While there are only about 20 British dairy herds on permanent OAD milking, more farmers there are using it as a flexible option in later lactation with grass-only system cows producing from 2000 litres to 4000 litres a lactation.
For both cases, somatic cell counts (SCC) should be well below 200,000 cells/ml to start with, vet Rachel Risdon from Westpoint Vets in Cornwall said. Most milk processors introduce milk cheque penalties at a threshold of 200,000-250,000 cells/ml.
“But it’s also very clear that a herd on the brink of 200,000 cells/ml will struggle to keep its bulk SCC down, especially if moving to OAD mid-lactation. For instance, a bulk count of 150,000 cells/ml probably goes up … to 250,000 cells/ml for a few days, then drops back down to a new level that’s just a bit higher than where it was before. It settles there for the rest of lactation. When a cell count starts above 250,000 cells/ml, however, it will be pushed to over 300,000 cells/ml. And although it drops, it creeps up for the rest of lactation, so you struggle to keep it in line.”
When herds drop down to OAD too late in lactation, Risdon finds yields plummet which pushes SCC up even more, due to the dilution factor.
“So it’s important not to go too far beyond mid-lactation, roughly six to seven months, before going OAD.”
Surprisingly, she doesn’t see a huge difference in clinical mastitis rates in herds OAD all season. Environmental flare-ups are possible in the first few days when dropping down to OAD, due to the udder not flushing out as often, which is where good stockmanship comes in.
“But it’s also vital to do bacteriology before considering OAD, whether a temporary or permanent option, particularly where herds have a contagious mastitis problem. If you have Staph aureus, for instance, don’t even do it.”
Bacteriology and a plan for appropriate dry cow therapy should be discussed with vets, and farmers shouldn’t assume a simple system with lower yielding cows only needs a teat sealant or a cheap antibiotic.
“Teat sealants are important where OAD herds are outwintering, or if the dry period is extended because cows are dried off sooner owing to a feed shortage,” she said.
“Tube use depends on the situation and appropriate use of antibiotics should be targeted cost-effectively.”
Because the udder is only being evacuated once every 24 hours, the extended milking interval gives mastitis-causing bacteria more time to do their damage. And when dropping a milking in later lactation, lower milk yields add a concentration effect.
Attention to detail during a OAD milking routine is critical and mastitis detection has to be ‘bombproof’, milking specialist Ian Ohnstad, of The Dairy Group, said.
“Everything you do has to be even better if you are only emptying the udder OAD,” he said.
“When a conventional herd introduces a third milking, the bulk cell count usually falls and it’s not just a yield dilution effect. It’s because the udder is being evacuated 50% more often, the interval between milkings is shorter, and there’s another opportunity to see a problem earlier.”
“Conversely, milking OAD, you have just one chance to see the udder. So teat preparation, milking routine, post-disinfection – all have to be spot-on from both a milk quality perspective and for mastitis control. The extended milking interval is a challenge.”
Herds dropping down to OAD part-way through lactation naturally see a big jump in cell count once the second milking stops. However, the increase lasts just 24-48 hours, DairyNZ says, and as the udder adjusts to less frequent milking, cell counts stabilise within a week. It reports that where a high bulk SCC continues, it’s from a few cows with persistently-high individual cell counts. Its standard guidance is that when there is any doubt about cell counts, the whole herd should be tested before cutting out a milking.
The Dairy Group delivers DairyCo’s Mastitis Control Plan (DMCP), with Ohnstad saying a structured plan for mastitis control can help. He describes it as an on-going strategy, rather than a one-off problem-solver.
“If a herd has a genuinely low incidence of mastitis, they should be aware that things can change and challenges can emerge. Knowing the patterns of the type of infections they get, allows a strategy to be put in place to hopefully prevent a problem emerging.”
The DMCP is all about risk management and risk avoidance. Data analysis is essential to the plan to come up with a diagnosis. But if a herd doesn’t test monthly SCC, or record its clinical cases of mastitis because it is seen as a cost, not a management tool, a diagnosis isn’t possible and the targeted nature of the plan is lost.
“When you do the mastitis control plan is irrelevant because the starting point is always a full analysis of 12 months’ historical data, together with a comprehensive farm visit and questionnaire. We use this information to come up with an action plan and regularly monitor it. Some of the plan is relevant all of the time; some of it is relevant only some of the time, such as dry cow management. Where all cows are dry at the same time, we can still discuss elements of dry cow management when the herd is milking, then schedule a visit once the herd has dried off.”
