Ewe Survival Research Articles

Effects of sire breed on ewe dystocia, lamb survival and weaned lamb output in hill sheep systems

A study was carried out on six hill farms, located in the main hill regions of Northern Ireland, over three breeding seasons to investigate the effect of sire breed on ewe dystocia, lamb survival and weaned lamb output. On each farm, groups of 26 to 40 purebred Scottish Blackface ewes (n = 3174) were crossed with Blackface, Swaledale, North Country Cheviot, Lleyn and Texel sires by natural service (year 1) and artificial insemination (years 2 and 3). Each of the mating groups was initially balanced for ewe age, live weight and condition score, and a total of 15 sires of each breed were used over the 3 years. In total, 2272 ewes were recorded at lambing, producing 3451 lambs, over the 3 years. Sire breed had a significant effect (P < 0.001) on lamb birth weight with Blackface and Swaledale the lowest and Texel the highest. The proportion of ewes with dystocia was higher with Texel sires compared with Lleyn, Swaledale and Blackface sires (P < 0.05). Ewes mated to Cheviot sires had more dystocia than those mated to Blackface and Swaledale sires (P < 0.05), while ewes mated to Lleyn sire breed had more dystocia (P < 0.05) than those mated to Blackface sire breed. Most of the incidence of dystocia was attributable to increased lamb birth weight (P < 0.001), and some to litter size (P < 0.05). Swaledale, Cheviot, Lleyn and Texel sire breeds increased the incidence of malpresentations (P < 0.05). Lamb live weight at weaning was higher with Texel- and Cheviot- and Lleyn-sired lambs compared with Blackface- and Swaledale-sired lambs (P < 0.01). The level of lamb mortality at birth was not affected by sire breed. However, lamb mortality at weaning was lower for Lleyn-sired lambs compared with the other lamb genotypes (P < 0.05). These results indicate that the use of sires from larger breeds, such as Lleyn and Texel, within the Blackface ewe flocks can increase lamb output, with no apparent detrimental effects on lamb mortality or ewe survival, but increased assistance at lambing will be required.

Estimates of economic values for traits of Arabic sheep in village system

A deterministic bio-economic model was used to estimate the economic values of different traits in Arabic sheep native to the Khuzestan province of Iran. In the studied system, variable costs accounted for about 98.5% of the total costs and among variable costs, feed costs had the highest proportion with 70.7%. Revenue sources included meat, wool, and manure, where meat was the most important one and formed 95.5% of total revenues. Economic value for a trait was estimated as the amount of change in the profit of system as its mean increased by one unit, while the means of other traits were constant. The most important trait in this system was litter size, followed by ewe survival, dressing percentage, and wool weight, respectively. Birth weight had a negative economic value but weight at older ages especially weaning weight and 12-month weight had positive economic values. The sensitivity of economic values of traits was investigated by changing feed and non-feed costs, meat and wool prices by ±10%. Results showed that economic values for dressing percentage and wool weight are not sensitive to change in costs. In addition, changes in marketing and management costs had no effect on the economic value for traits related to body weight in different ages. In general, the economic value for traits which showed sensitivity to the changes of costs, except ewe survival, decreased due to an increase in costs. The economic value for all traits, except birth and wool weight, changed because of a change in meat price. Increasing meat price meant a higher economic importance. Among different factors, meat price fluctuations had the most effect on the economic value of traits.

Body condition score as an indicator of ewe survival under extensive conditions

AbstractSurvival and mortality of extensive hill ewes are important commercial factors and valuable indicators of welfare, but difficult to study. Body condition scoring is a tried-and-tested management and monitoring tool which has been defined as a good predictor of fitness in ewes and is easily measured under hill farm conditions. This paper presents the results of a study on ewe survival rates in hill conditions in Scotland. Ewe performance and survival rates were measured in two contrasting hill flocks over a five-year period. Statistical analysis showed that mid-pregnancy body condition score was the most reliable indicator of subsequent ewe survival, followed closely by age of the ewe and environmental and management conditions. This study confirms that there are considerable welfare issues related to hill flocks and that improved winter nutritional management is a key component to good welfare and productivity. It also reinforces the view that body condition score is a good quantitative predictor of animal welfare and that poor mid-winter score indicates high risk of mortality, both at the flock and individual ewe level.

