Mastitis control: do the old ways still work? (Proceedings)

The development and effectiveness of the standard milking time hygiene practices and dry cow therapy were established in the 1960's. Because of the effectiveness of these practices, mastitis has evolved on many farms to primarily environmental rather than contagious pathogens. The purpose of this article is to perform a literature review (especially trying to find studies published after the year 2000) as to the effectiveness of the various mastitis control practices in today's progressive dairy farm.

Pre-dipping milk preparation

Pre-dipping with a germicide is used to kill bacteria on the teat surface and teat orifice and improves milk quality by helping to ensure that the teats a clean at the time of milking. Most studies indicate that pre-dipping with an effective germicide that is left on for the required amount of time is effective in controlling new environmental cases of mastitis. Oliver and others conducted a predipping efficacy study using 0.25% iodine and found that new mastitis infections by gram-negative bacteria were significantly lower in quarters with teats predipped and postdipped versus quarters receiving only postdip (Oliver et al., 1993). There were 48.6% fewer new infections due to major pathogens in the predipped quarters. In a more recent study of the efficacy of a phenolic-containing predip compared to a negative control, predipping was significantly more effective in preventing new intramammary infections (IMI) than was postmilking teat dipping alone (Oliver et al., 2001). Predipping is not thought to be very effective against preventing new IMI due to contagious mastitis pathogens. However pre-dipping is preferred over the use of water for udder preparation.

Single service towels

Single service paper or cloth towels are highly recommended to decrease the chance of transferring pathogens from one cow to another. This procedure is most important in controlling contagious pathogens and because most farms still have contagious pathogens, this control measure is still important. Fox (1997) investigated different methods to sanitize cloth towels and had the following results:

     1. The use of udder cloth towels and laundering towels between milkings is very economical as compared to use of paper towels.

     2. Laundering practices should include at least one of the following three practices: hot water wash; use of bleach; and hot air drying (all 3 or even 2 are not necessary).

     3. Washing towels in cold water only, without hot air drying and/or bleach, could result in the transmission of contagious mastitis pathogens.

Only one study could be found that investigated the ability of a medicated udder wipe product to reduce bacterial numbers on the teat surface premilking (Gibson et al., 2008). Although there was no significant difference between the 4 teat cleaning regimens (dry wipe with paper towel, alcohol-based medicated wipe, iodine-based dip and dry with paper towel and hypochlorite wash and dry with paper towel), numerically the dry wipe alone was the least effective.

Gloves

The use of gloves during milking has been strongly advocated by many in the dairy industry. Unfortunately, this strong advocacy is without strong research to back it up. In fact, until recently, there have been no published studies on the efficacy of glove use during milking. In theory, the use of gloves is thought to decrease the transfer of pathogens especially contagious pathogens via the milker's hands. A couple of studies have found that always wearing gloves while milking increased the risk of clinical mastitis (Peeler et al., 2000; O'Reilly et al., 2006). Wearing gloves for one year was not associated with a lower incidence of mastitis, and the authors are unaware of any evidence that wearing gloves reduces the incidence (O'Reilly et al., 2006). A more recent study stated that milker's wearing gloves during milking was a best-practice frontier because it was a cost-efficient measure despite it having a minimal effect on clinical mastitis (Huijps et al., 2010). The authors of this study could only find 3 articles that described the effects of wearing milkers' gloves (two are mentioned above, the third was not referenced...so it's not really clear why wearing gloves constitutes a "best-practice frontier").

Milking first lactation cows first

I could not find any recent studies that evaluated the effect of milking first lactation cows first. In fact, I could only find one study that evaluated this. Grommers and van de Geer (1979) reported that milking primiparous animals first failed to result in a significant decrease of the level of udder infection during the first half of lactation. Although not significant, they state that there was a rise in infection level among the older animals of the experimental group and a decline in the controls at the same time. This procedure was developed to help control contagious mastitis pathogens and may actually be a good practice in herds that have a high percentage of cows infected with contagious pathogens. In herds with good control of contagious pathogens, this procedure may not be appropriate because ~4% of heifers freshen with Staphylococcus aureus mastitis.

Complete milk-out (machine or hand stripping)

No studies could be found regarding this relatively old recommendation to help prevent mastitis.

Backflush system

No recent studies were found. However, the milking unit can be a source of contagious pathogens and studies have shown that backflushing can reduce the significance of the milking unit as a contagious mastitis fomite (Fox et al., 1991; Hogan et al., 1984). In a study by Smith et al., 1985, backflushing reduced numbers of staphylococci recovered from liners by 98.5% and Gram-negative bacteria by 99.5% as compared with unflushed liners. Backflushing significantly reduced new IMI by Corynebacterium bovis. However, there was no effect on incidence of new infections by staphylococci, streptococci, or coliforms. These results do not justify the use of backflushing in a herd with low prevalence of contagious pathogens. Thus, there is no overwhelming evidence that backflushing systems are worth the expense in herds with a low prevalence of contagious pathogens.

Milking machine maintenance

No studies could be found that compared mastitis rates between dairy herds that practiced routine milking machine maintenance and herds that did not. However, there are several older studies that document that the malfunctioning milking machine is an important risk factor in new IMI.

