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Effect of Pelleting and of Forage Maturity on Quality of Two Sub-Tropical Forage Grasses^{1 ,2,}

University of Florida, Agriculture Research and Education Center, Belle Glade 33430

Abstract

The objective was to define the effect of processing (green-chopped vs pelleted) and forage maturity (4 vs 8 weeks of regrowth) on voluntary intake, nutrient digestibility and passage rate of digesta from paragrass and St. Augustinegrass. Two trials were conducted in which in vivo digestibility and voluntary intake were measured. Each trial was a 2 x 2 x 2 factorial completely randomized design with two Angus-Brahman crossbred steers per outcome group. Rate of passage was estimated using Cr₂0₃ as a marker.

Pelleting resulted in 23% greater (P<.05) organic matter (OM) intake when based on metabolic body size. Digestibility was decreased by pelleting but digestible OM intake was increased by 8.5% (P<.05). Organic matter intake of paragrass decreased from 90.5 to 66.1 g/w^.75_kg/day (P<.05) with increased maturity, whereas that for St. Augustinegrass did not. Organic matter digestibility of paragrass was also depressed (P<.05) by increased maturity (63.6 vs 54.3%) from 4 to 8 weeks, whereas little depression was seen in digestibility of St. Augustinegrass (59.5 vs 58.0%).

The reduction in digestibility due to maturity and pelleting was most marked in the cell wall components of both grasses. Passage rate decreased and retention time increased with increasing maturity. Retention time of pelleted paragrass forage was significantly (P<.05) less than that of green chopped, but no significant differences were noted with St. Augustinegrass. The interactions of the effects of forage species with processing and maturity on forage quality were probably due to the physical and structural differences in the two plant species rather than chemical components, especially since very little differences were noted in chemical composition. Intakes of OM and digestible OM were correlated (P<.05) with rate of passage and retention time.

¹ Florida Agricultural Research Station, Journal Series No. 595.

² Appreciation is expressed to Mrs. Eilene Gibbens for typing this manuscript.

³ Present address: USDA, ARS, Route 3, El Reno, OK 73036.

⁴ Present address: Haspital 1210, Guadalahara, Jalisco, Mexico.

⁵ Department of Animal Science, University of Florida, Gainesville 32611.