Metabolizable energy requirement for maintenance estimated by regression analysis of body weight gain or metabolizable energy intake in growing pigs

OBJECTIVE: Feed energy required for pigs is first prioritized to meet maintenance costs. Additional energy intake in excess of the energy requirement for maintenance is retained as protein and fat in the body, leading to weight gain. The objective of this study was to estimate the metabolizable energy requirements for maintenance (ME(m)) by regressing body weight (BW) gain against metabolizable energy intake (MEI) in growing pigs. METHODS: Thirty-six growing pigs (26.3±1.7 kg) were allotted to 1 of 6 treatments with 6 replicates per treatment in a randomized complete block design. Treatments were 6 feeding levels which were calculated as 50%, 60%, 70%, 80%, 90%, or 100% of the estimated ad libitum MEI (2,400 kJ/kg BW(0.60) d). All pigs were individually housed in metabolism crates for 30 d and weighed every 5 d. Moreover, each pig from each treatment was placed in the open-circuit respiration chambers to measure heat production (HP) and energy retained as protein (RE(p)) and fat (RE(f)) every 5 d. Serum biochemical parameters of pigs were analyzed at the end of the experiment. RESULTS: The average daily gain (ADG) and HP as well as the RE(p) and RE(f) linearly increased with increasing feed intake (p<0.010). β-hydroxybutyrate concentration of serum tended to increase with increasing feed intake (p = 0.080). The regression equations of MEI on ADG were MEI, kJ/kg BW(0.60) d = 1.88×ADG, g/d+782 (R(2) = 0.86) and ME(m) was estimated at 782 kJ/kg BW(0.60) d. Protein retention of growing pigs would be positive while RE(f) would be negative at this feeding level via regression equations of RE(p) and RE(f) on MEI. CONCLUSION: The ME(m) was estimated at 782 kJ/kg BW(0.60) d in current experiment. Furthermore, growing pigs will deposit protein and oxidize fat if provided feed at the estimated maintenance level.