Effects of recent sexual experience and melatonin treatment of rams on plasma testosterone concentration, sexual behaviour and ability to induce ovulation in seasonally anoestrous ewes

The aim of this study was to determine whether advancing the seasonal changes associated with rams by treatment with exogenous melatonin and allowing the rams previous sexual experience would increase the proportion of anoestrous ewes ovulating in early July. North Country Mule ewes (n = 225) were grouped by live body weight and body condition score and allocated randomly to the following treatments: (i) isolated from rams (control; n = 25); (ii) introduced to rams (treatment 2); (iii) introduced to rams that had mated with ewes during the previous 2 days (treatment 3); (iv) introduced to rams implanted with melatonin (treatment 4); and (v) introduced to rams that were implanted with melatonin and had mated with ewes during the previous 2 days (treatment 5). Treatments 2-5 were replicated (2 x 25 ewes) and two rams were introduced to each replicate group. Introductions began on 4 July and were completed by 11 July. The rams were withdrawn from the ewes after 8 days. Melatonin was administered as a subcutaneous implant (Regulin((R))) on 22 May and again on 20 June. Blood samples were taken from all rams to determine plasma melatonin and testosterone concentrations (19 samples in 6 h). The behaviour of the sheep was videotaped continuously during the first 3 h after the ram was introduced. Ovulation was detected by an increase in plasma progesterone concentrations from < 0.5 ng ml(-1) to > 0.5 ng ml(-1). Mean +/- SE plasma melatonin concentrations were 649.7 +/- 281.4 and 18.3 +/- 2.4 pg ml(-1) in rams with and without melatonin implants, respectively (P < 0.001). Melatonin implants also increased plasma testosterone concentrations from 4.30 +/- 1.88 to 10.10 +/- 1.10 ng ml(-1) (P < 0.01), the libido of the rams and the proportion of ewes that ovulated in response to the rams (43 and 56% (treatments 4 and 5) versus 24% (treatments 2 and 3)). In conclusion, implanting rams with melatonin before introducing them to seasonally anoestrous ewes increases the proportion of ewes that ovulate in response to introduction of a ram, but previous sexual experience of rams appears to have little or no effect.     

The number of spermatozoa required by naturally mated ewes and the ability of rams to meet these requirements

The fertility of naturally mated ewes was compared with the number of spermatozoa deposited, and the number of times they were mated. The number of spermatozoa received was estimated from ejaculates flushed directly from the vagina of naturally mated ewes.In one experiment, maximum fertility was achieved with as few as 140 × 10⁶ spermatozoa. The percentage of pregnant ewes was similar in ewes mated once or more than once (68.4% vs. 72.5%). Similar results were obtained in one test of a further experiment but in a second test fertility was higher in ewes that were mated more than once. If this effect was due to the extra spermatozoa received, then ewes required 500 × 10⁶ spermatozoa to achieve maximum fertility. Half of the ewes were mated at their first oestrus after treatment with progestagens in the second experiment. The fertility of these ewes was similar to that of the remaining ewes, which were mated at natural oestrus.The mean number of spermatozoa ejaculated by individual rams varied from 140 × 10⁶ to 1050 × 10⁶, following depletion of the epididymal reserves of spermatozoa. The rams ejaculated an average of 9.1 × 10⁶ spermatozoa per gram of testis per day in the first experiment. The rams mated an average of 10.9 times per day in the first experiment, 6.9 and 6.1 times per day, respectively, for the first and second tests in the second experiment. The number of times that rams mated was highly correlated with the number of ewes with which they mated in the second experiment.     