Post-milking teat disinfection

In an introduction of a manuscript that I had submitted for publication in a journal in which I briefly mentioned the importance of post-milking teat disinfection, one of the reviewers indicated that "if you search the literature on naturally infected teat dipping studies which includes more than 10 herds with a negative control group, you will be surprised how little documentation there is on teat dipping and the effect of it". Although I was initially taken aback by this statement, in retrospect, I should not be surprised at all. When the carrying out of a procedure is left in the hands of the producers, a certain level of control is lost. I would venture to guess that teat dipping is seldom performed adequately (maybe adequate in an individual cow but certainly not the entire herd) during just about every milking. Whereas when the researchers are specifically controlling the teat dipping study, a much greater percentage of appropriate teat coverage takes place. I have scanned the literature for a multi-herd teat dipping trial that used non-dipped control cows or teats and could not find one. Post-milking teat disinfection is primarily utilized for control of contagious pathogens such as S. aureus. Barrier teat dips have been developed in hopes of providing some prevention of environmental pathogens. Foret and co-workers (2006) reported that experimental barrier dips were better able to reduce the total new IMI (primarily due to C. bovis IMI) when compared to a conventional iodine teat dip but a difference in the reduction in environmental pathogens was not observed. In a large multi-herd trial of 48 German dairy herds, the non use of post-milking teat disinfection was > 3 times more associated with the prevalence of mastitis than the use of post-milking teat disinfection (Fadlelmoula et al., 2007). A 1999 study by Barkema and others noted that postmilking teat disinfection was associated with an increased overall incidence rate of clinical mastitis (new infections were not mentioned). The explanation was that postmilking teat dipping decreased the percentage of quarters infected with minor pathogens leaving more quarters at risk of developing mastitis due to major pathogens in herds with low bulk tank somatic cell counts. Several papers have been published demonstrating the efficacy of post-milking teat dipping in helping prevent new IMI and its use should still be recommended today.

Type of bedding

There is really no doubt that keeping the bedding area clean and dry are important especially for environmental mastitis control. Likewise, there is little doubt that sand bedding is preferred over organic forms of bedding because sand bedding does not supply nutrients for mastitis pathogens and should therefore result in fewer cases of mastitis. A recent e-mail discussion on AABP highlights the fact that all sand is not equal and mastitis problems can still result from sand bedding. A 2010 study documented that mycoplasma can not only be found in recycled sand bedding but can survive for up to 8 months (Justice-Allen 2010). In the aforementioned study, both 0.5% sodium hypochlorite and 2% chlorhexidine were efficacious in eliminating mycoplasma from the contaminated bedding sand. It is important to note that the sand itself does not supply nutrients for mastitis pathogens but the organic debris that is in the sand. A 2008 study of 4 bedding materials found that digested manure solids supported the heaviest growth of Klebsiella pneumoniae followed by recycled sand which was followed by shavings; clean sand promoted the least amount of growth of Klebsiella (Godden et al., 2008). A study by Zdanowicz and coworkers found that coliforms and Klebsiella spp. were 2x and 6x (respectively) more numerous on the teat ends of cows bedded on sawdust than those bedded on sand; however Streptococcus spp were 10 times more numerous of teat ends of cows bedded on sand (Zdanowicz et al., 2004).

Dry-cow intramammary therapy

Dry-cow IMM therapy (DCT) has been part of mastitis control strategies for several years now. It is used primarily for preventing new IMI during the dry period and to eliminate existing IMI. It is an essential part of contagious mastitis control especially in herds that still have Streptococcus agalactiae. However, most herds have eradicated this mastitis pathogen and dry-cow IMM therapy has been called into question. A relatively recent meta-analysis of the literature regarding DCT for prevention of new IMI found that in 35 of 36 studies, treated quarters had fewer new IMI than non-treated quarters (not all were significantly different but the trend is clearly in favor of DCT) (Robert et al., 2006). This study also evaluated the efficacy of dry-cow therapy on specific mastitis pathogens. Dry-cow therapy was found to be highly successful in preventing new streptococcal IMI (both agalactiae and "environmental" streptococci) compared to non-treated controls. In regards to S. aureus, some studies demonstrated a significantly lower new S. aureus IMI rate among treated quarters versus non-treated controls; however other studies found a higher new S. aureus IMI rate among the treated quarters. No clear trend was noted among coliform and other organisms. The authors concluded that when the risk of new IMI is high, blanket DCT has a favorable impact but becomes limited when the risk of new IMI is low. Again, this study did not review efficacy of curing existing IMI. A meta-analysis of DCT evaluating cure rate of existing IMI found that DCT resulted in an average 78% bacterial cure whereas spontaneous cures occurred on average 46% of the time (Halasa et al., 2009). Significant cures for staphylococci and streptococci were noted but coliforms cures were not mentioned. The aforementioned manuscript only included a couple of studies conducted after the year 2000. A recent study evaluated the economics of the various dry cow therapy options and found the blanket DCT had the lowest combined total annual net cost of IMI compared to blanket DCT and teat sealant, selective DCT with or without teat sealant, and teat sealant alone (Halasa et al., 2010). Seems that DCT can still be routinely recommended but dairies with low SCC with ready ability to conduct milk culture may want to consider other dry cow mastitis prevention options.

References

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