The influence of earlier mating experience of ewes on their subsequent mating behaviour and reproductive performance

The animals used in the experiment consisted of 411 aged (parous), and 171 maiden ewes (18 months old) and 17 rams. In total 357 observations were made during mating (272 on parous and 85 on maiden ewes). The average mating time for the parous ewes was 58.26 s, and for the maidens 97.0 s. The difference was highly significant (P < 0.01). Mean numbers of mounts per ejaculation for parous and maiden ewes were 2.17 and 2.53 respectively. The difference was highly significant (P < 0.01) and was caused, among other factors, by the reluctant standing attitude of maiden ewes. The results confirm that difficulties exist in the serving fo maiden ewes.The reproduction indices were calculated on the basis of service during the first oestrus in the mating season. The pregnancy rate was 56.45% for older ewes and 54.04% for maidens, the difference being not significant. The lambing rate was 113.3% and 110.3% for parous and maiden ewes respectively, the difference being statistically insignificant. The absence of divergence of reproduction indices between the two groups suggests that the difficulty in serving maiden ewes is due to their lack of reproductive experience which does not influence their reproductive capacity.     

Frequency of chromosomal abnormalities in embryos from superovulated merino ewes

Chromosomal analysis was carried out on 48 Day 2-7 embryos collected from superovulated Merino ewes. Three embryos had abnormal chromosome complements (1 X 1N, 1 X 1N/2N, 1 X 3N), yielding an incidence of 6.25% abnormal embryos. It is concluded that superovulation does not cause an increase in the incidence of chromosomal abnormalities in embryos of Merino sheep.     

Metabolism of sulfur-containing amino acids by pregnant merino ewes

The availability and utilization of cystine and methionine were measured in single-bearing Merino ewes on three occasions, approximately 90, 110 and 130 days after mating, and the effects on these traits of sulfur amino acids (SAA) infused into the abomasum were also measured. Two levels of SAA were infused containing 0.5 or 1.0 g day-1 organic sulfur with DL-methionine contributing two-thirds and L-cystine one-third of the supplementary sulfur. The quantity of the diet offered was increased at each occasion so as to maintain maternal liveweight. The rates of irreversible loss of both cystine and methionine from plasma increased as pregnancy advanced, but the ratios between the rates of irreversible loss and intake of digestible organic matter (DOMI) did not vary with stage of pregnancy. The average daily rates of irreversible loss of cystine and methionine by the ewes consuming the diet alone were 13.6 and 119 mmol kg-1 DOMI respectively. The average rates of irreversible loss of methionine (Im, mmol h-1) and of cystine (Ic, mmol h-1) were both linearly (P less than 0.05) related to the rate of infusion of organic sulfur into the abomasum (s, g day-1): Im = 2.44 (+/- 0.33) s + 1.28 (+/- 0.13); and Ic = 0.16 (+/- 0.02) s + 0.30 (+/- 0.01). Five per cent of the rate of irreversible loss of cystine arose from trans-sulfuration of methionine by ewes consuming the ration only, but greater percentages (14 and 22%) were observed when the ration was supplemented with SAA (P less than 0.05). These transfer quotients were not influenced by stage of pregnancy. The stage of pregnancy did not influence the concentration of cystine or methionine in the plasma, but the abomasal infusions of SAA significantly increased the concentration of both SAA. The ewes consuming the basal diet were in positive balance for both nitrogen and sulfur. The retention of nitrogen did not vary with stage of pregnancy (average (s.e.), 5.8 (0.9) g day-1), but that of sulfur increased from 0.6 to 1.0 and 1.3 g day-1 in periods 1, 2 and 3, respectively (P less than 0.05). The retentions of nitrogen (N, g day-1) and of sulfur (S, g day-1) were linearly and significantly related to the rate of infusion of organic sulfur into the abomasum (s, g day-1): N = 2.7 (+/- 0.7)s + 4.4 (+/- 0.3); and S = 0.49 (+/- 0.03)s + 0.72 (+/- 0.01).(ABSTRACT TRUNCATED AT 400 WORDS)     

Effects of fasting ewes before mating on their reproductive performance

Border Leicester x Merino ewes were fasted for the first six days or the second six days of the oestrous cycle preceding mating in the fall season. When not fasting, ewes were grazed with a control group on irrigated pasture. Compared with control ewes, fasting had no effect on oestrous occurrence or fertilization but did reduce the ovulation rate, especially where fasting occurred early in the oestrous cycle.     

