Manure solids for bedding… Does it work?
Stall bedding materials have become increasingly expensive and difficult to find. This situation has prompted many dairy producers to search for more feasible alternatives such as sand or recycled manure solids. Although sand can be considered the ideal bedding source for dairy cows, not all producers are willing and able to convert to sand bedding as it presents some challenges related to manure management. So, what about recycled manure solids? Is anyone making it work in the Midwest? There was no research or survey we could find. As a result, Adam Husfeldt (my graduate student) and I went ahead and conducted an observational study in 38 dairy farms in Wisconsin, Minnesota, South Dakota, and Iowa that were using solids for bedding freestalls. We wanted to find out what management practices and bedding characteristics were associated with bulk tank SCC and, at the same time, evaluate animal welfare in these operations.
We documented various aspects of herd management including how solids were obtained and managed, what were their bedding practices, etc. Bedding, milk and feed samples were collected, cows were scored for hygiene, hock lesions and locomotion, and milking prep procedures were recorded. Our goal was to collect as much information as possible during the farm visit and from records throughout the year. In the end, 23 variables were used for our analysis of their association with bulk tank SCC. Four farms could not provide SCC information, so they were not used in the statistical analysis. The following are some results and observations:
- Yearly average bulk tank SCC was 275,000 cells/mL (range - 121,000 to 688,000 cells/mL). Eighteen percent of the herds had a yearly bulk tank SCC less than 200,000 cells/mL and 9% had more than 400,000 cells/mL. Digested manure solids were used on 23 (68%) farms, 7 (21%) farms used separated raw manure solids, and 4 (11%) farms used mechanically composted manure solids. All herds used pre and post-milking teat disinfection, individual towels for drying udders, and routine dry cow therapy at dry off.
- Type of manure solids used – digested, raw or composted – had no association with SCC. Some might find that surprising. Interestingly, although coliform counts in fresh bedding were zero for composted solids, 1,100 cfu/mL for digested solids, and 16,000 cfu/mL for raw solids, once the materials were used in the stalls, coliform counts were similar for all three bedding types (approximately 145,000 cfu/ml).
- Not associated with SCC: Percentage of culls due to mastitis, type of stall surface (deep bed vs. mattress), presence of contagious pathogens in milk, bedding frequency, presence of fans over the freestalls, use of automated scrapers, and stall bedding pH, NDF, non-fiber carbohydrates, total carbon and ash content.
- Variables associated with SCC: Cow hygiene scores, environmental Streptococci and coliform bacterial counts in bulk tank milk samples, type of housing facility used for dry cows, and stall bedding moisture, total N and total bacterial counts. These variables can be considered risk factors for high SCC; however, they are not necessarily causally related to SCC. They do suggest, however, that these are things to pay close attention to when using manure solids for bedding.
- Cows in this study were on the average cleaner than any other freestall study we have conducted. In spite of this, cow hygiene was still a significant risk factor for high SCC. The lowest percentile herds for SCC (which averaged 186,000 SCC) had an average hygiene score of 2.38; the highest percentile herds (average of 430,000 SCC) had an average hygiene score of 2.62. Cleaner cows are easier to prepare prior to milking and are less susceptible to mastitis. Stall maintenance and speed of moving cows to the parlor can influence cow hygiene.
- Counts of coliforms and environmental Streptococci in bulk tank milk are indicators of the quality of milking practices and milking equipment sanitation. Coliform counts in particular are often used to assess the effectiveness of cow preparation at milking time since the primary source of coliform bacteria is dirty teats.
- Stall bedding moisture was 45.5% for the lowest percentile herds and 59.5% for the highest percentile herds. Moisture is one of several essential factors necessary for bacterial growth in bedding materials. Therefore, it is important to keep bedding as dry as possible to minimize exposure to environmental mastitis pathogens. Additional methods to help dry stall bedding (use of a blower, good barn ventilation, adding equipment to remove moisture after separation) could help reduce stall bedding moisture.
In conclusion, excellent cow preparation at milking time, sanitation of milking equipment, cow hygiene, adequate dry cow housing, and bedding/stall management appear to be critical in maintaining a low SCC when using manure solids for bedding and making it work!
We sincerely thank all the dairy producers who participated in our study and colleagues Jim Salfer, Jeff Reneau and Kevin Janni for their input.