Mature Merino Rams Research Articles

Influence of Ellagic Acid and Ebselen on Sperm and Oxidative Stress Parameters during Liquid Preservation of Ram Semen.

Objective The purpose of the present study was to assess the effects of ellagic acid and ebselen on sperm and oxidative stress parameters during liquid preservation of ram semen. Materials and Methods In this experimental study, sixty ejaculates from six mature Merino rams were used. In experiment 1, the ejaculates were diluted in base extender contained ellagic acid at 0 (control), 0.5, 1, and 2 mM. In experiment 2, ebselen at 0 (control), 10, 20, and 40 μM were added to the extender. Sperm motility, viability, mitochondrial membrane potential, DNA integrity, lipid peroxidation (LPO), the antioxidant potential (AOP), and total glutathione (tGSH) were evaluated at 0, 24, 48, and 72 hours of preservation. Results Supplementation of ellagic acid at 1 and 2 mM resulted in higher sperm motility and viability at 0 hours of storage. Ellagic acid at 2 mM led to higher motility and viability compared to controls after 0, 24, and 48 hours of preservation and increased AOP after 24 and 72 hours. Higher tGSH was at 1 mM ellagic acid, compared to control after 72 hours. Addition of ebselen at a concentration of 40 μM increased motility at 24 and 48 hours and 10 μM produced the same effect after 48 and 72 hours of storage as well as higher viability, compared to the controls after 0 hours of storage. Sperm DNA integrity was significantly improved after 24, 48, and 72 hours with the addition of ebselen at 10 μM, and after 72 hours at 40 μM. Addition of 40 mM ebselen also reduced the LPO levels after 24 hours of storage compared to the controls. ConclusionThe results showed that supplementation of ellagic acid and ebselen in semen extender has a potential effect on sperm and oxidative stress parameters during liquid preservation of ram semen.

Protective Effect of Ergothioneine on DNA Damage of Post-Thawed Merino Ram Sperm

The objective of the current study was to evaluate the effects of antioxidant ergothioneine added to cryopreservation extender on DNA intergrity of Merino ram sperm. Semen samples from 5 mature Merino rams (1 and 2 years of age) were used in the study. Semen samples, which were diluted with a Tris-based extender containing ergothioneine at different doses and no antioxidant (control), were cooled to 5oC and frozen in 0.25 ml French straws. Frozen straws were then thawed at 37oC for 20 s in a water bath for evaluation. The addition of ergothioneine at doses of 1, 2 and 4 mM resulted in lower sperm with damaged DNA (5.4, 4.7 and 3.2%, respectively) than that of control (7.9%), thus reducing the DNA damage (P<0.01). Findings of this study showed that the increasing doses of ergothioneine supplementation in semen extenders, was of greater benefit to DNA integrity of frozen-thawed ram sperm.

Ergothioneine attenuates the DNA damage of post-thawed Merino ram sperm

The objective of the current study was to evaluate the effects of antioxidant ergothioneine added to cryopreservation extender on the DNA integrity of Merino ram sperm. Semen samples from 5 mature Merino rams (1 and 2years of age) were used in the study. Semen samples, which were diluted with a Tris-based extender containing ergothioneine at different concentrations and no antioxidant (control), were cooled to 5°C and frozen in 0.25ml French straws. Frozen straws were then thawed at 37°C for 20s in a water bath for evaluation of sperm DNA damage using the Comet test. The addition of ergothioneine at concentrations of 1, 2 and 4mM resulted in lower sperm with damaged DNA (5.4, 4.7 and 3.2%, respectively) than that of control (7.9%), thus reducing the DNA damage (P<0.01). Findings of this study showed that the increasing concentrations of ergothioneine in semen extenders, were of greater benefit to DNA integrity of frozen-thawed ram sperm.