Demography, population dynamics and sustainability of the Patagonian sheep flocks

Sheep production is the main agricultural activity in Patagonia. Since the middle of the 20th century, sheep numbers have declined steadly. We used historical records of stock numbers in four ranches to analyze the importance of regional factors so as to explain the decline of the Patagonian sheep flocks. We found that the stocks of all the four ranches declined with a similar trend but fluctuated independently, thus reflecting a complex interaction between regional and local factors. Aboveground net primary production (ANPP) and vegetation physiognomy explained most of the differences in the flocks declining rates. We estimated demographic parameters for two ranches differing in their average annual growth rates. From these demographic parameters, we constructed deterministic and stochastic matrix models to establish the relative contribution of demographic processes to the observed decline. Matrix models projected a faster decline than that observed in the ranch used to calibrate the model. This suggests that the recorded demographic parameters could drive most stocks to extinction in less than 100 years. We concluded that the observed dynamics would be generated by demographic processes, but extinction is delayed or avoided by a continuous intake of animals. Ewe survival was the most important parameter in controlling the growth rate of the flocks. The environmental stochastic model showed that the growth of the stocks was highly sensitive to increases in the frequency of good years (those that produce a positive growth) and in the transition from normal years to bad years. All these evidences point out the existence of biological constraints to sheep production in Patagonia: ANPP and vegetation structure would control flock population dynamics throughout its effects on key demographic parameters, ewe survival and marking rate (a recruitment measure). Our model results suggest that the decline in sheep numbers, and hence the sustainability of the activity, is driven, to a large extent, by the demographic characteristics of the flocks.

Economic values for traits in breeding objectives for sheep in the tropics: impact of tangible and intangible benefits

In traditional management systems in the tropics, sheep constitute a source of easily convertible capital for financing purposes and insurance, a means of cultural and ceremonial functions, and a source of prestige, meat, manure and skins. In this study, breeding objectives were derived for an indigenous tropical sheep breed under pastoral production. Economic values were calculated for five situations: (i) base accounting for both tangible and intangible roles of sheep; (ii) accounting for manure, skins and intangible roles; (iii) accounting for 20% of animals sold, insurance, manure and skins; (iv) accounting for intangible roles only; and (v) accounting for tangible roles only. Sensitivity analysis to different levels of financing and insurance benefit factors, reproduction, survival and live weight traits was performed for the situation accounting for both tangible and intangible roles, and with a constant number of ewes. The economic value for a trait considered in a particular situation was calculated from the difference between the average performance level of the trait before and after incrementing it by one unit. The traits considered were litter size, lambing frequency, pre-weaning and post-weaning lamb survival to 12 months, ewe survival, 12-month lamb live weight, mature ewe live weight, consumable meat and kg manure dry matter sold ewe −1 year −1. Generally, in descending order of the profits and economic values, the situations studied ranked as follows: (i), (v), (iii), (ii) and (iv). For the base situation, financing and insurance benefits accounted for 13% and 6% of the total revenues, respectively. Situation (v) had a profit that was about 35% lower relative to situation (i). In terms of genetic standard deviations, the economic values (US$ ewe −1 year −1) for the base situation were: 2.81 for litter size, 6.40 for lambing frequency, 0.02 for pre-weaning survival, 0.03 for post-weaning survival, 0.05 for ewe survival, 1.81 for 12-month lamb live weight, 0.43 for mature ewe live weight, 0.09 for consumable meat and 0.01 for kg manure dry matter sold (ewe −1 year −1). The economic values indicate that litter size, lambing frequency and 12-month lamb live weight are likely to be important traits in pastoral production. Sensitivity analysis showed that future economic values for all the traits considered, except kg manure dry matter sold ewe −1 year −1, might change depending on levels of intangible benefit factors. Ewe survival and mature ewe live weight were not responsive to changes in reproductive traits, and pre- and post-weaning traits, and vice versa. It is concluded that it is necessary to include the intangible roles of sheep in tropical breeding programmes.

Another one bites the dust: Does incisor-arcade size affect mass gain and survival in grazing ungulates?

