Introduction

• Mastitis is a complex, multi-factorial disease with numerous contributing factors that are primarily associated with environmental conditions and milking management.
• Historically, increased annual average milk production has been associated with a slight increase in the clinical mastitis rate and somatic cell count (SCC).
• Some early studies showed cows supplemented with recombinantly derived bovine somatotropin (Posilac) had a higher incidence of clinical mastitis compared to non-supplemented controls.
• Evaluation of data from 85 worldwide studies and two large post-approval monitoring programs (PAMP) demonstrated that there were numerical increases in the clinical mastitis rate in cows supplemented with Posilac compared to non-supplemented cows but that the difference was negated when adjusted for volume of milk produced.

Mastitis: The Disease and How It Is Influenced by Dairy Technologies Such as Posilac

Mastitis is a complex, multi-factorial disease. A number of bacterial agents have been identified as causing mastitis in the dairy cow. Management and environmental factors including season^1-3, parity^3-6, and stage of lactation^2,3 contribute to the infectivity, pathogenesis, and spread of the disease within the herd. Additionally, there is tremendous herd-to-herd variation in the incidence and prevalence of mastitis based on these management and environmental factors³ (Figure 1).

Any new production-enhancing technology for use in dairy cattle is accompanied with concerns as to how that technology might affect the incidence of various animal health conditions such as mastitis. rbST, Posilac, was introduced for commercial use in 1994. Numerous experimental and field studies have consistently shown that Posilac enhances milk yield in supplemented cows.^7-15 Results from two^7,10 of eight studies conducted prior to approval of Posilac showed an increase (P<0.05) in the incidence of clinical mastitis in cows supplemented with Posilac, while the other six studies^8,11-15 showed no effect. A study¹⁶ utilizing another rbST analog (somidobove, Elanco Animal Health, Greenfield, IN) also showed no association between rbST supplementation and the incidence or duration of clinical mastitis, the prevalence of infection with common mastitis pathogens, or SCC. A subsequent evaluation¹⁷ was conducted on the data from 85 preapproval rbST studies from eight countries. This summary included data from 15 full-lactation studies and 70 short-term studies and showed that rbST-supplemented cows had a numerically higher incidence of clinical mastitis compared to non-supplemented controls; however, the clinical mastitis incidence was identical in supplemented and non-supplemented cows at the same production level.

*Variability in clinical mastitis (CM) rates for stage of lactation, parity, season, and month of calving determined by calculating difference between the highest and lowest incidence for each parameter within the herds under study. Variability in the clinical mastitis rate among herds determined by calculating the difference between the highest and lowest incidence of CM among herds under study. Variability in the incidence of clinical mastitis rates based on rbST use calculated by determining the difference in CM incidence between herds under study using rbST and those herds not using rbST.
¹ Elanco Animal Health, Greenfield, IN.

Large post-approval monitoring studies, one utilizing 555 Holsteins from four Michigan herds (Study One)¹⁸ and the other involving 1,213 cows in 28 herds in four U.S. geographic locations (Study Two)¹⁹ showed similar results, with Posilac-supplemented cows having a numerically higher incidence of clinical mastitis. For example, in Study One, 127 cows were diagnosed with clinical mastitis cases during the monitoring period of which 85 occurred during Posilac supplementation. Of the 85 clinical mastitis cases, 47.1% occurred in control cows and 52.9% occurred in Posilac-supplemented cows, but the difference was not significant (P>0.05). In Study Two, the clinical mastitis rate prior to Posilac supplementation (pretreatment period) in control and Posilac-supplemented animals was similar for primiparous and multiparous cows (Table 1). During treatment (treatment period), the expected clinical mastitis rates determined from the Linear Mixed Model analysis for a 252-day standardized treatment period were 0.23 and 0.28 for control and Posilac-supplemented primiparous cows and 0.38 and 0.50 for control and Posilac-supplemented multiparous cows, respectively (Table 1). These differences were not significant (P>0.05), and when adjusted for level of milk production, the clinical mastitis rate and SCC linear score were essentially identical between groups.

Another study²⁰ designed to measure production responses to Posilac supplementation from northeast U.S. herds showed that log linear somatic cell scores and corresponding SCC were low for all herds, ranging from 3.08 to 3.22 (106,000 to 117,000 SC/mL) for the pre- and post-Posilac approval periods, and that SCC patterns were not affected by Posilac supplementation over the lactation. This study further showed that Posilac improved lactation yield and persistency over a four-year period and had no effect on culling²⁰.

