Mating Of Ewes Research Articles

A Cross-Sectional Study of Commercial Ewe Management Practices for Different Sheep Breeds across Southern Australia.

The management of ewes across southern Australia may vary with breed and can change over time and, as such, a greater understanding of producer management practices and the motivations that influence these practices is required. A cross-sectional study was performed by telephone interview with sheep producers managing Composite, Maternal, Merino or shedding ewe breeds mated in either spring, summer, or autumn. The surveyed producers were a unique subset of southern Australian producers. A large proportion of the surveyed producers followed current best practice guidelines for ewe mating and lambing nutritional management; however, some producers did not align with these targets. Further, some producers did not see the value in attaining the current recommendations. Pregnancy scanning was widely practiced, likely an artefact of the recruitment process; however, a few producers did not utilize this information for nutritional management at lambing time. Finally, most producers were active in their search for new information, seeking information regularly from a wide range of sources and reported making management changes within the last five years. Further work is required to understand why some producers are not adopting best practice where possible and to understand current barriers for adoption. Management guidelines for all sheep breeds are required to best manage sheep across southern Australia.

Breed and crossbreeding effects on growth, fitness and reproduction of commercial sheep in South Africa

The study aimed to assess additive breed effects for growth (birth, weaning and ewe adult weight), fitness (lamb survival and tick count under natural challenge) and ewe reproduction traits per ewe mated in Dorpers, the most common meat breed in South Africa (SA), and the SA Mutton Merino (SAMM) a prominent dual-purpose breed in SA extensive environments. Additionally, the reciprocal crosses between the two breeds were used to estimate dam breed effects and heterosis. No conclusive additive breed differences were found for lamb weight traits, lamb survival or tick counts. There was a suggestion that lamb survival of Dorpers was higher than that of their SAMM contemporaries, but significance could not be demonstrated. Crossbred progeny outperformed the midparent value by 7.1% for weaning weight. As far as mature ewes were concerned, mating weight was affected by breed combination with the mating weights of purebred SAMM ewes as well as crossbred ewes exceeding that of purebred Dorpers. Number of lambs born per ewe lambed was independent of the genetic group. The SAMM x Dorper group outperformed the pure breeds for number of lambs weaned per ewe mated (NLW). Contrasts for additive breed and maternal heterosis were not significant for NLW, but direct heterosis amounted to 32.5%. Crossbred ewes performed better than the pure breeds for total weight of lamb weaned per ewe lambed, direct heterosis amounting to 38.4%. The other contrasts were not significant. A lack of additive effects for traits, barring ewe mating weight suggested that the breeds performed similarly under the conditions of the study. Significant heterosis effects for weaning weight as well as number and weight of lamb weaned suggest a role for crosses between Dorpers and SAMMs in commercial lamb production enterprises.

The performance and profitability of plantain/clover pasture mixtures in East Coast farming systems

Yield and animal performance data from plantain/clover and resident ryegrass-based pastures were collected over several years from six properties on the East Coast of the North Island. This information was used in a FARMAX® model developed for a hypothetical farm based on data collected by the Beef + Lamb Economic Service. The hypothetical farm was 495 ha with 50 ha of flats used for silage and/or winter forage crop. The base model had a gross margin of $703/ha. The 50-ha flat block was modelled as if in a plantain rotation with two thirds in plantain and one third in annual ryegrass each year. The higher yields and better-quality feed on the plantain block improved animal performance and carcass weights. Early mating of one-year ewes for feeding on plantain provided a very high-returning enterprise. More ewes and lambs were killed early at heavier carcass weights with a premium before the onset of summer-dry conditions. This became a force multiplier across the entire farm as more feed was available for other stock and lamb carcass weights increased across the farm. Highest returns were generated by using the extra quality feed to increase ewe liveweights by 8 kg. Whilst ewe numbers had to be decreased, this was more than compensated for by the higher lambing percentage and greater number of lambs from mated hoggets. The combined effect was an increase in farm gross margin by around $200/ha and in farm returns of $100,000.

