THE RELATIONSHIP BETWEEN BODY-WEIGHT AND REPRODUCTIVE EFFICIENCY IN MEAT-TYPE CHICKENS

With improvements in growth rate of broiler chickens, the ability of m eat-type parent stocks to reproduce has been severely reduced. Broiler breeder chickens require dedicated programs of feed restriction to ma ximize egg production and chick production. The production of settable eggs is limited by poor shell quality as a result of a lack of coordi nation of the shell calcification process, and by a high incidence of multiple-yolked eggs. The erratic nature of oviposition in full-fed he ns, evidenced by multiple ovipositions in a 24-h period and by oviposi tions occurring during the dark period, indicates that such hens do no t abide by the principles of the ovulatory cycle that are accepted for egg-type hens. Fertility is reduced in overweight broiler breeders du e to reduced mating success (which limits sperm transfer to the female ), by a reduction in the duration of fertility, and possibly by impair ed sperm transport to the site of fertilization (because the normal pa ssage of developing eggs is more random than in egg-type hens). Fertil ity can also be poor due to problems with the male, including reductio ns in semen production and libido as well as poor physical coordinatio n. Embryonic mortality is high in the eggs of overweight hens, as such eggs are often poorly calcified, which results in increased shell por osity and egg weight loss. Overweight hens exhibit short laying sequen ces and may also have poor overall chick production due to an increase d incidence of first-of-sequence eggs, which have been demonstrated to exhibit an increased incidence of embryonic mortality.