Influence of surfactant supplementation and maceration on the feeding value of rice straw in growing-finishing diets for Holstein steers

¹ Universidad Autónoma de Baja California, México
² Department of Animal Science, University of California, Davis 95616

^* To whom correspondence should be addressed. E-mail: razinn{at}ucdavis.edu.

	Abstract

Two trials were conducted to evaluate the interaction of maceration process and surfactant (Tween 80) supplementation on feeding value of rice straw. Treatments were steam-flaked corn-based diets containing 14% forage (DM basis) as: 1) sudangrass hay; 2) ground rice straw; 3) ground rice straw plus 0.22% Tween 80; 4) macerated rice straw; and 5) macerated rice straw plus 0.22% Tween 80. In the maceration process, rice straw was passed through 2 sequentially placed pairs of corrugated rolls set at zero tolerance under ram pressure of 62,050 millibars similar to a conventional grain roller mill, except opposing rolls operated at different speeds (12 and 14 rpm, respectively). Sudangrass hay and rice straw (native and macerated) were ground through a 2.6-cm screen prior to incorporation into complete mixed diets. In trial 1, 125 Holstein steers (292 ± 1.7 kg) were used in a 188-d evaluation of treatment effects on growth performance and carcass characteristics. In trial 2, 5 Holstein steers (224± 3.5 kg) with cannulas in the rumen and proximal duodenum were used in a 5x5 Latin square design to evaluate effects on digestion. There were no interactions between maceration and surfactant on growth or carcass characteristics. Tween 80 did not influence the feeding value of rice straw. Compared with grinding alone, maceration of rice straw increased carcass adjusted ADG (6%, P < 0.10), G:F (6%, P < 0.05), and dietary NE (5%, P < 0.05); DMI was similar across treatments. Assuming NE_m and NE_g of sudangrass hay are 1.18 and 0.62 Mcal/kg, the NE_m and NE_g were 0.61 and 0.13 Mcal/kg for ground rice straw and 1.21 and 0.65 Mcal/kg for macerated rice straw. There were no treatment interactions on characteristics of digestion. Tween 80 did not influence ruminal or total tract digestion of OM, starch, NDF, or N. Compared with grinding alone, maceration of rice straw increased ruminal digestion of OM (7.7%, P < 0.10) and NDF (30.8%, P < 0.05), and total tract digestion of OM (2.3%, P < 0.10), NDF (21.1%, P < 0.01), and N (3.7%, P < 0.05). Total tract digestion of OM, NDF, starch, and N for the sudangrass diet corresponded closely with that of the macerated rice straw diets. Maceration increases the feeding value of rice straw to a level similar to that of good-quality (flag stage of maturity) sudangrass hay, which is attributable to increased OM and NDF digestion. Effects of surfactant supplementation on growth performance and digestion are not appreciable.

Key Words: cattle, digestion, maceration, performance, rice straw, surfactant