Evaluation of grass straw:corn juice silage as a ruminant feedstuff: digestibility, straw ammoniation and supplementation with by-pass protein

Abstract

Three experiments were undertaken to determine the feeding value of grass straw:corn juice silages compared to grass hay. In experiment 1 (70 d), the four basal diets were: 1) grass hay (GH) used as control treatment; 2) tall fescue straw:corn juice silage (50:50 wt./wt.)(FCJ); 3) urea treated tall fescue straw:corn juice silage (50:50, wt./wt.)(UFCJ); and 4) annual ryegrass straw:corn juice silage (65:35, wt./wt.)(RCJ). Ammoniation was performed by spraying the straw with urea solution having 1% raw soybean extract (urease source) to provide 3% urea (dry matter basis). Thirty-six beef heifers (9 per treatment) were fed these roughages ad libitum with a concentrate supplement (1.36 kg d −1). Out of nine heifers allotted per treatment, four were fed individually while the remaining five were group-fed. Feed intake (FI) (kg), average daily gain (ADG) (kg d −1) and feed efficiency (FE) (kg −1 BWG) in individually-fed heifers in experiment 1 were: 5.16, 0.671, 7.97; 5.40, 0.557, 10.00; 4.84, 0.58, 8.41; and 4.54, 0.523, and 8.92 for GH, FCJ, UFCJ, and RCJ, respectively. In group-fed heifers, FI and ADG were: 8.33, 0.71; 5.54, 0.564; 5.41, 0.568; and 5.92, and 0.38 for GH, FCJ, UFCJ, and RCJ, respectively. No differences ( P > 0.05) were observed in any trait, except that ADG in group-fed animals on the GH treatment was significantly higher ( P < 0.05) than in animals on the RCJ treatment. In experiment 2 (57 d), the same animals and same roughages were used but supplementation was changed in the FCJ, UFCJ, and RCJ treatments. In these three treatments, the concentrate was reduced to 682 g d −1, and alfalfa hay was offered at 1.36 kg d −1. The UFCJ group also received fishmeal at 125 g d −1 as a source of by-pass protein. FI (kg), ADG (kg d −1) and FE in individually-fed heifers were: 7.99, 0.91, 8.80; 8.89, 0.81, 11.33; 7.60, 0.97, 7.87; and 7.83, 0.76 and 10.37 for GH, FCJ, UFCJ, and RCJ, respectively. ADG was higher ( P < .05) in UFCJ vs. RCJ and FE was higher ( P < 0.05) in FCJ vs. UFCJ. In group-fed animals, FI and ADG (kg d −1) were: 8.43, 0.76; 7.19, 0.67; 6.79, 0.70; and 7.14, and 0.55 for GH, FCJ, UFCJ, and RCJ, respectively. ADG was higher ( P < 0.05) in GH vs. RCJ. In experiment 3, 12 sheep were used to determine in vivo digestibility of the four basal feeds (without supplementation) used in the first two experiments. Percent apparent digestibility of dry matter (DM), gross energy (GE), crude protein (CP), NDF, and ADF was: 60, 59, 46, 52, 56; 55, 56, 51, 46, 49; 59, 60, 74, 51, 57; and 55, 56, 30, 43, 50 for GH, FCJ, UFCJ and RCJ, respectively. Differences between GH and UFCJ were not significant ( P > 0.05) for DM, GE, NDF, and ADF digestibilities; however, CP digestibility differed ( P < 0.05). A similar pattern was noted between FCJ and RCJ. All digestibility parameters were higher ( P < 0.05) in UFCJ vs. FCJ. Digestible energy (MJ kg −1) was: 9.690, 9.569, 10.079 and 9.519 for GH, FCJ, UFCJ and RCJ, respectively. Feed intake was similar among the four treatments. It is concluded that straw:corn juice silages are about equal to medium quality grass hay in feeding value. Supplementation with alfalfa hay and fishmeal further improved performance.