Goat Milk Somatic Cell Count Situation In The United States
Milk production by the 1.5 million U.S. dairy goats has an estimated annual value of $500 million, but official statistics are mostly absent. There is a market imbalance, demand exceeding supplies. There also is a need for fair goat milk quality standards, which are inappropriate if they are copies of cow milk standards. Complicating this situation is that no widely acceptable routine methods exist for monthly monitoring of true leucocyte levels as indicators of presence or absence of subclinical or clinical mastitis in tank milk and individual goat milk. Furthermore, research has been lacking to establish acceptable goat milk somatic cell count levels, which must be valid for every month of the year when goats are at the end of lactation or in the middle or at the beginning.
The U.S. dairy goat industry is on the threshold of being recognized as a necessary and legitimate U.S. industry (Maxey, 1993). Dimensions of the U.S. goat milk industry have been reviewed (Kapture, 1985; Haenlein, 1981; 1986; 1994; Campbell, 1992). Official averages for somatic cell counts in milk of U.S. dairy goats are not publicly available, although this testing is offered and widely used by dairy cow farmers in the monthly Dairy Herd Improvement Association (DHIA) record keeping system. Parts of this paper have been presented at a recent Conference in Italy (Haenlein and Hinckley, 1994).
U.S. goat milk production is subject to the health regulations of the total U.S. dairy industry and the same quality standards as cow milk as long as research does not demonstrate reasons for different standards. In 1993 for the first time, the somatic cell count standard for commercial goat milk was kept at 1 million/ml, while the maximum allowance for commercial cow milk was lowered to 750,000, mainly because research data were accumulating to indicate physiological and microbiological differences between goat and cow milk independent of disease status, which would justify different standards between the two species without endangering human food safety (Haenlein, 1987; Atherton, 1992). While it is widely accepted that somatic cell counts are a valid indication of abnormal milk secretion, composition and mammary disease in cows, this does not appear to be the case for goat milk, at least not to the same extend, and therefore any maximum somatic cell count as a legal indication of goat milk abnormality has been considered to be inappropriate (Atherton, 1992; Lerondelle et al., 1992).
Slowing down the adoption of valid new quality standards for goat milk is the paucity of U.S. basic research in this field so far, despite increased research activity at 5 more Experiment Stations in Texas--Prairie View, Oklahoma--Langston, Georgia--Fort Valley, Alabama--Tuskeegee, Florida--Tallahassee during the last decade in addition to California--Davis, Texas--San Angelo, Pennsylvania--Philadelphia, New York--Cornell, Connecticut--Storrs, Delaware--Newark, and Massachusetts--Rutland. Much evidence has come instead from research in France, Italy, Spain, Finland, Greece, India, Iraq, Israel (Rota et al., 1993; Upadhyaya & Rao, 1993).
Also complicating adoption of goat milk standards is the fact of mostly seasonal dairy goat breeding and milk production being practiced in the United States (Table 1). Typically, U.S. dairy goats are in late lactation and low production when the goat milk market in the winter season is highest (Schultz, 1993). Price incentives are mostly missing to stimulate efforts of more successful all-year-round breeding and milking. Furthermore, many good dairy goat farmers are not located near processors or major consumer markets, making shipment of goat milk expensive and affecting quality of goat milk, if transportation is not in refrigerated trucks at least 3 times per week (Haenlein, 1992).
FACTORS AFFECTING SOMATIC CELL COUNTS
It has been shown that more frequent milking increases migration of neutrophils from blood into the mammary gland for more efficient phagocytosis and mammary gland defense against pathogen infections (Paape et al. 1992). However, many dairy goats are milked only once a day routinely.
Total and differential somatic cell counts differ with stage of lactation (Miller et al. 1991; Rota et al., 1993). If cows in a milking herd are in various stages of lactation always, a single maximum standard of somatic cell counts all year makes sense. If goats in a milking herd are only in one and the same stage of lactation mostly (because of seasonal breeding) at a certain sampling date, then an all-year-round single maximum standard of somatic cell counts does not make physiological nor legal sense for goats, actually is discriminating against dairy goat owners, is discouraging them from having a commercial goat milk enterprise and thus a viable goat milk industry is made impossible.
