Producers were asked to select one of six levels that best described their average BTSCC for the previous six months: <100, 100-199, 200-299, 300-399, 400-499, and 500+ (1000 cells/ml). For analysis purposes, the six levels were combined into three levels: low-BTSCC herds, < 200,000 cells/ml (30.1% of herds); medium-BTSCC herds, 200,000 to 399,999 cells/ml (51.6% of herds); and high-BTSCC herds, > 400,000 cells/ml (15.3% of herds).
In addition to milk production per cow, the Dairy '96 Study collected data on calves born alive, cull cow sales, cows sold to other producers and cows/heifers entering into the milking string. Value of milk production and calves at birth minus net cow replacement costs equal a gross margin or net value of production. It is measured on a per cow basis. (Net replacement cost equals cost of cows/heifers added to the milking string minus cull cow sales and cow sales to other producers.) Unfortunately, information on feed costs or other costs such as labor, and veterinary expenses were not collected and thus were not part of this analysis.
The association between BTSCC and average herd milk production and adjusted revenue per cow was estimated using a regression model that accounted for other factors that impact milk production or adjusted revenue per cow: herd size and location, bovine Somatotropin (bST) use, percent Holstein cows, intensive pasture grazing, average number of days cows were dry, use of Dairy Herd Improvement Association (DHIA) records, if the herd was primarily of breed registered cows, and changes in milk cow inventory.
Results
Medium-BTSCC herds produced 372 kg or 4.6% less milk per cow and high-BTSCC herds produced 959 kg or 11.9% less milk per cow than low-BTSCC herds (Table 1). In comparison, the National Mastitis Council reports calculated herd losses at 6% for BTSCC at 500,000 cells/ml and 18% for BTSCC at 1,000,000 cells/ml when compared to herds at 200,000 cells/ml or less. Thus, the milk production losses associated with Dairy '96 Study are similar to National Mastitis Council's calculated losses.
Based on milk priced at $286.60 metric ton ($13/cwt), medium-BTSCC herds generated $108 (5.2%) per cow less and high-BTSCC herds had $295 (14.1%) per cow less net value of production then low-BTSCC herds. Over 90% of the losses associated with BTSCC were due to reduced milk production.
Based on the herd distribution of BTSCC as reported in Dairy '96, losses associated with subclinical mastitis, when averaged across all herds in the country, would cost $110 per cow. Aggregated across all U.S. dairy cows (over 9 million head) annual loss associated with subclinical mastitis, as measured by BTSCC, would be approximately $1 billion.
References
National Mastitis Council, Inc. The Value and Use of Dairy Herd Improvement Somatic Cell Count.
Table 1. Production Losses Associated with Subclinical Mastitisa
|
Medium-BTSCC Herdsb (200,000-399,999 cell/ml) |
High-BTSCC Herdsb (400,000 + cells/ml) |
|
|
milk production loss kg/cow (%) $/cow |
372 (4.6%) $106.53 |
959 (11.9%) $274.82 |
|
|
|
|
|
calves born loss no./cow (%) $/cow |
0.027 (2.8%) $1.37 |
0.059 (6.2%) $2.99 |
|
|
|
|
|
net cow replacement $/cow (%) |
$0.11(<0.1%) |
$17.43 (6.5%) |
|
|
|
|
|
total production loss $/cowc (%) |
$108.00 (5.2%) |
$295.24 (14.1%) |
a. Based on regression model that included the following variables: medium and high BTSCC herds, herd size, location, DHIA use, bST use, intensive summer grazing, percent Holstein, registered herd, length of cow dry period, and change in cow inventory.
b. Compared to Low-BTSCC herds (< 200,000 cells/ml).
c. May not total due to rounding.