Ewe Weight Research Articles

Effects of severe undernutrition on body weight and fat tissue changes in dry Lacaune ewes

Effects of severe undernutrition on body weight and fat tissue changes in dry Lacaune ewes

Effects of severe undernutrition on body weight and fat tissue changes in dry Lacaune ewes

Effects of severe undernutrition on body weight and fat tissue changes in dry Lacaune ewes

Variation in reproduction and production of Poll Dorset ewes

Poll Dorset ewes were joined to Booroola Merino (n = 22) or Trangie Fertility Merino (n = 26) rams in single sire joinings during late summer/autumn of 1978, 1979, 1980 and 1981. Rams were changed each year and there were 1678 individual ewe joinings. A maximum of 527 ewes were used in any one year, and they represented 14 studs and varied in age, reproductive history and liveweight. The traits, litter size, maternal lamb survival, lambs weaned per ewe lambing and weight of lamb weaned per ewe lambing (kg at 100 days) were analysed for the effect of year, stud, age, lambs born and ewe liveweight. Litter size averaged 1-37, maternal lamb survival 0.70, and number of lambs weaned per ewe was 0.94. There were large variations in the reproductive traits due to year and stud and lesser effects due to age. Each extra kilogram of ewe liveweight at joining increased litter size by 0.012 and weight of lamb weaned by 0.39 kg, but had no significant effect on maternal lamb survival or number of lambs weaned. Multiple-bearing ewes weaned 0.72 more lambs and 16 - 2 kg more lamb weight than single-bearing ewes. Lamb survival was similar for singleand multiple-bearing ewes. Greasy fleece weight averaged 2.2 kg ewe-' and single bearing ewes produced 0.19 kg/ewe more than multiple-bearing ewes. Dystocia caused 53% and starvation/mismothering/exposure caused 23% of lamb deaths; the proportion of deaths due to starvation/mismothering/exposure increased with increasing ewe joining liveweight. The large variation between studs in reproductive performance partly reflected genetic differences between Poll Dorset flocks which could be exploited. Estimates of heritabilities ranged from 0.06 to 0.14 � 0.10 for the reproductive traits and were 0.10 � 0.12 for ewe liveweight and 0.16 � 0.20 for greasy fleece weight. However much of the between stud variation may also have arisen from early environmental effects. Estimates of repeatability ranged from 0.06 to 0.l5 � 0 05 for reproduction traits and were 0.44 � 0.06 for ewe liveweight at joining and 0.56 � 0.08 for greasy fleece weight.

アンモニア処理稲わら給与による妊娠末期～泌乳期母羊の飼養

Fifteen Suffolk ewes carrying twin fetuses were offered 0.6% live weight of concentrate at the basis of dry matter during last 6 weeks of pregnancy. Ewes were individually penned indoors on slatted wooden floors. All ewes gave birth to sound twin lambs. After lambing, seven ewes were offered 1.9%concentrate during first 8 weeks of lactation, and 0.9% concentrate during last 9 weeks of lactation (group HL). Eight ewes were offered 1.3% concentrate during the early lactation, and 1.5%concentrate during the last lactation (group MM). Ewes were offered ammoniated rice straw ad libitum from late pregnancy through into lactation. Lambs were offered starter from 2 weeks of age, and ammoniated rice straw from 8 weeks of age.Dry matter intakes of ammoniated rice straw were 0.8, 1.2 and 1.5%of body weight during late pregnancy, early and last lactation respectively. During late pregnancy, there were no differences in total intakes of crude protein and total digestible nutrients between two groups. These nutrient intakes of the ewes were higher for group HL compared with group MM during early lactation, and were higher for group MM compared with group HL during last lactation. In both groups, 3-hydroxybutyrate concentration in the plasma increased during late pregnancy until lambing and then declined throughout lactation. The rate of live weight loss in ewes was greater for group MM during early lactation, and were greater for group HL during last lactation. Two groups of ewes had similar average live weight at 17 weeks post-partum. The lambs of group MM had higher daily gain during 9 to 17 weeks of age, but the lambs of group HL and MM had similar average live weight at 17 weeks of age (36.2 and 39.2kg respectively).With the levels of concentrate used in this experiment, the change of concentrate level during lactation had no appreciable effect on the live weight of ewes and lambs at 17 weeks post-partum.

