Leptin is a 16-kDa protein that is synthesized by adipose tissue and is involved in regulation of feed intake, energy balance, fertility and immune functions. It has been shown that leptin gene influences milk performance in cattle -Liefers et al., 2002-. Leptin is related to both energy metabolism and reproduction and it was shown that leptin polymorphisms had significant effect on calving interval and weight at first calving in beef cows -Almeida et al., 2003-. In cattle, the leptin gene is located on chromosome 4 and consists of three exons. The aim of this study was to indicate polymorphism at the bovine leptin gene locus in Iranian Holstein dairy cows and its contribution to the first cumulative 60- d milk yield, 305-d milk yield, days to first breeding -DFB-, days open -DO-, and days from first breeding to conception -DFBC- in the previous lactations.

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