Replacement rearing is a major capital expense for dairy farms, and as such, it is a management area that merits continual improvement and fine-tuning. A group of researchers from the Guelph Food Research Centre in Guelph, Ontario, Canada, recently conducted a study examining the causes of calf mortality, including genetic ties to those causative factors.
Their work, published in the March 2013 issue of the Journal of Dairy Science, examined the survival outcomes of 1,588 Holstein heifer calves from birth until 90 to 120 days of age. First, they evaluated which factors surrounding birth increased a calf’s risk of mortality. They found that the factors that increased the likelihood of mortality included:
- Calves born in the fall (October to December)
- Low serum total protein
- Low weight
- Calves treated for illness in the first week of life
- Calves treated more frequently throughout the study period; and
- Calves treated for bovine respiratory disease
Next, they estimated the genetic parameters for requiring treatment for illness; survival; bovine respiratory disease; other diseases; height and weight. They found that heritabilities for treatment, survival and diseases were low. Moderate heritability was found for height, and significant heritability was determined for body weight. Body weight was found to have a tendency of favorable genetic correlation with treatment for diseases. In other words, calves with higher body weight in their first month of life were genetically more resistant to diseases and required less treatment than those with average body weight.
The researchers suggest one of two explanations for this relationship. Either heavier calves are in better health and are better able to resist disease; or calves that do become sick spend more energy fighting disease and thus are less able to gain weight. They concluded that data on calfhood disease and survival could potentially become a factor in future dairy genetic selection methods, but that further research and improved data collection are warranted.