Effects of dithioerythritol on ram semen after the freeze–thawing process

The aim of this study was to evaluate the effects of dithioerythritol added to cryopreservation extender on the post-thawed sperm parameters, lipid peroxidation and antioxidant activities of Merino ram sperm. Semen samples from 5 mature Merino rams (1 and 2years of age) were used in the study. Semen samples, which were diluted with a Tris-based extender containing 0.5, 1, and 2mM dithiothreitol and no antioxidant (control), were cooled to 5°C and frozen in 0.25ml French straws. Frozen straws were then thawed individually at 37°C for 20s in a water bath for evaluation.The addition of dithioerythritol at 0.5 and 2mM doses led to higher percentages of subjective motility (62.9±4.2% and 63.6±1.8%) compared to control (52.0±4.9%, P<0.05). As regards CASA motility, dithioerythritol 0.25 and 2mM (60.2±4.5% and 59.6±1.2%) groups were higher from that of control (44.2±8.7%, P<0.05). For the CASA progressive motility, 0.25, 0.5 and 2mM doses of dithioerythritol (22.0±2.1%, 21.7±2.5% and 24.0±1.2%) had increasing effect in comparison to control (15.0±2.5%). Dithioerythritol at 1 and 2mM doses for ALH provided higher values compared to the control (P<0.001) following the freeze–thawing process. Supplementation with dithiothreitol did not significantly affect the integrities of sperm membrane and acrosome, and mitochondrial activities. No significant differences were observed in biochemical parameters among the groups (P>0.05). Findings of this study showed that dithioerythritol supplementation in semen extenders, was of greater benefit to sperm motility of frozen–thawed ram sperm.

Effects of cysteine and ergothioneine on post-thawed Merino ram sperm and biochemical parameters

The aim of the current study was to evaluate the effects of cysteine and ergothioneine on the post-thawed sperm parameters, lipid peroxidation and antioxidant activities. Semen samples from 5 mature Merino rams were used in the study. Semen samples, which were diluted with a Tris-based extender containing l-Cysteine and l-(+)-Ergothioneine and no antioxidant (control), were cooled to 5 °C and frozen in 0.25 ml French straws. Frozen straws were then thawed individually at 37 °C for 20 s in a water bath for evaluation. Ergothioneine at doses of 2 and 4 mM increased percentages of subjective motility, VSL and VCL, compared to controls following the freeze-thawing ( P < 0.001). Ergothioneine at three different doses led to higher rates of progressive motility and VAP, compared to control groups ( P < 0.001). Cysteine and ergothioneine at three doses provided the higher rates of ALH, in comparison to no antioxidant group ( P < 0.001). As regards CASA motility, supplementation with antioxidants did not provide any significant difference on the percentage of post-thaw sperm CASA motilities, in comparison to the control. In regards of sperm membrane integrity, only cysteine 1 mM provided a greater protective effect, compared to control ( P < 0.001). Percentages of sperm with high mitochondrial activity were dramatically increased with cysteine at doses of 1 and 2 mM, compared to control ( P < 0.05). No significant differences were observed in sperm acrosome integrities among groups. CAT activity was increased significantly only in cysteine1 mM compared to control group ( P < 0.001). Cysteine at doses of 2 and 4 mM showed a tendency of increased activities of CAT when compared to control. But these increases were not statistically significant. Supplementation with antioxidants did not significantly affect activities of SOD and GPx. Findings of this study showed that ergothioneine supplementation in semen extenders, was of greater benefit to motility and motion characteristics of frozen-thawed ram sperm.

Chilled Storage of Ram Semen Improves with the Addition of Egg Yolk and Glycerol to Milk‐Based Extenders

This study aimed at comparing in vitro, ultra-heat-treated (UHT) skim milk and INRA-96(®) -based extenders supplemented or not with 5% egg yolk and/or 2% glycerol on sperm quality parameters along 72 h of preservation at 5 °C, using a factorial design. Semen from six healthy mature Merino rams was pooled and extended in each medium using a split sample procedure (six replicates) and chilled. Subjective motility (SM) (%), membrane integrity (MI) (%) and uncapacitated spermatozoa (US) (× 10(6) spermatozoa/AI dose) were used to assess the semen quality at 0, 12, 24, 48 and 72 h of preservation. UHT-based extenders yielded better (p<0.05) SM and MI than INRA-96(®) -based extenders (59.7% vs 57.9%; 60.2% vs 55.8%, respectively) but similar numbers of US (64.2% vs 62.3 × 10(6) sperm/AI dose, respectively) along the preservation time. Egg yolk-glycerol or just egg yolk as additives improved (p<0.05) the results compared with the base extenders without additives or just with glycerol. The sperm parameters assessed decline slowly from 0 to 48 h, with a sharp decline (p<0.05) at 72 h of preservation. In conclusion, UHT and INRA-96(®) were similar as base extenders, and the addition of 5% egg yolk plus 2% glycerol or just 5% egg yolk improved the quality of ram semen preserved at 5 °C, at least for 48 h. The combination of egg yolk-glycerol might provide extra protection in case of fluctuation of temperatures below 5 °C, commonly seen under field conditions.

