Breeding Ewes Research Articles

A comparison of sires of Suffolk and Dutch Texel breeds and ewes of Greyface, Suffolk Cheviot and Dutch Texel breeds in terms of food intake, prolificacy and lamb growth rates

AbstractA comparison was made over 2 years of sires of Suffolk and Dutch Texel breeds and ewes of Greyface (Border Leicester × Scottish Blackface), Suffolk Cheviot and Dutch Texel breeds in terms of food intake, prolificacy and lamb growth rates under a grass-based system of production. Suffolk Cheviot ewes consumed significantly more silage dry matter than the Greyface ewes in both years of the study. There was no overall difference between Greyface and Suffolk Cheviot ewes in terms of prolificacy. However lambs from Suffolk Cheviot ewes had a higher growth rate than lambs from Greyface ewes from birth to weaning in year 1 (P < 0·01). In the comparison of the three ewe breeds sired by Dutch Texel rams in year 2, Dutch Texel ewes produced a similar number of lambs to the other genotypes but had a higher incidence of difficult lambings, higher lamb mortality and consequently a lower number of lambs weaned. Purebred Dutch Texel male lambs had lower growth rates than crossbred Dutch Texel lambs (143 compared with 158 glday for lambs from Greyface ewes and 166 (s.e. 13.4) glday for lambs from Suffolk Cheviot ewes in year 1 and 183 compared with 251 and 248 respectively (s.e. 10.9) glday in year 2). Lambs sired by Suffolk rams had higher growth rates than those sired by Dutch Texel rams (252 compared with 224 (s.e. 5.4) glday) in year 2.

Effects of Texel or Rouge de l’Ouest genes in lowland ewes and rams on ewe prolificacy, lamb viability and weaned lamb output

AbstractAn evaluation of the effects of the proportion of Texel or Rouge de l’Ouest (Rouge) genes in ewes (0, 0·5 or 1·0; the remainder being Greyface (Border Leicester × Scottish Blackface)) on prolificacy, lamb viability and lamb output was undertaken. A comparison of Texel and Rouge sires was carried out on Greyface, Texel and Rouge ewes. Prolificacy was higher in Greyface compared with Texel ewes (P = 0·06) but was lower in Greyface compared with Rouge ewes (P < 0·001). Prolificacy was similar in Greyface and Texel × Greyface ewes mated to Texel rams and in Greyface and Rouge × Greyface ewes mated to Rouge rams. The level of dystocia was similar in Greyface and Texel × Greyface ewes but significantly higher in Texel ewes (P < 0·001). The proportion of Rouge genes in the ewe had no effect on the level of dystocia. Litter weight of lambs at birth was significantly heavier in Greyface (P < 0·001) and Texel × Greyface (P < 0·01) ewes compared with Texel ewes. The proportion of Rouge genes in the ewe had no significant effect on litter weight. Lamb mortality (no. of lambs born dead and died birth to weaning) was significantly greater with Rouge ewes compared with the other ewe breed types (P < 0·001). The number of lambs which died from birth to weaning was lower with Texel × Greyface compared with Greyface ewes (P < 0·01). Expressed on a unit metabolic weight basis, Greyface ewes produced a significantly greater weight of lamb compared with Texel (P < 0·05) and Rouge ewes (P < 0·001). Texel × Greyface ewes produced a significantly greater weight of Texel-sired lamb compared with Greyface (P < 0·01) and Texel ewes (P < 0·001).Sire had a significant effect on a number of parameters. The number of productive ewes was significantly lower in ewes mated with Texel sires (P < 0·001). Lamb birth weights and pre-weaning growth rates were greater with Rouge sires (P < 0·05). Number of lambs weaned per ewe lambed was significantly greater with Texel sires (P < 0·01). Overall weight of weaned lamb produced per ewe was not significantly affected by sire breed.

DOES THE BEHAVIOUR OF THE NEONATE INFLUENCE THE EXPRESSION OF MATERNAL BEHAVIOUR IN SHEEP?

