Interaction of dietary energy and protein on growth performance, carcass characteristics and digestibility in finishing barrows when fed at a constant digestible lysine to metabolizable energy ratio

Abstract

The objective of this study was to determine the performance response to changes in dietary fat, protein, and fiber content in finishing barrows while maintaining a constant apparent ileal digestible (AID) Lys to metabolizable energy (ME) ratio (AID Lys:ME). The experiment was conducted in 2 trials, each containing 25 individually penned pigs. In both trials, barrows (initial wt=85.3kg) were blocked by weight and assigned to one of five experimental diets (0.40, 0.44, 0.48, 0.52, and 0.56% digestible Lys) with a constant AID Lys:ME (1.44g/MCal). Lysine content was changed by altering the proportions of corn and soybean meal and energy was altered by the addition or removal of cellulose and fat. Diets contained 0.2% titanium dioxide as a digestibility marker. Pigs were fed experimental diets for 28d, and body weights, feed intakes, and ultrasound measurements of tenth rib backfat (BF) and loin eye area (LEA) were recorded on d 14 and 28. Blood samples were taken on d 28 to determine serum urea nitrogen (SUN), insulin, T3, and T4. A quadratic effect of increasing dietary Lys was seen on ADG on d 28 showing that the addition of Lys increased gain (P<0.01). Additionally, feed efficiency, energy intake, and Lys intake increased linearly as dietary Lys concentration increased from 0.40% to 0.56% AID Lys (P<0.01). Levels of T3 increased with increasing Lys (P<0.01), but there was no effect of diet on SUN, T4, or insulin. Ultrasound estimates of BF and LEA tended to increase linearly and quadratically, respectively, as dietary Lys increased (P<0.10). Digestibility of energy, protein, NDF, and hemicellulose increased linearly in pigs fed 0.40–0.56% AID Lys (P<0.05). These results demonstrate that formulating diets to meet the recommended AID Lys:ME is not sufficient to ensure optimal growth. Therefore, the concentration of protein and energy of the diet must be individually evaluated and corrected to obtain optimal growth and efficiency.