J. S. Hogan1 and K. L. Smith
The Ohio State University Department of Animal Sciences
Bacteria counts associated with untreated organic bedding materials were compared with those of bedding treated with either an alkaline commercial bedding conditioner, acidic commercial bedding conditioner, or hydrated lime. Bedding materials were recycled manure and kiln-dried sawdust. The effects of bedding treatments on bacteria counts differed between bedding types. Each of the bedding treatments significantly reduced bacteria counts in recycled manure prior to use. The alkaline conditioner and hydrated lime effectively inhibited bacteria counts in recycled manure for one day. Bedding counts and teat swabs of cows housed on recycled manure treated with the alkaline conditioner were reduced on day two. The use of the acid conditioner in recycled manure had little effect on bacteria counts in bedding. Sawdust differed from recycled manure in that bacteria counts in untreated sawdust prior to use were minimal and populations increased rapidly the first two days after use as bedding. The acid conditioner had a bacteriostatic effect in sawdust evident by the reduction of bacteria counts on day two. The alkaline conditioner and hydrated lime did not alter bacteria counts in sawdust compared with untreated sawdust. Antibacterial activity of each conditioner had deteriorated between day two and six in both beddings. The antibacterial activities of conditioners were related to the pH of bedding materials. The use of commercial bedding conditioners initially reduced bacterial counts, but the antibacterial effects had diminished between day two and six after use in bedding.
The bacterial populations in bedding closely reflect those on teat ends of cows managed in total confinement housing. Therefore, management practices that reduce microbial loads in bedding should reduce teat-end exposure and the incidence of intramammary infections caused by environmental mastitis pathogens. A common practice on farms using organic bedding is to add hydrated lime to the stalls to control bacterial populations. However, controlled trials have shown the addition of hydrated lime to organic bedding had minimal effect on controlling bacterial populations. Lime had a bactericidal effect in organic materials prior to placement in stalls, but the pathogen load in sawdust bedding treated with lime rapidly increased to that comparable in untreated sawdust. Consequently, the addition of lime to sawdust had minimal effect on controlling teat-end contamination.
The antibacterial activity of hydrated lime in sawdust was closely related to pH of the bedding. The pH of sawdust containing 10% (wt/wt) of lime can be extremely alkaline (approximate pH of 11.0) prior to use and decline precipitously toward neutrality by 48 hours after use in bedding. The use of germicides that maintained their antibacterial activity in the presence of organic material could possibly repress bacterial growth in bedding and reduce teat-end exposure. The purpose of the current trial was to compare bacterial counts associated with untreated organic bedding materials with those of bedding treated with either an alkaline commercial bedding conditioner, acidic commercial bedding conditioner, or hydrated lime.
The experiment was conducted at The Ohio State University’s Ohio Agricultural Research and Development Center. Cows were housed in a tie-stall barn. Beddings were 22 lb. per stall of recycled manure and kiln-dried sawdust. Recycled manure and sawdust were stored separately in covered sheds and were not composted before use as bedding. Bedding treatments were a granulated alkaline conditioner (Babson Bros., Naperville, Ill.), a granulated acidic conditioner (Babson Bros.), hydrated lime (Genlime Group, Inc., Genoa, Ohio), and untreated negative controls. Conditioners and lime were added at 2.2 lb. per stall on day zero. Each bedding and treatment combination was used to bed each of the eight sets of stalls for seven days. The trial lasted eight weeks so that stalls were exposed to all bedding treatments.
Bedding samples were collected immediately after fresh bedding was added to the stalls (day zero) and on days one, two, and six after use in the stalls. Samples were composites of bedding from the back one-third of each stall. Stacking capacity was 100%, and cows were rotated among stalls except that one cow remained in each of the eight sets of stalls for the duration of the trial. Teat swabs were collected from the right front teats of these cows (those remaining in the stalls for the duration of the trial) within one hour prior to bedding treatments on day zero and on days one, two, and six when bedding samples were collected.
The effects of bedding conditioners on bacteria counts differed between bedding types. The mean populations of each bacterial group in recycled manure exceeded 105 cfu/g prior to use as bedding. Each of the bedding treatments reduced total gram-negative bacteria, coliform, Klebsiella, and streptococci counts to below 103 cfu/g in recycled manure prior to use (Figure 1). The alkaline conditioner and hydrated lime both continued to reduce bacteria counts in recycled manure for one day. The alkaline conditioner had an advantage over hydrated lime in persistency of activity in recycled manure. Coliform, Klebsiella, and streptococci counts in recycled manure treated with the alkaline conditioner were reduced on day two compared with untreated recycled manure. Antibacterial activity of hydrated lime in bedding was diminished by day two. The use of the acidic conditioner in recycled manure had little effect on bacteria counts in bedding. Bacteria counts in recycled manure treated with the acidic conditioner rebounded comparable to that of untreated recycled manure by day one and remained constant through days two and six.
