Barren Ewes Research Articles

An extreme model of fertility in sheep demonstrates the basis of controversies surrounding antral follicle count and circulating concentrations of anti-Müllerian hormone as predictors of fertility in ruminants

Ovarian ultrasonography and measurement of circulating concentrations of anti-Müllerian hormone (AMH) have been used to estimate follicle number and predict fertility in mammalian females, but no study has evaluated follicle number and circulating concentrations of AMH in ewes known to differ in fertility. We tested the hypothesis that ewes that had failed to lamb (BARREN) in four consecutive annual breeding seasons of 21–35 d have fewer follicles and diminished circulating concentrations of AMH compared to closely matched ewes that consistently produced lambs (FERTILE) under the same breeding protocols. Once identified, BARREN ewes (n = 19) were paired by breed and sire to a FERTILE control ewe (n = 19) and reproductive tracts were recovered at necropsy. Visible antral follicles in both ovaries were counted and a representative cross section of one ovary was embedded for histological evaluation of pre-antral follicle numbers. Paired t-tests indicated that BARREN ewes had fewer antral follicles, fewer primordial follicles, and decreased circulating concentrations of AMH compared to FERTILE ewes (P ≤ 0.01), but there were ewes in each fertility classification that had ovarian phenotypes like the opposite fertility classification. The best technologies we have currently for estimating follicle numbers are ultrasonography and measurement of circulating concentrations of AMH, but no single technique is perfect for predicting fertility. A better understanding of the under-lying biological mechanisms linking AMH, folliculogenesis, and fertility is required to improve the use of measurements of follicle number for predicting fertility in livestock.

Nutritional Quality of Meat from Barren Merino Ewes in Comparison to Meat from Traditional Lambs.

In Spain, lamb consumption has decreased over the last few years. To increase farmers' income, we studied the nutritional quality of the barren ewes' meat in comparison to traditional lambs' meat with 10 barren ewes, 10 male lambs, and 10 female lambs from the Merino breed. We measured the subcutaneous fat, muscle color, and carcass tissue composition, as well as proximal composition, mineral, tocopherol, retinol, lutein, and cholesterol contents, and the TPA texture profile, fatty acid profile, and lipid oxidation of the meat. There was no effect of the animal type (males, females, and ewes) on the pH, and the differences in the subcutaneous fat color, lipid oxidation, and texture were irrelevant from a practical point of view. The tissue composition in the three groups of animals reflected a high percentage of saleable meat, with no penalty incurred for intensive fattening in any of the groups. The ewes' meat presented a higher percentage of moisture, collagen, ash, calcium, iron, α-tocopherol, and retinol than the lambs' meat. In addition, it had higher content of DHA and CLA and lower values for the ratio n6/n3, which is beneficial for health, although it also contained more fat, saturated fatty acids, and cholesterol than the lambs' meat.

176 Are Ovarian Reserve Parameters Related to Reproductive Tract Development and Fertility in Ewes?

Abstract There are differences between cows and ewes in ovarian reserve parameters. No major genes influencing follicle numbers have been identified in cows, whereas several genes have variants reported to influence follicle numbers in ewes. In contrast, antral follicle count is associated with fertility in cows, and we reported that beef cows that failed to conceive in 2 consecutive years had fewer antral follicles and smaller reproductive tracts than cows that had never failed to conceive. In the current study, we tested the hypothesis that ewes that had failed to lamb (BARREN) in 4 consecutive annual breeding seasons of 21– 35 d with rams that had passed a breeding soundness exam have fewer follicles and smaller reproductive tracts than ewes that consistently produced lambs (FERTILE) under the same breeding protocols. BARREN ewes (n = 19) were paired by breed, age, and sire to a FERTILE control ewe (n = 19) and reproductive tracts were recovered at necropsy. All visible antral follicles in both ovaries were counted and a representative cross section of one ovary was embedded for histological evaluation of primordial follicle numbers. The reproductive tract was weighed, and ovulatory status was evaluated. Paired t-tests indicated that BARREN ewes had 25.6 ± 5.0 fewer antral follicles per pair of ovaries, 17.3 ± 4.4 fewer primordial follicles per histological section, and 54.5 ± 18.7 g lighter reproductive tracts than FERTILE ewes (P ≤ 0.01). The odds of FERTILE ewes being ovulatory at necropsy were 2.25 that of BARREN ewes, but this did not differ from expectation by McNemar’s test (P = 0.13). The results indicate that size of the ovarian reserve influences fertility in ewes as it does in cows. USDA is an equal opportunity provider and employer.

