Selection Flocks Research Articles

PSXI-27 Comparison of live weight, backfat depth, and loin eye muscle measurements in ewe and ram lambs

Abstract Application of ultrasound carcass trait scanning in meat animals enhances the selection efficiency and accuracy. One hundred and sixty-two mixed age Katahdin ewes were selected based on ultrasound carcass traits and bred in a high lean muscle selection (n=81) and control (n=81) flocks, respectively in December 2019. Carcass traits including loin eye area (LEA), loin eye muscle width (LEW) and depth (LED), and back-fat depth (BFD) were measured for sires, dams, and their progeny lambs. Birth weight (BW), rearing rank, sex, and weaning weight (WW=90 d) and post weaning weight (PW=120 d) were recorded for progeny. Post-weaning live weight, LEA and BFD values were calculated for deriving an expected progeny difference lists and ewe replacements. Retaining ram lambs (25% male progeny) were recorded for live weight, carcass trait scanning, and breeding values estimate at six-month old as breeding sires. There was no difference between selection and control progeny for WW, PW, BFD and LEA measurements. Means for BW, WW, PW, LEA, LEW, LED, and FBD in progeny were 3.77 ±0.56, 22.13 ±2.98, 24.48 ±3.08 kg, 5.9 ±0.1cm², 4.4 ±0.5 cm, 1.9 ±0.2 cm and 2.9 ±2.6 mm. However, the WW, PW, LEA, and LEW were measured significantly (P < 0.05) greater for ram lambs (20.6 kg, 25.5 kg, 6.1 cm², 4.5 cm) over ewe lambs (19.5 kg, 23.8 kg, 5.7 cm², 4.3 cm). Single born lambs were significantly (P < 0.01) heavier at birth, weaning and post-weaning, and measured greater value for LEA and LED than twin birth or reared lambs. The statistical analysis showed WW was significantly (P < 0.01) correlated with PW (r=0.71) and both WW and PW correlated with LEA (r=0.5) but not with BFD. The result indicates that lean animal selection using ultrasound carcass trait scanning will improve early age selection efficiency and accuracy.

Productivity and Reproductive Performance of Mixed-Age Ewes across 20 Years of Selection for Ultrafine Wool in Uruguay

This study reports the phenotypic trends for wool, growth, and reproductive traits in mixed-age ewes after twenty years of genetic selection. Data were obtained from the Merino nucleus flock in Uruguay between 1999 and 2020. Overall, the aim of this selection flock was to reduce the fiber diameter (FD) and increase both the clean fleece weight (CFW) and live weight (LW). Data on ewe wool traits, LW, body condition score (BCS), the total number of lambs weaned (TLW), and the total LW of lambs weaned (TWW) across all lambing opportunities (1–8 mating seasons) were analyzed. Between 1292 and 2063 ewes were measured, depending on the trait considered. Ewe FD decreased by approximately 3 µm (19–16 µm), whereas greasy fleece weight (GFW) increased by 0.2 kg. This improvement in wool traits was accompanied by increases in LW at mating (3 kg), decreases in BCS at mating (approximately by 1 unit), and a small positive change in TWW across years. This study demonstrated that increasing farmer income by selecting for finer wool, heavier fleeces, and heavier animals can be obtained without compromising ewe lifetime reproduction.

