Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 1, 1999
Publication Date: N/A
Interpretive Summary: Previous research at this location has shown that the conversion of food energy to body tissue energy in ruminants is less for forage rations than for grain rations, primarily because of an increase in energy use by the digestive tract organs. The results of this study showed that the weight of the liver and digestive tract organs in lambs is increased as the amount of energy and forage in the diet increased. As a percentage of empty body weight (i.e. body weight minus undigested food), the weight of digestive tract organs increased when greater amounts of the forage ration was fed, but relative weights did not change when greater amounts of the grain diet was fed. Food intake and dietary forage increased the weights of the digestive tract organs by causing the number of cells to increase in each organ. The amount of energy used by cells from digestive tract organs was not affected by food intake or level of dietary forage. In light of the previous findings, this study demonstrates that forage rations increase energy use in digestive tract organs by causing an increase in organ weight, rather than altering cellular energy use.
Technical Abstract: We used twenty-eight lambs determine the effects of dietary forage-to- concentrate ratio and metabolizable energy (ME) intake on visceral organ growth and oxidative capacity of gut tissues. Lambs were assigned randomly to a factorial arrangement of dietary treatments consisting of diets containing either 75% orchard grass (OGD) or 75% concentrate (CD) fed at either .099 (LE) or .181 (HE) Mcal MEù (kg BW.75)-1ùd-1. After a 5 feeding period, lambs were slaughtered to obtain measurements of visceral organ mass and oxidative capacity of isolated epithelial cells. Lamb performance , as measured by DMI, ADG, efficiency of gain, was greater (P < .01) for both diets at HE intake. Likewise, lambs fed CD gained faster and more (P < .01) efficiently than lambs fed OGD. Total digestive tract (TDT) weight increased (P < .01) with HE intake and was greater (P < .05) in lambs fed OGD vs CD. As a percentage of empty body weight (EBW), TDT weight increased with ME intake in lambs fed OGD, but was unaffected by ME intake in lambs fed CD (diet intake, P < .05). Greater ME intake increased (P < .05) small intestinal epithelial and muscle mass, while jejunal epithelial mass was greater (P < .05) for lambs fed OGD vs CD. Rumen epithelial concentrations of DNA and RNA increased (P < .05) with greater ME intake. Total oxygen consumption by isolated ruminal and intestinal epithelial cells were unaffected by treatment. These data suggest that ME intake and level of dietary forage affect ruminal and intestinal growth via changes in cellular hyperplasia. Additionally, this study supports the concept that ME intake and diet composition alters gut energy expenditure, at least in part, through changes in mass rather than mass specific metabolism.