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This study compares two groups of 23 and 24 goats with different CSN1S1 genotypes, matched for lactation number and stage. During the first experimental period (4 weeks) half of the goats of each genotype received the control diet (CT) and the second half received a similar diet containing extruded linseed (EL diet). During the second experimental period, the two groups of goats were switched from the CT to the EL diet and from the EL to the CT diet, respectively. Results confirm the lower milk protein (-4.8 g/kg) and fat (-6.5 g/kg) concentrations in the low genotype group, whereas milk yield was slightly higher (+0.49 kg/d) and lactose concentration was unchanged. Between the genotype groups, there were differences in milk fat proportions of at least 25 FAs, particularly the C7 to C13 saturated FAs and C16:0, C18:0, C18:2n-6 and cis9,trans11-C18:2 acids. In addition, delta-9 desaturation ratios were higher in the low CSN1S1 group for C10:0, C14:0, C18:0, trans11-C18:1 and trans13-C18:1. This strongly suggests an effect on mammary delta-9 desaturase activity, especially for C18:0 and trans11-C18:1. It is likely that higher desaturation ratios in the low genotype, as well as observed changes in other FAs, could compensate for the lower synthesis of medium-chain FAs (C7:0-C13:0), thus contributing to maintenance of the melting point of milk fat in this genotype. The effect of the EL diet on milk FA proportions was highly significant for almost all FAs, along with increased milk fat content and decreased post-milking free FA concentration. Numerous interactions (significant but Of limited quantitative extent) between the CSN1S1 genotype and EL feeding were shown on milk composition, including 26 FA proportions or delta-9 desaturation ratios, and post-milking free FA concentration. (C) 2013 Elsevier B.V. All rights reserved.

International audience; The objective of this study was to evaluate genetic and non-genetic factors influencing characteristics of young buck semen production using a multivariate model that takes into account the longitudinal structure of data. Data were collected from 1989 to 2002 at two French A.I. centres. The data corresponded to 13151 and 9206 ejaculates of 758 Alpine and 535 Saanen bucks respectively, collected at the beginning of the first breeding season (September–December). The semen volume, the total number of spermatozoa, the concentration, the motility score of spermatozoa after freezing and the percentage of motile spermatozoa after freezing were registered for each ejaculate. Within-breed heritabilities and repeatabilities were estimated using a multivariate animal model using a power spatial covariance structure for environmental effect. For all characteristics and the two breeds, the main source of variation was the year–month interaction that interacted with the centre. We observed a decrease in years of motility score after freezing. Age and frequency of collection had a significant effect on semen volume and number of spermatozoa for both breeds, and on concentration of spermatozoa for the Alpine breed. No effect of these factors was found on the characteristics observed after freezing. Heritabilities for concentration, number of spermatozoa, semen volume, motility score after freezing and percentage of motile spermatozoa after freezing per ejaculate were respectively, 0.32, 0.15, 0.25, 0.12 and 0.05 for the Saanen breed and 0.34, 0.25, 0.29, 0.17 and 0.03 for the Alpine breed. Genetic correlations between volume and number of spermatozoa were respectively, 0.74 for the Alpine breed and 0.86 for the Saanen breed. Further study is required to compare the semen characteristics of young bucks with their mature production.