Abstract
Economic losses attributed to fly populations in cattle are estimated to exceed $1 billion in the U.S. Excessive populations of horn fly within wet calf barns can cause significant health concerns and are a nuisance. Many attempts to control these pests rely on external or internal insecticides to reduce adult populations of horn fly, however, by targeting the adult horn fly, producers are often inadvertently increasing the selection pressure with the result being insecticide resistant adult flies producing the next generation of larvae. An alternative method of controlling populations of flies in wet calf barns is the inclusion of Diflubenzuron larvicide in the milk replacer. The objective of this study is to evaluate the effectiveness of Diflubenzuron in Angus x Holstein wet calves across two different manure management systems. A total of 715 calves were evaluated across 3 different farms for a 7-week period. The manure management system at the first calf operation (PIT) housed 265 calves in individual calf pens over a slatted floor that allows waste to pass through into a collection pit that can be flushed daily with a total clean out once / calf crop, while the second (BED1; 250 calves) and third operations (BED2; 200 calves) used straw bedding and daily manual removal of wastes. Regardless of the operation, each calf is housed in a pen that is 1.67 m(2). Calves across all farms are fed a milk replacer twice per day with Diflubenzuron included at a rate of 8.19 mg Diflubenzuron / day starting on day 0. Beginning on day 3, calves were also offered a free choice creep feed containing 6.05 g/ton of Diflubenzuron. Fly control is recorded using yellow glue traps placed 2.5 meters above the calf pens on both sides of all calf barns. The number of flies caught in the traps were recorded each week and traps were refreshed. The PIT operation had a lower initial population of flies with just 1460 flies trapped in the first week while BED1 and BED2 recorded 4900 and 2844 flies, respectively. However, as expected, BED1 and BED2 recorded the greatest decrease in fly population throughout the study reducing populations by 97.3% and 81.0%, respectively, while PIT saw a reduction of only 63.0%. Based on the data presented here, inclusion of Diflubenzuron in the diet of dairy calves can be expected to reduce fly populations by the greatest amount (over 80%) in manure management systems where waste is not immediately removed and can be used in a pit-style manure management system to manage fly populations without selecting for insecticide resistance.