Incisor-arcade size affects foraging efficiency in grazing ungulates and should be under strong selective pressure. We investigated individual variation in incisor-arcade size and its relationship with body mass and survival in bighorn sheep (Ovis canadensis) at Ram Mountain, Alberta, Canada, over 9 years. In adult ewes, incisor-arcade breadth and depth decreased with age, probably as a result of tooth wear. We found no effects of incisor-arcade size on survival of lambs or adult ewes. In adult ewes, an apparent positive effect of incisor-arcade size on survival disappeared when age was accounted for. Incisor-arcade breadth and depth had no effect on summer mass gain in lambs or adult ewes. Although linear models suggested that arcade breadth in lambs was correlated with summer mass gain, a latent variable path analysis model revealed that the correlation was due to an allometric relationship of arcade breadth with body size. Variation in incisor-arcade size in bighorn sheep appears to be due to individual variation in body size and age rather than to directional selection.

Variable age structure and apparent density dependence in survival of adult ungulates.

Large herbivores have strongly age-structured populations. Because recruitment often decreases as population density increases, in unexploited populations the proportion of older adults may increase with density. Because survival senescence is typical of ungulates, ignoring density-dependent changes in age structure could lead to apparent density-dependence in adult survival. To test for density dependence in adult survival, we used data from three populations that underwent considerable changes in density. Bighorn sheep (Ovis canadensis) on Ram Mountain, Alberta, ranged from 94 to 232, mountain goats (Oreamnos americanus) on Caw Ridge, Alberta, varied from 81 to 147, and estimates of roe deer (Capreolus capreolus) older than 1year at Chizé, France, ranged from 157 to 569. We used recent developments of capture-mark-recapture modelling to assess the response of adult survival to changes in density when age structure was and was not taken into account. Survival rates were 10-15% higher during the prime-age stage than during the senescent stage for all sex-species combinations. When adults were pooled into a single age class there was an apparent negative effect of density on female survival in bighorns and roe deer, and negative trends for female mountain goats, male roe deer and male bighorn sheep. When age class was taken into account, there were no significant effects of density on adult survival. Except for male mountain goats, the strength of density dependence was lower when age was taken into account. In ungulate populations, age structure is an important determinant of adult survival. Most reports of density dependence in adult survival may have been confounded by changes in age structure.

Economic values for traits of meat sheep in medium to high production potential areas of the tropics

Breeding objectives were developed for meat sheep in smallholder production circumstances in the tropics. The traits considered were litter size, lambing frequency, pre-weaning, and post-weaning lamb survival to 12 months, ewe survival, lamb live weight at 12-month, mature ewe live weight, consumable meat, kg of manure DM sold per ewe per year and residual DM feed intake. Three evaluation situations were considered: (i) base with constant number of ewes, (ii) fixed feed resource and (iii) setting feed costs to zero. Sensitivity analysis of economic values to price levels of inputs and meat production was carried out. The fixed feed resource situation appropriately describes smallholder production circumstances. In the base situation, meat production accounted for about 88% of revenue and manure the remaining 12%. Variable costs represented about 95% of the total cost. For the fixed feed resource situation, economic values (US$ per ewe per year) were 12.94 for litter size, 10.18 for lambing frequency, 0.19 for pre-weaning lamb survival, 0.24 for post-weaning lamb survival, 0.36 for ewe survival, 1.02 for 12-month lamb live weight, 0.14 for mature ewe live weight, 0.51 for consumable meat, 0.08 for kg of manure DM sold (per ewe per year) and −0.04 for residual DM feed intake. Litter size and lambing frequency were the most important traits in a breeding objective for smallholder production. Relative to the base situation, setting feed costs to zero had similar results as the situation with restricted feed resource but resulted in larger differences. Sensitivity analysis of economic weights to changes in prices and production circumstances indicated that future economic values for traits might change dependent on levels of output and prices. The exceptions, with regard to changes in meat price are kg of manure DM sold per ewe per year and residual DM feed intake, and with regard to feed costs are consumable meat and kg of manure DM sold per ewe per year. Economic values for 12-month lamb live weight, mature ewe live weight, consumable meat, kg of manure DM sold per ewe per year and residual DM feed intake were not sensitive to changes in management and marketing circumstances. Caution is recommended when the breeding objectives presented here are applied not to disadvantage smallholders in poor climatic years, when farmers are at their most vulnerable situation.

