No abstract

Maximal animal performance may be limited by the ability of an animal to dissipate heat: the heat dissipation limitation (HDL) theory. Because the incidental heat produced during digestion [specific dynamic action (SDA)] varies among diets, the HDL theory predicts that lactating female mice consuming diets with lower SDA should have increased reproductive performance. Dietary fat has a lower SDA than dietary carbohydrate. Female mice were fed low (LF), medium (MF) or high (HF) fat diets (10, 45 and 60% energy from fat, respectively) from days 4-18 of lactation. HF- and MF-fed mice weaned significantly heavier litters than LF mice. This was because they not only consumed more energy [metabolisable energy intake (); HF: 306.5±25.0, MF: 340.5±13.5 kJ day] at peak lactation, but also delivered more milk energy to their pups [milk energy output (); HF: 203.2±49.9, MF 229.3±42.2 kJ day] than the LF-fed mice (=266.7±4.5, =164.60±30.59 kJ day). A mathematical model based on the predictions from the HDL theory showed that this effect was greater than predicted from differences in SDA between the diets. Fatty acid profiles of the diets, milk and pups showed significant correlations between the profiles. Besides reduced SDA, HF- and MF-fed mice were probably able to directly transfer absorbed dietary fat into milk, reducing the heat production of lactogenesis and enabling them to perform better than expected from the HDL model. In summary, HF and MF diets had beneficial effects on reproductive performance compared with the LF diet because they enabled mice to generate milk more efficiently with less incidental heat production.

Open-flow respirometry was used to measure the magnitude of specific dynamic action (SDA), the maximum rate of oxygen consumption and the length of time that the rate of oxygen uptake remained elevated above pre-feeding level in MF1 female mice fed different macronutrient diets. Irrespective of diet, the metabolic rate increased immediately after feeding and reached a maximum within 1.7 hours. The composition of the diet significantly altered the magnitude of SDA. SDA was highest for high protein-fed mice (9.4%), followed by high carbohydrate-fed mice (6.1%) and lastly high and medium fat-fed mice (3.9% and 4.5%).

A five-week feeding trial was conducted using 180 Cobb commercial broiler chickens to study the inclusion of sun dried Gliricidia sepium leaf meal (GLM) in broiler diets. The 21-day-old chickens were randomly allocated to four dietary treatments. Fifty, 100 and 150 g kg -1 levels of GLM were included in a nutritionally balanced diet. The control diet did not contain GLM. Feed and water were supplied ad libitum. Feed intake, feed conversion efficiency and body weight gains were significantly (P<0.05) depressed by the addition of GLM to the diets. Dietary treatment had a significant impact on liver and gizzard weights. The abdominal fat content of carcass decreased progressively with increased levels of GLM. The carcass dressing percentage in the group fed diet with 15% GLM was lower (P<0.05) than in control group. No mortality was recorded throughout the study. As the level of dietary GLM increased, there was a corresponding increase in the intensity of yellow pigmentation of the skin, shanks, feet and beaks of birds. It seems that 50 g kg -1 GLM can be included into diets of broiler chickens.