Performance of Djallonké Sheep under an Extensive System of Production in Faranah,Guinea

A total of 147 ewes, 4 rams and 188 lambs of their progeny of the Djallonké breed of sheep were used to study the factors affecting reproductive and growth traits and the causes of lamb mortality. Data on ewes were collected during a 12-month period, while those on the lambs born to 123 of the ewes were collected until they were 12 months of age. The average fertility and abortion rates were 0.84 and 0.09. The fertility rate increased and the abortion rate decreased with increasing age of the ewes (p<0.05). The number of lambs born per ewe joined, litter weight at birth per ewe joined and litter weight at weaning per ewe joined were 1.28, 3.5 kg and 17 kg, respectively. The average numbers of lambs born per ewe, lambs born alive per ewe, lambs born dead per ewe and lambs per ewe that died between birth and weaning were 1.53, 1.43, 0.03 and 0.3, respectively. The age of the ewes significantly (p<0.05) affected all these traits except the number of dead lambs and the index of fertility (94%). The age of the ewes significantly (p<0.05) affected the birth weight and the weight at 6 and 12 months of age, whereas the lambing season significantly (p<0.05) affected all the growth traits studied. The type of birth was the most important source of variation in body weights of lambs. Sex had no significant (p>0.05) effect on the growth traits studied. The complex `starvation–bad management–light body weight at birth' caused 48% of the lamb mortality between birth and weaning, while diarrhoea, pneumonia and internal and external parasites caused approximately 52% of the lamb mortality over the same period. The seasonal raw mortality rate of the lambs before weaning was highest in the humid season.     

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

Abstract

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.     

Evaluation of the ovine callipyge locus: IV. Genotypic effects on reproductive traits

A resource population of ewes derived from Dorset and Romanov grandparents was generated over 5 yr to provide genotypic and phenotypic data to estimate effects of each callipyge genotype on component traits of reproduction. Effects on ovulation rate were estimated from data recorded by examination of ovaries from serially slaughtered ewe lambs (n = 174) born in 1994 and 1995. Productivity and longevity through 5 yr of age were recorded on a total of 265 F2 ewes produced in 1996 through 1998. Number of lambs born, birth weights, and weaning weights of lambs were calculated for each ewe. Weaning weight was recorded for each lamb and adjusted for age to 56 and 32 d for dam- and nursery-reared lambs, respectively. Longevity was determined as a binary trait based on the presence or absence of the ewe in the breeding flock at 5 yr of age. Ewes generated 937 records for breeding weight and 925 records for conception rate, which was determined on ewes exposed and still present at the start of each lambing season. Seven hundred seventeen records were analyzed for traits based on the number of ewes lambing. Genotypes for the causative callipyge mutation were determined using a matrix-assisted laser desorption/ionization time-of-flight mass spectrometry assay. Each ewe was classified into 1 of 4 genotypes; NMatNPat, NMatCPat, CMatNPat, or CMatCPat, where N represents wild type and C represents the mutant allele. The mean ovulation rate of the ewe lambs genotyped NMatNPat was greater (P < 0.02) than that exhibited by NMatCPat; however, the estimated difference of 0.25 ovum in the ewe lambs did not affect the number born. The live weight of NMatCPat ewes at breeding was 2.5 kg less than that of other genotypes (P < 0.01). The callipyge genotype class did not significantly affect conception rates, fecundity, maternal ability, or ewe longevity. Maintaining a ewe flock to produce homozygous mutant rams for use in terminal sire mating systems presents no unusual problems from a reproduction standpoint.     

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.     

Factors affecting productivity of Rambouillet ewes mated to ram lambs

Objectives of this study were to estimate the magnitude of the effects of various factors associated with ewes and their ram lamb mates on fertility, prolificacy, lamb survival, lamb weaning weight and ewe productivity and to estimate the heritability and repeatability of each trait. Records from 731 ewe-years, 75 ram lamb sires and 616 lambs born from the University of Illinois Rambouillet flock were used. Ewes mated to single-born ram lambs had higher fertility rates (P less than .01), gave birth to lambs with higher survival rates (P less than .01), weaned lighter (P less than .05) individual lambs but weaned more weight of lamb per ewe exposed (P less than .01) than ewes mated to multiple-born ram lambs. Ram lamb breeding weight, ram lamb scrotal circumference, ewe breeding weight and ewe age had relatively large and positive effects on the composite trait of weight of lamb weaned per ewe exposed and significant effects on a number of the component traits. Heritability and repeatability estimates were, respectively, as follows: fertility, 3%, 3%; prolificacy, 34%, 19%; lamb survival, 15%, 8%; lamb weaning weight, 7%, 36%; and ewe productivity, 27%, 10%.     