Currently prevailing methods and testing equipment for cow milk has been found to be unreliable and inappropriate for goat milk (Poutrel & Lerondelle, 1983; Maisi, 1990; Atherton, 1992). There is a need for recalibration for goat milk and for methods, which identify differentially true leukocytes from total somatic cells. Once a direct microscopic cell count, correct routine stain and/or DNA test for true neutrophils in dairy goat milk is adopted, then the difference between calendar months coinciding with stage of lactation months still has to be resolved into a sliding scale of somatic cell count standards year-round.
A survey of 1,230 bulk milk tank samples from 103 commercial goat milk farms in 11 different U.S. states during 1984 to 1991 (Kapture, 1991), tested by the reliable direct microscopic cell count method, the Fossomatic and the Pyronin y-methyl green stain for somatic cell counts (SCC), showed large numbers of non-mastitic samples to be beyond 1 million SCC/ml. In April 10.1 percent, May 12.9, June 19.9, July 25.0, August 41.2, September 50.4, October 49.5, November 51.3, December 50.5, January 52.7, February 29.7, March 22.7 percent of the monthly tests were above 1 million SCC/ml, presumably in the illegal or "reject" range according to cow milk standards, with more than half during the late lactation months of September to January.
Tables 2, 3 and Figure 1 show monthly data for 2 years, not for milk tank herd totals, but for more than 2,000 individual goats on DHIA testing for SCC with similar trends between months and seasons as found in the above study with milk tank samples (Figures 2 and 3).
U.S. REGULATORY STANDARDS FOR SOMATIC CELL COUNTS IN GOAT MILK
Milk, which is shipped between U.S. states, is regulated for quality by the National Conference on Interstate Milk Shipments (NCIMS), an organization of state regulatory officials and federal Food and Drug Administration (FDA) officials from the Milk Safety Branch. Quality standards for milk, as set by the NCIMS, are stated in a document entitled the Pasteurized Milk Ordinance (PMO). Standardized laboratory methods for determining quality values are recorded in "Standard Methods for the Examination of Dairy Products" (Marshall, 1992). Prior to any change in laboratory methods or quality standards, the change must be justified to the NCIMS Laboratory Committee and approved by both the NCIMS voting delegates and the FDA.
Over the past 10 years, the Goat Milk Committee of the NCIMS has made recommendations for a separate set of standards for goat milk (Hinckley, 1984). The Committee has reviewed research literature, laboratory records and comparison studies conducted on cow and goat milk. The review indicated significant species differences which result in compositional differences. If normal goat milk is tested by cow milk criteria and methodology it may be judged to be abnormal, showing deviation from standard values. Species differences necessitate a separate set of legal milk quality standards for goat milk.
Standardization of somatic cell count regulations for goat milk encompasses two separate issues. The first is the use of appropriate methods. The apocrine milk secretory system of the goat mammary gland results in the presence of cytoplasmic particles in the milk, therefore, cell counts of 1.0 million /ml or more, as determined by screening tests, must be confirmed by direct microscopic somatic cell count (DMSCC) using a dichromal stain for the differential count. The U.S. official standard methods stain is the Pyronin-Y Methyl Green stain. Screening tests include the California Mastitis Test (CMT), the Wisconsin Mastitis Test (WMT) and electronic counting. The Coulter counter is not acceptable for goat milk (Poutrel & Lerondelle, 1983).
CURRENT U.S. RESEARCH
A study of 100 split samples done by a New York state regulatory laboratory, compared cell counts done by the Fossomatic test and by DMSCC (Marin, 1989). The counts from the Fossomatic were consistently higher than those done by DMSCC. The results indicate the continued need for a DMSCC confirmation after Fossomatic screening.