Abstract Maternal care is provided in response to cues from the offspring. The role of offspring stimuli in determining the quality of maternal care was assessed using the sheep (Ovis aries) as a model. The effects of variation in lamb behaviour on the expression of maternal behaviour in a hill (Scottish Blackface) and a lowland (Suffolk) breed of ewe was examined by embryo transfer of single embryos between the two breeds to give the four possible combinations of ewe and lamb. Labour was significantly shorter for both breeds of ewe when delivering Blackface lambs than Suffolk lambs. Blackface lambs were also significantly more active than the Suffolk lambs in the first 3 days after birth; there was no effect of maternal breed. Despite these differences in both length of labour and lamb activity at birth with lamb breed, the behaviours of the ewe associated with the onset of maternal care (e.g. licking the lamb, allowing the lamb to the udder, absence of aggressive behaviours) were unaffected by the breed of lamb. Suffolk ewes, however, were more likely to show an aversive reaction to their lamb, spent less time licking the lamb and were more likely to move as the lamb approached the udder. There was a significant influence of ewe breed on lamb sucking behaviour. Suffolk ewes received significantly more sucking attempts than Blackface ewes from both breeds of lamb. A higher sucking rate on Suffolk ewes continued over the first 3 days after birth. Other behaviours, such as playing, were specific to lamb breed and not affected by ewe behaviour at this time. These data suggest that offspring behaviour had no effect on the onset of bonding behaviours of the ewe. Neonatal lamb activity was also largely independent of the behaviour of their dam. However, sucking behaviour of the lamb was modified by ewe behaviour and this may affect the strength of the bond between ewe and lamb.

Ewe reproductive performance and growth rate of suckling-lambs on endophyte-infected perennial ryegrass pasture

Two groups (n=39) of Romney breeding ewes were maintained under the same grazing management on either endophyte-infected (E+) or endophytefree (E-) perennial ryegrass pasture for two years (1997-1998) following a one-year equilibration period. The ewes were naturally mated in March each year and ovulation rate at 1st mating was measured, and conception and the number of lambs born and weaned were recorded. All ewes were weighed monthly and lamb growth rates were determined between birth and weaning. Mean mating date was delayed by 1.8 days (P

Ewe–ewe and ewe–lamb behaviour in a hill and a lowland breed of sheep: a study using embryo transfer

Domestic sheep have a strong social tendency. The nature of this gregariousness, however, varies with season, breed, sex and age. In this study the social behaviour of two breeds of ewe (Suffolk and Scottish Blackface) was investigated over two years in two different environments. In addition, to examine whether lamb behaviour would affect the behaviour of the ewe, an embryo transfer study was carried out between the two breeds resulting in four combinations of ewe and lamb (Blackface ewe with Blackface lamb, n=25; Blackface ewe with Suffolk lamb, n=24; Suffolk ewe with Suffolk lamb, n=25; Suffolk ewe with Suffolk lamb, n=25). All ewes and lambs grazed together in Field 1 (year 1) and Field 2 (year 2). Field 1 was 9 ha and rather uniform; Field 2 was 21.4 ha and had two distinct regions: an upland and a lowland area. Blackface ewes preferentially associated with their own lamb whereas Suffolk ewes associated equally with their own lamb or another Suffolk ewe, there was no effect of lamb breed (percent observations with own lamb as nearest neighbour, Field 1: Blackface ewes=50.2%, Suffolk ewes=43.5%, P<0.05; Field 2: Blackface ewes=73.1%, Suffolk ewes=43.5%, P<0.001). Blackface ewes were also significantly closer to their lambs than Suffolk ewes, regardless of year or lamb breed (Blackface ewes=6.10 m, Suffolk ewes=11.54 m, P<0.001). When own lamb was not the nearest neighbour ewes associated with other ewes of the same breed as themselves (With same-breed ewe=88.4% of observations, with other-breed ewe=11.6%, P<0.001). In Field 1 the distribution of both breeds in the field was similar to one another but ewes maintained subgroups composed predominantly of their own breed ( P<0.001). The mean distance between ewes was the same for both breeds, however subgroups were significantly smaller for Blackface ewes (7.53 and 9.26 ewes for Blackface and Suffolk respectively, P<0.001). In Field 2 Blackface ewes were found mainly in the upland region of the field whereas Suffolk ewes were almost exclusively in the lowland areas. Mean distance between ewes increased markedly for Blackface ewes when compared to ewe–ewe distance in Field 1 but was unchanged for Suffolks (11.29 vs. 4.36 m for Blackface and Suffolk ewes respectively, P<0.001). Subgroup size also declined for Blackface ewes in comparison to Field 1 but increased for Suffolks (Blackface=3.10, Suffolk=11.31 ewes, P<0.001). Lamb breed had no effect on the social behaviour of either breed of ewe. The two breeds had differing behaviour in their relationship to their own lamb. Their relationship to other ewes, however, was significantly modified by the environment although the Blackface breed was less gregarious than the Suffolk under both conditions.

