This is a seasonal reminder about the importance of effective fly control in calf management. Actually, with the warm weather many of us have experienced so early this year, flies may already be a nuisance. When it comes to calves and their environment, we're primarily talking about two types of flies: house flies and stable flies.
House flies can carry or transmit disease, such as pinkeye and mastitis, and they are a primary nuisance for people. Female house flies lay their eggs in manure, wet organic material, spilled feed, compost piles and other decaying organic matter. Adults have sponging-type mouthparts, so they don't bite.
Stable flies, on the other hand, have piercing-type mouthparts, and they do bite. They pierce the skin to obtain blood meals and can cause quite a bit of stress, leading to decreased productivity. As with house flies, females lay eggs in manure, wet hay and other decaying organic matter.
The first time I wrote about flies was more than twenty years ago. And one thing that has certainly remained constant is that routine sanitation and clean-up are at the core of effective fly control. A good fly control program is built around that theme (which should be obvious when you consider where these flies lay their eggs). Clean up decaying silage and piles of spilled feed. Pay attention to starter feed that may accumulate under each calf's feed and water buckets. Don't let it build up. And of course, clean and sanitize all feeding and feed handling equipment.
The choice of bedding material can also have an impact on fly populations. Materials such as straw and wood shavings absorb more liquid and provide more organic substrates than sawdust or sand, for example. This doesn't mean they can't be used - they need to be managed in a way that minimizes their potential impact. The decision about appropriate bedding material for an operation should be based on farm-specific factors, one of which is fly control.
You can do a lot to take care of stable flies by mowing around the calf area. These flies live in nearby grassy areas, come in to feed and then fly back out. Mow at least 30-50 feet around where calves are housed to remove the living environment for stable flies. This may work to some degree for horn flies, too. These biting flies are about half the size of stable flies and congregate on the animal's back where they spend most of their time. Each horn fly can take 20-40 blood meals each day. Their scientific name fits them well, Haematobia irritans. These irritating flies lay their eggs in freshly deposited cow manure, so their relationship to the calf environment is somewhat different from house and stable flies.
There may be times when you decide to use a pesticide to knock down the adult fly population .You could have an unknown or unsuspected breeding ground or flies may migrate in. Using an adulticide on the adult fly population can temporarily reduce fly numbers, but it won't address the countless fly larvae getting ready to repopulate the airways.
There are a couple ways to reduce fly larvae populations. One is a biological approach which involves fly parasites that target house and stable fly larvae. These fly parasites are released on the premises and lay their eggs in fly pupae. The fly parasite larvae consume the pest fly larvae as they grow. Once they become adults, they can repeat the process, thereby reducing the fly population.
Another approach is to use a larvicide feed supplement. When added to feed, these larvicides pass through the digestive tract and into the manure where they deliver their effect. Organophosphates, such as Rabon®, have been around for a while and provide a toxic effect which disrupts the nervous system of larvae. A newer larvicide, ClariFly®, contains diflubenzuron which provides a very specific effect by inhibiting the formation of the fly's exoskeleton, preventing it from ever reaching adulthood.
Pre-weaned calves pose a particular challenge when using larvicides. Young calves don't consume a lot of dry feed and therefore require more larvicide per pound of feed than a more mature animal. For example, the necessary dose of diflubenzuron is 0.1 mg. per kg. of body weight. To achieve this dose, the amount of ClariFly® added to starter feed needs to reflect a calf's feed intake level. In other words, it's important to provide young calves with a starter feed that's properly formulated to achieve a larvicidal effect.
With good management under normal circumstances, calves begin consuming an appreciable amount of starter by the end of their second week of age, and by 3-4 weeks they are consuming enough ClariFly® to stop the development of fly larvae. If you remove the old bedding and start each calf off with new bedding, it will take a while for the calf's manure, urine, dropped feed, bedding etc. to build itself into a sustainable breeding ground for flies. This approach minimizes the amount of time a calf's manure does not contain ClariFly®, while at the same time providing the calf with ClariFly® protection that is already established from those calves around it.
For those operations using a feeding system where each calf consumes a large daily volume of milk/milk replacer, starter intake is usually reduced and delayed until much closer to the weaning process. This further increases the time calves remain unprotected when using a larvicide feed additive. The good news is that Central Life Sciences, the manufacturer of Clarifly® hopes to have a version of ClariFly® available this summer that can be added on-farm to milk and milk replacer.
Whatever fly control options you choose, the time to get going is about 30 days before you think flies will appear. Flies generally remain a concern until about 30 days after the first hard freeze. And if you live where is doesn't freeze, you don't really get a break.
Here's a link if you want more information about ClariFly®.