Straightbred comparison of a composite population and the Suffolk breed for performance traits of sheep

A terminal sire Composite population was formed by mating Columbia rams to Hampshire-Suffolk crossbred ewes. Subsequent generations were produced by inter se mating. The objective was to compare Composite sheep to purebred Suffolks for numerous performance traits. Young ewes lambing at 1 yr of age were evaluated separately from mature ewes (2, 3, 4, and 5 yr old) of each population. Composite and Suffolk populations did not differ significantly in components of litter weaning weight per young ewe joined. Mature Composite ewes produced more wool than Suffolk ewes. Fertility of mature ewes did not differ significantly between populations. The greater prolificacy (P less than .01) of mature Suffolk ewes was offset by a lower survival to weaning (P less than .01), particularly for twin-born lambs. Consequently, mature Composite and Suffolk ewes did not differ for number weaned and litter weaning weight per ewe joined. The average birth weight of lambs born to young and mature Composite ewes was greater (P less than .02) than the average birth weight of Suffolk lambs. The average weaning weight of lambs born to young Composite ewes was greater (P less than .05) than that of lambs born to young Suffolk ewes. Breed differences were not detected for preweaning daily gains, weaning weights, and postweaning daily gains of ewe lambs born to mature ewes. Likewise, weights of ewes at 125 d of age and weights of mature ewes at breeding did not differ significantly between breeds.(ABSTRACT TRUNCATED AT 250 WORDS)     

Individual animal risk factors for clinical mastitis in meat sheep in Norway

An m:n matched case–control study was conducted to identify risk factors for ovine clinical mastitis (CM). Data were from a national sheep registry and only ewes that lambed in the spring of 2004 were included. Eligible cases (n = 2857) and controls (n = 76,716) from 1056 flocks of meat sheep were matched on flock and conditional logistic regression was used for analysis of the data. CM risk was associated with age of the ewe and whether or not assistance at lambing was needed owing to dystocia; however, the effects of both these factors were modified by the number of lambs born. In ewes with 1 lamb, increasing age was associated with increased odds of CM (OR = 1.2 for each 1-year increase), while only a slight numerical increase in the odds was observed in ewes with >1 lamb. Dystocia was associated with increased odds of CM in ewes with 1 lamb (OR = 1.7) or 2 lambs (OR = 1.4), while no association was observed in ewes with >2 lambs. The odds of CM increased markedly with increasing number of lambs born to the ewe. For example, odds for 2-year-old ewes without dystocia were 6.7 times greater for those with >3 lambs than for those with 1 lamb. Compared with ewes of old Norwegian breeds, ewes of other breeds were more likely to experience CM (OR = 1.7). Ewes treated for CM at least once during the preceding 3 years had 4.0 times greater odds of CM compared with ewes without a CM history. It is likely that the effect estimates from this study, which are adjusted for breed and unaffected by inter-flock variations, are valid also for other meat sheep populations.     

Reproduction rate and viability of Merino,Nilagiri and halfbred Merino. I. Fertility,prolificacy and viability

Summary Lambing records from 482 Merino ewes, 533 Nilagiri ewes and 192 halfbred Merino ewes were used to estimate the number of ewes lambing per ewe inseminated, number of lambs born per ewe lambing, number of lambs weaned per lamb born and number of ewe lambs reaching joining age per ewe lamb weaned. Adult viability was studied by following through the life of 385 Merino ewes, 192 Nilagiri ewes and 61 halfbred ewes in the breeding flock from one and a half to seven and a half years of age. The genetic groups differed significantly for all the reproductive traits but not for adult viability. Lower values of number of ewes lambing per ewe inseminated compared to the number weaned and the number reaching joining age indicate that infertility and embryonic mortality were the main sources of loss.