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| Figure 1. Counts of gram-negative bacteria (A), coliforms (B), Klebsiella spp. (C), Streptococcus spp. (D), pH (E), and dry-matter percentage (F) in untreated recycled manure and recycled manure treated with hydrated lime, alkaline conditioner, or acidic conditioner. Counts were taken on days zero, one two, and six after treatments were used as bedding in tie stalls. |
Sawdust differed from recycled manure in that bacteria counts in untreated sawdust prior to use were minimal, and populations increased rapidly the first two days after use as bedding. The acidic conditioner was the most effective treatment for reducing counts in sawdust bedding. The acidic conditioner had a bacteriostatic effect in sawdust evident by the reduction of gram-negative bacteria, Klebsiella, and streptococci counts on day two (Figure 2). Antibacterial activity of the acidic conditioner had deteriorated by day six in sawdust bedding. Gram-negative bacteria, Coliform, and Klebsiella counts in bedding treated with hydrated lime were reduced approximately 10-fold compared with the counts in control sawdust on day one. The alkaline conditioner did not reduce bacteria counts compared with untreated sawdust.
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| Figure 2. Counts of gram-negative bacteria (A), coliforms (B), Klebsiella spp. (C), Streptococcus spp. (D), pH (E), and dry-matter percentage (F) in untreated sawdust and sawdust treated with hydrated lime, alkaline conditioner, or acidic conditioner. Counts were taken on days zero, one two, and six after treatments were used as bedding in tie stalls. |
The antibacterial activities of bedding treatments were related to the pH of bedding materials. The actions of the alkaline conditioner and hydrated lime were greater in recycled manure that had a near neutral pH. Addition of these conditioners to recycled manure initially elevated pH to an extreme alkaline range prior to use as bedding. As the pH of the recycled manure neutralized during use, the antibacterial effects of the alkaline conditioner and hydrated lime diminished. In contrast, the acidic conditioner was most effective in sawdust that had an initial pH of 4. The acidic conditioner reduced pH in sawdust compared with untreated sawdust for two days corresponding with the bacteriostatic effect of the treatment. Despite the extremes in pH of bedding after the addition of hydrated lime and the commercial conditioners, no changes in teat skin were detected by gross observations during the trial.
Transfer of bacteria from bedding to teat skin primarily occurs when the teats are in intimate contact with the bedding. The contact of teats with finely chopped bedding results in the attachment of bedding contaminated with bacteria onto the teat orifice. Therefore, bacteria counts on teat skin usually are reflective of the bacterial contamination of the bedding to which cows are exposed. Bacteria counts in bedding were positively correlated with bacteria counts from teat swabs in the current trial. In general, the reductions in specific bacterial groups in bedding related to treatments were reflected in similar reductions in teat swab counts (Figures 3 and 4).
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| Figure 3. Counts of gram-negative bacteria (A), coliforms (B), Klebsiella spp. (C), Streptococcus spp. (D) from teat swabs of cows bedded on untreated recycled manure and recycled manure treated with hydrated lime, alkaline conditioner, or acidic conditioner. Measurements were taken on days zero, one, two, and six after treatments were used as bedding in tie stalls. |
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| Figure 4. Counts of gram-negative bacteria (A), coliforms (B), Klebsiella spp. (C), Streptococcus spp. (D) from teat swabs of cows bedded on untreated sawdust and sawdust treated with hydrated lime, alkaline conditioner, or acidic conditioner. Measurements were taken on days zero, one, two, and six after treatments were used as bedding in tie stalls. |
An interaction was discovered between the effectiveness of antibacterial treatments and two organic bedding materials. This interaction was associated with the compatibility of antibacterial treatments with the pH of bedding. Hydrated lime and an alkaline conditioner were most effective in recycled manure that had a near neutral pH. Addition of these treatments to recycled manure created an alkaline environment in bedding and reduced bacterial counts. In contrast, the bacterial populations and pH in the sawdust were reduced most by an acidic conditioner. The antibacterial effects of each treatment had diminished between days two and six after use in bedding.
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) 263-3792, Fax (330) 263-3949; email:hogan.4@osu.edu