Fasting metabolic rate in hens. 1. Effects of body weight, feather loss, and activity.

Environmental factors affecting fasting metabolic rate (FMR) were quantified and a short-time recording system was developed. Discontinuous measurements of gas exchange of 1,120 medium weight brown egg layers were taken after 24 and 36 hr of starvation. Body weight (BW) and shank length (SL) were measured and feather cover and activity evaluated by scores. The FMR increased with deterioration of plumage cover. Differences between hens with complete feather cover (Score 1) and nearly naked birds (Score 4) were 8 kJ2/hr at night and 11 kJ/hr during the light phase. Fully fed hens measured during the light phase showed the same curvilinear relationship as starved birds. Only a small proportion of the heat increment generated by ingested food is used by poorly feathered hens to maintain body temperature. Gaseous exchange was affected by locomotor activity in the respiration chamber. The FMR of resting and quietly standing birds were 29.75 +/- 1.00 kJ/hr and 30.55 +/- 1.00 kJ/hr, respectively. During the prelaying phase, FMR showed an increment of 13 kJ/hr with a peak shortly before oviposition. The following exponential relationships between BW in kilograms, and SL in centimeters with FMR were estimated for light phase FMR = 18.52 BW .59 +/- .05 kJ/hr, R2 = .11; for dark phase FMR = 15.21 BW 54 +/- .04 kJ/hr, R2 = .17 and FMR = .32 SL 1.64 +/- .10 kJ/hr, R2 = .19. In poorly feathered strains, SL was as good a predictor of body size as BW. Correcting FMR data for feather loss changed regression coefficients and allometric functions significantly: for light phase FMR = 15.47 BW .74 +/- .03 kJ/hr and R2 = .15; for dark phase FMR = 13.11 BW .66 +/- .03 kJ/hr and R2 = .28.