Intracerebroventricular Infusion of Leptin into Mature Merino Rams of Different Metabolic Status: Effects on Blood Concentrations of Glucose and Reproductive and Metabolic Hormones

In mature Merino rams, nutrition is one of the external cues that most strongly affects the reproductive centres of the preoptic-hypothalamic continuum. The signalling pathways that link dietary status and the activity of the neurones that produce gonadotrophin-releasing hormone signals are thought to be partly hormonal in nature to reflect the amount of body reserves. Among the hormones thought to be involved are insulin and leptin. This study tested whether recombinant bovine leptin infused (0.4 microg/h) into the third cerebral ventricle would stimulate pulsatile luteinizing hormone (LH) secretion in mature Merino rams when their energy status was low or decreasing, during both chronic (fasting) and acute reductions of energy balance. Leptin may interact with other hormones that depend on energy availability, so we also monitored changes in circulating concentrations of insulin, thyroid hormones, growth hormone, prolactin and adrenocorticotrophin. Overall, our data do not support this hypothesis. The dietary regimes induced clear responses in the metabolic profiles of the animals but there was no clear effect of central leptin administration on LH pulse frequency. The relationships between the hormonal systems measured in the present study add weight to the contention that leptin plays only a permissive role in the nutritional control of the reproductive axis and that other hormonal signals (particularly insulin) or pathways are acting in concert with leptin to stimulate the reproductive axis.

220. Equine growth hormone enhances motility and extends longevity of ram spermatozoa in vitro

Sperm survival in vitro decreases with time at room temperature, but may be improved by treatment with recombinant bovine growth hormone in rats1, bulls2 and horses3. Two experiments investigated the effect of equine growth hormone (eGH) on the longevity of ram spermatozoa in vitro. The aim of experiment 1 was to determine if the addition eGH would improve the motility of ram spermatozoa after 24 h and identify any interaction with semen dilution rates used for ram semen preservation. Semen was collected from five mature Merino rams. Ejaculates were assessed for good quality and were diluted 1+50, 1+4, 1+3, 1+2 (semen+diluent) with a Tris-based cryoprotectant. Aliquots from each ram were mixed with eGH to achieve a final concentration of 100 ng/mL eGH and stored at 20°C for 24 h. Motility of spermatozoa was then assessed manually. eGH improved the motility of spermatozoa at all dilution rates compared to controls (P &lt; 0.0001) but most markedly in the 1 + 3 and 1 + 2 samples (42.6 ± 0.8% eGH v. 22.7 ± 2.6% control; 40.5 ± 1.4% eGH v. 22.7 ± 2.2% control, respectively, P &lt; 0.01). The aim of experiment 2 was to determine the optimum eGH concentration for improving sperm motility. eGH was added to aliquots of diluted semen (1+3 dilution rate) to produce samples with final concentrations of 1000, 100, 10 and 1 ng eGH/mL. The samples were placed in a water bath at 20°C for 24 h at which time the motility of sperm was assessed as before. Sperm motility was higher in the 100 ng/mL eGH sample (P &lt; 0.05; 39.6 ± 0.7%) compared to other concentrations (1000 ng/mL 11.8 ± 0.7%, 10 ng/mL 21.5 ± 0.7% and 1 ng/mL 11.3±0.7%). We conclude that growth hormone is effective in promoting the longevity in vitro of ram spermatozoa stored at room temperature, and that this effect is concentration dependent. (1)Breier et al. (1996). Endocrinology 137, 4061–4064.(2)Sauerwein et al. (2000). Dom. Anim. Endocrinol. 18, 145–158.(3)Champion et al. (2002). Theriogenology 57, 1793–1800.

