Pre-conditioning has major impact on calves’ immunity

Bovine respiratory disease has always been the most common cause of sickness and death loss in Canadian beef cattle and most of these losses occur shortly after weaning in calves that have been weaned, sold through an auction system and directly enter into the feedlot.

Data from a National Animal Health Monitoring Study in 2011 showed 16.2 percent of feedlot calves in the United States were treated for bovine respiratory disease, which was in fact an increase compared to previous surveys.

Bovine respiratory disease is also one of the major reasons why beef cattle receive antimicrobial drugs, and as we try to preserve our stewardship of antimicrobials for the future, we need to develop more ways to reduce our reliance on these products.

Preconditioning is a management practice that can reduce the occurrence of respiratory disease in weaned calves. It has been promoted for years but has always had relatively limited uptake by cow-calf and feedlot producers.

Preconditioning is defined on the Beef Cattle Research Council website as “a management method that prepares calves to enter the feedlot, reducing stress and disease susceptibility. Preconditioned calves are weaned at least 30 to 45 days before sale, put on a vaccination program, and introduced to processed feedstuffs, feed bunks and water bowls.”

It could be argued that the most important part of preconditioning is the act of separating the timing of weaning from the other stresses of entering the feedlot.

However, relatively few producers are incorporating preconditioning into their management of weaned calves. Dr. Melissa Moggy, Dr. Claire Windeyer and other researchers at the University of Calgary and the University of Saskatchewan evaluated these factors as part of the Western Canadian Cow Calf Surveillance project in a 2017 paper in the Journal of Animal Science.

That study showed that 70 percent of western Canadian beef cow-calf producers used abrupt weaning methods and slightly more than 50 percent shipped calves less than two days after weaning.

Moggy’s paper also probed some of the reasons for these choices. Labour issues, economics, and logistics were all part of the reasoning that producers used for not separating the timing of weaning from transporting calves to sale.

A recent paper published in the latest issue of the Journal of Animal Science from researchers at the University of Georgia is shedding more light on the biological and immunological effects of preconditioning.

It was a relatively small study that compared 10 commingled, sale barn origin calves to 10 single-source calves that had been weaned for 60 days. The researchers wanted to evaluate the differences between the immune status and the physiological status of these two groups of calves.

It was not surprising that the blood results from the sale barn origin calves showed more signs of dehydration and fat mobilization than the single origin source calves that had been pre-weaned.

Calves that go through sales barns in the southeastern U.S. may have had limited access to food and water before arrival at the feedlot or stocker operation and therefore would show signs of a negative energy balance and some dehydration.

In addition, the sales barn origin calves that were recently weaned showed multiple immunological deficits compared to the calves that came from a single source and were pre-weaned.

The recently weaned, auction market calves had reduced white blood cell responses that might suggest it would impair their ability to respond to vaccination. The researchers noted that their blood calcium levels were also lower and calcium is an important messenger for several immunological functions including immune cell activation.

The stressed calves also had a reduced activity of an important white blood cell known as the polymorphic neutrophil. These cells play an important role in the defence mechanisms in the lung and if they are limited in their ability to respond to an infection, it would make the calf more likely to become sick with respiratory disease.

We can’t draw huge conclusions from this study because it is relatively small and it is sometimes difficult to interpret how important the differences in immunological function are, but it does support some of the other studies that clearly demonstrate the benefits of preconditioning.

Can we continue to defend the practice of weaning a beef calf and then immediately adding to the stress by sending it through an auction yard, mixing it with many other calves and putting it into a feedlot?

Preconditioning programs have been implemented in the past and have certainly been controversial in terms of price bonuses for the cow-calf producer.

However, you can use simple calculators on the Beef Cattle Research Council website that can demonstrate the importance of the efficient weight gain that is created, allowing the cow-calf producer to create a significant economic benefit when preconditioning.

We also need to promote the benefits achieved by preconditioning in terms of animal welfare.

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