When Less May Mean More: Studies on Range Versus Shed Lambing In a Cold Desert Shrub Ecosystem

Range lambing was compared with shed lambing using 235 3/4 Targhee × 1/4 Finnsheep mature ewes. Pregnancy diagnosis was done with a realtime ultrasound unit 75 d after ram removal. Based on the estimated number of fetuses, ewes were assigned to either a shed or range lambing treatment group using a stratified random procedure. Ewes in the shed lambing group were given assistance as necessary and were placed in lambing pens for 2 to 3 d, then moved to mixing pens for a minimum of 3 d. Ewes in the range lambing treatment were placed on pasture approximately 12 d before lambing and were not disturbed until the average lamb age was approximately 25 d. Shed lambing increased the percentage of live lambs by 21 percentage units at 25 d of age compared to the range lambing group. This difference was largely due to increased survival of lambs from multiple births. The difference between lambing treatments was reduced to 5 percentage points by weaning. Lambs from the range lambing group were .9kg heavier at 25 d of age (P<.09) and 1.4kg heavier at weaning (P<.02). There was no difference in kilograms of lamb weaned per ewe, with the increased lamb survival in the shed lambed group offset by the heavier lamb weights in the range lambed group. Ewe death losses were higher (P<.11) in the range lambing group. Ewe weights were 5.4kg heavier (P<.001) at 25 d postlambing in the range lambing group and 1.9kg heavier at weaning. Results indicate that producers that have shed lambing facilities and want to maximize lamb crop should use pregnancy diagnosis and shed lamb ewes with multiple lambs and range lamb ewes with single lambs. However, producers that want to maximize net income should range lamb all ewes.

Production performance of prolific Javanese ewes

Production performance of Javanese ewes (483 ewes with 1263 records) in West Java, Indonesia, was evaluated. The focus was on the effect of prolificacy and environmental sources of variation on lamb survival (S) as a ewe trait and on lambing and weaning outputs. Non-carriers (FecJ +FecJ +), carriers (FecJ FFecJ +) and homozygotes (FecJ FFecJ F) for a gene affecting prolificacy, averaged 1.24, 1.95 and 2.59 lambs born, respectively. Prolificacy-year (PY) effects were significant, with FecJ FFecJ F animals being more sensitive to fluctuations. Repeatability for litter size was 0.51 and heritability 0.62. PY, gestation ewe weight gain (EGG) and parity significantly affected S. Singles, twins, triplets and quadruplets averaged 87, 69, 47, and 35% S, respectively, with fewer lambs surviving in these litter size categories in poor years. Repeatability of S was 0.19. Litter weaning weights (TWW) were influenced significantly by PY, parity and EGG. EGG contributed less than litter birth weight to the determination of S and TWW in all litters, although its contribution to TWW was proportionally higher than that to S. Repeatability of TWW was 0.20. Higher prolificacy led to a diminution of the ewe's body resources as indicated by EGG, therefore reducing the ewe's ability to support satisfactory birth weights of lambs and lactation, particularly under poor nutrition. With higher EGGs and survival rates under improved nutrition, a single copy of the FecJ F gene increased the productivity of ewes (TWW) by at least 18%; while under suboptimum nutrition, it had a negative effect. There is a need to investigate the nutritional management of animals having the FecJ F gene since the gene is widely distributed in most Indonesian sheep populations.

A comparison of diploid and tetraploid perennial ryegrass and tetraploid ryegrass/white clover swards under continuous sheep stocking at controlled sward heights. 2. Animal production