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Resumen Se utilizaron registros de nacimiento de 482 ovejas Merino, 533 ovejas Nilagiri y 192 ovejas Merino media sangre, para estimar el número de partos por oveja inseminada, número de corderos nacidos por parto, número de corderos destetados por corderos nacidos y número de corderos en edad de monta por cordero destetado. La viabilidad adulta se estudió siguiendo a través del tiempo, 385 ovejas Merino, 192 ovejas Nilagiri y 61 ovejas media sangre. La observación empezó al a?o y medio de vida, y continuó hasta los siete y medio a?os. Todos los grupos genéticos fueron significativamente diferentes en todos los aspectos reproductivos, más no en la viabilidad adulta. Los valores más bajos de número de partos por oveja inseminada, comparados al número destetado y al número de corderos en edad de monta, indican que la infertilidad y mortalidad embrionaria fueron las principales causas de dicha pérdida.

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Résumé On a utilisé les données d’agnelage de 482 brebis merinos, 533 Nilagiri et 192 métis mérinos pour estimer le nombre de brebis agnelant par rapport à celles inséminées, le nombre d’agneaux nés par brebis agnelant, le nombre d’agneaux sevrés par rapport aux agneaux nés et le nombre de jeunes brebis atteignant l’age de la lutte par rapport à celles sevrées. La viabilité des adultes a été étudiée en suivant au long de leur vie 385 brebis mérinos, 192 Nilagiri et 61 métis d’un troupeau d’élevage; l’age se répartissant de 1 an et demi à 7 ans et demi. Les groupes génétiques se différencient pour tous les paramètres de production mais non pour la viabilité à l’age adulte. La comparaison des valeurs les plus basses du nombre de brebis agnelant par rapport à celles inséminées, avec le nombre d’agneaux sevrés et le nombre atteignant l’age d’accomplement indique que l’infertilité et la mortalité des embryons sont les principales causes de perte.

     

Reproductive performance of Suffolk and Suffolk-cross ewes and ewe lambs exposed to vasectomized rams before breeding

Multiparous Suffolk and Suffolk-cross ewes were randomly allotted to treatments within breed and year to measure effects of ram exposure, during transition from anestrus to breeding activity, on reproductive performance. Treatments were: 1) ewes joined with two mature vasectomized Rambouillet rams for 15 d before breeding (DC), 2) ewes maintained across a net wire fence from two vasectomized rams for 15 d before breeding (FC) and 3) ewes maintained approximately 400 m away from rams (NC). At the end of the 15 d, all ewes were placed in one pasture and mated to three fertile Suffolk rams during a 34-d breeding season. A total of 96 Suffolk and 177 Suffolk-cross ewes was utilized during the 3-yr experiment. A greater (P less than .05) prebreeding ovulation percentage was observed in DC and FC than in NC ewes. Mating and lambing occurred approximately 6 d earlier for DC or FC ewes than for NC ewes. A similarly designed experiment was conducted using Suffolk and Suffolk-cross ewe lambs allotted to treatments within breed and year to measure effects of ram exposure during the natural breeding season, but prior to breeding. Treatment differences were not detected (P greater than .05) for date of first observed estrus, date of lambing, percentage of ewes lambing in the first 17 d of the lambing season, number of lambs born per ewe lamb exposed or number of lambs born per ewe lamb giving birth.     

Lamb wool shedding is a good predictor of ewe wool shedding

Interest in reducing labour costs due to shearing has led to development of breed types that shed their wool naturally. Selection at young ages can facilitate response. Reliability of predictions of adult from lamb wool shedding (WS) is thus key in the design of breeding programmes to increase shedding. Our objectives were to estimate heritabilities and genetic relationships between WS measured once in lambs and repeatedly in ewes and to assess the accuracy of lamb WS EBV to predict ewe WS EBV based on a multi-trait threshold or a repeatability model. Data were 4,971 lamb and 3,335 ewe WS records on a Romanov, White Dorper and Katahdin composite flock. For the multivariate model, WS heritability ranged from 0.47 ± 0.03 in lambs to 0.59 ± 0.04 at 1 year of age. For the repeatability model, WS in adult ewes was moderately heritable (0.50 ± 0.03) and repeatable (0.60 ± 0.02). Genetic correlations were 0.72 ± 0.04, 0.65 ± 0.05, 0.50 ± 0.09 and 0.51 ± 0.09 between lamb WS and 1st through 4th record, respectively. Given the moderately high heritability and high correlations between WS performance in lambs and ewes, selecting animals early in life would effectively increase WS in crossbred flocks.     

