Fertility Of Ewes Research Articles

Uterine morphology and reproductive phenomena in relation to number of embryos at different stages of gestation in prolific sheep

Forty prolific ewes of which half were superovulated with 800 IU PMSG were slaughtered on either d 30, d 70 of gestation or d 3–5 post-partum. At each slaughter date, the ewes were balanced for number of ovulations (1 to > 3 at d 30) or embryos (1 to 4 at d 70 and d 3–5 post-partum). Uterine length, width, surface and dry matter (DM); embryonic weight and DM; plasma progesterone at d 15 and 30 of gestation; and protein concentration in allantoic fluids were measured. Superovulated ewes averaged 5.8 CL vs. 3.1 CL for the control. On d 15 of gestation, plasma progesterone concentration increased from 4.87 ng/ml in ewes with 2 CL to 8.02 ng/ml for those with > 7 CL. The corresponding figures at d 30 were 4.19 and 9.44 ng/ml, respectively. Embryonic losses increased from 16.5% in ewes with 2 CL to 67.9% in those with > 7 CL. Length of uterine horns increased by 9.2, 7.7 and 4.1 cm for each increase in number of embryos present at the three slaughter dates, respectively. On d 30, only embryo DM showed a significant ( P <0.05) increase with increased number of embryos present. On d 70, length, width and uterine surface increased linearly with increase in number of embryos, however, little difference was observed between ewes carrying three and four embryos. Ewes slaughtered after they had lambed one, two or three lambs had significantly smaller and narrower uteri than those with four lambs. It is concluded that, in prolific as in non-prolific sheep the space available seems to be adequate for development of all embryos surviving the critical first 30 days of pregnancy.

Effect of active immunization against the amino-terminal peptide (alpha N) of the alpha 43 kDa subunit of inhibin (alpha 43) on fertility of ewes

Immunization against the amino-terminal peptide (alpha N) of the alpha 43 subunit of inhibin was shown previously to reduce fertility in ewes. The aim of this study was to examine the effects of active immunization of ewes against alpha N on egg recovery and fertilization rates. Ewes were immunized against alpha N immunogen, and were given 800 I.U. of pregnant mare's serum gonadotrophin at the end of treatment with intravaginal progesterone to synchronize the oestrous cycles. Control ewes received adjuvant only. The ewes were run with fertile rams, and 4 days after withdrawal of the progesterone device the oviducts were flushed to recover eggs and luteal structures on the ovaries were recorded. Eggs were recovered from 17/19 (90%) control ewes compared with 4/16 treated ewes (25%) (P < 0.01), and the egg recovery rates were 76% (45/59) and 17% (7/42) respectively (P < 0.001). The mean number of corpora lutea (CL) per ewe were similar (3.1 +/- 1.4 v. 2.6 +/- 1.0) but several CL in the treated ewes did not appear to have ruptured, and 2 treated ewes had cystic follicles and no CL. There were no apparent differences in either the fertilization rates or the stages of development of fertilized eggs between treated and control ewes. Antibody binding levels in follicular fluid were approximately half those found in peripheral plasma. It is concluded that immunization of ewes against alpha N leads to lowered fertility by suppressing ovulation, implicating alpha N in the normal ovulatory process.

Effects of PMSG and ram contact on the reproductive performance of progestagen-treated ewes during breeding and anestrous seasons

The objective of this study was to evaluate the efficacy of combinations of PMSG treatment and ram contact on the reproductive performance of progestagen-treated ewes during three different times of the year, Febraury (early anestrus), July (late anestrus) and October (breeding season). A total of 109 multiparous Dorset ewes was used. Ewes were treated with intravaginal progestagen pessaries for 12 days, injected with 500 IU PMSG at pessary removal and either isolated from rams prior to mating ( n = 12, February; n = 12, July; n = 8, October) or exposed to rams during pessary treatment ( n = 17, February; n = 12, July; n = 8, October). A third treatment group ( n = 18, February; n = 6, July; n = 8, October) received pessaries and ram exposure but no PMSG. An additional treatment of progestagen pessaries alone was included in October ( n = 8). There were no differences among treatments in their ability to induce estrus at different times of the year, but incidence of estrus tended ( P < 0.10) to be lower for PMSG treatment during the July breeding. During February, the use of pessaries with PMSG treatment increased ( P < 0.05) conception and lambing rates, whereas ram contact was without any beneficial effects. The trend was reversed during July breeding, when ram contact increased ( P < 0.05) fertility of progestagen-treated ewes compared with other treatment combinations. Pessaries alone were sufficient to attain acceptable levels of fertility and fecundity in October.

