October 8, 2009
Bison herd undergoes annual health check-up at roundup
By Melea Burke
Valley Journal
MOIESE — Bison may look peaceful grazing on a distant hillside, but corral them and separate one from its friends, and the giant is gentle no longer. The National Bison Range’s annual fall roundup offers plenty of excitement, and that’s why hundreds of visitors, from out-of-state tourists to buses full of local students, turned out to see the show on Monday and Tuesday.
The roundup is the Range’s annual herd health checkup and allows surplus bison to be separated from the herd. After the Range staff and volunteers gather the bison in a pasture near the corral, the animals are herded into the pen in small groups. Staff used a Jeep and a 4-wheeler to push the animals slowly down a narrow lane between two high fences, feeding the bison directly into the corral. Last year, round-up workers found that the bison, especially the unruly bulls, stay calmer in the confinement of the pens when they're moved slowly by vehicles rather than running from horses chasing them, as was the tradition in the past.
“They come in a lot calmer,” said Pat Jamieson, the Range’s outdoor recreation planner.
Once it’s separated from the group, each animal is weighed and has its microchip checked for identification and to determine if the animal should undergo testing or other treatment.
Calves have their blood drawn for DNA and disease testing, a few tail hairs pulled for genetic testing and a microchip — no larger than a grain of rice — inserted behind an ear for identification. But this year, there was no branding, something the youngsters would have been grateful for had they known what they were missing.
“(Bison Range administration) decided they could get all the information they need from the microchip,” Jamieson explained.
Workers gather blood samples from about half of the herd for testing for diseases like Johne's, which affects the small intestine and prevents the animal from absorbing nutrients from food, although there are no outward signs of the illness until the animal is full grown.
Adult cows get sonograms to determine if they're pregnant, and this year, the pregnant females also were fitted with VHF radio tracking collars.
This year, the roundup also marked the beginning of a bison reproductive performance study.
Historically, an average of 87 calves per 100 breeding age cows are found with the herd during the annual roundup. But in recent years, that percentage has dropped significantly, and no one’s really sure why, Jamieson said. So the U.S. Fish and Wildlife Service is working with Montana State University to study the decrease in calf production, starting with putting a unique tracking collar on each pregnant female during the roundup.
Blood samples from the pregnant cows will be compared to samples from previous years to look for any pregnancy trends. Workers will also collect fecal samples — which can be tested for hormone levels to see if the animal is still pregnant — from collared cows throughout the winter. And once calving is over, monthly spring and summer calf counts will help determine at what point during the reproductive cycle problems are occurring.
In comparison with the last two years, 2009 was actually a great year for the Range’s herd, Jamieson noted. Only 20 calves were born in 2007 and again in 2008, but this spring saw 65 calves join the herd. The National Bison Range maintains a herd of 325-250 bison, and when the herd is growing as it should, about 50 bison are removed during the fall roundup.
This year, 34 bison were auctioned off, and another 10 will be moved to the Rocky Mountain Arsenal National Wildlife Refuge in Colorado to supplement that herd. The removal of those bison will help bolster the food supply for the rest of the herd, which is a bit sparse due to drought.
“The forage isn’t the lushest it could be,” Jamieson said. |
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