Quantitation of the fertilising ability of fresh compared with frozen and thawed fowl spermatozoa.

The fertilising abilities of freshly-diluted and frozen and thawed fowl semen were compared by inseminating a wide range (0.2 to 1600 X 10(6] of doses of spermatozoa. These data demonstrated that there was a non-linear relationship between numbers of spermatozoa and the probability of fertilisation. It was concluded that a typical fertility trial, which assesses the percentage of fertile eggs laid by groups of hens inseminated with a fixed dose of semen, was inadequate for comparing the quality of semen samples. An alternative fertility trial is described, which involves assessing the numbers of spermatozoa required to fertilize a particular percentage of eggs laid. This modified method showed that the quality of frozen and thawed semen, in terms of its fertilising ability, was reduced to 1.6% of that of fresh semen.