A comparison of the frequency of lambing on the reproductive performance of finn dorset ewes

One of the major factors affecting the efficiency and profitability of sheep production is the number of lambs reared per ewe. In 1991 lambs reared per ewe accounted for 14% of the difference in gross margin per hectare between top third and average lowland spring lambing flocks (MLC, 1992). The hypothesis was developed that in managing the prolific ewe three possible management systems could be employed; frequent lambing (FL), early annual lambing (EAL), or late annual lambing (LAL). The choice of these lambing systems was based on minimising the problems of the prolific ewe. Of these systems FL (lambing on an eight month cycle), provided the best opportuity for achieving high numbers of lambs sold per ewe.

Conceptus development in vivo, endometrial and conceptus protein release in vitro following blastocyst transfer to ewes induced to ovulate at 28 days post-partum

The use of laparoscopic insemination to deposit semen into the tip of the uterine horn ensures fertilization in ewes induced to ovulate at 3-5 weeks post-partum. Acceptable pregnancy rates are achieved if embryos from post-partum donors are transferred to a normal uterine environment yet embryos rarely survive when transferred or returned to a post-partum uterus. Blastocyst transfer procedures were developed to test whether the post-partum uterus can support conceptus development during the period of rapid growth coincident with the maternal recognition of pregnancy. In Experiment 1, the efficiency of the blastocyst transfer procedure was determined using control ewes > 150 days post-partum. Eight of nine recipient ewes established pregnancies and 75% of blastocysts survived to term. In Experiment 2, blastocysts were transferred to control (n = 12) or post-partum (n = 10) recipients that had been induced to ovulate 28 days after lambing during the breeding season. Conceptus development was assessed 96 h after blastocyst transfer on Day 15 of the cycle. At this time, conceptus mass in the seven post-partum ewes which remained pregnant was generally lower than in the 11 corresponding control ewes. Conceptus and endometrial tissues were cultured separately for a further 24 h in vitro in the presence of [3H]leucine to determine production of oTP-1 and the pregnancy-specific endometrial protein p70 respectively. Oxytocin binding sites were measured in endometrial tissue. Following 96 h culture in a post-partum uterus the conceptus retained its competence to synthesize and secrete ovine trophoblast protein 1 (oTP-1) in vitro. However, despite normal oTP-1 production the conceptus tissue failed to completely suppress endometrial oxytocin receptor binding. The negative correlation between p70 production and oxytocin receptor density implies a possible role for this protein in the suppression of oxytocin receptor synthesis required to prevent luteolysis in pregnant ewes.

Fertility of superovulated ewes after intrauterine or oviducal insemination with low numbers of fresh or frozen-thawed spermatozoa.

Two experiments investigated the effects of number of spermatozoa inseminated and time and site of insemination of fresh and frozen-thawed semen on fertility in Merino ewes treated with intravaginal progestagen pessaries and a combination of pregnant mare serum gonadotrophin and follicle stimulating hormone. In Experiment 1, ewes were inseminated in the uterus or oviducts with totals of 10(4), 10(5), 10(6) or 10(7) fresh spermatozoa 44 or 68 h after pessary removal. Ova recovered 48 h later were classified as fertilized if they had cleaved. Proportion of fertile ewes (ewes with fertilized ova per ewes inseminated) and fertilization rate of ova (ova fertilized per ova recovered) were higher for inseminations 44 h (63% and 45%) than 68 h (38% and 19%) after pessary removal (P < 0.001). More ewes were fertile after oviducal (61%) than after intrauterine insemination (39%; P < 0.05), and with high (10(6) and 10(7)) than with low (10(4) and 10(5)) doses of spermatozoa for intrauterine (54% v. 24%; P < 0.05) but not for oviducal inseminations (63% v. 59%). Fertilization of ova was better after oviducal than after intrauterine inseminations (44% v. 22%; P < 0.001), and with high than with low doses of spermatozoa (45% v. 21%; P < 0.001). In Experiment 2, ewes were inseminated with 10(5), 5 x 10(5) or 10(6) total fresh or frozen-thawed spermatozoa in the uterus or oviducts, 44 h after pessary removal.(ABSTRACT TRUNCATED AT 250 WORDS)

