Recent analysis of TMS data for 2018 has revealed that cows were impacted by heat stress for a full six months and fresh-cow lactation performance is still affected.
Using the standard temperature humidity index (THI) and 72 THI as a cut-off point, the data recorded heat stress from April to September inclusive and its implications are still impacting metabolic disease incidence, fertility and milk yield.
“When cows are hot, they simply stop eating in an effort to cool down,” says Premier Nutrition’s Mark Hall.
“Unfortunately, the knock-on effects for this drop in nutritional intake, particularly if it continues for a considerable time, is an increased risk in ketosis and acidosis incidences, as well as fertility issues and, obviously, reduced milk yield and constituents.”
‘Leaky gut’ syndrome
However, recent work suggests that producers must also be concerned about in-calf, as well as fresh, cows.
“Heat stress is a driver for ‘leaky gut’ syndrome. This is when tight junctions between cells in the gut regress back into the cell, which opens up small gaps and this allows nutrients to ‘leak’ from the gut,” explains Mr Hall.
“These nutrients are lost in terms of their effectiveness and essentially means the calf is compromised nutritionally in utero, because the cow is using everything she has to counter her own heat stress while maintaining milk yield.
“The real impact comes post-birth though,” he adds. “The calf has effectively had to
adapt to ‘starvation conditions’ in utero, and when we follow this with
extremely high spec milk powders they struggle to cope with the insulin levels the high plain of nutrition brings about.
“It’s the equivalent of feeding a gourmet meal to a person who has been starved for a period of time, the body does not have time to adapt to the huge change in nutritional status.”