Phenotypic Responses to Selection for Ultrafine Wool in Uruguayan Yearling Lambs

This study evaluated the phenotypic trends for wool and growth traits of the fine Merino genetic nucleus in Uruguay. Data were collected from one-year-old lambs over a twenty-year period (1999–2018). The overall aim of the selection flock was to reduce fiber diameter with concomitant increases in fleece and live weights. Traits analyzed included fiber diameter (FD), greasy fleece weight (GFW), coefficient of variation of FD (CVfd), staple length (SL), scoured yield (SY), live weight post-shearing (LW), eye muscle area (EMA) and fat thickness (FAT). Data from approximately 5300 one-year-old male and female lambs were analyzed. During the study period, FD decreased by approximately 3 µm, whereas GFW and LW increased by at least 0.5 and 3.0 kg, respectively. There were interactions between the sex of the individual and the year for all wool traits. Except for FAT, all other traits were affected by the dam age. This study indicates that the selection program applied in the fine Merino genetic nucleus over a twenty-year period resulted in reductions in FD and increases in GFW and LW. Therefore, the results indicate it is possible to produce ultrafine wool in semi-extensive grazing systems without compromising other economically relevant traits in one-year-old lambs.

236 Comparison of ultrasound scanned loin eye muscle characteristics and back-fat depth measured in lean muscle selection and control Katahdin sheep flock

Abstract Sheep farming is an important enterprise for many farmers in US, and meat is a viable protein resource for human nutrition. However, increasing concern for health aspects of meat consumption has led consumers to demand a higher ratio of lean to fat tissues. Application of ultrasound carcass scanning in meat animal selection and marketing as a performance prediction will enhance the selection efficiency, accuracy and profitability. One hundred and sixty two mixed-age Katahdin ewes were evenly divided into a high lean muscle selection (n = 81) and control (n = 81) flock based on the prescreened ultrasound measures, including loin eye muscle area (LEA), loin eye muscle width (LEW), and depth (LED), and back-fat depth (BFD). The LEA is measured between the 12th and 13th ribs lateral and perpendicular to the vertical column and parallel to rib covering the longissimus dorsi muscle. Live animal measurements were conducted using ultrasound scanner fitted with a 3.5 MHz linear transducer (ExaGo, France) prior to fall breeding schedules. Live weight (LWT), body condition score (BCS) and FAMACHA score (FAM) were recorded. Data were analyzed using GLM procedures of SAS statistics. There was no difference between selection and control flocks for LWT, BCS and FAM; however, LEA, LEW, LED and BFD were significantly (P < 0.05) greater for the lean selection over control flock (Table 1). The correlation coefficients (P < 0.01) were found as moderate (r = 0.6) to high (r = 0.8) among LED, LEA, LEW and BFD, whereas these traits showed lower (r = 0.4) but significant (P < 0.01) correlations with LWT. The results indicate that lean muscle selection in sheep with ultrasound scanning of longissimus muscle characteristics will enhance the production efficiency and genetic gain and facilitate producing a high value meat product.

Different selection strategies for improvement of egg quality and hatching traits of Japanese quail

Abstract The present study evaluated the effect of different selection strategy (SS) on egg quality and hatching traits in four closed-bred flocks (CBF) of Japanese quail, already selected for higher 4-week body weight, and at three parental ages (PA). A total of 1620 eggs obtained from 540 quail breeders from the four CBF and three PA were used and the effects of three SS were investigated in relation to egg quality traits. For evaluation of SS on hatching traits, a total of 3240 quail hatching eggs were subjected to break out analysis. A completely randomised design in a factorial arrangement of 36 treatments with 9 replicates was applied. Treatments consisted of three selection strategies [pedigree based (PB), mass selected (MS) and random bred control (RBC)], four closed-bred flocks [Major (M), Kaleem (K), Saadat (S) and Zahid (Z)] and three parental age groups [10 (Y), 12 (P) and 14 (O) weeks]. Egg characteristics (egg weight, yolk index, Haugh unit score and shell thickness) and hatching traits (hatchability, infertile eggs, early embryonic mortality, late embryonic mortality and chick weight) were evaluated. Pedigree based selection significantly influenced hatchability, fertility, infertile eggs, early embryonic mortality, late embryonic mortality and chick weight. However, the results of different closed-bred flocks and age groups did not differ significantly. Regarding egg quality traits, significant effects of pedigree selection and closed-bred flocks were observed on yolk index and Haugh unit score. Age had significant effect on egg weight, yolk index, Haugh unit and shell thickness. It was concluded that pedigree-based selection among different age groups and closed-bred flocks had pronounced effects on egg quality and hatching traits in Japanese quail.