Overall Effects of Posilac Supplementation and Milk Yield on Mastitis and SCC

The label for Posilac states “Cows injected with Posilac are at an increased risk for mastitis (visibly abnormal milk) and may have higher milk somatic cell counts. Have comprehensive mastitis management practices in place on your dairy before using Posilac.”²¹ This cautionary statement was added based on observations from the original registration studies.^7-14 Results from a number of field studies both prior to and subsequent to Posilac registration have given mixed results regarding its overall effect on the incidence of clinical mastitis and SCC.

Between 1970 and 2008 average annual milk production in the United States increased by over 10,000 pounds or approximately 280 pounds per cow per year.²² Genetic improvement accounted for 55% or approximately 150 pounds per year of that increase.²³ Improvements in milk yield from genetic selection may be associated with increased susceptibility to clinical mastitis and SCC.²⁴ Strandberg et al.²⁵ demonstrated breeding programs without regard to mastitis control resulted in an annual increase in the incidence of clinical mastitis of 0.02 cases per cow per year. Using this relationship, a 2,000-lb increase in milk yield per year would equate to an additional 0.2 clinical mastitis cases per year. Cows supplemented with Posilac have an anticipated increase in milk yield of 10 lb per day or 2,000 lbs for a 200-day supplementation period.¹⁹ The additional 0.12 cases of clinical mastitis in Posilac-supplemented multiparous cows predicted by Collier et al.¹⁹ would equate to approximately one additional case per 10 lactations and would be approximately half that expected with a corresponding seven years of genetic and herd management related production improvements.

Supplement lactating dairy cows every 14 days beginning at 57 to 70 days in milk until the end of lactation. The label contains complete use information, including cautions and warnings. Always read, understand, and follow the label and use directions.

Summary

Extensive research with Posilac and its relationship to mastitis and SCC have in some cases demonstrated a numerical increase in the incidence of clinical mastitis in cows supplemented with Posilac. In large-scale post-approval monitoring programs, this increase has not been statistically significant (P>0.05). When numerical differences in the clinical mastitis rate were observed, they were less than anticipated for the increased level of milk production associated with Posilac supplementation. Any potential increase in the incidence of clinical mastitis in the Posilac-supplemented cow can be controlled by focusing on factors associated with the environment and milking management which have a much greater influence on the incidence of mastitis compared to Posilac use.

Author Information

David McClary, ELANCO Animal Health
Stephen C. Nickerson, University of Georgia

Selected References

1. Morse D, DeLorenzo MA, Wilcox CJ, Collier RJ, Natzke RP, and Bray DR. 1988. Climatic effects on occurrence of clinical mastitis. J. Dairy Sci. 71:848.

2. Smith KL, Todhunter DA, and Schoenberger PS. 1985. Environmental mastitis: cause, prevalence, prevention. J. Dairy Sci. 68:1531.

3. Hogan JS, Smith KL, Hoblet KH, Schoenberger PS, Todhunter DA, Hueston WD, Pritchard DE, Bowman GL, Heider LE, Brockett BL, and Conrad HR. 1989. Field survey of clinical mastitis in low somatic cell count herds. J. Dairy Sci. 72. 1547-1556.

4. Morse D, DeLorenzo MA, Wilcox CJ, Natzke RP, and Bray DR. 1988. Characterization of Clinical Mastitis Records from One Herd in a Subtropical Environment. J. Dairy Sci. 71:1396-1405.

5. Morse D, DeLorenzo MA., Wilcox CJ, Natzke RP, and Bray DR. 1987. Occurrence and Reoccurrence of Clinical Mastitis. J. Dairy Sci. 70:2168.

6. Elanco Animal Health, Data on file, Posilac full lactation studies.

7. Cole, JW, Eppard PJ, Boysen BG, Madsen KS, Sorbet RH, Miller MA, Hintz RL, Ribelin WE, Hammond BG, Collier RJ, and Lanza GM. 1992. Response of dairy cows to high doses of a sustained-release bovine somatotropin administered during two lactations. 2. Health and reproduction. J. Dairy Sci. 75:111.

