Ewe Prolificacy Research Articles

A comparison of Scottish Blackface and Cheviot ewes and five sire breeds in terms of lamb output at weaning in hill sheep systems

A study was carried out on six hill farms in Northern Ireland over 2 years (1996–1998) to investigate the effect of ewe and ram breed on ewe prolificacy, lamb viability and weaned lamb output. On each farm, groups of 40 Scottish Blackface ewes (mature weight of 53·8 kg) were mated to Scottish Blackface, Blue-Faced Leicester and Texel rams. Similarly, groups of 40 Wicklow Cheviot ewes (mature weight 63·7 kg) were mated to Cheviot, Suffolk and Texel rams. All ewe×ram breed combinations were present on each farm. Overall, ewe prolificacy was similar in Blackface and Cheviot ewes (1·52 and 1·55 (S.E. 0·026) lambs born/ewe lambed). However, there was a farm×ewe breed interaction (P < 0·001) indicating that, whilst prolificacy was similar in Blackface and Cheviot ewes on the majority of farms (4 out of 6), on one farm prolificacy was higher in Blackface and on another lower, compared with Cheviot ewes. There were no farm×breed interactions for any of the other main production traits. The proportion of ewes lambing without assistance was higher in Cheviot compared with Blackface ewes when crossed with Texel sires (P < 0·001). Cheviot ewes produced heavier Texel-sired lambs compared with Blackface ewes (4·76 versus 4·51 (S.E. 0·076) kg; P < 0·05). Mortality levels were similar in lambs produced from Blackface and Cheviot ewes. The weight of lamb weaned per ewe was higher in Cheviot compared with Blackface ewes (41·5 versus 38·8 (S.E. 1·01) kg/ewe lambed; P < 0·05). However, the weight of lamb weaned per kg of ewe metabolic weight did not differ significantly between the breeds.With Blackface ewes, the proportion of ewes lambing without assistance was lower for Blue-Faced Leicester compared with Blackface sires (P < 0·001). In addition, the proportion of ewes lambing without assistance was lower (P < 0·001) for Texel compared with both Blackface and Blue-Faced Leicester-sired lambs. Lamb birth weights were higher in Blue-Faced Leicester (P < 0·05) and Texel (P < 0·001) compared with Blackface-sired lambs (4·38, 4·51 and 4·09 (S.E. 0·076) kg, respectively). Similarly, the weight of lamb weaned per ewe lambed was higher (P < 0·001) with Blue-Faced Leicester and Texel compared with Blackface sires (39·8, 38·8 and 33·8 (S.E. 1·01) kg, respectively). The carcass weight of the male lambs 3 weeks post-weaning was significantly higher (P < 0·001) in Blue-Faced Leicester and Texel compared with Blackface-sired lambs (12·5, 12·0 and 10·2 (S.E. 0·20) kg, respectively). Carcass conformation classification was higher in Texel compared with Blue-Faced Leicester and Blackface-sired lambs (P < 0·001). Fat classification was higher in Texel (P < 0·01) and Blue-Faced Leicester (P < 0·05) compared with Blackface-sired lambs. With Cheviot ewes, a greater number of ewes lambed unaided (P < 0·05) with Cheviot and Texel compared with Suffolk-sired lambs. The number of lambs born dead was higher (P < 0·01) with Suffolk compared with Cheviot and Texel-sired lambs (0·14, 0·08 and 0·07 (S.E. 0·016) lambs born dead/ewe lambed, respectively). Growth rates were higher in Suffolk compared with Cheviot-sired lambs (P < 0·05). Overall, Suffolk (P = 0·06) and Texel (P < 0·001) sires produced a greater weight of lamb at weaning compared with Cheviot sires (40·0, 41·5 and 36·9 (S.E. 1·01) kg, respectively). Carcass weight of lambs 3 weeks post-weaning was higher for Suffolk (P < 0·05) and Texel (P < 0·01) compared with Cheviot-sired male lambs. Carcass conformation classification was higher in Texel and Suffolk compared with Cheviot-sired (P < 0·001) lambs. Fat classification was also higher in Texel compared with Cheviot-sired lambs (P < 0·05). Carcass chemical composition was not significantly affected by lamb genotype.

The inheritance of traits describing early lamb performance in Scottish Blackface sheep

Ewe prolificacy, lamb survival and early lamb growth are economically important traits, playing a major role in determining the profitability of hill sheep farms (Coningtonet al., 2000). In currently advocated selection strategies these traits are usually expressed as traits of the dam, however, relatively low heritabilities limit the genetic progress achievable (Coningtonet al., 2001). An alternative approach is to treat these traits, where appropriate, as traits of both the ewe and lamb. This study investigates reparameterisation of these traits as joint expressions of both lamb and ewe genotype, and considers the impact of the results on currently-advocated selection strategies.

