Research and Reviews: Dairy

Special Circular 163-99

Bacterial Counts in Sawdust Bedding

J. S. Hogan 1
K. L. Smith
The Ohio State University
Department of Animal Sciences

1 For more information, contact at: The Ohio State University, Ohio Agricultural Research and Development Center, 302 Pounden Hall, 1680 Madison Avenue, Wooster, OH 44691; 330-263-3801; e-mail: hogan.4@osu.edu

Abstract

Bacterial counts in untreated sawdust bedding were compared with those in sawdust bedding after the addition of lime and after daily replacement of bedding in the back one-third of the stalls. Addition of 2.2 lbs. of lime to 22 lbs. of sawdust reduces Gram-negative bacteria, coliforms, Klebsiella spp., and streptococci prior to use as bedding. Sawdust treated with lime also showed decreases in bacterial counts when compared with sawdust that was replaced daily and control bedding after one day in the stall. The decrease in bacterial populations was related to an increase in bedding pH. Mean pH in sawdust that contained lime was greater prior to use and was greater after day one in the stall compared with other treatments. After two and six days in stalls, bacterial counts and pH were similar among treatments. Dry matter content of bedding did not differ among bedding treatments. Bacterial counts in bedding were positively correlated with teat skin swabs. Gram-negative bacterial and Klebsiella spp. counts on teat swabs were lower for cows housed on bedding treated with lime on day two compared with those cows housed on control bedding and bedding that was replaced daily. Addition of lime to sawdust in the back one-third of the stalls caused a decrease in exposure of teats to environmental mastitis pathogens in bedding for one day.

Introduction

The number and the type of bacteria in bedding are related to the microbial load on teat ends and the rates of clinical mastitis in lactating dairy cows (Hogan et al., 1989). Organic materials such as straw, corn fodder, and sawdust often contain greater than 106 cfu/g of coliform bacteria when used as bedding (Bramley and Neave, 1975). Bacterial counts also differ within organic beddings; wood products often contain the greatest number of coliform bacteria (Rendos et al., 1975). Wood products, such as sawdust and shavings, have been found to be heavily contaminated with Klebsiella spp. Sawdust and wood shavings continue to be popular choices as bedding despite evidence that outbreaks of coliform mastitis within a herd are commonly attributed to contaminated bedding (Bramley, 1985).

The control of bacterial populations in organic materials often involves intensive management of stalls and bedding. A common practice on many farms that use wood products for bedding is to add hydrated lime to the stalls to control bacterial populations (Fairchild et al., 1982). Lime should elevate the pH and reduce the moisture content of the bedding to inhibit bacterial growth. Bramley (1985) reported that daily replacement of sawdust in the back one-third of stalls also reduced bacterial contamination of stalls. Reducing the coliform populations in the sawdust by daily replacement of bedding was associated with reduced clinical mastitis. Despite a number of studies that have investigated the merits of these bedding management practices, data are limited comparing the effectiveness of lime and daily replacement of bedding within a similar environment to control teat-end exposure to mastitis pathogens. The purpose of the current study was to compare the effects of lime and daily replacement of bedding on bacterial populations in sawdust and the bacterial flora of teat ends.

Materials and Methods

Experimental Design

The experiment was conducted at The Ohio State University's Ohio Agricultural Research and Development Center tie-stall barn. Each stall was a 5.5 x 5 foot concrete base with inlaid rubber mats. Three rows of tie-stalls were bedded with 22 pounds of kiln-dried sawdust (particle size <10 mm x 10 mm) and each row received one of three treatments: (1) daily replacement of sawdust in the back one-third of the stall, (2) addition of 2.2 pounds of hydrated lime spread evenly over sawdust in the back one-third of the stall on the days that stalls were cleaned and covered with fresh bedding, or (3) control sawdust bedding with no treatment. Three groups of four lactating cows were assigned to treatment groups. Cows were bedded on the same material for three consecutive weeks. Within each three-week period, all bedding was removed, stalls allowed to dry, and fresh sawdust was applied every seven days. After three weeks on a bedding treatment, cows remained in the same stalls and bedding treatments were changed. The trial lasted nine weeks so that cows were exposed to all bedding treatments.

