The effect of crude protein intake on fertility in young and old male broiler breeders.
Due to genetic selection and improvements in broiler growth traits there have been negative influences on fertility in broiler breeder parents. This is mainly related to excess body weight gain resulting in the inability to achieve successful cloacal contact during copulation and problems with the hierarchical formation of follicles in the ovary. Male broiler breeders are often fed a female ration which contains crude protein (CP) requirements for egg production, and may not be necessary for males. Protein is one of the most costly components of poultry feed, and overfeeding protein has a number of downsides. The impact of sub-fertile and unfertile males in the overall fertility of the flock could be large. Maximizing male fertility could ensure maximizing fertile egg production which would result in more broiler chicks without increasing the size of the breeding flock. The objective of this experiment was to investigate the effects of three different dietary CP intakes (96.8, 117 and 130 g CP/kg, low, medium and high respectively) on fertility in young and old male broiler breeders using some old and more recent fertility measures in an attempt to determine whether it would be justified to feed males a separate ration. Results showed that across all male ages no significant response in body weight (BW), sperm concentration and sperm mobility to dietary CP intake were seen. Although in the young males, birds on the high CP intake showed significantly (P<0.05) lower mean BWs than males on the low and medium CP intakes, and sperm mobility values were seen to be highest in birds receiving the medium CP intake across all male ages. The log number of inner perivitelline layer (IPVL) sperm holes was seen to increase with increasing CP intake (P<0.001) in males between 42 and 62 weeks of age (WOA) but showed no response in males from 27-41 WOA. The log number of IPVL sperm holes was seen to generally decrease with age in males from 27-60 WOA; however eggs collected two days postartificial insemination (PAI) had a similar log number of IPVL sperm holes, regardless of treatment, throughout the study. The mean number of IPVL sperm holes was seen to decrease as days PAI increased. There was a tendency for a superior response in fertility, predicted from IPVL sperm holes, from birds on the medium protein intake.