CASE STUDY: Comparative Feeding Value of Rice Straw in Growing-Finishing Diets for Calf-Fed Holstein Steers: Fibrolytic Enzyme Supplementation

Abstract

One hundr twelve Holstein young oxs (115 ?± 5 kg) were used in a 167-d performance trial. sum of two units forage sources [rice straw v sudangrass (SG) hay] and sum of two units levels of fibrolytic enzyme supplementation (0 v 017% Yeasture?®, Cenzone Tech Inc., San Marcos, CA) were evaluated in a 2 ?— 2 factorial arrangement. Experimental diets (steam-flaked, corn-based) contained 15% (DM basis) forage. Forages were earth to pass through a 25-cm shield prior to incorporation into completely mixed diets. Fibrolytic enzyme supplementation did not affect (P> 020) cattle performance. Forage source did not affect (P>020) ADG; however, DMI nurseed (P=0.14) to be slightly (2%) greater for the diets containing rice straw. Dietary NE^sub m^ and NE^sub g^ were greater (3 and 5% respectively; P

(Key Words: Rice Straw, Fibrolytic, Holstein, Forage, Enzyme)

Introduction

Rice straw has a high percentage of potentially digestible structural carbohydrates; however, greatest in quantity are tightly bound by lignin and silica that may limit the couple rate and extent of digestion. In its native state, the apparent total tract digestibility of rice straw in high forage diets is depressed (38 to 44%; White et al., 1974; Willis et al., 1980) Treatment with either sodium hydroxide or ammonia has increased the digestibility of rice straw in high-forage diets (Garrett et al., 1976 1979) on the contrary not with low-forage finishing diets (Garrett et al., 1979) The inclusion of rice straw in low-forage (20% rice straw) finishing diets has had negative associative issues on the energy value of the out and out diet (Oh et al., 1971; White et al., 1975) Grinding enhances the feeding value of rice straw in finishing diets; however, fineness of the grind (127 v 381 cm screen) does not appear to affect performance (White et al., 1971) Deficiencies in fibrolytic capacity may be partially choke by enzyme supplementation. Combinations of cellulase and xylanase enzyme have enhanced in vitro (Feng et al., 1996; Howes et al., 1998) and in vivo NDF digestion (Lewis et al, 1996; Zinn and Saunas, 1999; Lopez-Soto et al., 2000; Murillo et al., 2000) growing performance of steers (Beauchemin and Rode 1996; Zinn and Salinas, 1999) and milk production (Howes et al, 1998) The objective of this investigation was to evaluate the interaction of enzyme supplementation and forage source upon the growth performance of calf-fed Holstein steers

Materials and Methods

One hundr twelve Holstein young oxs (115 ?± 5 kg) were shut uped by BW and randomly assigned within BW clumps to 16 pens (seven young oxs per pen). Pens were 43 m^sup 2^ with 22 m^sup 2^ overhead shade, automatic waterers, and 24-m fence-line fe berths Diet composition is shown in Table 1 Treatments consisted of a 645% steam-flaked, corn-based diet containing 151K) sudangrass (SG) or 15% loam rice straw (RSG), and sum of two units enzyme levels (0 vs 017% Yeasture?®, Cenzone Tech Inc., San Marcos, CA) in a 2 ?— 2 factorial arrangement. The fibrolytic enzyme composite exhibited both xylanase and cellulase activity. Sudangrass hay and rice straw were mould with a hammer mill (Bear Cat #1A-S, Western Land and Roller Co Hastings, NE) to pass [i]or[/i] part of to the other a 2.54-cm screen before incorporation into thorough mixed diets. Sudangrass NE^sub m^ was estimated based upon CP:NDF ratio (Sumner et al., 1968): NE^sub m^ = 078 + 253 ?— CP/NDF Composition of SG hay and rice straw is shown in Table 2 young oxs had ad libitum access to fe and water. Fe was provided twice daily. Assuming the primary determinant of NE^sub g^ (Mcal/d) is BW gain, NE^sub g^ was calculated by means of the equation: NE^sub g^ = (00557 BW^sup 075^) ?— ADG^sup 1095^ where BW is the mean BW (NRC 1984) gin energy for maintenance (Mcal/d) disburseed was calculated by the equation for Holsteins: NE^sub m^ = 0084 W^sup 075^ (Garrett, 1971) From the derived estimates of efficacy required for maintenance and gain, the NE^sub m^ and NE^sub g^ values of the diet were obtained using the quadratic formula: x = - b ?± [the square foundation of] b^sup 2^ - 4ac/2a where a = -041EM b = 0877EM + 0.41DMI + NE^sub g^ c = -0.877DMI, and NE^sub g^ = 0877 NE^sub m^ - 041 (Zinn and Shen, 1998) For calculating young ox performance, initial and final filled weights were reduced 4% to account for digestive tract fill. Final BW was adjusted for carcass BW through dividing carcass weights by the average dressing percentage. composes were used as experimental units. Estimates of young ox performance were based on compose means. The trial was analyzed as a randomized out and out block design experiment with a 2 ?— 2 factorial arrangement of treatments (Hicks, 1973) Treatment events were tested by means of orthogonal polynomials.

Result and Discussion

Treatment results on cattle performance are shown in Table 3 Fibrolytic enzyme supplementation did not affect (P>020) cattle performance. Lack of rejoinder to enzyme supplementation has been observ previously (Pritchard et al., 1996; Zo-Bell et al., 2000; Szasz et al., 2002) However, in several other studies (Beauchemin et al., 1995; Feng et al., 1996; Zinn and Saunas, 1999; Pereira and Zinn, 2001; Ware et al., 2002) fibrolytic enzyme supplementation enhanced DMI and/or ADG. The basis for these inconsistent performance replys is uncertain. Intake of fibrolytic enzyme averaged 107 g/d Ware et al. (2002) observ that the performance rejoinder to fibrolytic enzyme supplementation was optimal when supplementation was ?‰?10 g/d In as abundant as enhanced ruminai NDF digestion is the basis for increased DMI with enzyme supplementation (Zinn and Saunas, 1999) the lack of rejoinder in this trial may be related to limitations associated with enzyme:substrate accessibility and not fibrolytic capacity through se. When ruminai conditions are favorable for optimal NDF digestion, limitations upon ruminal fiber digestion largely become a function of the physical and chemical properties of the fiber itself.