Peripheral blood lymphocyte subsets in fleece rot-resistant and -susceptible sheep

Objective To compare haematological values and lymphocyte phenotypes in the peripheral blood of fleece rot-resistant and -susceptible sheep.
Procedure Experiments were conducted on 2- and 3-year-old Merino rams, flock 1 (17 rams) and flock 2 (32 rams), respectively. Within each flock, individual rams were classified as fleece rot-resistant or -susceptible, based on established criteria. Total and differential white cell counts, and indirect fluorescent antibody tests specific for B cells and T cells were performed on all sheep. The concentration of various subsets of circulating lymphocytes was then determined in each sheep.
Results There were no significant differences between fleece rot-resistant and -susceptible sheep from either flock in the mean total or differential white cell counts. However, fleece rot-resistant rams in flock 1 did have a significantly higher concentration of circulating SBU-T1⁺ cells than fleece rot-susceptible rams from the same flock. No such difference was noted in the rams from flock 2. While all rams in flock 1 were free of clinical fleece rot, 24 rams in flock 2 (comprising all 17 fleece rot-susceptible and 7 of 15 fleece rot-resistant animals) had clinical signs of the disease. Fleece rot-free rams in this flock (irrespective of their classification as fleece rot-resistant or -susceptible) had significantly higher concentrations of circulating SBU-T1⁺ cells compared with fleece rot-affected animals. They also had significantly higher concentrations of circulating B cells, and total lymphocytes.
Conclusions An examination of peripheral blood lymphocyte subsets in fleece rot-resistant and -susceptible sheep revealed a possible association between resistance to fleece rot and the concentration of circulating SBU-T1⁺ cells.     

Epidermolysis bullosa in German black headed mutton sheep

In three flocks, 13 pure- and 1 crossbred German black headed mutton lambs were ascertained which had clinical signs of epidermolysis bullosa (EB). The three farmers reported of further 20 affected lambs with similar signs in their flocks in the past lambing seasons. The affected lambs were progeny of six rams and 17 ewes. Two rams and six ewes with affected offspring from two farms were used for a breeding trial. In the course of these experimental matings, 21 lambs were born, six of which were affected by EB. All lambs born in this trial underwent clinical and haematological examination and all the affected lambs had to be euthanised due to severe and progressing clinical symptoms. Clinical examinations in 20 affected lambs revealed shedding of claw horn, erosions and ulcers of skin and mucous membranes. Histopathology showed subepidermal splitting and blistering with intact basal keratinocytes. These findings together with the premature death of affected lambs within the first two months of life made a Herlitz type of junctional EB most likely. The results of the test matings demonstrated the genetic transmission and indicated an autosomal recessive mode of inheritance for this lethal condition.     

Comparison of Finnish landrace crossbred ewes with Columbia, Rambouillet and Targhee ewes on western range

The objective of this study was to compare reproductive efficiency and wool production of 1/4 Finn crossbred ewes with straightbred Columbia, Rambouillet and Targhee ewes. In Phase I, white-faces ewes (WF; Columbia, Rambouillet and Targhee) were bred to either rams of their own breed or Finnish Landrace X Rambouillet rams (F X R) to produce 821 lambs from 563 lambings. Ewes bred to F X R had similar average litter size and individual lamb weights at birth, 60 d and weaning as those bred to WF. Lambs sired by F X R had 7% higher (P less than .01) lamb weaned per ewe lambing for ewes bred to F X R rams. For Phase II, approximately equal numbers of F X R-sired (1/4Fx) and WF-sired female lambs produced in Phase I each year were exposed to Suffolk rams at yearly intervals beginning at 7 mo of age. At 1 yr of age, 1/4Fx had higher fertility (P less than .01) than WF (37.7% vs 1.3%), resulting in 14.0 kg more lamb weaned per ewe exposed to breeding. Mature (ages 2 to 6 yr) 1/4Fx ewes had similar fertility to mature WF ewes, but litter size, number of lambs at 60 d and weaning was .36, .24 and .22 lambs higher (P less than .01), respectively, for mature 1/4Fx. Progeny of 1/4Fx were lighter at birth (P less than .01), but not different (P greater than .05) at 60 d and weaning than those of WF. Survival to 60 d unadjusted and adjusted for birth weight was 4.6% (P less than .05) and 7.6% (P less than .01) higher, respectively, for 1/4Fx progeny than for WF progeny.(ABSTRACT TRUNCATED AT 250 WORDS)     

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.     

