There’s no doubt that dairy cattle are a very profitable part of the country’s ag economy, but transition cows are fragile animals. Getting them through the transition period without disease is going to be more profitable for producers during that lactation. However, if a transition cow experiences postpartum disease, it becomes an economic burden if she survives.
So what disease challenges do transition cows face, why and what can be done about it is what Marcus Kehrli, DVM, USDA National Animal Disease Center director talked about in the September Hoard’s Dairyman webinar, Bolstering Transition Cow Immunity.
A large study in the 1980s indicated cows showed the greatest rate of new infections in the mammary glands in the first two weeks after dry off and the first two weeks before calving.
Since most pathogens responsible for mastitis in dairy cows “don’t really have a whole lot of ability to cause disease if the immune system is working well,” evidence points to immune suppression converting subclinical infections into clinical disease like mastitis and retained placenta, Kehrli explained.
“Immunosuppression has many causes,” said Kehrli. “Many physiological transitions such as calving, shipping, transport, weaning, are all factors that will stress a cow’s immune system or a calf’s immune system.”
Vaccinating against the many pathogens that could cause mastitis is impractical. However, phagocytic cells, which are part of the animal’s innate immunity, are known to respond very quickly to try and kill pathogens. One type of phagocytic cell, neutrophils, are “essential for udder healthy — critical for preventing or resolving many postpartum diseases including mastitis and retained placenta,” said Kehrli.
A number of studies show a pattern of decline of immune capability which Kehrli and colleagues determined “have very critical importance for development of disease in cows.
Kehrli showed video of neutrophils rolling through the bloodstream surveilling for inflammation and moving out of the blood and into tissue to combat infection. Any delay in that inflammatory response “was a very poor prognosis for the cow.”
“It’s important to understand that this immune impairment begins and exists well before calving time,” Kehrli stressed.
Kehrli and colleagues wondered if they could use biotherapeutics to increase the circulating pool of neutrophils important for mastitis resistance.
They settled on a molecule called granulocyte colony stimulatory factor (G-CSF), a natural molecule of the immune system of all animals.
“It’s primary role is to increase production of neutrophils from the bone marrow where they are normally made,” said Kehrli. “It activates a critical adhesion molecule that would predict faster response but more efficient surveillance and also enhances a range of neutrophil functions.”
The first study done on G-CSF in the 1980s showed a profound effect on the immune system. Cows were given daily injections about two weeks before calving. It took about 10 days for cows to reach their peak response. Then they were challenged with different mastitis pathogens.
In one study, G-CSF reduced mastitis by nearly 47 percent, Kehrli reported. In another, cows cleared the infection by six hours compared to control cows that were culture positive for seven days. Control cows had fever and abnormal milk for five days, while those that received G-CSF were no longer running a fever after 12 hours and their milk was normal in appearance within 24 hours. Both studies were done on mid-lactation cows.
In a study on early lactation cows, with a lower dose of G-CSF treated for five days in a row starting three days after calving, there was a 50 percent reduction in the number of new infections, faster bacterial clearance rates, reduced severity scores, and improved milk production and feed consumption.
In 2016, the Federal Drug Administration (FDA) approved a form of G-CSF called pegbovigrastim (PEG-gCSF) for use in transition cows with the first dose to be given about seven days before calving and a second dose within 24 hours of calving.
The FDA conducted work with PEG-gCSF in four U. S. dairies, treating 320 cows, which showed a 35 percent reduction in clinical mastitis even though cows were treated seven days before calving and within 24 hours of calving. Kehrli said the work also showed a “lingering effect to reduce clinical mastitis within the first 30 days of milk,” and it also “reduced the failure to return to estrus as measured over the first 80 days of milk.”
The product was also evaluated after it was launched in Mexico on more than 5,000 cows in 17 Mexican dairies, which had a fairly low incident of mastitis naturally during the course of the study. The incidence of mastitis was still reduced by 25 percent, there was a reduction in the number of treatments, less discarded milk, a reduction in retained placenta and it improved the odds of cows being inseminated during the first 100 days in milk, according to Kehrli