Fertility in South Australian commercial Merino flocks: sources of reproductive wastage

To identify reasons for low fertility in the Merino in South Australia, we defined the extent and sources of reproductive wastage in flocks of maiden (n=14) and mature age (n=54) Merino ewes managed on 43 properties over 4 year. In a second study, reproductive wastage was examined in a very high ovulating flock of mature age South Australian Merino ewes heterozygous for the FecB gene, mated to lamb in either the autumn or spring. Losses in the latter flock were examined in less detail than the large-scale study, but allowed wastage to be partitioned between pre- and peri/post-natal sources. In the first experiment, reproductive wastage between mating and weaning was estimated at 59.7 potential lambs or ova lost per 100 ewes exposed to rams, representing 42.4% of ova shed. The main source of wastage occurred at lambing (55.6% of total loss), with death of twins a major contributor (35.3% of total loss). Other important sources of wastage were from partial failure of multiple ovulation (PFMO; 20.4% of total loss) and from ewes mating but not lambing (13.2% of total loss). Reproductive wastage did not vary with either age of ewe (maiden versus mature) or season of mating (October-December versus January-March). Mean ovulation rate, estimated as 141 per 100 ewes ovulating (range 100-200), varied with age of ewe (129 versus 144; maiden versus mature) but not with season of mating or year (1990-1991). Values for fertility, fecundity and lamb survival were 90, 127 and 73%, respectively. Fecundity of maiden ewes was lower than that of mature ewes (116 versus 130). Survival of single and twin lambs between birth and tail docking was 83 and 56%, respectively. Net reproductive efficiency, or lambs weaned per 100 ewes exposed to rams, averaged 81 (range 31-122). In the second experiment, mean ovulation rate of FecB Merino ewes was 316 per 100 ewes ovulating, with 242 ova (potential lambs) lost between ovulation and tail docking. This loss was equally shared between pre- and peri/post-natal sources (123 versus 119), and demonstrates severe limitation of the Merino to successfully bear and rear multiple litters. We concluded that future research in commercial Merino flocks be focused on lamb mortality, particularly of twins, and on PFMO, the major source of embryo loss.     

Reproductive response and LH secretion in ewes treated with melatonin implants and induced to ovulate with the ram effect

Two experiments were conducted to examine the effects of treating seasonally anoestrous ewes with melatonin before ram introduction on reproductive response, and on LH secretion in anoestrous ewes induced to ovulate by rams.In Experiment 1, a total of 667 ewes from three flocks involving Merino (Flock 1, N = 149), Merino entrefino (Flock 2, N = 325) and Rasa Aragonesa (Flock 3, N = 203) breeds were used. Within each flock, ewes isolated from rams since the previous lambing were assigned at random to receive melatonin implants of Regulin (75, 175 and 105 in Merino, Merino entrefino and Rasa Aragonesa flocks, respectively) or to serve as untreated controls (74 in Merino, 150 in Merino entrefino and 98 in Rasa Aragonesa flocks). Fertile rams were introduced into all flocks 5 weeks after implantation in March (Flocks 1 and 2) or April (Flock 3), and remained with the ewes for a 50 day mating period. Percentage of ewes with luteal activity at ram introduction did not differ between melatonin treated and control ewes in any flock. There were no significant differences in either the mean interval from ram introduction to lambing or the distribution of lambing. Implantation with melatonin resulted in an improvement of prolificacy in all three flocks, although this only reached statistical significance in the Merino flock (1.15 vs. 1.03 in treated and control ewes, respectively, P < 0.05). Fertility was increased significantly (P < 0.05) in the Merino entrefino flock (64.5% in treated vs. 51.3% in control ewes).In Experiment 2, two trials were undertaken utilizing a total of 63 ewes. Trial 1 involved 24 mature Manchega ewes and Trial 2 involved 39 Merino ewe lambs. Half of the animals in each trial received a Regulin implant on 28 February (Trial 1) or 12 March (Trial 2) and the remaining half acted as controls. Rams were introduced 5 weeks after implantation and remained with the ewes for a 25 day period. In both trials, anoestrous ewes at ram introduction were bled at 20 min intervals for 3 h before and 5 h after ram introduction and then at 3 h intervals over the next 24 h for assessment of plasma concentrations of LH. Secretion of LH before or following introduction of rams was not affected by melatonin. Both treated and control anoestrous ewes in each trial responded to introduction of rams with an increase in the frequency of the LH pulses (P < 0.05), but no significant changes were detected in pulse amplitude or mean levels of LH. A preovulatory surge of LH was detected between 8 and 26 h after ram introduction, but neither mean interval from ram introduction to the peak of LH surge, nor the magnitude of the LH peak, was influenced by melatonin treatment.Results from this study show that: (1) melatonin implants administered during early seasonal anoestrus have the potential to improve reproductive performance in Spanish breeds of sheep, but the response is conditioned by breed, management system and environmental factors; (2) melatonin did not modify the secretion of LH in anoestrous ewes induced to ovulate by the ram effect under our experimental conditions.     