Transcriptome analysis unraveled potential mechanisms of resistance to Haemonchus contortus infection in Merino sheep populations bred for parasite resistance

Haemonchus contortus is one of the most pathogenic gastrointestinal nematodes in small ruminants. To understand molecular mechanisms underlying host resistance to this parasite, we used RNA-sequencing technology to compare the transcriptomic response of the abomasal tissue, the site of the host-parasite interaction, of Merino sheep bred to be either genetically resistant or susceptible to H. contortus infection. Two different selection flocks, the Haemonchus selection flock (HSF) and the Trichostrongylus selection flock (TSF), and each contains a resistant and susceptible line, were studied. The TSF flock was seemingly more responsive to both primary and repeated infections than HSF. A total of 127 and 726 genes displayed a significant difference in abundance between resistant and susceptible animals in response to a primary infection in HSF and TSF, respectively. Among them, 38 genes were significantly affected by infection in both flocks. Gene ontology (GO) enrichment of the differentially expressed genes identified in this study predicted the likely involvement of extracellular exosomes in the immune response to H. contortus infection. While the resistant lines in HSF and TSF relied on different mechanisms for the development of host resistance, adhesion and diapedesis of both agranulocytes and granulocytes, coagulation and complement cascades, and multiple pathways related to tissue repair likely played critical roles in the process. Our results offered a quantitative snapshot of changes in the host transcriptome induced by H. contortus infection and provided novel insights into molecular mechanisms of host resistance.

Effects of Multi-Trait Selection on Phenotypic and Genetic Changes in Japanese Quail (Coturnix coturnix japonica).

The present study in Japanese quail was aimed to develop multi-trait genetic selection program for a meat type sire line utilizing the mixed-model methodology. In total, 2000 pedigreed quail were formed the basis of the research where a multi-trait animal model was performed. A flock consisting of a total of 160 families (1 male: 3 female) was developed from the initial flock (base population of sire line), so as to obtain a selection flock sire line. Body weight at 5 weeks of age was chosen as a primary selection criterion in flock. The age at point of inflection derived from Gompertz growth curve, feed conversion ratio between 3 to 5 weeks of age, and carcass yield at 5 week of age were determined as selection criteria. Multi-trait BLUP methodology was carried out for genetic improvement of birds. In flock, 25 percent of males and females with highest breeding value were selected to produce next generation. Genetic parameter estimates, realized genetic parameters, selection responses, and genetic trends were obtained. Significant (P<0.01) selection responses for body weight, age at point of inflection, feed conversion ratio, and carcass yield traits on generations were observed. The results of the study revealed that the negative genetic relationships exhibited between some studied traits had overcame by modern poultry breeding methods such as selection via multi-trait BLUP.

Nutrient partitioning of Merino sheep divergently selected for genetic difference in resistance to Haemonchus contortus

This research was designed to determine if divergent genetic selection for resistance to Haemonchus contortus had produced correlated changes in the metabolism of amino-nitrogen in the absence or presence of H. contortus infection. Partitioning of amino acid-nitrogen between tissues was determined in 42 Merino weaner wethers from the CSIRO Haemonchus selection flock, increased resistance to Haemonchus (IRH), decreased resistance to Haemonchus (DRH) and random bred control (C) selection lines. Weaner wethers were fed a restricted diet (9.8MJME/kgDM, 86gMP/kgDM) calculated to allow a gain of 125g/d bodyweight throughout the experimental period and were either worm-free or trickle infected with H. contortus. At 8 weeks post-infection animals were injected with 15N-labelled duckweed directly into the abomasums. Animals were euthanased at either 6 or 24h after the injection to collect tissue samples for calculation of percentage recovery of 15N in tissue and to determine abomasal worm counts. Worm egg count and worm counts at week 8 of infection were lower in animals from the IRH line. IRH animals had a lower N digestibility, increased oxidation of amino acids and lower N balance but whole-body protein flux was unaffected. Amino acid metabolism, as assessed from 15N uptake and excretion in response to H. contortus infection, differed between IRH and DRH animals. In IRH animals a greater recovery of 15N in the thymus and abomasal smooth muscle indicated greater partitioning of amino acids towards the immune response. In DRH animals an increased recovery of 15N in the spleen, in response to infection, may be a possible adaptation. It appears that divergent selection for worm egg count has not been associated with symmetrical changes in amino acid metabolism, but rather the partitioning of amino acid resources reflects each selection line's independent response to infection.

