Previous research has shown that sperm mobility is a primary determinant of fertility in fowl. Sperm mobility denotes the net movement of a sperm population, and males can be characterized by phenotype. Sperm acylcarnitine content differs between low and high sperm mobility phenotypes. The release of acyl groups from phospholipids within sperm depends on the action of the enzyme phospholipase. Inhibition of phospholipase A��� (PLA���) activity eliminates sperm motility, thereby rendering sperm immobile. This research was performed to test whether cPLA��� was expressed differentially in roosters characterized by low or high sperm mobility phenotype. cPLA��� expression in the two phenotypes was compared using reverse transcription - polymerase chain reactions. The cDNA amplified was a 352 nucleotide fragment encoding the Ca����� binding domain of cPLA���. Two sequential experiments were performed using full- and half-sib roosters. In the first experiment (n=3 full�� sibs per phenotype), cPLA��� expression was greatest in testes from the high phenotype relative to ��-actin or 18S rRNA (P < 0.05 and P < 0.0057, respectively). The average cPLA��� : ��-actin ratios for high and low sperm mobility phenotypes were 0.63 �� 0.260 (mean �� SEM) and 0.32 �� 0.123, respectively. The cPLA��� : 18S rRNA average ratios were 0.74 �� 0.158 and 0.38 �� 0.135 for high and low sperm mobility phenotypes, respectively. In the second experiment (n=6 half-sibs per phenotype), the high mobility phenotype also showed greater (P < 0.023) expression of cPLA��� relative to the 18S rRNA control with averages of 0.74 �� 0.141 and 0.49 �� 0.104 for high and low sperm mobility phenotypes, respectively. Moreover, sequence analysis of the nucleotide fragment showed no difference between phenotypes. cPLA��� expression clearly differed between sperm mobility phenotypes. It was concluded that a difference in the regulation of cPLA��� mRNA expression contributes to variation between lines of roosters generated by selection for sperm mobility. / Graduation date: 2001