At the summer meeting of the Professional Dairy Managers of Pennsylvania, Dr. Hayley Springer, Penn State Extension veterinarian, discussed the challenges in developing both everyday and enhanced biosecurity plans for dairy farms.
Everyday biosecurity includes measures taken daily on the farm, especially regarding visitors. Enhanced biosecurity involves extra steps producers are prepared to take in the event of a foreign animal disease outbreak.
“The key to biosecurity is preventing disease,” said Springer. “The best way to understand what biosecurity practices to put in place is to understand how disease is spread.”
Springer listed seven ways in which disease is spread: vector, iatrogenic, direct contact, oral, aerosol, fomite and reproductive.
Vector-borne diseases are spread primarily by insects. Springer said Theileria, a blood disease, is transmitted by the Asian longhorned tick (a new invasive species). Cattle that spend time on pasture are at highest risk.
“It’s important to check animals for ticks,” said Springer, who suggested submitting ticks for species identification. “If we know where ticks are, we know where disease is.” The biosecurity measure for Theileria and other vector-borne diseases is controlling the vector.
Pinkeye is also a vector-borne disease. “One of the ways pinkeye can be transmitted is by flies,” said Springer, “but flies are not required – they are a mechanical vector.”
Iatrogenic transmission occurs when humans transmit disease, such as when needles are reused. Humans can transmit bovine leucosis through rectal palpation sleeves. Springer cited a Cornell University report that indicated 50% of cattle condemnations at a Northeastern slaughter plant were due to lymphoma.
Direct contact between animals can spread disease. Bovine viral diarrhea (BVD) is transmitted via direct contact, so it’s important to not introduce BVD-positive animals to the herd.
With oral transmission of disease, fecal-oral is the most common route, especially among calves. Johne’s disease is spread by the fecal-oral route. Spread of disease via aerosol transmission occurs with bovine respiratory disease.
Fomites are inanimate objects such as brushes, shoes and buckets that can transmit disease. “Cryptosporidium is a fomite-borne disease,” said Springer. “When a calf has cryptosporidium, they excrete huge numbers of oocysts – the infectious particles. Fewer than 25 oocysts can cause disease in calves, and a quarter teaspoon of oocysts can infect thousands of calves.”
Reproductive disease transmission is uncommon, and the dairy industry has eliminated the risk of contagious reproductive disease thanks to AI and the stringent biosecurity practices of AI companies.
Springer cited an incident that occurred on a dairy farm in Colorado but which could happen anywhere. A farm expansion included a new building with a 60-cow rotary parlor, a separate hospital area and a parlor for fresh cows. The original cowherd numbered 350; it increased to 2,500 milking cows after the expansion.
“They purchased cows and heifers from 15 different sources,” said Springer. “All of the sources had a single mycoplasma negative on a bulk tank culture.” It’s important to understand that mycoplasma is not consistently detected via bulk tank cultures, especially if disease is at low levels. “Typically, we would recommend multiple bulk tank cultures to demonstrate a herd is truly clear of mycoplasma,” she said.
Despite rigid protocols, the farm saw 560 new mycoplasma mastitis cases in the first 17 months. “We know mycoplasma mastitis is particularly challenging because it doesn’t respond to any of the antibiotics available to treat it,” said Springer. “It’s also contagious and can be spread through the parlor. When they looked at the 560 mycoplasma mastitis cases, 88% had had a previous visit to the hospital pen with a negative culture.”
The other disheartening aspect of mycoplasma is that it doesn’t stop at mastitis. Multiple calves had respiratory disease, swollen joints, drooping ears and head tilt – all classic mycoplasma signs.
Springer said the outbreak came at a high cost to the dairy. Milk cultures for mycoplasma cost more than $100,000. Culturing for mycoplasma is challenging because it doesn’t grow under typical culture conditions. Because mycoplasma mastitis can’t be treated, the dairy had to cull heavily.
The dairy also incurred the expense of added labor in hospital pens due to the high number of sick animals and had to discard milk. Calves with swollen joints had reduced average daily gains, and many calves were lost.
Calves on the farm had received four quarts of raw colostrum within four hours of birth, followed by pasteurized waste milk. “That’s a good colostrum program,” said Springer. “Where was the gap?”
The gap in opportunity to prevent a mycoplasma outbreak was with raw colostrum and milking units. Springer related the development of an everyday biosecurity program to what happened at the Colorado dairy.
“The first step is to identify risks,” said Springer. “Where are the risks of disease introduction or disease spread in the herd? Then identify gaps. Develop protocols to reduce the risk of disease transmission. One of the most important things in developing protocols is making sure everyone is using them properly. People are important in everyday biosecurity.”
On the Colorado farm, all cattle were mycoplasma negative on a single bulk tank culture. “This is where it’s important to bring in advisors,” said Springer. “Testing wasn’t enough because mycoplasma doesn’t multiply in milk.”
One challenge with mycoplasma is that it’s transmitted by direct contact, oral contact, aerosol, fomites and reproductively. The most common fomite in mycoplasma transmission is the milker unit. Multiple cultures on incoming animals would have helped identify positive animals and slow the outbreak. Quarantine is also important: new animals should be housed and milked separately.
As for the 88% of infected cows that had a previous visit to the hospital pen with a negative culture, Springer said there’s a good chance those animals acquired mycoplasma while in the pen. The farm identified the hospital pen as a high-risk transmission site and trained workers to fully understand mastitis and how it spreads.
“They made sure workers understood the methods to prevent mastitis transmission during milking – clean gloves and not sharing towels between animals,” Springer said. Workers were trained in proper treatment technique and milking machine disinfection.
Prior to worker training, the farm experienced one to two new mycoplasma cases daily. After training, new cases dropped to about one to two per month, and most positive animals had no history in the hospital parlor. But while milker training took care of direct contact and fomite transmission, calves were still becoming infected.
“Raw colostrum is a significant risk of oral transmission of this disease, so they heat-treated colostrum,” said Springer. “They trained employees to recognize early signs of respiratory disease and moved sick calves to outdoor hutches to reduce aerosol transmission.”
Springer said the new FARM manual includes good information on dairy farm biosecurity.
“If we have good everyday biosecurity protocols ahead of time, we shouldn’t see disease outbreaks,” she said.
by Sally Colby