Staphylococcus aureus diversity and subclinical mastitis

This is the first study I’ve found that was interested in cataloging bacterial diversity among subclinical (or asymptomatic) infections. While they may be less threatening to the animal’s overall health, these infections have great significance in the world of animal agriculture, where they restrict growth (or in this case, milk production), and encourage the use of medicated feeds which in turn motivate people to purchase organic products. Identifying the risk factors and causes of these infections could therefore impact both the management of food animals, and any legislation defining how and when medications can be used. With that in mind, let’s jump back into mastitis, and everyone’s favorite gram-positive, S. aureus.

It’s because of my plasmids, people can’t help but stare.
Image from http://cellimagelibrary.org/

S. aureus is one of many bacteria that cause mastitis, however it is of additional importance as it often causes chronic or recurring cases of mastitis that result in unusable milk and discomfort of the animal. In this study, the authors investigated 11 dairy farms where they expected to find S. aureus, based on previous culture findings at each farm. They defined cows that they took milk samples from as having new or chronic infections based on somatic cell counts (SCC) in the milk. If values were >200,000 cells/mL for the month of collection the infections were considered new, whereas if cell counts were  >200,000 cells/mL for more than 2 months, those infections were considered chronic. They took a single milk sample from each teat of the infected cows, for a total of 1,354 mammary glands from 350 cows.

Pulse field electrophoresis was used to identify the different subspecies/serotypes/pulsotypes (pick your word), and to identify the genes coding for enterotoxin production that had been amplified by PCR. An ELISA test was used last to detect the presence of several enterotoxins.

As the majority of exposure to enterotoxins produced my S. aureus is through milk and dairy products, subclinical infections of S. aureus are very important as a food safety control point. Unlike cows with clinical cases that are removed from production, cows with subclinical infections continue to contribute milk that makes it to the consumer, provided that the SSC is <750,000 cells/mL. The authors were unable to detect a large amount of enterotoxin in their samples, but many of the pulsotypes contained the genes coding for their production. Other studies cited by the author report the common presence of these genes in S. aureus  samples, but expression rates are inconclusive or unexplored. This means that theoretically, subclinical cows could be introducing these bacterial toxins into consumer milk in small amounts.

It’s difficult to tell how significant these amounts might be. Toxic doses of one of the enterotoxins, “Toxic Shock Syndrome Toxin 1”, has been found to be as low as 100 micrograms/Kg in miniature pigs. The concentrations that may be introduced through contaminated milk, and the bioavailability when ingested, should be explored. Takeuchi et al. (1998) were able to detect the presence of TSST- 1 in bulk milk tanks, but no one has yet to quantify the amounts of TSST- 1 potentially present in pasteurized milk.

All that being said, what good is this new information? It can be argued that because these infections are chronic and/or subclinical that these strains of S. aureus aren’t very pathogenic, but they’re still causing inflammation. By identifying common serotypes and factors leading to the subclinical infection of a herd, perhaps there are simple management changes that can prevent infection. Milking is an almost sterile procedure, with sanitation of the teats both prior and following milking, wearing gloves, and forestripping; but there could be other tricks that would target risk factors related to the spread of subclinical pathogens, especially those that are specific to a location.

 

ResearchBlogging.org

Bulanda M, Zaleska M, Mandel L, Talafantova M, Travnicek J, Kunstmann G, Mauff G, Pulverer G, & Heczko PB (1989). Toxicity of staphylococcal toxic shock syndrome toxin 1 for germ-free and conventional piglets. Reviews of infectious diseases, 11 Suppl 1 PMID: 2928643

Oliveira L, Rodrigues AC, Hulland C, & Ruegg PL (2011). Enterotoxin production, enterotoxin gene distribution, and genetic diversity of Staphylococcus aureus recovered from milk of cows with subclinical mastitis. American journal of veterinary research, 72 (10), 1361-8 PMID: 21962279

Takeuchi, S., Ishiguro, K., Ikegami, M., Kaidoh, T., & Hayakawa, Y. (1998). Production of toxic shock syndrome toxin by Staphylococcus aureus isolated from mastitic cow’s milk and farm bulk milk Veterinary Microbiology, 59 (4), 251-258 DOI: 10.1016/S0378-1135(96)01253-9

Do organic animal operations encourage management decisions that negatively impact animal welfare? Part 3

Here’s the final portion of my paper: Do organic animal operations encourage management decisions that negatively impact animal welfare?

If you’ve missed the other posts, you can check out part 1, part 2,  or read the entire paper here.

 

_____________________________________________________

Conflict Between the Organic Approach and Welfare Ideals
Despite measures taken to promote prevention, a certain amount of disease is permissible in a healthy ecosystem and the restrictions placed on organic producers by both their certification requirements and ethos can create dilemma’s that could potentially harm animals. Several classic examples of species specific situations have been examined where the animal welfare approach taken by organic producers can be considered detrimental to the animal.

