As a veterinarian who is passionate about animal health and producing high-quality dairy foods, I am embarrassed as I watch the EU force us (the U.S. dairy industry) to produce milk with an SCC below 400,000. Why haven’t we chosen to establish this SCC level on our own? I know the arguments. Our PMO is focused on food safety, not quality and shelf life issues, and there is no research to date that connects a cell count up to 750,000 with any increased disease risk from human consumption. The problem is today’s consumer views food safety and quality as synonymous – and we need to have the same view. Ironically this SCC reduction mandate is in direct conflict with a major paradigm shift that is currently underway in the U.S dairy industry. What is the paradigm shift? We appear determined to replace the “gold standard” for dairy cow bedding of new, washed, dry sand with something else. I use the term alternative bedding systems to describe everything other than deep-bedded, dry, washed, virgin sand in well-designed freestalls that keep cows comfortable and clean. Dr. Andy Johnson puts it this way, “Once you walk away from the gold standard, you choose your own poison for milk quality problems.”
I know the arguments for this paradigm shift sound reasonable. The increasing pressure from manure management regulations, the cost of buying bedding, the lure from green energy, the wear and tear on equipment to pump and haul sand, the increasing availability of equipment that promises to produce bedding for “free,” the improved cow comfort with bedded- pack areas and other regional factors. However, the dirty little secret is, when you stop using the gold standard bedding, you will have more clinical mastitis and increased bulk tank somatic cell count (BTSCC).
Over the years I have seen versions of the following alternative bedding systems: chopped straw, whole straw, chopped hay, recycled sand, manure squeezings after a digester (DMS or bio-solids), manure squeezings from raw manure, green sawdust, dry sawdust, corn stalks, bean stubble, chopped paper, ground cereal boxes (with cereal), dry grain hulls, dirt lots groomed, dirt lots ungroomed, manure packs groomed, manure packs ungroomed, bare cement, mattresses, deep bedding, shallow bedding, no bedding. I observe tremendous variation in milk quality results from alternative beddings. No two recycled sands or manure solids are the same. It’s all about moisture and organic load. Obviously drier is always better. Bacteria die or form spores without moisture.
Organic load is the newest measurement offered during laboratory analysis of alternative beddings. Organic loads above 5 percent appear to increase the risk of clinical mastitis cases. The more organic load in any type of bedding, the greater the risk for clinical mastitis cases.
When it comes to interpreting the colony forming unit (CFU) counts of bacteria in bedding material, there are no clearly defined cut points to determine good versus bad bedding. One million CFU’s per gram of bedding has been used as a dividing line in the past. This number came from one line in a research paper published several years ago and does not reflect the variation I see on farms that are experiencing increased cases of mastitis from environmental pathogens that are nowhere near the million CFU threshold. Research three years ago by Dr. Nigel Cook from the University of Wisconsin suggested that coliform counts in bedding as low as 250,000 appeared to drive an increase in clinical coliform mastitis cases on certain farms.
I observed a few farms this past winter that voluntarily reduced the amount of fresh water being used to rinse recycled sand during mechanical separation and subsequently experienced a significant increase in clinical mastitis cases when the sand with a higher organic load was put back under the cows.
So for me the bottom line is, “cows don’t lie,” and a dairy cow is a nearly perfect, portable, microbiological laboratory. She is constantly reporting to us the delicate balance between resistance versus exposure that her mammary gland is experiencing in the environment we ask her to live in. ( See Figure 1 ). As the scale shows, increasing your cows’ resistance will decrease the incidence of mastitis. Conversely, if resistance remains constant but exposure increases, mastitis cases will increase. Your cows will not lie.
Let’s use this concept to troubleshoot a dairy with an increased incidence of mastitis this summer. The types of mastitis cases in this herd ranged from Grade 1s (abnormal milk) to Grade 2s (abnormal milk with a swollen quarter) to Grade 3s (toxic mastitis with a swollen quarter). Culture results from clinical cases revealed environmental streps and coliforms as the predominant pathogens. Several of the Grade 3 cases either died or had to be culled. So what caused this summertime flare-up?
A. Decreased resistance
1. Heat stress and lower dry matter intakes decreased the herd’s immune function.
2. Heavy spring calving led to overcrowding stress.
3. Low milk prices delayed milking equipment maintenance, leading to slow take-offs.
4. Delayed take-offs created overmilking and led to excessive hyperkeratosis.
B. Increased exposure
1. Feed quality changed with a greater risk of molds and mycotoxins in the summer heat.
2. Bedding CFU counts increased in warm weather … especially coliforms.
3. Dirtier cows entering the parlor put pressure on the milkers to clean teats completely.
4. New milkers and a hot parlor led to dirty teat ends when units were attached.
With decreased resistance and increased exposure, the obvious result is increased clinical mastitis. And for every new clinical case, your herd is being infected with three to five subclinical cases. Remember these are true infections; they just have normal- looking milk, so they go unnoticed for extended periods of time. Only the increase in SCC will identify these mastitis cases. This explains why your BTSCC stays high for weeks to months after you make changes to decrease the incidence of new clinical mastitis cases.
Because the new 400,000 BTSCC is a rolling three-month geometric average, you cannot take the risk of just keeping your monthly average under the 400,000 limit. One expert is suggesting that to be safe you need to keep your BTSCC in the 250 to 275 range consistently to protect yourself from an unexpected SCC spike pushing your SCC average over 400,000.
The three critical points necessary to reduce and maintain a low BTSCC are:
1. Maintain your milking equipment in good working order. Have it evaluated regularly by a trained professional. Get a second opinion from an independent expert if you have unanswered questions.
2. Keep your cows clean and comfortable all the time. Be careful not to eliminate critical feed ingredients during tight financial times. Immune function is important for milk quality and reproduction.
3. The milking prep procedure is critical in reducing new environmental mastitis cases. Low bacteria counts on the teat ends make the difference. Bacteria can be wiped off or killed. Towel work by the milkers is essential, with wiping teat ends the most critical step. The germicide in the pre-dip must be able to kill 5 logs of bacteria even in the presence of heavy organic loads from alternative beddings. PD
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