Key Points:

• The FDA concluded that the use of POSILAC^® is safe.
• Studies show dairy herds supplemented with POSILAC remain as healthy as non-supplemented herds and show no increase in mastitis cases.
• There is a much larger variation in the number of clinical mastitis cases due to factors other than bST use (e.g. season, parity, stage of lactation).
• Milk is effectively monitored for antibiotics and other illegal drug residues.
• The U.S. milk supply is regarded as one of the safest in the world.

Mastitis is generally recognized as a very costly disease to the dairy industry which manifests itself in lowered milk yield, increased costs of production, and reduced milk quality (3). Therefore, it is critical to determine the impact of any new technology on mastitis. Several factors predispose the dairy cow to mastitis, such as season, parity, herd, stage of lactation and environment. A positive relationship between milk yield and incidence of mastitis has been observed, with higher producing cows being more susceptible to mastitis incidence (1). The supplementation of dairy cows with bST does not alter this relationship (1). A discussion on the use of POSILAC as a tool that increases milk production and its relationship to mastitis follows.

In the Freedom of Information Act Summary (2) for POSILAC bovine somatotropin, the Food and Drug Administration (FDA) concluded that POSILAC supplementation may increase the risk of clinical and sub clinical mastitis, and milk somatic cell counts (SCC) in some dairy herds. Product labeling reflects those possible effects. The elevation in SCC was well within the SCC range of high quality milk. Also, on a per unit of milk basis, the increase in mastitis attributed to POSILAC (approximately 0.1 case/cow/305 day lactation) was about 4 to 9 times less than the effects of season, parity, stage of lactation and herd-to-herd variation. The FDA also noted that the slight increase in mastitis was not a health concern because the clinical cases were not atypically difficult to treat. The duration of cases was similar for cows supplemented with POSILAC and control cows. The FDA concluded that the use of POSILAC was not biologically significant in the overall incidence of mastitis per unit of milk produced and not a public health concern because of 1) the huge variation in the number of clinical mastitis cases due to other factors, and 2) the standard monitoring of milk for safety already in place. The increase in clinical mastitis in animals supplemented with POSILAC has little practical significance when compared to other herd factors. Increases in mastitis are 4-9 times more likely through the effects of season, parity, herd, or stage of lactation (4,5), than through the use of POSILAC.

Clinical trial data in the U.S. from over 480 cows indicated that during POSILAC supplementation the percentage of cows with mastitis and the cases per 100 cow-days were higher in cows supplemented with POSILAC as compared with controls (4). Although mastitis incidence was statistically increased in POSILAC-supplemented cows, the distribution of mastitis incidence across the entire lactation was similar in both supplemented and non-supplemented cows.

Somatic Cell Counts

During the treatment period, SCC were higher in some (but not all) groups or herds supplemented with POSILAC. Average SCC tended to increase in both the cows supplemented with POSILAC and control cows as lactation progressed (4). The range in SCC in eight herds averaged over the treatment period was 97,000-284,000 in the control cows and 178,000-264,000 in the supplemented group (4). The SCC levels for all cows were well within the normal ranges for high-quality milk.

Effective use of bST requires that sound mastitis and milking management practices be continued (1), as well as the management practices utilized in higher producing cows.

In summary, cows supplemented with POSILAC may be at an increased risk for clinical mastitis. Whether or not supplemented cows actually experience mastitis is affected by typical management factors. Thus, the label reads "Mastitis management practices should be thoroughly evaluated prior to initiating use of POSILAC.

General Recommendations

To simplify understanding of the mastitis complex, and to develop recommendations for the management of mastitis, it is useful to consider the three major factors involved: the microorganisms as the causative agent of the disease, the cow as the host, and the environment which can influence both the cow and the microorganisms.

The following general recommendations should be followed in a mastitis management program:

• Keep the cows' environment clean and stress-free. Environmental hygiene (backflushing, segregation) plays a key role in mastitis prevention.
  
  
• Monitor Somatic Cell Count (SCC) in bulk tank, and individual cows causing increased bulk tank SCC.
  
  
• Culture persistently mastitic cows to evaluate affecting microorganism and target control and prevention.
  
  
• Use proper milking procedures:
  
  
  • Wash only teats and lower udder surfaces
    
    
  • Dry each teat thoroughly with individual paper towels
    
    
  • Check quarters for abnormalities each milking by stripping
    
    
  • Make sure milking machine is properly adjusted and disinfected between cows
    
    
  • Dip or spray teats, especially post-milking, with an effective teat dip
    
    
• Evaluate dry cow management practices:
  
  
  • Dry-off procedures
    
    
  • Dry cow therapy
    
    
  • Dry cow nutrition
    
    
  • Transition period feeding and management
    
    
  • Fresh cow management
    
    
• Develop a complete herd health program.
  
  
• Cull chronically-infected cows.
  
  
• Assure cows are consuming a balanced ration that optimizes immune function.
  
  
• Nutrition and care during the dry period are very important.
  
  
• Prevention of new infections and reducing the duration of actual infections is of foremost importance in a mastitis management program.

References

1. Bauman, D.E., B.W. McBride, J.L. Burton, and K. Sejrsen. 1994. Somatotropin (bST): International Dairy Federation technical report. Bull. Intl. Dairy Fed. No. 293.
2. FOI. 1993. FDA Freedom of Information Summary. POSILAC(r) (sterile sometribove zinc suspension) for increasing milk production in lactating dairy cows. New Animal Drug Application 140-872. Sponsored by The Agricultural Group of Monsanto Company.
3. National Mastitis Council. Current Concepts of Bovine Mastitis. 1987. 3rd Edition.
4. Technical Manual for POSILAC bovine somatotropin. Revised May 1994. Monsanto Company. pp. 6.1-6.7
5. White et al. 1994. Clinical mastitis in cows treated with sometribove (recombinant bovine somatotropin) and its relationship to milk yield. J. Dairy Sci. 77:2249.

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