Selection for high and low oxygen consumption-induced differences in maintenance energy requirements of mice

Maintenance energy requirements (MER) of mice selected for high (H) or low (L) oxygen consumption (OC) were compared. Forty-four mice from H and L OC lines were weaned at 3 weeks and divided into four experimental groups: group A were sacrificed at 4 weeks; group B were fed ad libitum, and groups C and D were fed 2.8 and 2.4 g/day, respectively, from 4 to 8 weeks of age. Groups B-D were sacrificed at 8 weeks. Chemical components were estimated for all groups. MER was estimated using a model that partitioned metabolizable energy intake into that used for maintenance, and protein and fat deposition. The feed conversion ratio for the B group was significantly higher in the H than in the L line. Feed intake for metabolic energy content per metabolic body size was significantly also higher in the H line, whereas accumulated energy content per metabolic body size was significantly higher in the L line. MER of the H line was greater than that of the L line (P < 0.10). These results suggest that selection for H or L OC produced differences in chemical components, feed efficiency, and MER between the H and L lines.

Estimation of the net energy requirements for maintenance in growing and finishing pigs

The objective of this experiment was to determine the net energy requirements for maintenance of growing and finishing pigs using regression models. Thirty-six growing (27.38 ± 2.24 kg) and 36 finishing (70.25 ± 2.61 kg) barrows were used and within each phase. Pigs received a corn-soybean meal diet fed at 6 levels of feed intake, which were calculated as 0, 20, 40, 60, 80, or 100% of the estimated ad libitum ME intake (2,400 kJ ME/kg BW(0.6)·d(-1)) of the pigs. Measurements were conducted on 6 pigs per feeding level and per stage of growth. After a 5-d adjustment period, barrows in the fasted treatment were kept in respiration chambers for 2 d to measure the fasting heat production. Barrows in the other treatments were kept individually in respiration chambers for a 5-d balance trial followed by a 2-d fasting period. Heat production (HP) in the fed state was measured and feces and urine were collected in the balance trial. The total HP increased (P < 0.01) with increasing feeding levels. Fasting HP increased (P < 0.01) as previous feeding level increased and was less (P = 0.012) in finishing pigs than growing pigs if calculated per kilogram BW(0.6) per day. When using an exponential regression analysis, ME requirements for maintenance were estimated at 973 and 921 kJ/kg BW(0.6)·d(-1) and NE requirements for maintenance were estimated at 758 and 732 kJ/kg BW(0.6)·d(-1) for growing and finishing pigs, respectively. The efficiencies of using ME for growth and for maintenance were estimated at 66 and 78.7% for growing and finishing pigs, respectively. It is concluded that exponential regression between HP and a wide range of ME intake may be used as a new method to determine the NE requirement for maintenance.

Plasma leptin, glucose and non-esterified fatty acid variations in dromedary camels exposed to prolonged periods of underfeeding or dehydration

The involvement of plasma leptin in the adaptation of dromedary camels to harsh conditions such as food or water shortages was studied through 2 experiments. In experiment 1, fourteen female camels were either fed at 68% of maintenance energy requirements (MER) during 112d (n=4) or overfed at 134% of MER during the first 56d and then underfed at 17% of MER the next 56d (OV-UN, n=5), or underfed and then overfed for the same durations and energy intake levels (UN-OV, n=5). Weekly plasma samples showed that leptin, glucose and non-esterified fatty acid (NEFA) concentrations were significantly modulated by energy intake level. NEFA increased sharply but transiently in underfed camels of the UN-OV or OV-UN groups, whereas glucose and leptin concentrations decreased with underfeeding and increased with overfeeding with more significant effects in camels that were previously overfed or underfed, respectively. In experiment 2 twelve female camels were either normally watered (n=6) or dehydrated (n=6) during 23d and then rehydrated during 4d. Dehydration specifically increased blood hematocrit, plasma NEFA and glucose whereas leptin decreased slightly. For both experiments, leptinemia was positively related to hump adipocyte volume. Taken together these results provide new data for a better understanding of lipid and energy metabolism in camels.