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Shedding of Disease-causing Pathogens in Cattle

By Acidosis and Shipping Fever, Cattle, Cow-Calf, Feedlot, Pre-Conditioning No Comments

Almost every multi-celled organism on the planet is capable of shedding pathogens of one sort or another. In environments with large, dense populations, such as those of cattle, shedding of disease-causing viruses and bacteria can cause widespread disease rapidly. An understanding of how shedding occurs amongst cattle provides insight into preventing the outbreak of disease and consequential profit loss.

What is shedding?

Shedding is the expulsion of disease-causing microorganisms into the environment. When a pathogen has matured and reproduced within the host’s body, it must find a way to spread. Some of the most common ways cattle shed these germs is through their manure, coughing and sneezing and sharing common feeding and watering areas. When there are multiple animals living within close quarters, the likelihood of widespread infection increases.

How does shedding occur?

Viral, bacterial and fungal shedding occur via a variety of routes – pathogens can be introduced into the environment via the GI tract (Escherichia coli), respiratory tract (bovine respiratory syncytial virus – BRSV), oro-nasal (foot-and-mouth disease virus – FMDV and Mycobacterium bovis), ocular (infectious conjunctivitis – pink eye), reproductive tract (brucellosis) and even through the skin and hooves (dermatophytosis – ring worm).

Respiratory Tract

Shedding via the respiratory tract is perhaps the most common cause of infection in cattle. Secretions such as saliva and mucus can be aerosolized when an animal coughs or even just breathes, forcing millions of disease-causing pathogens into the environment. Some of these diseases are airborne and must be inhaled by other animals to cause infection, while others can land on fur or other surfaces and be taken into the nasal or oral cavity and lead to infection.

The incidence of transmission (particularly with inhaled microorganisms) increases exponentially when there are close quarters, such as a cattle transport or crowded pens at a sale barn or feedlot. Animals that are stressed and compromised will be more likely to contract diseases in these environments than those that are healthy and in a positive energy balance.

GI Tract

GI tract shedding is another common route for infection, as manure is regularly excreted into the environment and animals will tread through it, lay in and then, while browsing or cleaning themselves or each other, ingest the pathogens contained in the infected manure. Another issue is housing that is not frequently cleaned of excrement. Microorganisms can thrive in wet conditions, populating not just the fecal matter but the soil, as well. Feed bunks and watering sources may become contaminated with infected feces or soil, creating an even larger problem, as the majority of animals in a given space will be exposed.

Bacterial infections are of particular concern with this route of spread. Viral contagions often cannot live outside of a host for extended periods of time; however, many bacterial agents are capable of living in a non-host environment for extended periods of time and through extreme weather fluctuations. Therefore, infections such as Salmonella sp. and E. coli can get out-of-hand so quickly.

Oro-nasal Route

Some infectious microorganisms are spread easily via the oro-nasal route through saliva and mucous membrane secretions. This includes diseases such as foot-and-mouth-disease virus (FMDV) and Bovine papular stomatitis. An animal must come in direct contact with the contaminated surface, such as feed bunks or through licking or touching noses with an infected animal.

Ocular Route

Certain diseases such as pink eye are spread through contact with contaminated secretions from the eyes, and to a lesser extent the nose and mouth, due to the structure of the nasolacrimal ducts. The majority of eye infections in cattle are caused by bacteria. The most common means of spread for these infections is direct contact or rubbing of faces on fences, feeders, etc. It is also possible for these secretions to be deposited on grass or brush where other cattle may frequent and become exposed.

Genital Route

Brucellosis sp. are commonly shed through the reproductive tract in cattle. Placental fluids and vaginal discharges of infected cows can infect other cattle that may lick the infected animal. Feed and water sources can also become easily contaminated, creating the potential for widespread infection.

Additionally, there are numerous venereal diseases that can be shed but are only spread through the mating of infected animals, making these pathogens less likely to affect feedlot operators.

While the shedding of infectious microorganisms cannot be completely prevented, measures can be taken to help keep the impact to a minimum. Reducing stresses on animals, including providing high-quality feed and clean water, a calm environment and proper handling and a solid sick treatment protocol can go a long way towards helping prevent disease outbreaks in cattle operations.

The Impact of Mannheimia haemolytica on the High-Risk Herd

By Acidosis and Shipping Fever, Cattle, Feedlot No Comments

Mannheimia haemolytica is a bacterial contagion that is one of the main organisms responsible for the broader scope of bovine respiratory disease (BRD). M. haemolytica is frequently found in conjunction with Pasteurella multocida, with both bacteria typically presenting as secondary infections in compromised animals (most commonly following viral infections or significant stress events). It often leads to pneumonia, causing irreversible lung damage in the infected cow.

