BACTERIAL CONCENTRATIONS AND SAND USAGE IN FREE STALLS BEDDED WITH FRESH OR RECYCLED SAND

Abstract

Many dairy operations using a flush system to clean the free stall barn collect sand in a settling basin and recycle it for bedding. This practice reduces bedding cost, but it is not clear if recycled sand increases exposure to mastitis causing bacteria. A 12-month experiment was conducted to determine the effect of using fresh or recycled sand on bacterial exposure and sand usage in free stalls fitted with four commercial sand retaining devices. Free stalls were bedded each week and sand samples collected for analyses of dry matter (DM), organic matter (OM), and bacterial concentrations. The DM and OM content of fresh and recycled sand used for bedding averaged 96.6 and 96.3% DM and 0.6 and 1.1%, respectively, for fresh and recycled sand. Samples of sand collected from each of the bedding systems contained similar concentrations of DM and OM which averaged 98.0 and 98.2% DM and 1.1 and 1.1% OM, respectively for fresh and recycled sand. Concentrations of Bacillus cereus, Bacillus subtilis, Bacillus gram negative and gram positive species, and Klebsiella sp. were higher (P < 0.05) in recycled sand used for bedding. Concentrations of most other organisms were numerically higher in recycled sand. Concentrations of Bacillus cereus, Bacillus subtilis, Bacillus gram negative and Staphylococcus sp. were higher (P < 0.05) and Streptococcus dysgalactiae lower (P < 0.01) in free stalls bedded with recycled sand compared with fresh sand. Concentrations of Bacillus cereus, Bacillus subtilis, and Streptococcus dysgalactiae were higher (P < 0.01) for free stalls fitted with either Pack Mat or Sand Mizer than control or Sand Trap sand retaining devices. Although concentrations of coliform tended to be higher (P < 0.10) for recycled sand, no differences were observed in concentrations for sand retaining devices. Even though differences were observed between fresh and recycled sand, concentrations of all bacteria were below the threshold normally thought to cause mastitis. The amount of sand required to maintain free stalls in our study ranged from 28 lb/d for stalls fitted with the Sand Trap (P < 0.01) to 40.8 to 41.5 lb/d for the control stalls or those fitted with the Pack Mat or Sand Mizer. These results indicate that recycled sand can be used for bedding free stalls without risk of increasing the incidence of mastitis or somatic cell count when free stalls are properly maintained.