Fertility in South Australian commercial Merino flocks: relationships between reproductive traits and environmental cues

High levels of reproductive loss have been reported in commercial Merino flocks (n=68) from the cereal/livestock and high rainfall zones in South Australia (Kleemann DO, Walker SK. Fertility in South Australian commercial Merino flocks: sources of reproductive wastage. Theriogenology 2005;63:2075-88). Relationships between reproductive traits (estrus, ovulation, fertility, fecundity, lamb survival) and environmental end points (liveweight, condition score, temperature at mating, chill index at lambing) are reported in this paper. They were analysed within season of mating (October to December; January to March) and age of ewe (maiden as 1.5-year-old, mature as older). Incidence of estrus was positively related (P<0.05) to condition score in the October to November interval. Return rate to service was positively (P<0.05) influenced and fertility was negatively (P<0.05) influenced by the number of days ambient temperatures were > or =32.0 degrees C during mating, indicating that high ambient temperatures may reduce embryo survival. Liveweight and, to a lesser extent, condition score, accounted for significant proportions of variation associated with ovulation rate (39.3 and 12.7%, respectively). Ovulations per 100 ewes increased by 1.8 per kg increase in liveweight over all flocks. Ovulatory response to liveweight increased (P<0.01) from the October to December to the January to March period of mating (1.5 versus 3.4 ovulations per kg, respectively). Overall, a flock's fertility and fecundity increased by 0.27 and 1.42% per kg increase in liveweight, respectively. Reproductive wastage from partial failure of multiple ovulations (PFMO) was positively related to liveweight (P<0.01) and ovulation rate (P<0.001). Survival of single lambs was positively and curvilinearly related to maternal liveweight and condition score measured in late pregnancy (P<0.05). Linear relationship of these variables for twin lamb survival was significant for condition score only. Single and twin lamb survival were also positively related to liveweight and condition score at mating (P<0.05). We concluded that nutritional cues have a major impact on reproductive traits in commercial Merino flocks in South Australia; it sets the potential number of lambs (ovulation rate) and influences survival of lambs as early as at mating. Indications are that high ambient temperatures may influence embryo survival. It is recommended that future research efforts focus on: (a) prenatal nutritional influences on the physiology of mother-offspring behaviours at birth; and (b) possible peri-conceptional dietary factors controlling embryo loss resulting from partial failure of twin ovulations, to improve reproductive efficiency in the Merino.     

Bio-economic modelling of sheep meat production systems with varying flock litter size using field data

