By Robert Tremblay
Dr. Dan Shock presented a summary of his research on the factors that influence the summer rise in bulk tank somatic cell count (BTSCC) in Ontario at the recent dairy research communication and extension event at the University of Guelph. The summer rise refers to the increase in BTSCC that regularly occurs in the summer and early fall on dairy farms in Ontario and elsewhere.
Shock noted that just about half of dairy herds experienced the summer rise. Even so, close to 25 % of herds did not experience a summer rise in their BTSCC. Of those farmers who agreed to allow their herds to participate in his research, Shock identified herds that did and did not experience the summer rise. He collected data from each of the herd groups over several visits during 2013.
When he scored cows in the two different herd groups for farm cleanliness, he found that herds in the high summer rise group were more likely to have an increase in the number of cows that scored as dirty. He also found that there was a rise in the percentage of cows that had teat end lesions too. When Shock evaluated pre-milking udder prep, he found that herds with a higher summer rise scored lower on teat end cleanliness than herds that had a smaller summer rise. He also found that herds with a higher summer rise were farmers that milked a higher number of cows every hour on average.
These findings pointed to this conclusion: herds with a high summer rise in BTSCC likely had more cows that developed udder infections from bacteria in the barn rather than from an increase in mastitis from contagious bacteria or other microbes. When Shock cultured milk from individual cows with high SCC on each of the farms, he found exactly that. More high SCC cows in herds with a high summer rise were much more likely to be infected with gram-positive bacteria that are normally found in barns.
What does this mean? Shock concluded that the summer rise in BTSCC was likely due to an increased risk of new udder infections from bacteria in the barn environment. The fact that summer is a busy time likely caused pre-milking prep to be rushed. It likely also cut into the time that would normally be devoted to barn chores so that cows were dirtier coming into the parlour.
Another researcher, Morgan Overvest, reported on her research on feeding solid feeds to calves that were being fed high levels of milk (12 litres per day.) Overvest offered calves four different ration options, three combinations of concentrate with or without hay or cow TMR as she tapered down the amount of milk being offered. She then followed their intake and growth. TMR didnt work out very well because its moisture content was too high and its nutrient density was too low to meet the calfs needs.
What she did find, though, was that offering chopped hay along with the concentrate or mixed into the concentrate did not have a negative impact on how much calves ate or how well they grew.