Intramuscular progesterone injection decreases sperm functionality and fertility in broiler breeder roosters

Chicken seminal plasma contains a high content of sex steroids including progesterone (P4). According to a published study, in vitro supplementation of P4 to the semen resulted in decreased fertility in the White Leghorn chicken; however, it is not known if increased P4 production in vivo is associated with decreased sperm fertility. Therefore, the aim of the present experiment was to study the effect of P4 injection on semen characteristics and fertility in broiler breeder chickens. Eighteen roosters and 55 laying hens of the Cobb 500 strain at 47 weeks of age were used in this experiment. Initially, semen was collected twice a week for 3 weeks and semen characteristics including the semen volume, sperm concentration, sperm motility, percentages of live and abnormal sperm, and sperm membrane integrity (using the hypo-osmotic swelling test; HOST) were determined. Then semen from each rooster inseminated to 3 hens and we evaluated sperm penetration, egg fertility and fertility duration. Subsequently, the roosters were injected with P4 (150 mg of the long-acting medroxy- progesteroneacetate) in the pectoral muscle and the above-mentioned measurements repeated. Progesterone injection decreased the sperm motility by 10%, membrane functionality (integrity) by 40%, egg fertility rate by 24% and number of days to first non-fertile egg by 3 days. However, sperm penetration of the perivitelline membrane increased about 60% (P