The effect of an induced molt using a nonfasting program on bone mineralization of white leghorns.

To determine changes in bone mineralization during molt, 66-wk-old White Leghorns were assigned to either a fasted molting regimen using feed removal for 10 d, followed by the ad libitum consumption of cracked corn for 7 d and a pullet developer diet for 10 d or a nonfasted molting regimen lasting 27 d that included the ad libitum consumption of a diet containing 71% wheat middlings and 23% corn. Both molting regimens restricted light to 8 h/d, and water was provided ad libitum. At 28 d postmolt, hens from both molting treatments were returned to a regular egg-laying diet and 16 h/d of photoperiod. Control hens consumed a regular egg laying diet and were kept on 16 h/d of light throughout the study. Using dual-energy x-ray absorptiometry, bone mineral density (BMD) and bone mineral content (BMC) of the left tibia were measured in 7 live hens per treatment immediately prior to, during, and following the molt. Results showed that by 28 d postmolt, BW loss was 22 and 18% in the fasted and nonfasted molting regimens, respectively (P < or = 0.0001). Compared with premolt values, tibial BMD at 28 d postmolt decreased 35 and 18% in the fasted and nonfasted molt groups, respectively (treatment x age interaction, P < or = 0.0001). Similarly, tibial BMC values decreased 39 and 27% in the fasted and nonfasted molt groups, respectively (treatment by age interaction, P < or = 0.01). The tibial BMD and BMC of controls at 28 d postmolt were similar to premolt values. Recovery in tibial BMD and BMC of fasted and nonfasted hens occurred by 126 d postmolt with values similar to controls. These results suggest that a nonfasted molting regimen is less deleterious to tibial BMD and BMC than a fasted molting regimen.