Reproductive and production efficiency of Chios ewes under an accelerated breeding system

In a 5-year period, 145 Chios ewes, managed to lamb 3 times in 2 years, produced 464 lambing records, averaging 2.67 lactations (range 1–7). A group of 119 Chios ewes, maintained concurrently, was managed to lamb once a year as control. All ewes in the accelerated breeding systems were exposed to rams for rebreeding following weaning (42 ± 3 d post partum), with the exception of those lambing in November and December, which were rebred in April. All ewes, regardless of system, were handmated and oestrus was detected twice daily using vasectomized teaser rams. Ewes on both systems were kept indoors throughout the year and minimum grazing was practiced. Milk production was computed from monthly test-day records following weaning and reflects commercial yield. Ewe fertility in the accelerated breeding system (60%), although lower than that of the control group (92%), could be considered satisfactory. Differences in conception within the accelerated system probably reflect seasonal fertility. Lambing interval in the present study (294 days), appears to be realistic for dual purpose breeds. Ewes on the accelerated lambing system produced more lambs and total lamb weight per ewe at weaning than controls, despite the twice as high abortion rate. Total milk production per ewe, although somewhat higher in the accelerated breeding system, was not significantly different from control ewes. The use of prolific breeds appears to be advantageous for accelerated breeding systems.

Conceptus development following blastocyst transfer to ewes induced to ovulate at 28 days post-partum

The use of laparoscopic intrauterine insemination to deposit semen directly into the tip of the uterine horn thus bypassing the involuting uterus ensures fertilization in ewes induced to ovulate at 3 to 5 weeks post-partum. Acceptable pregnancy rates are achieved if embryos from post-partum donors are transferred to a normal uterine environment (60%; Wallace, Robinson &amp; Aitken, 1989a) but embryos rarely survive when transferred or returned to a post-partum uterus (0-25%; Wallace, Robinson &amp; Aitken, 1989b; McKelvey, Wallace, Robinson &amp; Aitken, 1989). Furthermore, when conceptus development was assessed at Day 16 after insemination only a small sub-set of post-partum ewes remained pregnant, suggesting that any defect in the maternal/embryonic dialogue which may inhibit the re-establishment of pregnancy in post-partum ewes occurs prior to this stage (Wallace, Ashworth, Aitken &amp; Cheyne, 1991).In the current study a novel blastocyst transfer procedure was developed to test whether the post-partum uterus can support conceptus development during the period of rapid growth coincident with the maternal recognition of pregnancy.

Effects of heating the testes and epididymides of rams by scrotal insulation on fertility and embryonic mortality in ewes inseminated with frozen semen.

Fertilization rate and embryonic mortality were assessed in 636 ewes inseminated in each uterine horn with 50 x 10(6) frozen spermatozoa from four control rams and from four rams submitted to a moderate (1.4-2.2 degrees C), but repeated, intermittent (16 h/day for 21 consecutive days) increase in their subcutaneous scrotal temperature by means of scrotal insulation. Pregnancy was assessed twice in each ewe from concentration of progesterone in blood plasma at 17 days and by ultrasound at 65 days after insemination. No differences were observed in the pregnancy rate at 17 days between ewes inseminated with semen collected from control rams (56.0, 65.2, 66.7 and 60.3%) and from heated rams (60.6, 71.8, 63.6 and 48.2%) before or after 4, 15 and 21 days of heating, respectively. In contrast, the rate of embryonic mortality between 17 and 65 days after insemination was significantly higher at days 4, 15 and 21 in the heated rams (78.7, 78.6 and 93%) than in the control rams (55, 59 and 65.7%). These results indicate that an intermittent slight, but repeated, increase in the subcutaneous scrotal temperature could induce a significant increase in the embryonic mortality rate. As these changes were apparent on day 4 of heating, an effect must have occurred on sperm stored in the epididymis.