Sheep meat producers derive the majority of income from sales of weaned lambs, determined by flock conception rates, litter size, and lamb survival. Field data from commercial flocks can inform sensitivity analyses of the effect of litter size on flock productivity, feed demand, and gross margin. This study adapted an established bio-economic model of a flock of breeding ewes informed by statistical relationships (from linear models) between flock litter size (lambs born per ewe lambing) and production factors (such as flock barren rate, litter birth type and lamb birth weight) identified using 156 145 animal records from the Irish national sheep breeding database. Sensitivity analyses were undertaken to investigate the effects of flock litter size on flock production, feed demand, and gross margin. Results showed that as flock litter size increased, the proportion of lambs born as multiples increased, with 14 % of lambs born as singles when flock litter size was 2.2 lambs born per ewe lambing. Flock gross margin increased from €2 205 to €7 730 as litter size increased from 1.0 to 2.0 lambs born per ewe lambing. As litter size increased from 1.0 to 2.2 lambs born per ewe lambing, flock gross margin increased linearly by, on average, €52 per 0.01 increase in litter size. At a litter size of > 2.2 lambs born per ewe lambing, flock gross margin increased on average €12 per 0.01 increase in litter size. At a litter size of 2.2 lambs born per ewe lambing, flock efficiency (at 65.0 kg of lamb weaned per ewe presented for breeding), weaning rate (at 1.5 lambs weaned per ewe presented for breeding; not including excess lambs from large litters sold within a week after birth and thus not weaned on-farm), and gross margin (at €8 500) began to plateau. The results indicate lower marginal returns in gross margin at very high flock litter size, due to the lower value of additional lambs born as triplets and quadruplets compared with single- and twin-born lambs. However, the diminishing economic returns occurred at higher flock litter size than are currently biologically achieved in most flocks. Quantification from this analysis demonstrates how the value of increasing the number of lambs born changes at very high flock litter size, which can inform the priorities and performance benchmarking for international sheep meat production industries.     

Factors influencing lamb survival in a high fecundity Booroola Merino x South Australian Merino flock

The effects of year of lambing, age of ewe and litter size on lamb survival and birthweight, and the effects of ewe mating weight and pregnancy wastage (ovulation rate minus litter size) on birthweight were examined in Booroola Merino x South Australian Merino ewes. Year of lambing, litter size and their interaction were significant (P<0.001) sources of variation for lamb survival. When birthweight was included as a linear and quadratic covariate for lamb survival, year of lambing and litter size and their interaction remained as statistically significant sources of variation. Year of lambing, litter size and pregnancy wastage contributed significantly (P<0.05) to variation in birthweight. Ewe liveweight at mating was not an important source of variation (P>0.05). Birthweight was significantly (P<0.05) reduced with an increase in pregnancy wastage. Improvement of birthweight of multiple birth lambs has some potential for increasing lamb survival. Other factors influencing lamb survival (year of lambing, litter size, pregnancy wastage) require further study so that strategies for reducing lamb loss in high fecundity Merino flocks can be developed.     

Influence of classification levels of ram sexual activity on spring breeding ewes

Ram lambs (7–8 months old) and mature rams (19–20 months old) were used to evaluate the effect of classification levels of male sexual performance on reproductive performance of ewes during spring breeding. In Exp. 1, sexually active ram lambs with high (1.8±0.3; n=5) and low (0.9±0.2; n=5) sexual performance scores (HP and LP; mean±S.E.M.) were used in single sire breeding pens. Ewes (n=305) were stratified by age and assigned to 10 pens for 34 days starting in late March. For Exps. 2 and 3, two replicates were conducted for 2 years with sexually active mature rams in a single sire mating scheme. For Exp. 2, HP rams (n=5) averaged 3.6±0.2 ejaculations and LP rams (n=7) 1.8±0.2 ejaculations for sexual performance scores based on nine, 30 min serving capacity tests (SCT). Polypay ewes (n=152 to 153 per year) were stratified by age and assigned to pens each year for 34–38 days starting in late March for years 1 and 2. For Exp. 3, HP rams (n=6) averaged 3.7±0.1 ejaculations and LP rams (n=10) 2.3±0.1 ejaculations for sexual performance scores based on 18, 30 min SCT. Polypay ewes (n=229 in year 3 and n=244 in year 4) were stratified by age and assigned to pens each year for 34 days starting in late March. In Exp. 1, lambing rates for ewes bred to HP versus LP ram lambs did not differ (65.8 versus 53.0; P=0.20). Prolificacy tended (P=0.06) to be increased by 0.1 lambs in ewes bred by LP ram lambs. Total number of lambs born per ewe present at lambing, and lambing distribution were not altered by HP and LP ram lambs. In Exp. 2, lambing rates for fall-lambing ewes bred to mature HP or LP rams did not differ (58.1 versus 60.1; P=0.78). In Exp. 3, lambing rates for fall-lambing ewes bred to mature HP or LP rams did not differ (74.3 versus 69.0; P=0.35). There was no difference (P>0.10) between years for Exp. 2 or Exp. 3, and mature HP and LP rams did not affect the other reproductive variables monitored. Analyses of the combined data for Exps. 2 and 3 indicated only a year difference (P<0.001) in lambing rates and total lambs born. Present studies indicate that different sexual performance classifications for ram lambs and mature rams did not alter lambing rates or distribution of lambing of Polypays bred in late March to April. These results indicate that HP and LP, sexually active, Polypay rams and ram lambs with average to high quality semen can provide a source of rams for spring breeding Polypays in ambient conditions and that there was no advantage to using HP over sexually active LP ram lambs or rams.     