Evaluation of Dorset, Finnsheep, Romanov, Texel, and Montadale breeds of sheep: II. Reproduction of F1 ewes in fall mating seasons

Objectives were to estimate effects of sire breed (Dorset, Finnsheep, Romanov, Texel, and Montadale), dam breed (Composite III and northwestern whiteface), mating season (August, October, and December), ewe age (1, 2, and 3 yr), and their interactions on reproductive traits of F1 ewes. A total of 1,799 F1 ewes produced 3,849 litters from 4,804 exposures to Suffolk rams during 35-d mating seasons over 3 yr. Ewes were weighed at breeding. Conception rate and ewe longevity (present or absent at 42 mo of age) were determined. Number born and litter birth weight were recorded, and number and weight at weaning and 20 wk of age were analyzed separately for dam- and nursery-reared litter mates. Total productivity through 3 yr of age for each ewe entering the breeding flock was calculated as the sum of 20-wk weights for dam- or nursery-reared lambs. Interactions of sire breed x mating season, sire breed x ewe age, and mating season x ewe age were generally significant, whereas interactions of sire breed, mating season, and ewe age x dam breed were seldom detected. Interactions of sire breed x mating season were often due to changes in rank as well as magnitude, indicating the importance of matching sire breed to a specific mating season. The number born to Dorset-, Texel-, and Montadale-sired ewes was not affected by dam breed; however, Finnsheep-sired ewes out of northwestern whiteface dams were more prolific than Finnsheep-sired ewes out of Composite III dams, and the opposite situation existed for Romanov-sired ewes. Least squares means of sire breeds (P < 0.001) for total productivity of dam-reared lambs were 98.5, 103.5, 106.9, 124.6, and 154.9 kg/ewe entering the breeding flock for Texel, Dorset, Montadale, Finnsheep, and Romanov, respectively. Superior reproduction of Romanov-sired ewes was due to greater conception rate and prolificacy for each mating season and ewe age, as well as greater ewe longevity. Total productivity of F1 ewes by Composite III dams (125.6 kg) was greater (P < 0.001) than for ewes born to northwestern whiteface dams (109.7 kg), and the effect of mating season increased (P < 0.001) from August to October to December. Litter weight at 20 wk of age of 2- and 3-yr-old ewes was similar but greater (P < 0.001) than for 1-yr-old ewes. Experimental results provide comprehensive information about the appropriate use of these breeds in crossbreeding systems to meet specific production-marketing objectives.     

Effectiveness of photoperiod stimulation on reproductive performance of sheep housed continuously indoors on an accelerated breeding schedule.

Over five breeding periods, the reproductive performance (fertility, prolificacy and fecundity) of three strains of sheep housed continuously indoors was measured. The sheep were maintained as two separate flocks, A and B, with similar genetic background on an eight month accelerated breeding schedule under one of three lighting regimes, abrupt, contracted or constant, to induce ovarian activity. Overall fertility to one estrus was 59%. For flock A, fertility was greatest under the contracted lighting regime and lowest under the constant lighting regime; the opposite was true for flock B. Among the three strains, fertility was lowest for the Dam 2 strain in flock A. Prolificacy averaged 1.8 lambs per ewe lambing and was similar under each of the three lighting regimes. Fecundity (averaging 106%), the number of lambs born per 100 ewes exposed to rams, generally followed the pattern of fertility.     

Lifetime production of 1/4 and 1/2 Finnsheep ewes from Rambouillet, Targhee and Columbia dams as affected by natural attrition

Lifetime production of first-generation 1/4 and 1/2 Finnsheep crossbred ewes from Rambouillet (R), Targhee (T) and Columbia (C) dams was compared with that from randomly selected purebred R, T and C ewes. All 1,190 ewes, representing nine breed groups, were managed under range conditions and mated annually to Suffolk rams. Lifetime production was evaluated as the total lamb and total wool production per ewe from the time each entered the breeding flock at 7 mo of age through the period each remained in the flock (potentially seven producing years). Culling was for debilitating unsoundness only. The study was designed to determine the average lifetime production per breed group as affected by natural ewe attrition. Orphan-reared lambs were not included in lamb production nor were foster lambs, except those actually born in and reared by the groups. Differences among pooled breed groups (1/4 Finns, 1/2 Finns and purebreds) were not significant for average final age in the flock (5.1, 5.1 and 4.9 yr, respectively), but differences were significant (P less than .01) for lifetime lamb and wool production. Average lifetime fleece weights of 1/4 and 1/2 Finn ewes were only 95 and 82% as high, respectively, as those of purebreds. However, 1/4 and 1/2 Finn ewes had 34 and 46%, respectively, higher numbers of lambs weaned (at 130 d) and 30 and 38% higher total weight of lamb weaned than purebreds.(ABSTRACT TRUNCATED AT 250 WORDS)     