Feed intake and digestion in the summer and fall by different breeds of ewes consuming forages differing in quality

Sixteen penned, nonpregnant ewes (>3 years of age) of four breed groups (St. Croix, S; St. Croix×Texel, ST; Polypay×Texel, PT; Gulf Coast Native, N) were used in an experiment (west-central Arkansas; 2×4×2 factorial arrangement of treatments) to determine effects and interactions in feed intake and digestion of breed group, forage quality (mature bermudagrass, L; late-boot endophyte-free fescue, H), and season (summer, S; fall, F). Summer temperature humidity index [dry bulb temperature + (0.36×wet bulb temperature) +41.2°C] was considerably above and near 72 at 1600 and 0700 hours, respectively. Organic matter digestibility was similar between seasons for H but lower ( p<0.05) in the summer vs. fall for L (46.1, 51.7, 61.9, and 62.3% for L–S, L–F, H–S, and H–F, respectively; SE 0.98). A comparable interaction between forage quality and season occurred in digestible OM intake (514, 607, 878, and 852 g day −1 for L–S, L–F, H–S, and H–F, respectively; SE 25.0). Digestible OM intake was similar among breed groups with L but greater ( p<0.05) for ST and PT than for S and N with H (27.8, 30.3, 30.3, 26.5, 39.1, 49.5, 46.7, and 38.7 g kg −1 BW 0.75 for L–S, L–ST, L–PT, L–N, H–S, H–ST, H–PT, and H–N, respectively; SE 1.52). Digestible OM intake differed between low and high quality forages more in the summer than fall and varied among breed groups more with high vs. low quality forage; season did not alter the influence of forage quality on breed group differences.

Pattern of FSH secretion from birth to 4 months of age in two Moroccan ewe breeds varying in prolificacy

Plasma FSH concentration was monitored weekly for 17 weeks starting at birth in two Moroccan breeds differing in prolificacy: D'man (rate of ovulation=2.9, n=10) and Timahdite (rate of ovulation=1.1, n=10). Plasma FSH concentrations increased progressively from birth until 17 weeks of age in both breeds. In ewe lambs, there appear to be genotype differences for FSH at specific times during the neonatal period. Mean plasma FSH concentrations were significantly higher in D'man compared to Timahdite ewe lambs at 4–7 and 12 weeks of age ( p<0.0001, p<0.0009, p<0.006, p<0.002 and p<0.01, respectively). These results demonstrate that the D'man ewe lamb of high prolificacy is characterized early in life by elevated basal plasma FSH concentrations.

Variability in the expression of maternal behaviour in primiparous sheep: Effects of genotype and litter size

