During the hectic days and nights of calving season, a few calves may die and producers blame themselves for negligence.
Unexplained calf losses may have more to do with problems among the animals themselves, says Cheryl Waldner, epidemiologist with the Western College of Veterinary Medicine.
“We lose these calves and we just don’t know why,” she said.
Waldner was co-leader of an extensive beef cattle production study released this spring to assess the impact of oil and gas emissions on livestock. But as researchers monitored 200 herds with about 30,000 head across Western Canada for the 2002 production cycle, they collected data on a number of common health issues.
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The study found there are some associated health concerns with exposure to sour gas but more problems stemmed from infectious diseases like bovine viral diarrhea and birth defects. For calves born in areas with higher sulfur dioxide exposure, there was a small but significant increased risk that they would die in their first three months.
“There was definitely a small association with exposure to emissions to the oil and gas industry,” Waldner said.
The study showed the 23 percent of calves that are going to die before weaning do so within the first two days of life. Half of calf deaths before weaning, not counting stillborns, occur in the first week after birth.
“A lot of the calves that we lose, we are losing very quickly in that first week of birth. Intuitively, as producers we know that but there are obviously things going on with that calf during gestation,” she said.
Pinpointing the cause of death might encourage producers to modify nutrition or vaccination programs to reduce costly losses.
The findings have already prompted proposals for follow-up on specific questions.
For example, the vet college is working with Alberta Beef Producers to gather information on the causes of lesions and thyroid problems. These were among the top five reasons calves are aborted or are stillborn.
Researchers found in some cases there was no thyroid hormone present or that the calves had poor muscle development. Further research might tell them the cause.
Another confounding problem is ulcers in slightly older calves.
“It tends to be your best looking calf and you find this 200 pound calf that appeared to be perfectly healthy the day before that is dead,” Waldner said.
Abomasal ulcers were more prevalent than previously thought and need more research.
“It has been a frustrating problem but the research that has been done so far hasn’t been able to come up with something that we can actually do to intervene and reduce the incidence.”
A serious problem affecting many herds is bovine viral diarrhea. However, Canadian researchers are not sure how many herds are exposed and the study did not reveal one region having greater prevalence than others. They did not test all the cattle in the study but did find 18 herds with persistently infected calves. Those BVD infected cattle gain less and tend to be treated for a range of other diseases throughout their lives.
BVD can display a dramatic variability in severity depending on the strain encountered by the herd and the herd’s level of protection. It can cause abortions, weak calves, defects and calves persistently infected with the virus.
Only about five percent of infected animals develop clinical signs of the disease. It could be troublesome in pregnant cows.
“One of the most common scenarios is if they get infected early in pregnancy, they deliver these calves that are persistently infected with the virus,” Waldner said.
The calves may die before they are one year old, but throughout their short lives they spread the virus among the rest of the herd and harm the next generation.
The virus is passed in the feces and secretions from the nose, mouth, milk and semen. Fecal contamination of food and water sources, as well as aerosol droplets and direct contact, are major routes of transmission.
Ranchers need to talk to their veterinarians about prevalence of the disease in their area and treatment options available. This includes various types of vaccination and practising stricter biosecurity. This means taking care when bringing new animals into a herd.
“You need to understand where your cattle are coming from that you are buying and how much a risk they might pose to your herd,” she said.
If there are more than average abortions or stillborns, consult a veterinarian for a diagnosis.
“One of the things that concerned me the most was the effect of being exposed to this infection on fall weaning weights of those calves.”
Research suggested eight to nine percent of herds have persistently infected calves. Calves exposed to infection were on average 10 kilograms lighter at weaning.
“That’s a lot of money if you look at a herd and you look at the number of cattle one calf could be in contact with,” Waldner said.
