What Is the Current Milk Quality in the U.S.?

Scott J. Wells, Stephen L. Ott
Centers for Epidemiology and Animal Health, USDA-APHIS-VS
Fort Collins, Colorado USA

Consumer purchasing decisions are the ultimate measure of product quality. Who are the customers of US dairy products and what are their concerns?

Currently, the vast majority of US milk production is consumed domestically. A recent dairy consumer marketing study by Dairy Management, Inc., showed that a household "gatekeeper" (usually Mom or Dad) has a heavy influence on in-home consumption (Sowa, 1997). This is especially important since children less than 18 years of age drink 46% of the milk volume consumed. As media sources continually emphasize food quality and safety and potential risks to human health and well-being, these concerns are of high interest to many consumers, especially to parents.

Because of these concerns, the US dairy industry should focus on improving and documenting the quality and safety of dairy products. Three quality issues will be discussed in this paper: bulk tank somatic cell count, chemical residues, and microbiological pathogens.

Milk Somatic Cell Count

Though the US does not have a national system for compiling and monitoring milk quality information, efforts have been made to collect available data and make this data usable. In 1995, we reported the status of US milk quality monitoring (Wells and Ott, 1995) using Dairy Herd Improvement Association individual cow somatic cell count information. We also described plans to begin a bulk tank somatic cell count (BTSCC) monitoring system to better estimate US milk quality. This system, a collaboration between the National Mastitis Council Milk Quality Monitoring Committee, USDA's Agricultural Marketing Service and Animal and Plant Health Inspection Service-Centers for Epidemiology and Animal Health (CEAH), has been developed and continues to expand.

Bulk tank somatic cell count (BTSCC, a measure of the number of white blood cells per ml of raw milk) was chosen as an indication of milk quality. BTSCC reflects the levels of infection and resultant inflammation in the mammary gland of dairy cows and provides an indirect measure of the processing quality of milk. While BTSCC is not a public health concern, reasons to monitor BTSCC include: domestic consumer demands for high quality, processor need for high quality raw milk, to help improve cow udder health, and potential pressure from international markets for documentation of the quality of our dairy products.

CEAH received data from five USDA Agricultural Marketing Service (USDA-AMS) Federal Milk Marketing Orders during 1994 and 1995 and eight orders in 1996 (USDA-APHIS-VS, 1997a). Participating Federal Milk Market Orders collected BTSCC data from dairy operations through dairy cooperatives as part of multiple component pricing. These orders combined included dairy producers from 22 states. The participating Federal Milk Market Orders provided total pounds of milk produced during the month and BTSCC data by month for each dairy producer. The BTSCC was an average for the month. The participating federal milk market orders assigned each producer a code number to maintain confidentiality.

Dairy producers in the eight orders shipped a total of 14.5 billion pounds of milk in January through March 1996, equal to approximately 37 percent of the total US milk production during this time (USDA-NASS, 1996). These orders represented 47,210 producers in July 1996, or 45 percent of those with permits to sell Grade A or manufacturing grade milk (Olson, 1996). This system represented greater than 65 percent of milk shipped and greater than 50 percent of producers with permits to ship milk in Iowa, Indiana, Michigan, Minnesota, New Mexico, Ohio, Texas, and Wisconsin.

How is the US doing in terms of milk quality? From the BTSCC monitoring data, during the winter and spring, average BTSCC (arithmetic mean) is below 350,000 cells/ml (Figure 1). As the weather warms up, average BTSCC rises to a peak in August and falls as the weather cools.

Another trend is related to herd size. During 1995, the weighted average of BTSCC for larger herds was less than that for smaller herds (Figure 2). Herds that shipped more than 95,000 pounds of milk per month had weighted average BTSCC below 325,000 cells/ml during the non-summer months with an increase to 400,000 cells/ml in August. Herds that shipped less than 45,000 pounds had a weighted average BTSCC above 375,000 cells/ml that peaked in August at 525,000 cells/ml. This difference in weighted average BTSCC between large- and small-size herds suggests that smaller herds have room for improvement in health management and resultant milk quality. This warrants further investigation.

Before we congratulate ourselves, we need to recognize that the Europeans have lowered their limit on BTSCC to 400,000 cells/ml, less than the US limit of 750,000 cell/ml. While most US producers could meet this tougher European standard, it is clear that some would not. Countries with lower BTSCC limits, including the European Community, are likely to use lower BTSCC limits as a marketing tool in dairy export markets.