The effects of ewe genotype and litter size on the expression of maternal behaviour in primiparous sheep were investigated using a lowland breed selected for growth (Suffolk) and a less-selected hill breed of sheep (Scottish Blackface). Focal animal observations were carried out on 58 Blackface (37 singles and 21 twins) and 57 Suffolk ewes (20 singles and 37 twins) during the 2 h after the birth of each lamb. Overall labour was shorter for Blackface ewes compared to Suffolk ewes (62 vs. 84 min, respectively, P<0.05), and shorter for first-born twin lambs compared to singletons. Lambing assistance was required by significantly more Suffolk ewes (25.4%) than Blackface ewes (10.8%, P=0.05) and more by single lambs than twins. Although some aspects of negative maternal behaviour were shown by both breeds of primiparous ewe, Suffolk ewes were more likely to abandon a lamb ( P=0.063), and were significantly more likely to be aggressive towards their lamb ( P<0.05) and to withdraw from the lamb ( P<0.01). Increased exposure to the lamb led to a reduction in negative maternal behaviour in both breeds. Blackface ewes devoted significantly more time to grooming their lambs in the immediate postnatal period (first 2 h after the birth of a lamb) spending 81% of the first 30 min grooming compared to only 47% in Suffolks ( P<0.001). Twin lambs received less grooming attention than singles, and second-born twin lambs received only 65% of the grooming of first-born twins. Blackface lambs were more active than Suffolk lambs in all aspects of their behaviour and made significantly more sucking attempts in the recording period ( P<0.001). Blackface ewes displayed more cooperative behaviour to lamb sucking attempts than Suffolk ewes (standing for 19.49% of sucking attempts in the first 30 min vs. 1.92% in Suffolks; P<0.001). This resulted in significantly more Blackface lambs sucking unaided compared to Suffolk lambs (72.2% vs. 36.7% for Blackface and Suffolk lambs, respectively, P<0.001). Significantly more Suffolk lambs died in the postnatal period than Blackface lambs (8.4% of lambs vs. 1.1%, P<0.05). This study has demonstrated that significant genotype differences exist between breeds of sheep in many aspects of both maternal and neonate behaviour and these may compromise the survivability of the lamb. It is suggested that a high level of selection for growth characteristics alone may lead to a deterioration in maternal ability unless these behaviours are specifically included in selection programmes.

Vocalisations between mother and young in sheep: effects of breed and maternal experience

This experiment was designed to investigate the function of vocalisations of the parturient ewe to her lambs in two breeds of sheep, a highly selected lowland breed (Suffolk), and a less selected hill breed (Scottish Blackface). Sheep have a specific lambing vocalisation, the low-pitched bleat or "rumble", that is made almost exclusively to the lamb. The hypothesis was that this "care-giver" bleat will be important in the formation of the ewe-lamb bond. Ewes also make high-pitched bleats, considered to be "protest" or distress bleats, after the birth of the lamb. Vocalisation data were collected from inexperienced and experienced ewes of both breeds, and their lambs. Additionally, an embryo transfer study between the two breeds was carried out to investigate interactions between ewe and lamb bleating. Low-pitched bleating was higher in primiparous ewes than multiparous ewes, and highest in primiparous Blackface ewes (mean bleat rate: primiparous Blackface=7.04, multiparous Blackface=2.73, primiparous Suffolk=3.99, multiparous Suffolk=2.18; P<0.005). An increase in litter size, or raising lambs of a different breed, had no effect on the rate of low-pitched bleating. The number of Suffolk ewes making high-pitched bleats was greater than Blackface ewes (61.4% vs. 35% for Suffolk and Blackface ewes respectively, P<0.01) and the rate of bleating increased with twin litters. Suffolk lambs had a higher bleat rate than Blackface lambs (mean bleat rate: Blackface=0.252, Suffolk=0.622, P<0.01), and lambs born to a primiparous ewe had a higher bleat rate than lambs with a multiparous dam (P<0.05). Birth of the second twin lamb caused a doubling in individual lamb bleat rate in both breeds. Ewe low-pitched bleat rate is, therefore, affected by intrinsic factors, ewe breed and experience, but not by characteristics of the lamb in the immediate postnatal period. The function of the bleat may be to strengthen bonding with the lamb, and the higher rate in primiparous ewes may reflect both the immaturity of the system in inexperienced animals and a slower rate of bond formation. High-pitched bleating is affected by ewe breed and may reflect the likelihood of separation of the ewe from the lamb. Lamb vocalisations are modified by their rearing experience, and appear to represent a signal of need. Increased domestication of the Suffolk breed may have led to an increase in lamb vocalisations.