Effect of zinc supplementation on the reproductive performance of grazing Merino ewes

Two experiments were carried out in Western Australia to investigate the effect of zinc supplementation, on the reproductive performance of grazing Merino ewes. We found that supplemental zinc, when provided prior to mating and throughout pregnancy, increased the number of lambs produced by 14% (P<0.05) in both experiments. An intermediate zinc treatment, when supplementation was begun later in pregnancy gave a 9% (P<0.01) increase in the number of lambs in one experiment and no increase in the second. Lamb birth weights were increased by zinc supplementation in Experiment 1 and in Experiment 2, 12–20-week-old lambs from zinc supplemented ewes were 2.1 kg heavier than those from nonsupplemented controls. Plasma zince levels decreased significantly during pregnancy and lactation, but were increased at some sampling dates by 20–25% by zinc supplementation.     

Increased plasma LH levels in seasonally anovular merino ewes following the introduction of rams

Seven seasonally anovular Merino ewes, isolated from rams, were bled every 10 min for 12 h. Rams were introduced the following day, after a further 2 h of sampling every 10 min, and samples were taken for the following 10 h. Three days after the introduction of rams, the ewes underwent laparoscopy, and four had ovulated.Radioimmunoassay of plasma samples revealed pulsatile rhythms in the concentration of LH, with the frequency of pulses varying between ewes, from about once hourly to once every 10 h. Upon the introduction of rams, LH secretion increased within 10 min in six ewes, of which four ovulated within 3 days. There is apparently a relationship between the pattern of LH secretion after introducing the rams, and the ovulatory response that can be expected.     

Fertility studies in young and mature merino ewes 2. Sperm transport

Samples of cervical mucus were collected from young and mature ewes at different stages of oestrus. The migration rate of spermatozoa (time taken to travel 410 mm) was not different in samples of mucus from young and mature ewes. Spermatozoa were unable to penetrate the mucus in 7 27 samples, five of which were collected about 16 hours after onset of oestrus. Migration rate in samples collected between 10 and 16 hours after onset of oestrus was significantly slower than in samples collected in the first five hours of oestrus. The transport of spermatozoa in young and mature ewes was also studied by observing distribution of spermatozoa in the female genital tract 26 to 27 hours after hand-mating. There were no significant differences between young and mature ewes either in mean sperm count or in variation of mean sperm numbers in all sections of the tract.     

Condition-dependent reproductive success in bighorn ewes

Individual bighorn ewes ( Ovis canadensis ) at 4–14 years of age were 1.5% heavier preceding years when they weaned a lamb than preceding years when their lamb died before weaning. Intra-individual differences in mass between years of successful and unsuccessful reproduction appeared independent of a ewe's multiyear average mass. Relative mass loss both in the winter before and in the winter after a given repro-ductive episode increased with reproductive success. Long-term monitoring of individual mass and reproductive success is a promising technique to study life histories in capital breeders, because it allows to partially account for differences in reproductive potential.     

