Worst performers rise highest in milk quality improvement

The study analysed data in 30 million records from 2009-10 to 2013-14. The biggest improvement in the anonymous survey was among the worst performers – the bottom quartile. Their bulk milk somatic cell count (BMSCC) dropped on average 70,000 cell/ml.

This study was done to quantify the changes in milk quality across New Zealand, McDougall told the milk quality section of the NZ Veterinary Association conference.

There were changes to the way milk quality was dealt with through that period, he says. Fonterra put much work into helping farmers with milk quality and a number of processors brought in stratified payments systems.

DairyNZ did a major revamp of the SAMM plan, now SmartSAMM, the training industries revamped their courses and the veterinarians improved their skills particularly via the Healthy Udder Service and Advanced Mastitis Training (see sidebar for details)

"The fundamental question is, has all this effort made a difference?" he asked.

They analysed the milk data from Fonterra during every pick-up from all their suppliers over five years. The herds' identities were unknown but they knew which day the milk supply went into Fonterra, the BMSCC and the volume.

The herds were categorised as year-round or seasonal, and according to regions, supply times and volumes over 12 months. Herds were divided into four quartiles according to the average mean BMSCC in 2009-10: up to 150,000 cells/ml; 150,000-199,000; 200,000 to 250,000; and greater than 250,000.

The BMSCC in 52,000 herd years was a mean of 198,000 cells/ml over the five years. There was a statistical decline in BMSCC over the five years.

It wasn't linear – it rose or fell each year - low in 09-10, significantly higher in 2010-11, then a big step down in 11-12, up in 12-13 and down in 13-14.

"I don't quite understand it – whether it is farmer psychology, that they have a good year, they drop their SCC and they think 'that's fine, I'll take my foot off the brake a little bit'," says McDougall. "Cell count goes up and they think 'oh damn we've stuffed up' and they step and then do another step down. I suspect that might be the case."

In respect of the supply time, the seasonal calving herds had significantly lower SCC than all-year-round herds (less than 30 days break in the year).

McDougall says that makes biological sense: with the year-round calving herds there's greater risk of cow-to-cow transmission. Risk of transmission lessens if a whole herd is dried off, particularly if using blanket dry cow therapy. "You stop transmission for a period of time.... It is easier to manage containing pathogens in those systems."

The best quartile herds in 2009-10 stayed significantly lower over the whole five year and conversely herds in the worst quartile in bulk SCC had a significantly higher BMSCC over the whole five years.

"One of the take-home messages is, if you have a well managed herd and you do things well, you tend to stay there. Whatever their farm systems are, whatever their policies are, they continue to work and they continue to have low cell-count herds.

"Conversely herds that have poor or high SCC tend to stay there for exactly the same reasons – they tend to presumably keep doing bad management practices, poor culling decision, poor diagnostics – whatever it is – and they don't change.

"That's not to say farmers can't change. But the take home message is, if they continue doing 'business as usual' they will stay where they are; they aren't miraculously going to go down [in cell count].

"Having said that, interestingly the herds that made the greatest change over the five years were those worst at the beginning."

The herds in the best quartile basically stayed the same – flatlined. The herds in the worst quartile in 2010 significantly tracked down (in cell count) over the five years. They were still on average the highest SCC but they have tracked down.

He says Mark Blackwell of DairyNZ's SmartSAMM programme said at the beginning it would be the worst ones that gave them the biggest win. He was right.

"That makes sense: they've got the greatest room to move. They can institute presumably fairly easy management practices to get change. The guys doing really well... they're fine, business as usual."

An interesting result was that the variation in BMSCC depended on where the average of your herd sat. If you have a low BMSCC with an average under 100,000 per year the standard deviation is low. However if your average is sitting at 350,000 the variation is much larger. Their median standard deviation is 80,000 compared to about 30,000 for the lower end.

"The take home message is, if you want to run your herd at 250,000 that's fine but the day-to-day variation is such that you will break – you will be non-compliant at times."

The spring herds were less likely to have a BMSSC grade and that declined more across the period of the study. "So fewer and fewer herds were non-compliant."

McDougall says interestingly with those under 100,000 there are still 2-3% of herds that are non-compliant at times. So if a herd owner chooses to run BMSCC at 200,000 and thinks that will stop them from being non-compliant, they are wrong, he says.

Seventy percent of herds averaging 200,000-250,000 sent non-compliant milk at least once per season. If people really want to stop grades they have to run their bulk milk a lot lower than 200,000 – down to the 150,000 level.

The highest producing herds by volume had the lowest probability of sending non-compliant milk. In larger herds the BMSCC are less volatile because of the volume effect and potentially better systems.

Comparing 2009-10 to 2013-14, every category of herd improved, whether good or bad at the beginning. The high cell count herds had the biggest improvements.

But even the top 10% improved over the five years.

"So even though their averages didn't shift very much in that top quartile, if you get right down into the very best herds they were still improving over those years – as did the very worst herds."

In the 2013-14 data the top 10% of herds are achieving an average of less than 100,000; the top 25% are less than 150,000 and the median herd at that time was doing 165,000.

"We are still talking about 150,000 being our target and that is a nice clear simple number. But top performing herds are achieving less than 100,000 which is a spectacularly good result, but it is achievable," he says.

"BMSCC has declined over the last five years – that is consistent across region and supply types. So whether they are autumn, spring or year-round all of those groups of herds have come down

"The greatest decline has occurred in herds that were worse at the beginning. The worst quarter have had the biggest drop – about 60-70,000 cells. The number of non-compliant bulk tanks (grades) has declined."

BMSCC is more variable in smaller herds and in herds running a higher-than-average BMSCC.

"I am going to be a bit controversial and say maybe the biggest wins we can get are with the larger herds because if they are producing more milk they will have more impact on the total number of white cells going into supply.

"You could argue that if you could drop the BMSCC in the very large herds that would have the greatest net benefit to the national BMSCC."

He says the worst quartile in 2009-10 had its average come down 70,000 but the distribution was uneven.

"There were herds that made 150,000 changes in cell count – there were others that went very little distance."

Scott McDougall thanked Brendan Radford and the IT team at Fonterra for providing the data, the financial support of DairyNZ, and the contribution of Mark Blackwell and Jane Lacy-Hulbert of DairyNZ in helping develop the project and Ian Potts of Anexa Animal Health who did database development work.