The impact of forced isolation on acute phase response and duration of lung
lesions in preweaned group-housed dairy calves
Background and Justification
The dairy industry represents an economic impact of approximately 26.5
billion dollars in Wisconsin (Dairy doing more, 2013). Disease in heifers has longterm implications that affect the economic viability of a dairy (Stanton et al., 2012).
Additionally, animals that are sick for a longer period of time will incur higher
treatment and labor costs. Therefore, understanding how to properly care for sick
animals, and thereby lessening the length of illness, can positively impact the
profitability of a dairy, and more importantly, can improve animal welfare.
In the United States, multiple housing options are utilized for calf rearing.
Traditionally, preweaned calves were housed individually without contact with
conspecifics to mitigate disease transfer. However, the utilization of group-housing
is increasing due to more efficient labor use (Kung et al., 1997), increased calf
growth (De Paula Vieira et al., 2010), the preference of calves to obtain full social
contact (Holm et al., 2002), and cognitive bias when calves are raised in isolation
(Gaillard et al., 2014).
The two most common illnesses that affect preweaned calves are diarrhea
and bovine respiratory disease (BRD). In 2006, 12% and 23.9% of preweaned
heifers were affected with BRD and diarrhea, respectively (USDA, 2010).
Furthermore, respiratory disease and diarrhea combined account for approximately
79% of deaths in preweaned heifers (USDA, 2010). Therefore, providing proper
care to ill animals may ameliorate these high mortality rates.
Sickness behavior is a term used to describe a set of highly organized and
evolved set of behaviors that is hypothesized to be an adaptive response that
increases an individual’s chance of survival (Hart, 1988). These behaviors include
anorexia, isolation from the group, and increased lying. Moreover, sickness
behavior is motivational and an animal will perform or not perform these behaviors
based on external factors (Aubert, 1999), which can include fear, hunger, or
competition for resources. Because exhibiting sickness behavior is hypothesized to
increase survival (Hart, 1988), sick calves should be in an environment that
facilitates this behavioral response to illness. Therefore it is imperative that the
optimal environment for a sick animal be determined.
Research involving sickness behavior in group-housed calves shows that sick
calves spend more time lying, visit the feeder fewer times per day, and have longer
feeding bout durations compared to healthy pen mates (Borderas et al., 2009).
Similarly, calves challenged with lipopolysaccharide (LPS), which induces a sickness
response, spend less time lying compared to control calves (Borderas et al., 2008).
Group housing increases the competition among calves for resources such as time at
the feeder (Purcell and Arave, 1991). Self-isolation is a part of sickness behavior
that has been observed in cattle; adult cattle will self-isolate when ill (Proudfoot et
al., 2014) and calves with BRD appear isolated from conspecifics (Cramer and
Stanton, submitted). These behaviors represent differences between sick and
healthy calves. Therefore, management practices must be in place to care for sick
calves. Further understanding the isolation behavior of sick calves can help
determine the optimal design for a sick pen. Most pens on farms are designed to
care for healthy animals. As such, designated sick pens that meet the needs of ill
animals are necessary to reduce suffering (Millman, 2007). Understanding the
impact of moving an ill animal to a specialized individual pen will greatly advance
the care for sick calves on dairy farms.
The diagnosis of BRD can be challenging because it is multifactorial. Clinical
signs are the most common method of diagnosing BRD in calves (McGuirk, 2008).
However, approximately 80% of calves that do not have clinical signs of BRD have
lung lesions on ultrasounds (Ollivett, 2014). Therefore, there appears to be a large
proportion of calves with subclinical BRD. Lung ultrasound can help identify
subclinical BRD and is practical for on-farm use, has been validated, and is highly
sensitive for the identification of lung lesions in calves (Ollivett, 2014). Viral
infection leads to compromised lung epithelium followed by bacterial colonization
from pathogens normally found in the upper respiratory tract (Caswell et al., 2007;
Moeller et al., 2013). This process leads to neutrophil accumulation in the lung
tissue (Caswell et al., 2007), and these lung lesions can be identified on ultrasound.