Konya Karapınar İlçesi Orta Anadolu Merinoslarında Sezon İçinde Koç Etkisinin Farklı Uygulamasının Döl Verimine, Aşım ve Doğum Süresine Etkisinin Araştırılması (II)

Bu çalışmada koç katım sezonunda koç etkisinin farklı uygulamalarının sürüdeki koç katım, doğum sezonu ve döl verimine etkisi araştırıldı. Sürülere aynı tarihte koç katımından sekiz gün sonra işletmelerden birinde koçlar altı gün süreyle ayrılırken (İşletme I) diğer işletmede (İşletme II) koçlar ayrılmadı. Koçların ayrıldığı işletmede koçların tekrar katımından sonraki 19 günde koyunların (271/300) %90,3’ünde aşımlar gerçekleşti. Koçların ayrılmadığı işletmede ise 50 günde koyunların (388/400) %97’sinde aşımlar gerçekleşti. Her iki işletmede de çiftleşmeler elde aşım ile gerçekleştirildi. Uygulama yapılan işletmede aşım sezonu 39 günde tamamlanırken diğer işletmede 65 günde tamamlanmıştır. Araştırmanın yapıldığı işletmeler doğum süreleri yönünden değerlendirildiğinde; uzaklaştırma yapılan işletmede doğuran koyunların (254/291) %87,3’si doğumların yoğunlaştığı 20 günde gerçekleşti. Doğum sezonu 41 günde tamamlandı. Uygulama yapılmayan işletmede ise doğuran koyunların (326/373) %87,4’ü doğumların yoğunlaştığı 29 günde gerçekleşirken, doğum sezonu 63 günde tamamlandı. Uygulamalar arasında aşım sezonu süresinde fark olduğu (P< 0.05) ancak doğum süresinde fark olmadığı tespit edildi. (P≥0.05). Kuzu veriminde uygulamalar arasında fark olmadığı belirlendi (P≥0,05). Değerlendirmeler istatistiki olarak Chi-Square yöntemi ile karşılaştırıldığında aşım ve doğum süreleri açısından uzaklaştırma yapılan işletme lehinde önemli olduğu görülmektedir. Sonuç olarak koç katım mevsiminde koçların sürüye 8 gün katılıp 6 gün ayrılması sonrasında tekrar katılması, aşım ve doğum sezonunun zaman olarak daha kısa sürede tamamlanmasını sağlamakla birlikte istatistiki fark oluşturmadığı belirlenmiştir.

Placental development during early pregnancy in sheep: nuclear estrogen and progesterone receptor mRNA expression in the utero-placental compartments

Sex steroid hormones are major regulators of uterine and placental growth and functions, as well as many other biological processes. To examine the mRNA expression of nuclear estrogen (ESR1 and 2) and progesterone (PGRAB and B) receptors in different compartments of the uterus and placenta, tissues were collected in experiment 1 on days 16, 20, and 28 after natural mating (NAT) and on day 10 after estrus (nonpregnant controls [NP]); and in experiment 2 on day 22 of NAT, and pregnancies established after transfer of embryos generated through mating of FSH-treated ewes (NAT-ET), in vitro fertilization (IVF), or in vitro activation (parthenotes). In experiment 1, ESR1 expression in endometrial stroma (ES), endometrial glands (EGs), and myometrial blood vessels (MBVs), ESR2 in endometrial blood vessels (EBV), PGRAB in ES, and PGRB in ES, EG, and MBV was greater in pregnant than NP ewes depending on the day of pregnancy. The day of pregnancy affected the expression of ESR1 in MBV, ESR2 in EBV and MBV, and PGRAB in ES. In experiment 2, ESR1, PGRAB, and PGRB in EG, but not in other compartments, was greater in NAT-ET than NAT, and PGRB was greater for NAT-ET than IVF. These data demonstrate that ESR and PGR expression differ in pregnant versus NP ewes in selected compartments and was affected by pregnancy stage or embryo origin in selected utero-placental compartments. Thus, sex steroid hormone mRNA expression is differentially regulated in a spatiotemporal manner in the uterus and placenta and is affected by the application of assisted reproductive technology in sheep.

