Bovine respiratory disease (BRD) in young dairy calves can have profound production and economic consequences in the short-term and even later in life. BRD will occur in both milk-fed and weaned dairy calves. Amy Stanton, PhD, Department of Population Medicine, University of Guelph, says BRD in milk-fed calves will occur throughout the milk feeding period with BRD in weaned dairy calves usually occurring in a more contained time period, usually around movement to a new facility or upon first mixing.
Early intervention of respiratory cases in dairy calves is critical to reducing the short- and long-term effects of the disease. Early detection involves understanding sickness behaviors and responding quickly. “Sickness behavior occurs in all mammals and is a coordinated set of responses to infection,” Stanton explains. “This includes people such as when they get the flu. These behaviors are performed, and we have evolved to perform them, to increase the potential for survival. Now, they can be used to identify animals early in order to treat them.”
Stanton says we are still identifying how sickness behaviors are presented in cattle but from other species we know they include:
* Decreased appetite. Is this subtle or pretty dramatic at the onset of sickness? It can be either. Decreased appetite in milk-fed calves alters depending if they are fed ad libitum or restricted. Early signs for ad libitum fed calves are more likely to be decreased appetite while limit fed calves are less likely to try the milk feeder when they are not eligible to be fed (decrease in unrewarded visits to feeder) (Svensson & Jensen, 2007; Borderas et al. 2008; Borderas et al. 2009).
* Decreased energy/lethargy. How is this displayed? Calves are more likely to be lying down. Stanton also uses the “encouragement to rise score” (see “Score” box) to assess this.
* Decreased thirst. Is this subtle or dramatic? This can be hard to detect without close monitoring.
* Apathy. For example, the calf doesn’t care about human interaction or the feed bucket being filled up.
* Energy conservation. Lying down is a great way to conserve energy. “Short-lying,” with the head tucked into body, may be one indicator.
* Depression. Indicators include poor coat quality, lowered head, apathy, dull eyes, tail and ear carriage.
* Fever. Fever alters the environment within the body, making it less hospitable to pathogens, but it has a high metabolic demand. “Other behaviors appear to coincide with this increase in order to conserve energy,” Stanton says, “such as decreased appetite and thirst, lethargy or apathy, decreased social interactions and decreased grooming.”
“All of these behaviors and clinical signs have been shown to increase the potential of surviving an infection without medical intervention,” Stanton notes. Some of these behaviors have been addressed in calves but further research is needed.
In Stanton’s current study investigating the behavior of individually housed calves between zero–8 weeks of age, 800 calves were observed, three times between zero and 8 weeks of age. “We looked at various measures which we suspected could help us identify sick animals based on sickness behavior,” she explains. Calves’ behavioral responses were compared with their ADG during the study, and using producer-identified diseases, Stanton compared “healthy animals” (defined as no diagnosed disease within 10 days prior to or following a disease event), to calves with diarrhea (defined as calves with producer diagnosed diarrhea either three days before or after behavioral observation performed).
Stanton’s results included:
* “Statue standing” (see photos) and holding the neck below the chest in calves less than 2 weeks of age was associated with lower ADG. “These two postures were selected based on what we expect is the motivation for them,” Stanton says. “The statue-standing calf appears tense through the abdominal area. This behavior is usually observed when animals have visceral pain, and we expect that this will be observed during the clinical phase of the disease.” Stanton says this observation is based on preliminary research showing that when pain relief is provided, calves are less restless and recover faster from C. parvum diarrhea, as measured by grain intake and activity (Todd, 2007).
Short-lying should be monitored associated with clinical diarrhea. “This is a posture which will help maintain body temperature,” she says. She adds to make sure calves are dry and the addition of deep straw bedding above the legs will help with energy conservation and has been shown to decrease the risk of BRD (Lago, 2006).
* Lethargy (encouragement to rise) score greater than 3+ between 6–8 weeks old is associated with decreased ADG. “Young calves may be hindered in their ability to stand, but by this age, calves should stand with very little encouragement,” Stanton says. “If they do not, they should be examined closer.” She adds that this score may have to be altered to fit the individual farm, but if the calves have very little response or are slow to respond to a person’s entry into their space, this may be a sign of disease.
* Willingness to approach is a less sensitive measure, but Stanton says because milk-fed calves associate people with food as well as having natural curiosity, if suddenly individuals fail to display this behavior, astute calf care personnel may pick up on subtle signs of inappetance or apathy. She says in her studies if a stationary observer stands near the pen, within 60 seconds more than two-thirds of healthy calves approach the observer and just over one-third of calves with diarrhea approached the observer.
Identifying poor growth
Factors that can cause poor growth in a dairy calf include poor nutrition, BRD, diarrhea, failure of passive transfer, stress, poor environment and more. “Basically, poor growth is an indicator that something has gone wrong in your management,” Stanton says. “For instance, calves that do not gain weight post-weaning is an indicator that they were not ready to be weaned, or the wean was too stressful. This should be addressed by improving pre-weaning management.” Stanton says this could include performing a more gradual wean and monitoring calf starter intake.
Identifying causes of poor growth is challenging since so many variables can affect it. “Basically, we are looking for calves that are not performing as expected,” Stanton notes. “These are animals that either due to increased energy demands due to disease or decreased appetite, are below the targeted weight gain. These animals are most likely to require some attention due to either the need for treatment or additional attention to increase their feed intake, especially calves during or shortly after the weaning process.”
Encouragement to rise score
Amy Stanton, PhD, University of Guelph, says using an “encouragement to rise” score can give you an indication of sickness in calves.
0 Already standing.
1 Stands in response to single vocal encouragement.
2 Stands after gate opens and second vocal encouragement.
3 Stands after observer enters pen and third vocal encouragement.
4 Must make contact with calf to rise.
Economic effects of BRD in dairy calves
Amy Stanton, PhD, University of Guelph, says young dairy calves that have experienced a bovine respiratory disease (BRD) episode can have long-term economic effects such as:
* Calves with BRD following movement to group housing have lower average daily gain than their healthy herdmates for up to four months after first treatment. In a study, at 1 year of age, BRD calves weighed 30 lbs less than their healthy herdmates.
* BRD decreases survival to first calving both through mortality and increased risk of culling.
* It’s been shown for over 20 years that heifers that have had BRD as a calf and do calve, are more likely to calve later in life (Waltner-Toews, et al, 1986; Correa et al, 1988). This is still occurring, despite changes in disease and cattle management, as shown in Stanton’s current research.