Longitudinal dynamics of co-infecting gastrointestinal parasites in a wild sheep population.

Within-year variation in infection is a ubiquitous feature of natural populations, but is determined by a complex interplay of environmental, parasitological and host factors. At the same time, co-infection is the norm in the wild. Longitudinal dynamics of co-infecting parasites may therefore be further complicated by covariation across multiple parasites. Here, we used fecal parasite egg and oocyst counts collected repeatedly from individually marked wild Soay sheep to investigate seasonal dynamics of six gastrointestinal parasite groups. Prevalence and abundance tended to be higher in spring and summer, and abundance was higher in lambs compared to adults. We found that within-year variation in highly prevalent strongyle nematode counts was dependent on adult reproductive status, where reproductive ewes had distinct dynamics compared to males and barren ewes. For similarly prevalent coccidia we found an overall peak in oocyst counts in spring but no differences among males, barren and pregnant ewes. Using multivariate mixed-effects models, we further show that apparent positive correlation between strongyle and coccidia counts was driven by short-term within-individual changes in both counts rather than long-term among-individual covariation. Overall, these results demonstrate that seasonality varies across demographic and parasite groups and highlight the value of investigating co-infection dynamics over time.

Influence of feeding different types feed blocks as supplementary feed on the reproductive performance of Awassi ewes grazing cereal stubble

This study was conducted to investigate the Influence of feeding different types feed blocks as supplementary feed on the reproductive performance of Awassi ewes grazing cereal stubble. These types were feed blocks enriched with cottonseed meal (CSM) or Brewers’ grain (BG) as sources undegradable protein (UDP). Ninety-six Awassi ewes (mean live weight 42.2 Kg), aged 3-4 years were allocated into three groups according to ewes live weight and body condition score.Group (C): Control (No Supplement) stubble grazing only.Group (FBC): FB enriched with CSM supplement plus stubble grazing.Group (FBB): FB enriched with BG supplement plus stubble grazing.All ewes were run as one flock during cereal stubble grazing. The feed blocks were fed to animals (supplementary groups) after their return from grazing wheat and barley stubble (28 days prior to mating and 54 days after introduction of rams). Rams run with the flock during the mating period. The results showed that feeding feed blocks enriched with CSM and BG as supplementary feed resulted considerable improvement in weight gain (P<0.05), body condition score (P<0.05), conception rate (13-16), lambing percentage (25-33%), twinning percentage (13-18%) and decreased the proportion of barren ewes (19 vs. 6 and 3%). Inclusion of small amount of high moisture brewers grain by-product (9%) as sources of undegradable protein in the feed blocks formula as replacement for costly cottonseed meal resulted a dramatic effects on the reproductive performance of Awassi ewes especially twinning rates and lambing rate.

High mortality in a sheep flock caused by coinfection of louping ill virus and Anaplasma phagocytophilum

Fifty-three of a mixed flock of 180 one-year-old lambs (hoggs) and older, barren ewes (ewes that were non-pregnant or had not lambed that spring) died in May 2019 following introduction...

Management strategies, reproductive performance and causes of infertility in sheep flocks in the central region of Saudi Arabia.

The objectives of this study were to identify the management strategies, reproductive characteristics, and causes of the infertility in sheep flocks in the central region of Saudi Arabia. Reproductive data were collected from 43 Awassi flocks containing 12,012 heads and 16 Najdi flocks having 2867 heads. Reproductive tracts of females culled from breeding from these flocks (Awassi, n = 127; Najdi, n = 32) were collected from slaughterhouses to detect the common pathological lesions. The results showed that most flocks contained large number of animals housed mainly in shelters and involved small number of workers. Few managers had high school education and very few farms relied on breeding records, regular veterinary visits, and the use of modern reproductive techniques. Sheep flocks with large number of animals; low-educated and less-experienced managers showed higher stillbirth rate than other flocks (P = 0.02). Sheep housed in shelter demonstrated greater lambing rate than sheep managed between grazing and shelter systems (P = 0.03). Ewes bred seasonally had greater lambing rate than those bred all year (P = 0.03). Non-functioning ovaries, pyometra, and ovarian-bursal adhesion were the common findings in the culled barren ewes. In conclusion, reproductive efficiency of sheep in the central area of Saudi Arabia could be improved by reforming some management approaches, justifying workers/animals ratio, instructing sheep breeders, and controlling genital diseases.