AbstractPerformance of continuously stocked Mule ewes nursing Suffolk‐cross twin lambs over three grazing seasons, between April and August, was compared on swards of N‐fertilized diploid perennial ryegrass (D), tetraploid perennial ryegrass (T) and tetraploid perennial ryegrass with white clover (TC), the latter receiving no fertilizer N. Sward height was maintained by variable stocking rate close to a target of 4–6 cm (constant treatment) from turnout and compared in July and August with a rising sward height treatment (target 6–8 cm).Lambs on TC swards had significantly higher (P &lt;0·001) liveweight gains compared with lambs on T swards by 41 gd‐1 in April–June and by 68gd‐1 in July‐August. Live weight and body condition score of ewes in August were significantly higher (P&lt;0·001) on TC compared with T swards, by 11·3 kg and 0·75 respectively. Rising sward heights in July–August increased live‐weight gain of lambs compared with constant sward heights by 102, 39 and 54gd‐1 in consecutive years, associated with sward height increases of 0·9, 0·5 and 0·6cm respectively. Rising sward height increased ewe live weight and body condition score by 5·1 kg and 0·3 respectively, compared with results from constant sward heights. Effects of sward height and sward type were additive.T swards had a significantly (P&lt;0·01) 16% greater overall lamb output than the D swards due mainly to a 10% higher achieved stocking rate. Stocking rates of ewes on TC vs T swards were 40, 13 and 12% lower in April‐August in successive years. The higher liveweight gain of lambs on the TC swards resulted in lamb outputs of 76, 105 and 101% of the T swards in successive years, showing that grass/clover swards containing over 20% clover could produce similar lamb output ha‐1 to grass swards given 150–180 kg N ha‐1.

Return to estrus and endocrine patterns in early postpartum, spring-lambing ewes treated with melatonin

Effects of exogenous melatonin during the early postpartum period on endocrine patterns and return to estrus were examined in 18 mature (3 to 6 years) Debouillet ewes. Six ewes received daily (i.m.) injections of 2 ml safflower oil at 1600 hours beginning on Day 8 post partum (Day 0 = parturition) and continuing through Day 28. The remaining 12 ewes (6/group) received similar injections except the safflower oil contained either 2.5 or 5 mg melatonin. Serum was collected hourly from all animals on Days 8 and 27 from 1600 hours (before treatment) to 2200 hours and at 0630 hours on the following morning. Samples were collected frequently after injection (i.m.) of GnRH (50 μg/ewe) on Day 29. Daily blood samples were taken on Days 8 through 29 and on alternate days from Day 30 through Day 38, and progesterone was determined to monitor ovarian cyclicity. Ewe weights were not affected (P > 0.20) by melatonin. Lamb weights on Days 7, 32 and 60 were not affected by maternal melatonin treatment; however, adjusted weaning weight (21.8, 23.7 and 24.7 ± 1.3 kg, respectively) increased linearly (P = 0.13) with increasing melatonin treatment. Serum growth hormone, insulin and LH were unaffected (P > 0.10) by exogenous melatonin. However, serum prolactin decreased linearly in ewes treated with 0, 2.5 or 5 mg melatonin on both Days 8 and 27. Serum progesterone remained below 1 ng/ml in all ewes during the first 38 days post partum, indicating that ovarian cyclicity was not induced by melatonin. Interval from parturition to return to estrus was not reduced (P = 0.13) by exogenous melatonin between Days 8 and 28 post partum. Melatonin administration increased serum melatonin and decreased serum prolactin but did not influence early postpartum cyclicity in spring-lambing Debouillet ewes.

Heat stress during mid-pregnancy in sheep and the consequences for placental and fetal growth

SUMMARYAn experiment was conducted at Toorak Research Station, Julia Creek, in semi-arid northern Australia (141° E, 21° S) during 1990 to determine the relationship between placental and fetal weight in sheep after placental growth had been restricted by chronic heat stress during mid-pregnancy. Placental and fetal weight were measured in single bearing ewes housed either in a thermoneutral environment throughout pregnancy, or in a heated room between the 30th and 80th days of pregnancy followed by a thermoneutral environment until the 140th day of pregnancy. The placental weight of the heat-treated ewes was lower than that of the control ewes at the 80th (P&lt; 0·05) and 140th (P&lt; 0·01) days of pregnancy. Fetal weight and dimensions did not differ significantly between control and heat-treated ewes at the 80th day of pregnancy, although fetal weight (P&lt; 0·01) and fetal dimensions (P&lt; 0·05) for the previously heat-treated ewes were lower than those for the control ewes at the 140th day of pregnancy. Placental and fetal weight at the 140th day of pregnancy were correlated (P&lt; 0·05) with the rectal temperature of ewes measured at 08.00 and 16.30 h during the period of heat-treatment, but not with the change in rectal temperature between 08.00 and 16.30 h. It was concluded that restricted placental growth in heat-treated ewes retarded fetal growth during late pregnancy even in the absence of heat treatment, and it is suggested that selection of ewes which can maintain normal rectal temperatures during periods of heat stress would produce lambs of normal birthweight in a hot climate.

