Energy expenditure and physical activity in domestic fowl kept on standard and interrupted lighting patterns.

1. The energy expenditure (H) and physical activity of laying hens were measured under lighting regimes of 14L:10D (standard), 2L:10D:2L:10D (interrupted) and (15 X (13 min L:47 min D]: 9D (fragmented). 2. Neither of the intermittent regimes produced a significant change in total daily energy expenditure, although large alterations occurred in the distribution of H between the lighting phases. The absence of change in total H resulted from the combined effects of greater H in the light in the intermittent regimes, greater H in darkness during the interrupted day than at night and slightly greater H at night in the intermittent regimes. 3. Physical activity count, like H, was redistributed over time but, unlike H, was also significantly reduced in total; changes in the energy cost of unit activity, however, were such that no reduction occurred in the total amount of H attributable to activity. 4. In the standard groups, 90% of total activity costs were incurred in the light; in the fragmented-day and interrupted-day groups, respectively, 7% and 55% of total activity costs were incurred in the light periods and 85% and 30% in daytime darkness. 5. In terms of both H and activity, there was clear differentiation between night darkness and subjective-day darkness. 6. Even when the energy cost of activity was excluded, significant differences remained between H at night, H in the light and H in daytime darkness.

Energy and nitrogen retention and loss in broiler chickens genetically selected for leanness and fatness.

1. A breeding programme based on the assessment of the body fat content of broilers by measurement of plasma very low density lipoprotein concentration has resulted in 2 lines with significantly different body fat contents. 2. Energy and nitrogen intake and retention were measured in 63- to 70-d-old females from each line during 5-d periods of indirect chamber calorimetry. Results obtained by this technique were compared with results from a previously published growth trial incorporating carcase analysis at 49 d. 3. Body weight, metabolisable energy intake, heat production, energy retention and efficiency of energy retention did not differ significantly between the fat and lean lines. 4. The proportion of energy retained as crude protein and the efficiency of crude protein retention were significantly greater in the lean line. 5. In terms of whole-body energy and nitrogen exchanges, the essential difference between the lines was therefore in the partition of the same quantity of retained energy between fat and protein deposition. 6. The results were consistent with a higher rate of breakdown of amino acids in the fat line; because heat production did not also increase, a greater proportion of retained energy therefore became available for storage as fat.

Maintenance energy requirements of laying hens: a comparison of measurements made by two methods based on indirect calorimetry.

1. The aims of this study were to compare maintenance metabolisable energy requirement estimates obtained in laying hens by two methods of respiration calorimetry, to investigate the changes in the heat production and energy retention of laying hens associated with temporarily reduced energy intake and to demonstrate the errors caused by using inappropriate values of net efficiency of energy utilisation (k) when extrapolating to maintenance energy requirement from a range of energy retention values. 2. One of the methods used regression of a range of energy retentions on energy intakes, followed by interpolation of zero energy retention; the other method employed extrapolation to zero energy retention from a single level of energy intake and retention. 3. Maintenance energy requirements derived from the two methods were similar. There was no indication that repeated temporary reduction of energy intake for the regression method gave a reduced value for maintenance energy requirement. The main potential advantage of the single-point method is therefore rapidity. 4. The single-point method relies for accuracy either on fixing an energy intake near the expected maintenance or on having a very accurate value for k. For example, the error attributable to using an assumed net efficiency (k) value of 0.7 when the true value was 0.8 was shown to vary between 0 if energy retention was measured at the equilibrium point and about 70 kJ/kgW0.75 d, or +15%, if energy retention was measured in the fasted state. 5. Stability of heat production and energy intake was approached after 2 d of reduced energy intake.

Heat production by the mature male turkey (Meleagris gallopavo): preliminary measurements in an automated, indirect, open-circuit multi-calorimeter system.

The energy metabolism of mature male turkeys (Meleagris gallopavo) was determined in a computer-controlled indirect multi-calorimeter system of which the design and operation are described. Daily heat production did not change significantly during an initial 6-d period in the calorimeter chambers. Food intake was at first sufficient to promote a rate of energy retention significantly greater than zero, but decreased to give negative energy retention on day 6; mean energy retention for the whole 6-day period was significantly greater than zero. Heat production was affected little by fasting for 72 h, although the respiratory quotient decreased to 0.72 within 48 h; the heat increment of feeding was therefore small (about 5% of metabolisable energy). Fasting heat production, scaled on metabolic body size (bodyweight in kg)0.75, was similar to that of mature male domestic fowl (Gallus domesticus). Heat production after refeeding was similar to that recorded during the 6 d before fasting. There was a pronounced circadian rhythmicity of heat production in both fed and fasted birds.

Circadian variation in the metabolic rate of growing chickens and laying hens of a broiler strain.

1. Circadian variation in the heat production rate of young broiler chickens and laying broiler hens was studied by indirect calorimetry. 2. Variation in heat production rate was synchronised by the light cycle both in the 23-h light:1-h dark regime of the growing chickens and the 14-h light:10-h dark regime of the laying hens. 3. The relative amplitude of the decrease during the dark phase was about twice as great during the 10 h of darkness afforded the adult hens as it was during the 1-h period of darkness experienced by the growing birds.

The effects of partial defeathering on energy metabolism in the laying fowl.

1. The effects of a complete removal of feathers from the neck and/or breast on the energy metabolism of laying hens were measured by indirect calorimetry. 2. The daily heat production of fed birds was significantly increased if feathers were removed from the entire neck plus breast region but not if the neck only or breast only were denuded. 3. Removal of feathers from neck plus breast led to a 10% increase in food consumption. 4. The partially-defeathered birds laid more eggs.

Effects of food intake regulation on the energy metabolism of hens and cockerels of a layer strain.

1. Indirect calorimetry was used to study the effects on the energy metabolism of cockerels and hens after peak lay of a hybrid layer strain of regulating food or energy intake to 80% of ad libitum for an extended period of time. 2. Regulation of food intake decreased fasting and fed heat productions per bird and per unit metabolic body weight (kg0.75). 3. Maintenance energy requirements (per kg0.75) of both sexes were reduced about 20% by regulation; maintenance requirements of cockerels were about 30% lower per kg0.75 than hens on the same treatments. 4. Reducing the intake of all nutrients by 20% had the same effect on the energy metabolism of cockerels as restricting energy alone by the same amount. 5. Gross efficiency of egg production, in terms of both mass and energy, was higher when intake was regulated. During weeks 21 to 52 of restriction, daily egg mass output was significantly higher in hens fed ad libitum. 6. After 52 weeks of food regulation, restricted hens weighed 20% less and their total carcass energy was 36% less than hens fed ad libitum; similar effects were found in the cockerels.

An automated multi-calorimeter system: preliminary experiments on laying hens.

1. An open-circuit, automated, multi-calorimeter system for studies on the energy metabolism of the fowl is described. 2. Discontinuous observations of 10-min duration once each hour for 22 h gave good agreement with continuous observations throughout 22 h. 3. It is essential to train each hen before a series of calorimeter experiments. 4. A distinctive pattern of light-entrained, diurnal variation of metabolic rate has been observed in starving and fed birds of two laying strains.