Prenatal survival in relation to peri-ovulatory phenomena and the site of ovulation in sheep: A review

Differences in ovarian follicular dynamics between ewe breeds and between lines within breeds were shown to result from a different follicle recruitment and selection process. Synchrony and asynchrony of embryos were shown to depend largely on luteinizing hormone (LH), progesterone and oestrogen levels in ewes before, during and post-mating. GnRH therapy suggested that the endocrine environment prior to ovulation has a fundamental influence on luteal function and hence on prenatal survival (PS). The decreasing effect of multiple ovulation on uterine efficiency was higher in androstenedione-immune Border Leicester×Merino (BL×M) than in immunized BL×Booroola Merino (BM) ewes. Exogenous progesterone increased lambing rate in Polypay (P) but not in Targhee ewes. The 200% of maintenance feeding level reduced plasma progesterone concentrations on day 12 near the threshold critical for embryo survival in M ewes but not in BL×Scottish Blackface ewes. The latter maintained pregnancy rate (PR) and PS at the same levels as the controls. In unilaterally twin ovulating ewes, foetal mortality was significantly lower in ewes in which distributive embryo migration occurred. Within this ovarian class, survival was lower in the Cheviot, probably because of a lower migration frequency, than in the Blackface breed. More embryos migrated in unilaterally twin ovulating M ewes in autumn than in summer mating, with a higher incidence of loss of one embryo in the latter season. A higher incidence of successful migration was observed in unilaterally twin ovulating BL×M than in M ewes. The higher mortality of a migrating embryo, compared with the nonmigrating, was attributed to an asynchronous environment in the contralateral horn, since ovine trophoblastine (oTP-1) might have preferentially altered the uterine environment of the ipsilateral horn. Studies on oTP-1 and protein in uterine flushings and on conceptus development at day 13 in ewes that displayed short or long oestrous cycles, as well as further studies on unilaterally ovariectomized ewes with two or three conceptuses, suggest that the ovine embryo stimulates the migratory process locally, in interaction with the dam. This review raises the question whether and to what degree pre-, peri-, as well as, post-ovulatory phenomena and the site of ovulation can be interacting factors for determining PS, especially in multiple ovulating sheep as a function of breed and breed–environment interactions.

Effect of Coyote Removal on Sheep Depredation in Northern California

We used 13 years of historical data to investigate effects of coyote (Canis latrans) removal on depredation of domestic sheep. The 2,168-ha study area maintained >1,000 breeding ewes that produced lambs yearly. Records from 1981 through 1994, which included numbers of sheep, numbers of sheep known killed by coyotes, known numbers of coyotes removed, and annual numbers of trapper hours were summarized and analyzed on a yearly, seasonal, and monthly basis. We used regression analysis and found that annual, seasonal, or monthly depredation losses were not correlated with number of coyotes removed. Both annual number of lambs killed and number of coyotes removed were positively correlated with number of trapper hours. We used a cross-correlation analysis to detect any relation between coyote removal and subsequent depredation losses at all monthly intervals from 0 to 24 months. We found a trend of low negative correlation between depredation losses and number of coyotes removed for lags of 2-12 months, suggesting some reduction of sheep killing due to control efforts. Low correlations within years may be due to inconsistent removal of depredating coyotes while removing primarily young, nondepredating coyotes. Lack of correlation between years may have occurred because past control efforts have not had a lasting reduction on coyote density due to immigration, the compensatory nature of control efforts on coyote mortality, reproductive compensation in the resident coyote population, or all 3 factors.

Incidence of Premature Luteal Regression in Ewes Superovulated with a Single Injection of Follicle-Stimulating Hormone Combined with Equine Chorionic Gonadotropin.