Population Growth, Fecundity, and Survivorship in Recovering Populations of Bighorn Sheep

AbstractThe single greatest obstacle to the restoration of large, healthy, populations of bighorn sheep (Ovis canadensis) in the western United States is epizootic outbreaks of bronchopneumonia that may kill 20–100% of the animals in populations. Although the species is capable of rapid initial growth rates following restoration into new habitat (λ = 1.23–1.30 have been observed), these rates of increase are typical only a few years following the release of a population, and then most populations either decline to extirpation or remnant status (&lt;30 animals) or remain at &lt;100 individuals. We studied the fecundity and survivorship of three increasing, and three declining and suspected diseased, populations of bighorn sheep (the latter were subjected to outbreaks of bronchopneumonia) located in or near several large national parks in the western United States from 1991 to 1996. Titers verified both population categories were exposed to the bacteria Pasteurella haemolytica serotypes 3; 4; and 3, 4, 10; Moraxella sp., and parainfluenza‐3 and bluetongue (BT) viruses. Pregnancy rates of adult ewes were not different in increasing or decreasing populations (pooled rate = 0.93; p = 0.57), but pregnancy rates of yearlings were lower (0.00 for decreasing vs. 0.33 for increasing populations), initial production of lambs and annual recruitment of lambs was lower (0.14, decreasing vs. 0.66, p &lt; 0.05). Adult survival was lower during the first year of an epizootic, 0.62, in one population, but recovered to 0.85 by the second and subsequent years. Survival of adult rams was variable in diseased populations; in two populations rams appeared to be disproportionately impacted, but in a third population rams survived better during the epizootic. In all the increasing park (unhunted) populations, adult ram survival (0.94 ± 0.01) was higher than adult ewe survival (0.89 ± 0.02) (p = 0.10), in contrast to published information from hunted populations where ram survival was lower. Removal of about 20% of one population for restorations severely impacted one declining population. Removals of 12–20% appeared to be excessive and were not readily compensated for in the Canyonlands National Park desert bighorn population. Disease was a significant limiting factor to restoration of bighorn sheep in the study areas; six of 11 total recovering populations we monitored closely were negatively influenced by apparent disease at some time during our observations.

Body mass and survival of bighorn sheep

In ungulates, body mass is often positively correlated with juvenile survival, but little is known of whether body mass affects survival of other age-classes. We studied two marked populations of bighorn sheep (Ovis canadensis) in Alberta, Canada, to determine if body mass affected the survival of different sex –age classes. Chest girth at weaning was correlated (P &lt; 0.0001) with survival of bighorn lambs in the Sheep River population. In the Ram Mountain population, body mass in mid-September had a stronger effect upon survival than mass in early June, mass gain in summer, or mass loss in winter. Body mass at weaning was correlated with lamb survival (P = 0.004). In both study areas, relationships between size and survival of lambs were similar for the two sexes. At Ram Mountain, survival of yearling and adult males seemed to be independent of body mass. Light yearling females were less likely to survive than heavy yearling females. Among females aged 3 – 6 years, body mass had no effect on survival. Among females 7 years of age and older, mass in mid-September had a weak but significant (P = 0.03) effect on survival. Females were slightly lighter in mid-September in their last year of life than in the rest of their adult life. Maternal expenditure is unlikely to affect the survival of prime-age ewes, but may have a detrimental effect on the survival of older ewes.

Effects of feeding wash-water solids on health and performance of ewes and lambs.

Diets containing 0, 10, or 20% dried wash-water solids (WWS) from a milk processing plant were fed to 48 Hampshire crossbred wews (average weight 58.1 kg) for 3 yr. Data were obtained on BW gains, hematology, tissue elements, and survival for ewes and BW gains, tissue elements and survival for their lambs. Ewes fed 20% WWS gained less (P < .05 ) BW during gestation and lactation in yr 1 and had lower BW (P < .05) in yr 2 and 3 than those fed 0 or 10% WWS. Lambs from ewes fed 20% WWS gained less (P < .05) BW in yr 2 and 3. Hematology variables of ewes, survival of ewes and survival of lambs were not effected by diet. Although WWS-containing diets contained high concentrations of Ca, P, Mn, and Fe and moderate concentrations of Mo, Mg, and Zn, diets had few effects on tissue elements in ewes and lambs. Concentrations of some tissue elements were less (P < .05) in lambs in yr 2 and 3 than in yr 1. Wash-water solids can be incorporated into ruminant diets, providing a disposal alternative that recycles and conserves nutrients. Long-term feeding posed only minor or negligible health of safety problems. Because fo low energy and N availability and high ash content, WWS probably should be limited to 10% or less of conventional diets.

