Effect of single versus group housing from the first week of life on the performance, immune responses, and well-being of Holstein calves.



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Recent worldwide concern for animal well-being has raised many questions considering animal housing. Currently, many believe that gregarious animals should be housed in groups in order to maintain natural behavior. Unfortunately, there is not a consensus within the scientific community with regard to the definition of well-being, or even how to precisely and accurately measure animal well-being. Thus far, some criticize that “legislation driven” research is not properly conducted. Therefore, researchers typically collect physiological, immunological, and endocrine measurements that correlate with symptoms of subjective characteristics. By evaluating immune response measurements, blood metabolites, protein activity, and intake; we can better ascertain proper animal welfare, enhance animal well-being, and begin to make changes that provide better living conditions.

In Experiment I, calves were enrolled and housed in outdoor individual and group pens (n = 3) within the first week of life. After a short acclimation period, whole blood samples were collected to measure innate immune responses and blood metabolites that may distinguish stressed or diseased animals from those possibly experiencing better well-being. Milk replacer and calf starter intakes, gains, disposition, and fecal scores were recorded daily. Behavioral data were also collected in order to determine social development differences between housing scenarios that could result in heightened stress, fear, disease transmission, and risk of future dysfunctional behavior. Frequency of observations and samplings were amplified prior and during weaning to more precisely evaluate physiological and behavioral changes as a result of weaning stress. Once weaned and of appropriate age and weight, calves were randomly commingled outdoor into groups (n = 5) to distinguish further effects of post-wean commingling that occurs in production.

In Experiment II, calves were enrolled and housed in indoor individual and group pens (n = 2 and 3) within the first week of life. The intent of this experiment was to replicate group housing of outdoor calves, but in a more homogenous indoor environment with closer animal interactions to determine if the effects were similar as observed in outdoor situations or more affected by external stimuli such as ventilation, disease transmission, and enhanced perception of sound and sight due to close proximity of neighboring pens. 

Replication of experiments may aid in distinguishing if group housing has an effect on calf well-being in two separate and common housing methods. Evaluation of data from both scenarios will lead to more understanding of group housing by considering the performance, immunological, and behavioral responses to environmental and interactive stimuli. 
When housed outdoor, group-housed calves experienced greater dry matter intake resulting in increased average daily gain. Incidence of cross-sucking was heightened in group-housed calves, consequently amplifying horizontal disease transmission and stimulating activation of neutrophils of the innate immune system compared to individually housed calves. As interaction with pen-mates became evident to researchers, grouped calves became more evasive to human contact and showed more behavior characteristic of fear when in a novel environment compared to individually housed calves. In order to discourage intersucking or milk stealing, calves were swayed to suckle a dry nipple. Therefore, more labor time was spent with group-housed calves to assure proper intake of nutrients. When later commingled, outdoor group-housed calves had enhanced gains. 

As in outdoor group housing, competition within indoor group pens resulted in increased post-wean intake, but possibly more activity and physical interaction did not allow for increased gain in these groups. Common inadequate ventilation and high humidity noted in indoor housing scenarios could result in narrow environmental variation among treatments. Horizontal transmission of pathogens was not limited to pens because calves resorted to reaching around, through, or over wall separations to attain interaction. As this was the case, there was little difference in innate immune responses or blood metabolites as a possible result of calf-to-calf interactions and/or lack of treatment effect. Indoor calves were in much closer proximity with each other, allowing for visual, audible, and limited physical interaction. Close proximity of pens also allowed social interaction by all animals in the barn, creating less varied behavioral differences than seen in outdoor calves. The dilution effect due to homogeneity of the environment and stimuli led to equal reaction of all indoor calves in the commingling period. In turn, group housing can increase post-wean intake, but social interaction, environment, and disease transmission control all affect the responses of performance, the innate immune system, and proper behavioral development.