The incidence of premature corpora lutea (CL) regression was investigated in three different breeds (Merino × polled Dorset: MD, Suffolk: S, and South-Down: SD), parous and non-parous ewes (a total of 46 ewes) treated for superovulation during and out of the breeding season. Superovulation was induced with a single injection of 20 mg porcine follicle-stimulating hormone (pFSH) 2 days and 500 IU equine chorionic gonadotropin (eCG) 1 day, respectively before the removal of synthetic progestogen (40 mg FGA) vaginal sponges inserted for 12 days. All ewes were inseminated into the uterus with fresh-diluted or frozen-thawed semen by laparoscope, and a number of newly formed and regressed CL were recorded. Breed difference significantly (P<0.005) affected the incidence of premature regressed CL; S (6.3%, n=16) ewes were less in the proportion of the incidence of regressed CL than MD (37.5%, n=16: P<0.05) and SD (71.4%, N=14, P<0.01) ewes. The use of non-parous ewes and treatment during autumn tended to result in higher rates of incidence of premature CL regression than the use of parous ewes and treatment during spring. These results indicate that the incidene of premature CL regression in superovulated ewes was influenced by not only season and parity but also by breed of ewes used for superovulation treatment.

Interactions between ewe and lamb genotype and sucking success in neonatal lambs

Perinatal lamb mortality remains a major economic and welfare concern in sheep farming with 80-90% of pre-weaning lamb losses occur in the immediate postnatal period (Haughey, 1993). One of the predominant factors in the death of neonatal lambs is failure of ewe-lamb bonding leading to delay or lack of sucking. Successful sucking requires the co-ordinated expression of appropriate behaviour from both the ewe and lamb. Previously we have demonstrated an interaction between ewe and lamb breed in the rate of successful sucking (Dwyer et al., 1996) with Blackface lambs having a higher rate than Suffolk lambs but also a higher rate with Suffolk ewes than with Blackface ewes. In the present study we investigated the role of ewe responses to lamb sucking attempts in determining the sucking success of neonatal lambs.

Productivity of prolific sheep : Economic analysis

The existence of major gene in the Indonesian sheep breeds has been revealed in three different genotypes which are further implied that different levels of feeding and management are necessary to realize the potential benefits for each genotype . The variability in the ewe production as a result of the differences in genotype and management levels were then evaluated by economic analysis . The result shows that improvement in management practices resulted in an increase of production ofindividual breeding ewe (BS). However, since these increases in performance required additional cost for higher input value, as it was indicated in the total production cost, attention must be given toward the decision as to which genotype to raise at what level of feeding management . This study has shown promising results to facilitate the decision makers in that direction, for example, ewes with FecJFFecJ` genotype gained the highest gross margin when they were treated with high level of feeding management. The next best alternative was followed by FecJ FFecJ F genotype. Furthermore, in the situation where low level of feeding management being practiced, ewes carrying the FecJF gene did not show their superiority since they gained lower gross margin compared with the non-carrier ewes. Key words : Prolific sheep, gross margin

Response of Catecholamines to Manual Teat Stimulation or Machine-Milking of Lacaune and Friesen Dairy Ewes

Increased sympathetic activity, including peripheral release of catecholamines, has been hypothesized to inhibit the milk ejection reflex by blocking the release of oxytocin, by blocking the effect of oxytocin at the mammary gland, or both. We attempted to relate differences in milking characteristics of Lacaune and East Friesen ewes to the degree of sympathetic arousal, responses of catecholamines and oxytocin to machine-milking and to manual teat stimulation followed by milking. Peripheral concentrations of epinephrine, 67±6 pg/ml for Lacaunes and 57±5 pg/ml for Friesens, were essentially constant. Peripheral concentrations of norepinephrine averaged 682±68 pg/ml for Lacaunes and 250±54 pg/ml for Friesens. Elevated norepinephrine concentrations during the pretreatment period were associated with the inhibition of oxytocin responses. When norepinephrine concentrations during the pretreatment period exceeded 300 pg/ml for Friesens, or were rising and exceeded 700 pg/ml at initiation of the experimental period for Lacaunes, oxytocin release was inhibited. Results from this study clearly showed that basal concentrations of norepinephrine vary with breed of ewes and provided the first direct evidence that increased sympathetic activity can result in central inhibition of the milk ejection reflex.

