Sperm number required for maximum fertility of chicken semen processed for freezing

Two independent experiments were designed to determine the number of sperm needed for maximum fertility of chicken semen processed for freezing. Pooled semen samples were either diluted 1:2 or 1:5 with the Beltsville Poultry Semen Extender, while undiluted samples served as controls. Samples were then subsequently processed (pre-freeze), according to the Beltsville method, as if they were going to be frozen. At two stages of processing, after 2-hr holding at 5 degrees C in the absence of dimethylsulfoxide (DMSO) and after an additional 2-hr holding at 5 degrees C in the presence of 4 p. 100 DMSO, aliquots were removed and tested for fertility. Each test hen was intravaginally inseminated with either 100, 300, or 600 million sperm from undiluted or processed semen samples. The number of sperm required for the undiluted controls was determined to be 100 million sperm whereas the fertility of samples processed with 4 p. 100 DMSO was significantly lower than the undiluted controls regardless of the sperm number inseminated or the dilution rate. Dilution rate did influence the number of sperm required for samples cooled for 2 hrs at 5 degrees C in the absence of DMSO. In samples diluted 1:2, 100 million sperm were needed for maximum fertility, whereas 300 million sperm were needed with samples diluted 1:5.