Effects of underfeeding and refeeding on weight and cellularity of splanchnic organs in ewes

We assessed the effects of a long and severe period of underfeeding, follow ed by a rapid refeeding with a high-concentrate diet, on weight, protein ma ss; and cellularity of the splanchnic organs in adult ewes. Twenty-four ewe s, allocated to four groups of six, were fed a forage diet (50% regrowth of natural grassland hay and 50% wheat straw) either at maintenance (groups M and MO) or at 40% maintenance (groups U and UO) for 78 d. Groups M and U w ere then slaughtered, and groups MO and UO were subsequently overfed a high -concentrate diet (52% hay, 20% barley, 16% rapeseed meal, 4% fish meal, an d 8% Megalac) at 236% maintenance for 26 d before being slaughtered. During the experiment, feed was adjusted to maintain feed supply at a constant pe rcentage of animal requirements. After slaughter, fresh weight, dry weight, and protein mass of the reticulorumen, omasum, abomasum, small intestine, large intestine, and liver were measured. Cellularity was assessed from nuc leic acids and protein contents for both ruminal mucosa and muscular-serosa layers, jejunum, and liver. The concentrations of ubiquitin and cathepsin D mRNA were measured in ruminal mucosa and muscular-serosa layers and in je junum. Underfeeding decreased protein mass of splanchnic organs, especially in liver (-29%) and reticulorumen (-39%). Refeeding previously underfed an imals increased protein mass of liver (+102%) and small intestine(+59%). No carry-over effect of the previous level of intake (UO vs MO) was observed on the protein mass of splanchnic tissues after 26 d of refeeding. Variatio ns in liver mass were mainly due to hypertrophy, as determined by the prote in:DNA ratio, whereas variations in small intestinal mass were mainly due t o hyperplasia, as determined by the amount of DNA. By contrast, changes in rumen mass associated with increasing ME intake seemed to be related to hyp ertrophy in the muscular-serosal component and hyperplasia in the epithelia l component. The concentrations of ubiquitin and cathepsin D mRNA in the ru men and jejunum were not modified by feeding level, demonstrating that the expression of these genes for proteolytic enzymes was unchanged under these conditions.