The implications of controlling grazed sward height for the operation and productivity of upland sheep systems in the UK. 3. The effect of choice of genotype, level of nitrogen fertilizer and lamb:ewe ratio

Grazed sward surface height was controlled within the range 3·25–4·75 cm during spring and summer in two experiments. In Experiment 1, the effects of stocking two breeds of ewe of similar size but different potential levels of reproductive performance [Brecknock Cheviot (C) and Beulah Speckled Face (B)] at different annual stocking rates of twelve (SR12) and twenty (SR20) per hectare, rates of nitrogen fertilizer of 100 (N100) and 200 (N200) kg N ha−1 annum−1 and different lamb:ewe ratios (C1·2, B1·2 and B1·5) were measured in four treatments (SR20N200C1·2; SR20N200B1·2; SR20N200B1·5; SR12N100C1·2) replicated three times. In each of three years animal performance and yield of silage from areas of pasture surplus to grazing requirements were measured. In Experiment 2, breed B was compared with the Welsh Mule (W) breed, a larger with a higher potential reproductive performance, at two stocking rates, two rates of nitrogen fertilizer and two lamb:ewe ratios set on the basis of results from Experiment 1 (SR18N200B1·5; SR12N100B1·5; SR18N200W1·5; SR18N200W1·7). The treatments were replicated three times. The same terminal sire (Suffolk) was used in both experiments. A primary aim of the experiments was to test the validity of the experimental procedures used for comparing breeds of sheep where nutrition is provided predominately from grazed pastures. In Experiment 1, there was no difference between breeds C and B in the live weights of individual lambs at weaning at the same SR (20), N rate (200) and lamb:ewe ratio (1·2). Breeds C and B produced similar total yields of lamb (633 kg lamb ha−1± 10·5) and silage (193 kg DM ewe−1± 37·7), but breed B had a higher level of potential reproductive performance (1·59 vs. 1·37 lambs ewe−1: P &lt; 0·001). The treatments SR20N200B1·5 and SR12N100C1·2 produced, respectively, greater and lesser yields of lamb (725 vs. 384 kg lamb ha−1, P &lt; 0·001) and lesser and greater yields of silage (123 vs. 327 kg DM ewe−1, P &lt; 0·001). In Experiment 2, the live weight of lambs at weaning from breed W were heavier than from breed B (29·1 vs. 26·2 kg lamb−1, P &lt; 0·01) but there was no significant difference in total yield of lamb weaned between breeds W and B at the same SR (18), N rate (200) and lamb:ewe ratio (1·5) (747 kg lamb ha−1± 19·2), or in the yield of silage (66 kg DM ewe−1± 16·4), but breed W had a higher potential reproductive performance (1·85 vs. 1·58 lambs ewe−1, P &lt; 0·05). The treatments SR18N200W1·7 and SR12N100B1·5 produced, respectively, greater and lesser yields of lamb (840 vs. 473 kg lamb ha−1, P &lt; 0·001) and similar and greater yields of silage (60 vs. 141 kg DM ewe−1, P &lt; 0·05). The experimental approach adopted and the management protocols used provided a basis for ranking the performance of the breeds of ewes examined at appropriate levels of annual stocking rate, N‐fertilizer input and lamb:ewe ratio.

Rick factors for seroprevalence of ovine lentivirus in breeding ewe flocks in Nebraska, USA

The prevalence of and risk factors for ovine lentivirus (OLV) infection in 1466 breeding ewes in nine US Meat Animal Research Center (MARC) flocks were determined using a recombinant transmembrane protein (rTM) enzyme-linked immunosorbent assay (ELISA) to detect serum anti-OLV antibodies and define infection. Based on multivariable logistic regression, confinement birth and rearing (odds ratio (OR) = 1.6), older weaning ages (OR = 1.1 week −1), and older age (OR = 1.3−2.5 year −1 beyond age 1 year) were significantly associated with higher OLV prevalence in ewes. Prevalence also varied significantly by flock, with Finnsheep and Texel ewes having the highest prevalences and Booroola Merino and Suffolk ewes having the lowest prevalences. These findings support the hypothesis that management control efforts should concentrate on events early in the life of sheep, as this period is associated with factors which can modulate the risk for OLV infection.