Divergent ghrelin expression patterns in sheep genetically resistant or susceptible to gastrointestinal nematodes

Gastrointestinal nematodes are a major problem for pastoral ruminant production systems. This problem could be reduced by the application of breeding strategies that select for nematode resistant sheep, but no suitable molecular markers are available. Research selection flocks containing lines that are resistant (R) or susceptible (S) to gastrointestinal nematodes provide an excellent resource for discovering selectable markers, and for studying the underlying mechanisms of an effective anti-nematode response. In this study we have used a combination of quantitative real time PCR assays and ELISA to determine if nematode challenge impacts on the expression of the satiety-regulating hormone ghrelin. The expression responses were then compared between the selection flock R and S lines. The results show that the basal levels of ghrelin in plasma were greater than 2-fold higher in nematode naïve S line sheep. Three days after a primary nematode challenge divergent ghrelin expression patterns were observed between the selection lines, with levels increasing in R sheep while decreasing in S sheep. After a secondary challenge this trend was repeated, but following a third challenge ghrelin expression levels rose in both R and S sheep, by which time the S animals had acquired an effective immune response to the nematodes, as measured by a significant reduction in faecal egg output. Importantly, this phenomenon was observed in gene expression studies in gut tissues and also in ELISA measurements of ghrelin peptide levels in plasma. A regression analysis showed that ghrelin transcript expression in the gut accounted for >40% of the variation in faecal egg count measured following Haemonchus or Trichostrongylus infection. We therefore hypothesise that the direction of ghrelin expression (up or down) immediately following nematode exposure may play an important role in regulating the differing anti-nematode responses that occur in the R and S lines. Such differences identify ghrelin as a previously unrecognized factor influencing the acquisition of immunity to nematodes.

Rumen function and digestion of Merino sheep divergently selected for genetic difference in resistance to Haemonchus contortus

The aim of this experiment was to investigate the effect of Haemonchus contortus infection on rumen function and digestion of Merino sheep from lines divergently selected for genetic resistance to H. contortus. Rumen function and whole-tract digestibility were determined in 29 Merino weaner wethers from the CSIRO Haemonchus selection flock, increased resistance to Haemonchus (IRH), decreased resistance to Haemonchus (DRH) and random bred control (C) selection lines. Wethers were fed a restricted low quality roughage diet (5.9 MJ ME/kg DM, 29 g MP/kg DM) to maintain weight and were either uninfected (NIL) or infected with H. contortus (INF). Measurements were taken at week 7 of infection, while animals were housed in metabolic crates. Animals were then euthanased to determine abomasal worm counts. IRH had significantly lower worm egg count than DRH and C lines however, adult worm and larval counts, though lower in IRH animals, did not differ significantly. DM and OM digestibility and in sacco degradability of IRH and DRH selection lines were greater than C animals. Rumen function of animals from the IRH line was altered in response to H. contortus infection with an increase in fluid outflow and turnover rate and a decrease in propionic acid concentration. These changes may be a component of a greater host resistance and begin to explain the failure of IRH animals to translate lower worm egg count into greater bodyweight gain.