The second issue relates to elevated cell counts in milk produced from disease free udders. A study of 380 goats in New York concluded that non-infected goats from goat farms with excellent management practices often had milk somatic cell counts of 1.0 million cells/ml or above (Wilson, 1993). Another study in cooperation with the University of Vermont concluded that the tremendous variation observed in somatic cell counts from goats made it difficult to interpret the significance of somatic cell counts in goat milk (Randy, 1990). In a study of 560 goat samples by the University of Connecticut it was found that mid-lactation, non-mastitic goat milk often had somatic cell counts of 1.0 million cells/ml or above (Hinckley, 1990). This refutes the conclusion by Harmon (1994) from research with cow milk that "except for normal diurnal variation, few factors other than infection status have a significant impact on milk somatic cell counts." At least this conclusion is not valid for goat milk.
Research at the USDA Experiment Station with flow cytometry indicate that the granulation and density of somatic cells in goat milk differs from that of somatic cells in cow milk, indicating different competency and functionality, that lead to a necessity of higher number of cells (Dulin et al., 1983; Drake et al., 1992).
The position of the U.S. Goat Milk Subcommittee of the NCIMS is that due to inherent differences between cows and goats, goat milk with a somatic cell count of 1.0 million cells/ml can be produced from a healthy, non-mastitic udder and therefore, is quality milk (Hinckley, 1991; Atherton, 1992). The need for a separate standard for goat milk was recognized by the NCIMS. The goat milk standard remained at 1.0 million cell/ml, when the cow standard was lowered to 750,000 cells/ml in 1993.
Atherton, H.V. 1992. Using somatic cells and antibiotic tests for determining the quality of goat milk. In: Proceedings, National Symposium on Dairy Goat Production and Marketing, T.A. Gipson et al., ed., Langston University, Oklahoma, pp. 128-135.
Campbell, L.S. 1992. Status of the dairy goat industry: An ADGA perspective. In: Proceedings, National Symposium on Dairy Goat Production and Marketing, T.A. Gipson et al., ed., Langston University, Oklahoma, pp. 1-9.
Drake, E.A., Paape, M.J., DiCarlo, A.L., Leino, L. and Kapture, J. 1992. Evaluation of bulk tank goat milk samples. Proceedings, 31st Annual Meeting of the National Mastitis Council, Arlington, VA, 236 pp.
Dulin, A.M., Paape, M.J., Schultz, W.D. and Weinland, B.T. 1983. Effect of parity, stage of lactation, and intramammary infection on concentration of somatic cells and cytoplasmic particles in goat milk. Journal of Dairy Science, 66:2426-2433.
Haenlein, G.F.W. 1981. Dairy goat industry of the United States. Journal of Dairy Science, 64:1288-1304.
Haenlein, G.F.W. 1986. Dimensions of the goat milk industry in the USA. In: Production and Utilization of Ewe's and Goat's Milk. International Dairy Federation Bulletin No. 202: 215-217.
Haenlein, G.F.W. 1987. Cow and goat milk aren't the same - especially in somatic cell content. Dairy Goat Journal 65:806.
Haenlein, G.F.W. 1992. Alternatives in dairy product market. Proceedings Sheep and Goat Industry Development Symposium, A.D. Scarfe, ed., Tuskeegee University, Alabama, 66-76.
Haenlein, G.F.W. 1994. Status and prospects of the dairy goat industry in the U.S. Proceedings, American Dairy Science Association Annual Meeting, Minneapolis, MN., 689.
Haenlein, G.F.W. and Hinckley, L. 1994. Somatic cell count situation in USA. Proceedings, Conference Somatic Cells and Milk of Small Ruminants, Bella, Italy, Sept. 24 - 27, 13 pp.
Harmon, R.J. 1994. Physiology of mastitis and factors affecting somatic cell counts. Journal of Dairy Science 77: 2103-2112.
Hinckley, L.S. 1984. The somatic cell count issue. Dairy Goat Journal, 62:48.
Hinckley, L.S. 1990. Revision of the somatic cell count standard for goat milk. Dairy Food and Environmental Sanitation, 10:548-549.
Hinckley, L.S. 1991. Quality standards for goat milk. Dairy Food and Environmental Sanitation, 11:511-512.
Kapture, J. 1985. Profile of goat milk marketing in the U.S. United Caprine News (6):25-27.