The molecular mechanism of sheep seasonal breeding and artificial regulatory techniques for estrus and mating in anestrus

Seasonal breeding is an important factor limiting sheep production efficiency. Detailed analysis on the molecular mechanisms of seasonal breeding is the premise for improving estrus and mating rate of sheep during anestrus. Recent research showed that under long-photoperiod and short-photoperiod conditions, a series of changes in signaling molecules and cell morphology could be observed in ovine seasonal reproduction pathway. Based on the molecular mechanisms of seasonal reproduction, several technologies or methods for inducing estrus and mating of ewes in anestrus have been developed. In this review, photoperiod-induced changes in signaling molecules and cell morphology in pituitary and hypothalamic tissue are first summarized in terms of the molecular mechanisms and characteristics of seasonal reproduction. The application effect, advantages and disadvantages for applying these technologies for inducing estrus and mating of ewes in anestrus are then discussed, thereby providing the critical insights in identifying a new technology, which is environmentally friendly and efficient, to improve breeding rate in anestrus.

Laparoscopic intrauterine insemination in superovulated Chios breed ewes

Superovulation was induced by i.m. administration of 8.8 mg o-FSH in 8 standard doses. Using only one trocar, 0.3 ml of diluted semen (300X106 spermatozoa) was deposited intraluminally, 24-28 hours after oestrus expression, with a 20GX75 mm needle without any fixation of the uterine horns. The duration of the procedure was approximately 5 min per animal. The oocytes-zygotes collection was carried out 18-24 hours after insemination by flushing of the oviducts. The percentage of the collected zygotes varied between donors from 44.44% to 100%. Fertilization was confirmed by the existence of two pronuclei in 121 out of 140 collected oocyteszygotes. Out of the 26 ewes, in 14,10 and 2 the percentage of fertilized oocytes were 100%, 80.55% and 44.44%, respectively. The results from this study are compared with those from other laparoscopic techniques, cervical insemination or natural mating of superovulated ewes. The feasibility for the application of this method in embryo transfer programmes and in intrauterine insemination with frozen ram semen, is also discussed.

Impact of young ewe fertility rate on risk and genetic gain in sheep-breeding programs using genomic selection

Genomic selection could be useful in sheep-breeding programs, especially if rams and ewes are first mated at an earlier age than is the current industry practice. However, young-ewe (1 year old) fertility rates are known to be lower and more variable than those of mature ewes. The aim of the present study was to evaluate how young-ewe fertility rate affects risk and expected genetic gain in Australian sheep-breeding programs that use genomic information and select ewes and rams at different ages. The study used stochastic simulation to model different flock age structures and young-ewe fertility levels with and without genomic information for Merino and maternal sheep-breeding programs. The results from 10 years of selection were used to compare breeding programs on the basis of the mean and variation in genetic gain. Ram and ewe age, availability of genomic information on males and young-ewe fertility level all significantly (P < 0.05) affected expected genetic gain. Higher young-ewe fertility rates significantly increased expected genetic gain. Low fertility rate of young ewes (10%) resulted in net genetic gain similar to not selecting ewes until they were 19 months old and did not increase breeding-program risk, as the likelihood of genetic gain being lower than the range of possible solutions from a breeding program with late selection of both sexes was zero. Genomic information was of significantly (P < 0.05) more value for 1-year-old rams than for 2-year-old rams. Unless genomic information was available, early mating of rams offered no greater gain in Merino breeding programs and increased breeding-program risk. It is concluded that genomic information decreases the risk associated with selecting replacements at 7 months of age. Genetic progress is unlikely to be adversely affected if fertility levels above 10% can be achieved. Whether the joining of young ewes is a viable management decision for a breeder will depend on the fertility level that can be achieved in their young ewes and on other costs associated with the early mating of ewes.

Superovulatory response and embryo development in ewes treated with two doses of bovine somatotropin