Voluntary feed intake and diet selection of Merino sheep divergently selected for genetic difference in resistance to Haemonchus contortus

This research was designed to determine if divergent selection for resistance to Haemonchus contortus had produced correlated changes in voluntary feed intake and diet selection. Voluntary feed intake, diet selection and production were determined in 54 Merino weaner rams from the CSIRO Haemonchus selection flock, increased resistance to Haemonchus (IRH), decreased resistance to Haemonchus (DRH) and random bred control (C) selection lines. Weaner rams were fed ad libitum either a high (9.2 MJ ME/kg DM, 90 g MP/kg DM) or moderate (6.3 MJ ME/kg DM, 30 g MP/kg DM) quality diet and given the choice between the two diets, when uninfected (NIL) or infected with H. contortus (INF). Symmetrical response to divergent selection for worm egg count (WEC) was not matched by a symmetrical change in feed intake and there was no difference in diet selection between selection lines. Feed intake, growth and wool production of DRH animals remained the same as that of IRH, yet DRH animals had five times greater WEC than IRH. This study begins to explain the mechanisms that allow resistant animals to effectively prevent establishment and/or development of H. contortus, by maintaining a greater immune response to infection through higher circulating eosinophils, plasma globulin and IgG 1 antibody titres. Susceptible animals have displayed resilience by improving feed conversion efficiency and increasing protein synthesis.

Expression of genes in gastrointestinal and lymphatic tissues during parasite infection in sheep genetically resistant or susceptible to Trichostrongylus colubriformis and Haemonchus contortus

Resistance to an acute gastrointestinal nematode (GIN) infection is dependent on the ability of the host to recognise the parasite and mount a protective Th2 response. It is hypothesised that lambs which are genetically susceptible to GIN will differentially up-regulate Th1-type genes and therefore remain susceptible to chronic parasitism compared with genetically resistant lambs which will differentially up-regulate Th2-type genes and clear the parasite infection. Two selection flocks, in which lines of Merino sheep produced lambs genetically resistant or susceptible to GIN, were acutely challenged once or thrice with either Haemonchus contortus or Trichostrongylus colubriformis. Faecal-egg counts (FECs), and plasma and tissue anti-parasite (H. contortus or T. colubriformis) antibody isotype responses showed that resistant animals challenged three times with T. colubriformis established a protective Th2 response (negligible FEC, IgG1 and IgE) whereas susceptible animals required multiple challenges to establish a significant IgG1 response despite FECs remaining high. Trichostrongylus colubriformis elicited a more pronounced host response than H. contortus. RNA extracted from tissues at the site of each parasite infection and associated lymph nodes were interrogated by microarray and quantitative PCR analyses to correlate host gene expression to FECs and antibody responses. The IFN-gamma inducible gene cxcl10 was up-regulated in the susceptible line of the Trichostrongylus selection flock sheep after a tertiary challenge with the parasites H. contortus and T. colubriformis. However, a uniform pattern of genes was not up-regulated in resistant animals from both selection flocks during both parasite infections, suggesting that the mode of host resistance to these parasites is different, although some similarities in host susceptibility were apparent.

Stress-strain properties of individual Merino wool fibres are minor contributors to variations in staple strength induced by genetic selection and nutritional manipulation

