Interaction of Compudose 200® and resistance to parasites on growth of steers of two cattle breeds

Abstract

SUMMARYThis study sought to determine whether increases in live weight (LW) of steers implanted with Compudose 200®, a growth promotant that contains 17β-oestradiol, arose in part from increases in resistance of those steers to cattle ticks and gastro-intestinal nematodes (worms) to which the steers were exposed while they were growing. Half of a group of interbred Hereford × Shorthorn (HS) and interbred Brahman × HS (BX) steers was implanted with Compudose 200 on two occasions 200 days apart. Half of each of the implanted and nonimplanted groups in each breed was treated every 3 weeks to control cattle ticks and worms. All animals grazed together and were regularly monitored for parasite burdens and LW changes. Both breeds responded positively to Compudose 200, to which BX responded most, and to treatment to control parasites. Resistance to either ticks or worms was unaffected by the presence of the implant so that, within each breed, increases in LW gain in response to the implant were similar regardless of parasite control. Thus the increases in LW gain resulting from the use of Compudose 200 arose directly from the action of the implant on metabolism, not indirectly through any effect on resistance to parasites.