The half-life of follicle-stimulating hormone in ovary-intact and ovariectomized booroola and control merino ewes

To determine whether the high ovulation rate of the Booroola Merino ewe could be explained by FSH metabolism we have tested the proposition that FSH may have a longer half-life in the plasma of Booroola Merino ewes than in control ewes. The half-life of plasma FSH was determined by removal of the pituitary gland, to abolish FSH secretion into the peripheral circulation, and monitoring by repeated blood sampling the subsequent decline in plasma FSH concentrations. The half-life of FSH was similar in Booroola (103 +/- 14 (s.e.m.) min, N = 8) and control (116 +/- 8 min, N = 9) ewes. However, when ewes that had been ovariectomized at least 6 months earlier were hypophysectomized, the half-life of FSH was increased from 110 + 8 min in ovary-intact ewes (N = 11) to 1101 +/- 49 min (N = 6) (P less than 0.001) with no difference between the two Merino strains. We conclude that changes in the circulating half-life of FSH do not account for the high fecundity of the Booroola but that ovariectomy can alter the half-life of FSH secreted by the pituitary gland.     

Sources of variation in the reproductive performance of ewes inseminated with frozen-thawed ram semen by laparoscopy

Fertility data from 8 artificial insemination programs, involving more than 5000 ewes and 110 rams in 3 flocks, were analyzed to determine variation due to individual AI program and ram in the reproductive performance of ewes inseminated with frozen-thawed semen by laparoscopy. The semen had been previously frozen by commercial AI centers in either pellets or straws. Both AI program and individual ram affected the proportion of ewes pregnant and the number of fetuses per ewe inseminated, but not the number of fetuses per pregnant ewe. Semen samples from 97 of the rams used were analyzed on a Hamilton Thorn HTM 2000 image analyzer for sperm concentration, percentage of motile and progressively motile spermatozoa, mean progressive velocity, and mean linear index. The correlations between these traits and reproductive performance obtained after insemination were calculated. There was large variation in the quantity and quality of the frozen semen, but only the number of total and motile spermatozoa inseminated per ewe was correlated with fertility (0.25 and 0.26, respectively). Regression analysis showed that none of the traits measured were useful for predicting fertility.     

Effects of retention of fetal membranes on subsequent reproductive performance of dairy ewes

Seventy-one pairs of ewes with or without retention of fetal membranes in the previous lambing season, were included in a cohort study of 25 flocks in southern Greece; in 27 pairs regulation of the breeding cycle was applied, whilst in the other 44 pairs natural mating took place. The following measures of reproductive performance were calculated: cycling rate, mating rate, return-to-estrus rate, abortion rate, lambing rate, total lambs born per ewe, liveborn lambs per ewe, stillbirth rate, lamb-bodyweight per ewe; furthermore, the incidence risk of retention of fetal membranes during the lambing examined in this study was also calculated. No statistically significant differences were observed in the reproductive performance among ewes that had or had not retained their fetal membranes during the previous lambing, whether the breeding cycle was regulated or not. The incidence risk of retention of fetal membranes among ewes that had not retained its placenta in the previous lambing was 1.6%, whilst that among ewes that had retained its placenta in the previous lactation was 0%. It is concluded that retention of fetal membranes did not appear to adversely affect subsequent reproductive performance of ewes.     

Effect of insulin on feed intake and reproductive performance of well-nourished nulliparous ewes

Eighty-four nulliparous ewes were used to examine the effect of short-term insulin treatment on feed intake and reproductive performance. Following estrus synchronization, ewes were observed for estrus (= Day 0) and were penned individually beginning on Day 7. Ewes were fed twice daily and feed intake was recorded. On Days 9 through 13, ewes were treated s.c. with 1 IU/kg BW insulin (n = 44) or an equivalent volume of saline (n = 40). On Day 14, ewes were placed with fertile rams and number of ewes in estrus (bred) was recorded. Thirty days post-breeding, ewes were checked for pregnancy via ultrasonography. Feed intake and percentage of ewes in estrus did not differ between saline- and insulin-treated ewes. Similarly, neither pregnancy rate (69 +/- 8.7% vs. 80 +/- 8.1%, respectively) nor lambing rate (61 +/- 8.9% vs. 78 +/- 8.4%, respectively) differed between treatments. The number of lambs born per ewe was, however influenced by a breed-group effect (P < 0.0002). Romanov ewes had more (P < 0.001) lambs than the other breed groups in the study. Therefore, treating well-nourished, nulliparous ewe lambs with insulin did not increase reproductive efficiency, possibly because the ewes were already at a maximal nutritional and/or reproductive state.     