Relationship between sexual behavior classifications of rams and lambs sired in a competitive breeding environment

The objectives for this study were to 1) determine the relationship between sexual performance class and lambs sired in a competitive mating environment, and 2) determine whether the male-oriented ram test is valid. Fifteen 2- to 3-yr-old whitefaced rams classified as female-oriented, with high or low sexual performance, or classified as male-oriented were used in a multiple-sire breeding arrangement. Five groups of approximately 200 ewes each were exposed for 21 d to 3 rams per group consisting of 1 ram from each class. Rams were blocked for sexual class, and those with close genetic relationship were assigned to different pens. Genomic DNA was prepared from blood collected from 15 rams, 934 ewes, and 1,757 lambs. Up to 4 microsatellite markers were used to determine a lamb's sire. Of 884 ewes with identifiable lambs (known sires), 178 ewes had single lambs, 408 had multiples sired by 1 ram, and 298 had multiples sired by more than 1 ram. The sexual partner preference test used to identify male-oriented rams did not absolutely reflect their sexual performance during competitive breeding. In contrast to only mounting and servicing males in preference tests before breeding, male-oriented rams sired 480 lambs from 330 ewes. Serving capacity tests predicted sexual performance of high and low sexual performance rams. High performance rams impregnated more ewes (499 vs. 258; P < 0.05) and sired more lambs (756 vs. 357; P < 0.05) than did low performance rams, respectively. Low performance and male-oriented rams did not differ for ewes impregnated or lambs sired. We conclude that 1) sexual partner preference tests used to classify male-oriented rams were not absolute in reflecting their breeding performance in a competitive breeding environment; 2) serving capacity tests predicted that high performance rams would breed more ewes than low performance rams and sire more lambs than either low performance or male-oriented rams; and 3) under the conditions of this study, low performance and male-oriented rams did not have an adverse impact on the overall breeding outcome. Combined, low performance and male-oriented rams sired 81 more lambs than did high performance rams, but this required twice as many rams to obtain approximately equal breeding results. Therefore, we suggest that serving capacity tests should be used to select high performance rams, reduce number of rams with marginal sexual performance, and make decisions on ram numbers needed.     

Broomfield Corriedales: a strain of sheep selectively bred for resistance to footrot

Broomfield Corriedales originate from a 15-year programme of selective breeding from sheep that evaded footrot when deliberately subjected to field challenge. To determine whether this policy may have resulted in improved resistance to footrot, trials were set up in which representative animals from the Broomfield blood-line were challenged with footrot by either experimental or natural infection, together with Corriedale sheep of similar age and sex but from flocks in which the disease is not known to occur. In another approach, the occurrence of footrot was compared in the offspring of Broomfield and of non-Broomfield sires mated with randomly selected ewes in a commercial Corriedale flock in which the condition was prevalent. Finally, the effects of natural challenge in Broomfield lambs were compared with those in a selection line of Corriedale lambs of which both parents had a history of chronic footrot disease. Footrot affected significantly fewer sheep of the Broomfield blood-line and to a markedly lesser degree than those chosen for comparison under identical challenge conditions. Where present, foot infections in Broomfield animals also tended to be less invasive and less persistent. Reduced footrot prevalence was also demonstrated in three birth cohorts of first-cross offspring of Broomfield sires relative to the offspring of other sires, though differences were not significant at all inspections. These findings, considered as a supplement to the historical development of the Broomfield flock, offer encouraging prospects for breeding programmes to enhance the resistance of sheep to footrot disease.     

