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ABSTRACT
Sheep milk fat contains several components that may provide human health benefits, such as monounsaturated fatty acids and conjugated linoleic acid (CLA). Most of the CLA in ruminant milk is synthesized in the mammary gland by the action of the enzyme stearoyl-CoA desaturase (SCD) on circulating vaccenic acid (trans-11 C18:2; VA). Previous studies have found significant associations between polymorphisms in the SCD gene and the fatty acid composition of ruminant products, including sheep milk. Based on this, we performed a quantitative trait loci (QTL) analysis of an ovine chromosome (22) that harbors the SCD gene for effects on milk fatty acid composition traits and classical milk production traits. We identified a suggestive QTL influencing the CLA/VA ratio with the maximum statistic at position 26 cM of the studied chromosome, whereas the SCD gene has been mapped to position 41.6 cM. The individual introduction of 4 SCD single nucleotide polymorphisms in the QTL model did not cause a reduction of the variance explained by the QTL, which suggests that the SCD gene is not directly responsible for the detected effect in the Churra population studied herein. This conclusion was supported by the lack of any significant association identified between the 4 SCD single nucleotide polymorphisms and the CLA/ VA ratio. This association analysis suggested a possible effect of the SCD gene on milk fat percentage in Churra sheep. An independent confirmation of these primary results will be required before attempting its practical implementation in selection programs.
Key words: quantitative trait locus, milk fatty acids, stearoyl-CoA desaturase, dairy sheep
INTRODUCTION
The fatty acid (FA) composition of ruminant milk is an important variable that affects the nutritional value of dairy products and influences their manufacturing properties (Jensen et al., 1990; Bauman et al., 2006). Sheep milk is mainly consumed as cheese, which may be considered an unhealthy product by some consumers because of its high fat content. On average, sheep milk fat comprises more than 60% saturated FA (SFA), 28% monounsaturated FA (MUFA), and 6% polyunsaturated FA (PUFA; Cabiddu et al., 2003, 2005). However, it also contains several components that may provide benefits to human health, such as MUFA and conjugated linoleic acid (CLA). Conjugated linoleic acid is a collective term for isomers of linoleic...