Effects of egg of origin and chick post-hatch nutrition on broiler live performance and meat yields

The weight of hatching eggs can influence broiler live performance regardle ss of hen age. Egg composition is altered with egg weight, but such alterat ions do not seem to have major effects on broiler growth and processing yie lds. The chick hatches with a yolk sac which provides nutrients for the tra nsition to independent feeding. Alterations in egg weight and composition d o not affect the proportion of yolk sac to body weight as much as its compo sition, particularly with eggs from very young hens. The contents of the yo lk sac are high in fat and protein but very low in carbohydrate, which coul d lead to ketosis with prolonged fasting. Enhancing the first feed with eit her carbohydrate or gluconeogenics such as propionic acid may alleviate thi s ketosis and help early development. The digestive system of the chick is physically complete at hatching but is not fully competent at nutrient retr ieval as many enterocytes are orientated to immunoglobulin uptake. Villi le ngth and enzymatic activity increases with feeding, reaching maturity withi n a few weeks. Access to food and water after hatching varies, and long del ays until placement are common. These delays cause losses in live performan ce. Loss in body weight due to late placement or undernutrition may also af fect early muscle development. These adverse effects extend to marketing ag e and reduced meat yield. Factors that affect early chick development are g aining interest as the length of time to market progressively decreases and the chick's first days represent an increasing proportion of the total tim e for production.