Animals responding to severe local or systemic inflammation will have a fever, muscle weakness, lethargy and malaise generally expressed by reluctance to move around or associate with herd mates, will groom less, will lie down more, will go off-feed and drink less, explains Mark Spire, DVM, Intervet Schering-Plough Animal Health.
The immune system can release pro-inflammatory responses, which come at a cost to the animal. Immune response to infection requires vast amounts of energy for tissue repair, increased metabolism and fever maintenance. Fever alters eating and drinking behavior. Cattle with pneumonia spend less time eating and drinking and have reduced feed efficiency.
Cattle try to reduce heat loss during a time of fever by postural changes such as lying down and tucking up, piloerection of the hair and shifting blood flow from the skin to the deeper organs. They also increase heat production through shivering and in the case of calves, metabolism of brown fat. Prolonged response to infection can lead to muscle breakdown as fuel for the immune system and energy requirements. Even if they recover, there can still be economic losses due to effects on the carcass, especially fat deposition.
But cattle can also show sickness behavior without having pneumonia, which can be due to a combination or large volume of pro-inflammatory products used on arrival. Sickness behavior can be from endotoxins from vaccines, rumen upset, acidosis, injuries or any inflammation in an organ system. The use of multiple products on arrival can have an additive stress effect and increase inflammation. “Make it a simple program on arrival,” Spire says. “And choose the products wisely. Vaccines may contain a small amount of endotoxin, but using several of those at one time can be detrimental.”
Severe injection site reactions can also make an animal more reluctant to move to the feeder or water when other animals are present, which is an avoidance mechanism due to the pain response. Age at weaning may influence the inflammatory response, and stacking on stress events such as transportation, castration, dehorning and other procedures may also contribute to inflammation.
“Cattle display sickness behaviors that may indicate they are ill, but it cannot be assumed that it is BRD and we should not arbitrarily treat or revaccinate them,” Spire says. He recommends doing a good physical examination on a calf that is pulled for sickness and taking the time to watch the calf to help determine if you’re dealing with a case of BRD or something else. “A lot of times they will show you what’s going on.”
A key indicator for respiratory disease is respiratory rate. If a calf is in a normal environment, BRD will alter respiration. “The same goes with flaring nostrils; he’ll change his facial expression when there is lung involvement. If I want to pick him out for treatment, I will listen to the lungs.”