This study evaluated whether the administration of 50 and 100mg bovine somatotropin (bST) at the start of synchronization and at the time of natural mating in ewes improves the ovulation rate, embryonic development and pregnancy rate of transferred embryos. Forty-eight donors were assigned to three treatments: the bST-100 treatment (n=15) received 100mg bST at the start of synchronization and at natural mating, the bST-50 treatment (n=15) received 50mg bST on the same schedule as the previous group, and the control (n=18) did not receive any bST. Two embryos were transferred to each recipient (n=121): 35 received embryos from bST-100; 50 received embryos from bST-50, and 36 received embryos from the control. The superovulatory rate, percentage of recovered structures, cleavage rate, percentage of transferable embryos, embryo quality and development and pregnancy rate were analyzed using the GENMOD procedure of SAS. The number of corpora lutea and the cell number were analyzed using the GLM procedure of SAS. The insulin and IGF-1 concentrations were analyzed with ANOVA for repeated measures. The bST application did not affect the superovulatory rate, number of corpora lutea and recovered structures (P>0.05). The numbers of transferable embryos and embryos reaching the blastocyst were higher (P≤0.01) in the bST-50 (96.4±3.6% and 69.0±7.8%) than the bST-100 (93.0±4.5% and 27.2±38.9%) and control (87.7±5.4% and 50.4±6.4%) groups. The insulin and IGF-1 concentrations were higher (P<0.05) in the bST-treated groups, but the insulin concentration was higher (P<0.05) in the bST-100 group than in the bST-50 group. The pregnancy rate was similar (P=0.21) in ewes receiving embryos from the two treatments [bST-50, (70.0%); bST-100, (62.5%), and control, (56.6%)]. The administration of 50mg bST at the start of synchronization and at natural mating in superovulated ewes was concluded to enhance the proportion and development of transferable embryos. However, bST did not affect the pregnancy rate of transferred embryos.

Effect of body condition score and body weight of Sanjabi ewes on immune system, producti ve and reproducti ve performance

Total 80 Sanjabi ewes (2–5 years old and 50–85 weight domain) were selected in animal unit of Mehregan farm. The ewes were divided to 4 treatment groups according to body condition score of (2, 2.5, 3, 3.5 ≤). Blood samples were collected from non-pregnant ewes, then after mating, two weeks before expected lambing and at lambing day. Blood samples of newborn lambs were also taken from the jugular vein at birth and 7 days of age. The reproductive parameters such as number of lambs born per lambing, kg of lambs born per ewes mating, pregnancy period and lamb birth weight were determined. Some blood metabolites such as glucose, total protein, albumin and globulin were determined. The white blood cell and differential leukocyte counts were also measured. The result of this experiment indicated that BCS = 3 had a significant effect (P &lt; 0.05) on the kg lambs born per ewes. Ewes with BCS = 3 had a better performance in the percentage of lambs born per ewes at mating, while the lambing rate reduced in ewes with BCS of 3.5 or more. Birth weight of lambs was significantly affected by BCS of their ewes (P &lt; 0.05). There was a significant effect of BCS on plasma FSH concentration in ewes with BCS more than 3 but no significant difference was seen in blood metabolite in this study. Colostrum productions and the lamb birth weights were affected by body condition score of ewes. The white blood cell counts, neutrophils and lymphocytes counts did not change between ewes and lambs. It is concluded that BCS had a significant effect on kg lambs born per ewes, birth weight of lambs, lambs weaning weight and colostrum productions (P &lt; 0.05) and the score of 3 at mating time could optimize profitability of Sanjabi ewes.

The effectiveness of supplemental administration of progesterone with GnRH, hCG and PGF2α on the fertility of Tuj sheep during the non-breeding season

This study investigated the effects on fertility parameters of combined administration of flugestone acetate, GnRH, hCG and PGF2α to Tuj ewes during the non-breeding season. In the study, 60 Tuj ewes were separated into four groups. Seven days before administering an intravaginal gestagen (20mg Flugestone acetate, sponge) to the ewes in Group I (GI, n=15), they were given an injection of GnRH (8.4μg Buserelin acetate). Seven days after the sponge was administered, the ewes were given a second intramuscular injection of GnRH. The sponge was left in the vagina for 14 days. Immediately after removing the sponge, an intramuscular injection of PGF2α (15mg) was administered. The ewes in Group II (GII, n=15) were administered hCG injections at a dose of 1000IU/ewe instead of the GnRH injection that was given to the first group. The ewes in Group III (GIII, n=15) were only administered intravaginal sponge. The ewes in Group IV (n=15) were kept as a control group and were not given any treatment. Immediately after the sponges were removed, rams were introduced in all groups, ensuring that ewes exhibiting estrus were mated. The percentage of ewes exhibiting estrus was found to be significantly higher in all the study groups (GI, GII and GIII) than in the control group (GIV) (P<0.05). It was determined that the pregnancy ratio for ewe mating at the first estrus was higher in group GII than in all the other groups (46.6%) (P<0.05). The overall pregnancy rate and lambing rate was found to be significantly higher in GII (100%) than the other study groups (GI: 66.6% and 66.6%; GIII: 66.6% and 46.6%, respectively, P<0.05) as well as the control group (GIV: 6.6% and 0%, respectively, P<0.01). On day 7 after the sponge was administered, the mean plasma progesterone level (3.64ng/ml) was found to be higher in the ewes in GII, and this difference was found to be statistically significant (P<0.01). We concluded in this study that administering hCG and vaginal sponges to Tuj ewes during the non-breeding season had a positive effect on pregnancy and lambing rates.

