Guts and bugs: The good, the bad, the ugly – Dr. Jenn Rowntree, Vita Plus

By Jenna Hurty-Person, Progressive Dairyman
Calf diarrhea is a costly, but common, problem on today’s dairies. In fact, according to the 2014 National Animal Health Monitoring System (NAHMS) data, diarrhea was responsible for 56 percent of pre-weaned heifer deaths. In addition, recent research shows, even when calves overcome the disease challenge, negative consequences still exist in the form of reduced first lactation milk production and increased age at first calving. Thus, preventing diarrhea is essential to raise healthy calves.

During her presentation at Vita Plus Calf Summit, Dr. Jenn Rowntree, Vita Plus calf and heifer specialist, shared her insights on why a healthy gut is essential to raise healthy calves.

The mucosal immune system
The mucosal immune system lines the entire gastrointestinal (GI) tract and serves as a line of defense against invading bacteria. Intrinsic to this, Rowntree said, is the calf’s gut microbiome, which consists of good bacteria in the GI tract. This microbiome is essential to the calf’s health as it plays a critical role in the calf’s metabolism, GI tract regulation, and immune response by detecting, preventing, and eliminating bad bacteria from the GI tract.

In addition to the bacteria, the mucosal immune system possesses physical and chemical barriers to protect the calf from pathogens. The physical barriers are the mucus layer, which traps microbiota, and the epithelium, which contains the tight junctions. These tight junctions act as the primary regulator of intestinal barrier function. The chemical barriers limit the growth of bad bacteria and protect the good bacteria in the mucosa layer. In addition, the antimicrobial peptides act as part of the chemical barrier to help ID and kill pathogens.

Unfortunately, this important component of the calf’s immune system is not impervious and can be damaged by stress, antibiotics, and invasive and opportunistic pathogens, such as Clostridium perfringens, Cryptosporidium parvum, coccidia, rotavirus and coronavirus.

To help limit negative impacts on gut health, producers are advised to limit calf stress. When an animal is stressed it releases hormones that cause the gut environment to shift and make it easier for bad bacteria to take over and overwhelm the calf’s immune system, causing it to become ill.

Antibiotics are not necessarily the answer either and should only be used when necessary, Rowntree said, since they target good bacteria as well as bad. In fact, in some cases, antibiotics can make it easier for bacteria to take over, since the good bacteria have been diminished, causing a microbial imbalance. With this in mind, Rowntree suggested that calves with diarrhea and a normal appetite, but no fever, be monitored closely, and given electrolytes, while calves that have diarrhea, no appetite, and a fever be given a broad-spectrum antibiotic and electrolytes. Rowntree noted this should always be done under vet supervision and guidance as situations will vary.

To give calves the best chance at staying healthy, Rowntree said producers need to do three things:

1. Promote a diverse gut microbiome through a robust mucosal immune system and good nutrition
2. Limit stress
3. Reduce exposure to pathogens through proper biosecurity protocols

Focus on nutrition
At birth, the calf’s microbiome is almost or completely nonexistent, but that changes drastically in the first 24 hours. This change is important as the sooner the good bacteria can establish themselves, the harder it is for bad bacteria to get established. Because of this, Rowntree advised producers to feed calves at least 4 quarts of high-quality, clean colostrum within four hours of birth. The glucose in the colostrum acts as a natural probiotic and feeds the good bacteria. This helps them become established more quickly to protect the calf.

To further assist with calf gut health development, Rowntree said she has seen farms have good success feeding small amounts of colostrum for the first two weeks of life in addition to the initial 4-quart colostrum feeding at birth. She suggested doing this by freezing colostrum in ice cube trays and adding one colostrum cube per calf per feeding.

Next, producers need to focus on milk quality and quantity. Milk should be clean and free of harmful bacteria, have a similar osmolality to cow’s milk, and be fed at a rate of 12 to 14 percent solids. In addition, Rowntree said producers need to feed calves enough milk to not only meet their energy requirements for growth, but support the calf’s immune function, even during extreme temperatures.

Rowntree also advised producers to provide calves with high-quality calf starter as soon as possible. Doing so not only promotes rumen development and facilitates early weaning, but also increases the calf’s ability to fight disease. It does this by encouraging an earlier expression of antimicrobial defense molecules, which help identify and kill pathogens and positively impact the GI tract barrier function and immune responses.

Finally, feeding probiotics can greatly assist in the calf’s gut health and development as these are a source of live, viable beneficial bacteria or yeast that interact with the gut’s microflora, epithelium and immune cells. The one caution Rowntree had was producers need to know where the probiotics come from as they need to get them to the calf in a live form for maximum benefit. Probiotics, she said, can still be beneficial to the calf when they’re dead, but that is not always the case.

Limit calf stress
As was already mentioned, stress can have a detrimental impact on the GI tract environment calf health. To mitigate this, producers should focus on these seven areas:

• Minimize pain associated with procedures whenever possible
• Avoid simultaneous stressors – dehorning, vaccines, moves
• Wean gradually
• Control temperatures – avoid heat or cold stress (40 to 70 degrees F is ideal)
• Provide a dry, well-bedded environment
• Ensure adequate ventilation, volume and area per calf
• Control flies

Minimize pathogen exposure
Rowntree said she likes to think of pathogen exposure like a balancing act. On one side of the scale is the calf’s immune system, and on the other is pathogen exposure. The goal of the farm should be to keep this balance always tipped in the calf’s favor through proper biosecurity and biocontainment practices by mitigating pathogen exposure and by providing the calf with the necessary tools to fight off disease exposure when it does occur.

The reality is diarrhea and the pathogens that cause it will always have some presence on a dairy farm. However, with the proper tools and management, producers can reduce its prevalence on their farm and give sick calves the tools they need to overcome that disease challenge.