Effect of flat bate feeding in late pregnancy on colostrum and lamb production of prolific ewes

In the final 2 weeks of pregnancy there is a large increase in the protein requirement of the ewe for udder growth and colostrum production (Robinson, 1985). Ewe dry matter (DM) intakes fall during late pregnancy (Forbes, 1970) so meeting the theoretical requirements at this stage can be difficult.The trial was designed to compare the effect of providing the required protein on a flat-rate or a ‘step-up’ feeding system on lamb and colostrum production.Sixty-two Cambridge ewes aged 1 to 9 years and scanned as carrying 2 to 6 lambs were used. Ewes were housed and sheared approximately 2 months pre-partum and fed a complete diet at a restricted level and hay ad libitum until the commencement of the trial at 4 weeks pre-partum.

Colostrum and lamb production of prolific ewes

The prolific ewe can be regarded as a valuable asset only if she produces viable lambs and, at the same time, sufficient colostrum to meet their needs for energy (MJ) and immunoglobulin (Ig) in the first days of life.The energy requirements of the lamb will depend on its weight and the climatic conditions of its surroundings. Mellor and Murray (1986) recommend 180 ml colostrum per kg body weight during the first 18 h of life for lambs born indoors and 210 ml/kg body weight for lambs born in field conditions. The Ig requirement of the lamb will depend on its size and the disease challenge of the environment into which it is born.Although lower immunoglobulin G (IgG) levels have been recorded in dead lambs compared with live lambs (Halliday, 1968 and 1978; Khalaf, Doxey, Baxter, Black, FitzSimons and Ferguson, 1979), it has been shown that many lambs having low serum IgG levels do survive (Halliday, 1974) and some with high levels die (Halliday, 1978).The minimum intake of colostrum required for passive immunity is not known, but it is probably considerably less than that needed to meet the energy requirements (Mellor and Murray, 1986). Spedding, Treacher and Penning (1970) showed that as little as 8 g colostrum per kg lamb birth weight can provide protection from disease. Under poor conditions of hygiene this would probably not be sufficient. It thus seems likely that provided that the energy requirement of the lamb is met by feeding it colostrum, the Ig requirement will also be met.

The Effects of Moderate Heating of the Testes and Epididymides of Rams by Scrotal Insulation on Body Temperature, Respiratory Rate, Spermatozoa Output and Motility, and on Fertility and Embryonic Survival in Ewes Inseminated with Frozen Semena

The Effects of Moderate Heating of the Testes and Epididymides of Rams by Scrotal Insulation on Body Temperature, Respiratory Rate, Spermatozoa Output and Motility, and on Fertility and Embryonic Survival in Ewes Inseminated with Frozen Semen^a

Effects of facial eczema on ewe reproduction and postnatal lamb survival in Romney sheep

Abstract Mating and lambing data from the Romney facial eczema (FE) selection flocks at Ruakura were collated in order to study the effects of FE susceptibility on subsequent reproduction. The data analysed were ewe fertility (numbers of ewes lambing, as a % of those joined), litter size at birth, and postnatal lamb survival. Two of the flocks, selected for resistance (R) or susceptibility (S) to FE, were established from similar foundation stock in 1975. Two other flocks were established in 1982, with foundation stock different from the R and S flocks, one of them (P) being bred for resistance, alongside a contemporary control (C) flock. The data comprised 3520 matings and 2847 lambings of ewes in 1982–90. The FE challenge was administered by intubation to young males and (in some years) to young females, using the fungal toxin, sporidesmin. Susceptibility to a given FE challenge was measured as an increase in concentration of the serum enzyme, gamma-glutamyltransferase (GGT). The loge transformed GGT va...

