J. Anim Sci.
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J. Anim Sci. 1987. 64:578-585.
© 1987 American Society of Animal Science
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Efficacy of Actaplanin Fed on a Twice-Weekly Basis to Grazing Stocker Heifers1

C. C. Chase, Jr.2, R. D. Randel2 and L. H. Carroll3

Texas A&M University,2, Overton 75684 and Eli Lilly and Company, Dallas 75234

Abstract

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 weighed 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<.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<.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<.01) as actaplanin increased from 600 to 1,200 mg, while ADG for heavy-weight heifers increased linearly (P<.10). Feeding 900 mg actaplanin elicited a positive response in both weight categories. Ruminal fluid samples were collected from the light-weight heifers on d 31 and 84 at 4, 24, 48, 72 and 96 h post-feeding. On both d 31 and 84, actaplanin-fed heifers had lower molar proportions of ruminal acetate and greater propionate. Less consistent ADG for 600- and 1,200-mg actaplanin-fed heifers during the last 39 d may be explained by lower total volatile fatty acid concentrations compared with the 900-mg level. The data are interpreted to indicate that if both light- and heavy-weight heifers are considered, 900 mg actaplanin fed twice weekly may maintain weight gains in heifers grazing forages during periods of low nutritive value.

Footnotes

1 Journal Paper TA 20846, Texas Agr. Exp. Sta.

2 Texas A&M Univ. Agr. Res. and Ext. Center, Overton 75684.

3 Eli Lilly and Co., Dallas, TX 75234.






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Copyright © 1987 by the American Society of Animal Science.