Fertilization and early embryonic development in androstenedione-immunized Merino ewes

Ewes were immunized against androstenedione (Fecundin) and assigned to be mated 14 days (179 ewes Group C) or 25 days (174 ewes Group B) after a booster immunization with Fecundin. The anti-androstenedione titres at these times were 6790 and 3240 respectively (P less than 0.01). The remaining 169 ewes were untreated controls (Group A). Ewes were mated to entire rams (12 rams to 180 ewes) at their second oestrus after synchronization of oestrus. Immunization against androstenedione caused a shortening of the time from sponge removal to mating (Day 0) and a decrease in the percentage of ewes mated by the rams. Also, ovulation rate was increased after immunization (P less than 0.01), being 1.42, 2.16 and 1.93 for Groups A, C and B respectively. Egg recovery rates on Day 2 were lower in immunized ewes and there was some indication that fertilization rates were lowered. On Day 13 after mating a higher proportion of blastocysts was recovered from ewes in Group A than from those in Groups B and C. Immunization resulted in lower fertilization rates and smaller blastocysts with lower mitotic indexes (P less than 0.01). At Days 24-32 of pregnancy fetal weight was lower in the immunized ewes. At all sampling stages, the proportion of ewes pregnant (fertility) was lowered in immunized ewes. The results of the present study show that significant reproductive wastage occurs in androstenedione-immunized Merino ewes, with lower rates of embryo recovery and delayed embryonic development being found in comparison to controls.(ABSTRACT TRUNCATED AT 250 WORDS)     

The contribution of the male to ovine embryogenesis in an in vitro embryo production system

The differences in the embryo production potential of four rams used in a commercial embryo transfer program were examined in both in vivo and in vitro embryo production systems. Processing frozen-thawed spermatozoa through Percoll density gradients prior to in vitro insemination eliminated differences in the estimates of sperm viability between the four rams, and yet, differences in embryo production persisted throughout the in vitro culture period. However, there was no effect of ejaculate within ram on embryo production rates. In addition, the timing of the onset of the differences between the rams at each stage of in vitro embryo development were revealed. Ram 2 differed from ram 4 in the proportion of fertilized oocytes at 17 h post-insemination (pi) and by 52 h, ram 3 differed from ram 4 in the proportion of cleaved embryos, and the observed differences between ram 1 and ram 2 in their blastocyst production were initiated prior to activation of the embryonic genome. Once differences in embryo development rates were detected among the four rams, they persisted throughout the in vitro culture period. The reduced in vitro fertilization (IVF) rates from ram 2 compared with the other rams was paralleled in vivo by the significantly lower proportion of embryos recovered from ewes mated to ram 2, and this was further exacerbated by a significantly lower embryo survival rate after transfer. However, the subtle differences observed in the timing of the contribution of each sire to embryo development during in vitro culture were not able to be detected in vivo. However, the higher proportions of transferable quality blastocysts obtained from ewes mated to ram 4 did not result in increased embryo survival throughout the remainder of gestation. Therefore, in this study, the blastocyst production potential for a particular sire, either in vitro or in vivo, does not necessarily reflect the potential for the production of live offspring.     

Effects of nutritional supplements on testicular size and the secretion of LH and testosterone in Merino and Booroola rams

Six Booroola and six Merino rams were fed either a diet which maintained constant live weight or the same diet plus a supplement of high protein lupin grain for 15 weeks, and changes in live weight and testicular volume were measured. Serial blood samples taken for 24 h before the start and 9 weeks after the treatment began were assayed for plasma LH and testosterone and the resulting profiles were analysed for pulses of both hormones. Five weeks later, the animals were given two intravenous injections of 1 μg gonadotrophin-releasing hormone (GnRH) 1 h apart in order to measure pituitary gland responsiveness. A further week later the animals were injected intravenously with 500 μg human chorionic gonadotrophin (hCG) and the levels of testosterone were measured in samples taken after 1.5 h to estimate the testicular responsiveness.The nutritional supplement stimulated testicular growth in both genotypes, so that at the end of the treatment period the testes had increased significantly (P<0.01) in volume by 66% in the Merinos and by 63% in the Booroolas. The live weights also increased, but by relatively less (34% and 43% for supplemented Merinos and Booroolas). The rates of increase in both testicular size and live weight were similar for the two breeds. There were no significant effects of diet on the tonic secretion of LH or testosterone, or on responsiveness to GnRH or hCG.The intervals between LH pulses were significantly shorter (P<0.05) in Booroola rams than in Merino rams both before and after treatment (5.8 h vs. 11.6 h before treatment). The breed differences in LH secretion were mimicked by the testosterone profiles. In the Booroolas, five of the twelve LH profiles contained groups consisting of two to four individually identifiable pulses, each of which elicited a separate pulse of testosterone. A pulse group was observed in only one profile from the Merinos (P=0.06). There were no significant differences between the genotypes in any other parameter of LH or testosterone secretion, or in their responsiveness to GnRH or hCG.It was concluded that (i) nutritional supplements will stimulate testicular growth in both Merino rams and Booroola rams; (ii) the increase in testicular size does not appear to involve an increase in the responsiveness of the testis to LH; and (iii) there are both qualitative and quantitative differences between the genotypes in the patterns of secretion of LH and testosterone which may be associated with the differences in their fecundity.     