Characteristics of the Romanov Breed by the BMP-15 Locus Responsible for Prolificacy in Sheep

The actual problem in identifying a prolificacy gene in Romanov breed sheep is considered. The new diagnostic method to identify the polymorphic gene of the bone morphogenetic protein 15 (BMP-15) influencing prolificacy in the Romanov sheep has been proposed based on the surveys. The frequencies of occurrence of the normal (wild-type) and mutant alleles and the genotypes present at a locus responsible for prolificacy in sheep are revealed. The quantitative indicators, including the numbers of lambs at birth and at weaning and the barren and culled ewes, were recorded with taking into consideration the genotypes at the BMP-15 locus. The correlation between the frequency of occurrence and the number of the produced posterity and among the barren and culled Romanov ewes were ascertained. It was indicated that the highest percentage of the lamb output at birth and at weaning was typical for the ewes homozygous (MM) for a mutant allele. The animals referred to as heterozygous genotypes (WM) appeared in the second position. The highest percentage of the culled and barren ewes was recorded in the carriers of the WW homozygote. Based on the obtained results, it has been concluded that the genotypes at the BMP15 locus should be taken into consideration when selecting the ewes with regard to their fertility. However, further researches into the determined phenomenon in the Romanov sheep are required to improve this performance, since multifetal pregnancies in some WW-group ewes have been registered.

Development of Improved Preventive and Treatment Strategies for Controlling of Toxoplasmosis in Saudi Arabia

Toxoplasmosis causes severe public health problems and has great veterinary and economic importance worldwide. The present study aims mainly to develop an improved preventive and treatment program for controlling toxoplasmosis in sheep and goats. This study was performed on sheep and goats farm containing 357 animals (300 sheep and 57 goats). This farm had a large numbers of barren ewes, history of abortions (below 4 months), stillbirths, malformations and neonatal losses. Blood samples were collected to determine humeral antibody responses and prevalence of toxoplasmosis. Sections of normal and abnormal tissues were fixed using 10% buffered formalin for histopathological examination. Different and new drug regimens and strategies were used for controlling toxoplasmosis. Sixty-four out of 357 sheep and goats were clinically affected with 17.9% overall morbidity rate. These animals showed certain clinical symptoms of toxoplasmosis, such as abortions and stillbirth. The seroprevalence rate was 15.4%. The titers of ELISA were high before treatment in positive cases while after treatment the titers were decreased for certain level that continued to the end of study. The field treatment revealed that the affected sheep and goats treated with camel lactoferrin (cLf) and chemotherapy combination regimen significantly reduced the overall severity of toxoplasmosis with reduction in IgG titers better than those treated with chemotherapy alone (Pyrimethamine and sulfamethazine) or cLf alone. In conclusion, cLf and chemotherapy combination regimen was success in control of toxoplasmosis in small ruminants.

Outbreak of leptospirosis: reproductive losses in sheep

Sheep are considered less susceptible to leptospirosis than other livestock species, and reports of reproductive problems are scarce in scientific literature. Thus, our objective was to report an epidemic outbreak of leptospirosis in a flock in southern Brazil, causing economic impact represented by several numbers of abortions and barren ewes. From a flock of 602 sheep, 79 ewes had problems during gestational period. Blood samples were collected from 25 of these 79 ewes, 10 with confirmed abortion, 10 barren, and 5 ewes that delivered normally. Serum was separated and subjected to serological evaluation. Samples were examined for Leptospira antibodies by the microscopic agglutination test (MAT) as well as subjected to a differential diagnosis for toxoplasmosis and neosporosis. From the 25 sera analyzed, 19 (76 %) were positive while 6 (24 %) were negative, with single serovar response observed in 12/19 (63.16 %) while mixed serovar positivity was observed in 7/19 (36.84 %). Regarding to serovar prevalence, Hardjo titration was observed in 15/19 (78.95 %) and Wolffi in 9/19 (47.37 %). No samples were positive for toxoplasmosis or neosporosis. Therefore, based on the serological results reached by MAT, it is possible to strongly suggest the participation of Leptospira spp., especially serovars Hardjo and Wolffi, in the reproductive flaws reported in this short communication.