Why worry about the European standard when US exports only 2 to 3 percent of its production and little of it to Europe? The US dairy industry has an opportunity to increase exports since world trade liberalization rules will limit Europe's ability to subsidize its dairy exports and world demand for dairy products should remain strong. For example, Russia is increasing its imports of dairy products, especially cheese, as consumer substitute cheese for meat due to high meat prices (Parker, 1997). However, US ability to capitalize on this export opportunity could be limited if importing countries adopt the European standard for BTSCC and will not accept dairy products processed from milk above 400,000 somatic cells/ml.

Domestically, producers need to be concerned about high BTSCC due to BTSCC association with mastitis. Past studies have demonstrated high somatic cell counts are related to reduced milk production per cow. The USDA National Animal Heath Monitoring System (NAHMS) Dairy '96 Study included questions related to BTSCC and mastitis. Study findings showed that, when averaged across all herds, BTSCC in excess of 100,000 cells/ml "reduced" the nation's milk production per cow by 838 pounds, or 5 percent in 1995 (Ott, unpublished preliminary information).

Several studies have estimated the herd cost of mastitis on a per cow basis (Miller et al., 1993; Miles et al., 1992; DeGraves and Fetrow, 1991; Hoblet et al. 1991; Kaneene and Hurd, 1990; Weigler et al., 1990; Kirk and Bartlett, 1988; Blosser, 1979; and Dobbins, 1977). Clinical outbreaks of mastitis have been estimated to cost approximately $58 per cow (range of $31 to $94) in 1996 dollars. The greatest cost, however, is not with clinical cases and their treatments, lost production and dumped milk, but with subclinical production losses. When subclinical costs are included, the economic impact of mastitis rose to $184 per cow (range of $114 to $256). Using NAHMS Dairy '96 Study data, economic impact of mastitis was estimated to be $131 per cow with cost based on lost milk production value at $13/cwt and additional replacement cow costs (Ott, unpublished preliminary information). No treatment expenditures were included in this analysis of NAHMS data. Nationally, mastitis costs producers an estimated $1.2 to $1.7 billion, or approximately 6 percent of the value of production.

Due to recognition of the importance of mastitis and milk quality, US dairy producers have largely adopted certain recommended mastitis prevention measures, as documented by the recent NAHMS Dairy '96 Study. This study showed that 89% of US dairy producers reported use of teat dips after milking. Seventy-seven percent of producers reported use of dry cow treatment in all or almost all cows with another 15% reporting use of dry cow treatment in selected cows (USDA-APHIS-VS, 1996b).

It is difficult to gauge consumer reaction to somatic cell count levels in milk. We do know that per capita milk consumption has steadily declined for the past three decades, especially for whole milk. While we are not suggesting that high somatic cell count is responsible for this decline, it does demonstrate that the dairy industry can ill afford to lose milk drinkers due to perceived quality concerns. Consumer concerns about quality can be seen in consumption of bottled water. Bottled water consumption exceeded whole milk consumption in 1993 and if current trends continue, bottled water could surpass lowfat milk consumption before the decade is over. The key point is that though tap water is cheap, consumers are willing to purchase more expensive bottled water of perceived high quality.

Chemical Residues

To prevent chemical residues in milk and dairy products, the US Pasteurized Milk Ordinance requires all bulk milk tankers be sampled and tested for antibiotics in the penicillin family. In fiscal year 1996, only 0.104% of 3.4 million truck tanker loads were reported with violative residues (GLH, Inc, 1997). In addition, in the past several years a great deal of effort has been expended to educate veterinarians and dairy producers on the importance of antibiotic and drug residue prevention, including development of the Milk and Dairy Beef Quality Assurance Program. Despite participation by only 11% of dairy producers by January 1996 (USDA-APHIS-VS, 1996a), a higher percentage of producers have been made aware of this issue through veterinary resources, media, and other sources. In sum, antibiotic and drug residues is are receiving a great deal of attention at this time with very low occurrence of violative residues.

Microbial Pathogens

Salmonellosis, listeriosis, campylobacteriosis, and E. coli O157-associated disease are bacterial diseases of humans associated with food products, including dairy. These diseases result in up to an estimated 5,000 deaths per year. The cost of these bacterial foodborne diseases in the US ranges from $1.6 to $5.4 billion annually (Buzby et al., 1996), although dairy products are responsible for only a small proportion of these costs. These cost estimates do not include lost sales resulting from media publicity associated with outbreaks, which can be devastating to the individual companies involved.

Compounding problems associated with bacterial foodborne diseases is the size of modern food processing plants. As processing plants become larger, the distribution of product increases which increases the potential number of people affected and geographic distribution, should an outbreak occur.