Progeny test of ram lambs selected for low ultrasonic backfat thickness or high post-weaning growth rate

Ram lambs were selected from a total of 1206 lambs in 8 industry Coopworth ram breeding flocks. Eight rams were selected randomly (one from each flock), 8 were selected on the basis of a low live weight-adjusted ultrasonic backfat thickness (lean) and 8 for a high post-weaning growth rate (PW gain). Rams from a Coopworth line specially selected and bred for low ultrasonic backfat (lean selection) were also included in the progeny test in which the rams were single sire mated to 1.5 year old Coopworth ewes. Birth and weaning weights were recorded for a total of 474 female and 371 male progeny. The males (progeny of 31 sires) were slaughtered between January and April at an average hot carcass weight (HCW) of 12.56 kg and carcass growth and carcass fatness parameters recorded. The carcass composition data were analysed using the allometric equation by covariance on HCW. The adjusted mean values of carcass water content were significantly higher for the progeny of the lean selection rams (7.58 kg) than forthe other 3 sire classes (7.49, 7.46 and 7.41 for the lean, PW gain and controls respectively) indicating that they were leaner. Other indicators of carcass fatness also revealed marked differences between the sire classes. There were also marked effects of slaughter date with lambs slaughtered earlier being leaner (after adjustment for HCW) than lambs slaughtered later in the season. The results indicate that selection of sires on the basis of ultrasonic backfat thickness or post weaning live weight gain can be expected to result in the production of leaner lamb carcasses.     

Perinatal mortality in lambs of ewes exposed to cultures of Diplodia maydis (= Stenocarpella maydis) during gestation.

During 1987 when cob rot was rife, perinatal losses were reported in flocks and herds that had been exposed to diplodiosis. The affected lambs or calves were either stillborn or died soon after birth. Dosing trials at the Onderstepoort Veterinary Research Institute involving 82 ewes revealed that 66% of the offspring of dams exposed to cultures of Diplodia maydis (= Stenocarpella maydis) in the second trimester of pregnancy and 87% of lambs of ewes exposed in the third trimester were born dead or died soon afterwards. A status spongiosus similar to that of the field cases was present in the white matter of the brains of all the affected lambs. The lambs of ewes that had shown nervous signs and those of ewes that had not shown such signs were equally affected. The experiments also clearly demonstrated that foetuses were much more susceptible to diplodiosis than the adults, e.g. in the third trimester 87% of the lambs were affected compared to only 44% of the dams. No perinatal mortalities were recorded in the group exposed to the culture in the first trimester. Ewes developed significant resistance to intoxication after initial exposure to the culture and both the length of gestation and birth mass of the affected lambs were less than those of their untreated counterparts.     

BMPR-IB基因在寒泊羊群体中的增羔效应、遗传规律及育种应用分析

旨在揭示BMPR-IB基因在寒泊羊种群中的多态性及遗传学规律,探讨将BMPR-IB基因第746位碱基发生的A→G突变（FecB突变）作为分子标记进行绵羊多胎品种选育的科学性。本研究对寒泊羊育种核心群的健康种公羊、繁殖母羊、羔羊共计1 267只绵羊个体进行采血,利用PCR-RFLP方法判定个体BMPR-IB基因位点的基因型并进行群体遗传学分析。对繁殖母羊共计980胎次的产羔记录进行统计,分析FecB突变、胎次及产羔季节对胎产羔数性状的影响。统计所设计杂交组合后代共计167只健康羔羊的基因型比例。结果表明,BMPR-IB基因在寒泊羊种群中有BB、B+和++3种基因型,其基因型频率分别为1.97%、73.40%和24.63%,等位基因B和+的频率分别为38.67%、61.33%;BB、B+和++基因型繁殖母羊的平均胎产羔数分别为2.69、1.91、1.57只,目前寒泊羊种群的胎产羔数平均为1.85只;若经过品种选育使寒泊羊个体中增加一个B基因拷贝,胎产羔数预期增加0.44只;父母本杂交组合为B+×++的后代中B+和++基因型的比例为1.11：1,父母本杂交组合为B+×BB的后代中BB和B+基因型的比例为0.82：1,均符合孟德尔分离定律;预测经过6个世代的选育,可使寒泊羊种群母羊基本实现胎产羔数2只的育种目标。本研究结果为绵羊育种实践中制定选种和选配方案提供了理论基础。     