Associations between housing and management factors and reproductive performance in 327 Norwegian sheep flocks.

BackgroundHousing sheep in insulated, warm buildings, which is common in Norway, involves high buildings costs, but has not been reported to improve health and performance. Few studies have dealt with the association between housing and management and reproductive performance.Data on housing and management during the indoor period from a questionnaire were merged with herd level data from the Norwegian Sheep Recording System, and the material included 327 sheep flocks. Associations between housing and management factors and reproductive performance were analyzed by means of multivariate regression models and grouped logistic regression.ResultsThere was no difference in reproductive performance between warm and cold housing. Number of live born lambs born per pregnant ewe was highest in flocks with 10 or less ewes per pen, and lowest in flocks with more than 40 ewes per pen. Rate of barren ewes was lowest, and number of lambs per ewe at the end of the indoor period was highest in flocks where the sheep were regrouped according to number of foetuses (lambs) identified by scanning. A higher total number of lambs born per pregnant ewe and lambs per ewe at the end of the indoor period were found where other available housing facilities or outdoor areas were used in addition to the main housing unit in the lambing season. The rate of stillbirths was lowest on farms where sheep was the only animal production. None of the factors evaluated had any significant association with mortality of live born lambs in the indoor period. Lowest number of lambs per ewe at the end of the indoor period was found on farms where other family members/hired labour were caretakers as compared with the farmer or spouse/cohabitant, and highest numbers were found where caretakers were older than 60 years of age. Reproductive performance was lower in the Spæl Breed than the Norwegian White Sheep.ConclusionHousing systems per se are of minor importance, whereas management practices in the indoor period should be expected to improve reproductive performance.

Impact of Schmallenberg virus on British sheep farms during the 2011/2012 lambing season

British sheep farmers were invited to complete a questionnaire about the impact of Schmallenberg virus (SBV) on animal health, welfare and their own emotional wellbeing during the 2011–2012 lambing season,...

A mail survey of factors affecting performance in 627 selected sheep flocks in south-eastern Norway

Factors influencing rate of barren ewes, number of lambs born per pregnant ewe, and autumn live weight of the lambs were studied in 627 Norwegian sheep flocks based on herd level data from the Norwegian Sheep Recording System and a mailed questionnaire to the sheep farmers. The following factors were significantly associated (P<0.05) with rate of barren ewes: breed, herd average lambing date, type of production/age of farmer, routines for treatments for parasites, and housing type. Number of lambs born per pregnant ewe was significantly associated with rate of barren ewes, herd average lambing date, breed, percentage grass silage of total roughage, and no separation of gimmers during the housing period. Corrected autumn live weight of the lambs was significantly associated with breed, flock size, lambs born per pregnant ewe, no separation of gimmers during the housing period, and type of summer pasture.

Effect of Body Condition and Supplementary Feeding on the Reproductive Performance of Awassi Ewes

