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 season1-3, parity3-6, and stage of lactation2,3 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 two7,10 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 studies8,11-15 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.
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.
|Clinical mastitis case rates (per/cow) per standardized 252 days at riska|
|a Rates calculated from least square means from the Linear Mixed Model analysis of logistics.|
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.
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.
David McClary, ELANCO Animal Health
Stephen C. Nickerson, University of Georgia
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6. Elanco Animal Health, Data on file, Posilac full lactation studies.
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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.