Effects of an array of dietary treatments and length of feeding on ruminal methane emission and other variables in hair sheep

Abstract

Eighteen Katahdin sheep ewes (initial body weight [BW] = 73.7 ± 1.76 kg and age = 5.2 ± 0.56 yr) and 18 St. Croix ewes (54.7 ± 1.33 kg BW and 4.1 ± 0.42 yr) were used in an experiment to determine effects of dietary level of Sericea lespedeza (Lespedeza cuneata; 5.8% condensed tannins and 10.3 % crude protein, dry matter [DM] basis) and other supplemental ingredients on BW, feed intake, digestion, energy metabolism, ruminal methane emission, and levels of blood and ruminal fluid constituents. Diets were consumed ad libitum and included a concentrate supplement at approximately 0.45 % BW (DM). Alfalfa (Medicago sativa) was the basal forage for control (CON), ionophore (ION; lasalocid at 33 mg/kg DM), coconut oil (3%; CCO), and soybean oil (3%; SBO) diets, and forage in moderate- and high-lespedeza diets was a 1:1 mixture of alfalfa and lespedeza and all lespedeza, respectively (ALF:LES and LES, respectively). There were four 6-wk periods, with digestion assessed in wk 4 and measures with a respiration calorimetry system in wk 5. Although there was a three-way interaction involving dietary treatment, breed, and period, average forage intake was greater for LES than for CON, ION, CCO, SBO (P < 0.05), and ALF:LES (P = 0.062; 988, 1072, 1265, 987, 951, and 1057 g/day for CON, ALF:LES, LES, ION, CCO, and SBO, respectively; standard error of the mean [SEM] = 69.4). Dietary level of lespedeza had marked effects (P < 0.05) on digestion of organic matter [OM] (69.2, 57.6, 50.3, 66.3, 66.0, and 68.7 %; SEM = 1.57) and nitrogen (78.3, 65.3, 46.8, 71.4, 73.9, and 75.7 %; SEM = 1.81), with digestible OM intake numerically lower (P > 0.05) for diets with lespedeza and for ION (697, 607, 589, 598, 635, and 690 g/day for CON, ALF:LES, LES, ION, CCO, and SBO, respectively; SEM = 50.4). There was a treatment by period interaction (P < 0.05) in ruminal methane emission relative to digestible energy intake, but overall, emission was greatest among treatments (P < 0.05) for CON (12.33, 9.92, 10.24, 10.41, 8.91, and 8.66 % for CON, ALF:LES, LES, ION, CCO, and SBO, respectively; SEM = 0.730). Average daily gain (ADG) was greatest among treatments (P < 0.05) for SBO (54, 28, 18, 40, 56, and 98 g; SEM = 13.2). Many findings are not closely aligned with those of previous studies with goats. For example, effects of lespedeza on feed intake and ruminal methane emission were greater in the first than second half of the experiment, though interactions observed could not be clearly attributed to factors such as microbial adaptation. The effect of the SBO diet on ADG with the alfalfa-based diet deserves future research attention.