Efficacy of actaplanin fed on a twice-weekly basis to grazing stocker heifers

Brahman (16), Brangus (32) and Simmental X Brahman (16) open heifers were assigned to four treatment levels and two body weight categories. The weight categories were light (250 kg) and heavy (306 kg). Treatment groups were 0, 600, 900 and 1,200 mg actaplanin.head-1.feeding-1 with feeding only on Monday and Friday. Heifers were group-fed .91 kg/head of supplement (95% soybean meal: 5% molasses) containing actaplanin. Heifers grazed eight Coastal bermudagrass pastures throughout the experiment (July 29 to November 15, 1982). After 75 d on experiment, an additional 1.36 kg of a commercial 14% crude protein supplement was fed on the days that actaplanin was not fed. All heifers were weighted and rotated among pastures at 14-d intervals (last weight period was 11 d) as an attempt to equalize forage availability among groups. Over the entire experiment (109 d), light-weight heifers that were fed actaplanin responded (P less than .01) with greater average daily gain (ADG; .37, .35, .21 kg/d; 600, 900, 1,200) compared with controls (0 mg; .18 kg/d). A trend in response (P less than .10) to actaplanin feeding occurred for heavy-weight heifers (.23, .38, .34 kg/d; 600, 900, 1,200 mg vs controls (.22 kg/d). For light-weight heifers, ADG decreased lineraly (P less than .01) as actaplanin increased from 600 to 1,200 mg, while ADG for heavy-weight heifers increased linearly (P less than .10).(ABSTRACT TRUNCATED AT 250 WORDS)