Nonruminant Nutrition: Sow & Gilt Nutrition

A study was conducted to investigate how the allocation of energy to growth and maintenance differs between rainbow trout and Atlantic salmon and how the diet affects energy allocation. Rainbow trout and Atlantic salmon were handfed to satiation four isoenergetic diets (DE = 20 MJ/kg) with different digestible protein/digestible energy ratios (DP/DE), i.e., 24, 22, 20, and 18 g/MJ, achieved through reduction of DP level (53 to 39%) and increase of lipid level (19 to 26%). Intake of metabolizable energy (ME), protein (PD), and lipid (LD) gain were determined. Data were analyzed by multivariate analysis of PD and LD on ME. Maintenance energy requirements (MEm) and efficiency of ME utilization for PD (kp) and LD (kf) were estimated. The fraction of ME intake above maintenance for PD (X) was defined as linear function of body weight with slope (d) and intercept (c) estimated simultaneously with the above parameters. The MEm did not differ (P > 0.05) between rainbow trout and Atlantic salmon (20 kJ/day/kg0.8). On the other hand, Kp, c, and d were significantly different (P < 0.05) between the two species, independently of the diet. The ME intake above MEm channeled towards PD (c) was higher in salmon than trout (57 vs. 55%; P < 0.05). The change in partitioning of ME toward PD due to the change in body weight was negative for trout (d = -0.18) while it was positive for salmon (d = 0.16). The values of d agreed well with the increase of LD/PD with body weight for trout and the decrease of LD/PD with body weight for salmon which may have been related to the maturation status of this fish and the associated loss of lipid observed with maturing salmon. The Kp was significantly higher for salmon compared to trout (0.52 ± 0.06 vs. 0.43 ± 0.06; P < 0.05) and independent of the diet while Kf was 0.81 ± 0.13 irrespective of species or diet. Lower cost of protein deposition for salmon compared to trout suggests differences in protein metabolism between these two species. Studies on protein turnover rates and metabolic utilization of nutrients for PD are required to gain insight on kp differences between salmon and trout.