Submitted to: Poultry Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/11/2005
Publication Date: 7/11/2005
Citation: Mazzuco, H., McMurtry, J.P., Kuo, A.Y., Hester, P.Y. 2005 The effect of pre- and postmolt diets high in n-3 fatty acids and molt programs on skeletal integrity and insulin-like growth factor-I of white leghorns. Poultry Science. 84:1735-1749. Interpretive Summary: Osteoporosis has been recognized as a problem in the laying hen industry for many years due to their high sustained rates of egg production. Induced molting is currently used in layer replacement programs. The molting process has been shown to have an adverse affect on layer skeletal integrity. Prior research has shown that feeding diets high in omega-3 and -6 fatty acids can improve bone integrity in growing chickens. It has been reported that these dietary fatty acids improve bone strength by raising the synthesis and secretion of insulin-like growth factor-I, a peptide hormone essential to normal bone development. This study was conducted to monitor the carry-over effect pre- and post molt diets containing high omega fatty acids on the skeletal integrity of egg laying hens, and to determine the influence of these diets on circulating growth factor concentrations. The results of this study have shown that a non-fasted molt as compared to fasted molt is less deleterious to bone mineralization, that the inclusion of omega fatty acids in the diet had little effect on skeletal integrity, and that circulating growth factor levels were profoundly affected by molting. The results of these experiments will be of interest to other scientists.
Technical Abstract: This study investigated changes in bone integrity and circulating levels of insulin-like growth factor I (IGF-I) of hens subjected to two distinct molting regimens and fed pre- and post molt diets either high or low in omega-3 fatty acids (FA). A dual energy X-ray absorptiometer determined bone mineral density (BMD) of the tibia and humerus of 45 live hens from 62 to 76 wk. Densitometric scans were also conducted in excised tibia and humerus at 66, 71, and 76 wk of age. Concentrations of IGF-I were monitored using homologous RIA at the same ages. The molting treatments consisted of 10 d fasting + cracked corn for 7 d + pullet developer diet for 10 d or a non-fasting molt (wheat-middlings based diet for 27 d). Five wk prior to and after either molt treatment, birds were fed one of two diets containing dietary omega-6/omega-3 FA ratios of 0.6 or 8.0. At the end of the molt (71 wk of age), tibial BMD drop 30% and 11% in fasted and non-fasted molt regimens, respectively, regardless of dietary FA content. The BMD of the humerus also decreased during molt with the exception of hens subjected to a non-fasted molt and fed omega-3 FA diets in which their BMD values were similar to or greater (at 73 wk of age) than controls during the entire experimental period (treatment by bone by age, P < 0.0001). Induced molt affected IGF-I (treatment by age interaction, P < 0.0001) and the response was the same regardless of molt regimen (fasting vs non-fasting). A decrease in IGF-I 54 h post molt was noted; however, from 13 to 43 d post molt, all molted birds showed elevated IGF-I as compared to controls. In conclusion, a non-fasted molt as compared to fasted molt was less deleterious to bone mineralization, dietary omega-3 ratios in the pre- and post molt diets had little effect on the decline of skeletal integrity during molt, and circulating IGF-I levels were profoundly affected by molt.