FORAGE AND SPLANCHNIC TISSUE MASS IN GROWING LAMBS - EFFECTS OF DIETARY FORAGE LEVELS AND SOURCE ON SPLANCHNIC TISSUE MASS IN GROWING LAMBS

Forty-two crossbred lambs (33.4 kg initial body weight; twenty-four we thers and eighteen ewes) were used in a 42 d experiment with a 2 x 3 f actorial treatment arrangement to determine effects of forage level an d source on splanchnic tissue mass. Diets were 250 and 750 g/kg of cho pped lucerne (Medicago sativa) (A), ryegrass (Lolium multiflorum)-whea t (Triticum aestivum) (RW) or bermudagrass (Cynodon dactylon) (B) hay, with the remainder being maize-based concentrate. Five lambs per trea tment were slaughtered at the end of the experiment and measurements m ade of internal organs and contents of the gastrointestinal tract (GIT ). Digestible organic matter intake (DOMI) on the 7 d preceding slaugh ter was 0.89, 0.83, 0.90, 0.83, 0.77 and 0.61 (SE 0.05) kg/d, and live -weight gain was 0.20, 0.17, 0.18, 0.10, 0.10 and 0.07 (SE 0.02) kg/d for diets A-25, RW-25, B-25, A-75, RW-75 and B-75 respectively. Total GIT mass (fresh) was higher (P < 0.05) for 750 than 250 g forage/kg an d for B than RW (4.80, 4.57, 5.55, 5.84, 5.99 and 6.91 kg for diets A- 25, RW-25, B-25, A-75, RW-75 and B-75 respectively). Nonfat organic ma tter was 259, 295, 292, 303, 277 and 264 g for the total GIT; 93, 102, 103, 106, 95 and 97 g for the reticulo-rumen (forage level x type (di et A v. diets RW and B) interaction; P < 0.05); and 204, 196, 202, 177 , 156 and 127 g for the liver (SE 10) with diets A-25, RW-25, B-25, A- 75, RW-75 and B-75 respectively. In summary, differences in properties of forage A and the grasses at 250 g/kg diet may have influenced GIT mass independent of energy intake and digesta mass. Conversely, with 7 50 g dietary forage/kg, higher digesta mass for diet B than diet RW ap peared responsible for high reticulo-rumen mass relative to DOMI. Grea ter digesta mass for 750 than 250 g forage/kg may have elevated intest inal tissue mass/DOMI with diets A and B but not with diet RW, for whi ch NDF digestibility was highest.