VISCERAL ORGAN MASS IN WETHERS CONSUMING DIETS WITH DIFFERENT FORAGESAND GRAIN LEVELS

Crossbred wethers (72; 33 +/- 0.6 kg live weight) were used to investi gate interactions among forage source, cereal grain inclusion and leve l, and length of feeding on visceral tissue mass. Wethers consumed lon g-stemmed alfalfa ((A) Medicago sativa; early bloom), bermudagrass ((B ) Cynodon dactylon; 6 to 8 weeks of regrowth) or ryegrass (Lolium mult iflorum; early head emergence)-wheat (Triticum aestivum; anthesis (RW) ) hay and approximately 0, 20 or 40% ground corn (0, 20 and 40, respec tively) for 49 or 98 d. Digestible organic matter intake ranked (P < 0 .05) B < RW < A and was increased (P < 0.05) by grain inclusion (perio d 1: 0.62, 0.75, 0.73, 0.28, 0.45, 0.49, 0.57, 0.57 and 0.69 kg/d; per iod 2: 0.73, 0.91, 0.96, 0.30, 0.49, 0.56, 0.55, 0.73 and 0.91 kg/d); mean empty body weight was 37, 40, 40, 34, 35, 36, 36, 38 and 39 kg (S E 1.2) for A-0, A-20, A-40, B-0, B-20, B-40, RW-0, RW-20 and RW-40, re spectively. Total gastrointestinal tract tissue mass was lower (P < 0. 06) for B than for A or RW (1.98, 2.11, 1.97, 1.69, 1.78, 1.78, 1.84, 1.93 and 1.95 kg), and epithelium comprised a greater(P < 0.05) propor tion of ventral ruminal tissue for A versus RW or B (25, 27, 27, 19, 2 2, 21, 20, 25 and 21% for A-0, A-20, A-40, B-0, B-20, B-40, RW-0, RW-2 0 and RW-40, respectively). Liver mass was 0.48, 0.51, 0.57, 0.34, 0.4 0, 0.40, 0.41, 0.49 and 0.44 kg in period 1 (SE 0.037), and 0.53, 0.56 , 0.49, 0.38, 0.41, 0.41, 0.42, 0.43 and 0.51 kg in period 2 (SE 0.022 ) for A-0, A-20, A-40, B-0, B-20, B-40, RW-0, RW-20 and RW-40, respect ively. In conclusion, cereal grain inclusion increased digestible orga nic matter intake and decreased gastrointestinal tract and liver mass relative to digestible organic matter intake similarly regardless of f orage source, grain level or feeding period length. Thus, effects of c ereal grain inclusion on peripheral tissue energy availability should be greater than expected based on digestible organic matter intake and , relative to conditions without supplemental grain, such differences should decrease with increasing forage quality and feeding period leng th as digestible organic matter intake increases. (C) 1997 Elsevier Sc ience B.V.