Increasing reproductive rates in tropical sheep by means of embryo transfer

One to three embryos were transferred to three groups each of 12 Kenya Merino ewes to establish if uterine capacity is a limiting factor to reproductive performance in this breed of sheep, in a tropical environment. A fourth group of 12 ewes received three embryos following superovulation. Multiple transfers increased the number of lambs born per pregnant ewe. However, although superovulation significantly (P<0.01) increased endogenous progesterone levels in Group 4 recipient ewes, it did not improve either their conception or lambing rates. Peri- and post-natal losses increased with the number of embryos trnasferred and with the litter size. Consequently, the same number of lambs were weaned per recipient ewe in all four groups. It is concluded that although the uterine capacity of the Kenyan Merino ewes is higher than their natural ovulation rates require, increasing the litter size will not necessarily increase the number of lambs weaned.     

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.     

Interaction between lactation, photoperiodism and male effect in German Merino ewes

A study with 93 German Merino ewes was performed from January until the end of March to clarify the relative importance of lactation, photoperiodism and ram effect on cyclic activity and lambing data. Ovarian activity was registered by progesterone concentrations in blood plasma three times weekly. Half of the ewes were kept under supplemental light (20 h/day) for the last 6 weeks of lactation and additionally 3 weeks post-weaning, the other half were kept under natural photoperiod but were weaned simultaneously. Thereafter, light was reduced to natural photoperiod and rams were introduced to half of the ewes, of both light reduced and photoperiod group. Ewes entered cyclicity during lactation gradually, but at weaning 56% of photoperiod ewes and 53% of supplemental light ewes were still acyclic. After weaning, resumption of cyclic activity before ram introduction was more pronounced (P<0.05) in the photoperiod group (75% cyclic) than in the supplemental light group (51% cyclic). Ram introduction led to cyclicity in all ewes. Light reduction without ram slightly increased cyclicity but 57% were still acyclic. In the photoperiod group without ram no ewe entered cyclicity and two ewes even ceased cycling again. Data show that German Merinos still have a remarkable lactational anoestrus but are extremely sensitive to ram. Light reduction has no direct effect on cyclicity but is likely to contribute to the elevated ovulation rate so that a combination with the ram effect led to a higher lambing rate (1.94) compared to photoperiod and ram (1.55).     

Clinical evaluation of reproductive ability of rams

Clinical evaluation of reproductive ability of rams is an integral part of sheep health management programs. The majority of problems adversely affecting the reproductive ability of rams can be easily detected with clinical evaluation. The procedure is easy to perform, has a small cost and does not require specialized support from a veterinary laboratory. As a management procedure, the method should be applied two months before the breeding season, in order to detect problems, which would adversely affect the reproductive ability of rams. It should also be performed when selecting ram-lambs as replacement sires in a flock; their first evaluation should be performed at weaning, followed by another two examinations: two to four months later and before the first mating season of these rams. The method should also be performed before the purchase of any ram as sire in a flock. Regular monitoring of reproductive ability of rams in a flock contributes to early diagnosis of disorders. As a diagnostic procedure, the method should be performed during the investigation of reproductive problems within a flock. During the evaluation of reproductive ability of rams, various clinical findings can be detected and their importance can vary. In general, rams should be in good condition and have healthy genitalia, normal libido and the ability to mate the ewes. Clinical evaluation of rams is performed in the following stages: (a) history-taking, (b) evaluation of the ratio “ewe:ram” in the flock, (c) general clinical examination, (d) clinical examination of the genitalia, (e) ultrasonographic examination of the genitalia and (f) evaluation of libido. Veterinary advice is important, in order to incorporate the clinical evaluation of reproductive ability of rams into the health management of sheep flocks.     