Efficacy of a multivalent Bacteroides nodosus vaccine against foot rot in sheep in Britain

A multivalent Bacteroides nodosus foot rot vaccine was tested by comparing the prevalence of foot rot in 317 vaccinated ewes and lambs with the prevalence in 422 unvaccinated control sheep. The vaccine conferred statistically significant protection against foot rot. The vaccine also demonstrated a therapeutic effect in animals with foot rot, after one injection.     

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.     

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)     

Effects of alternative lamb production systems, terminal sire breed, and maternal line on ewe productivity and its components.

The 4 yr productivity of 25% (QF; n = 533) and 50% (HF; n = 531) Finnsheep ewes exposed to either Suffolk or Columbia rams in one of three production systems was monitored to test the effects of system, terminal sire breed, maternal line, and their interactions on annual market lamb production. Ewe lambs and yearlings were randomly assigned to either a high-input accelerated lambing system (HIGH), a high-input annual system (MED), or a low-input annual system (LOW). Nursery facilities were available for weak lambs or those born in triplet or more births for the HIGH and MED but not for the LOW systems. Accelerated lambing protocol required early weaning. Sex-adjusted lamb weaning weights were corrected to within-system mean ages of 42 d for HIGH and 70 d for MED and LOW. The HIGH ewes weaned 1.55 lambs per year compared with 1.46 for MED and 1.18 for LOW (P less than .01). However, because of early weaning, HIGH yielded the lowest weight of weaned lamb per year. The MED ewes weaned 5.9 and 11.1 more kilograms of lamb per year than the LOW and HIGH ewes, respectively (P less than .01). The HIGH system may be economically feasible if young lambs could be inexpensively grown to feeder or market lamb weight. The HIGH ewes did not, however, increase lamb numbers in proportion to increased exposures compared with the annual systems. Breed-group effects for ewe productivity (kilogram of lamb weaned per ewe per year) were consistent across management systems, although some interactions among breed group and system were present for components of productivity. Suffolk rams yielded an advantage of 1.6 kg of weaned lamb per exposure over Columbia rams (P less than .05) due to a 3% better lamb survival (P less than .01) and heavier weaning weight, especially in the LOW system. The HF ewes weaned .1 more lambs per exposure than QF ewes (P less than .01); .06 of the lambs were nursery-reared. However, lambs from HF ewes had a 2% lower survival rate (P less than .05) and were 1.4 kg lighter at weaning (P less than .01), so overall productivity among HF and QF ewes was similar.     

The development of a new breed of sheep in Colombia

A new breed of sheep has been developed in Colombia by crossing Scottish Blackface rams with the indigenous Criolla ewes and then interbreeding the progeny, with selection based on performance. It has been given the name Manchada Paramuna. The breed has been developed to provide the small producer (campesino) with a breeding ewe which has a high level of fertility, a good fleece, and which produces lambs with high survival rate and good growth rate.     

Effects of ram preexposure and ram breed on fertility of ewes in summer breeding

Suffolk x Rambouillet ewes were used in two consecutive years to test the ability of Dorset and Suffolk yearling rams to stimulate ovulation and estrus in early summer (late June and July) breeding. After spring weaning about June 1, ewes were randomly divided into three groups and for 2 wk either were isolated from rams or were preexposed to either yearling Dorset or Suffolk rams by penning of rams in proximity to ewes. Ewes then were rerandomized into two groups for joining with either yearling Dorset or Suffolk rams fitted with marking harnesses. Serum progesterone profiles and crayon marks were used as indicators of ovulation and estrus. Overall lambing rate was not different among preexposure treatments for the 2 yr. However, early lambing rate (in the first 14 d of lambing season) was significantly affected by preexposure group (24% for Dorset vs 9% for Suffolk and 10% for isolation), especially in the 2nd yr (31% for Dorset vs 8% for both Suffolk and isolation). Ewes preexposed to Dorsets also lambed 10 d earlier (P less than .05) than ewes preexposed to Suffolks in yr 2, but the groups did not differ in yr 1. Ewes exposed to Dorset rams for breeding had higher overall lambing rates than ewes bred to Suffolks (75% vs 54%), especially in the 1st yr (77% vs 48%). Lambs sired by Dorset rams were born 6 d earlier in yr 1 (P less than .05) but only 1 d earlier in yr 2. Data from both years indicate that Dorsets are superior to Suffolks in ability to sire lambs in fall lambing systems.     