Effects of ewe age and season of lambing on prolificacy in US Targhee, Suffolk, and Polypay sheep

Factors affecting ewe prolificacy (number of lambs born per ewe lambing) were evaluated using records on 9705 Targhee, 12,721 Suffolk, and 7231 Polypay lambings from flocks participating in the US National Sheep Improvement Program. Factors considered were ewe age and season of lambing. Prolificacy was affected by age of the ewe ( P<0.001) and was highest for ewes lambing between 4 and either 7 (Polypay) or 8 (Targhee and Suffolk) years of age. Effects of lambing at younger ages were similar for Targhee and Polypay. Relative to mature ewes, prolificacy was reduced by 0.6–0.7 lambs in 1-year-old ewes, about 0.3 lambs in 2-year-old ewes and about 0.1 lambs in 3-year-old ewes. Effects of ewe age were smaller in Suffolk, with reductions relative to mature ewes of 0.47, 0.13, and 0.01 lambs in 1-, 2-, and 3-year-old ewes. Prolificacy of older (>8-year-old) ewes was consistently reduced by 0.17–0.20 lambs relative to adult ewes. Within the 1-year-old age class, age in months further affected prolificacy of Suffolk and Polypay but not Targhee ewes. For these two breeds, prolificacy of 15-month-old ewes averaged 0.21 lambs more than that observed for 12-month-old ewes. Seasonal differences in prolificacy were large for Targhee and Polypay ( P<0.001) but not for Suffolk ( P=0.23) and the distribution of lambings among seasons differed ( P<0.001) for all breeds. 22% of adult Polypay ewes, but only 1% of Targhee and Suffolk ewes lambed in summer and autumn. Prolificacy was highest in winter and spring lambings (December through May) and did not differ importantly among months within this period. Average prolificacy of 3- to 6-year-old ewes lambing in winter and spring was 1.75 for Targhee, 1.91 for Suffolk, and 2.13 for Polypay. For age groups with at least 10 observations, prolificacy in autumn (September through November) was reduced by an average of 0.14 lambs in Suffolk and 0.24 lambs in Polypay (very few Targhee lambed in autumn). Prolificacy in summer (June through August) was reduced by an average of 0.18 lambs in Targhee and 0.31 lambs in Polypay (very few Suffolks lambed in summer). Adjustment of prolificacy records for effects of ewe age is therefore necessary in genetic evaluation programs. Seasonal effects on prolificacy are probably best handled by placing ewes that lamb in different seasons in different contemporary groups.

Economic values for ewe prolificacy and lamb survival in New Zealand sheep

Economic values of changes in ewe prolificacy (EP) and two lamb survival traits were quantified for situations where each trait is changed by either quantitative genetic selection or the introduction of major genes for prolificacy. The economic value of EP was shown to be highly variable ($11.55 to $24.26 for lambs born per ewe lambing) across farm types. The economic values of the Booroola and Inverdale genes which affect EP also varied substantially from farm to farm. Values ranged from $5.24 to $16.23 per ewe lambing for a single allele of the Booroola gene and from $4.69 to $12.53 for a single allele of the Inverdale gene. The additional value of a second allele of the Booroola gene was relatively small or negative (−$0.76 to $2.29). The key factors influencing variability in economic values for EP were shown to be: 1, the current average level of flock prolificacy; 2, the relative survival rates of lambs born in alternative litter sizes and 3; slaughter of lambs at fixed age versus fixed weight. The economic values for survival until 24 hours post-partum per lamb born and for survival from 24 hours post-partum until weaning per lamb alive at 24 hours were moderately variable across farm types ($0.22 to $0.28 and $0.31 to $0.36 respectively for an improvement of 1%).

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 &lt; 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 &lt; 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 &lt; 0·001) and Texel × Greyface (P &lt; 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 &lt; 0·001). The number of lambs which died from birth to weaning was lower with Texel × Greyface compared with Greyface ewes (P &lt; 0·01). Expressed on a unit metabolic weight basis, Greyface ewes produced a significantly greater weight of lamb compared with Texel (P &lt; 0·05) and Rouge ewes (P &lt; 0·001). Texel × Greyface ewes produced a significantly greater weight of Texel-sired lamb compared with Greyface (P &lt; 0·01) and Texel ewes (P &lt; 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 &lt; 0·001). Lamb birth weights and pre-weaning growth rates were greater with Rouge sires (P &lt; 0·05). Number of lambs weaned per ewe lambed was significantly greater with Texel sires (P &lt; 0·01). Overall weight of weaned lamb produced per ewe was not significantly affected by sire breed.

Effects of human chorionic gonadotropin (hCG) and phenobarbital on the reproductive performance of fat-tailed Ghezel ewes