The influence of breeding intensity on above- and below-average sexual performance rams in single- and multiple-sire breeding environments

Two studies were conducted to evaluate the relationship between serving capacity scores and breeding performance of rams. The first study was conducted to determine whether rams with above or below mean serving capacity scores could perform equally in greater and lesser breeding intensity, single-sire mating schemes. The second study was conducted to determine whether rams with above and below mean serving capacity scores could perform equally well when only one or two ewes were in estrus daily in a multiple-sire breeding scheme (two rams/pen). Rams (n=68) were ranked according to average number of ejaculations recorded in serving capacity tests. Sixteen rams with the greatest scores (above-average) and 16 rams with least scores (below-average) were identified for breeding. Half of above-average and half of below-average rams were used in the two studies. For study 1, each ram was individually introduced to 23 estrus-synchronized ewes for 9 d to simulate high breeding intensity. Rams were given a 5-d rest before they were individually introduced to 23-24 naturally cyclic ewes for 17 d (low breeding intensity). For study 2, 16 rams were paired across ram types, and each pair competed for 20 ewes for 18 d (8 pens). For study 1, ewe fertility (ewes lambing/ewes present at lambing) and number of lambs born were greater (P<0.001) for above-average (0.67+/-0.03 and 27.6+/-1.2, respectively) than for below-average rams (0.39+/-0.07 and 15.3+/-2.7) with greater breeding intensity. Ewe fertility and lambs born did not differ for above-average (0.91+/-0.03 and 37.8+/-1.9, respectively) and below-average rams (0.86+/-0.03 and 39.0+/-1.9) with less breeding intensity. For study 2, number of ewes lambing (99+/-8.0 compared with 72+/-13.6; P=0.12) and number of lambs sired (149+/-18.5 compared with 101+/-22.8; P=0.14) did not differ between above- and below-average rams, respectively, in direct competition. Sexual classifications based on serving capacity tests are related to breeding performance of rams in certain breeding environments. When breeding intensity is greater, above-average rams impregnate more ewes and sire more lambs than below-average rams. When only a small number of ewes are in estrus daily, below-average rams for serving capacity scores perform as well as above-average rams in multiple-sire and single-sire breeding environments. We suggest that above-average rams should be used to reduce number of rams required when breeding intensity is greater.     

Estrus without ovulation in puberal ewes

In three groups of puberal sheep, one of young Merino ewes and one of Merino ewe lambs at Armidale, Australia, and one of Perendale ewe lambs at Hamilton, New Zealand, 20, 33 and 6.6% respectively of the animals failed to ovulate at their first estrus. Duration of estrus and intensity of overt estrous symptoms in these animals were the same as in their ovulating contemporaries. While the anovulatory estrus was followed by estrus with ovulation in most animals, many of the Merino lambs had a second anovulatory estrus and then went into anestrum. In some animals, failure of ovulation was followed by luteinization of a large follicle. In the Perendale lambs, the inter-estrous period following an anovulatory estrus was 15.9 days compared to 16.7 days in their ovulating contemporaries. The occurrence of anovulatory estrus in these three different groups of animals suggests that it is common in the first breeding season of young ewes. Lambing percentage probably is reduced below the expected level by the presence in the flock of ewe lambs that have had an estrus but not yet reached puberty.     