Bedding Samples

Samples were collected immediately after fresh bedding was added to stalls (day zero) and one, two, and six days after each of the weekly changes in stalls with sawdust treated with lime and in control stalls. Bedding samples were collected immediately after fresh bedding was added to stalls on day zero and prior to removal of bedding on days one, two, and six in stalls where bedding was replaced daily. Samples were a composite of bedding from the back one-third of each stall. Dry matter and pH were measured. Bacterial populations in bedding were enumerated as described by Hogan et al. (1989).

Teat Swabs

Teat swabs were collected from the right front teat of each cow within one hour prior to bedding treatments on days zero, one, two, and six. Swabs were obtained as described by Rendos et al. (1975). Briefly, sterile cotton swabs were moistened in a swab solution of phosphate buffered saline (PBS) containing 0.1% sodium thiosulfate before swabbing. Teat ends were sampled by rotating a moistened swab five times around the exterior teat orifice. Swabs were placed into a test tube containing 4.0 ml of the swab solution. Teat tubes containing swabs and swab solution were maintained on ice until bacteriological analyses were initiated within one hour. Test tubes were shaken vigorously for 20 seconds, and appropriate dilutions of rinse solution were plated on agar media.

Results and Discussion

Treatment Effects on Bedding Counts

Bacterial counts and pH differed among bedding treatments prior to use and after one day in the stalls. Addition of lime to sawdust reduced each bacterial count compared with bacterial counts in untreated sawdust prior to use as bedding on day zero. The reduction in bacterial counts coincided with a difference in the pH of the bedding but not with dry matter. Average pH of sawdust containing lime on day zero was 12.1 compared with 4.5 for untreated sawdust. Mean dry matter prior to use as bedding was similar between untreated sawdust (89.9%) and sawdust treated with lime (91.3%). Coliform and Klebsiella spp. counts on day zero were below the sensitivity of the plating procedures (<102 cfu/g) in each of the nine samples of sawdust plus lime. Streptococcal counts in sawdust treated with lime prior to use were <102 cfu/g in 78% of the samples. In contrast, prior to use as bedding, only 50 and 6% of untreated sawdust samples had coliform and streptococcal counts <102 cfu/g, respectively.

Gram-negative bacteria, coliforms, Klebsiella spp. (Figure 1), and streptococci (Figure 2) each continued to be lower in bedding treated with lime compared with bedding replaced daily or compared with untreated control bedding after one day in the stall. Bacterial counts did not differ between bedding replaced daily and untreated control bedding. Mean pH (Figure 3) on day one was greater in sawdust containing lime (pH = 9.8) than in bedding replaced daily (pH = 7.1) and control sawdust (pH = 7.0). Dry matter did not differ among bedding treatments after one day in the stall.

Figure 1. Klebsiella spp. counts in untreated sawdust (slashed bar), sawdust
treated with lime (hatched bar), and sawdust replaced daily (open bar) on days 0,
1, 2, and 6 after use as bedding in tie stalls.

Figure 2. Streptococcal counts in untreated sawdust (slashed bar), sawdust
treated with lime (hatched bar), and sawdust replaced daily (open bar) on days 0,
1, 2, and 6 after use as bedding in tie stalls.

Figure 3. Mean pH in untreated sawdust (slashed bar), sawdust treated with lime
(hatched bar), and sawdust replaced daily (open bar) on days 0, 1, 2, and 6 after
use as bedding in tie stalls.

Treatment effects on bedding variables were limited after one day in the stall. The ability of lime to alter bacterial counts and pH apparently was diminished within 48 hours after application. The only difference among treatments was that Klebsiella spp. counts on day two were reduced in bedding that was treated with lime compared with bedding that was replaced daily. Klebsiella spp. counts did not differ between bedding treated with lime and control bedding on day two. Gram-negative bacteria, coliforms, and streptococci did not differ among treatments on day two. Mean pH and dry matter also were similar among treatments on day two. Bacterial counts, pH, and dry matter did not differ among treatment groups on day six.