Genetic and non-genetic factors affecting Lori-Bakhtiari ewe body weight and its relationship with productivity

The data set used in this study consisted of 22,493 records of ewe body weight, measured a maximum of four times per year on 1935 ewes, collected from 1989 to 2007 inclusive from a Lori-Bakhtiari research flock at Shooli station in Shahrekord. Genetic and non-genetic parameters were estimated using restricted maximum likelihood and GLM procedure in multi-trait animal model. The model included the fixed effects age of ewe, stage of production and year of recording, and random effects direct additive genetic, permanent environmental and residual. The animal model was employed to identify the effect of ewe body weight (as classification and continuous variable) on ewes productivity traits. The age of ewe, stage and year of production had significant ( p < 0.01) effect on ewe body weight. The least squares means of ewe body weight ranged from 55.78 to 65.01 kg, increasing with age of ewe, the maximum body weight observed in 5 years old group and then decreased in the older age groups. The lowest ewe weight was seen at mating. The maximum ewe weight observed after parturition and decreased after weaning and at shearing. The heritability estimates of ewe weight at different stages of production as various traits were high (0.40–0.49). The estimates of genetic correlation between ewe weights at different stages of production were high and ranged from 0.89 to 0.99. Ewe body weight at mating affected all traits related to ewe's productivity significantly ( p < 0.05 or 0.01). There was a rising pattern in conception and lambing rate as weight of ewe increased up to overall mean plus 5 kg (56.59–61.58 kg) and a decline thereafter. The least squares means of number of lambs born and weaned, total litter weight (kg) at birth and weaning per ewe exposed increased with increasing ewe weight at mating. The total litter weight (g) at birth and weaning per kg body weight of ewe exposed decreased with increasing ewe weight at mating. The least squares means of total litter weight (g) at birth and weaning per kg metabolic body weight of ewe (BWT 0.75) exposed increased with ewe weight up to overall mean plus 5 kg and then declined. Thus, the highest productivity was for ewes ranging in weight from mean plus and minus 5 kg at mating in Lori-Bakhtiari ewes (56.58 ± 5 kg).

Nutritional and flock management options to reduce methane output and methane per unit product from sheep enterprises

The daily methane output of sheep is strongly affected by the quantity and digestibility of feed consumed. There are few widely applicable technologies that reduce the methane output of grazing ruminants without limiting feed intake per head or animal numbers. In contrast, there are many opportunities to increase the amount of animal product generated per unit of feed eaten. These include improving growth and reproductive rates of livestock and will reduce methane emission per unit of product (called emissions intensity) for individual animals. Producer responses to such improvements through changes to stocking rate and total area grazed will have a major effect on the total emission and profitability of the enterprise. First mating of ewes as lambs (~7 months of age) rather than as hoggets (~19 months of age) reduces the emissions intensity of self-replacing flocks but not that of flocks for which replacement ewes are purchased. Selection of sheep for improved residual feed intake reduces emissions intensity at the individual animal level as well as at the enterprise level. At present, emissions policies that motivate farm managers to consider generating fewer emissions rather than more profit or product are lacking.

Can audio–visual or visual stimuli from a prospective mate stimulate a reproductive neuroendocrine response in sheep?