Selection for reproductive rate in Rambouillet sheep: Estimated genetic change in reproductive rate

Rambouillet sheep were selected for high or low reproductive rate based on an index of reproductive rate, reproductive INDEX = dam's total lifetime lambs born/(age in years-1). Selected ewes were first born in 1969. A random bred control line was established from the remaining foundation ewes with the first ewes born in 1973. Genetic variances were estimated with REML procedures for reproductive index and number of lambs born or weaned either per ewe exposed for breeding or per ewe lambing. Heritability of reproductive index was 0.26. Heritability for number of lambs born were 0.11 and 0.12 and for number of lambs weaned were 0.04 and 0.04 per ewe exposed for breeding and per ewe lambing, respectively. Breeding values for the reproductive index were estimated using the full animal model (BLUP) with the complete numerator relationship matrix on reproductive index, with fixed effect of year of birth of ewe and breeding values for number of lambs born or weaned either per ewe exposed for breeding or per ewe lambing, estimated with the fixed effects of year of birth of ewe and age of ewe and the random effect of permanent environmental effect among repeated lambing records. Genetic change was estimated as the regression of breeding value for reproductive index and number of lambs born or weaned either per ewe exposed for breeding or per ewe lambing on year of birth of the ewe. High and low lines both responded to selection for reproductive index as compared to the control line (P<0.01). The high line increased at a rate of b = 0.0134 ± 0.0006 reproductive index units and the low line decreased at a rate of b = − 0.0098 ± 0.0005 reproductive index units per year. Response to selection for reproductive index resulted in b = − 0.0074 ± 0.0007 and b = 0.0163 ± 0.0006 lambs per ewe exposed for breeding, and b = − 0.0041 ± 0.0002 and b = 0.0075 ± 0.0002 lambs weaned per ewe exposed for breeding in the low and high lines, respectively. There was a greater response to selection in the high line compared to the low line. These results indicated that the reproductive index did respond to selection.     

Genetic basis of variation in reproductive performance. I. Ewe lambs treated with fluorogestone acetate and PMSG in a controlled environment

This study involved records on fertility, prolificacy, multiple birth, fecundity, body weight and age at breeding of 2380 ewe lambs from 432 sires of three synthetic strains developed at the Animal Research Centre, Ottawa, Canada. Ewes were divided into two equal flocks which were bred to lamb alternately at 4-month intervals under an 8-month breeding cycle. Lambs were housed indoors, in a controlled environment, on expanded metal mesh floors in windowless barns and were bred in January, May and September at the end of a period of short days. Ewes that lambed were generally heavier and slightly older at breeding as were ewes that lambed to mating at the synchronised estrus. Though not significant, trends demonstrating seasonal differences in the heritabilities of all reproductive traits were observed. Paternal half-sib estimates showed fertility, prolificacy, multiple births and fecundity were non-heritable in ewes lambing to matings at the synchronized estrus. Heritability estimates for prolificacy and multiple birth were 0.22 and 0.13, respectively, in ewes lambing to matings at the synchronized plus follow-up estrus, suggesting that slow genetic progress can be achieved in these traits from selection. Heritability estimates ranged from 0.03 to 0.22 for body weight and from 0.28 to 0.54 for age at breeding. Ewes that lambed showed lower values than all ewes exposed. Phenotypic correlations between reproductive traits and either body weight or age at breeding were low and ranged from 0.04 to 0.09. There were higher estimates of genetic correlation of prolificacy (and multiple birth) with either body weight or age at breeding in ewes lambing to matings at the combined estruses. Indirect selection of ewe lambs based on age and body weight at breeding may be an effective alternative to direct selection for genetic improvement of prolificacy and multiple birth.     

Control of oestrus in ewe lambs and yearling ewes with medroxyprogesterone acetate and fluorogestone acetate