8. Downer, JV, Patterson DL, Rock DW, Chalupa WV, Cleale RM, Firkins JL, Lynch GL, Clark JH, Brodie BO, Jenny BF, and De Gregorio R. 1993. Dose titration of sustained-release recombinant bovine somatotropin in lactating dairy cows. J. Dairy Sci. 76:1125.

9. Eppard, RJ et al. 1991. Response of dairy cows to high doses of a sustained-release bovine somatotropin administered during two lactations. 1. Production response. J. Dairy Sci. 74:3807.

10. Pell AN, Tsang DS, Howlett BA, Huyler MT, Meserole VK, Samuels WA, Hartnell GF, and Hintz RL. 1992. Effects of a prolonged-release formulation of sometribove (n-methionyl bovine somatotropin) on Jersey cows. J. Dairy Sci. 75:3416.

11. Remond B, Cisse M, Ollier A, and Chilliard Y. 1991. Slow release somatotropin in dairy heifers and cows fed two levels of energy concentrate. 1. Performance and body condition. J. Dairy Sci. 74:1370.

12. Rijpkema YS, van Reeuwijk L, and Hard DL. 1990. Responses of dairy cows to treatment with sometribove (r-BST) during three consecutive years. Livest. Prod. Sci. 26:193.

13. Skarda J, Markalous E, Slaba J, Krejci P, Skardova O, and Zednik J. 1992. Effect of methionyl bovine somatotropin in a prolonged-release vehicle on milk production, hormone profiles and health in dairy cattle. J. Dairy Res. 59:499.

14. Thomas J W, Erdman RA, Galton DM, Lamb RC, Arambel MJ, Olson JD, Madsen KS, Samuels WA, Peel CJ, and Green GA. 1991. Responses by lactating cows in commercial dairy herds to recombinant bovine somatotropin. J. Dairy Sci. 74:945.

15. Whitaker DA, Smith EJ, Kelly JM, and Hodgson-Jones LS. 1988. Health, welfare and fertility implications of the use of bovine somatotropin in dairy cattle. Vet. Rec. 122:503.

16. McClary DG, Green HB, Basson RP, and Nickerson. 1994. The Effects of a Sustained-Release Recombinant Bovine Somatotropin (Somidobove) on Udder Health for a Full Lactation. J. Dairy Sci. 77:2261.

17. White TC, Madsen KS, Hintz RL, Sorbet RH, Collier RJ, Hard DL, Hartnell GF, Samuels WA, de Kerchove G, Adriaens F, Craven N, Bauman DE, Bertrand G, Bruneau P, Gravert GO, Head HH, Huber JT, Lamb RC, Palmer C, Pell AN, Phipps R, Weller R, Piva G, Rijpkema Y, Skarda J, Vedeau F, and Wollny C. 1994. Clinical mastitis in cows treated with sometribove (recombinant bovine somatotropin) and its relationship to milk yield. J. Dairy Sci. 77:2249.

18. Judge LJ, Erskine RJ, Bartlett PC. 1997. Recombinant bovine somatotropin and clinical mastitis: Incidence, discarded milk following therapy and culling. J. Dairy Sci. 80:3212.

19. Collier RJ, Byatt JC, Denham SC, Eppard PJ, Fabellar AC, Hintz RL, McGrath MF, McLaughlin CL, Shearer JK, Veenhuizen J J, and Vicini JL 2001. Effects of sustained release bovine somatotropin (Sometribove) on animal health in commercial dairy herds. J. Dairy Sci. 84:1098.

20. Bauman DE, Everett RW, Weiland WH, and Collier RJ. 1999. Production responses to bovine somatotropin in northeast dairy herds. J. Dairy Sci. 82:2564.

21. Posilac product label. 2009. Elanco Animal Health, Greenfield, Ind.

22. United States Department of Agriculture. National Agriculture Statistics Service. 2008. http://www.nass.usda.gov/QuickStats/PullData_US.jsp

23. Shook GE. 2006. Major Advances in Determining Appropriate Selection Goals. J. Dairy Sci. 89:1349.

24. Schutz MM. 1994. Genetic evaluation of somatic cell scores for the United States dairy cattle. J. Dairy Sci. 77:2113.

25. Strandberg E and Shook GE. 1989. Genetic and economic response to breeding programs that consider mastitis. J. Dairy Sci. 72:2136.

Posilac® is a trademark of Elanco’s brand of recombinant bovine somatotropin. ©2009 Elanco Animal Health.