Do birds pose a health problem in your dairy barn?

Monday, October 3, 2011

There's little documentation on the overall risks birds present to farms. Experts tend to discount the risk of salmonella, but some are concerned that E. coli can be passed between cattle and starlings

by MARY BAXTER

From a bird's eye view, a barn is just a big nest or a giant feed dish. But too many birds in the barn can pose health risks to a dairy herd and indirectly affect the quality of the milk they produce. 

Scott Weese, associate professor in pathobiology at the Ontario Veterinary College in Guelph, says that there are two main concerns: bringing infectious diseases in from the outside and transmitting disease from farm to farm. Salmonella has traditionally posed the greatest risk, but questions are also being raised about wildlife's role in transmitting anti-microbial resistance and pathogens such as E. coli 0157.

Because of pasteurization, the risk to human health from salmonella in cows is "minimal," notes Rick Knill, a partner with Mitchell Veterinary Services.  Even for cattle, low levels of salmonella usually won't be an issue. Add environmental stresses such as heat, humidity or feed changes, however, and the bacteria can trigger a bloody diarrhea or septicemia, a generalized blood infection.

"I've had situations where we've had salmonella in the barn's water trough and that's been a concern," Knill says. "But it's hard to say is it directly caused by birds."

Contamination of feed can also affect the quality of feed and consequently the cows' feed intake, he adds.

David Pearl, an assistant professor in the department of population medicine at the Ontario Veterinary College, has been working with a group of U.S. researchers (led by Jeffrey LeJeune, a professor in food safety extension at the Ohio State University's College of Veterinary Medicine) to study whether European starlings could play a role in spreading E. coli 0157 in dairy cattle. The strain does not affect cattle but can cause severe illness in people. He says there's a lot of concern about the birds in the United States, where it's estimated they account for $800 million in feed losses annually.

The researchers established in principle that E. coli can be passed between cattle and starlings. In the field, they found that the prevalence of E. coli usually peaks in cattle in late summer or early fall, a time when the birds are in the barns a lot more. Moreover, as the number of starlings per milking cow on  the farms studied increased, the amount of shedding of E. coli increased. They also found that some of the birds shared the same subtypes of the strain with the cattle in the barns they visited.

"Obviously the birds aren't the origin of 0157, but they may be involved in spreading it around and increasing the prevalence that way," Pearl says. The researchers are applying for funding to explore whether the birds help spread anti-microbial resistance and other pathogens.

Pearl says there has been much research into birds' transmission of disease to livestock, some of it giving surprising results. He points to one study that challenges the popular assumption that barn swallows are involved in the transmission of salmonella, where the researcher "looked at a lot of farms and a lot of barn swallows, but never found any salmonella in the birds at all." He points out that the presence of risk depends on many variables: for example, the type of pathogen involved, the bird species and its feeding pattern, as well as the type of livestock in question.

There is little documentation of the overall impact of the risks birds present to farms, Pearl says. How much effect an intervention might have is another potential area of study. The challenge is to find the money because such studies would be expensive. From an industry perspective, however, the birds' contribution to feed loss and potential to spread disease would likely justify such research, he suggests.

Gauging how much of a problem bird infestations pose to Ontario's dairy farms is difficult. Alex Hamilton, field services and Canadian Quality Milk program manager at Dairy Farmers of Ontario, says free stall barns are particularly vulnerable, because "there are big doors that are open all the time and birds can get in."  

Starlings are not the only problem, according to those on the front line of defense. Dan Frankian, CEO of Hawkeye Bird Control Inc., a pest control company based in the Halton Hills, deals with 14 to 15 dairy farmers a year. In his experience, pigeons present the majority of problems.

Dean Stanbridge, vice president and technical director, Direct Line Sales and Supplies Corp., a pest control product wholesaler in Burlington, says the English sparrow is another common pest. Sparrows are more difficult to control than starlings (which are larger and roost outside of barns) because they will settle in cracks, crevices and holes, he explains.

Both Frankian and Stanbridge stress preventative measures, such as reducing entry points to the barn, eliminating access to feed and tackling external attractions such as access to food, water or shelter. Netting will work to keep birds out, but the cost (about $3 a square foot) can be prohibitive, Stanbridge says.

Resident populations have to be removed. If they are not dispatched, they will return, he advises. Strategies include traps and temporary mist-nets (a nylon net that's almost invisible once hung) on barn exits and using scare tactics to flush out elusive birds. Frankian discourages the use of devices such as sonar, sounds or motion detectors to scare birds away. "I've yet to find one that works."

Also think twice before taking a gun to the birds inside the barn, he cautions: "I've heard of a few farmers shooting them, but unfortunately sometimes they miss and it goes through their ceiling."

Frankian uses a pellet rifle for pigeons, but only at night when the birds can't see each other. "The minute you shoot the first one, the rest already know what's going on," he explains. He will sometimes use birds of prey, such as small or medium-sized hawks.

Stanbridge is hesitant to set birds of prey loose in barns. "If the sparrow's well established, it's just going to tuck itself back into its dark little crack or crevice."

Moreover, only a couple of breeds are small enough to manoeuvre in the constrained quarters.

Hamilton wonders if encouraging falcons to nest in the area might be the answer. He recounts one farm family's experience with a falcon recording. Initially, they "didn't think much of it," he says. Then falcons settled nearby. The family credits the recording for attracting them. "They clean out any birds that are there." BF