Stimuli from a prospective mate increase the secretion of luteinising hormone (LH) in sheep. This ‘male effect’ in ewes and ‘female effect’ effect in rams is predominantly mediated by olfactory signals, though it is thought that non-olfactory signals play synergistic or substitutive roles. In this study, we tested whether exposure to visual or audio–visual stimuli from a prospective mate would stimulate an increase in LH secretion in ewes (Experiment 1) and rams (Experiment 2). In Experiment 1, groups of eight Merino ewes were exposed to one of three stimuli midway through a frequent blood-sampling regimen: full ram contact, still images of rams, a video of ewes and rams mating. Control ewes (n = 8) were completely isolated from rams. Exposure to still images of rams appeared to stimulate an increase in mean LH concentrations (P < 0.05) and tended to increase LH pulse frequency (P < 0.1), but the response was significantly smaller than that observed in ewes exposed to rams (P < 0.01). Audio–visual stimuli had no effect on any parameters of LH secretion (P > 0.1). In Experiment 2, Merino rams were allocated to either an Exposure (n = 7) or a Control (n = 7) group. Exposure rams underwent two exposure periods midway through a frequent blood-sampling regimen; exposure to still images of ewes and audio recorded during mating of ewes and rams (audio–visual exposure); exposure to oestrous ewes (ewe exposure). Control rams were sampled at the same frequency but remained isolated from ewe stimuli. Exposure of rams to the audio–visual stimuli did not affect any parameters of LH secretion (P > 0.1). In contrast, exposure to oestrous ewes increased LH pulse frequency (P < 0.05) and advanced the onset of the next LH pulse (P < 0.05). In conclusion, visual signals appear to be involved in eliciting the neuroendocrine response of ewes to rams and are of greater importance to this phenomenon in ewes (male effect) than rams (female effect). However, overall the visual and audio–visual signals used in this study were far less effective than stimulus animals, suggesting that these stimuli are less important than olfactory signals, or a combination of olfactory and audio–visual signals.

Vegetation dynamics and livestock performance in system-scale studies of sheep and cattle grazing on degraded upland wet heath

Upland wet heaths in the UK are of international conservation significance but high grazing pressure by sheep has caused widespread degradation. Restoration by reducing sheep numbers is not always successful if competitive grasses such as Molinia caerulea become dominant. Cattle can reduce grass biomass but their utility as a conservation tool is also dependent on economic viability. This study assessed the effect of two sheep-only and two mixed cattle-plus-sheep grazing regimes on vegetation and livestock performance over 4 years at a system scale on a 103 ha heterogeneous degraded wet heath. Grazing regimes were sheep all year at 1.5 or 0.66 ewes ha −1 with 25% removed in winter, with or without dry Continental cross suckler cows at 0.75 cows ha −1 for up to 10 weeks in summer. In mixed grazing paddocks, M. caerulea cover declined substantially in vegetation types where it was abundant. Calluna vulgaris declined slightly in the mixed grazing paddocks, primarily because of localised trampling. M. caerulea increased in the sheep-only paddocks and C. vulgaris declined slightly despite low grazing indices. Other changes in plant community composition were minor. Cow daily liveweight gains were adequate to regain body condition prior to calving, but these and ewe mating weights and lamb weaning weights were lower in paddocks with 1.5 than 0.66 ewes ha −1. Ewe and lamb performance were similar in mixed and sheep-only paddocks at each ewe stocking rate. Cows can be grazed with sheep to remove M. caerulea biomass without detriment to livestock performance, although the stocking levels used in this study would not be sustainable every year. Despite reduction of M. caerulea biomass, there was no evidence that heathland vegetation was being restored after 4 years. Restoration by grazing alone probably requires longer timescales and agri-environment schemes should avoid prescribing stocking levels regardless of livestock species.

Ram novelty and the duration of ram exposure affects the distribution of mating in ewes exposed to rams during the transition into the breeding season