SELENIUM - RESPONSIVE UNTHRIFTINESS OF YOUNG MERINO SHEEP IN CENTRAL VICTORIA

A trial was carried out to determine whether selenium responsive unthriftiness existed on a property in the Strathbogie ranges of Central Victoria where unthriftiness of young sheep has been a problem for 10 to 20 years. White muscle disease had been diagnosed on the property in the previous year and on other properties in the area. Eighty Merino ewes and lambs were allotted to one of 4 groups in a 2 x 2 factorial designed trial in which sodium selenite (0.1 mg/kg) was given orally to ewes and/or lambs at marking time and to treated lambs at 3 monthly intervals thereafter. Selenium treatment of the ewes had no significant effect on subsequent lamb performance. Selenium treatment of the lambs produced significant responses: mortality in treated groups was 0% compared with 17.5% in untreated groups; body weight gains were 1.9 kg higher at both weaning and one year of age in treated than in untreated lambs; mean fleece weight was 14.4% higher in treated lambs and they produced 39% more wool than the surviving untreated lambs.     

Synchronization of estrus and reproductive performance of ewes treated with synthetic progestogens administered by subcutaneous ear implant or by intravaginal sponge pessary

Experiments were conducted to compare the efficacy of synthetic progestogens administered by subcutaneous ear implant or intravaginal sponge to induce a synchronized estrus in adult ewes and ewe lambs and to evaluate reproductive performance (fertility and litter size) to breeding at the synchronized estrus. Experimental animals were representative of three strains maintained in total confinement and exposed to a synthetic light regimen which alternated at intervals of 4 mo from 18 h day length to 10 h day length/24 h. Treatments were applied at different times of the year at the end of a low light cycle. Implants contained Norgestomet (3 mg) impregnated in a polymethacrylate polymer (Implant H) or impregnated in a silastic polymer containing 1.05 (Implant S1), 1.78 (Implant S2) or 2.60 mg (Implant S3) Norgestomet, respectively. Intravaginal sponges contained 40 mg Fluorogestone Acetate. Implants or sponges were left in situ for 12 d and 500 IU pregnant mares' serum gonadotropin was injected im at the time of removal. Following treatment with Implant H, 96% of ewes were judged to be in estrus at 48 h after implant removal. Fertility of adult ewes and ewe lambs (6 to 7 mo of age at time of breeding) at the synchronized estrus were similar after implant H or sponge treatment, but litter size was higher (P less than .05) for adult ewes treated with sponges. The percentages of adult ewes marked by rams within 60 h after removal of silastic implants or intravaginal sponges were similar. There was a tendency for ewe lambs to be marked later than adult ewes and for adult ewes treated with Implant S1 and Implant S2 to be marked earlier than ewes treated with Implant S3 or sponges. Higher percentages (P less than .05) of adult ewes and ewe lambs lambed to breeding at the synchronized estrus after treatment with Implant S2 or Implant S3, respectively, than after treatment with Implants S2 or sponges.     

