Influence of genetic selection for antibody production against sheep red blood cells on energy metabolism in laying hens

Genetic selection in chickens has been utilized to enhance immune responses that may influence resistance to diseases. It is important, however, to investigate the effects of this selection on other physiological processes. Therefore, this study was conducted to determine whether selection for antibody (Ab) production against SRBC has an effect on energy metabolism. Laying hens from three lines were used in this study, two of which were selected for 15 generations for Ab response against SRBC, and the third was nonselected and randombred. The hens used were from four different groups. The first two groups were from the lines that were selected for either high (SH) or low (SL) Ab production. The second two groups were control birds (nonselected) that had either high (CH) or low (CL) Ab titers that were similar to those in the SH and SL lines, respectively. The birds were housed in climate-respiration chambers. Body weights and energy metabolism were measured. Body weights of SL hens were significantly (P < 0.05) higher than those of SH hens. However, the BW for the two nonselected groups were similar but significantly less than the SL group. Energy partitioning was similar in all groups; however, ME for maintenance for the selected groups (119 kcal…kg–0.75…d–1) was numerically, but not significantly (P < 0.09), higher than that of the nonselected groups (112 kcal…kg–0.75…d–1). These results suggest that divergent selection for Ab may result in an increase in the requirements of energy for maintenance, which is not directly related to the amount of Ab produced. Furthermore, these results support previous findings of the presence of a negative correlation between BW and the levels of Ab in selected lines

Effect of melatonin and lighting schedule on energy metabolism in broiler chickens

The effect of melatonin and lighting schedule on energy metabolism in broiler chickens was studied. Eight groups of six female broiler chickens each were assigned to a continuous lighting schedule [23 h light (L):1 h darkness (D)] or an intermittent lighting schedule (1L:3D), and were fed a diet with or without melatonin (40 ppm). At 21 d of age, the chickens were placed in respiration chambers for 20 d. Energy and nitrogen balances, heat production and physical activity were measured per group. The only effect of melatonin on energy metabolism, was a decreasing effect on activity-related heat production. The intermittent lighting schedule induced improved feed conversion, higher metabolizability of the diet, and lower physical activity compared to continuous lighting. No interactions between melatonin and lighting schedule were found on energy metabolism traits. Lighting schedule strongly affected daily heat production pattern (total, activity-related, and nonactivity-related heat production). Melatonin had a reducing effect on activity-related heat production during the day, especially during light periods. The present study demonstrated that reduced energy expenditure for physical activity, caused by the supplementation of melatonin to the diet, might be a reason for the often observed improvement of feed conversion. Furthermore, this study showed that feed conversion was improved with an intermittent lighting schedule, which was related to higher metabolizability and lower energy expenditure on physical activity, compared to continuous lighting