A production based targeted selective anthelmintic treatment regime for grazing dairy calves

Abstract

Recent studies have highlighted the risk of anthelmintic resistance in dairy heifer calves due to use of neo suppressive drenching regimes. For these systems, effective parasite control and reduced anthelmintic usage can be achieved through targeted selective treatment (TST} anthelmintic regimes. However, recent investigations in sheep and cattle suggest that FEC is a poor indicator of which individuals are likely to benefit from treatment. This investigation sought to determine if a production based TST was an effective targeted selective treatment option for dairy calves over time and across a variety of farms. Studies over three years, across a number of farms evaluated the performance of various groups of Friesian and Friesian x Jersey calves (n=100+) in two different grazing systems. In system 1 calves were grazed in front of the main milking herd whereas in system 2 where calves were sent for grazing off farm. Within each grazing system calves were allocated into two groups (n-=50) with one group treated on a monthly basis , a neo suppressive treatment, (NST) and the second group were treated on individual basis by their failure to reach a production target (TST). Calves were monitored at monthly intervals for Individual FEC and live weights (LW) from around 4 months of age until 1 O months of age. Results from year 3 confirm initial trial findings with substantial reductions (p=0.001) in drench usage in TST treated groups, ranging from 57% to 73 %. As LWG targets increased over the three years the number of TST animals needing treatment also increased. In year 3, on three of the four farms there was no significant difference seen between LWG of NST and TST calves. This supports earlier findings which suggested that as you approach a 50% treatment frequency, difference in LWG between NST and TST groups were eliminated. The adoption of a production based TST appears to reduce drench usage without compromising calf production and would tie in nicely with industry recommendations to frequently monitor calf liveweights during their first grazing season.