The effects of recombinant bovine interferon-α on fertility in ewes

Recombinant bovine interferon-α I1 (rBolFN-α) may be useful for enhancing fertility in sheep because it has extensive sequence homology with ovine trophoblast protein-1. To test the effectiveness of rBolFN-α, several experiments were performed in which bred females were given intramuscular injections of rBolFN-α around the time of maintenance of the corpus luteum. Treatment with rBolFN-α enhanced the fertility of ewes that were bred via natural service or embryo transfer of whole or demi-embryos. Interferon treatment was successful in enhancing lambing rate if injections were given twice daily from Days 11 to 18, 12 to 14, 12 to 15 or 12 to 16. Overall, the lambing rate for ewes bred via natural service was 94/126 (74.6%) for control ewes and 101/126 (80.2%) for rBolFN-α treated ewes. Litter size was not affected by treatment. Interferon treatment was not successful in increasing the lambing rate if given as a single injection on Day 12 or as a series of once-daily injections from Days 11 to 16. These results demonstrate that rBolFN-α can increase the lambing rate in ewes.

Colostrum production by prolific ewes

The production of colostrum by prolific ewes is of particular importance because of the increased demand of larger litters. Robinson (1985) has shown that there is a sharp increase in the ewe's net protein requirement for udder growth and colostrum production in the last 2 weeks pre-partum.The trial was designed to investigate the effect of level of protein in the diet during the last weeks of pregnancy on the quantity and quality of colostrum produced by prolific ewes.Forty-four Cambridge ewes aged 2 to 7 years and scanned as carrying two to four lambs were used. Ewes were housed and sheared approximately 2 months pre-partum and fed a complete diet at a restricted level and hay ad libitum until the commencement of the feeding trial at 2 weeks pre-partum. The ewes were then individually penned until 5 days post partum. During this period the ewes were fed ad libitum one of the two complete diets detailed in Table 1 together with hay ad libitum.

Effect of premating injections of insulin on fertility and prolificacy of ewes

Ninety-six Suffolk ewes received daily injections of either long-acting insulin (1.0 IU kg−1) or saline for 3 consecutive days after introduction of rams. Basal serum LH concentrations were higher (P &lt; 0.05) in insulin-treated ewes (P &lt; 0.05) but concentrations of estradiol-17B and the magnitude of the preovulatory LH surge were unaffected. Interval to breeding, pregnancy rate and subsequent litter size were not influenced by treatment (66.6 vs. 63.3 h, 69 vs. 74% and 1.65 vs. 1.69 for insulin and saline-injected ewes, respectively). Key words: Insulin, sheep, fertility, prolificacy

Ovarian and endocrine responses of merino ewes following treatment with PMSG and GnRH or PMSG antiserum

Forty-eight mature merino ewes were treated in the breeding season with intravaginal progestagen pessaries and 1200 IU pregnant mare serum gonadotrophin (PMSG). The ewes were randomly allocated into four treatment groups. Group 1 served as controls; Groups 2 and 3 received an i.v. injection of 100 μg of synthetic gonadotrophin releasing hormone (GnRH) 12 or 24 h after pessary withdrawal (PW), respectively; and, Group 4 received a s.c. injection of 2 ml of ovine PMSG antiserum (A/S) 24 h after PW. Injecting GnRH at 12 h, advanced the time to onset of ovulation, but reduced the total follicular response (corpora lutea plus large follicles) and numbers of corpora lutea. The total follicular response was similar in Groups 1, 3 and 4, but the numbers of corpora lutea were higher in ewes injected with GnRH or PMSG A/S 24 h after PW compared with control animals. The mean peripheral plasma peak levels of oestradiol-17β (E 2) per follicle and progesterone per corpus luteum were reduced following treatment with GnRH or PMSG A/S. Moreover, treatment with GnRH advanced the time to and magnitude of the luteinising hormone peak. It was concluded that treatment with GnRH or PMSG A/S at the appropriate time may improve the superovulatory response of ewes to PMSG by increasing the proportion of developing follicles which ovulate. These treatments may also have beneficial effects on the fertility of superovulated ewes by limiting peri-ovulatory oestrogen secretion.