Diallel cross of three Moroccan breeds of sheep: II. Reproductive performance and productivity of purebred ewes.

A diallel cross involving three Moroccan breeds of sheep (Sardi, Beni Guil, and D'man) was analyzed by least squares procedures. A total of 456 ewes were mated to 22 rams and this resulted in 528 lambs born from 412 ewes. D'man ewes had by far the highest general performance as measured by total weight of lamb weaned, even though the average live weight per lamb was the lowest for the three breeds; this resulted from the higher number of lambs weaned per ewe for the D'man. The least squares means for litter size at birth per ewe lambing were 2.04, 1.01, and 1.11 for D'man, Beni Guil, and Sardi ewes, respectively. The comparable figures for litter size at weaning were 1.55, .90, and .99, respectively, and the least squares means for total weight of lamb weaned were 20.7, 16.9, and 18.2 kg for D'man, Beni Guil, and Sardi ewes, respectively. The comparable figures for total weight of lamb weaned per 100 kg of ewe weight were 71.1, 44.3, and 41.1 kg/100 kg for D'man, Beni Guil, and Sardi ewes. Conversely, D'man rams had the poorest breeding performances of the rams of the three breeds, and Beni Guil rams had the lowest litter mortality. The breed of ram had only small and nonsignificant effects on all measures of fertility and ewe productivity. The least squares means for number born/ewe lambing were 1.36, 1.35, and 1.44, respectively, for D'man, Beni Guil, and Sardi rams; the comparable least squares means for number weaned per ewe lambing were 1.10, 1.18, and 1.16, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Liveweight, fleece weight and prolificacy of Romney ewes carrying the Inverdale prolificacy gene (FecX I) located on the X-chromosome

The effect of the Inverdale prolificacy gene (FecX I) on liveweight, fleece weight and reproductive performance was measured in the 2-year-old progeny of three carrier (I) Romney rams and eight non-carrier (+) Romney rams. There was no effect of FecX I on liveweight at first mating (19 months of age) or fleece weight at 13 months of age. Records from 82 progeny of FecX I I rams and 221 progeny of + rams showed that one copy of the gene increased litter size by 0.58 ( P<0.001). Mean litter size of carrier ewes was 2.17, and 32% of litters had three or more lambs. FecX I had no significant pleitropic effects on barrenness, embryonic mortality or lamb mortality, although embryonic mortality and lamb mortality were both affected as a consequence of the effect of FecX I on ovulation rate. Embryonic mortality was 13% ( P<0.001) higher in carrier ewes but at a common ovulation rate (ovulation rate= 2) there was no significant difference. Neonatal lamb mortality was 14% higher ( P<0.001) from ewes carrying FecX I but when only singles and twins were compared there was no significant effect. The net result was that lambs alive at 1 day of age per ewe lambing averaged 1.36 for carrier ewes and 1.19 for non-carriers.

Sensitivity of breeding objectives to prices and genetic parameters in Australian Corriedale and Polwarth dual-purpose sheep

A profit equation was developed for Australian Corriedale and Polwarth dual-purpose sheep kept for both wool and lamb production. Ten traits contribute to income and costs and were included in the breeding objective. These encompass wool production, fibre diameter, and feed intake of breeding ewes and hogget ewe replacements; sale weight and carcass fat depth of lambs; and reproductive rate and mature weight of ewes. The relative economic value for each trait in the enterprise was calculated from the profit equation using income and costs for 1 year. Overall gain ($A) and gain in each trait in the breeding objective from selection using an index of hogget greasy fleece weight, hogget fibre diameter, dam's number of lambs weaned, lamb weight, and lamb fat depth are reported. The sensitivity of the genetic changes in each trait in the breeding objective and index coefficients were assessed for a range of prices of products and feed costs. Sensitivity to changes in heritabilities and genetic correlations was also assessed. The incorporation of these maternal traits into LAMBPLAN is discussed. For the standard parameters and prices used, gain in leanness accounted for one-third of overall gain ($/ewe. s.d. of selection). Other traits that contributed to overall gain were fibre diameter (28%), reproduction (18%), and growth (14%). There was a small gain through feed intake (8%), and a very small loss in wool weight. Measures of fatness, growth, and fibre diameter were the important traits in the selection index. Inclusion of hogget greasy fleece weight and dam's number of lambs weaned each added &lt;1% to the efficiency of the selection index. Varying the sale price for lamb and the price differentials for fibre diameter and fat depth had the greatest impact on overall gain. High lamb price increased gains in both reproduction and lamb weight, whereas, high price differentials for fibre diameter and fat mainly increased gains in the particular trait. A large range in prices for wool had very little effect on the individual traits or overall. Changing feed costs had little effect on overall gain, although high feed cost reduced gains from reproduction which were compensated by reduced feed intake. Halving the heritability value for each trait reduced overall gain, largely through reduction in the trait. Varying the genetic correlations of wool production with other traits had little effect. However, when genetic correlations of reproduction with weight, fat, and fibre diameter were varied there were changes in overall gain, largely through reproduction.

