No abstract

SummaryA total of 1156 records collected at three experimental farms (Agricultural Research Institute, Athalassa, Orites) from 1978 to 1981, were used to study environmental and genetic factors influencing udder characteristics and milk production in Chios sheep. All udder traits were recorded following weaning (42 ± 3 days) concurrently with the first milk recording (7 ± 3 days after weaning). Most traits studied were significantly affected by flock and year of lambing. Seasonal effects were significant for udder circumference, test-day milk and total milk production. Lactation number had a linear effect on udder circumference, udder depth, udder floor and udder quality, but a quadratic influence on milk production. Milk production was significantly affected by udder floor, but not by udder quality and milking ease.Most heritability estimates, except for udder floor (0.18 ± 0.09) and milking ease (0.01 ± 0.07), were moderate to high, ranging from 0.27 ± 0.09 to 0.83 ± 0.12. Udder depth and udder circumference, traits that probably best describe the type and volume of the udder, had moderate to high estimates of heritability and were positively correlated (genetically and phenotypically) with milk production. All three production traits (test-day, 90-day and total milk yield) had moderate to high heritability estimates and were highly correlated with each other both genetically and phenotypically.

Data on 1474 lactation records obtained from 1972 to 1978 were used to study environmental and genetic influences on production characters in the Damascus goat. Year and month of kidding had a significant effect on 90-and 150-day milk production after weaning, lactation length and litter weight at weaning (P < 0-01), but no influence on litter weight at birth. Milk production after weaning was not related to litter weight at birth or at weaning. Age of goat at kidding had a significant quadratic effect on milk production, and litter weight at birth and at weaning. No such effects were found for lactation length.Estimates of heritability, from paternal half-sib correlations, for 90-and 150-day milk production were similar (0-29 (s.e. 0-14)). The genetic correlation between 90-and 150-day milk yield (0-92 (s.e. 0-03)) was high, indicating that part and whole lactation yields are influenced by the same genes. The phenotypic correlations among milk yield traits and lactation length were also high and positive.

Data on 1542 Damascus kids, collected from 1977 to 1981, were used to study environmental and genetic factors influencing pre-weaning and post-weaning growth traits of kids. Season of birth, type of birth, sex of kid and dam lactation number were the environmental factors investigated. Phenotypic and genetic parameters were estimated from paternal half-sib correlations. The average sire family size was 17·2 kids. Single kids were heavier at birth, at weaning and at 140 days of age than twins or other multiples (P < 0·01). Male kids were heavier (P < 0·01) and grew faster (P < 0·01) than female kids from birth to 140 days of age (4·7 and 4·2 at birth, and 29·2 and 24·6 kg at 140 days, respectively). Dam lactation number significantly affected pre-weaning growth, but had no effect on the post-weaning growth rate of kids.Heritabilities for birth, weaning and 140-day weights, and pre-weaning and post-weaning growth rate, were 0·31 (s.e. 0·08), 0·27 (s.e. 0·07), 0·21 (s.e. 0·07), 0·16 (s.e. 0·06) and 0·22 (s.e. 0·07), respectively. Genetic correlations were mostly high and all positive, especially between weaning weight and 140-day weight (0·82 (s.e. 0·08)), and pre-weaning growth rate and 140-day weight (0·80 (s.e. 0·10)). The corresponding phenotypic correlations were also high and positive (0·71 and 0·67, respectively). No genetic antagonisms were found among the characters studied. Response to selection for post-weaning growth should be effective.

The objective of this work was to identify single nucleotide polymorphisms (SNP) in the ovine acetyl-coenzyme A acyltransferase 2 (ACAA2) gene and investigate their association with milk production traits. Molecular characterization was accomplished by sequencing the entire coding region and the 3' and 5' untranslated regions (UTR) of the ACAA2 gene from individuals of the Chios sheep bred in Cyprus. All exons appeared to be monomorphic except for the last exon, for which a single SNP located in the 3' UTR of the gene (HM537015:g.2982T>C) was detected. Mixed model association analysis, using SNP data from 318 animals from 104 paternal half-sib families and first-lactation phenotype and pedigree information on 2,405 ewes revealed that this SNP was significantly associated with milk yield. The significance of the SNP effect persisted when milk yield information up to the third lactation was analyzed. Both alleles at the locus segregated at similar frequencies. The T allele was associated with increased milk yield and exhibited partial dominant action. Animals with the g.2982TT or g.2982CT genotype had significantly higher milk yield than those with the g.2982CC genotype, with the g.2982T allele having an additive effect of 13.4 (± 4.7) kg and a dominance effect of 7.9 (± 6.1) kg. Based on estimated allelic effects and sample allele frequencies, the g.2982T>C SNP explained 10% of the additive genetic variance for milk yield. A putative mode of action through nutrient metabolism is discussed.