US – Heat stress hinders vaccine efficacy more than anything else cattle are likely to encounter on a farm, says a leading US viral infections expert.
Transportation and dry-off can interrupt the immunity process but heat is the “worst by far”, the Total Dairy conference heard yesterday.
Comparing it to “choosing your poison”, Dr Chris Chase, South Dakota State University said intensive agriculture inherently posed many stressful situations to cattle.
He admitted that dry-off is a stressful day for dairy cows, but heat is number one.
“It doesn’t take a lot of heat,” said Dr Chase. “Cattle can be in transport for ninety minutes to two hours and the effect on immune status is practically minimal – top is heat stress.”
Vaccination involves different cells combining. A critical stage requires T-cells and B-cells to bind, or “do the dance”. A synapse is built here, activating the T-cells.
“If T-cells aren’t activated the vaccine won’t work,” he explained. “The synapse has a hard time staying together.”
He explained that “lactation always trumps immunity”, warning that the fresh cow was the worst cow to vaccinate.
He said US farms understandably time vaccination based on convenience, which is often following transportation as cattle are handled. On beef operations this frequently means when they are stressed from transportation.
“To me this is not a good time to vaccinate but you have to consider the further stress of gathering them in again,” he said.
“If you are seeing beef cattle off from low pasture to high pasture, you might not see them for four of five months.”
“Animals off transport can be dehydrated, have low energy – its not a good time to respond to a vaccine.”