**12. Influence of dietary supplementation on mammary health**

Another management tool to reduce the level of infection and SCC when heifers calve as well as throughout lactation is through dietary supplementation. Diet plays a role in udder resistance to infection because certain nutrients affect various mammary resistance mechanisms, namely: (1) leukocyte function, (2) antibody transport, and (3) mammary tissue integrity. In one study, heifers received selenium (0.3 ppm/day) and vitamin E (50 to 100 ppm/day) supplementation starting 60 days prepartum (Hogan et al., 1993). A selenium booster injection (50 mg) was administered 21 days prior to freshening, and the dietary supplementation was continued throughout lactation. Dietary supplementation reduced staphylococcal and coliform infections at calving by 42%. Although rate of new infection during lactation did not differ from unsupplemented controls, the duration of infection caused by organisms other than *Corynebacterium bovis* was reduced 40 to 50% in supplemented heifers. Clinical mastitis in supplemented heifers was reduced 57% in early lactation and 3.2% throughout lactation, and the mean SCC was lower. Thus, vitamin E and selenium improved udder health of heifers, and the effect of dietary supplementation was most evident at calving and in early lactation.

In a more recent study, dairy heifers were fed a daily supplement beginning at 5 months of age containing an immunostimulant composed of B-complex vitamins and yeast extract (Eubanks et al., 2011). Compared with unsupplemented control animals, those supplemented with the immunostimulant exhibited greater leukocyte expression of Lselectin and interleukin-8 cell surface receptors, suggesting the capability for a greater immune response to bacterial infection. Preliminary results also showed a lower incidence of *Staph. aureus* mastitis in supplemented heifers.

## **13. Conclusions**

354 Milk Production – An Up-to-Date Overview of Animal Nutrition, Management and Health

**Figure 10.** Udder of a 10-month-old heifer illustrating horn flies and lesions on teat ends.

(Owens et al., 2000).

and earn quality premiums for their product.

In a subsequent trial, the daily dietary supplementation of an insect growth regulator helped to suppress fly populations but not enough to prevent new cases of mastitis in dairy heifers

Lastly, the use of an insecticidal pour-on every 2 wk for 6 wk followed by treatment with insecticidal ear tags reduced fly populations and decreased the incidence of new *Staph. aureus*  by 83% during a 6-mo trial in heifers during the warm season in Louisiana (Owens et al., 2002). Mastitis in heifers caused by *Staph. aureus* was associated with SCC in excess of 10 million/ml. These studies demonstrate that, during the warm and humid months of the year, horn flies do serve as vectors in the transmission of heifer mastitis, which is associated with elevated SCC in these young dairy animals. Although research has not been conducted to show this same association in lactating and dry adult cows, it is assumed that fly populations play some role in the elevation of mastitis and SCC observed in the hot summer months. And, with the proposed reduction in the SCC legal limit to 400,000/ml in the USA, and in light of the fact that milk buyers are imposing their own limits, some as low as 250,000/ml, it is imperative that dairymen utilize all possible means to prevent new cases of mastitis and their associated SCC. A simple fly control program can serve as an important adjunct to the basic 5-point plan of mastitis control and assist dairymen in lowering their bulk tank SCC

replacing them was impractical from a management standpoint.

increased from 17.1 to 52.4% (3.1-fold increase). As observed above, infections were associated with marked elevations in SCC. However, after 2 months, tags fell off and

> Prevalence of mastitis in unbred, breeding age, and pregnant dairy heifers is higher than formerly realized. Infected mammary quarters, especially those with *Staph. aureus* IMI exhibit reduced secretory potential and marked leukocyte infiltration and accompanying inflammation. Both nonlactating and lactating commercial antibiotic infusion products have been used successfully to cure existing infections and reduce SCC, and nonlactating therapy prevents new IMI with environmental streptococci. However, the goal is to prevent new infections from occurring in these young dairy animals through management strategies aimed at vaccination, fly control, and dietary supplementation. Results of experimental and commercial vaccine trials illustrate that immunization will reduce *Staph. aureus* mastitis in heifers at calving between approximately 45 and 60%, with reductions in SCC of 50%. Likewise, a fly control program for heifers will decrease incidence of *Staph. aureus* mastitis by up to 83%. Lastly, dietary supplementation to boost the immune systems of heifers has been shown to reduce incidence of mastitis at calving as well as to lower SCC. As global milk quality standards become more stringent, management practices based on curing existing infections and preventing new IMI in heifers will ensure that these young dairy animals enter the milking herd free of mastitis with low SCC. Such practices should be considered for incorporation into dairy herd health programs in herds suffering from a high prevalence of heifer mastitis, especially that caused by *Staph. aureus*.

## **Author details**

Stephen C. Nickerson *University of Georgia, USA* 

#### **14. References**


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**Author details** 

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Stephen C. Nickerson *University of Georgia, USA* 

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