This study compared the affect of short-term and continuous exposure to rams during the transition between anoestrus and the breeding season on the distribution of mating and subsequent lambing. Further, within ewes continuously exposed to rams we investigated the effect of replacing these rams every 17 days with ‘novel’ rams. During August (late anoestrus, Northern Hemisphere), multiparous, North of England mule ewes were allocated to one of four groups: SVR ewes were exposed to vasectomised rams for 24 h on Day 0 (short term; n = 109), RVR ewes were exposed to vasectomised rams for 24 h on Days 0, 17 and 34 (short term; n = 113); PVR ewes were exposed to vasectomised rams on Day 0 and remained with the same rams for the duration of the pre-mating period (continuous; n = 104); NVR ewes were continuously exposed to vasectomised rams from Day 0 with the rams replaced with ‘novel’ rams every 17 days (continuous; n = 113). Blood samples were collected from a subset of ewes ( n = 22 per group) to monitor progesterone. On Day 50, harnessed, entire rams were introduced for mating and raddle marks recorded daily for the first 17 days. The median date of mating occurred 1 day earlier in NVR ewes than PVR ewes ( P < 0.05). A synchrony score calculated from the blood sampled ewes showed that the distribution of mating was more synchronised in PVR and NVR ewes than SVR and RVR ewes ( P < 0.001). PVR and NVR ewes had an earlier onset of cyclic activity than RVR ewes ( P < 0.01). However, only NVR ewes differed from SVR ewes in this variable ( P < 0.05). Within ewes lambing to first service, the median date of lambing of PVR, NVR and SVR ewes occurred at least 2 days earlier than RVR ewes (at least P < 0.05). Further, PVR and NVR ewes had a more compact distribution of lambing than SVR and RVR ewes ( P < 0.05) and lambing was more compact in NVR ewes than PVR ewes ( P < 0.05). In conclusion, ewes in continuous contact with rams prior to mating had a more synchronised distribution of mating and lambing than ewes given only short-term exposure to rams. This distribution of mating in continuous ram exposed ewes can be further enhanced by periodic exposure to novel rams.

The effect of progesterone supplementation post mating and shearing of ewes in early pregnancy on the reproductive performance of ewes and birthweight of lambs

AIM: To determine whether short-term progesterone supplementation post mating or shearing of ewes in early pregnancy affected either the proportion of ewes that lambed or that had multiple lambs, or the birthweight of lambs. METHODS: Romney ewes (n=457) were synchronised in oestrus using controlled internal drug-releasing (CIDR) devices containing progesterone, and mated to Romney rams over a 5-day period. The mid-point of mating (Day 0) occurred 2 days after the withdrawal of CIDR devices. Ewes mated (n=397) were randomly allocated to one of four treatment groups: shearing at Day 5, shearing at Day 30, no shearing, and no shearing plus progesterone supplementation using a CIDR device inserted on Day 3 for 6 days. During the period from Day 5 to Day 27, six harnessed Suffolk rams were placed with the ewes and matings recorded. At Day 48, all ewes that did not return to the Suffolk rams were scanned for pregnancy using ultrasound. At Day 140, single- and multiple-bearing ewes were set-stocked at 15.1 and 12.2 ewes/ha, respectively, and equivalent numbers of ewes from each treatment group were placed in each paddock. Blood samples from 10 unshorn and 10 progesterone-supplemented ewes were collected on Days 3, 6 and 9, and analysed for plasma progesterone concentrations. Lambs were identified to their dam and weighed within 12 h of birth, and again at 27 and 93 days after the mid-point of lambing. The ewes were weighed at regular intervals throughout the trial. RESULTS: Plasma progesterone concentrations of supplemented ewes were higher than those of unsupplemented ewes (3.28 vs 1.75 ng/ml) on Day 6 (p=0.02) but not on Day 9 (4.58 vs 4.63 ng/ml). Treatment of ewes had no effect on either the proportion of ewes which lambed to the synchronised mating period or that had multiple lambs. Lambs born to ewes shorn at Day 30 tended (p=0.09) to be heavier at birth (by 0.28 kg) than those born to unshorn ewes but this effect was not evident when data were corrected for length of gestation. Neither shearing at Day 5 nor progesterone supplementation had any effect on the birthweight of lambs, and the treatment of ewes had no effect on the survival rate of lambs to weaning. CONCLUSIONS: Progesterone supplementation for 6 days beginning 3 days post mating did not increase either the proportion of ewes that lambed or that had multiple lambs, or the birthweight of lambs. Shearing 5 days after mating had no significant effect on the reproductive performance of ewes and need not be avoided, but is unlikely to result in an increase in lamb birthweight. Shearing ewes at Day 30 may result in an increase in the birthweight of lambs but, ideally, ewes should be further advanced in pregnancy before shearing is undertaken.

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.

