Costs for health care of Holstein cows selected for large or small body size
Diseases such as mastitis, displaced abomasum (DA), ketosis, cystic ovaries, metritis, and lameness can severely affect the profitability of dairying through veterinary treatments, additional labor, lost milk sales, and involuntary culling. A study we published in the September 2012 issue of the Journal of Dairy Science compared health care costs of Holstein cows selected for large versus small body size in a long-term selection project at the University of Minnesota Northwest Research and Outreach Center in Crookston.
The Holstein cows were selected for large versus small body size beginning in 1966. During 1966, 60 Holstein cows were paired by sire and were randomly assigned to one of two genetic groups (large or small) for body size. Except for service sire selection, both heifers and cows were managed together and identically in a tie-stall barn. The long-term selection project using divergent sire selection continued for more than 40 years. Throughout the years of the study, service sires were required to be in the top 50% of bulls for production among the active AI bulls available in the United States at the time of selection. Other than production levels, AI bulls were selected solely based on a body size index [0.5 (stature) + 0.25 (strength) + 0.25 (body depth)]. The three most extreme bulls for transmitting large and small body size were selected once each year from the summer genetic evaluations of the USDA for production and from Holstein Association USA, Inc. for body size.
Health care was recorded on an incidence basis from March 28, 1985, to June 17, 2002. Health treatments were recorded by category, and actual cost for 188 different types of veterinary treatments, health supplies and drugs were assigned at 2010 values. Also, the amount of labor in minutes required by farm workers for each health treatment was recorded. Fixed costs for veterinary supplies and drugs were the means from seven vendors serving Minnesota during the summer of 2010. Costs of veterinary procedures were the means of costs across three veterinary clinics in Minnesota. The study included 486 daughters of 84 Holstein AI bulls.
Across the first three lactations of cows, the body size lines tended to differ significantly for health care cost (Table 1). Averages for total cost of health care across lactations were $54.15 and $38.09, respectively, for the large-line and small-line cows, and the health costs were 30% higher (difference of $16.06 divided by the average for the large line) for large-line cows than the small-line cows. Most of the difference (83%) of total health cost for the body size lines across the lactations was due to the significant difference for displaced abomasum (DA). Also, locomotion (8%) contributed significantly to the difference for total health cost across the lactations.
Averages of total health cost by lactation number are in Table 2. Health care costs decreased for both large-line and small-line cows from first lactation to second lactation, but then increased during third lactation for small-line cows. The difference for health care cost was statistically significant during first lactation and second lactation for large-line cows compared to small-line cows. However, the body size lines did not differ significantly for health care cost during third lactation.
|Table 1. Total health costs and percentage of total health costs by health category for body size lines.|
|Large size line||Small size line|
|Health category||Average ($)||Percentage of total||Average ($)||Percentage of total||Difference of averages ($)||Difference of percentage|
|**P<0.01, *P<0.05, †P<0.10 for statistical significance.|
|Table 2. Average of total cost for health care for large and small body size cows and lactation number.|
|Lactation||Large line||Small line||Difference|
|**P<0.01, *P<0.05 for statistical significance.|
Greater cost for health care was incurred for cows selected for large versus small body size in this study. The difference of the body size lines for total health cost was mostly attributed to an increase in cost of treatment for displaced abomasum (DA). Consequently, the Holstein cows in the large line were economically disadvantaged compared to those in the small line for health care cost, which is an important contributor to profitability of dairying. Cows that require less health care are also preferable from an animal welfare point of view. Therefore, continued selection for larger body size of cows may not be justifiable.
Holsteins in North American have been selected for increased body size for many years. Final type scores from the Holstein Association USA continue to place more favorable ratings on cows with larger body size through the use of body size composite. The Net Merit index of the USDA places a negative weight on body size composite but the TPI index of the Holstein Association USA does not. Minimizing health care needs of dairy cows is important from both economic and animal welfare points of view.
Jennifer Becker is a graduate student at the University of Minnesota. Dr. Brad Heins is the dairy scientist and herd manager for the University of Minnesota West Central Research and Outreach Center at Morris. Dr. Les Hansen is dairy geneticist in the Department of Animal Science at the University of Minnesota-Twin Cities Campus.
Published in Dairy Star November 24, 2012