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

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 ME requirements for maintenance (MEm) by regressing body weight gain against ME intake (MEI) in growing pigs.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 BW0.60·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 (REp) and fat (REf) every 5 d. Serum biochemical parameters of pigs were analyzed at the end of the experiment.The ADG and HP as well as the REp and REf linearly increased with increasing feed intake (p < 0.010). β-hydroxybutyrate (BHBA) concentration of serum tended to increase with increasing feed intake (p = 0.080). The regression equations of MEI on ADG were MEI, kJ/kg BW0.60·d = 1.88 × ADG, g/d + 782 (R2=0.86) and MEm was estimated at 782 kJ/kg BW0.60·d. Protein retention of growing pigs would be positive while REf would be negative at this feeding level via regression equations of REp and REf on MEI.The MEm was estimated at 782 kJ/kg BW0.60·d in current experiment. Furthermore, growing pigs will deposit protein and oxidize fat if provided feed at the estimated maintenance level.