This paper investigates the contribution of single fibre stress-strain properties to variations in staple strength induced by both selective breeding for staple strength and nutritional manipulation. Merino weaners (n = 40), selected from ‘sound’ and ‘tender’ lines of staple strength selection flocks, were allocated to feeding regimes designed to induce liveweight changes simulating typical Mediterranean seasonal changes. Average staple strength differed by 5 N/ktex between ‘sound’ and ‘tender’ selection flocks and 18 N/ktex between extreme nutritional treatments. The force-extension properties of individual wool fibres (n = 100 per sheep) were measured using a single fibre strength meter. After normalising for differences in fibre cross-sectional area at the point of break, the key parameters used to describe the stress-strain curve for each fibre were: Young’s modulus (GPa), yield stress (MPa), stress at 15% strain (MPa), stress at break (MPa), strain at break (%) and work to break (MPa). The average stress-strain properties of single fibres differed widely between individual sheep. Stress at break ranged from 163 to 235 MPa (44% range), strain at break ranged from 21 to 44% (103% range) and work to break from 43 to 71 MPa (65% range). There were no significant differences in any of the single fibre properties between the staple strength selection flocks, nor was there any significant interaction (P &gt; 0.05) between staple strength selection flock and nutritional regimes. Nutritional regime had a significant effect on stress at break, strain at break and work to break, but none of the single fibre stress-strain properties removed any appreciable variance in staple strength over and above that accounted for by differences in along- and between-fibre diameter variation. There appears to be little scope for improvement of single fibre stress-strain properties as a means of increasing staple strength in normal production environments. Selection directly for staple strength or indirectly using the fibre diameter variability traits is an effective method to improve staple strength.

Effects of weaner nutrition on sire and flock rankings: a re-analysis of historical data

Early work in the 1950s on the wool growth response of sheep from diverse genotypes for wool production in response to varying planes of nutrition at pasture did not show the significant genotype × environment interactions exhibited in later pen studies with the same or very similar genotypes. However, this early study used a log-transformation on all traits to adjust nutritional effects for scale. Re-analysis of the original (i.e. untransformed) data shows that superior genetic merit for clean fleece weight, different sire progeny groups or selection flocks is more apparent when hogget ewes are fed a high plane of nutrition at pasture. However, only in the case of flocks was the interaction statistically significant, and this interaction was insignificant when data were either log-transformed, or when an appropriate test that accounts for scale-type effects was applied. When left untransformed, the data are, thus, in agreement with the subsequent pen studies that examined data on untransformed clean wool production.

Similar improvements in reproductive performance of male line, female line and parent stock broiler breeders genetically selected in the UK or in South America

1. Field data on the reproductive performance of parent stock and grandparent female line and male line broiler breeders were extracted from a commercial database covering the years of hatch from 1989 to 2002. The data were from the UK, Western Europe, Central and South America and Japan. Quadratic regression curves were fitted to the data to estimate the long-term phenotypic trends in total egg production, hatching egg production, chick numbers, hatchability and female mortality. 2. Changes in performance over time were similar in the UK, Western Europe and Central and South America and are consistent with the suggestion that genetic selection in separate breeding programmes in the UK (supplying the UK and Western Europe) and Brazil (serving Central and South America) was associated with similar improvements in the performance of commercial parent stock and grandparent flocks. Changes in performance in Japan (supplied from the UK) were different but recent performance was similar to those in the other regions. 3. The mean annual improvements over 10 years to 2002 for male line, female line and parent stock, respectively, were 0·4, 1·7 and 1·7 for total egg number; 0·5, 1·8 and 1·6 for hatching egg number; 0·6, 1·8 and 1·3 for total chick production; 0·25, 0·47 and 0·09% for hatchability; and −0·69, −0·05 and −0·41% for female mortality. 4. The results are consistent with claims that significant genetic change in pedigree selection (nucleus) flocks by the primary breeding company are reflected in substantial improvements in reproductive performance in commercial flocks. The presence of similar rates of improvement in different geographical regions as a result of genetic selection in two continents representing tropical and temperate regions suggests that genotype–environment interactions for reproduction traits are not important.