Productivity of three synthetic Arcott sheep breeds and their crosses in terms of 8-mo breeding cycle and artificially reared lambs

Body weights of 6066 lambs and ewe productivity based on 3579 records in an 8-mo breeding cycle were analysed. Lambs were from three synthetic Arcott breeds (Canadian, Outaouais and Rideau; one synthetic sire strain and two synthetic dam strains), their two dam strain crosses, the Suffolk and Finnish Landrace (two unselected control) breeds, and specific three-breed crosses sired by the Canadian and Suffolk breeds. Important influences of year-month of birth, sex of lamb, age of dam or ewe, type of birth were observed in a controlled environment (housed indoors year-round on expanded metal mesh floors in windowless barns with light controlled by time clocks). Canadian ewes were more fertile and fecund than Suffolk ewes, but similar in gestation length and weight at breeding. Body weights of Suffolk lambs at 21 d and 91 d of age were significantly lower than those of Canadian lambs. Although Rideau ewes weighed more at breeding than Outaouais ewes, fertility, prolificacy, fecundity, total lamb weights at 21 d and 91 d of age per ewe lambing and lamb survival were similar. Reproductive performance of Finnsheep ewes was similar to Outaouais and Rideau ewes ( P>0.05). In contrast, Finnsheep lambs had significantly lower body weights than Outaouais and Rideau lambs. Ewe weight at breeding and total lamb weight per ewe lambing were lighter in Finnsheep ewes than Outaouais or Rideau ewes. Although not significant, purebred Outaouais and Rideau ewes excelled in growth and reproductive performance compared to their crossbred contemporaries. Growth performance of specific three-breed cross lambs from rams of the Canadian and Suffolk breeds mated to Outaouais and Rideau cross ewes were similar. Although not significant, there was an overall advantage in favour of specific three-breed crosses compared to the Outaouais and Rideau breeds, and their crosses. Specific three-breed cross lambs were similar to purebred Canadian lambs in body weight. Results demonstrated that the Arcott breeds and their crosses had outstanding reproductive ability and rapid growth rate in a controlled environment with artificial rearing of all lambs and 8-mo breeding cycles.

Increased litter size in Rambouillet sheep: I. Estimation of genetic parameters.

The variance and covariance components needed to estimate heritabilities of and genetic correlations among litter size, ovulation rate, scrotal circumference, and BW in a flock of Rambouillet sheep were estimated using REML via an expectation-maximization type algorithm. The heritability estimates from univariate analyses were .14, .21, .25, .36, and .15 for litter size, ovulation rate, scrotal circumference, 180-d BW of females, and 180-d BW of males, respectively, and average heritability estimates from bivariate analyses were .19, .20, .20, .34, and .10 for litter size, ovulation rate, scrotal circumference, 180-d BW of females, and 180-d BW of males, respectively. The genetic correlation between litter size and ovulation rate was near unity. Body weight in ewes had a moderate genetic correlation with both litter size (.22) and ovulation rate (.20) and a low residual correlation with both litter size (.03) and ovulation rate (.09). The genetic correlation between BW in rams and scrotal circumference was 0, whereas the residual correlation was .71. The genetic correlations of scrotal circumference with litter size and ovulation rate were -.25 and +.20, respectively.