Effect of ewe ovine lentivirus infection on ewe and lamb productivity

We used a previously described sensitive and specific ovine lentivirus (OLV) recombinant transmembrane (rTM) protein enzyme-linked immunosorbent assay (ELISA) to detect anti-OLV antibodies and define OLV infection in breeding ewes from nine US Meat Animal Research Center (MARC) flocks. We estimated the production impacts of dam rTM ELISA seropositivity on ewe and lamb productivity in the birth-to-weaning interval using production data from 1466 breeding ewes (of which 1242 actually lambed) and their 2452 lambs born in spring 1992 using several multiple linear and logistic regression models. By adjusting for lamb weaning age, gender, type of birth and rearing, birth difficulty, dam age, and flock, the component of ewe or lamb productivity related to ewe OLV infection alone was isolated. The rTM ELISA-negative ewes produced significantly more total weight of weaned lamb per ewe-lambing (3.84 kg) and per ewe ram-exposed (4.95 kg) compared to their OLV-positive flockmates. Negative ewes also weaned 0.11 more lambs per ewe-lambing and 0.09 more lambs per ewe ram-exposed, gave birth to 0.13 more lambs per ewe ram-exposed, and were more likely to lamb after breeding (odds ratio (OR) = 1.9) compared to equivalent OLV-positive ewes. Lambs reared by OLV-negative ewes weighed 0.15 kg more at birth, gained 8 g more per day through weaning, and weighed 0.59 kg more at 56-day weaning. Preweaning mortality was lower (OR = 0.8) among lambs born to OLV-negative compared to OLV-positive ewes, although this difference was not significant. Our results suggest that subclinical OLV infection has important detrimental effects on sheep production which occur in cumulative fashion from breeding through weaning and that OLV control efforts may be financially justified in some sheep flocks.

The effects of ewe live weight and body condition score around mating on production from four sheep breeds in extensive grazing systems in Uruguay

AbstractEwe live iveights were recorded 4 weeks prior to mating, at the beginning of mating and 22 to 23 days later over a period of 3 years in a flock of some 300 breeding ewes comprising approximately equal numbers of Australian Merino, Ideal (Polwarth), Merilin and Corriedale breeds in a pastorally based grazing system in Uruguay. Multiple-bearing ewes were generally heavier than single-bearing ewes which in turn were heavier than ewes which did not conceive, these differences being greatest in 3- and 4-year-old ewes (i.e. in their second and third breeding seasons). Body condition scores of non-pregnant ewes were lower than those of pregnant ewes, particularly in the 3-and 4-year-old age groups. Ewe live weights achieved prior to, during and at the end of the mating period and the body condition score achieved 4 weeks prior to mating all had significant influences on the number of lambs born (P &lt; 0·01) but there were no significant effects of changes in either live weight or body condition over the 4 weeks prior to mating or during the mating period. The effect of body condition score over the range from 2·0 to 4·0 was to increase the proportions of single- and multiple-bearing ewes and to decrease the proportion of non-pregnant ewes such that the number of lambs born per ewe mated increased from 0·94 to 1·38. Fleece weights differed significantly between breeds, Corriedales having the heaviest fleeces and Merilins the lightest (4·26 and 3·22 kg respectively). Wool production was also significantly and positively affected by age (P &lt; 0·01) and by ewe weight at mating (P &lt; 0·01). The results demonstrate the importance of giving preferential nutritional treatment to younger ewes to ensure a satisfactory subsequent lambing performance and improved wool production.

Variations in the maternal behaviour of primiparous, single-bearing ewes of a hill and a lowland breed of sheep

Perinatal lamb mortality can account for up to 20% of annual lamb losses, and at least a third of these deaths can be attributed to maternal factors (Mellor, 1988). Improvement in the quality of maternal behaviour may, therefore, lead to a reduction in lamb deaths. In order to identify if there is a genetic component to the expression of maternal behaviour, the behaviour of a lowland (Suffolk) and a hill (Scottish Blackface) breed of parturient ewe were quantified after the birth of a single lamb.