Ruminally undegraded intake protein in sheep fed low-quality forage: Effect on weight, growth, cell proliferation, and morphology of visceral organs

To determine the influence of increasing levels of supplemental ruminally u ndegraded intake protein (UIP) on visceral organ weights, growth, cell prol iferation, and morphology, 20 mature ewes of mixed breeding were fed a 6.55 % CP grass hay:straw mixture (40:60) and assigned to one of four supplement al treatments. Supplements were control (no supplement) and low, medium, an d high levels of UIP. After 42 to 46 d on treatment, ewes were infused i.v. with 5-bromo-2-deoxy-uridine (BrdU, a thymidine analog used to provide an index of the rate of intestinal cell proliferation) and slaughtered Ih late r. Visceral organs were weighed, and subsamples were obtained to evaluate v isceral DNA, RNA, and protein contents (frozen samples) as well as intestin al morphology (fixed samples). Final BW; eviscerated BW (EBW); total viscer al weight; and liver fresh, dry, and dry fat-free weights were increased (P <.10) in protein-supplemented ewes compared with controls, but were not in fluenced by increasing levels of UIP. Tissue weights of duodenum, jejunum, ileum, cecum, and colon were not greatly influenced by treatment. There wer e no differences among treatments in intestinal DNA and protein concentrati ons and the ratios RNA:DNA and protein:DNA. Jejunal RNA concentration and c ontent was increased (P <.10) in low compared with medium and high treatmen ts. Jejunal RNA content also was decreased (P <.10) in high compared with t he medium UIP treatment. Liver RNA and protein contents were increased (P < .10) with protein supplementation. In contrast, contents of RNA, DNA, and p rotein in duodenum, ileum, cecum, and colon were not influenced by treatmen t. In addition, neither the rate of intestinal proliferation (BrdU labeling ) nor intestinal morphology (crypt depth, villus length, or villus width) w ere affected by treatment. These data indicate that the influence of protei n supplementation on visceral growth involves primarily the liver and not t he intestines. These data also indicate that visceral growth, except in jej unum, are not altered by differing levels of UIP supplementation.