Factors affecting reproductive performance and estimates of genetic parameters of litter size in Horro sheep

Conception and lambing rate, and litter size were studied on data from a flock of Horro sheep. The CATMOD and GLM procedures of SAS were used for the analysis of these traits. A sire, direct additive genetic and a repeatability animal model were employed to obtain estimates of heritability and repeatability for litter size. The results obtained showed that year of mating, age and weight of ewes at mating and number of previous parities had significantly (P&lt;0.01) affected the rate of conception and lambing while weight of rams at mating has shown no significant effect (P&gt;0.05). An increase in both conception and lambing rates was observed with the increase in weight of ewes up to about 36 kg and declined thereafter. Ewes which previously had no or one parity had lower conception and lambing rates compared with ewes in later parities. However, a decline in both conception and lambing rates was also observed in old ewes. Year of lambing, parity and weight of ewes at mating had a highly significant (P&lt;0.01) effect on litter size. The overall mean litter size in the flock was 1.34 with annual means ranging from 1.18 to 1.55. Litter size increased with parity from 1.26 in primiparous ewes to 1.44 for ewes of parities five and above. With respect to weight of ewes at mating, litter size increased by 2.5% for each kg increase in weight at mating. The estimates of direct heritability (h2) for litter size were 0.17, 0.11 and 0.06 under the sire, direct animal and repeatability models. Repeatability was estimated to be 0.12. Since heritability and repeatability estimates of litter size are low, genetic improvement by selection may not bring sizeable impact in increasing litter size. Therefore flock management for optimal age structure and optimal weight of ewes at mating should receive due consideration to improve rates of conception, lambing and litter size in Horro sheep.

Phenotypic and genetic relationships between lamb and ewe traits for the Sabi sheep of Zimbabwe

Genetic and phenotypic correlations were estimated between lamb and ewe traits in a flock of Sabi sheep reared at the Matopos Research Station. Direct additive estimates of heritability were: 0.28 ? 0.04; 0.17 ? 0.00; 0.25 ? 0.01; 0.39 ? 0.01; 0.59 ? 0.01; 0.50 ? 0.01; 0.68 ? .03; 0.12 ? 0.003; 0.25 ? 0.01; 0.11 ? 0.00; 0.12 ? 0.00; for birth weight, weaning weight (120 days), 12 month weight, 18 month weight, ewe mating weight, post partum weight, ewe weight at weaning of lamb, total weight of lamb weaned, slaughter weight, hot and cold carcass weights respectively. Genetic correlations between birth weight and other weights to 18 months were high (0.75-0.85), whilst the relationship between weaning, 12 month and 18 month weight was close to unity. The genetic correlation between birth weight and ewe weights (mating, post-partum and dam weight at weaning of lamb) were moderate viz. 0.51 ? 0.08, 0.40 ? 0.09, 0.49 ? 0.07 respectively and were close to unity at 18 months of age viz. 0.96 ? 0.02, 0.92 ? 0.03, and 0.84 ? 0.03 respectively. Total weight of lamb weaned was moderately correlated to birth weight (rg = 0.46 ? 0.15) but tended to be highly correlated with 18 month weight (0.92 ? 0.10) and ewe weights (0.75 ? 0.09-0.91 ? 0.07). The genetic correlation between birth weight and slaughter and carcass weight was moderate and was high at 18 months. The heritability estimates from a univariate logit transformed analysis for fertility, prolificacy and lamb survival were 0.08 ? 0.04, 0.22 ? 0.03, and 0.01 ? 0.02 respectively. The genetic correlation between fertility and lamb weight and ewe weights was low (-0.08 ? 0.004, to 0.06 ? 0.02) and some estimates had large standard errors. The genetic correlation between prolificacy and birth weight was close to zero. The genetic correlations between prolificacy and weaning weight, 12 month weight, 18 month weight, ewe mating, post-partum and ewe weight at weaning were 0.07 ? 0.02; 0.12 ? 0.00; 0.07 ? 0.02; 0.22 ? 0.00; 0.13 ? 0.00; 0.24 ? 0.00 respectively, and that between fertility and prolificacy was negative (-0.17 ? 0.07). Genetic correlations between lamb survival and birth weight, weaning weight, 12 month weight, 18 month weight and total weight of lamb weaned were 0.18 ? 0.00, 0.26 ? 0.00, 0.15 ? 0.00, 0.15 ? 0.00, 0.13 ? 0.00 respectively. Selection for birth weight and total weight of lamb weaned have possible uses in a selection index for the Sabi flock. South African Journal of Animal Science, Vol 31, Issue 3, Oct – Dec (2001) pp.215-222Key WordsFat-tailed hair sheep, Production, Reproductive traits, Lamb survival, Correlations