Alternative use of Karakul sheep for pelt and lamb production in Botswana. I. Reproduction and growth performance

Performance data of 9800 Karakul, Namaqua Africander, Blackhead Persian sheep and their various crosses were collected from July 1986 to September 1987 in the Southern Kalahari desert of Botswana. Karakul lambs may be used either for pelt (Persian lamb) or for meat production. The purpose of this study was to assess the overall productivity of Karakul sheep and their crosses with local mutton breeds for producing both pelts and lambs for meat. Annual number of lambings per ewe averaged 1.39, litter size 1.007. In flocks with predominantly Karakul breeding, 43% of Karakul lambs were slaughtered for pelt production. Body weight of ewes in the first month post-partum was 40.8 kg, lamb weight at 150 d was 27.4 kg. Neither genotype nor management class had a significant influence on the annual number of lambings per ewe, or body weight of ewe and lamb. Season of birth, lambs being pelted or reared, and flock-within-management class had significant effects on these traits. During the study period, 13.2% of lambs were recorded as having died, 6.4% were home slaughtered, 18.0% sold and 8.0% of all disposals could not be traced; for adult sheep, the corresponding rates were 4.3%, 3.7%, 12.5% and 5.6%, respectively. Average flock productivity was estimated to be 27.7 kg lamb per ewe and year, 0.67 kg lamb per kg ewe and year, and 1.71 kg lamb per kg 0.75 ewe and year.

Sheep flock productivity and management in Meknes province, Morocco

Flocks from six counties in Meknes province, Morocco, were studied for flock management and losses. Sixteen of the 220 flocks were assessed for effects of flock management and seasonality on lambing rates and the weight of ewes and lambs during weekly visits of the flocks (1984–1986). Lambing rate, ewe weight at lambing, birth weight and weight gains increased with higher levels of supplemental feeding. Mean lambing rate for the 16 flocks was 81.3% (1984–1985) and 79% (1985–1986). Mean lambing rates were 69.9% (1984–1985) and 67.9% (1985–1986) in low nutrition groups, 82% for both years in moderate nutrition groups and 91.5% (1984–1985) and 98.3% (1985–1986) in high nutrition groups. Reproductive efficiency reached 44% (1984–1985) and 16% (1985–1986) in individual flocks on a low level of nutrition compared with 86.7% (1984–1985) and 100% (1985–1986) in individual flocks on a high level of nutrition. Results suggest that sheep flock productivity can be increased by improving management and nutrition.

Increasing lambing percentage by androstenedione immunoneutralization in synchronized ewes with or without PMSG

The present study was undertaken to determine the potential of active immunization against androstenedione to increase lambing percentage in dairy ewes synchronized with progestagen with or without PMSG. Ewes (n=200) which were milked twice daily by milking machine were alloted randomly to either the immunized or the nonimmunized (control) group. Ewes in the immunized group were given two injections of the immunogen Fecundin (2 ml) 3 wk apart. All ewes were synchronized with intravaginal sponges inpregnated with Cronolone (30 mg); then half of the ewes in each group (Ia and IIa) were given an injection of PMSG (330 IU) on the day of sponge removal. Ewes in groups Ib and IIb did not receive PMSG. Rams were introduced to all ewes the day after sponge removal, which in the immunized groups (Ia and Ib) was 21 after the second injection of Fecundin. The lambing percentage for immunized ewes that were given PMSG was significantly higher than for those not given PMSG (Ia vs Ib, P<0.05), and it was much higher for either of the control groups (nonimmunized, P<0.01). The lamb weight of control ewes was significantly higher than the immunized ewes (P<0.05), while the litter weight of immunized ewes was significantly higher than that of the controls (P<0.05).

Optimum ewe size in desert Barki sheep

A total of 1789 records of 644 Barki ewes, collected during 1963–1977, were analysed for effects of weight of ewe, year and age of ewe on number of ewes conceived per ewe joined, number of lambs born per ewe joined, number of lambs weaned per ewe joined, kg weaned per ewe joined and g weaned per kg metabolic body weight of ewe joined (GW/kg 0.75). However, only 1194 records of 524 ewes were available to study effects of the same variables on number of lambs weaned per ewe lambing, kg weaned per ewe lambing and g weaned per kg metabolic body weight of ewe lambing (GW/kgL 0.75). Weight of ewe affected ( P < 0.01) all traits with a significant influence of linear and quadratic components. Ewes ranging in weight from 46 to 50 kg had the maximum productivity. However, judging by GW/kg 0.75 or GW/kgL 0.75, ewes ranging in weight from 41 to 45 kg were the most efficient. Year affected ( P < 0.01) all traits while ago of ewe, independent of age, had no significant effect on all traits.

