BIG SKY, Mont. — Mycoplasma bovis has plagued cattle for years, causing respiratory disease, arthritis and mastitis, among other ailments. But only since 1999 has it been associated with bison.
Karen Register, a research microbiologist with the U.S. Department of Agriculture’s national animal disease centre, wants to know why.
She has undertaken a study of M. bovis in bison and has preliminary results.
The pathogen is more virulent in bison than in cattle, she told those at the International Bison Conference July 5.
In cattle, it is often a secondary invader that follows on other illness or stressors and is seldom the cause of death.
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In contrast, M. bovis is frequently identified as the primary cause of death in infected bison.
Register said there is compelling evidence, though not proof, that novel variants of M. bovis have emerged, which could explain the difference.
She also seeks to learn when the pathogen first began to circulate in bison and to examine the role of healthy bison in its spread.
“One of the big questions we’d like to answer is, can healthy bison act as carriers for M. bovis,” she said.
“The answer is important be-cause it has implications for monitoring practices, for biosecurity practices and for understanding what kinds of measures are reasonable and appropriate if you should encounter M. bovis in a healthy animal in your herd.”
Data on bison with which to study that question is limited, but Register did find and use samples from bison collected from 18 American and 17 Canadian herds in the 1980s through 2015.
She learned that some bison carried the M. bovis pathogen years before its effects were noticed in herds. Multiple herds in both countries had animals carrying the pathogen.
Register said management practices might play a role. Bison raised in feedlots or more tightly penned conditions than free-roaming grass-fed animals had a higher rate of M. bovis.
Though she was not prepared to make definitive conclusions, “it does seem reasonable to conclude that there is an association be-tween the use of more intensive management practices and carriage (of M. bovis) in healthy animals in a herd.”
Dr. John Church, a veterinarian and associate professor at Thompson Rivers University in Kamloops, B.C., said the debate over finishing bison on grass or in a feedlot situation continues to rage, and not because of M. bovis or any other disease risk.
Some bison producers favour the grass-fed model as part of bison’s natural image in the minds of consumers.
However, Church said finishing bison on grass isn’t economical in colder climates.
“If we were living in New Zealand, where the grass grows virtually year round, or Hawaii or Vancouver Island off the coast of B.C., where they get grazing 10 months of the year, grass-fed beef is pretty easy,” he said.
“That connection to preserving the grasslands, it’s a tremendous story but there’s challenges, right? It’s challenging in northern climates trying to raise bison.”
Finishing bison in feedlots can reduce the time to market, increase carcass weight, improve grades and provide a consistent product, while allowing producers to raise more bison on a limited land base.
However, care must be taken with rations to prevent acidosis.
“Bison have not been selected in breeding programs to perform on high grain finishing rations. Cattle, we’ve been doing it for a hell of a lot longer,” said Church.
In his talk, he referenced a University of Saskatchewan study that concluded a high grain diet is viable for finishing bison but requires a higher level of management.
However, Church said bison in finishing diets with 80 percent rolled barley had high levels of acidosis, which he thinks constitutes animal abuse.
A key point in the U of S study, which Church said did not get enough emphasis, was the fact that the average daily gain of bison was no different in animals on a backgrounding diet of 45 percent rolled barley and the finishing diet with 80 percent.
Church said his own studies show finishing bison on grass and providing an additional pea screening pellet had good results with no acidosis issues.
“Seasonal supplementation with a pea screening pellet is a reasonable management strategy to alleviate seasonal grazing pressure while retaining a fatty acid profile which is very, very similar to grass fed beef.”
