Effect of high levels of monensin during the growing period on subsequent breeding performance of adult broiler breeders.

The breeding performance of broiler breeder chickens previously raised on high levels of monensin was evaluated. The birds were raised on concrete floors in an open-sided pullet brooding and growing house. At 21 weeks of age monensin feeding was stopped and birds were placed in the breeder house. A breeder ration formulated to contain 2,920 kcal metabolizable energy and 16% crude protein was fed to all the birds irrespective of the growing system used. A standard feeding allowance and lighting program as recommended by Indian River International was followed during the laying period. The parameters determined were body weight uniformity at 21 weeks of age, egg production, egg weight, shell weight, shell thickness, feed conversion (kilograms feed/dozen eggs), mortality, fertility, and hatchability. Assays for monensin residue in the breast muscle, liver, and abdominal fat were run at 52 weeks of age (31 weeks after monensin withdrawal). Birds grown on high levels of monensin were not as uniform in body weight at 21 weeks of age as the restricted controls. Only birds fed 400 ppm of monensin with a low protein diet during the growing period showed a significant reduction in egg production, shell weight, and shell thickness. There were no significant differences among the growing systems in mortality during lay, fertility, hatch of fertile eggs, and hatch of total eggs. Monensin was not detectable (less than .1 ppm) in the liver, abdominal fat, and breast muscle.(ABSTRACT TRUNCATED AT 250 WORDS)