The effect of the F gene on male reproductive traits in Booroola × South Australian Merino rams

The effect of the Booroola (Bo) F gene on the reproductive development of Bo × South Australian Merino ($\text{1}\text{2}\text{Bo}$) rams was examined. Half Bo rams were offspring of FF (homozygous carrier), F+ (heterozygous carrier) or ++ (homozygous non-carrier) Bo sires, so that the expected frequency of $\text{1}\text{2}\text{Bo}$ rams carrying the gene should be approximately 1.0, 0.5 or 0.0, respectively. The genotype of each Bo sire was defined on the basis of the proportion of daughters with ? 3 ovulations. The reproductive development of the $\text{1}\text{2}\text{Bo}$ rams corresponding with each sire genotype was studied between 5 and 15 months of age. Traits recorded were: live weight, testicular volume, preputial adhesion score, semen volume, semen density, proportion of rams with ejaculates containing spermatozoa, proportion of rams that mounted and proportion of rams that served oestrous ewes. There were no significant differences among sire genotypes in the traits studied, except for preputial adhesion score (FF < F+ = ++, P < 0.05) and proportion of rams that mounted (FF = F+ < ++, P < 0.05) at 5 months of age. The relevance of these differences is not known but could result from sampling problems. It is concluded that (1) the F gene had no discernible role in male reproductive development between 5 and 15 months of age and (2) the traits examined did not allow a distinction between carrier and non-carrier rams of the F gene.     

The fertilizing capacity of ram testicular spermatozoa,freshly collected and after storage in cauda epididymal fluid

Epididymal fluid may contain substances which promote development of the fertilizing capacity of testicular spermatozoa under in vitro conditions, provided that the spermatozoa are exposed to such substances for long periods of time. In an attempt to resolve this question, the fertilizing capacity of testicular spermatozoa was assessed before and after storage in cauda epididymal fluid and comparisons made with ejaculated spermatozoa from the same rams. Of the 13 eggs examined from the group of ewes inseminated with ejaculated spermatozoa 61.5% were found to be in the 2-to 8-cell stage. No fertilized eggs were recovered from ewes impregnated with freshly collected testicular spermatozoa. Nor were any cleaved eggs obtained from the group of ewes inseminated with testicular spermatozoa stored in cauda epididymal fluid at 4°C for 7 to 11 days. We suggest there-fore, that in order to develop maximal fertilizing capacity, mammalian spermatozoa must be exposed to specific concentrated testicular and epididymal secretions in a sequential order and within strict time limits.     

Female effect in sheep. I. The effects of sexual receptivity of females and the sexual experience of rams

When in contact with receptive or non-receptive ewes, the presence of females increased LH peak frequency both in experienced and inexperienced rams (P less than 0.05). The highest response was found in experienced rams stimulated by sexually receptive ewes. In this group only, the mean testosterone levels increased during stimulation (P less than 0.05). Sexual behavior did not differ between experienced and inexperienced males. The sexual receptivity of the females and the sexual experience of rams appear to interact and thus facilitate the rams' LH and testosterone responses to the presence of ewes.     

