|GALLOWAY SR, D|
Submitted to: Livestock Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/27/1996
Publication Date: N/A
Interpretive Summary: Internal organs such as the gastrointestinal tract and liver are very metabolically active, accounting for a large proportion of whole body heat production and amino acid metabolism. Therefore, factors influencing splanchnic tissue metabolism could markedly impact the quantity of nutrients available for use by peripheral tissues. However, dietary characteristics that influence mass of visceral organs under common production conditions, such as with ad libitum feed consumption, have not been studied extensively. Hence, objectives of this experiment were to determine effects of different forage sources and grain levels on feed intake, digestibility, performance and visceral organ mass in growing wethers after different lengths of feeding. Mass of the gastrointestinal tract was greater for wethers consuming temperate than tropical grass hay, corresponding to an effect of grass type on reticulo-ruminal mass, which appeared partially due to physiological workload as characterized by digestible organic matter intake. Results of this experiment indicate that digesta mass may influence tissue mass less with moderate- to high-quality forage than with ones of low to moderate quality. Furthermore, a relatively greater proportion of increased peripheral tissue accretion with grain supplementation may result from enhanced efficiency of splanchnic tissue metabolism with tropical than temperate grass, and generally greater live weight grain with legumes vs grasses and for temperate vs tropical grasses involves not only differences in digestible nutrient intake, but also different proportions of absorbed nutrients metabolized by splanchnic tissues.
Technical Abstract: Crossbred wethers (72; 33 +/- 0.6 kg) were used to determine effects of ad libitum consumption for 49 or 98 d of different forage sources and supplemental grain levels on visceral organ mass. Wethers consumed long-stemmed alfalfa (A), bermudagrass (B), or ryegrass-wheat (RW) hay and approximately 0, 20 or 40% ground corn. Digestible organic matter intake was greater (P<0.05) for A than for grasses, for RW vs B and with than without grain (period 1: 617, 749, 733, 277, 445, 486, 565, 574 and 686 g/d; period 2: 726, 905, 960, 298, 493, 564, 554, 726 and 907 g/d for A-0, A-20, A-40, B-0, B-20, B-40, RW-0, RW-20 and RW-40, respectively). Total gastrointestinal tract tissue mass was greater (P<0.06) for A than for grasses and for RW than for B (1.98, 2.11, 1.97, 1.69, 1.78, 1.84, 1.93 and 1.95 kg for A-0, A-20, A-40, B-0, B-20, B-40, RW-0, RW-20 and RW-40, respectively), with the difference between A and grasses primarily due to mass of intestinal tissues and that between grasses to reticulo-ruminal mass. Liver mass was 0.48, 0.51, 0.57, 0.34, 0.40, 0.40, 0.41, 0.49 and 0.44 kg in period 1 (SE 0.022) for A-0, A-20, A-40, B-0, B-20, B-40, RW-0, RW-20 and RW-40, respectively. Mass of gastrointestinal tract tissues was moderately correlated with digestible organic matter intake but was not significantly related to digesta mass. Appreciable variability in liver mass not accounted for by digestible organic matter intake was attributable to gastrointestinal tract mass. In conclusion, dietary grain inclusion may decrease splanchnic tissue energy consumption relative to absorbed energy more with tropical than with temperate grass or legume, thereby lessening differences among forage sources.