle weight) and weights of some organs (liver, lungs, and spleen). The Se treatment (both early and late) also resulted in lower concentrations of glucose, triglycerides, and cholesterol when compared to the control group. These effects were different when Se injection was performed during organogenesis or rapid fetal development. The results from this study suggest that there are beneficial effects of gestational Se injection of rabbit dams on important productive traits of their progeny.

Sexual performance and semen quality of pubertal lambs treated with different weaning methods.

The objective of this study was to determine the effect of the weaning method on lamb stress, body weight, sexual behavior, and semen quality of Saint Croix male lambs. The present study was carried out during the late spring and summer of 2018 in the northeast of Mexico. Sixty male lambs born as twins or triplets (3.2  ±  0.6 kg birth weight) and weaned at 60 d of age (19.21  ±  1.8 kg weaning weight) were divided into two weaning methods: complete separation from the dams (CS; the lambs were moved to a pen that was at 500 m of distance from the dams) and separation with contact from the dams (SCD); the lambs were physically separated by a steel mesh that prevented the lambs from having the possibility of sucking milk from their mothers, but they maintained permanent visual and auditory contact. Cortisol levels were determined 3 d before and 7 d after weaning. Lambs were evaluated as 3-month-old lambs for sexual behavior and semen quality for 9 weeks. The effects of the weaning method (M), week (W), and the interaction M  × â€¯W were significant on body weight and cortisol levels ( P < 0.001 ). The SCD lambs had higher cortisol levels at 3, 5, and 7 d after weaning than CS lambs ( P < 0.001 ). The CS lambs had higher body weight during the first 4 weeks after weaning than SCD lambs ( P < 0.001 ). The weaning method had no effect on scrotal circumference, sexual behavior, and semen quality traits, except for progressive sperm motility, being better for the lambs that were completely separated ( P < 0.05 ). The results from this study show that complete separation of lambs and ewes at weaning is an effective method to reduce lamb stress and improve lamb growth after weaning, but it did not have long-term effects on sexual behavior and semen quality of Saint Croix male lambs.

Environmental factors and interval from the introduction of rams to estrus in postpartum Saint Croix sheep.

The objective of this study was to determine whether season and total rainfall during the breeding season, sheep parity, and/or litter size affect the interval from the introduction of rams to estrus (IRE) in hair Saint Croix sheep in northeastern Mexico. An analysis was made of 874 services performed during 9 years, introducing the rams into the sheep flock after an isolation period of 60 days during the postpartum period. Estrus was recorded twice daily during 35 days. Year and season influenced significantly on the interval between ram introduction and estrus length (P < 0.01). Winter IRE length (7.9 ± 0.1 days) was shorter than in the other three seasons (11.1 ± 0.2, 11.1 ± 0.1, and 16.2 ± 0.2 days in summer, autumn, and spring, respectively) (P < 0.01). An interaction was observed between rainfall and season, then by rainfall between 0 and 100 mm, IRE was shorter (P < 0.05) in winter (6.8 ± 0.3 days), and by rainfall between 100 and 199 mm, IRE was shorter (P < 0.05) in autumn (10.2 ± 0.5 days); however, when rainfall was beyond 200 mm, IRE length was shorter (P < 0.01) in summer (4.8 ± 0.5 days) than in autumn (14.5 ± 0.3 days). The IRE length was also longer in first lambing ewes (P < 0.05) and was not affected by litter size. In the present study, several factors, including the breeding season, rainfall and parity, directly influenced the interval between the male introduction and the onset of estrus by Saint Croix hair sheep.

Singleton or twin male lambs: Effects on their reproductive development.

Because intrauterine environment differs between twins and singletons, twin-born lambs are often studied when effects of fetal programming are evaluated. In sheep, fetal programming might have effects on reproductive physiology and behavior after sexual maturation. The aim of this study was to compare sperm output and sexual behavior in developing singleton- or twin-born lambs of similar body weight. Singleton lambs (n = 12) and twin (n = 9) male-male lambs were used. From 5.4 until 9.1 months of age, body weight, scrotal circumference (every 3-4 weeks), sexual behavior (every 14 days) and semen characteristics (every 28 days) were evaluated. In the third ejaculate, singleton lambs ejaculated a larger volume of semen than twins (P = 0.03). Considering a pool of the three ejaculates, twin lambs ejaculated semen with a greater sperm concentration than singleton lambs (P = 0.015). There was an interaction between group and time to the onset of courtship behavior (P = 0.02) and a tendency for an interaction in the number of mount attempts (P = 0.052). Singleton-born lambs, during the first evaluation period began courtship behavior earlier than twin-born lambs (P < 0.0001). In conclusion, there were only slight differences in semen and sexual behavior between male ram lambs born as singletons or twins with similar weight. Male ram lambs born as singletons initiated the courtship behavior earlier than twins during the first sexual behavioral evaluation period, ejaculated a larger volume of semen in the third consecutive ejaculate, and there was a lesser sperm concentration in the three ejaculates.