Two experiments were conducted in a large flock of Berrichon purebred and Romanov × Berrichon F₁ crossbred ewes. In experiment 1, 157 ewe lambs were placed in six groups according to season of mating and maternal breed. Within each group equal numbers of females were treated with either medroxyprogesterone acetate (MAP) or fluorogestone acetate (FGA)-impregnated sponges for 14 days; dosage of PMSG at the time of sponge removal was 500 and 300 I.U. respectively for pure and crossbred. In experiment 2, 111 dry yearling ewes of the Berrichon breed were involved, of which 35, 51 and 25 had either a short lambing to treatment interval (approximately 3 months), a long lambing to treatment interval (approximately 6 months), or were primiparous or nulliparous. They were also treated either with MAP or FGA.The conception rates were extremely high (overall near 86%) in ewe lambs and not significantly affected by seasons or breeds or treatments. Prolificacy and number of lambs per ewe mated were higher in the F₁ crossbred group than in pure Berrichon females (respectively 1.91 vs. 1.34 lambs/mated ewe). No significant difference between the two progestagens could be observed for any of the productivity criteria. Fertility was equally satisfactory in yearlings (overall near 85%) irrespective of the interval between lambing and mating. However, the fertility of the nulliparous ewes (those that failed to conceive as ewe lambs) was significantly lower (72%). The number of lambs per ewe mated was 1.78 in yearlings with a 6-month interval from lambing to mating but was not significantly different from the numbers recorded in the other two groups (1.37 and 1.36). As in experiment 1, there was no difference in the results obtained after either of the two progestagen treatments.In conclusion, progestagen treatment has been shown in both ewe lambs and yearlings to be a very effective means of increasing lamb production in large flocks. This was achieved in ewe lambs regardless of the season and, in dry yearling ewes, regardless of the interval from lambing to mating in the anoestrous season.     

Effectiveness of a short-term treatment with progesterone injections on synchrony of lambing and fertility in tropical hair sheep

The efficacy of using a low cost system for delivering progesterone as part of an estrous synchronization protocol in sheep was evaluated. In experiment 1, Barbados Black Belly ewes (n=34) and ewe lambs (n=35; 37.5±0.9 kg) were assigned to be untreated, control animals (C), or to receive PGF(2α) on d0 (PG), or receive two injections of progesterone (200mg, i.m. each) on D -5 and on D -2.5, prior to PGF(2α), on D 0 (2PPG). Treatment with 2PPG increased the proportion of animals lambing to the first service (P<0.05), an effect that was greater in ewe lambs than ewes (treatment × parity; P<0.05). The interval from ram introduction to lambing and the mean lambing day was less (P=0.04) in the 2PPG-treated animals compared to control animals. In Experiment 2, lactating ewes from experiment 1 (n=61) 60-85 days postpartum were assigned within parity and number of lambs reared to remain nursing (S; n=29) or weaned (W; n=32) 3 weeks prior to treatment with the 2PPG protocol. There was no effect of treatment on the proportion of animals lambing to the first service or overall, interval from ram introduction to lambing and lambing interval. An 8-month lambing interval was observed in ewes in which estrus was synchronized regardless of physiological state. In conclusion, the two-progesterone injection synchronization protocol may be used as a practical low cost and efficient method of synchronizing estrus to reduce the lambing interval and maximize productivity in tropical breeds of sheep.     

Effect of ram exposure at the end of progestagen treatment on estrus synchronisation and fertility during the breeding season in ewes

Two experiments were conducted to examine the effects of ram exposure during the breeding season, in combination with progestagen treatment on estrus synchronization, fertility the LH surge and ovulation in ewes. Experiment 1 was subdivided into experiments 1a and 1b. In all experiments cross-bred ewes were treated with an intravaginal sponge for 12-14 days and three days before sponge withdrawal ewes were divided into control (no further treatment; n=191, 103 and 50 for experiments 1a, 1b and 2, respectively) or ram exposed (three mature rams per 50 ewes were introduced; +Ram; n=187, 99 and 49 for experiments 1a, 1b and 2, respectively). At sponge withdrawal ewes in Experiments 1a and 2 received 500 IU eCG and rams were removed from all the +Ram groups. In Experiments 1a and 1b, raddled, entire rams were introduced to ewes 48 h after sponge withdrawal. The timing of mating was recorded and ewes were maintained until lambing. In Experiment 2, estrus behavior was determined every 4 h and the time of the LH surge and ovulation were determined from a subset of 10 ewes per group. In Experiment 1a, less +Ram ewes were bred by 48 h after ram introduction (control 98% versus +Ram 89%, P<0.001) and in Experiments 1a and 1b 14% fewer (P<0.05) of the ewes bred in the first 3 h after ram introduction lambed to that service. In Experiment 1a, ram exposed ewes had a lower litter size than control ewes (1.93+/-0.06 versus 1.70+/-0.06 lambs per ewe; P<0.05). In Experiment 2, rams advanced (P<0.05) estrus, the LH surge and ovulation by 2-6 h compared with control ewes. We speculate that exposure of ewes to rams increased LH secretion and that this in turn increased follicle development and the production of oestradiol that led to a more rapid onset of estrus, the LH surge and ovulation compared to control ewes. Unexpectedly, ewes that were bred had lower fertility in the +Ram groups than control groups.     