The effect of nutrition in mid pregnancy and ewe liveweight change on birth weight and management for lamb survival in highly fecund ewes

The effect of moderate undernutrition in mid pregnancy on lamb birth weight and survival of single- and multiple-bearing ewes is reported. A total of 1220 ewes of 3 crossbred types with different fecundity, Booroola Merino x Dorset (BD), Trangie Fertility Merino x Dorset (TD) and Border Leicester x Merino (BLM), were examined over 2 years. The treatments were low (L) and high (H) nutrition at pasture for 4 weeks from about day 75 of pregnancy. Ewe liveweight of the L group at the end of the treatments was 5 kg lower in 1984 and 8 kg lower in 1985 (P&lt;0.01) than the H group. The differences were smaller by late pregnancy and post-lambing. The L treatment increased (P&lt;0.01) birth weight by 0.16 kg in 1984 but had little effect in 1985. Litter size had the greatest effect on birth weight (P&lt;0.01). Ewe crossbred type and lamb sex effects were also significant (P&lt;0.01), although they tended to be reduced for higher order births. Nutritional treatment had no effect on gestation length. Ewe liveweight at joining and weight gains before and after the treatment period significantly affected birth weight and accounted for the large difference in birth weight between years (0.7 kg). Ewe weight gain during the treatment period in mid pregnancy had no significant effect on lamb birth weight. Nutritional treatment in mid pregnancy had no effect on lamb survival. Litter size significantly affected lamb survival, although inclusion of birth weight in the model reduced the effect. Weather conditions, as measured by chill index, significantly (P&lt;0.01) affected lamb survival in 1984 but accounted for less variation in 1985 (P&lt;0.05). Lamb survival for ewes was ranked BLM &gt; TD &gt; BD. Maximum survival was achieved at birth weights of 4-5 kg from BD and TD ewes and 5-6 kg from BLM ewes. The L treatment reduced (P&lt;0.01) ewe greasy fleece weight by 0.15 kg but did not affect staple strength. Plasma glucose concentration at the end of treatment was lower (P&lt;0.01) for L ewes, but there was no difference between L and H ewes in late pregnancy. Glucose declined with increasing fetal number. Plasma B-hydroxybutyrate concentration was lower for the H group than for L, and also for BLM than TD and BD ewes (P&lt;0.01).

Simulation of life-cycle efficiency of lamb and wool production for genetic levels of component traits and alternative management options

A deterministic computer model was used to predict effects of genetic improvements in performance and of management options on life-cycle flock TDN input per unit of empty body weight (EBW) or carcass lean (CLN) equivalent value of market lamb, cull ewe, and wool output from a pure breeding system of sheep production for sheep fed to maintain normal weight. Relative values per kilogram for market lambs, cull ewes, and clean wool were 1 to .33 to 2.04 in lamb empty body equivalent, but 1 to .33 to 1 in lamb carcass lean equivalent. A 10% increase in lamb viability improved TDN/EBW or CLN by -15 to -20% for high to low lambing rates. Corresponding smaller gains were -7 to -11% for fertility, -3 to -13% for lambing rate, -1 to -3% for wool growth rate, -1 to -5% for milk production without creep feeding, -2 to -1% for mature size to about 70 kg, and -.6 to -.9% for precocity of fertility. Increasing leanness 10% improved TDN/CLN by -3 to -1% but increased TDN/EBW 3% because of higher maintenance requirements of leaner sheep. Higher protein requirements for increased lambing rate, milk production or leanness, or greater increases in non-feed than in feed costs, would mean only slightly less reduction of TDN/output than shown. Creep feeding was beneficial only for prolific, low-milking stock. Flushing reduced adverse effects of restricted feeding. Different values for wool vs meat or for costs of feed vs non-feed inputs would change results. These estimates for relative economic importance of traits apply to derivation of optimum criteria for selection among breeds or crosses, or within-breeds used in rotation crossbreeding, but would differ for specialized terminal-sire or maternal breed roles.