The effect of photoperiod on testis weight and comb area of male broiler breeders

From the literature, it is evident that broiler breeder pullets exhibit photorefractoriness, and while it is assumed that male broiler breeders respond in a similar manner to females, it would be beneficial to determine if this is the case. This would enable lighting programmes to be designed that will ensure maximum fertility of both males and females. Male broiler breeders were housed in light-tight rooms and given constant photoperiods of 8, 10, 12, 14, 16 or 18 h/d. One or two birds were sampled from each room weekly from 71 to 232 d, and the remaining birds at 467 d, and testis weights measured. There was no significant difference between left and right testis weights, so the average was used in the analyses. Digital images of the head were recorded prior to slaughter and of four birds in each room weekly. The area of the comb was measured using image analysis software. The relationship between comb area and average testis weight was determined by regression analysis, with a logistic curve being best at fitting the data. A positive, significant (P<0.001) relationship was observed with 69% of the variance in average testis weight being accounted for by comb area. Thus, comb area could provide a reasonable, non-invasive technique to assess fertility. At 165 d, average testis weights, as well as comb areas of birds not slaughtered, showed strong evidence that males exhibit juvenile photorefractoriness in a manner similar to females. Males on shorter photoperiods matured faster than those on photoperiods of 14 h and longer. As the birds aged, the effects of photorefractoriness wore off, but at the end of the experiment adult photorefractoriness was again evident, with birds on 14 h and longer having smaller average testis weights, and therefore, no longer responding to the stimulatory photoperiod. __________________________________________________________________________________