Effect of double interspiking on fertility, behavior, and blood parameters in broiler breeder males reared under heat stress conditions

Broiler breeders experience a natural decline in fertility levels as a flock ages. A male management practice such as double interspiking could be applied to counteract this decline. Our objective was to investigate the effects of double interspiking on flock fertility, testosterone concentrations, stress responses, and behavioral responses of broiler breeders in heat stressed environments. Two hundred and eighty-eight broiler breeder pullets and thirty-six broiler breeder roosters (Ross 708) were assigned to three groups at 21 weeks of age (WOA). All three groups were housed in slatted floor pens in which room temperature cycled from 23.8 to 30 C to mimic heat stressed environments. Double interspiking was carried out between two pens at 42 and 52 WOA. Beginning at 32 WOA, eggs were set every two weeks, candled at day 12, and percent fertility calculated. Concentrations of the hormones testosterone and corticosterone (CS) were measured by radioimmunoassays at specific time points in the experiment. Lymphocytes and heterophils were counted in order to calculate heterophil:lymphocyte (H:L) ratios. Behavior was monitored with Panasonic video cameras which recorded video footage using the Noldus MPEG Recorder from 1900 hr to 2100 hr at specific time points. Recordings were analyzed, and frequency of specific behavioral responses of individual (preening, feather ruffling, wing flapping), male-to-male (fighting, pecking, retreating), and male-to-female (attempted and completed mating) behaviors were assessed. The introduction of unfamiliar roosters resulted in a fertility increase (P<0.01) between control and spiked birds after the first interspike and a sustainment of fertility levels after the second interspike. Testosterone concentrations declined (P<0.0001) from 1.95ng/mL to 0.11ng/mL as the birds aged. Corticosterone concentrations differed among bird groups and was elevated (P=.0333) for both groups that were interspiked. H:L ratios were also different among bird groups with all birds housed in the interspiked rooms showing higher ratios. Double interspiking increased the occurrence of male-to-male interactions, but there were no significant differences in male-to-female or individual behaviors. Regardless of treatment, there was a decrease in male-to-female behaviors as the birds aged. Double interspiking does show promise as a tool to increase fertility levels in a broiler breeder flock.