A male sheep linkage map comprising 191 microsatellites was generated from a single family of 510 Awassi-Merino backcross progeny. Except for ovine chromosomes 1, 2, 10 and 17, all other chromosomes yielded a LOD score difference greater than 3.0 between the best and second-best map order. The map is on average 11% longer than the Sheep Linkage Map v4.7 male-specific map. This map was employed in quantitative trait loci (QTL) analyses on body-weight and growth-rate traits between birth and 98 weeks of age. A custom maximum likelihood program was developed to map QTL in half-sib families for non-inbred strains (QTL-MLE) and is freely available on request. The new analysis package offers the advantage of enabling QTL × fixed effect interactions to be included in the model. Fifty-four putative QTL were identified on nine chromosomes. Significant QTL with sex-specific effects (i.e. QTL × sex interaction) in the range of 0.4 to 0.7 SD were found on ovine chromosomes 1, 3, 6, 11, 21, 23, 24 and 26.
Summary Genetic aspects of antibody responses in two commercial, multivalent vaccines were examined in 2 974 Merino sheep, representing the progeny from 129 sires in four major bloodlines. All lambs were vaccinated twice, between 2 and 4 months of age, with a clostridial vaccine containing antigens against five clostridial species. Approximately half (1 239) the progeny from all sires were also vaccinated at 16 months of age, with a Dichelobacter nodosus vaccine containing whole‐cell antigens from all nine major serogroups (A–I). ELISA antibody titres to Clostridium tetani and Clostridium chauvoei were measured 2 weeks after booster vaccination. K‐agglutinating antibody titres, against all serogroups of D. nodosus, were measured on three occasions–following primary vaccination (V1), 3 and 8 weeks following booster vaccination (V2). Mean antibody titre on all three occasions (MEAN POST‐VAC), and changes in antibody titre between V1 and V2, and after V2, were analysed as additional antibody traits for D. nodosus. For both clostridial and D. nodosus antibody traits, year of birth and flock were major fixed effects. Sex of the lamb was not important in the case of clostridial antibody titres, but ewe hoggets had consistently higher D. nodosus antibody titres compared to those for ram hoggets from the same cohort. Based on restricted maximum likelihood (reml) analyses, heritability estimates for C. tetani and C. chauvoei were 0.12 (± 0.04) and 0.24 (± 0.07). Preliminary estimates for maternal effects showed additive maternal genetic variance for C. tetani and C. chauvoei (0.09 ± 0.05 and 0.17 ± 0.07). Maternal environmental effects appeared negligible. Heritability estimates of D. nodosus antibody titre for all nine serogroups ranged from 0.22 to 0.66 following V1, and were approximately 40% higher than those following V2 (range 0.17–0.44), which in turn were approximately 50% higher than estimates for persistence of titre (range 0.08–0.32). Genetic correlations for antibody titre at consecutive samplings were high, and the heritability estimates for MEAN POST‐VAC titre for each serogroup of D. nodosus were: A (0.51), B (0.58), C (0.41), D (0.24), E (0.34), F (0.33), G (0.26), H (0.34), and I (0.35). Genetic correlations for antibody titres among the nine D. nodosus serogroups ranged from moderately negative (–0.40) to strongly positive (0.87). Similarly, genetic correlations between clostridial and D. nodosus antibody titres ranged from –0.08 to 4–0.41. C. tetani antibody titre showed a genetic correlation of +0.50 with C. chauvoei titre. It was concluded that significant additive genetic variation exists in Merino sheep for vaccine response to commercial vaccines. However, there was no strong evidence for common genetic control of immune response to different antigens. Zusammenfassung Krankheitsresistenz bei Merinoshafen. V. Genetische Heterogenität der Reaktion auf Vakzine mit Dichelobacter nodosus und Klostidienantigene Genetische Aspekte de Antikörperreaktion auf zwei komerzielle multivalente Vakzinen wurden an 2...
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