PSX-16 The impact of free-choice diet selection on feed efficiency and oxidative stress in growing sheep.

Abstract The objective of this study was to examine the effect of diet choice on feed efficiency and oxidative stress in growing lambs. Previous research has indicated that providing animals free-choice in selecting diet components may improve performance and overall animal wellbeing compared to being fed a TMR. Twenty-six wethers (BW ~ 30 ± 6.5 kg) over a 64-day period were blocked by body weight and randomly assigned to individual raised pens. From d -14 to -1 lambs were fed a pelleted control diet and allowed to acclimate to pen space. On d 0, lambs where weighed again, and randomly assigned within block to one of 2 treatment diets: 1) Pelleted control diet (CON) formulated to meet vitamin and mineral requirements and containing 46% ground corn, 28% alfalfa, and 16% soybean meal on an as-fed basis, or 2) Free-choice diet (FCD) of pelleted alfalfa and pelleted ground corn offered ad-libitum and similarly formulated to meet vitamin and mineral requirements. Blood samples were taken via jugular venipuncture on d 0, 25, and 50 and analyzed for oxidative stress markers. Animal performance (ADG) was determine based on weekly body weight collections, and orts of each diet were recorded daily prior to feeding determine dry matter intake. Over the experimental period, there was a treatment x block interaction (P = 0.02), with FCD lambs in the heavy block having a higher ADG (0.23 kg/d) than CON lambs (0.17 kg/d). While DMI had numerical differences, there was no significant differences between the treatments or treatment by block interaction (P > 0.24). Similarly, for gain:feed there was a significant treatment x block interaction (P < 0.05), however after separating the means no significant difference was observed between blocks. The results of this study indicate that offering lambs free-choice in selecting from primary diet ingredients may positively improve animal performance without impacting feed efficiency.