Pamuk tohumu küspesinin tannik asit ve lignosülfonat ile muamelesinin koçlarda bazı besin maddelerinin sindirilme derecesi ve rumende parçalanma özellikleri üzerine etkisi

This study involved two separate experiments to determine the effects of tannic acid and lignosulfonate treatments of sunflower seed meal on the digestibility and rumen degradability characteristics of some nutrients in rams. Sunflower seed meal was treated with 3, 6 and 9% tannic acid, 5 and 10% lignosulfonate. In the first experiment, the digestibility coefficients of dry matter, organic matter and crude protein of sunflower seed meal samples were determined by a faeces collection method using 5 merino rams aged 1.5 years and weighing 66.5 kg. Tannic acid treatments of sunflower seed meal at the level of 3, 6 and 9% did not have any effect on in vivo crude nutrient digestibility. Crude protein digestibility values were not affected by the treatment of 5% lignosulfonate of sunflower seed meal but were decreased significantly (p<0,01) by the the treatment of 10% lignosulfonate. In the second experiment, four ruminally cannulated mature merino rams were used to measure the rumen degradability characteristics of dry matter, organic matter and crude protein of meal samples. The maximum potential degradability value of crude

Rumen degradability characteristics of xylose treated canola and soybean meals

This study was carried out to determine the effects of xylose treatments (5, 10 and 20 g/kg DM) of canola meal (CM) and soybean meal (SBM) on in situ rumen degradability characteristics in sheep. In the experiment, three ruminally cannulated mature Merino rams were used to measure in situ rumen degradability characteristics of dry matter (DM), organic matter (OM) and crude protein (CP) of meal samples. CM and SBM were treated with xylose (5, 10 and 20 g/kg DM). Xylose treatment reduced maximum potential degradability values of DM, OM, CP for SBM but not for CM. Rumen effective protein degradability values of CM and SBM ( k=0.02, 0.05 and 0.08 h −1) were decreased by all treatments. Effective degradabilities of DM, OM, CP ( k=0.05 h −1) were 0.643, 0.628 and 0.772 for untreated canola meal (UCM) and 0.622, 0.608 and 0.546 for untreated soybean meal (USBM), respectively. Effective crude protein degradability values ( k=0.05 h −1) of CM treated with xylose (5, 10, and 20 g/kg DM) were 0.73, 0.67 and 0.60, respectively. Treatment of SBM with 5, 10 and 20 g/kg of DM caused a reduction in the effective crude protein degradability at the rate of 37, 48 and 65% compared with USBM, respectively. It was concluded that CM and SBM proteins can be effectively protected from degradation in the rumen by xylose treatment.

Morphometric and endocrine analyses of the effects of nutrition on the testis of mature Merino rams.

The effects of nutrition on the testis were investigated in groups of five mature Merino rams that were fed either a sub-maintenance (low) diet or a supra-maintenance (high) diet for 69 days. Testosterone, oestradiol and inhibin were measured in blood plasma sampled simultaneously from jugular and testicular veins after an i.v. injection of 200 ng ovine LH kg-1. Plasma concentrations of testosterone, inhibin and oestradiol were higher in testicular than in jugular vein plasma for both diets (P < 0.01). After the LH injection, jugular plasma testosterone increased more rapidly (P < 0.01) in rams fed the high diet than in rams fed the low diet. This was not seen in the testicular vein. Oestradiol concentrations were higher in rams on the high diet than in those on the low diet, in both the testicular (P < 0.0001) and the jugular vein (P < 0.02). Diet did not affect inhibin concentrations. Testes were surgically removed and processed for light microscopy. Testicular mass and seminiferous tubule length and diameter were higher with the high diet than the low diet (P < 0.01). The number of Sertoli cell nuclei per testis was also affected (high diet: 120 +/- 6 x 10(8); low diet: 77 +/- 7 x 10(8); P < 0.001), whereas the proportion of testis occupied by Sertoli cell nuclei was not affected. The number of Leydig cells per testis was not affected by diet, but Leydig cells occupied a greater volume of testis in rams on the high diet than in those on the low diet (P < 0.001). The effects of nutrition on Leydig and Sertoli cells are consistent with changes in the endocrine and exocrine functions of the testis. The finding that Sertoli cell population was altered in adult rams may be explained by the GnRH-independent effects of nutrition.

