Two weeks after spiking, a decrease in fertility from 96% to 82% was observed in a 48-week-old broiler breeder flock. Hatchability in the flock was about 86%. Necropsy of 25 males revealed severe testicular atrophy in 60% of the birds. Histopathology of the testes demonstrated no spermatogenesis in most of these birds. No evidence of infectious disease was discovered, and no infectious agents were isolated. Further investigation on the farm revealed standing water in the house, due to heavy rains, and wet and caked litter; this resulted in decreased feed consumption, for at least 5 days prior to submission to the diagnostic laboratory, and a corresponding decrease in body weight of the birds. In conclusion, a combination of a recent introduction of replacement (spiking) males, poor environmental conditions, and decreased feed consumption led to the loss of weight, testicular atrophy, and decreased or no spermatogenesis in individual birds, collectively resulting in decreased flock fertility.