Problems associated with broiler breeder entry into lay: a review and hypothesis

Aggressive (i.e. over-) feeding of broiler breeder females in the period preceding onset of lay results in higher mortality and subsequent deleterious effects on egg and chick production (the ʹover-feeding complexʹ). An intriguing aspect of the overfeeding complex is its close parallel, albeit at a lower level, to the well known ʹErratic Oviposition and Defective Egg Syndromeʹ (EODES) obtained when feeding female broiler breeders ad libitum. This is consistent with many studies showing that partial restriction (quasi-ad libitum feeding) results in partial expression of EODES (quasi-EODES). To explain the strong deleterious effects caused by rather minor over-feeding during this critical transition period, we propose that the very severe feed restriction of the growing pullet needed to prevent the onset of EODES, combined with the genetic increase in breast meat proportion achieved by intense selection over the past two decades, results in a situation where, during the critical weeks of maturation leading up to the first egg, the body lean mass must increase greatly at the same time that the ovary is maturing. During pullet maturation, empirically determined recommended feeding plans optimally balance the need to provide the rapid increase in muscle mass needed to achieve body lean mass threshold for entry into lay, with the need to maintain the ovary in a state of sufficient restriction to avoid appearance of quasi-EODES. With feed intake delicately balanced in this manner, even minor overfeeding tips the balance in the direction of quasi-EODES resulting in the appearance of the over-feeding complex. This may have been exacerbated in the past decade by a shift in the physiological control of EODES from body weight to feed intake.