Effects of nutrition on testicular growth in mature Merino rams actively immunized against GnRH

Nutrition-induced changes in testicular size in Merino rams appear to involve both GnRH-dependent and -independent pathways. This hypothesis was tested by feeding mature Merino rams that had been actively immunized against BSA or GnRH conjugated to BSA a diet that maintained initial body weight or the same diet supplemented daily with 1.5 kg of lupin grain. Blood was sampled every 20 min for 24 h on days-1, 19 and 70 relative to the change in diet. The plasma was used to assess the effects of treatments on changes in LH, FSH and testosterone concentrations. In the group immunized against BSA, FSH increased in lupin-supplemented rams compared with maintenance-fed rams, while LH and testosterone were not affected by diet. In comparison, the concentrations of LH, FSH and testosterone were significantly lower in the group immunized against GnRH than in rams immunized against BSA, but none of these endocrine variables was affected by nutrition. With both immunization treatments, the testes were significantly larger in lupin-supplemented than in maintenance-fed rams. In the group immunized against BSA, this difference was caused by testicular growth in lupin-supplemented rams, whereas in the group immunized against GnRH, lupin supplementation effectively maintained testicular mass, rather than allowed the regression observed in maintenance-fed rams. In conclusion, differences in testicular growth that were induced by dietary treatments in rams immunized against GnRH were not associated with changes in gonadotrophin or testosterone secretion. This supports the hypothesis that part of the effect of nutrition on testicular growth is independent of changes in GnRH secretion. The differences in testicular size observed in control rams were of similar magnitude to those observed in treated rams, but associated with large differences in plasma FSH concentrations, suggesting that this hormone plays an important role in this effect.

The effect of nutrition on testicular growth in mature Merino rams involves mechanisms that are independent of changes in GnRH pulse frequency.

In mature Merino rams, changes in diet to below or above the requirements for maintenance of body weight lead to changes in gonadotrophin secretion and testicular growth. However, the effects on testicular growth persist for much longer than those on LH and FSH secretion so that the gonadal and gonadotrophin responses are poorly correlated over time. This suggests that the gonadal effects may be partly independent of changes in the hypothalamic secretion of GnRH, an hypothesis tested in this study. In a short-term experiment (November, late spring, non-breeding season), we tested whether a high frequency of exogenous GnRH pulses could override the endogenous system and mimic the change in gonadotrophins seen in rams fed a high plane of nutrition. Mature Merino rams (scrotal circumference (mean +/- S.E.M.) 33.6 +/- 0.5 cm, body weight (mean +/- S.E.M.) 59.0 +/- 0.9 kg) were fed 900 g chaff + 1.6 kg lupin grain (High diet) or 360 g chaff + 60 g lupin grain (Low diet) and infused with 8 pulses of GnRH or saline daily for 5 weeks (n = 5/group). Blood was sampled every 20 min for 12 h on days-1 and 14 relative to the start of treatments. Relative to pre-treatment levels, LH pulse frequency and FSH concentrations were decreased on day 14 in saline-infused rams fed the Low diet and increased in saline-infused rams fed the High diet (P < 0.001). In GnRH-infused rams, gonadotrophin secretion was not affected by diet and the patterns of secretion of LH and FSH were similar to those in saline-infused rams fed the High diet. This model was used for a more complete endocrine analysis in a longer experiment designed to test the hypothesis that the effect of nutrition on testicular growth is partly independent of changes in the secretion of GnRH. The same treatments were imposed for 35 days on a different group of similar rams in March (autumn, mid-breeding season). Body weight and scrotal circumference were measured weekly and blood was sampled on days -1 and 14. On days -1 and 35, testosterone secretion in response to LH was tested by injecting exogenous ovine LH (NIADDK-oLH-25; 200 ng/kg body weight) to all rams. Body weight increased in rams fed the High diet and decreased in those fed the Low diet (P < 0.001) and was not affected by treatments as in experiment 1.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of nutrition on testicular size and the concentrations of gonadotrophins, testosterone and inhibin in plasma of mature male sheep.