Social dominance affects the development of sexual behaviour but not semen output in yearling bucks.

Goats are polygynous seasonal mammals that establish dominant-subordinate relationships, especially in bucks. The aims of this study were to: 1) compare the reproductive development of dominant and subordinate young bucks allocated in dyads, and 2) determine if their previous dominant position affect their response to grouping. Twenty-four young bucks were allocated in dyads when they were 4 mo old, and the dominance position (DP) [dominant (DB) or subordinate buck (SB)] was determined with a test of competition for food. Body weight, scrotal circumference, semen quality and sexual behaviour toward an oestrous ewe were weekly determined during 8 weeks beginning when the bucks were 8 mo old. Body weight, scrotal circumference, and seminal parameters were not affected by DP. Dominant bucks tended to begin sexual courtship earlier than SB bucks (P = .09), but displayed less flehmen (P = .0008) and tended to display less ano-genital sniffings (P = .053). However, DB bucks displayed more lateral approaches (P = .019), attempted to mount, mounted, and mated the oestrous doe more times (P < .0001, P = .0002 and P < .0001, respectively) than SB bucks. In the 9th week, all the bucks were grouped, cortisol and testosterone serum concentrations were measured, and agonistic and sexual behaviour between bucks were recorded during the first day. Semen was collected and evaluated 4 and 9 days after grouping. Cortisol concentration increased (P = .037), but testosterone decreased (P < .0001), after grouping the animals, without differences according to their DP. The DB tended to display more lateral approaches toward other bucks than SB bucks (P = .06), but there were no effects of DP in any other behaviour. Sperm concentration and the total number of sperm in the ejaculate decreased after grouping (P = .01 and P = .009 respectively. In conclusion, in the conditions of this study, dominance relationships affected sexual behaviour but not body or testicular size or semen output in young bucks allocated in dyads. Dominant bucks were more effective displaying sexual consummatory behaviours. Grouping all the bucks together displayed a strong stress response that affected testosterone secretion and sperm output which was of similar magnitude in bucks that were dominant or subordinate individuals before.

Effects of exogenous enzymes and application method on nutrient intake, digestibility and growth performance of Pelibuey lambs.

Pelibuey sheep is the main breed in the tropical and subtropical regions of Mexico, and high demand of sheep meat has favored the finishing of lambs in feedlots with diets containing high levels of grains. The objective of this study was to evaluate the effects of exogenous enzymes (EE) and application method on nutrient intake and digestibility and performance of growing Pelibuey lambs. Treatments were based on comparison of two different methods of adding an enzyme product (sprayed on the total mixed ration or applied orally to the lambs) versus control treatment (no added enzyme). Twenty-one Pelibuey lambs, weighing 15.7 kg (SD = 1.8 kg) initial body weight, were individually housed in shaded pens and assigned randomly to one of the three enzyme treatments. At the end of study (lasting for 45 days), three lambs from each treatment were randomly selected and adapted to a pants and harness designed for fecal collection to measure nutrient digestibilities. Total body gain and average daily gain were affected (P < 0.05) by supplemental EE. The application method of EE had significant (P < 0.05) effect on FCE and FCR, but no effects were observed on nutrient intake. Supplemental EE did improve (P < 0.05) the digestibilities of dry matter, organic matter, neutral and acid detergent fiber, but no differences were observed in crude protein digestibility. The application method of EE had significant (P < 0.05) effect on the digestibility of acid detergent fiber. Supplemental EE can improve body weight gain and nutrient digestibilities without affecting nutrient intake in Pelibuey lambs, but the results of feed conversion efficiency and acid detergent fiber digestibility depend on the application method used of the EE.