Optimal dietary energy and amino acids for gilt development: Growth, body composition, feed intake, and carcass composition traits

The objective of this study was to determine if body composition of developing gilts could be altered at the onset of estrus by ad libitum feeding diets differing in standard ileal digestible (SID) lysine and ME using levels that are within those used in practice by pig producers in the United States. Crossbred Large White × Landrace gilts (n = 1,221), housed in groups, were randomly allotted to 6 corn–soybean diets in a 2 × 3 factorial arrangement formulated to provide 2 SID lysine and 3 ME levels. Gilts received grower diets formulated to provide 0.86 (low) or 1.02% (high) SID lysine and 2.94 (low), 3.25 (medium), or 3.57 (high) Mcal of ME/kg from 100 d of age until approximately 90 kg BW. Then, gilts were fed finisher diets containing 0.73 (low) or 0.85% (high) SID lysine and 2.94 (low), 3.26 (medium) or 3.59 (high) Mcal of ME/kg until 260 d of age. The medium SID lysine and medium- ME diets were based on an informal survey from the U.S. commercial swine industry to obtain average levels that are currently being formulated for developing gilts. Gilts were weighed and backfat thickness and loin area were recorded at the beginning of the trial and then every 28 d. Feed intake (FI) was recorded as feed disappearance within the pen at 2-wk intervals. Lysine (g) and ME (Mcal) consumed were calculated based on diet formulations. At approximately 260 d of age, gilts were slaughtered and warm carcass weight and fat thickness were recorded. There were no differences between lysine or ME levels for growth and body composition, except for backfat, which was slightly greater for gilts fed a high-ME diet. Gilts fed high-ME diets had a lower FI but a greater ME intake compared with gilts fed low ME (P < 0.05). Additionally, gilts fed the high-ME diet had lower FI and lysine intake per kilogram of BW gain when compared with gilts fed low- or medium-ME diets (P < 0.05). However, there was no difference in the megacalories consumed per kilogram of BW gain among treatments (P > 0.05). Carcasses from gilts fed the high-ME diet were 3.3 and 2.5 kg heavier than those from gilts fed the low- or medium- ME diets (P < 0.05). Despite significant differences in the lysine:ME ratio in the diets, no changes in growth or body composition occurred, likely due to compensatory changes in FI in response to dietary ME content. Caloric efficiency (Mcal to deposit 1 kg of BW) was similar among treatments.