Effects of diet forage : concentrate ratio and metabolizable energy intakeon visceral organ growth and in vitro oxidative capacity of gut tissues insheep

We used 28 crossbred wether lambs to determine the effects of dietary forag e:concentrate ratio and metabolizable energy intake on visceral organ growt h and oxidative capacity of gut tissues in lambs. Lambs were assigned rando mly to a factorial arrangement of dietary treatments consisting of pelleted diets containing either 75% orchardgrass or 75% concentrate fed once daily at either .099 or .181 Meal ME.(kg BW.75)(-1).d(-1). After a 52-d feeding period, lambs were slaughtered to obtain measurements of visceral organ mas s and composition and oxidative capacity of isolated epithelial cells. Lamb performance, as measured by DMI, ADG, and efficiency of gain, was greater (P = .0001) for both diets at high ME intake. Likewise, lambs fed 75% conce ntrate gained faster and more (P less than or equal to .01) efficiently tha n lambs fed 75% forage. Total digestive tract (TDT; includes rumen, reticul um, omasum, abomasum, and intestines) weight increased (P = .0001) with ME intake and was greater (P = .03) in lambs fed 75% forage than in those fed 75% concentrate, As a percentage of empty body weight (EBW), TDT weight inc reased with ME intake in lambs fed 75% forage, but it was unaffected by ME intake in lambs fed 75% concentrate (diet x intake, P = .03). Liver weight increased (P = .0001) with ME intake and was greater (P = .005) in lambs fe d 75% concentrate vs 75% forage; however, liver weight as a percentage of E BW was increased (P = .0002) with ME intake but was unaffected by diet. Gre ater ME intake increased (P less than or equal to .02) small intestinal (SI ) epithelial and muscle mass of 15-cm sections, whereas jejunal epithelial mass was greater (P = .01) for lambs fed 75% forage vs 75% concentrate. Rum en epithelial concentrations of DNA and RNA increased (P less than or equal to .02) with greater ME intake, whereas SI concentrations of DNA and RNA w ere largely unaffected by diet or ME intake. The activity of Na+-K+-ATPase increased in ileal epithelium (P less than or equal to .02) with ME intake and concentrate in the diet, but activity in ruminal epithelium increased ( P = .05) with concentrate. Total oxygen consumption by isolated ruminal and intestinal epithelial cells was unaffected by treatment. These data sugges t that ME intake and level of dietary forage affect ruminal and intestinal growth via changes in cellular hyperplasia. Additionally, this study suppor ts the concept that ME intake and diet composition alter gut energy expendi ture, at least in part, through changes in mass rather than mass specific m etabolism.