Effects of rapid inbreeding and of crossing of inbred lines on conception rate, prolificacy and ewe survival in sheep

AbstractThe effects of four generations of inbreeding, to achieve inbreeding coefficients (F) of 0·25, 0·375, 0·50 and 0·59, on conception rate, prolificacy, litter weight at birth and survival of breeding females, have been studied in sheep. Crosses of inbred lines were also examined. Three breeds, Scottish Blackface, Cheviot and Welsh Mountain, and the crosses among these breeds, were involved. Analyses were carried out both for the data overall and within inbred lines.Conception rate at the first oestrus at which the ewe was mated (in each year) declined almost linearly from 0·71 (F2 generation - inbreeding F = 0·0) to 0·44 (F = 0·59) with line crosses showing 0·78 conception rate. The corresponding results following up to three rounds of services at successive oestrous periods were 0·91, 0·74 and 0·97 respectively. Analyses within lines showed a steeper rate of decline in conception rate to 0·33 (F = 0·59) following first services and 0·63 following up to three successive periods. This indicates that the lines with the best conception rates survived the inbreeding process better.Prolificacy, the number of lambs born per ewe lambing, dropped from 1·73 (F = 0·0) to 1·37 (F = 0·25) and thereafter more slowly to 1·24 (F = 0·59). Line crosses were no better than the initial non-inbred generation (F2 and the purebred equivalent O2). Within-line analysis gave the same results.The effects of inbreeding on litter weight at birth mirror closely those for prolificacy.Ewe survival declined linearly with inbreeding. There was a 1·2-fold increase in the risk of death for every increase in the inbreeding coefficient (F) of 0·1 (analysed by using a proportional hazard model).In general, there were no significant differences between purebred and crossbred sheep in the effects of inbreeding. For conception rate, prolificacy and litter weight (for which the point was examined) the changes with inbreeding could not be explained, statistically, in terms of dominance alone, suggesting, therefore, that epistasis is also involved.

Performance of Polypay, Coopworth, and crossbred ewes: II. Survival and cumulative lamb and wool production over 4 years.

Six ewe genotypes, generated by mating Coopworth (C), Polypay (P), and Suffolk (S) rams to P and Coopworth-type (Ct) ewes, were exposed to Hampshire rams for spring lambing from 1987 through 1990. Data from 1,013 exposures and 973 resultant lambings were used to analyze reproductive traits and cumulative ewe productivity over 4 yr. Ewe body and fleece weights were also analyzed. Ewes from S sires weaned the heaviest lambs and ewes from P sires weaned the largest number of lambs, resulting in similar total weight of lamb weaned per ewe mated. Coopworth-sired ewes weaned the least total weight of lamb per ewe mated. Ewes weaning twins produced 54% more total litter weight per ewe than those weaning singles. Annual ewe survival averaged 95%, ranging from 93% for S x P and C x P ewes to 97% for P x Ct and C x Ct ewes. When cumulative number and weight of lamb produced was assessed on the basis of all ewes starting the trial, P-sired ewes were highest, followed in order by daughters of S and C sires. Suffolk-sired ewes (67 kg) were 13% heavier than daughters of P rams and 19% heavier than daughters of C rams. Adjustment of lamb production for ewe metabolic body size resulted in C-sired ewes being more efficient than the heavier S-sired ewes. Coopworth-sired ewes produced 32% more wool than ewes sired by the other two breeds. Differences in wool production between ewes weaning one or two lambs were small.(ABSTRACT TRUNCATED AT 250 WORDS)

Reproduction, growth and survival of Merino ewes and lambs in south-western Queensland and their response to trace element supplementation