An investigation of the possible effects of subclinical iodine deficiency on ewe fertility and perinatal lamb mortality

A controlled supplementation trial was performed in an assumed iodine-deficient Romney ewe flock in the Manawatu. Significantly more twin litters were born to iodine-supplemented ewes than to control ewes. Furthermore, the perinatal mortality rate in lambs born to iodine-supplemented dams was significantly lower than in lambs born to control dams. Ewe age and the use of different lambing paddocks for iodine-supplemented and control ewes may have been confounding factors. In both iodine-supplemented and control ewes, serum T₃ and T₄ concentration values remained above the currently used “normal” range throughout the trial period.     

Relationships among Puberty,Muscle and Fat,and Liveweight Gain during Mating in Young Female Sheep

Greater depths of muscle are associated with better reproductive performance in ewe lambs, but, in adult ewes, reproductive performance also seems to vary with liveweight gain during the mating period. Therefore, in a large field study with Merino ewe lambs, we tested whether the relationships among eye muscle depth (EMD), fat depth (FAT) and reproductive performance depend on liveweight gain during the mating period. We selected lambs with a wide range in phenotypic values for depths of eye muscle (EMD) and fat (FAT) and assigned them to dietary treatments designed to achieve low (LOW, n = 244) or high (HIGH, n = 237) rates of liveweight gain during a 28‐day mating period. The LOW treatment maintained live weight, whereas the HIGH treatment gained 179 ± 3.8 g/day (p < 0.001). From those ewe lambs that attained puberty, first oestrus was detected at live weight 37.8 ± 0.2 kg and age 232 days. The proportion of ewes that attained puberty increased with EMD (p < 0.01). Ewes from the HIGH treatment were more fertile (pregnant ewes per 100 ewes exposed to rams) and had a higher reproductive rate (foetuses in utero per 100 ewes exposed to rams; p < 0.001) than those from the LOW treatment. Fertility and reproductive rate were positively correlated with weight gain during mating as well as live weight at the start of mating, FAT and EMD (p < 0.05 to <0.001). We conclude that faster growth, due to either extra nutrition during mating or higher phenotypic potential for fat and muscle, will increase reproductive performance in ewe lambs mated at 8 months of age.     

Effects of sarcoptic mange on the reproductive performance of ewes and transmission of Sarcoptes scabiei to newborn lambs

In each of two experiments, the reproductive performance of ewes naturally infested with sarcoptic mange and of uninfested ewes was assessed in in-season natural breeding conditions (experiment I) or in out-of-season controlled breeding conditions (experiment II). A statistically significant difference was observed in the total lambs born per ewe (infested ewes, 1.2; controls, 1.6), in the liveborn lambs per ewe (infested ewes, 1.2; controls, 1.5) and in the lamb body weight per ewe (infested ewes, 3.33kg; controls, 4.53kg) under natural breeding conditions, as well as in the lamb body weight per ewe (infested ewes, 3.37kg; controls, 4.14kg) among ewes under controlled breeding conditions. No adverse effects were observed in the other reproductive indices, cycling rate, mating rate, return-to-oestrus rate, abortion rate, lambing rate and stillbirth rate. Sarcoptic mange was observed in the offspring of infested ewes after 30 days and in the offspring of uninfested controls 60 days after their birth.     

Comparison of Booroola Merino and Finnsheep: effects on productivity of mates and performance of crossbred lambs

Booroola Merino (BM) and Finnsheep (FS) rams were mated to FS and crossbred (CO) ewes to compare their effects on the productivity of their mates and the performance of their progeny. Effects of breed of ram and the interaction of breed of ram X breed of ewe were no significant for fertility, total number born, number born alive, litter birth weight, or number of lambs weaned by the ewe or in the nursery. Birth weights of FS- and BM-sired lambs were equal, but FS-sired lambs were heavier at weaning and 147 d of age. Compared with BM-sired lambs, survival from birth to weaning of dam-reared lambs was greater for FS-sired lambs produced by CO dams than for FS-sired lambs produced by FS dams. At a constant live weight, FS-sired lambs had a heavier carcass with less external fat thickness than BM-sired lambs. Percentage of ewe lambs reaching puberty was lowest and age at puberty was highest for the BM X CO cross; relatively small differences existed between the other three genotypes for these traits. Ewe lambs sired by BM had a greater ovulation rate than FS-sired ewe lambs. Embryo mortality was greater in BM X CO ewe lambs than in ewe lambs of the other three genotypes; the difference was larger for ewes with three ovulations than for ewes with two ovulations. The net result was that BM X CO ewe lambs averaged slightly fewer lambs born than FS X CO ewes. The BM X FS ewe lambs had larger litters than the FS ewes due to a substantially higher ovulation rate and only a slightly lower overall embryo survival rate. With the exception of ovulation rate and litter size, FS rams produced lambs with a more desirable level of performance than did BM rams.     