Effect of PMSG on the reproductive performance of totally confined ewes bred at synchronized estrus

The reproductive performance (fertility, prolificacy and fecundity of totally confined sheep in a controlled breeding program at the Animal Research Centre (ARC) was analyzed to evaluate the effect of pregnant mares' serum gonadotrophin (PMSG) on ewes synchronized for estrus with fluorogestone acetate (FGA). PMSG did not significantly enhance reproductive performance. Fertility for ewes receiving 500 IU PMSG was 57% and for ewes not receiving PMSG it was 47%. Corresponding values for prolificacy were 2.4 and 2.2, and for fecundity, 144 and 103%. The reproductive performance was not affected by any of the other factors (flock, strain, lighting regime, ram age or reproductive status of the ewe) indigenous to the controlled breeding program for sheep housed in total confinement.     

Fetal growth and reproductive performance in ewes administered GnRH agonist on day 12 post-mating

Reproductive performance and fetal growth was determined in GnRH (4 microg synthetic GnRH agonist, Receptal) administered (i.m.) to ewes on day 12 post-mating (n = 103) compared to control ewes (n = 97) during the breeding season. Plasma progesterone and LH concentrations were analyzed. A total of 13 ewes was slaughtered on day 45 of pregnancy (six from control, seven from GnRH treated groups). GnRH administration on day 12 post-mating increased plasma progesterone concentration (4.39+/-0.25 ng/ml) compared to control group (3.43+/-0.15 ng/ml) on days 13-15 post-mating (P < 0.01). GnRH administration also increased plasma LH concentration between 1 and 4 h after GnRH administration (P < 0.01). Pregnancy rate was higher in GnRH treated group (84%) than control (66%) group (P < 0.05). The ewes in GnRH administered group had more twins (P < 0.05) than those in control group. The ovarian weights (P < 0.05) and the number of corpora lutea (CL) (P < 0.01) were greater in ewes slaughtered on day 45 of pregnancy in GnRH treated group than those in control group. GnRH administration on day 12 post-mating did not have any effect on products of conception at day 45 of pregnancy except on crown-rump length (CRL) of fetuses and cotyledon weight. CRL of fetuses and cotyledon weight in GnRH treated group was higher than those in control group (P < 0.05). In conclusion GnRH administration improved reproductive performance of ewes when administered on day 12 post-mating probably through its beneficial effect on embryo survival by enhancing luteal function, but not through stimulating fetal growth.     

The influence of age on reproductive performance in the Brown Thornbill

I examined age effects on reproduction in the Brown Thornbill Acanthiza pusilla in Canberra, Australia. I found that the reproductive performance of both males and females improved with age, although only age-related improvement in male performance had a significant effect on annual reproductive success. Reproductive success improved with male age as a result of improved performance during two stages of the breeding cycle: first-year males were less likely to fledge young than those aged two or more, while both first and second-year males were less successful at raising fledglings to independence than males of three or more. Male performance appears to improve over three years as they gain experience at provisioning nestlings and caring for fledglings without attracting predators, rather than as a direct result of improved foraging skills. In contrast, reproductive success only improved slightly with female age, although females of two or more years initiated their first clutch earlier in the season than one-year-old females, and tended to be more likely to re-nest if a breeding attempt failed. The poor performance of young females appears unlikely to be related to their foraging ability but may be associated with costs imposed by dispersing to a breeding vacancy earlier in the year. Although the reproductive performance of Brown Thornbills improves considerably with age I found no evidence that performance improved as a result of repeated breeding attempts with the same partner.     