This study was conducted to evaluate the effect of body condition score (BCS) and supplementary feedingon the reproductive performance of Awassi ewes.One hundred sixty Awassi ewes aged 3-5 years (Average live weight 47.41±0.76) were used in acompletely randomized design. Six weeks before mating ewes were screened for their body conditionscore (BCS) and divided into two groups, low BCS (&lt;2.0) and high BCS (&gt;2.0) and ewes in each groupwere subdivided according to BCS and to non-supplemented and supplemented groups (n=40 ewes).Therefore, the four groups were:1. Group (LBCN) = Low Body Condition Non-supplemented.2. Group (LBCS) = Low Body Condition Supplemented.3. Group (HBCN) = High Body Condition Non-supplemented.4. Group (HBCS) = High Body Condition Supplemented.All ewes received ad libitum barley straw, and (350g DM/ewe/day) whole barley grains. The supplementedgroups (groups 2 and 4) were fed Mating Feed Blocks (MFB) ad libitum. Mature fertile Awassi rams(Three rams / group) were run with each group.The results showed that the pre-mating, mating, andpost-mating condition scores and body weights of the non-supplemented Ewes (Groups 1 and 3) aremaintained throughout the trial. Ewes offered supplementary feed the supplemented ewes (Groups 2and 4) gained in body condition score and weights, the differences were not significant. The BCS andweights at mating for supplemented groups are 2.12, 2.64 and 46.11, 53.38 kg for groups 2 and 4respectively. The results showed that the reproductive performance of Awassi ewes improved considerablydue initial BCS and MFB supplementation. The percent of ewes lambed after mating during the first andsecond estrus cycles were significantly (P&lt;0.05) affected by ewes' initial BCS and MFB supplementation.The percent of ewes lambed in first cycle were 50%, 77%, 72.3% and 87% for groups LBCN, LBCS,HBCN and HBCS respectively. Supplementation of low BCS ewes resulted a significant (P&lt;0.05)improvement in conception rate (17.5%) and lambing rate (12%). The results have not shown anysignificant of initial BCS and supplementation on twinning percentage. The percent of barren ewes at endof the trial was higher (20%, P&lt;0.05) in LBCN compared

Lambing season and fertility of fat-tailed ewes under an extensive production system are associated with liveweight and body condition around mating

The objective of this study was to investigate to what extent fertility and lambing season of fat-tailed ewes raised under an extensive production system are related to liveweight, body condition and changes around mating. Ewe liveweight and body condition score (BSC) were recorded in June, July and August over a period of 3 years (1999–2001) in 11 flocks (eight flocks of Kurdi breed and three flocks of Kurdi × Sanjabi crossbred). Both Kurdi and Sanjabi are native fat-tailed breeds in western Iran. In total, 3278 lambing records relating to 1592 ewes and data on mating date, liveweight and BCS of 1930 ewes (3975 records) were used for statistical analyses. The statistical model for bodyweight and body condition data included fixed effects of breed group, flock nested within breed group, year, the future lambing status following summer breeding (barren, autumn lambing and winter lambing), ewe age and all two-way interactions. Breed group had a significant effect on ewe liveweight (P &lt; 0.01). However, there was no significant difference between BCS of the two breed groups around mating. Ewe liveweights measured in June, July and August had significant effects on fertility and lambing season (P &lt; 0.01). Ewes that produced lambs were generally heavier at mating than barren ewes (P &lt; 0.01). Autumn-lambing ewes were heavier than winter-lambing ewes in June and July (P &lt; 0.01). Effects of changes in liveweight on fertility and lambing season were significant (P &lt; 0.01). The effects of BCS in June, July and August (P &lt; 0.01) and changes in BCS during the mating period (P &lt; 0.05) on fertility and lambing season were also significant. The mean BCS (in June and July) of autumn-lambing ewes was greater than that of the winter-lambing and barren ewes (P &lt; 0.05). The proportion of autumn-lambing ewes significantly increased as BCS in July increased, whereas the proportion of barren ewes decreased (P &lt; 0.01). Fertility was associated with age so that as the age of the ewes increased from 2 to 7 years, the proportion of barren ewes significantly decreased from 29 to 5% (P &lt; 0.01). There was a relatively high proportion of very thin ewes of 2 and 3 years of age. These findings imply that low body condition is a particular problem in younger ewes suggesting the importance of giving special nutritional treatment to younger ewes to reduce the proportion of barren ewes.

