Sunday, May 28, 2023

Feedlots and respiratory diseases: Beware of seasonal fluctuations

Estimated reading time: 6 minutes

  • Of all the diseases present in livestock, respiratory tract infections have the greatest impact on a feedlot’s profitability.
  • Lung infections are often due to cattle being exposed to periods of stress.
  • The degree of stress feedlot cattle are exposed to is higher than that of their veld-reared counterparts.
  • The first clinical signs of respiratory diseases are often limited to slight depression and suppressed appetite.
  • Respiratory diseases are not unique to the South African feedlot industry. Worldwide, it places an enormous economic burden on feedlot owners.

Of all the diseases present in livestock, respiratory tract infections have the greatest impact on a feedlot’s profitability. And the changing of seasons puts even more pressure on cattle’s immune system than usual. Seasonal fluctuations are accompanied by either dry and dusty or very wet conditions. Feedlot owners must therefore be prepared and monitor their animals.

Lung infections are often due to cattle being exposed to periods of stress. Dr Andy Hentzen, veterinarian and lecturer at the University of Pretoria, says producers need to take note of the interaction between viruses and bacteria. “Viruses are the first organisms that cause damage, paving the way for bacteria such as Pasteurella and Histophilus to enter the lungs. Viruses damage and reduce the efficiency of the cilia (fine, hairlike structures that prevent dust and bacteria from entering the lungs) and cause ciliary dyskinesia.”

The four main viruses associated with respiratory infection in feedlots are infectious bovine rhinotracheitis (IBR), bovine viral diarrhoea (BVD), bovine respiratory syncytial virus (BRSV) and Parainfluenza-3 virus (PI-3).

“These are airborne viruses. Animals that crowd together have a greater chance of being exposed to a larger number of infectious organisms,” he says. “It’s easier for diseases to spread when animals are bunched together in trucks and in the feedlot. In contrast, animals are able to move around feely in the veld, thus reducing the changes of diseases spreading in a herd.”

Calves typically come from more than one farm, and they are therefore potentially exposed to pathogens to which they have little or no resistance.

Read more about the differences between feedlot versus veld finishing.

Stress factors in the feedlot

Dr Hentzen agrees that feedlot animals, especially upon first arriving at the complex, are subjected to stress. “This stress is a catalyst for making animals sick. Stress supresses immunity, which increases animals’ susceptibility.”

Dr Alnora le Riche, veterinarian and technical consultant with a special focus on ruminants at Elanco Animal Health, says that although everything possible is done to keep animals happy and healthy by way of the correct handling and transport procedures, balanced rations, vitamin and mineral supplements and vaccination, the fact remains: The degree of stress feedlot cattle are exposed to is higher than that of their veld-reared counterparts, simply because we take them from a natural environment and place them in an intensive production system.

Apart from the new environment, herd hierarchy and competition at the feed trough, processes such as vaccination, deworming and treatment for ectoparasites can also lead to handling stress. Moreover, the environment, especially dust, contributes to reduced resistance. “A feedlot is dusty because there are no trees and grass.” This is especially true in seasons and areas with low rainfall.

Although producers do put measures in place, such as spraying dirt roads and installing sprinklers in kraals, dust remains a major challenge. “The feed cattle ingest in feedlots is usually finely ground. Furthermore, animals kick up and inhale dust and manure when they move around.”

Read more about the Sernick Group’s farmer development programme here.

Seasonal changes

Dr Le Riche says temperature fluctuations, such as those associated with the changing season, increase the chances of animals contracting diseases. “Just as people are susceptible to respiratory infections in spring and autumn, animals are also at greater risk during this time,” she says.

Dr Hentzen adds that timely treatment is essential. “Sick animals that do not receive timely treatment will die.” Those that do survive after treatment will not grow as they should, which of course affects feedlot profitability.

“The sicker the animal, the higher the chances of death and the animal not reaching its full genetic potential or performing at its best.”

Treatment and prevention

The first clinical signs of respiratory diseases are often limited to slight depression and suppressed appetite. Dedicated employees whose main task it is to spot sick animals as early as possible and isolate them for treatment are therefore an important investment for any feedlot.

The animal will eventually become depressed, its head will hang, and a thick yellow nasal discharge will become more prominent. The animal’s body temperature can rise above 41,5°C.

As soon as a producer suspects that an animal has a respiratory infection, he or she needs to call in help. “Consult a veterinarian as he or she will be able to make the correct diagnosis and prescribe the best treatment.”

However, veterinarians and medication come at considerable cost. How can producers ensure their weaners are as healthy as possible before sending them off to a feedlot? “The best course of action is to wean calves at least two weeks before they go to the feedlot. This will prevent calves from having to deal with weaning stress on top of all the other unavoidable stress factors,” says Dr Hentzen. “Calves also need to be vaccinated against the viruses and bacteria that can cause respiratory diseases.”

When in the feedlot, the aim at all times should be to keep animals’ stress levels as low as possible. Some of the main aspects to manage are crowding of animals, trough feeding space, water and ration quality, as well as the way workers handle animals (calm demeanour, no loud noises, correct driving methods, pen layout that is ‘cattle friendly’ and without strange objects that can cause injuries).

Read more about the Animal Diseases Act.

Economic implications

Respiratory diseases are not unique to the South African feedlot industry. Worldwide, it places an enormous economic burden on feedlot owners.

In February 2020, an article in the Journal of Animal Science singled out bovine respiratory disease (BRD) as being the biggest health issue plaguing the modern feedlot industry. The article “Economic effects of bovine respiratory disease” found that BRD is the single biggest health risk to the American feedlot industry and leads to inferior carcasses. At the time, it was calculated that this disease is costing American feedlots between US$800 and US$900 million annually.

In 2011, local veterinary feedlot consultant, Dr Shaun Morris, spearheaded a study on the influence of BRD on South African feedlots. According to historical information, lesions were detected in approximately 42,8% of all South African feedlot animals’ lungs post slaughter; however, 69,5% of these animals were never treated for respiratory diseases.

He says that in addition to the fact that an untreated respiratory disease can lead to increased resistance to antibiotics, it also has a severe effect on a producer’s profitability since affected cattle fail to gain the weight they should.

Twenty years ago, research into the economic impact of respiratory diseases on feedlots revealed an important finding: The warm carcass weight of animals that had received one round of treatment for a respiratory disease was less than that of healthy animals. This study, “Evaluation of health status of calves and the impact on feedlot performance: Assessment of retained ownership program for post weaning calves”, was published in 2002 in the Canadian Journal of Veterinary Research.

According to the study, the yield of weaner calves treated once for BRD was up to US$40,64 less than that of a healthy animal, while animals treated twice resulted in an average income loss of US$58,35. Animals that received three or more treatments ultimately resulted in a loss of at least US$291,93. – Susan Marais, Stockfarm

For further information, contact Dr Andy Hentzen at andreas.hentzen@up.ac.za, Dr Alnora le Riche at alnora.le_riche@elancoah.com, or Dr Shaun Morris at shaun@octavoscene.co.za.