Teat End Swabs

Bacterial counts in bedding profoundly affect the microbial populations on teat skin. The prolonged contact of the udder with bedding provided a physical means of transferring bacteria onto teat skin. The adherence of bedding on teat skin increases the population of transient flora including environmental mastitis pathogens (Hogan et al., 1990).

In the present study, the treatment effects of lime on bacterial populations in sawdust bedding had a similar impact on teat swab bacterial counts. Gram-negative bacterial (Figure 4) and Klebsiella spp. (Figure 5) counts on teat swabs were lower for cows bedded on sawdust treated with lime compared with control and daily replacement of sawdust bedding on day two. Coliform and streptococcal counts on teat swabs did not differ among treatments on day two. Gram-negative bacterial, coliform, Klebsiella spp., and streptococcal counts on teat swabs did not differ among treatments on days zero, one, and six.

Figure 4. Gram-negative bacterial counts on teat end swabs for cows bedded on
untreated sawdust (slashed bar), sawdust treated with lime (hatched bar), and
sawdust replaced daily (open bar) on days 0, 1, 2, and 6 after use as bedding in
tie stalls.

Figure 5. Klebsiella spp. bacterial counts on teat end swabs for cows bedded on
untreated sawdust (slashed bar), sawdust treated with lime (hatched bar), and
sawdust replaced daily (open bar) on days 0, 1, 2, and 6 after use as bedding in
tie stalls.

Comparing counts on teat swabs within treatments, cows on bedding plus lime had lower Klebsiella spp. counts on day one than on days zero and six. Gram-negative bacterial, coliform, and streptococcal counts on teat swabs did not differ among days zero, one, two, and six for cows on bedding plus lime. Teat swab counts did not differ among days zero, one, two, and six for cows on either control bedding or daily replacement of bedding. Correlation coefficients between bedding counts and mean teat swab counts by bacterial groups were 0.66 for Gram-negative bacteria, 0.62 for coliforms, 0.78 for Klebsiella spp., and 0.90 for streptococci.

Conclusions

Adding lime to sawdust significantly reduced bacterial counts in the bedding for one day. The decrease in bacterial populations appeared to be related to an increase in bedding pH. Daily replacement of bedding had a minimal effect on bacterial counts in bedding and on teat skin.

References

Bramley, A. J. 1985. The control of coliform mastitis. Page 4 in Proc. Natl. Mastitis Counc. Las Vegas, NV. Natl. Mastitis Counc., Inc., Madison, WI.

Bramley, A. J., and F. K. Neave. 1975. Studies on the control of coliform mastitis in dairy cows. Br. Vet. J. 131:160.

Fairchild, T. P., B. J. McArthur, J. H. Moore, and W. E. Hylton. 1982. Coliform counts in various bedding materials. J. Dairy Sci. 65:1029.

Grier, P. H. 1985. Dynamics of bacterial populations in bedding materials. M.S. Thesis. The Ohio State University, Columbus.

Hogan, J. S., K. L. Smith, K. H. Hoblet, P. S. Schoenberger, D. A. Todhunter, W. D. Hueston, D. E. Pritchard, G. L. Bowman, L. G. Heider, B. L. Brockett, and H. R. Conrad. 1989. Bacterial counts in bedding materials used on nine commercial dairies. J. Dairy Sci. 72:250.

Hogan, J. S., K. L. Smith, D. A. Todhunter, and P. S. Schoenberger. 1990. Bacterial counts associated with recycled newspaper bedding. J. Dairy Sci. 73:1756.

Rendos, J. J., R. J. Eberhart, and E. M. Kesler. 1975. Microbial populations of teat ends of dairy cows and bedding materials. J. Dairy Sci. 58:1492.

Zehner, M. M., R. J. Farnsworth, R. D. Appleman, K. Larntz, and J. A. Springer. 1986. Growth of environmental mastitis pathogens in various bedding materials. J. Dairy Sci. 69:1932.