Increased ewe prolificacy and lambing rates, under certain conditions of sheep husbandry, may be economical and desirable. This paper reports on the effects of human chorionic gonadotropin (hCG) and phenobarbital (PB) on fertility and lambing rate in fat-tailed Ghezel sheep. One-hundred and five cyclic ewes (1.5 to 7.5 years of age) were randomly allotted to seven groups. Estrus was synchronized with two intramuscular injections of a prostaglandin F 2α analogue (PGF 2α), eight days apart. Four groups were randomly assigned to the hCG and three groups to PB experiments. Twenty-four hours after the second injection of PGF 2α, the ewes in four groups were injected (i.m.), either with 1 ml normal saline (control) or with 125, 250 or 500 IU hCG. Prolificacy of the ewes which conceived at first estrus increased in ewes receiving 500 IU of hCG, as compared with control group (an increase of 0.5 lamb/ewe) but fertility and lambing rate decreased in hCG-treated groups ( P<0.05). Nine days after the second injection of PGF 2α, ewes in the three remaining groups were orally fed empty gelatin capsules (control), 1.0 or 1.5 g of PB per day until the next estrus. Prolificacy and lambing rate increased ( P<0.05) in ewes which received 1.0 g of PB (1.57 and 146.5%, respectively), as compared with the control groups (1.17 and 100.3%, respectively). It is concluded that daily feeding of 1.0 g of PB from day 7 of the estrous cycle until the next estrus period is an effective method of increasing lambing rate. hCG also increases the prolificacy, but it greatly decreases fertility and lambing rates. Since hCG is more convenient to administer on a flock basis, further experiments to improve its efficacy are warranted.

SHEEP PRODUCTION ON DRYLAND LUCERNE

On dryland at Winchmore Irrigation Research Station in Mid Canterbury high levels of lamb production were obtained during 12 years in a self-contained lucerne/supplementary forage farmlet. The system established lucerne under a barley crop and used turnips with Italian ryegrass and Tama ryegrass in the lucerne renewal rotation. Lucerne hay and barley grain and straw were conserved for supplementary feed. Stocked at 15 ewes/ha, lamb meat production varied from 210-300 kg/ha between years. This variation reflected the effect of dry summer conditions on both lucerne growth and the establishment of the supplementary crops which in turn influenced ewe prolificacy and lamb growth. Because of yield variability and increasing costs, use of annual forage crops in a dryland sheep unit is questioned. Keywords: grazing, management, forage crops, lamb production

Columbia and Suffolk Terminal Sire Breed Effects

Summary An experiment that utilized the Suffolk breed as a standard of comparison was de- signed to evaluate the Columbia breed as a potential terminal sire breed. Lambs were born in 1978 to 333 Finncross ewes bred to Colum- bia (18) or Suffolk (10) rams. Breed of sire did not significantly affect ewe prolificacy, litter viability, number of lambs weaned per ewe lambing or litter weaning weight at 49 days of age. Litters sired by Columbia rams were lighter (P<.10) at birth than Suffolk-sired litters. Suffolk-sired lambs had higher (P< .05) birth weights, preweaning daily gains and wean- ing weights than lambs sired by Columbia rams. Sire breed effects on postweaning daily gain and 154-day weight were not significant but favored progeny of Suffolk rams by 4 and 2%, respectively. Columbia-sired lambs had lower leg conformation scores (P<.01), less fat depth (P<.05) and less percentage kidney fat (P<.10) than Iambs sired by Suffolk rams. Progeny of Columbia rams tended to have a greater esti- mated percentage of trimmed retail cuts (P< .10) and less carcass weight per day of age (P<.10) than Suffolk-sired lambs, while produc- tion of retail cuts per day of age was compara- ble for the two breed groups. Lambs sired by Suffolk rams had higher carcass conformation scores (P<.10), maturity scores (P<.05) and flank firmness scores (P<.10) than progeny of Columbia rams. Sire breed effects on carcass quality grade were not significant. We conclu- ded that Columbia rams produced progeny comparable in lean growth rate and carcass quality to progeny sired by Suffolk rams and Cooperation of the Nebraska Agr. Exp. Sta., Univ. of Nebraska at Lincoln, is gratefully acknowl- edged. 2 Roman L. Hruska US Meat Animal Research Cen- ter, AR, SEA. a Present address: Anim. Sei. Dept., Texas A&M Univ., College Station 77843. that the Columbia breed may serve effectively as a terminal sire breed. (Key Words-. Sheep, Ewe Productivity, Growth, Carcass Composition, Quality Grade.)

Reproductive efficiency of Iceland sheep

Iceland sheep are found to be relatively early maturing and the level of reproductive efficiency in the flock is raised by breeding from ewe lambs. Ram lambs are normally used for mating. Ewe prolificacy is progressively being increased by genetic selection for a higher lambing rate in conjunction with improvements in feeding. Lamb mortality is kept at a relatively low level by close supervision at lambing and disease control.

The duration of oestrus in ovariectomized Finnish Landrace and Scottish Blackface ewes following progesterone and oestrogen treatment.

Summary. The relationship between the duration of induced oestrus and the characteristics of the progesterone-oestrogen treatment used for its induction was investigated and described. The regression of the duration of oestrus on the dose of oestrogen was found to be 0·0032 and 0·0045 days/μg in the Blackface and Finnish Landrace ewes, respectively. The duration of oestrus was also increased by approximately 40% following the division of a particular dose of oestrogen into two units given 24 hr apart. The mean durations of induced oestrus over all treatments, 1·52 and 1·92 days, respectively, in the Blackface and Finnish Landrace ewes, were significantly different. It was concluded that the relationship between ewe prolificacy and the duration of natural oestrus arose at least in part from differences in the pattern of oestrogen secretion around the time of ovulation.