Seasonal variation in testicular volume and sexual behavior of Chios and Serres rams

The seasonality of testicular volume and sexual behavior in two Greek breeds of sheep, Chios and Serres, was studied using 10 mature rams of each breed. The rams were kept out of breeding during 2 consecutive years. Live weight was recorded at monthly intervals. Testicular volume was measured at 2-week intervals using an orchidometer. Sexual behavior was recorded at 4-week intervals by exposing rams to oestradiol-treated ovariectomized ewes. The total number of mounts and matings, and the reaction time to first mount and mating were recorded. Chios rams were heavier than Serres rams (87.4 +/- 2.0 kg versus 76.4 +/- 1.9 kg, respectively). All traits varied significantly with month but only testicular volume exhibited a clear seasonal trend in both breeds, with a maximum volume in July-August and a minimum in February-April. Number of mounts showed clear seasonal trend in the Chios breed, with maximum in November. Number of mounts was significantly correlated with length of daylight (-0.18 and -0.21 for Chios and Serres, respectively; P < 0.01) and relative humidity (0.14 and 0.17 for Chios and Serres, respectively; P < 0.05). Testicular volume was positively correlated with air temperature (0.28; P < 0.01) and relative humidity (-0.23; P < 0.01) in the Serres breed only. Results of this study suggest that the testicular volume and number of mounts exhibit seasonal variation in the Chios and Serres 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.     

Estimates of early embryonic loss in ewes mated to rams selected for high and low prolificacy

Two closed lines of sheep selected for high and low prolificacy were established in 1969. Rams within each line were selected on the basis of their dams' lambing records. Foundation ewes were assigned at random to selected rams, and no ewe selection was practiced until replacement yearlings were selected for mating. Selection of the rams used to mate the foundation ewes resulted in more lambs born per 100 ewes exposed to the ram (P<.10) and more lambs born per 100 ewes lambing from the high line rams (P<.05).Seven rams from each line were then used to estimate fertilization rate and embryonic survival rate when mated to an unrelated group of ewes. There was no difference in ovulation rate or fertilization rate of ewes mated to low and high line rams. Percent eggs recovered per CL was 80 and 92 (P<.01) for low and high line rams, respectively. At 35 days 82 and 86% of the ewes were pregnant, and 84 and 93% of the CL were represented by embryos in the pregnant ewes mated to low and high lines, respectively. Estimated embryonic survival rates were 81 and 89% in ewes mated to low and high line rams, respectively.     

The ovine sexually dimorphic nucleus,aromatase, and sexual partner preferences in sheep

We are using the domestic ram as an experimental model to examine the role of aromatase in the development of sexual partner preferences. This interest has arisen because of the observation that as many as 8% of domestic rams are sexually attracted to other rams (male-oriented) in contrast to the majority of rams that are attracted to estrous ewes (female-oriented). Our findings demonstrate that aromatase expression is enriched in a cluster of neurons in the medial preoptic nucleus called the ovine sexually dimorphic nucleus (oSDN). The size of the oSDN is associated with a ram's sexual partner preference, such that the nucleus is 2–3 times larger in rams that are attracted to females (female-oriented) than in rams that are attracted to other rams (male-oriented). Moreover, the volume of the oSDN in male-oriented rams is similar to the volume in ewes. These volume differences are not influenced by adult concentrations of serum testosterone. Instead, we found that the oSDN is already present in late gestation lamb fetuses (～day 135 of gestation) when it is ～2-fold greater in males than in females. Exposure of genetic female fetuses to exogenous testosterone during the critical period for sexual differentiation masculinizes oSDN volume and aromatase expression when examined subsequently on day 135. The demonstration that the oSDN is organized prenatally by testosterone exposure suggests that the brain of the male-oriented ram may be under-androgenized during development.     

Direct responses in males and correlated responses for reproduction in females to selection for testicular size adjusted for body weight in young male lambs

Selection based upon testicular diameter adjusted for body weight at 6, 10 and 14 weeks of age was used to produce two lines of sheep, with either high or low testicular size. Ten generations of selection were carried out and the estimate of the realized heritability of the selection criterion was 0.53 +/- 0.01. There were significant positive correlated responses to selection for testicular diameter at 6, 10 and 14 weeks of age, but the correlated responses in body weight at these ages were negative. In mature females, there were significant negative correlated responses to selection in premating body weight in the 1st, 2nd and 3rd breeding season and in the day of the first oestrus in the 2nd breeding season. Litter size per ewe mated had a small positive correlated response to selection in the second breeding season. This latter response appeared to be due to a positive correlated response in fertility, ewes from the High-line having a significantly higher probability of conceiving to a single mating than those from the Low-line. There was no significant correlated response in ovulation rate or litter size per ewe lambing and the genetic correlation between these traits and the selection criterion is likely to be close to zero. This may be due to the adjustment for body weight used, but it is possible that, in any event, body weight in young rams may be a better predictor of female ovulation rate than testicular diameter. These results do not rule out the possibility that testicular size in rams older than those selected would provide a good predictor of genetic merit for female ovulation rate.     