Subclinical BRD may have a profound impact on animal performance, behavior, and
welfare.
The immune response of calves with clinical BRD has been well documented.
Specifically, the acute phase response has been implicated as part of the immune
response to clinical BRD. The acute phase response includes the production of acute
phase proteins, which include haptoglobin, serum amyloid A, and alpha1- acid
glycoprotein. These acute phase proteins serve as immune markers of clinical BRD
during both viral (Heegaard et al., 2000; Grell et al., 2005) and bacterial infections
(Schroedl et al., 2001; Dowling et al., 2004). However, the acute phase response has
not been studied in calves with subclinical respiratory disease. The immune
response of calves with subclinical BRD is important for early disease detection,
treatment decisions, and understanding the pathophysiology. Furthermore, the
management of sick calves may impact this immune response.
The objectives of this study are 1) to determine the impact of forced isolation
on the duration of lung lesions in calves with subclinical BRD and 2) to determine
the impact of forced isolation on the acute phase protein response during BRD.
Materials and Methods
Calves will be in group pens from 1 week of age until 7 weeks (weaning).
Calves in the group pen will be given 12L of pasteurized whole milk per day via an
automated feeder. Health scores will consist of scoring calves for clinical signs of
BRD (McGuirk, 2008) and lung ultrasounds. Health scores will be performed on
every calf, 5 times per week, by research staff. Clinical BRD (cBRD) will be defined
as calves that score 6 or greater on the BRD scoring chart (Table 1). Subclinical BRD
(sBRD) will be defined as calves that have an ultrasound score of 2 or greater (Table
1). Enrollment of calves will be limited to calves that have sBRD and no clinical
signs of BRD. Upon identification of calves with sBRD, calves will be systematically
randomized to one of two treatment groups: 1) calves with sBRD that will remain in
the group pen (GROUP) or 2) calves with sBRD that will be moved to an individual
pen (ISO). Calves in ISO will be offered 12L of pasteurized whole milk per day via
bottle. Calves in both treatment groups will have ad lib access to water.
After treatment assignment, calves will continue to undergo health scores to
determine the duration of lung lesions. Blood samples will be taken from calves
with sBRD on day 0 (day of identification of sBRD) and daily for 10 days thereafter.
Blood serum will be analyzed for concentrations of haptoglobin, serum amyloid A,
and alpha1- acid glycoprotein. These concentrations will be compared between ISO
and GROUP calves.
Because isolation is a component of sickness behavior, provision of this (ISO)
will provide an environment that is more conducive to recovery. Because lung
lesions are due to a neutrophil accumulation, there is an immune response taking
place in calves with sBRD. Thus, we expect ISO calves to have a decreased duration
of lung lesions and therefore fewer days of an immune response (as indicated by
acute phase proteins). If ISO unexpectedly is very detrimental to animal welfare,
assignment of calves to ISO will be ceased. At this time, we would continue to
observe the acute phase response to sBRD in GROUP calves.
Table 1: BRD scoring chart for clinical signs of disease
Clinical Parameter
0
Normal, serous
Nasal Discharge
discharge
Ocular Discharge
Normal
Ear Position
Normal
Cough Score
No cough
Rectal
Temperature
UltraSound Score
100-100.9
0-1
2
BRD Scoring Chart
1
2
Small amount of
Bilateral, cloudy or
unilateral, cloudy
excessive mucus
discharge
Mild ocular
Moderate bilateral
discharge
ocular discharge
Ear flicking
Slight unilateral ear
drop
Induce single cough Induce repeated
coughs or occasional
spontaneous cough
101-101.9
102-102.9
3-5
Lobar Pnuemonia
3=1 lobe
Normal Lobular Pnuemonia
4=2 lobes
5=3 or more lobes
3
Coupious, bilateral
mucopurulent nasal
discharge
Heavy ocular
discharge
Severe head tilt or
bilateral ear droop
Repeated
spontaneous
coughing
>= 103
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