Transcriptional profiling ofOvis ariesidentifiesOvar-DQA1allele frequency differences between nematode-resistant and susceptible selection lines

Gastrointestinal nematodes are a major cause of disease in grazing livestock; however, individual animals differ in their response to infection. To identify genes whose expression correlates with resistance status, transcriptional profiling of resistant and susceptible sheep was undertaken. Transcription profiles were taken at three time points during the growth of lambs. The number of genes differentially expressed increased as animals were exposed to longer nematode challenge. Almost 300 genes, with a variety of functions, were differentially expressed overall, although genes more highly expressed in resistant animals typically had major histocompatibility complex (MHC) II, free radical scavenging or smooth muscle-specific functions. The Ovar-DQA1 gene was 8.4-fold more highly expressed in resistant animals. This was due in part to a higher frequency of DQA1 null alleles in susceptible animals. The null allele of DQA1 was also associated with susceptibility in a separate selection flock, presenting the hypothesis that failure to present parasite antigens to immune cells led to nematode susceptibility. To test this hypothesis, commercial rams from three breeds were genotyped for the null allele of DQA1. The homozygous null allele was associated with susceptibility in only one of the three breeds tested indicating that the null allele does not cause susceptibility to intestinal parasites per se but is probably in linkage disequilibrium with additional polymorphisms in the MHC region. A combination of these polymorphisms may contribute to susceptibility in some populations. The extent of linkage disequilibrium between polymorphisms may vary from breed to breed or population to population.

Le programme français d’éradication de la tremblante du cheptel ovin fondé sur l’utilisation de la génétique

Les travaux conduits en ovins laitiers dès 1993 dans des élevages ovins atteints de tremblante ont permis de connaître la fréquence des allèles sensibles du gène PrP selon les races considérées, vérifier le risque accru de tremblante pour ces génotypes, et tester la faisabilité d’une sélection sur le gène PrP et son efficacité sur le risque de tremblante dans les troupeaux. Ils ont ainsi contribué à l’émergence de l’outil génétique pour éradiquer la tremblante dans les élevages atteints. Depuis 2002, le programme d’éradication de la tremblante mis en place en France par le Ministère de l’Agriculture, est fondé sur le génotypage du gène PrP : il vise à éradiquer à court et moyen terme la tremblante dans les élevages atteints, tout en renforçant la résistance génétique à moyen et long terme de l’ensemble du cheptel national, compte tenu des délais de renouvellement des cheptels femelles. Avoir choisi d’asseoir le programme national de sélection sur le dispositif existant d’amélioration génétique du cheptel national, organisé dans le cadre de la loi de l’Elevage de 1966, est manifestement un point clé pour expliquer la mise en oeuvre rapide et efficace du programme dès la première année, confirmant la mobilisation massive de tous les maîtres d’oeuvre des schémas de sélection des ovins en France : les évolutions conjointes constatées pour les fréquences alléliques en faveur de l’allèle ARR, les index de sélection pour les caractères de production et les indicateurs de gestion de la variabilité génétique sont une bonne illustration de l’application des objectifs assignés aux programmes de sélection. L’encadrement national, conduit par l’INRA, l’Institut de l’Elevage et France UPRa Sélection (Unité de Promotion et de sélection de Race), s’attachera, dans les prochaines années, à vérifier et à aider à la mise en oeuvre des quatre objectifs du programme national de sélection, en particulier la fourniture de reproducteurs résistants pour les élevages atteints, la gestion de la variabilité génétique dans les noyaux de sélection et la diffusion vers les élevages de production. Ce programme repose sur les points clés d’universalité de la résistance génétique à la tremblante en situation de contamination naturelle et d’absence de porteurs sains, qu’il faudra en permanence continuer de valider.

Molecular analysis and nematode resistance association of a polymorphism at the 5′ end of the sheep IgE gene