Temperature scrotale et fertilite chez le belier

Numerous animal studies have shown that elevated testicular, scrotal or ambient temperature induces alterations in spermatogenesis that reduce fertility. In this study, fertilization rate and embryonic mortality were assessed in 636 ewes inseminated in each uterine horn with 50 × 10⁶ cryopreserved spermatozoa from one of either four control rams or four rams submitted to a moderate (2°C), but repeated intermittent (16 hours/day for 21 consecutive days), elevation in their subcutaneous scrotal temperature by means of scrotal insulation. Pregnancy was assessed twice in each ewe at 17 days (blood plasma progesterone) and 65 days (ultrasound) after insemination. No differences were observed in the 17-day pregnancy rate between ewes inseminated with semen from control or experimental rams at up to 21 days of scrotal heating. In contrast, the rate of embryonic mortality between 17 and 65 days post-insemination was significantly higher after 4, 15 and 21 days of treatment in the experimental rams (78.7, 78.6 and 92.7 % respectively) compared to the control rams (55.0, 59.1 and 69.4 % respectively). These results indicate that ani intermittent slight increase in scrotal temperature induces a significant increase in embryonic mortality rate. As these changes were already apparent after only 4 days of scrotal heating, the effect must have ocurred either on the epididymis or on the spermatozoa stored in the epididymis     

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.     

Effects of sire breed on ewe dystocia, lamb survival and weaned lamb output in hill sheep systems

A study was carried out on six hill farms, located in the main hill regions of Northern Ireland, over three breeding seasons to investigate the effect of sire breed on ewe dystocia, lamb survival and weaned lamb output. On each farm, groups of 26 to 40 purebred Scottish Blackface ewes (n = 3174) were crossed with Blackface, Swaledale, North Country Cheviot, Lleyn and Texel sires by natural service (year 1) and artificial insemination (years 2 and 3). Each of the mating groups was initially balanced for ewe age, live weight and condition score, and a total of 15 sires of each breed were used over the 3 years. In total, 2272 ewes were recorded at lambing, producing 3451 lambs, over the 3 years. Sire breed had a significant effect (P < 0.001) on lamb birth weight with Blackface and Swaledale the lowest and Texel the highest. The proportion of ewes with dystocia was higher with Texel sires compared with Lleyn, Swaledale and Blackface sires (P < 0.05). Ewes mated to Cheviot sires had more dystocia than those mated to Blackface and Swaledale sires (P < 0.05), while ewes mated to Lleyn sire breed had more dystocia (P < 0.05) than those mated to Blackface sire breed. Most of the incidence of dystocia was attributable to increased lamb birth weight (P < 0.001), and some to litter size (P < 0.05). Swaledale, Cheviot, Lleyn and Texel sire breeds increased the incidence of malpresentations (P < 0.05). Lamb live weight at weaning was higher with Texel- and Cheviot- and Lleyn-sired lambs compared with Blackface- and Swaledale-sired lambs (P < 0.01). The level of lamb mortality at birth was not affected by sire breed. However, lamb mortality at weaning was lower for Lleyn-sired lambs compared with the other lamb genotypes (P < 0.05). These results indicate that the use of sires from larger breeds, such as Lleyn and Texel, within the Blackface ewe flocks can increase lamb output, with no apparent detrimental effects on lamb mortality or ewe survival, but increased assistance at lambing will be required.     