Fertility of superovulated ewes following intrauterine or oviducal insemination with fresh or frozen-thawed semen

Two experiments were conducted with mature Merino ewes to investigate the effects of time and site of insemination of fresh and frozen-thawed semen on the fertility of superovulated ewes. In Experiment 1, each ewe was treated with an intravaginal progestagen sponge and PMSG and/or FSH. They were inseminated in the uterus with fresh or frozen-thawed semen (approximately 100 x 10(6) motile sperm) at 24, 44 or 64 h after sponge withdrawal. Ova were recovered at 88 h after sponge withdrawal and classified as fertilized if they had pronuclei or had cleaved. Mean fertilization rates of recovered ova were 60.0, 93.7 and 87.8% for fresh semen and 46.1, 98.2 and 26.1% for frozen-thawed semen at each of the insemination times (24, 44 and 64 h) respectively. Overall, fertilization rates were higher for fresh semen than for frozen-thawed semen (P less than 0.01), but there was an interaction with time of insemination (P less than 0.01). Following insemination with frozen-thawed semen at 64 h, only 61% of the fertilized ova developed to the 2- to 4-cell stage by the time of embryo recovery; this was less than in any of the other groups (P less than 0.05). In Experiment 2, ewes were inseminated with 100 x 10(6) motile fresh or frozen-thawed semen in the uterus or in the oviducts at 64 h after sponge withdrawal.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of GnRH and hCG Injections on Lambing Rate of Estrus-Induced Ewes during the Non-breeding Season.

Four experiments were conducted to improve fertility using Suffolk ewes induced estrus by an intravaginal sponge impregnated with 60 mg medroxyprogesterone acetate (MAP) and PMSG treatments during the non-breeding season. Timing (Experiment 1) or dosage (Experiment 2) of a single injection of a synthetic GnRH after sponge removal or at the induced estrus, and effect of a 600 IU PMSG injection (one day before or at the time of sponge removal) combined with either 100 μg GnRH or 500 IU hCG injection at estrus (Experiment 3) were investigated. In Experiment 4, estrous ewes were treated with saline, 100 μg GnRH at estrus, 250 IU hCG injections or an insertion of MAP sponge on Days 10 to 12 after mating, or a combined treatment of GnRH at estrus and hCG after mating. Timing (36, 48 or 60 hr after sponge removal) and dosages (0, 25, 50 or 100μg) of a GnRH injection did not affect lambing rate and prolificacy. The timing of a PMSG injection also did not affect lambing rates, and neither GnRH nor hCG injection improved the fertility of ewes. Pregnancy and lambing rates were not significantly different between the treatments in Experiment 4. The present results indicate that a single GnRH or hCG injection at the induced estrus, successive injections of hCG on Days 10 to 12 after mating, or a combined treatment with a GnRH injection at estrus did not increase the fertility of ewes.

Straightbred comparison of a composite population and the Suffolk breed for performance traits of sheep.

A terminal sire Composite population was formed by mating Columbia rams to Hampshire-Suffolk crossbred ewes. Subsequent generations were produced by inter se mating. The objective was to compare Composite sheep to purebred Suffolks for numerous performance traits. Young ewes lambing at 1 yr of age were evaluated separately from mature ewes (2, 3, 4, and 5 yr old) of each population. Composite and Suffolk populations did not differ significantly in components of litter weaning weight per young ewe joined. Mature Composite ewes produced more wool than Suffolk ewes. Fertility of mature ewes did not differ significantly between populations. The greater prolificacy (P less than .01) of mature Suffolk ewes was offset by a lower survival to weaning (P less than .01), particularly for twin-born lambs. Consequently, mature Composite and Suffolk ewes did not differ for number weaned and litter weaning weight per ewe joined. The average birth weight of lambs born to young and mature Composite ewes was greater (P less than .02) than the average birth weight of Suffolk lambs. The average weaning weight of lambs born to young Composite ewes was greater (P less than .05) than that of lambs born to young Suffolk ewes. Breed differences were not detected for preweaning daily gains, weaning weights, and postweaning daily gains of ewe lambs born to mature ewes. Likewise, weights of ewes at 125 d of age and weights of mature ewes at breeding did not differ significantly between breeds.(ABSTRACT TRUNCATED AT 250 WORDS)