Many eyes or many ewes: vigilance tactics in female bighorn sheep Ovis canadensis vary according to reproductive status

In gregarious animals, there is usually a negative relationship between individual vigilance and group size. This effect of group size is generally explained by increasing probability of predator detection (the many‐eyes hypothesis) and by the dilution of risk occurring in larger groups. Few studies have attempted to examine the specific implications of either hypothesis on the expected vigilance pattern of an animal. Here we examine whether reproductive status affects vigilance patterns in bighorn sheep Ovis canadensis ewes. We also test whether the observed vigilance patterns are consistent with predictions from dilution or detection models of vigilance. Although vigilance decreased with increasing group size, vigilance tactics differed between barren and lactating females. Lactating ewes relied solely on predator detection. In contrast, barren ewes benefited from both detection and dilution effects when group size increased and adjusted vigilance effort according to the proportion of lactating ewes in their group. It is generally assumed that gregariousness increases safety. Here we further show that reproductive status influenced how animals reduce predation risk and that some individuals take advantage of the vigilance effort provided by others.

Effect of the nutritional environment and reproductive investment on herbivore–parasite interactions in grazing environments

Parasitism is a serious challenge to herbivore health and fitness. To avoid parasites, herbivores avoid grazing near feces, creating a mosaic of contaminated tall avoided areas (tussocks) and noncontaminated short grazed areas (gaps). The mosaic represents a nutrition versus parasitism trade-off in that feces-contaminated tussocks are localized concentrations of both forage resources and parasites. Here, we use a grazing experiment with a natural tussock–gap mosaic to determine how the nutritional environment and reproductive effort affect sheep grazing decisions when faced with this trade-off. There were 3 animal treatments (Barren ewes, ewes suckling a single lamb, and ewes suckling twin lambs) and 2 environment treatments (low and high nitrogen). Sward selection and grazing behavior were measured using focal observations on grazing ewes. Sheep showed an overall strong and significant avoidance of tussocks across all treatments. However, there was a reduction in the avoidance of tussocks by ewes on the low-nitrogen (low-N) plots. Ewes suckling twins showed a reduced avoidance of tussocks compared with barren ewes. Lactating ewes in low-N environments further reduced their avoidance of tussocks. Ewes with twins, which are at greatest risk from parasites, had the greatest contact with feces and thus parasites, especially in low-N environments. We conclude that twinbearing ewes accept the increased risk of parasitism in order to gain the nutrients required to support increased reproductive effort, thus increasing their investment in current offspring at the cost of increased risk of parasitism and thus future potential reproductive attempts. Key words: feces avoidance, fitness, grazing, maternal investment, parasite risk. [Behav Ecol]

Effects of protein supply and reproductive status on local and systemic immune responses to Teladorsagia circumcincta in sheep

The effects of protein supply and reproductive status on circulating antibody responses and local inflammatory cell counts were investigated in parasitized sheep, with local immune responses assessed through a recently refined abomasal cannulation methodology. We hypothesized that if breakdown of immunity has a nutritional basis, then protein scarcity would result in a breakdown of immunity to Teladorsagia circumcincta in both periparturient and non-reproducing (barren) ewes. Twin-bearing and barren, abomasally cannulated ewes were fed at either 0.8 or 1.3 times protein requirements from 3 weeks before until 6 weeks after parturition ( n = 6). All sheep were trickle infected at a rate of 10,000 infective larvae (L 3) per day, for 3 days per week throughout the experiment. Faecal egg counts remained virtually zero in all barren ewes, whilst protein supplementation reduced faecal egg counts in the periparturient ewes during most of the periparturient period. Final worm burdens, taken at 6 weeks into lactation, were lower for the barren ewes than for the lactating ewes, whilst protein supplementation reduced worm burdens in the latter. Protein supply did not affect mucosal mast cell counts, which were consistently higher for the barren ewes than the periparturient ewes, but were temporarily decreased around parturition. Barren ewes and protein supplemented lactating ewes had higher globule leukocyte counts than the unsupplemented lactating ewes. Protein supplementation increased eosinophil counts in the lactating ewes though only during the later part of the lactation period. Plasma IgA anti-L 3 antibody was similar for all ewes, but IgE anti-L 3 antibody was higher for the protein supplemented periparturient ewes compared to the unsupplemented periparturient ewes and all barren ewes. It is likely that the combination of low protein requirements and large body protein reserves did not result in breakdown of immunity to T. circumcincta for the barren ewes. These results suggest that changes in mucosal mast cell and eosinophil counts are not necessarily associated with changes in host resistance to T. circumcincta. However, the data support the view that increased globule leukocyte counts and plasma IgE anti-L 3 antibody may be associated with nutritionally improved expression of immunity in periparturient ewes.

