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.

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.

Effect of Social Rank upon Estrus Induction and Some Reproductive Outcomes in Anestrus Goats Treated With Progesterone + eCG

We evaluated the possible role of the social rank [R] (i.e., low-LSR, middle-MSR, or high-HSR) in anestrus goats exposed to a P4 + eCG [D] (i.e., 100 or 350 IU) estrus induction protocol (EIP). Adult, multiparous (two to three lactations), multiracial, dairy-type goats (Alpine-Saanen-Nubian x Criollo goats (n = 70; 25°51' North) managed under stall-fed conditions were all ultrasound evaluated to confirm anestrus status while the R was determined 30 d prior to the EIP. The variables of estrus induction (EI, %), estrus latency (LAT, h), estrus duration (DUR, h), ovulation (OVU, %), ovulation rate (OR, n), corpus luteum size (CLS, cm), pregnancy (PREG, %), kidding (KIDD, %), and litter size (LS, n) as affected by R, D, and the R × D interaction, were evaluated. While OVU and CLS favored (p < 0.05) HSR (96% and + 1.04 ± 0.07 cm), an increased (p < 0.05) LS occurred in D350 vs. D100 (2.06 ± 0.2 vs. 1.36 ± 0.2); neither R nor D affected (p > 0.05; 38.5%) KIDD. However, EI, LAT, DUR, OR, and PREG were affected by the R × D interaction. The HSR group had the largest (p < 0.05) EI % and DUR h, irrespective of D. The shortest (p < 0.05) LAT occurred in D350, irrespective of R. While the largest (p < 0.05) OR occurred in HSR and MSR within D350, the HSR + D350 group had the largest PREG (p < 0.05). These research outcomes are central to defining out-of-season reproductive strategies designed to attenuate seasonal reproduction in goats.

Changes in melatonin concentrations in seminal plasma are not correlated with testosterone or antioxidant enzyme activity when rams are located in areas with an equatorial photoperiod

In temperate climates, photoperiod and melatonin regulate ram reproduction, modulating hormonal secretions, sperm quality, and seminal plasma composition. Information on the effect of an equatorial photoperiod (12L:12D) on ram reproduction, however, is scarce, and no data on hormonal concentrations and antioxidant enzyme activity in seminal plasma have been reported. Thus, the variation was investigated of melatonin and its relationship with testosterone and antioxidant enzyme activity in the seminal plasma of three sheep breeds in Colombia, when there was a consistent photoperiod during two dry and two rainy seasons per year. Semen was collected once a week from 12 mature rams (four of each breed: Colombian Creole, Hampshire, and Romney Marsh). Seminal plasma was obtained by centrifugation. The concentration of melatonin and testosterone were quantified along with the enzymatic activity of glutathione peroxidase (GPx), glutathione reductase (GRD), and catalase (CAT). Correlation analyses between melatonin and testosterone concentrations or enzymatic activity were also performed. Melatonin concentration was affected by season (P < 0.05) but not breed, with lesser concentrations in the first rainy season. Testosterone concentration, however, was affected by breed and season, with greater concentrations (P < 0.01) in the Hampshire and Romney Marsh rams during the second dry season. Regarding antioxidant enzyme activity, there was only seasonal variation in GPx activity (P < 0.05). When correlation analyses were used for data assessments, there was a negative correlation between melatonin and testosterone concentrations in Hampshire rams. In conclusion, melatonin concentrations in seminal plasma of rams that were located in an area with an equatorial photoperiod was affected by the climatological season but there was no positive correlation with testosterone concentration or antioxidant enzyme activity.

Social rank during pre-pubertal development and reproductive performance of adult rams

Reproductive performance of rams when they were 1.5 and 2.5 years old during two breeding seasons was investigated. The objective was to compare the reproductive performance of the rams on the basis of their social ranks, which had been scored for each subject during the lamb development stage. The subjects were aged matched Corriedale x Milchschaf rams (n=12: all singles born during the same week from multiparous ewes) were used. Data were collected from the five rams with greater (GR) and lesser (LR) social rank scores when lambs. These data included body weight, scrotal circumference, sexual behavior toward estrual ewes (e.g. incidence of ano-genital sniffing, lateral approaches, Flehmen, mount attempts, actual mounts, and mounts with ejaculations, and ejaculation/total mount ratio) during a 30-min period, and semen variables (semen volume, mass motility, individual sperm motility and total number of spermatozoa in the ejaculate). During the first breeding season, GR rams were heavier (62.9+/-2.7 kg) than LR rams (69.4+/-3.0 kg; P<0.0001). There were no differences in scrotal circumference or testosterone concentration measures. Semen volume was greater in GR rams (0.5+/-0.1 mL compared to 0.7+/-0.1 mL for GR and LR rams; P<0.004), but it tended to have a greater percentage of abnormal spermatozoa. Although some courtship behaviors were more frequent in LR rams (lateral approaches and Flehmen) and ejaculation/total mount ratio of LR rams also tended to be greater, mounting activity (mount attempts and mounts) was more frequent in GR rams. During the second year, GR rams still tended to be heavier (83.3+/-2.0 kg compared to 85.9+/-2.4 kg; P=0.09) but had smaller scrotal circumference than LR rams (37.5+/-0.2 cm compared to 36.5+/-0.6 cm; P<0.045). Semen characteristics were not different for the rams, but mass motility tended to be greater for LR rams. Generally, LR rams displayed more lateral approaches, showed Flehmen more often, mounted with ejaculation more often, and tended to have a greater mount with ejaculation/total mounts ratio. Conclusions were courtship of rams may differ in line with the social status they had as lambs although there are not clear effects on other sexual behaviors or semen characteristics.