Mid-piece length of spermatozoa in different cattle breeds and its relationship to fertility.

Recently positive correlation has been found between oxygen consumption (ZO2) in bull spermatozoa and non-return rates and concluded that an increase in ZO2, characteristic of the freeze/thaw process, was possibly associated with mitochondrial membrane damage during this procedure: alternatively, sperm may be hyperactivated through the capacitation-like effects of freezing/thawing. We speculated that the morphology of spermatozoa may be associated with their rate of ZO2 and fertility: for example, sperm mid-piece length where mitochondria are located. Such a relationship has not been investigated before, particularly in context of commercial cattle breeding programmes and bull fertility characteristics. Sperm biometry was performed on ejaculates obtained from 34 bulls representing six breeds: Holstein (yearlings and mature), Friesian, Belgian Blue, Aberdeen Angus, Charolais and Limousin. Five ejaculates were collected from every bull and from each sample a semen smear was fixed and stained with eosin/nigrosin: the mid-piece length of 40 sperm with normal morphology was measured in every sample. Data were analysed by breed, age and within each bull. Significant differences (p<0.01) between ejaculates in 9/34 bulls was found, as well as differences (p