When it comes to keeping calves healthy, age matters, according to a researcher at North Carolina State University.
“Age is dynamic and variable, unlike breed and gender,” said Danielle Mzyk, graduate research assistant in the College of Veterinary Medicine. “It’s not just one parameter. It represents changes in the body composition, liver, kidneys and GI tract, especially for animals less than 6 weeks old.”
Mzyk talked about “Impact of Age on Antibiotic Distribution and Efficacy in Calves” at the recent Calf and Heifer Congress in East Syracuse, sponsored by Cornell Extension and Cornell Pro-Dairy.
Mzyk said that age also affects immunology, drug efficacy and disease processes.
“Calves aren’t little adults,” she said. “They have different body composition. We don’t have a lot of approved drugs for pre-ruminant calves.”
Calves have less body fat, more extracellular water and immature immune responses, among their differences from adult cows.
Mzyk is studying whether drugs are absorbed and metabolized differently by pre-ruminant calves. Learning the answer could help operators know how to better treat sick calves, she said.
Mzyk thinks that oral absorption by pre-ruminant calves may enable them to better handle medications.
“They don’t have to break it down,” she said.
Factors that affect parenteral absorption — areas other than the mouth, mostly likely through injection — include passage of fluid in the area of injection, rate of drug penetration through capillary endothelium, disease and hydration status.
“If a calf is dehydrated, blood flow to the area is decreased,” she said. “Injecting into an abscess isn’t the best way to treat an abscess.”
Since calves tend to have a lot extra cellular water and less fat, that can affect dosing, she said. This factor causes a decrease in distribution of lipophilic drugs and increased distribution of hydrophilic drugs.
“Going on-label for dosing isn’t necessarily the right way to go,” she said.
Young calves also have immature GI tracts, so they can’t metabolize drugs in the same way as adult animals.
“As for a dosing schedule, there’s no one set definition,” she said. “Management and genes make a difference.”
Sick calves often become dehydrated because of their illness, which can skew dosing. Inflammation affecting calves with respiratory disease may affect distribution, too, and the drug may become more concentrated, which may not mean better treatment, Mzyk said.
Sick calves don’t frolick as much as usual. The animal will experience less blood flow to extremities and their bodies will give preferential blood flow to vital organs. This is important for medication delivered subcutaneously, she said, as it will decrease the medication’s absorption.
Mzyk said that dairymen should increase hydration and electrolytes when treating calves, but to do so cautiously.
“You can get the drug to where you want it to go, but they can eliminate the drug faster,” she said.
Mzyk said that illnesses such as some strains of salmonella have become more antibiotic resistant, especially when treating calves. However, she thinks the dairy industry is headed toward more vaccines.
“We can’t just keep using antibiotics,” she said. “We need to prevent illness.”
Source: Lancaster Farming