Genetic effects on ewe productivity of crossing D'man and Sardi breeds of sheep

Data from 364 ewes of Sardi (S), D'man (D), S x DS, DS x S, S x D, D x S (F1), F2, D x DS and DS x D breed groups mated to F1 rams were analyzed for fertility, number of lambs born alive, litter size at weaning, litter weight at weaning per ewe joined and mean lamb weight at 60 d. Each ewe was exposed in two seasons and had one or two lambings. Effects of breed group were significant for all traits. The highest number of lambs born alive and litter size at weaning were recorded in D'man (1.84 and 1.45, respectively) and D x DS (1.81 and 1.43, respectively). F1 ewes (S x D and D x S) had the highest fertility (.94) and litter weight at weaning per ewe exposed (13.8 kg). Mean lamb weight at 60 d was highest for S x DS and Sardi ewes (13.4 kg and 13.2 kg). D'man additive effects were positive and significant for number of lambs born alive, litter size at weaning and litter weight at weaning per ewe joined; were significant but negative for mean lamb weight at 60 d; and were not significant, although positive, for fertility. Significant individual heterosis was found for fertility, litter weight weaned and mean lamb weight at 60 d. Maternal heterosis and direct epistatic recombination effects were small for all traits.     

Prevalence and effect of subclinical ovine progressive pneumonia virus infection on ewe wool and lamb production

The prevalence of infection with ovine progressive pneumonia (OPP) virus and its effects on ewe wool and lamb production were investigated in a flock of 2,976 ewes of 6 breed types (Rambouillet, Targhee, Columbia, Polypay, 1/4 cross Finnsheep, and 1/2 cross Finnsheep). Prevalence of seropositivity was significantly (P less than or equal to 0.01) lower among Rambouillet and Targhee breeds (44 and 42%, respectively), intermediate in Polypay, Columbia, and 1/4 cross Finnsheep (approximately 53%), and higher among 1/2 cross Finnsheep (62%). Seropositivity increased with age in all breed types from 11% at 1 year of age to 93% at greater than or equal to 7 years of age. Lateral disease transmission is indicated by linear increase of seropositivity prevalence with increasing age, including that in sheep greater than 6 years old. Subclinical infection with OPP virus had no apparent detrimental effect on number of lambs born, lamb viability, birth weight, number of lambs weaned, or growth rate of single and twin lambs, compared with findings for noninfected sheep in the same flock. Mature ewe body weight and grease fleece weight did not differ between subclinically infected seropositive and seronegative ewes. Subclinical infection with OPP virus does not appear to have an adverse economic effect on ewe wool and lamb production. Culling rate attributable to clinical manifestation of infection with OPP virus must be accurately determined before the true effects of virus infection on production can be determined and an eradication program can be recommended.     

Frequent lambing of sheep flocks in Spain: productivity and management consequences

The first part of this paper reviews the Spanish literature dealing with the possibility of increased lambing frequency in Spanish flocks. Seasonal anoestrus occurs in all the Spanish breeds considered, although even in the most unfavourable month some sexual activity is observed, such as in Aragonesa flocks, where it reaches up to 80% in some years. The percentage of cyclical ewes in spring is favourably influenced by good feeding levels and by the introduction of males previously removed from the flock for a few months.In the second part we deal with the results obtained in several commercial farms in Aragon differing in mating management. No hormone treatments are used in these farms. In the farms where orderly and short matings are practised more lambings (1.39 vs. 1.29) and more lambs/ewe/year (1.76 vs. 1.40) are obtained than in those with continuous or nearly continuous mating periods. They can also choose the most favourable dates to obtain their lambs with regard to sale prices and ewe supplementary feed costs. In these conditions, Romanov × Aragonesa ewes give 40% more lambs/ewe than Aragonesa ewes without decreasing the number of lambings per year.