|Galloway Sr, D|
Submitted to: Small Ruminant Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/19/1996
Publication Date: N/A
Interpretive Summary: Differences among grass sources in efficiency of absorbed nutrient metabolism have not been extensively studied. Therefore, objectives of our experiment were to determine effects of different grass sources and qualities on feed intake, digestibility, performance, and visceral organ mass in growing wethers after 42 or 84 d. Greater mass of the reticulo-rumen after 84 than 42 d, a similar proportion of epithelial tissue in the ventral rumen and lower digestible organic matter intake after 84 d imply a greater proportion of absorbed energy used by the gastrointestinal tract with the long vs short feeding period. Conversely, similar small intestinal tissue mass after 42 and 84 d and a lower proportion of epithelial tissue in the jejunum after 84 d suggest less energy consumption by the small intestine in the second 42-d period than in the first, probably being at least partially compensatory for the difference in reticulo-ruminal tissue energy use. A greater proportion of variability in liver mass was explained by total gut mass than by digestible organic matter intake. These results suggest substantial effects of physical attributes of digesta resulting from different low- to moderate-quality grasses on gastrointestinal tract mass and, thus, energy use. Similarly, gastrointestinal tract tissue mass apparently had marked influence on liver mass and heat production. Hence, elucidation of dietary forage characteristics with major impact on mass and perhaps properties of digesta altering gastrointestinal tract tissue mass and energy consumption could lead to modifications for increased peripheral energy availability and tissue accretion.
Technical Abstract: Crossbred wethers (72; 31+/- 0.5 kg) were used to determine effects of different grass sources and qualities on visceral organ mass after 42 and 84 d. Wethers consumed ad libitum bermudagrass (BER; Cynodon dactylon) (H, 24-d regrowth; M, 42-d regrowth; L, full-season growth) or orchardgrass (ORC; Dactylis glomerata) (H, late vegetative to pre- anthesis; M, post-anthesis; L, seed in dough stage). Digestible organic matter intake averaged 730, 603, 550, 592, 514 and 387 g/d (SE 32.4) for BER-H, BER-L, ORC-H, ORC-M and ORC-L, respectively. total gastrointestinal tract digesta mass (fresh weight) was greater (P=0.01) for BER than for ORC (8.14, 8.36, 8.00, 7.64, 7.21 and 6.71 kg for BER-H, BER-M, BER-L, ORC-H, ORC-M and ORC-L, respectively). Mass of the reticulo-rumen (722, 675, 617, 606, 577 and 512 g; SE 20.6) and small intestine (659, 620, 548, 585, 521 and 484 g; SE 25.9) were greater (P<0.01) for BER than for ORC, and liver mass generally differed similarly (period 1: 389, 406, 318, 390, 321 and 286 g, SE 10.2; period 2: 405, 392, 346, 372, 369 and 289 g, SE 10.6, for BER-H, BER-M, BER-L, ORC-H, ORC-M and ORC-L, respectively). A slightly greater proportion of variability in reticulo-ruminal mass was attributable to digesta mass than to digestible organic matter intake, although only digestible organic matter intake related to small intestinal mass. Liver mass was more highly related to gastrointestinal tract mass than to digestible organic matter intake. In conclusion, these results suggest substantial effects of physical attributes of gastrointestinal tract digesta (i.e., mass) that differ among low- to moderate-quality grasses on mass and, thus, energy consumption of splanchnic tissues.