Kapture, J. 1991. Milk conference focus: Somatic cell counts. Dairy Goat Journal (6):370; (7):415.
Lerondelle, C., Richard, Y. and Issartial, J. 1992. Factors affecting somatic cell counts in goat milk. Small Ruminant Research, 8:129-139.
Maisi, P. 1990. Milk NAGase, CMT and antitrypsin as indicators of caprine subclinical mastitis infections. Small Ruminant Research, 3:493-501.
Marin, A. 1989. Report of the New York Department of Agriculture and Markets Dairy Laboratory. Proceedings, Annual Meeting of the Goat Milk Subcommittee of the National Committee on Interstate Milk Shippers, Frankfort, KY.
Marshall, R.T. 1992. Standard Methods for the Examination of Dairy Products. American Public Health Association, Washington, D.C., 16th edition, pp.343-345.
Maxey, K. 1993. 1993: A year of progress. Dairy Goat Journal (11):392-393.
Miller, R.H., Paape, M. J. and Fulton, L. A. 1991. Variation in milk somatic cells of heifers at first calving. Journal of Dairy Science, 74:3782-3790.
Paape, M.J., Capuco, A.V., Lefcourt, A., Burvenich, C. and Miller, R.H. 1992. Physiological response of dairy cows to milking. Proceedings International Symposium on Prospects for Automatic Milking. A.H. Lipema et al., ed., PUDOC Sci. Publ. Wageningen, EAAP publ. No. 65:93-105.
Poutrel, B. and Lerondelle, C. 1983. Cell content of goat milk: CMT, Coulter Counter and Fossomatic for predicting half infection. Journal of Dairy Science, 66:2575-2579.
Randy, H.A., Caler, W.A., Heintz, J.F. and Pankey, J.W. 1990. Observations on dairy goat milk quality. W.H. Miner Agricultural Research Institute, Chazy, NY, Mimeo Rpt.
Rota, A.M., Gonzalo, C., Rodriguez, P.L., Rojas, A.I., Martin, L. and Tovar, J.J. 1993. Effects of stage of lactation and parity on somatic cell counts in milk of Verata goats and algebraic models of their lactation curves. Small Ruminant Research, 12:211-219.
Schultz, L. 1993. Is there a national milk shortage? Dairy Goat Journal (11):432-433.
Upadhyaya, T.N. and Rao, A.T. 1993. Diagnosis and threshold values of subclinical mastitis in goats. Small Ruminant Research, 12:201-210.
Wilson, D.J., Stewart, K.N. and Sears, P.M. 1993. Factors affecting somatic cell counts in dairy goats. Proceedings, 32nd National Mastitis Council Annual Meeting, Kansas City, MO, 210 pp.
* (S. Smith, Provo, Utah, personal communication)
* (S. Smith, Provo, Utah, personal communication); SCC = somatic cell count; Fossomatic data; DIM = days in lactation; Milk kg/day/goat; % low SCC < 283,000; % high SCC > 1.13 million; Average SCC in 1,000; rolling herd average 365-day milk production 835 kg/goat.
* (S. Smith, Provo, Utah, personal communication)
Figure 1. Annual kidding distribution of dairy goats on DHIA in Western United States (S. Smith, Provo, Utah, personal communication; n = 3,293 in 1992; 4,017 in 1993)
Figure 2. Relationship of stage of lactation to average somatic cell counts in milk of dairy goats on DHIA in Western United States (S. Smith, Provo, Utah, personal communication)
Figure 3. Relationship of stage of lactation to average somatic cell count percentage above 1.13 million in milk of dairy goats on DHIA in Western United States (S. Smith, Provo, Utah, personal communication)
Send comments or links to firstname.lastname@example.org
Cooperative Extension Education in Agriculture and Home Economics, University of Delaware, Delaware State University and the United States Department of Agriculture cooperating. John C. Nye, Dean and Director. Distributed in furtherance of Acts of Congress of May 8 and June 30, 1914. It is the policy of the Delaware Cooperative Extension System that no person shall be subjected to discrimination on the grounds of race, color, sex, disability, age, or national origin.