Semen parameters and hormone concentrations in stallions subjected to long-term estrogen administration

Summary Eight pony stallions were paired by estimated daily sperm output (DSO) and randomly assigned to one of two treatments in a randomized block experiment. Stallions received 44 μg/kg BW estradiol cypionate (ECP) or an equivalent volume of physiological saline solution on alternate days during the breeding season. Blood samples collected immediately preceding each injection were assayed for luteinizing hormone (LH), estradiol-17β (E 2 ) and testosterone (T). Semen was collected twice weekly, 3.5 days apart, to evaluate sperm motility and total number of sperm per ejaculate. Prior to and after 4, 8 and 12 weeks on treatment, semen was collected once daily for 7 days to determine DSO. Data were separated into 9 periods (10 days each) for statistical analysis and subjected to analysis of variance for a randomized block design to determine treatment effects. There were no differences (p>.05) between groups for DSO or LH prior to initiation of treatment. Testosterone was higher (p 2 was higher (p 2 was higher (p .05) were seen after 60 days for DSO or after 60, 70 or 80 days for total sperm per period. ECP stallions had higher (p