Effect of Energy Intake Level, Body Weight, and Pig Genotype on the Dynamics and Composition of Growth and Maintenance Energy Requirement in Growing Pigs between 25 and 125 kg BW

To estimate energy requirements for growing pigs, information is required about the partitioning of energy intake between body protein deposition (PD), body lipid deposition (LD) and maintenance energy requirements. These aspects are likely to vary between pig genotypes (PG). Metabolizable energy requirements for maintenance (MEm) may be estimated from physical or chemical body composition. The objectives of this experiment were to determine the effect of energy intake (EI) on chemical body composition, as well as the dynamics of PD, LD and MEm, in growing gilts of two PG (purebred Yorkshire, Y, and commercial cross bred, C) between 25 and 125 kg BW, using the serial slaughter technique.

A total of 32 pigs from each PG (Y and C; 2 two equal blocks) were allotted to one of two EI (70 and 90% of calculated voluntary daily intake according to NRC, 1998). Chemical body composition (ratio between body lipid to body protein mass, BL/BP) was determined at 25 (n=2), 50 (n=3), 75 (n=4), 100 (n=3), and 125 (n=4) kg BW. Corn, wheat, and soybean meal based diets were formulated and pelleted; essential nutrient exceed requirements for maximum PD. Retained energy (RE) was calculated as PD x 23.7 kJ/g + LD x 39.6 kJ/g. The MEm was calculated as the difference between ME intake and ME requirements for growth (PD x 43.9 kJ/g + LD x 52.8 kJ/g). Both RE and MEm were calculated for each 25 BW range. Results were subjected to Analysis of Variance using the Proc Mixed of SAS v9.1 (SAS, Inst., Cary, NC). Initial BW was used as a Covariate when growth performance was evaluated. Differences among Treatment were assessed using the Tukey Honesty Significant Difference Test.

There were no interactive effects of EI and PG on growth performance, BL/BP, Ld, Pd, RE, and MEm (P>0.10). Across various BW ranges, C pigs grew faster than Y pigs (P<0.05; 903 vs. 868 g/d, respectively) and daily BW gain increased with EI (P<0.01). Similarly, PD and LD increased with EI (P<0.05), whereas PD was higher (P<0.10; 145 vs. 132 g/d) and LD lower (P<0.10; 187 vs. 211 g/d, respectively) for C pigs than Y pigs. Throughout the experiment, BP content was higher and BL was lower for C pigs that for Y pigs (P<0.01). The BL/BP was lower for C pigs than Y pigs and increased with EI and BW for both PG (P<0.05). For all BW ranges, except 25 to 50 kg BW, RE was not influenced by genotype (25 to 125 kg BW: 10.85 vs. 11.35 MJ/d for C and Y, respectively; P>0.10), even though LD/PD was lower in C pigs compared to Y pigs (25 to 125 kg BW: 1.29 vs. 1.64 g/d; P<0.002). Daily MEm between 25 and 100 kg BW, but not differ between 25 and 125 kg BW, was influenced by both PG (13.2 vs. 11.7 MJ/d for C and Y, respectively; P=0.065) and EI (11.7 vs. 13.2 MJ/d for 70 and 90% of voluntary DEi, respectively; P=0.058). Across treatments, higher MEm coincided with lower BL/BP, indicating that BL/BP should be considered when estimating MEm.

Mass and distribution of main chemical components such as body protein and body lipid are affected by energy intake, body weight and pig genotype. Higher metabolizable energy requirements for maintenance are associated with lower BL/BP ratio. The latter implies that a simple ME partitioning model, relating MEm to BW, is insufficient to represent EI and PG effects on energy partitioning.

Keywords. Metabolizable energy, body composition, pigs.