Transmitted effect of purebred versus crossbred rams on rate and variability of lamb growth

The performance of 457 fall-, 510 winter-and 640 summer-born lambs from several years was examined to compare the progeny of purebred Hampshire (H) or Suffolk (S) and crossbred (S X H or H X S) rams for mean and variability of growth rate. Eight rams (four crossbred and four purebred) were mated to white-faced crossbred ewes each season with a total of 37 rams represented in the study. Individual rams were exposed to approximately 30 ewes each season. Purebred-sired lambs were slightly heavier at birth than crossbred-sired lambs averaged over seasons (P = .10). The differences in birth weight between purebred- and crossbred-sired lambs were .08 kg (P = .28); .15 kg (P = .20) and .13 kg (P = .03) for fall, winter and summer seasons, respectively. For 70-d weight and average daily gain from weaning to market weight (ADG), the differences between purebred- and crossbred-sired lambs were not consistent over seasons. Purebred-sired lambs were 1.62 kg heavier (P = .02) at 70 d of age for the winter season, but were .26 (P = .44) and .27 kg (P = .48) lighter than crossbred-sired lambs for the fall and summer lambing seasons, respectively. Differences in ADG between lambs sired by purebred and crossbred rams were -27 (P = .01), 35 (P = .01) and 5 g/d (P = .28) for fall, winter and summer seasons, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)     

Stochastic simulation of Manchega sheep breed selection scheme. Impact of artificial insemination, progeny testing system and nucleus size on genetic progress and inbreeding

Manchega is a local Spanish sheep breed located in the region of Castilla la Mancha, Actually there are 0.8 million of milked ewes. The selection scheme of Manchega breed (ESROM) started in 1988, involving a selection nucleus composed by 103,887 ewes distributed in 106 flocks. Results obtained from the ESROM has been moderate in comparison with other similar European schemes. By this and other reasons, to develop a specific tool to study the ESROM system seems to be necessary.

The objectives of this work were to develop a genetic simulation model based on the ESROM real system and to study the effects on genetic progress and inbreeding level achieved from different rates of AI used, the progeny test system and the selection nucleus size.

An additive infinitesimal model was assumed for the trait 120 days Total Milk Yield (TMY). Five alternatives selection criteria (two per each group of animals to be selected), differentiated on their selection intensities, were associated to the selection of lambs for future artificial insemination rams, natural mating rams and ewes. All selection decisions were based on periodical genetic evaluations (BLUP), using an animal model with repeated measures. 60 specific cases were studied, each one with 20 replicates.

An average true genetic progress per year ranging from 1.04% to 2.10% in AI rams and 0.59% to 2.11% in ewes were observed. Results of phenotypic progress varied from 0.44% to 1.83% per year. True inbreeding levels of ewes at year 17 were between 0.218% and 1.879%.

The model used had the expected behavior. In general, the studied selection scheme had its better results (maximum genetic progress), when AI rate was equal or greater than 50%, a greater number of new rams were tested per year (75 and 44) and a selection nucleus size equal or greater than 9000 ewes (30 flocks). Selection intensity of natural mating rams had a great impact on the genetic progress, especially when the use of AI was low. The greater the nucleus size, the higher the genetic progress, but an operative scheme from around 9000 initial ewes could be established.

Results observed demonstrate the existence of some critical areas, which could be verified on the real system in order to improve their effectiveness. In this framework, the ESROM could develop two complementary strategies: to improve the selection system of Natural Mating Rams (selecting only sons of AI rams) and/or to increase the levels of AI until 50%.     

Detection of polymorphisms in the prion protein gene in a population of Irish Suffolk sheep

Natural scrapie is associated with polymorphisms in the prion protein (PrP) gene. In Suffolks, codon 171 is the codon at which most variation is found; RR171 is thought to be associated with resistance to developing the clinical signs of the disease and QQ171 is associated with susceptibility to the disease. The objectives of this study were first to determine the PrP genotypes of Suffolk stock rams in Ireland, and secondly to compare the genotype profiles of ram lambs from flocks where a breeding programme based on the genotype AA136RR154RR171 had been initiated and from flocks where there was no breeding programme based on PrP genotype. Approximately 13 per cent of the stock rams genotyped in the Irish population were genetically susceptible to showing the clinical signs of the disease. However, lambs from farms that had initiated a selective breeding strategy for RR171 over the past year had a larger proportion of RR171 and a smaller proportion of QQ171 than the stock rams or ram lambs from farms not applying a breeding strategy.