The effects of cobalt (Co), selenium (Se), copper (Cu) and Co + Se + Cu plus manganese, iodine and zinc (All) supplements on the liveweight change, fleece weights, reproduction and survival of Merino ewes and their lambs were studied on 3 commercial properties (W, B and G) in south-western Queensland during 1978 and 1979. There was no significant effect of supplementation on ewe and lamb liveweights or ewe fleece weights in 1978 (723 mm rain). In 1979 (303 mm rain), ewes given Co and All supplements were significantly (P&lt;0.05) heavier than all other ewes at weaning, but lamb weaning weights were not improved by any supplements. Zinc and manganese may have only been effective for a short period following dosing. Weaner lambs given supplements of Co, Se and Co+Se had significantly (P&lt;0.05) higher greasy fleece weights (3.67 kg) than unsupplemented lambs (3.38 kg). In 1978, there was no significant effect of supplementation on reproductive rate. On property W, only 68% of maiden ewes successfully mated and this flock had a significantly (P&lt;0.05) higher rate of reproductive wastage (27%) than did flocks on properties B (12.5%) and G (16.5%). The mean liveweights of maiden ewes for properties W, B and G in this year were 39.1, 35.1 and 37.1 kg, respectively. In 1979, ewes given the All supplement had significantly (P&lt;0.05) lower overall rates of reproductive wastage (12.2%) than did ewes without supplement (30.2%). Supplementary treatments did not improve ewe or lamb survival. In 1978, ewe mortality between joining and weaning was significantly (P&lt;0.05) higher on property W (24.2%) than on property G (7.0%). In 1979, there were no significant effects of either age or property on ewe mortality between joining and weaning. Neither trace element supplementation to ewes nor the sex of the lamb had a significant effect on lamb survival between marking and weaning.

The nutrient status of sheep grazing on a dry Mitchell grass pasture association in central-western Queensland.

The lambing performance of a group of ewes grazing a dry Mitchell grass pasture association in central-westem Queensland was recorded and found to be very poor. A portion of the ewe flock received a urea-molasses supplement those ewes did not exhibit an increase in lamb or ewe survival and it is likely that most did not consume the supplement. One week prior to the ewes' expected date of lambing, intact wethers and other wethers with oesophageal fistulas or rumen and abomasal cannulas were grazed on the pasture and the intake and digestion of nutrients by these animals were determined. Extrapolating the results from the wethers to the ewes indicated that the major limiting nutrients for the ewes were energy and, at least during the latter stages of lactation, rumen digestible nitrogen. Other nutrients that may have been deficient in the diet were copper and zinc.

A genetic analysis of the components of lifetime productivity in Scottish Blackface sheep

ABSTRACTReproductive performance, body growth, wool production and ewe survival were examined in Scottish Blackface sheep. The data set was from a large randomly selected population maintained under hill conditions between 1954 and 1974. Paternal half-sib analyses of variance were used to estimate heritabilities and genetic correlations, while maternal half-sib analyses of variance indicated the relative importance of maternal effects (both genetic and environmental).Among reproductive components, the heritability of fertility (ewes lambing per ewe mated) and lamb survival (lambs weaned per lamb born) were about zero. Litter size (lambs born per ewe lambing) had an estimated heritability of 0·12 (s.e. 0·04) and a repeatability of 0·22 (s.e. 0·02), indicating some scope for improvement. Additionally, the strong genetic correlation between adult body weight and litter size (0·66, s.e. 0·18) suggested greater response from a combination of indirect selection (on body weight) and direct selection (on dam's litter size). Prior to weaning, direct genetic effects on body weight were very small (heritability less than 0·1) with a large influence of maternal environment. After weaning, these maternal influences gradually diminished and the heritability of weight increased. Genetic correlations between body weights showed a similar increasing trend with age. Genetic improvement of early growth rate would be more effective by selecting on a post-weaning rather than a pre-weaning body weight. Fleece weight had a high heritability (about 0·5) but was genetically uncorrelated with other measures of performance. Ewe survival had a small genetic component although estimates of heritability were very imprecise.