Prevalence of M. haemolytica in the Feedlot Setting

While M. haemolytica is fairly common to find in the living environments and upper respiratory tracts of most healthy cattle without causing issues, it does lead to secondary infections amongst compromised high-risk feeder cattle. In the case of M. haemolytica, it is responsible for pneumonia that can, at best damage the lungs, and at worst result in mortality of the infected individual.

In a study from the University of Georgia1, nasopharyngeal swabs (NPS) were taken during processing from a group of 169 high-risk feeder, sale barn bull and steer calves. They were also given the macrolide antimicrobial tulathromycin (2.5 mg/kg SQ) upon arrival at processing. Of those cattle, 27 (16%) swabbed positive for M. haemolytica (with 1 cow or 3.7% swabbing positive for a multi-drug resistant strain [MDR] of M. haemolytica). At 10 – 14 days a second NPS was taken from each of the 169 cattle with an alarming 123 (72.8%) showing positive cultures for M. haemolytica with 122 animals testing positive for a MDR strain of M. haemolytica. This offers a good idea of just how common it is to find M. haemolytica in high-risk stocker cattle and the waning or ineffective results seen with metaphylactic use on these groups.

How M. haemolytica Gains a Foothold in the Feedlot

Stocker cattle tend to be a mixed lot – some are healthy while others are in poor condition when they reach the sale barn. Knowing the background of any given sale barn calf is almost impossible.

  • Was it vaccinated properly?
  • Did the mother receive adequate nutrition during and after her pregnancy?
  • Was she vaccinated properly to ensure her and her calf’s immunity?
  • Did that calf have adequate weaning time?
  • How long has it been since its last meal? Is it already experiencing sub-acute ruminal acidosis (SARA)?

Unfortunately, these factors can have a huge effect on a calf’s ability to fight off disease and withstand the stresses of transitioning from its point of origin to the preconditioner’s lot.

M. haemolytica and Shipping Fever

“Shipping fever” is the common term for bovine respiratory disease (BRD), a complex of multiple diseases that can have detrimental impacts on stocker cattle. There are numerous viral diseases at play when looking at BRD – the most common include Infectious Bovine Rhinotracheitis (IBR), Bovine Viral Diarrhea (BVD – also a major contributor to scours), Parainfluenza Type-3 Virus (PI-3) and Bovine Respiratory Synctial Virus (BRSV).

Animals with weak or compromised immune systems are at greatest risk for developing shipping fever. With the stress of shipping – this includes handling, transport, lack of feed and water during transport, inhospitable weather and/or truck conditions, etc. – the calf’s immunity is put under significant stress. Because shipping fever is so prevalent, it’s common practice to administer a metaphylactic such as tulathromycin as they’re loaded for transport to help combat any secondary bacterial diseases that could contribute to “shipping fever”. Unfortunately, while this may help with bacterial infections that are already present, it doesn’t typically last long enough to address later-onset infections such as M. haemolytica.

When a cow is experiencing the ravages of shipping fever the immune system is under siege.  It is at this point that M. haemolytica can become a full-blown disease, invading the lungs, and causing pneumonia. As mentioned above, even with a metaphylaxis, the incubation time of M. haemolytica is such that it comes to fruition around the time the effects of the metaphylactic agent will be dwindling.

In some cases, cattle may contract M. haemolytica and recover without intervention; it’s often assumed that they “got over it” but the reality is that a good deal of lung damage may have occurred. This can become evident in that cow’s slower or reduced gain, stamina during handling, etc.

What Makes High-Risk Cattle Susceptible to M. haemolytica?

A high-risk cow is already in the “danger zone” for developing numerous problems. These cattle fall into several loose categories that can make them incredibly vulnerable to disease. It’s important to remember that the majority of a cow’s immune system lies within the rumen (about 80%). When viewed from that angle, it is no wonder that so many calves experience shipping fever and subsequent M. haemolytica secondary infections. Some of the factors that predispose a calf to issues include:

  • Unweaned calves. A calf that has not been properly weaned has not learned to eat on its own. It is also likely that its rumen is not fully developed, making it difficult for it to produce the necessary immunity to fight off disease. A calf that isn’t yet eating on its own can suffer from scours and acidosis.
  • Underweight calves. If a calf goes into the sale barn underweight it will surely arrive at the feedlot even more depleted. According to a review on transportation shrink by Ohio State University Extension, “Most of the shrinkage occurs during loading and in the first part (25 miles) of a trip. Cattle may lose half as much in 25 miles as they do in 200 miles. As the time increases, so does shrinkage, but at a slower rate than the first few miles.”2
  • Generally stressed calves. Calves that are being handled, moved to new environs, comingled with new cattle, etc., experience a high level of stress. Excessive stress releases cortisol which suppresses the immune system.
  • Undeveloped or under-developed rumens. Calves that have not been properly weaned and started on forage tend to have undeveloped rumens. This means that it is difficult to get them to start feeding and if and when they do, they don’t have the proper gut flora to adequately ruminate their feed.
  • Calves that refuse to eat or drink. In instances where a calf refuses to take in feed and water, they become quickly predisposed to being thrown into SARA.
  • Excessive antibiotic use prior to shipping. A metaphylactic program can be a vital part of keeping a herd healthy, however, the overuse or use of the wrong antibiotics can kill off beneficial gut flora, making it impossible for the rumen to function at peak levels.

Because the majority of a cow’s immune system lies within the gut, any one of the points above, or a combination of, can spell disaster for a calf with a weak rumen. This usually indicates it will have an equally weak immune system.

Use of Metaphylactics and M. haemolytica

The use of metaphylactics in the stocker cattle industry has proven to be both a blessing and a curse. When used prudently and properly, metaphylactics can help prevent widespread disease amongst groups of incoming cattle. However, if used carelessly or in excess, the benefits of metaphylactic use quickly become null.

Metaphylactics are used throughout an entire group of cattle under the assumption that they may be sick or will become sick in the near future. They might be administered in the form of an injection or added to feed. This is a much less time-consuming process than pulling individual sick calves and treating them independently of the herd.

A healthy calf with a strong immune system should be able to fight off serious infection on its own. The help of a metaphylactic agent may nip in the bud many diseases that are lurking but haven’t taken hold. This is assuming that the calf actually receives a therapeutic dose of the chosen drug. In cases when the metaphylactic is added to the feed, the consumption and dosage can be quite variable.

Consider a calf that is not fully weaned or is stressed and not eating. It may consume small amounts of treated grain, but not enough to achieve therapeutic drug levels adequate enough to treat the problem. This is when antibiotic-resistant strains of bacteria develop and create a bigger issue than the one originally being treated.

Unfortunately, while metaphylactic use may be effective against many bacterial diseases, it is usually not particularly helpful in the case of M. haemolytica. This is because of the longer incubation time of M. haemolytica. If a calf is exposed to Mannheimia haemolytica at the sale barn or upon reaching its destination, it still has about two weeks before it might show any signs of illness. In the case of a calf given a metaphylactic at the time of sale or when arriving at the feedlot, that drug’s efficacy will be wearing off at around the same time that the incubation period for M. haemolytica will be ending. This creates the perfect timing for the bacteria to multiply and flourish in the body of the calf.

The other piece of this puzzle is the effect antibiotics can have on ruminal health. If a calf already has a weakened immune system with poor ruminal development, the likelihood that the metaphylactic agent used will destroy any remaining gut flora and thus throw the calf into scours and/or acidosis increases exponentially.

Why Immune System Development is Key in Preventing M. haemolytica

As previously mentioned, around 80% of a calf’s immune system lies in its rumen. Much of this immunity is received from its mother until it is naturally weaned. Because most calves must be prematurely weaned, this puts them at a disadvantage for developing a mature, fully functioning immune system.

The importance of a heifer’s health cannot be stressed enough when it comes to giving calves the best possible chance to start out healthy and realize maximum gains. A heifer that is depleted or experiencing SARA is not going to be able to put the necessary resources towards the development of her calf. Her immune system will be stressed, meaning the antibodies she is passing on, both in-utero and post-partum will not be nearly as potent as those that come from a healthy dam.

The milk quality will also be compromised – vital nutrients and other components that encourage proper development of a calf will be lacking. This makes it likely that the calf will require more milk to get its minimum requirements met, further depleting the dam.

Properly preparing a heifer for calving can save time and vital resources. A proper vaccination program for all cows is essential to help guarantee a calf’s latent immunity. This helps not only prevent scours in the post-natal calf, but also allows them to receive adequate antibodies throughout the duration of their nursing time.

Other Ways to Reduce the Prevalence of Shipping Fever and M. haemolytica

While there is no magic bullet for completely eliminating shipping fever or M. haemolytica, the risks can be greatly reduced.

The top way to keep the rumen functioning (and thus the immune system) is to get calves eating and drinking right away. They can be on transport trucks anywhere from a few hours to a few days without access to feed or water. During this time their ruminal health is incredibly compromised, predisposing them to acidosis and scours. As the acid concentration in the rumen increases, the appetite wanes, making it more and more difficult to get calves to consume feed and water. The best way to combat this is to bring the ruminal pH back into balance, thus stimulating the appetite.