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 immunization of ewes against steroids as a means of increasing prolificacy in a mediterranean environment

Four experiments are reported in which the reproductive performances of Merino ewes in the Mediterranean environment of the south of Western Australia were examined following active immunization of the ewes against the steroids androstenedione (AD) and oestrone (OE) using DEAE-dextran adjuvant. The immunogens and protocols used were modified between experiments as the compounds and procedures required to elicit higher, reliable performances were improved.The changes in performance following treatment with the AD immunogens relative to those recorded for untreated ewes ranged from 0.12 to 0.38 ovulations per ewe ovulating, 0 to 62.1% multiple births, −13.9 to 37.5% lambs born, and −24.5 to 18.8% lambs marked to ewes present at the end of lambing.The respective figures for the ewes treated with the OE immunogens were −0.04 to 0.56 ovulations per ewe ovulating, 3.5 to 64.7% multiple births, −21.1 to 44.4% lambs born, and −28.3 to 55.6% lambs marked.Whereas liveweight of the ewes at joining did not have a major effect on their performance, nutrition had an important influence, with the better fed pregnant immunized ewes having more multiple births (42.4 vs. 14.0%, P<0.01). A late December joining gave better results than an early February joining.Immunization against either steroid produced consistent increases in ovulation rates but there was not always a corresponding gain in the percentage of lambs born, whilst further losses occurred to lamb marking. The lack of a consistent and large improvement in the lambing performance of steroid immunized ewes in these experiments may have been associated with a depression in the pregnancy rate of the ewes. If this problem was overcome, immunization could improve the overall reproductive performance of well fed Merino ewes in Mediterranean environments now that the AD immunogen is commercially manufactured.     

Freemartinism and FecX allele determination in replacement ewes of the Rasa Aragonesa sheep breed by duplex PCR

A new naturally occurring mutation in the fecundity gene BMP15 in the Rasa Aragonesa sheep breed (Ovis aries) has been found to affect prolificacy. This mutation (FecX^R allele) is a deletion of 17 base pairs that leads to an altered amino acid sequence, and this alteration increases prolificacy in heterozygous ewes but causes sterility in homozygous ewes. Selection of repository lambs with the FecX^R allele increases rates of twins and multiple lambing and thereby also increases the probability of lambing freemartins that will become sterile. In this sense, an accurate, reliable, and quick method was developed by duplex polymerase chain reaction (PCR) for sex, amplifying an ovine-specific Y chromosome repetitive fragment, and BMP15 genotype determination in replacement ewe lambs. The BMP15 fragment served as an internal control of the amplification and detected the FecX^R allele, avoiding a false negative and then a mistake in freemartin detection. This assay uncovered 6 freemartin females among 195 replacement ewes from 7 different commercial flocks and 1 experimental flock. Furthermore, 1554 rams from 64 commercial flocks were also analyzed to identify FecX^R rams. This analysis identified 103 rams hemizygous for the FecX^R allele and 1 heterozygous ram. Because this gene is located on the X chromosome, this heterozygous animal is a freemartin ram that is co-amplifying the DNA from XX and XY lymphocytes. These results confirm the usefulness of this multiplex PCR assay for detecting phenotypically sexed females, freemartins, and the BMP15 genotype to detect highly prolific ewes in commercial flocks and to assist breeders in selection of repository lambs.