Predicted and realized responses to selection for an index of bone length and body weight in Scottish Blackface sheep 2. Correlated responses in lifetime productivity

ABSTRACTA selection experiment with Scottish Blackface sheep was used to compare predicted and realized correlated responses to selection. Three lines were maintained between 1956 and 1974 in which selection was either at random or for high and low values of an index of cannon-bone length at 8 weeks of age adjusted for body weight at the same age.There was no evidence of asymmetrical responses in any trait. Selection for increased cannon-bone length, adjusted for body weight, resulted in (i) increased body weights at all ages between birth and maturity, (ii) increased reproduction rate, principally from increased litter size but also from small responses in ewe fertility and lamb survival and (iii) decreased survival of adult ewes. The realized genetic correlations were relatively small (up to 0·3) but mostly significantly different from zero, whereas base population genetic correlation estimates were very imprecise. The realized responses in reproduction rate were probably a consequence of the genetic response in body weight.

Effects of including lupins with cereal grain rations on the production of lambing ewes during drought

In this experiment, 520 Border Leicester x Merino ewes 2 or 6 years of age and pregnant to Dorset Horn rams were held under simulated drought conditions and fed drought rations. Similar weights of oats or wheat with 0, 15, 30, 45 or 60% lupin grain were fed from 2 weeks before till 9 weeks after lambing, in 1979. Mean improvement in production as a result of including lupins in diets was 3 kg in liveweight of ewes, 6% (per ewe lambing) in ewe survival, 24% (per lamb born) in lamb survival, 41 g/day in lamb growth rate and 0.3 kg in ewe greasy fleece weight. The major response was to the increase in proportion of lupins from 0 to 15%. Type of cereal grain did not affect these responses. Wool from all treatments except oats alone was weakest in the first 4 weeks after lambing. Wool from 4% of ewes fed wheat alone was down-graded because of the ease with which staples broke under tension. The total number of lambs born in 1980 was not affected by previous treatment, even though ewes previously fed oats in 1979 had more twins than those fed wheat and the previous feeding of lupins decreased the number of ewes bearing single lambs.

The effects of the timing of management actions on the performance of a grassland sheep flock

SummaryA production system is defined which involves the production of lambs from crossbred ewes kept in a cool, temperate grassland environment at an altitude of 250–300 m. Within the production system, an investigation was carried out on the effect of the timing of weaning, pre-mating treatment (flushing) and concentrate feeding before lambing in a flock of 180 Border Leicester (♂) × Scottish Blackface (♀) ewes maintained for a production span of four lamb crops. Weaning treatment had no significant effects on changes in live weight or body condition score. Pre-mating treatment affected live weight and condition at mating. It did not affect the number of lambs born but had a significant effect on the subsequent birth weight of twin lambs in the 1st year it was applied but not thereafter. The timing of introduction and total quantity of concentrate feed affected the birth weight of lambs from ewes at their first lambing (24 months old) but not subsequently. There were no long-term effects of treatment on ewe survival or on the production characters measured. The results are discussed in relation to the seasonal patterns of grass supply and the normal limits of commercial practice. In this study, when grass and forage were in reasonable supply, pre-mating management and concentrate feeding were not critical to ewe performance. Only in circumstances of an unusual grass shortage and also in young ewes did these factors have significant effects on performance.

Effects of different stocking intensities in early life on the productivity of Merino ewes grazed as adults at two stocking rates. 3. Survival of ewes and their lambs, and the implications for flock productivity

A stocking rate of 20 sheep/ha in adult life was associated with greater mortality of ewes and their lambs than a stocking rate of 10 sheep/ha, but mortality was not affected by the nutrition of the ewes in early life. Survival of lambs born as twins to weaning was 42% at the high stocking rate and 72% at the low. Corresponding values for singletons were 73 and 87%. Differences in survival of singleton but not twin lambs were established during the first 5 d of life. Mortality of ewes was greater at a high stocking rate and by nine years of age approximately twice the number of ewes had died at the high as at the low stocking rate. Incisor wear and losses were greater in sheep stocked as adults at the high stocking rate, and within this flock was more marked in ewes reared at a low than in those reared at a high stocking rate. Severe wear and loss of incisor teeth were not correlated with cumulative mortality at 108 months. Data reported in this and in the two previous papers in this series were synthesized into a computer model which was used to predict wool production and the numbers of lambs and surplus ewes available for sale when culling age was varied from four to eight years. Wool production and the numbers of surplus sheep available for sale were predicted to be greater at the higher stocking rate with the exception of the number of surplus female lambs available from flocks in which their mothers were culled at six years or earlier.