Filth fly production and parasitism in heifer rearing pens bedded with straw, hardwood sawdust, and pine shavings

This study compared different bedding materials in heifer rearing pens for their potential to produce filth flies and affect efficacy of beneficial pteromalid wasps. The study was conducted at University of Minnesota’s Southern Research and Outreach Center in Waseca, MN, and repeated in 2009 and 2010. Each year, nine pens containing 7 heifers each were randomly bedded with straw, sawdust, or shavings, and sampled biweekly for 12 weeks to quantify numbers of fly pupae, adult flies, and parasitoids emerging per pen.  Fewer fly pupae were recovered from sawdust (7%) bedded pens than either shavings (46%) or straw (47%).  Fewer adult flies were recovered from sawdust (8%) than either shavings (58%) or straw (34%).  Fewer parasitoids were recovered from sawdust (4%) than either shavings (17%) or straw (79%).  These results suggest that dairy producers could use sawdust or shavings rather than straw to reduce filth fly populations.  Also, bedding choice could affect the success of parasitoid populations.  Pens bedded with straw or shavings will potentially produce more filth flies than pens bedded with sawdust, depending on the abundance of beneficial parasitoids.