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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.

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.

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Summary — The effects of milking method (machine milking, machine milking and hand stripping, hand milking) and of post-milking suckling on milk yield and milk fat percentage of Chios ewes were investigated in 2 separate trials over a 5-wk period following weaning at 6 wks of age. The effects of post-milking suckling and creep feeding versus creep feeding alone on the growth of lambs were also examined over the same period. Differences in the commercial milk (kg per ewe over the experimental period) between milking/rearing methods in trial 1 (machine milking, 51.5; machine milking and hand stripping, 58.3; machine milking and suckling, 52.3) and in trial 2 (machine milking, 67.5; machine milking and suckling, 66.8; hand milking, 71.4; hand milking and suckling, 69.7) were not significant (P > 0.05). In addition to the commercial milk, ewes suckling their lambs after milking produced between 18.8 and 22.4 kg/ewe,. and differences in total milk (commercial plus suckled yield) between milking/rearing methods in each trial were significant (P < 0.05). In both trials, machine milked ewes sucking their lambs for 10-15 min after the morning and afternoon milkings, had a reduced fat content of commercial milk compared with ewes in the other treatment groups. In trial 2, following a post milking intravenous injection of oxytocin (2 IU), ewes on the post milking suckling treatments produced significantly more milk than those on the non-suckling treatments (0.44 vs 0.17 kg/ewe, respectively). In trial 1, the growth of the post-milking suckling group of lambs was 11.5% higher than that of the non-suckling group, while in trial 2, no treatment differences were observed in the growth of lambs.milking method / suckling after milking / milk production / lamb growth sont pas significativement affectés par la méthode de traite (P > 0,05). Mais, en plus du lait commercial, les brebis qui sont tétées par leurs agneaux après la traite, produisent entre 18.8 8 et 22.4 kglbrebis de lait supplémentaire. Ainsi, la production laitière totale (lait commercial + lait tété) deviennent elles significativement différentes, qu'il s'agisse de l'essai 1 ou de l'essai 2 (P < 0,05). Toutefois, dans les deux essais, les brebis tétées par leurs agneaux après les traites du matin et de l'après-midi, produisent un lait commercial moins riche en matières grasses. Le lait résiduel obtenu au cours de l'essai 2 après une injection intraveineuse de 2 UI d'ocytocine s'avère être supérieur chez les brebis tétées après la traite (0,44 kglbrebis) contre 0,17 kglbrebis chez celles qui ne le sont pas). Enfin, au cours de l'essai 1, la croissance des agneaux ayant été après la traite a été amélio-rée de 11,5% par rapport à celle du groupe totalement sevré, mais cette amélioration na pas été constatée au cours de l'essai 2. méthode de traite / tétée après la traite / production laitière des brebis / croissance des agneaux