AIPL RESEARCH REPORT SCC1 (12-99) |
Somatic cell counts of milk from 1998 Dairy Herd Improvement herdsR.H. Miller and H.D. NormanAnimal Improvement Programs Laboratory, ARS-USDA, Beltsville, MD 20705-2350 301-504-8334 (voice) ~ 301-504-8092 (fax) ~ rlaipl@aipl.arsusda.gov ~ http://aipl.arsusda.gov |
Test-day data from all herds enrolled in Dairy Herd Improvement (DHI) somatic cell testing during 1998 (91% of all DHI herds) were examined to assess the status of national milk quality. All test-day data within a herd were included regardless of breed. Cows with records that failed AIPL editing procedures (for example, no sire identification) were excluded. However, the somatic cell counts (SCC's) of milk from such cows probably do not differ greatly from those from other cows in the herd. Although somatic cell score (SCS) is reported to AIPL, SCS was converted back to SCC in cells/milliliter (SCC = 2(SCS–3) × 100,000) for calculating herd and State averages.
Table 1 shows for each State the total number of herd test days, the average number of cows per herd on test day, the average milk yield and SCC on test day, and the percentages of herd test days that exceeded four levels of SCC: 750,000, 600,000, 500,000 and 400,000 cells/ml. The current legal limit for bulk tank SCC is 750,000 cells/ml for Grade A producers; the lower limits have been proposed as future maximums. State and national average daily milk yields were weighted by the number of cows per herd test day. Herd, State, and national average SCC's were based on SCC's from individual cows that were weighted by milk yield on test day. Information from Alaska and Hawaii was not included because of extremely limited data.
Nationally, average SCC during 1998 was 318,000 cells/ml, which was higher than the national averages of 307,100 cells/ml for 1996 and 313,500 cells/ml for 1997. The percentages of herd test days that exceeded 750,000, 600,000, 500,000, and 400,000 cells/ml were 4.5, 10.1, 17.8 and 30.3, respectively. Thus, 4.5% of test-day milk samples from DHI herds that participated in somatic cell testing exceeded the present legal limit for SCC of bulk tank milk. This percentage may be an overestimate of the percentage of herds that would have exceeded the legal limit for SCC of bulk tank milk on test day because the milk of cows treated for mastitis just prior to test day is excluded from the bulk tank. Also, the percentage of herd test days that exceeded the legal limit would have been higher than the percentage of herds that were rejected from the market because market exclusion only occurs after repeat violations.
Variation among States was large. Average SCC's were lower in the far West and higher in the Southeast. Although climatic conditions (temperature and humidity) probably contributed to regional SCC differences, SCC differences between geographically adjacent states were substantial, which suggests that mastitis-control regimes have an impact under similar climatic conditions.
Greater efforts to improve milk quality are needed. In the future, State
and national SCC's will be summarized annually so that changes in SCC and
trends in milk quality can be detected.