For public health risks due to microbial pathogens, a multiple barrier system is used to reduce risk to human food supply. Pasteurization is effective in reducing health risks from dairy products, but problems have, albeit rarely, occurred, and it is prudent to set up other barriers to pathogen entry into the food chain. Multiple barriers used to prevent risks from dairy foods include on-farm milk inspection, milk pasteurization, hazard analysis and critical control points (HACCP) systems to reduce risks from milk processing, and consumer education to assure adequate refrigeration of dairy products.

What other barriers can be effective at the farm-level? On-farm microbiological barriers were outlined in an address to the National Mastitis Council in 1996 (Christ, 1996). These barriers included: (1) eradication of certain cattle diseases, (2) herd certification programs for diseases to document low risk herds, and (3) use of best management practices for other diseases to show evidence of low risk.

In terms of eradicable diseases of public health and international concern, the US is in a favorable position. Brucellosis is nearly eradicated from domestic cattle and bison. The US is on a timetable to eradicate bovine brucellosis by the end of 1998 and there were only 11 newly infected brucellosis reactor herds reported from April through June 1997 (USDA-APHIS-VS, 1997b). Eradication efforts directed towards bovine tuberculosis have also been effective, with only five known infected cattle herds reported in the first half of 1997 (USDA-APHIS-VS, 1997b).

A second method of documenting freedom from certain cattle diseases is participation in herd certification programs. Bovine leukosis virus (BLV) and Johne's disease herd certification programs are currently an option in some states. There is no conclusive evidence of human health risk from either of these pathogens. However, some groups are concerned about the possibility of M. paratuberculosis being one of the agents causing Crohn=s disease. The National Johne's Working Group is in the midst of efforts to increase Johne's disease familiarity among dairy producers and allied industries and to re-evaluate a model herd certification program to increase interest in participation. Although bovine leukosis virus has not been of high concern in the US, it is of higher interest in other countries. Though no evidence of public health risk exists, BLV may become a trade barrier in the future from countries with more active control programs. Control programs may become another marketing tool used by competitor countries in dairy export markets.

Use of best management practices related to reduction of certain pathogens on-farm has been an area of strong interest and debate in the US recently. Issues of consideration include practices related to biosecurity to prevent entry of pathogens into a herd and management practices used to control spread of pathogens within a herd and to reduce their prevalence.

Introduction of cattle is a key issue for between-herd biosecurity. Most of the biosecurity issues considered to date have been related to control of cattle health issues. Since dairy herds have been expanding in size, attention should be paid to low-risk methods of introducing cattle. Isolating introduced cattle is one option but, due to lack of appropriate facilities, is impractical for milking cows on many operations and therefore used infrequently. Isolating herd replacements is an option for use in heifers introduced before calving. Diseases to consider screening purchased cattle for prior to herd entry include: bovine viral diarrhea (BVD) disease (test for antibody or require vaccination), Johne's disease (require herd of origin to document freedom from disease), and mastitis (require herd of origin to document low risk using individual cow SCC information as well as herd SCC and culture information). According to the NAHMS Dairy '96 Study (USDA-APHIS-VS, 1996a), only 16% of US dairy producers reportedly require BVD tests and 47% require BVD vaccination before entry of cattle. Only 26% require herd of origin information relative to individual cow SCC information, and 15% require herd of origin bulk tank SCC information before cattle entry. Clearly, educational efforts are needed to expand dairy producer familiarity with biosecurity issues and their ramifications for animal health issues, aside from any consideration of biosecurity for public health concerns.

We are at a very early stage in developing documented management practices related to reduction of fecal shedding of certain pathogens such as E. coli O157 and Salmonella. Research is needed to document effectiveness of use of certain management practices in reducing shedding. However, efforts are intensifying with the start of USDA-FSIS monitoring of Salmonella in meat processing plants in January 1998 as part of the Pathogen Reduction and HACCP System. Because of the fecal origin of these bacteria, a focus area of best management practices may be the manure handling and delivery system.

Though public health risks from microbiological pathogens are currently low, human outbreaks of foodborne diseases from milk and dairy products do occasionally occur. The evolution of antibiotic resistant pathogens and consumer concerns are driving changes to reduce risks to even lower levels.


Though interest in expanding the role of US dairy foods in international markets is growing, the vast majority of US dairy products are consumed by the US market. Concerns about milk quality and chemical residues have led to systems to improve certain aspects of milk quality and safety, including BTSCC and residue testing systems. These efforts, along with milk pasteurization, have led to high US milk and dairy product quality and safety. A challenge for the future is to continue development of additional barriers to microbial pathogens to meet consumer demands and expectations.


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Figure 1

Figure 2

Presented at the National Mastitis Council 37th Annual Meeting, January 1998. Published in the 1998 National Mastitis Council Annual Meeting Proceedings, pg. 10

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