The effects of nutrition on the hypothalamo-pituitary-gonadal axis were studied in three groups of six mature Merino rams that were fed for 56 days with a ration that maintained their initial live mass (intermediate diet: 675 g chaff plus 175 g lupins), the same ration with a lupin supplement (high diet: 675 g chaff plus 825 g lupins), or about half of the intermediate ration (low diet: 475 g chaff plus 125 g lupins). Lupin seed provides a highly (95%) digestible source of energy and protein. Plasma concentrations of LH, FSH, testosterone and inhibin were measured in blood samples collected over 24 h on the day before dietary treatments began (day-1), then on days 0, 1, 5, 14, 28 and 56. Compared with the intermediate diet, the high diet significantly increased live mass within 14 days and testicular size within 28 days, and these differences increased steadily throughout the experiment. Plasma FSH concentrations and LH pulse frequency increased within 5 days, but these effects were maintained for only 14 days. Decreasing the nutritional status reduced live mass and testicular size within 7 days, led to a low LH pulse frequency that persisted throughout the experiment, but did not affect FSH concentrations. Significantly less testosterone was secreted over 24 h in the low dietary group than in the intermediate or high group until day 28. The high group tended to secrete more than the intermediate group, but only at the beginning of the experiment when LH pulse frequencies differed between these groups.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of frequency of ejaculation and undernutrition on the size and tone of the ram's testes

Replicated experiments were conducted to examine the effects of frequency of ejaculation (0, 5 or 10 ejaculations/day for 15 days; 3 rams/subgroup) and undernutrition (100%, 60% or 20% of maintenance for 28 days; 6 rams/subgroup) on the size and tone of the testes of mature Merino rams. Rams fed at 20% of maintenance experienced reductions of 15% in live weight and 35% in testicular volume. Comparable values for rams fed at 60% of maintenance were 10% and 33% respectively. Rams which ejaculated 5 times a day suffered no reduction in live weight or testicular volume. However, contemporaries ejaculated 10 times a day experienced a 10–15% reduction in testicular volume ( P < 0.01). The tone of the testes was not closely related to changes in testicular volume induced by either undernutrition or frequent ejaculation. After 15 days (the length of the shorter experiment) the reductions (means of both replicates) in testicular volume were of the order of 14% when fed at 60% maintenance, 16% when ejaculated 10 times daily, and 19% when fed at 20% maintenance. It is concluded that both undernutrition and frequent ejaculation may contribute to the reduction in testicular size (or volume) frequently observed in rams during paddock mating. It is suggested that increased physical activity may be at least partly involved in the observed ejaculation response.

Serological, bacteriological and pathological changes in rams following different routes of exposure to Brucella ovis

Mature Merino rams were exposed to Brucella ovis by contact with infected semen, using either ewe transmission, intrapreputial, intranasal or intrarectal inoculation of infected semen or intrapreputial inoculation of B. ovis culture. Thirty-six of the 41 rams developed significant complement fixation (CF) test titres, but only 9 of these reactors showed clinical, bacteriological or pathological evidence of infection. Infection occurred in some of the rams from all groups. The results are discussed in relation to the transmission of the disease and the significance of CF titres in rams exposed to B. ovis.

Serological, bacteriological and pathological changes in rams following different routes of exposure to Brucella ovis.

Mature Merino rams were exposed to Brucella ovis by contact with infected semen, using either ewe transmission, intrapreputial, intranasal or intrarectal inoculation of infected semen or intrapreputial inoculation of B. ovis culture. Thirty-six of the 41 rams developed significant complement fixation (CF) test titres, but only 9 of these reactors showed clinical, bacteriological or pathological evidence of infection. Infection occurred in some of the rams from all groups. The results are discussed in relation to the transmission of the disease and the significance of CF titres in rams exposed to B. ovis.

Reproductive hormone secretion and spermatogenic function in thyroidectomized rams receiving graded doses of exogenous thyroxine.