It’s also important that a calf’s immunity start being built from day one. This includes ensuring that it is receiving adequate amounts of high-quality milk from the mother and not being exposed to stressors such as weather extremes, crowded living spaces, dirty environs or being subjected to improper or excessive handling. This naturally keeps the pH in check; when a calf is exposed to stress, administering buffering agents can stop the SARA process in its tracks.

Ensuring that the immunity continues to function benefits an animal in two ways – it keeps the calf on the right track for proper immune development and increases the efficacy of vaccinations. The chances of a healthy calf developing shipping fever and subsequent M. haemolytica go down markedly when a good care protocol is followed.

While it’s not possible to ensure that every calf is completely free of disease, it is possible to minimize the impact of shipping fever and M. haemolytica on the overall herd. The fewer animals that become sick, the greater the realized profits come harvest time. Prudence in antibiotic use and a keen eye on ruminal health can make the difference between a healthy, productive herd and one that sees more losses than gains.

Six Tips for Successfully Grazing Cornstalks

By Acidosis and Shipping Fever, Cattle, Cow-Calf, Feedlot No Comments

Finding economical feed sources that provide adequate nutrition is a major concern for producers. Grazing cornstalks offers producers a great opportunity to utilize a by-product that might otherwise go to waste. Turning cattle out after harvest allows the corn farmer and cattle producer to work together towards a mutually beneficial goal; the farmer’s fields are cleared of leftover plant matter and the producer can feed his cattle inexpensively.

The quality of feedstuffs will vary depending on several factors, including the weather, how long the stalks have been standing, how much grain is still left, etc.

Here are five tips for making the most of your cornstalk grazing program:

  1. Know what you’re feeding. Assess the amount of grain remaining following harvest. Do this prior to turning cattle out. Adjustments to supplementation will depend on how much corn is left in the field.
  2. Support optimum rumen pH. Rumen microbes take time to adjust to the increase in starch in the diet. When microbe populations must shift in composition to process starches, it can take around two weeks for this adjustment to take place. Bloat becomes a concern during this transition, so supporting a proper rumen pH is essential to ensure that there are not major increases in rumen acid (which can lead to microbe die-off and sub-acute ruminal acidosis).
  3. Be prepared to supplement protein. Cornstalks and grain are low in protein, making it necessary to boost the daily protein intake through supplementation. A non-protein nitrogen (NPN) may need to be used to help increase the breakdown and utilization of proteins. It is important to maintain a proper nitrogen-to-starch ratio to help support microbes and stave off bloat.
  4. Vitamin A is key. Vitamin A is most abundantly present in green plant matter – for cattle, lush pastures are the main source of naturally-derived vitamin A. Unfortunately, both cornstalks and grain are markedly low in vitamin A. It will be necessary to supplement vitamin A on a daily basis to cattle grazing on cornstalks.
  5. Provide loose salt and minerals. Cornstalks and grain lack in many essential minerals and the salts needed for the proper functioning of every system in an animal’s body. Phosphorus, for example, is vital for proper digestion, while adequate calcium must be available for lactating cows. Loose salt and mineral supplementation allow for customization depending on regional soil deficiencies and the particular needs of the animals being turned out for cornstalk grazing.
  6. Consider tubs for supplementation. Tubs offer a great all-in-one solution for the supplementation of cattle. Many offer regional formulas to address specific deficiencies unique to the areas they are formulated for. In addition to salt and mineral supplementation, tubs make it possible to fill in the gaps in the nutritional profile of cornstalk grazing without breaking the bank.

Using cornstalk grazing as an economical way to feed cattle is a great way to take advantage of by-product resources. Establishing that fine balance between affordability and optimum conversion may take a little research and work, but the end result can mean more dollars in your pocket come sale time.

Lice Season is Approaching – Are You Ready?

By Cattle, Cow-Calf, Feedlot, Pre-Conditioning No Comments

When cold weather sets in, many cattle producers can take a sigh of relief as fly season draws to a close. However, the winter doesn’t herald complete freedom from external parasite concerns. It’s only starting for cattle lice.

Winter – the season of the louse

While always present on cattle, these opportunistic parasites spend the summer months laying low and not reproducing.  Because they are sensitive to sunlight, they tend to hide in dark places on the underside of an animal’s body, and especially when the haircoat is short and provides no protection. Lice take advantage of the cooler weather, shorter days, and longer hair coats to start laying eggs and wreaking havoc.

