Increasing persistency in lay and stabilising egg quality in longer laying cycles. What are the challenges?

Abstract

In the past 50 years, selection starting initially at the breed level and then using quantitative genetics coupled with a sophisticated breeding pyramid, has resulted in a very productive hybrid for a variety of traits associated with egg production. One major trait currently being developed further is persistency of lay and the concept of the "long life" layer. Persistency in lay however cannot be achieved without due consideration of how to sustain egg quality and the health and welfare of the birds in longer laying cycles. These multiple goals require knowledge and consideration of the bird's physiology, nutritional requirements, which vary depending on age and management system, reproductive status and choice of the selection criteria applied. The recent advent of molecular genetics offers considerable hope that these multiple elements can be balanced for the good of all in the industry including the hens. The "long life" layer, which will be capable of producing 500 eggs in a laying cycle of 100 weeks, is therefore on the horizon, bringing with it the benefits of a more efficient utilisation of diminishing resources, including land, water, raw materials for feed as well as a reduction in waste, and an overall reduced carbon footprint.

Figure 1.

Stylised representation of how increasing the laying cycle to 90–100 weeks will significantly reduce the number of multiplier hens and hence the overall shape of the breeding pyramid.

Figure 2.

Simplified summary of the endocrine control of the principle components of egg formation. Reproduction is ultimately controlled by GnRH-I neurones in the hypothalamus region of the brain which integrate environmental and internal endocrine signals (not shown). GnRH-I peptide released from the median eminence of the hypothalamus stimulates the pituitary gland (represented at the top of the diagram) to release luteinising hormone (LH) and follicle stimulating hormone (FSH). These gonadotrophins stimulate the development and growth of follicles in the left ovary. The developing follicles in turn secrete the sex steroids, oestrogen and progesterone, which are responsible for the spectacular growth of the oviduct which produces the egg white, membranes and shell. Oestrogen and progesterone also have a direct effect on the liver by initiating synthesis of the various yolk constituents and on the gut by enhancing the uptake of dietary derived calcium. Furthermore osteoblasts in the long bones start forming medullary bone rather than structural bone in response to oestrogen. The rate at which calcium is removed from the blood during egg shell formation is greater than the mean rate of calcium absorption from the diet, and the balance is made good by the mobilisation of principally medullary bone reserves.