We’ve all got our fingers crossed for plenty of rain and low spore counts over the next few months but managing bulk milk somatic cell count (BMSCC) is also a common challenge on dairy farms throughout autumn.
Although SCC spikes and grading are most common during spring calving, the number of cows with subclinical infections (high SCC but normal looking milk and udder) increases in late lactation because contagious bacteria have been spread throughout the season by the milking process. This effect is worsened by decreasing milk production at this time of year, which means that BMSCC can easily drift upwards, typically doubling from the lowest point in lactation. This means that if your lowest BMSCC of the season is around 200, your herd is highly likely to be grading by the end of the season without intervention.
When your BMSCC starts increasing (particularly when it is over 300) it is important to assess the cause and take action before it creeps over 400. A rapid drop in milk production combined with an increasing BMSCC should prompt an evaluation of the cows’ diet, particularly in dry seasons when relying heavily on supplement feeding; an imbalanced diet leading to low milk production will affect BMSCC by making the milk more concentrated. If your herd’s production is steady or only decreasing gradually, a rise in BMSCC will be due to infected cows within the herd so identifying and managing these cows is the key to preventing BMSCC grading. Clinical mastitis cases still happen late in the season, so watch for clots on the filter sock and other signs of mastitis (e.g. enlarged quarter).
The most valuable tool to identify problem cows is herd testing, as it allows identification of individual high SCC cows as well as providing milk production data. Low production high SCC cows are a clear priority to be removed from supply, as they can make a large contribution to BMSCC but are not making a meaningful contribution to the amount of milk in the vat. Late in the season it is not worth trying any lactating cow treatments on high SCC cows (the cure rate is too low to make it worth the cost) so culling or dry off are the two main options. Although farmers are often concerned about losing milk production by removing high SCC cows from supply, the remaining cows will benefit from increased feed supply leading them to increase their milk production, so you can dry off up to 10% of the herd without significantly impacting production.
Please talk to your vet to talk about reducing your herd’s BMSCC and choosing the best management strategy for your problem cows.