Effect of nutritional flushing on the productivity of Finnish Landrace ewes

In the autumn (October–December), Finnish Landrace ewes aged 1 year (yearling), 4–5 years (mature) and 7–8 years (older) were fed forages with no supplemented (control) or supplemented daily with 150 g (diet 150) or 300 g (diet 300) of concentrates per ewe in order to determine the effect of energy supply to initiate flushing on ewe productivity. Concurrently, in the summer (August–September), yearling and mature ewes were fed 0, 300 or 450 g of concentrates daily for 17 or 34 days. Concentrate supplement prior to and during mating had little effect on the live weight, however mature ewes gained weight in the summer. In the autumn, increasing proportion of concentrate in the diet reduced the length of the mating period in the yearling ewes (P=0.03) however, diet combination had no significant effect of age on conception. In August and early September, flushing did not hasten the onset of estrus and only 25% of the young ewes and 83% of the adult ewes were mated successfully. The flushing diet had no effect on the prolificacy in yearling and older ewes. In contrast, prolificacy and number of lambs weaned increased (P<0.05) for mature ewes on diet 150. In the autumn, there was a significant influence of flushing on the litter weight at birth and live weight gain from birth to weaning for older ewes however, diet 300 and the control were similar. Although litter weight at birth and weaning tended to be higher in the summer for ewes supplemented with concentrate for 34 days, the number of ewes required for a significant influence due to diet and length of flushing combination were not adequate. It was concluded that little is to be gained in lamb production by flushing ewes of the Finnish Landrace breed.     

Evidence for an annual reproductive rhythm independent of food availability in male Creole goats in subtropical northern Mexico

The aim of this study was to determine if there is a seasonal pattern of sexual activity dependent on food availability in male Creole goats in subtropical Mexico. The study was conducted in the Laguna Region in the State of Coahuila, Mexico (26 degrees N). Male Creole goats (n = 8) were kept in a shed, fed alfalfa ad libitum and given 200 g of concentrate daily throughout the study. Live weight and testicular weight were determined every 2 wk. Sexual behavior and sperm production were determined monthly. Blood samples were obtained weekly to determine testosterone plasma concentrations. All variables were subjected to sinusoidal modeling procedures and showed important seasonal variations (P < 0.0001) with different phase angles for body weight, testicular weight and testosterone plasma concentrations. The nadir of live weight occurred in November and the peak in May. The lowest testicular weight (90 g) and testosterone plasma concentrations (0.1 ng/mL) were observed in January and February, respectively, while the peaks were observed in July and August (145 g and 10 ng/mL, respectively). Ejaculation latency also varied during the study, being low between May and November (96 sec) and reaching a peak in April (183 sec). Minimum number of spermatozoa per ejaculate occurred between February and April (1.4 x 10(9) cells/ejaculate) while the maximum number was observed between May and September (2.8 x 10(9) spermatozoa/ejaculate). Progressive sperm motility was low between January and April (3.04 on average) and high between May and November (about 3.55 on average). The percentage of live spermatozoa diminished between January and April (68% in April) and then increased to values around 80% between May and November. These results lead us to conclude that male Creole goats in Northern Mexico, fed constantly throughout the year, exhibit seasonality in their reproductive activity. Intense sexual activity occurred between May and December.     

Importance of behavioural stimuli in ram-induced ovulation in seasonally anovular Corriedale ewes

Three groups of about 65 seasonally anovular Corriedale ewes were penned and exposed to rams on November 4, 1989. A fourth group (n=64) was maintained in a 3-ha paddock and also exposed to rams on the same date. The sexual behaviour exhibited by rams in contact with penned ewes was recorded during nine simultaneous observation sessions lasting 2 h each.

Five days after ram introduction, incidence of ovulation and ovulation rate were higher (P < 0.01) in adult than in 1.5-year-old ewes. Among penned adult ewes, a greater (P < 0.05) incidence of ovulation was recorded in ewes maintained in contact with rams and oestrous ewes (95.8%) than in ewes exposed to either rams with or without recent experience with oestrous ewes (68.7 and 57.1%, respectively). The fourth group, exposed to rams in field conditions, exhibited a lower (P < 0.05) incidence of ovulation (31.9%) than any other group. No differences among treatments were detected in 1.5-year-old ewes. The incidence of ovulation was associated (r=0.99, P<0.05) with the sexual behaviour displayed by the rams.

It was concluded that the sexual behaviour of the rams plays an important role in ram-induced ovulation and that the continuous presence of oestrous ewes is necessary for the maximum efficacy of the technique in Corriedale ewes.