Previous work using Southern analysis of genomic DNA detected a polymorphism at the 5′ end of the sheep and cattle IgE gene. Identical length differences found between fragments following digestion with restriction enzymes indicated that the basis for the polymorphism was an insertion/deletion event. To characterise the polymorphism, the entire cattle and sheep Cε genes were sequenced including 668 bp of 5′ untranslated DNA. Sequence comparison revealed a high degree of similarity between the ovine and bovine genes at both the nucleotide and amino acid level. A feature of the 5′ untranslated DNA was the presence of an 87 bp repeat starting at −365 upstream of the Cε start site. PCR primers were designed to span most of the 5′ untranslated sequence, including the repeat unit, and used to amplify genomic DNA from a panel of 40 sheep. Three alleles were found with frequencies of 0.7, 0.29, 0.01 which were identical to the Southern analysis results. Sequencing of the two commonest alleles revealed the basis for the polymorphism was a 36 bp deletion from the 87 bp repeat. Association studies in a sheep selection flock phenotypically assessed for parasite resistance found a highly significant association between one of the IgE alleles and resistance to the intestinal nematode parasite Trichostrongylus colubriformis ( P=0.005). Attempts to confirm this finding in two other flocks using linkage analysis and genotype association failed to find any significant associations between the IgE polymorphism and resistance to either T. colubriformis or Haemonchus contortus.

Selection for ultrafine Merino sheep in New Zealand: heritability, phenotypic and genetic correlations of live weight, fleece weight and wool characteristics in yearlings

AbstractMerino yearling records from 1988 to 1992 birth years in ultrafine wool selection and random control flocks at Tara Hills High Country Station, New Zealand were analysed for live weight, fleece weight and wool characteristics. Estimates of heritability, genetic and phenotypic correlations among traits using REML methods are presented. Heritabilities (h2) of birth, weaning, autumn, spring and summer live weights and greasy and clean fleece weights were estimated as being 0·35, 0·34, 0·44, 0·43, 0·49, 0·24 and 0·28 respectively; while h2 of yield, fibre diameter, coefficient of variation in fibre diameter, staple crimp, staple length, staple strength, position of break, resistance to compression, bulk, CIE Y and CIE Y-Z were estimated to be 0·58, 0·59, 0·60, 0·45, 0·71, 0·13, 0·18, 0·46, 0·38, 0·38 and 0·42 respectively. Genetic correlations were found to be high among the live weights but low to moderate among fleece weight and wool characteristics. Heritability estimates of fibre diameter, fibre diameter variation and staple length were found to be higher in New Zealand fine wool Merinos than most of those reported in the literature. The results indicate that selection for reduced fibre diameter will have little effect on other major production traits such as live weight and fleece weight.

Correlated responses to selection for or against facial eczema susceptibility in Romney sheep in New Zealand

Genetic selection for or against susceptibility to facial eczema (FE) in Romney sheep began in 1975, with the establishment of a resistant (R) selection flock, a susceptible (S) selection flock, and later (in 1982) a control (C) flock. For all but the initial years, rams were identified by performance testing with a sporidesmin challenge, then ranked on relative elevation of the liver enzyme, gamma glutamyltransferase (GGT), measured in serum. A different dose rate of sporidesmin was used for performance testing in the R and the S flocks, with a balanced half of the C‐flock animals being tested at each dose rate. Results are reported here up to the 1997‐born lamb crop. Mixed‐model animal‐model methods were used to determine the direct responses to selection, expressing results as breeding values for loge GGT. Correlated responses were monitored in lambs for weights, fleece weight, and survival, and in ewes for reproductive traits. Up to 1997, a 9‐fold difference in GGT concentration, 3 weeks after challenge, was achieved between the R and S lines. Selection line differences in correlated traits were significant (P < 0.01) for weaning and January weights (with the R line 5–6% lighter than the S line), whilst the R line yearlings produced 8% heavier fleeces (P < 0.05). Ewe reproductive differences among lines were small, and nonsignificant for the overall trait (numbers of lambs weaned per ewe mated), but there were significant ram differences in fertility among lines, with highest fertility in the R line. Using a multi‐variate restricted maximum likelihood analysis, genetic correlations of lamb production traits with loge GGT were consistent in sign with the selection‐line responses, i.e., for animals which were more resistant (with lower GGT), both weaning and autumn weights decreased slightly, and both yearling weight and fleece weight increased slightly.