This study aimed to obtain a better understanding of the relationship between circulating thyroxine (T4) concentrations and reproductive endocrine function in the ram. Mature Merino rams were thyroidectomized and supplemented with 0, 30, 100 and 300% of normal T4 for 10 weeks. Thyroidectomy had no apparent effect on spermatogenic function but interfered with sperm maturation, the latter being returned to normal by 30% T4 replacement. Circulating testosterone levels were reduced by thyroidectomy and restored to control levels by 30% T4; when T4 levels were supranormal (300%), circulating testosterone levels were again reduced. The lowered circulating testosterone levels in thyroidectomized rams occurred as a result of suppressed testosterone secretion from the testis, observed under basal conditions and also following LH-releasing hormone (LHRH) and human chorionic gonadotrophin injection. In thyroidectomized rams, sex hormone binding globulin (SHBG) levels were depressed without changes in testosterone clearance rate (TCR), while in rams with supranormal T4 levels, TCR was increased without changes in SHBG levels. Subnormal levels of T4 also restored to normal the reduced LH pulse frequency in thyroidectomized rams. Reduced LH pulse frequency, together with diminished LH release following LHRH injection in thyroidectomized rams, suggested effects of T4 at the hypothalamo-pituitary axis. The present study demonstrates that complete lack of thyroid hormones suppresses normal reproductive endocrine function in the ram, but that this can be restored to normal by 30% T4 replacement. The results support the theory that T4 plays a permissive rather than a regulatory role in reproductive function in males.

Spermatogenesis, seminal characteristics and reproductive hormone levels in mature rams with induced hypothyroidism and hyperthyroidism.

Mature Merino rams were made hypothyroid by daily oral drenching with methylthiouracil or hyperthyroid by daily subcutaneous injections of thyroxine for 8 weeks. Neither hypothyroidism nor hyperthyroidism had any apparent effect on either spermatogenesis or daily sperm production, but motility of ejaculated spermatozoa and circulating testosterone concentrations were reduced in both conditions. The ratio of testosterone concentrations in plasma from the internal spermatic vein to those in peripheral blood plasma was higher in hyperthyroid (21.2 +/- 3.5) than in control (11.1 +/- 4.4) and hypothyroid (7.6 +/- 1.4) rams. The basal secretion rate for testosterone was slightly lower in hypothyroid rams and testosterone responses to human chorionic gonadotrophin and after LH-releasing hormone (LHRH) were very much reduced. Basal serum LH levels were low in both hypothyroid and hyperthyroid rams compared with controls whereas there were no differences in FSH levels. The LH response to exogenous LHRH was reduced in hypothyroid rams but not in hyperthyroid rams. Serum prolactin levels on the other hand were higher than control in both hypothyroid and hyperthyroid rams. Reduced testosterone secretion in hypothyroid rams indicates that the normal function of Leydig cells depends on an adequate level of thyroid hormones. The decrease in circulating testosterone concentrations in hyperthyroid rams with normal secretion rates suggests an increased testosterone clearance rate in these animals. The decreased spermatozoal motility in hypo- and hyperthyroid rams suggests that the lowered testosterone level in these animals has altered the androgen-dependent maturation of spermatozoa in the epididymis.(ABSTRACT TRUNCATED AT 250 WORDS)

Mating activity and reproductive performance in Merino flocks where ram percentages are 1.0, 0.5 and 0.25

Mature Merino rams were joined at rates of one ram to 100 ewes (1.0%), one ram to 200 ewes (0.5%) and one ram to 400 ewes (0.25%) in paddocks at Richmond, New South Wales. Fresh rams were introduced each day of joining and mating activity was measured and behaviour was studied by direct observation. Thirty-eight days after the removal of entire rams, the ewes were slaughtered and reproductive tracts were collected and examined. As ram percentage fell so also did services per ewe (4.3 to 2.2), number of ewes that mated (6.2 to 3.3/d) and the percentage of ewes that became pregnant (88.8 to 60.4%). Ram service activity remained constant as the number of ewes per ram increased. There were increases in the number of oestrous ewes in physical contact with and crowding the rams and in the number of ewes returning to be served in the second period of joining. The study suggests that the percentage of mature Merino rams joined with mature Merino ewes should not be less than one, because below this value, reproductive performance declines. The decline may be due to oestrous ewes crowding around the ram, thus preventing rams from increasing service activity thereby reducing services per ewe, ewes mated and ewes pregnant.