Lice emerge from their hiding places (folds of skin, mainly) as the hair coat increases in length, usually around late October into November and December. They can inhabit any part of an animal, but they seem particularly bothersome on the neck, shoulder, back and topline.

Consequences of uncontrolled lice infestation

Even though small numbers of lice are always present on healthy cattle, they are also opportunistic and will take advantage of cattle that are experiencing abnormal levels of stress. This stress may come from weather extremes, nutritional deficiencies, or other factors. Typically, a stressed animal will have higher levels of blood cortisol, the stress hormone that, in larger amounts, will cause a decrease in appetite and immune suppression.

A weakened immune system opens an animal up to a number of potential problems, external parasites being just one of them. Even in normally healthy animals, a significant lice infestation can have detrimental effects to their ongoing health.

Cattle that are experiencing the uncomfortable symptoms of lice will spend the majority of their time attempting to relieve the itching, taking them away from their number one job: eating. This can have dire consequences, considering their rumen health is dependent on a steady intake to function properly.

Some of the most significant effects an infestation can have include:

  • Reduced feed intake
  • Shrink
  • Higher susceptibility to infection
  • Cold stress (from rubbing off protective hair coat)
  • Reduced milk quality and production in cows (especially important for those fall calves)

Symptoms of lice infestation

The signs of lice infestation often manifest with animals rubbing, scratching and licking various areas on their bodies. Fence lines may be the first indicator of a problem, with tufts of scratched-off hair deposited in the barbs. Upon closer inspection of the animals themselves, there may be areas of raw, abraded skin or even crusted-over patches. When the itching becomes severe enough, they may even rub the majority of their winter coats off, leaving them susceptible to cold stress.

Cattle with severe infestations will also lose weight, as they are occupied with trying to relieve the irritation caused by the biting and chewing of these parasites. In the absence of feed intake, they can also experience sub-acute ruminal acidosis (SARA), leading to rumen microbe die-off and reduced nutrient absorption, opening them up to infection.

Types of lice found in cattle

There are two different groups of lice that the different species are divided into: sucking lice and chewing lice. Sucking lice feed on body fluids and skin secretions produced by the host, while chewing lice consume hair, skin and debris found on the body of their hosts.

Some of the most common species of louse found on cattle include the short-nose cattle louse (Haematopinus eurysternus), the biting or chewing louse (Bovicola bovis), the little blue cattle louse (Solenopotes capillatus) and the short-nose cattle louse (Haematopinus eurysternus). The variety of species can vary somewhat depending on region.

Heading off a serious infestation

One of the biggest mistakes made by producers is treating for lice too soon. Oftentimes, calves that are being weaned in the late summer and fall, prior to being moved to feedlots or pasture will be treated with either a pour-on dewormer or injectable dewormer. While this may have a small impact on the lice that are semi-dormant, it will not easily reach them if they have not moved to the upper portions of the animal. This means treatment is wasted and won’t prevent infestations from developing once the weather has truly gotten cold.

Pour-ons have shown the greatest efficacy, but the timing must be right. Early winter is an ideal time to treat for lice. It’s important to communicate with your herd veterinarian, as they will be able to advise on the most effective and economical timing.

How to help cattle that have already been affected

Even with good management, the weather can sometimes be a bit tricky and a serious infestation will occur. These animals will need a little extra help to regain their health and be able to withstand winter conditions. Here are a few things you can do to help your animals if they’re in this situation:

  • First and foremost, under the care of your herd vet, treat your cattle with a good pour-on dewormer formulated to kill the specific types of lice you are dealing with. Eliminating the cause of the irritation will help eliminate stress and allow any wounds to heal.
  • Treat ALL animals – even those that appear to be unaffected.
  • Base dosing on the weight of the animal. Too little and the product won’t work properly; too much is like pouring money down the drain.
  • Ensure complete coverage. The deworming product must come in contact with the lice themselves (or the areas they may migrate to) in order to be effective.
  • Help them reestablish normal eating patterns. This may require that problems like SARA are addressed. Neutralizing the rumen’s pH will encourage them to resume eating.
  • Support gut microbes. The rumen is responsible for 80% of the immune system’s ability to function. A very large part of this depends on a healthy microbial population. If the microbe balance has been disrupted, it will be necessary to provide nutritional support that will feed not only the animal but its damaged microbial colonies.
  • Take measures to help prevent recurrences, such as retreating at appropriate intervals during the winter months.

The time, money, and effort spent to properly treat your animals at the right times is a wise investment for the overall well-being of your herd. It will not only save them the discomfort of a lice infestation but can help boost your bottom line in the long run by preventing unnecessary shrink and illness.

© 2019 Pro Earth Animal Health.

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