Tropical Grasslands (1995) Volume 29, 102–110

Performance, dry matter intake, digesta kinetics, and ruminal fermentation of steers grazing Sorghum halepense at three stocking rates

DARRELL L. RANKINS, Jr.1 and DAVID I. BRANSBY2

1Department of Animal & Dairy Sciences, and
2Department of Agronomy & Soils, Auburn University, Alabama, USA

Abstract

A 2-yr study was conducted to evaluate performance, intake, digesta kinetics, and ruminal fermentation patterns of steers grazing Sorghum halepense (johnsongrass) at 3 stocking rates. Grazing lasted for 70 d in 1990 and 87 d in 1991. In 1990, stocking rate did not affect bodyweight gain, forage intake, quality of oesophageal masticate, or ruminal fermentation patterns; however, increased stocking rate decreased particulate and fluid dilution rates (22 and 37%, respectively), without affecting dry matter fill or fluid volume. In 1991, increased stocking rate decreased steer gains and total gain/ha, but did not affect quality of oesophageal masticate, intake or ruminal fermentation patterns. As in 1990, increased stocking rate decreased particulate flow rate and tended to decrease ruminal fluid dilution rate. Increased stocking rate also increased dry matter fill, but did not affect ruminal fluid volume. In 1990, quality of oesophageal masticate samples decreased from June through August, which was associated with decreased intake and rates of passage, as well as altered ruminal fermentation patterns. In 1991, seasonal changes were less pronounced. Johnsongrass provided steer average daily gains of up to 0.55 kg/d for 87 d with continuous stocking. Stocking rate affected rates of particulate and fluid passage in steers independent of changes in forage quality.

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