A new strategy for superior reproductive performance of ewes bred out-of-season utilizing progestagen supplement prior to withdrawal of intravaginal pessaries

Two experiments were conducted to examine the effect of progestagen supplement 24h prior to intravaginal pessary withdrawal on reproductive performance of seasonal anestrous ewes. Ewes in each experiment were allocated to treatment and control and all were induced to estrus using either intravaginal MAP (Exp. 1; n=24) or CIDR-G (Exp. 2; n=28) pessaries for 12 days. Half of the ewes in each experiment were supplemented 24h before withdrawal of pessaries with either 10mg oral MAP tablets (Exp. 1) or 25mg i.m. progesterone (P(4)) administration (Exp. 2; P(4)-supplement-treated group). Fertile rams were allowed with the ewes at sponge removal (Day 0, 0h) and estrus was monitored at 6-h intervals for 3 days. Blood samples were collected for measurements of P(4) (Exp. 1 and Exp. 2) and LH (Exp. 2). In both experiments, the percent of ewes in estrus was greater (P<0.05) and intervals to estrus were longer (P<0.05) in progestagen-supplement-treated than control ewes. In Exp. 2, the occurrence and magnitude of LH surges were greater (P<0.01) and intervals to onset of LH surge were longer (P<0.01) in P(4)-supplement-treated than control ewes. In Exp. 2, P(4) supplement elevated P(4) levels from 1.8+/-0.1ng/mL on Day -1 to 4.2+/-0.3 on Day 0 (P<0.001). Following pessaries removal, P(4) concentrations fell to basal values on Day 1 in both groups and remained low until Day 5. Then, P(4) concentrations increased and remained elevated through Day 19 in all (100%) progestagen-supplement-treated in Exp. 1 (12/12) and Exp. 2 (14/14) and in only 5/12 (41.7%) and 6/14 (42.9%) control ewes, respectively. These ewes were confirmed pregnant by ultrasonography and lambed on Day 149.2+/-0.2 following Day 0. In conclusion, progestagen supplement 24h prior to removal of pessary can be used successfully to improve reproductive performance of ewes bred out-of-season.     

Effects of follicular status at treatment on follicular development and ovulation in response to FSH in Spanish merino ewes

Cyclic Spanish Merino ewes were treated on Day 13 of the estrous cycle with 12 mg, i.m., FSH-P in saline (n = 9) or propylene glycol (n = 24), currently with 100 micrograms, i.m., Cloprostenol (Day 0). From Day-6 to Day 0, the ewes were observed daily by transrectal ultrasonography, after Day 0, ultrasonography was performed every 12 h for 72 h. Sizes and locations of > or = 2 mm follicles were recorded at each observation. The ovulation rate was determined by laparoscopy on Day 7 after estrus. The number of ovulations ranged from 0 to 6 in ewes treated with FSH-P in saline and from 0 to 16 in ewes receiving FSH-P in propylene glycol (P < 0.05). In the latter group, the response was bimodally distributed; about half of the females had 1 ovulation, whereas the remainder had > 4 with a mean of 7 ovulations. The ovulation rate was associated with 2 characteristics of the largest follicle present at treatment (Day 0). First, if the largest follicle on Day 0 had not changed in diameter from Day-1 to Day 0, then 7 of 9 ewes had > 3 ovulations; if the largest follicle had either increased or decreased, only 8 of 24 ewes had > 3 ovulations (P < 0.05). Second, there was a linear trend (P < 0.07) for ovulation rate to decrease as the persistence of the largest follicle at treatment increased; no ewe in which the largest follicle on Day 0 remained present for more than 36 h ovulated more than 6 follicles. As with the ovulation rate, the numbers of large follicles on Days 1.5, 2 and 2.5 varied with the interaction of change in diameter of the largest follicle on Day 0 from Day-1 to Day 0 and with vehicle. In summary, the superovulatory response was affected by the change in diameter from Day-1 to Day 0 of the largest follicle on Day 0 and the period required for that follicle to regress after treatment with FSH-P and cloprostenol.