FEED-INTAKE AND APPARENT DIGESTIBILITY OF HAY-SUPPLEMENTED BRASSICA DIETS FOR LAMB

Animal performance on brassica diets often does not reflect laboratory estimates of the nutritive value of the herbage. Hay supplementation of brassica pastures should increase diet DM and fiber intake and dilu te anti-quality factors. The optimal hay:brassica ratio needed to achi eve desirable animal performance, however, has not been established. E ffects of changing the hay:brassica ratio on feed and water intake, ap parent digestibility of diets, thyroid status, and anemia were examine d in five Dorset-cross wether spring lambs (initial BW 32.8 +/- 3.2 kg ). The experimental design was a 5 x 5 Latin square with 21-d periods (7 d of adaptation, 6 d of intake measurement, and an 8-d digestion tr ial with jugular blood drawn on last day). Diets contained chopped gra ss hay and tyfon (turnip x Chinese cabbage hybrid) at five hay:tyfon r atios (DM basis): 100:0; 75: 25; 50:50; 25:75; and 0:100. As the propo rtion of tyfon in the diet increased, there were linear increases (P < .05) in ad libitum DMI (922 to 1,359 g/d), total water intake (1.75 t o 13.06 L/d), digestible DMI (401 to 952 g/d), and apparent digestibil ity of DM (55.9 to 86.3%), CP (52.9 to 84.5%), and neutral detergent s olubles (57.2 to 88.5%). Hay plus tyfon diets exhibited negative assoc iative effects for apparent digestibility of NDF, ADF, and cellulose. Plasma thyroxine and triiodothyronine, packed cell volume, red blood c ount, and hemoglobin concentration were not affected by diet. Tyfon in fluenced DMI and apparent digestibility of diets in a manner similar t o that of a concentrate.