Seasonal changes in tissue weights in Scottish Blackface ewes over multiple production cycles

AbstractHill ewes undergo large changes in body fat and muscle weight throughout the annual production cycle as they contend with the pressures of reproduction and lactation, as well as harsh environmental conditions. This study modelled seasonal changes in fat and muscle weights in Scottish Blackface hill ewes throughout their productive lifetime using random regression statistical techniques.Scottish Blackface ewes (no. = 308) were scanned using computed tomography (CT) four times per year, from 2 until 5 years old. Heritabilities of tissue weights were estimated at 2-weekly intervals throughout the productive life of the ewe. Genetic correlations between tissue weights at the same point in the production cycle at different ages, and between tissue weights at different events within each annual production cycle were predicted. Animal solutions from random regression analyses were used to estimate tissue weights, from pre-mating at 2 years old to weaning at 5 years old. The effects of litter size in the current and previous production years on fat and muscle weights were investigated.Correlations between CT tissue weights and those predicted by a sin/cos random regression model were 0.87, 0.84, 0.88 for carcass fat, internal fat and muscle respectively. Heritabilities ranged from 0.31 to 0.90 for carcass fat weight, 0.21 to 0.68 for internal fat weight and 0.26 to 0.57 for muscle weight, throughout the productive lifetime of the ewe. Heritabilities were highest during mating for fat weights, and during the dry period and lambing time for muscle weights. Heritabilities of tissue weights in 3-year-old ewes were higher than in other age groups. Genetic correlations were 1.00 between tissue weights at the same scanning event at different ages, but ranged from close to zero to 0.97 between scanning events within age groups. Clearly environmental variation across time was large. The number of lambs produced in both the current and the previous year influenced tissue levels. Ewes that did not produce lambs (barren) in a given year carried more muscle during that year than ewes producing lambs. As ewes aged, barren ewes carried increasingly more carcass fat and muscle than ewes with lambs. Barren ewes also had significantly more muscle during the following year than ewes that had weaned lambs. Ewes that reared twins had significantly less carcass fat the following year than singleton-bearing or barren ewes. These effects of previous litter size increased significantly with age.

Evaluation of Ewe Performance in 795 Selected Sheep Flocks in South-Eastern Norway

A study of ewe performance was undertaken in 795 sheep flocks based on data from the Norwegian Sheep Recording System. Herd level data included in the annual report for 1998 were used as the basis for the study. Average flock size was 75.3 ewes. The material was considered as representative of the better and more motivated sheep farmers in the mountain valley regions in south-eastern Norway. The average number of lambs born per ewe, inclusive (and exclusive) of barren ewes, was 1.89 (2.02), and of autumn lambs (those surviving from birth in the spring to autumn) 1.60 (1.66). The average autumn weight of the lambs corrected to 145 days of age was 42.4 kg, giving an overall performance of 67.9 kg lambs live weight per ewe. When including artificially reared lambs, overall performance was 70.4 kg per ewe.Artificial rearing of lambs, mostly triplets which had been removed from the ewe, was practised on 395 of the farms. In the 74 flocks with a rate of artificial rearing of more than 10% of all lambs, overall performance per ewe was 13.3 kg higher than in flocks with no artificial rearing. Total lamb mortality from birth to autumn recording, including stillborn lambs, was 12.44%. Mortality had a skewed distribution, some flocks having very high mortality figures. The arithmetic means (and medians) for mortality were as follows: 2.75 (2.29)% stillbirths, 2.93 (2.30)% died during the indoor feeding period, 0.88 (0.00)% at spring pasture, and 6.16 (4.40)% at summer pasture. In regression models using Proc Genmod in SAS®, it was found that average number of autumn lambs per ewe was negatively associated with the rate of barren ewes, late lambing date (flock average day in year when lambing took place), and total lamb mortality. The corrected autumn weight of the lambs was positively associated with the average number of lambs born per ewe and non-fertility rate, and negatively associated with flock size and total lamb mortality. The Dala breed had a positive effect on number of autumn lambs per ewe, and Spæl breed a negative effect on corrected autumn live weight of the lambs.