It should be noted that while there is evidence that there is a reluctance to use prohibited medications and chemicals to treat disease on organic farms (Vaarst and Bennedsgaard, 2001), both the Code of Federal Regulations (CFR) and IFOAM standards explicitly state that organic livestock producers must not withhold medical treatment from a sick animal in an effort to preserve that animals organic status (IFOAM, 2005; National Archives and Records Administration, 2012a; Riddle, 2008, 2012).
Dairy
Management of mastitis in organic dairies is a commonly discussed example of when health of the individual and a reluctance to accept the financial loss associated with antibiotic use can potentially harm the animal. Herd health, in general, has not been shown to be significantly different between organic and conventional dairy herds, and some data suggests that the incidence of disease may actually be lower in organic herds, though the reasons for this are unknown (Lund and Algers, 2003; Lund, 2006). Interestingly, the ban on antibiotics for clinical use is more of a concern within U.S. boarders, as the majority of certification standards in the European Union allow antibiotic use to treat clinical disease without jeopardizing the organic status of the animal (Ruegg, 2009). However, the strict FDA guidelines for organic milk production not only prohibit the use of antibiotics in organic livestock, but do not allow the use of any compounds with an antimicrobial effect that are not approved by the FDA for organic production (National Archives and Records Administration, 2012a). Currently, there are zero antimicrobials approved for use in organic animals (Ruegg, 2009). This leaves organic dairy producers extremely limited in their options for treatment when faced with a cow that has mastitis. With few options available, Zwald et al. (2004) were able to find that farmers who switched to organic production began to seek information on treatments from other organic farmers as opposed to veterinarians. This trend is not seen in countries where antibiotic options are available to organic dairy farmers (Hamilton et al., 2006).

So what options are available to organic dairy producers in the U.S.? Once again, prevention is key, but research has shown that rates of mastitis are similar between organic and conventional dairy operations (Lund and Algers, 2003; Lund, 2006). This indicates that treatment must be part of a management plan, even if the organic ethos prevents any attempts to interfere with natural processes through antimicrobial intervention. Certain drugs are available for use on the CFR’s approved substances list with increased withdrawal times to maintain the high standards expected in organic milk production (Riddle, 2008; National Archives and Records Administration, 2012a). These drugs include certain anti-inflammatory drugs that would be useful in treating fever and inflammation associated with mastitis. Beyond pharmaceuticals, therapeutic care including frequent milking is a recognized way to discourage bacterial growth within the affected quarters. Combined with approved anti-inflammatory drugs, frequent milking and supportive care constitutes a common mastitis treatment on organic dairies in the United States (Ruegg, 2009).

Many organic farmers will also attempt to utilize complementary and alternative medicines; however, almost all of the products available have not been evaluated in peer reviewed studies for efficacy. Immunoboost, a USDA licensed immune stimulant sold in the U.S., has been evaluated but has not shown to have any significant effect on the treatment of mastitis (Ruegg, 2009). Other various remedies including peppermint, aloe, and garlic have been utilized by organic farmers as intramammary treatments, however the efficacy of these options is doubted, and their use is prohibited by the FDA (National Archives and Records Administration, 2012a). It appears that without recovery using simple supportive care, any medical intervention necessary to prevent unnecessary pain or distress for non-responsive mastitis cases will result in the loss of a producing animal for that organic operation. This creates a potential welfare risk, as the USDA organic requirements do not specify a point when prohibited treatments must be used, and the decision to discontinue organic treatment resides solely with the farmer.
Poultry
Poultry producers face a distinctive management change when converting to organic as free choice medicated feeds containing antibiotics are commonly used to manage disease and promote growth (Love et al., 2010). Organic poultry is also currently under increased pressure from consumers (Love et al., 2012) to provide a safe and antibiotic free product, which could indicate an increased reluctance to treat conditions using pharmaceuticals. Following the prevention management strategy, organic poultry producers may use a variety of feed supplements including probiotics, prebiotics, organic acids, and plant extracts that have had minimal and sometimes contradictory efficacy reviews (Griggs and Jacob, 2005). Once again, treatment needs to be a key part of the management strategy of the organic producer, and the increased public scrutiny over medication use in poultry has the potential to encourage famers to withhold medication as has been shown in other species (Lund, 2006).

One of the most contested animal welfare debates surrounding organic poultry is regarding the space required by the USDA regulations to remain organic (Kijlstra and Eijck, 2006). While the law only requires year-round access to the outdoors, shade, shelter, exercise areas, fresh air, clean water for drinking, and direct sunlight (appropriate for the species, age, and climate) (National Archives and Records Administration, 2012a); organic farmers have adopted the term “free-range”, which unfortunately like the word “natural,” has no legal meaning. Nonetheless, open access to runs follows the third of Frasier et al.’s welfare ideals in allowing chickens to exhibit natural behaviors and thus have better welfare. The trade-off, however, is that while we have defined the major focus of disease management in organic operations as prevention based, free ranging chickens are more susceptible to predation, outbreaks of cannibalism, parasite exposure, coccidiosis and ascarid infections, and interactions with wild fowl that transmit dangerous diseases such as avian influenza (Verhoog et al., 2004; Kijlstra and Eijck, 2006; Lund, 2006). In order to keep with organic standards, all of these animals must continue to have access to the outdoors, and prohibited pharmaceuticals cannot be fed to treat outbreaks of disease or treat the higher rate of parasites that are found on organic operations (Lund, 2003). Clearly, should there be an outbreak of disease or cannibalism, an ethical dilemma is created between the first two ideals concerning the physical and mental needs of the animal, and the third to maintain natural conditions.

The various dilemmas discussed indicate that organic producers face additional pressure, both financially and in public relations, to avoid the use of treatments that would compromise the organic status of that animal. However, prioritizing animal welfare to include aspects beyond the scope of the clinical health of individual animals can potentially change the way welfare is perceived by conventional farmers and the general public. If an ecocentric rather than an individualistic perspective is considered, and positive experiences can be provided for the animal by indulging its natural behaviors and ecological niche, perhaps some stress events like occasional infections are an acceptable trade-off. Given that a higher incidence of disease has not been found, and that organic producers are required by law not to restrict care to maintain an organic status, it can be determined that organic livestock production does not encourage decisions that negatively impact animal welfare. However, it is recommended U.S. should adopt the EU policy of allowing antibiotics to be used in clinical cases without removing the organic status of that animal. With adequately increased withdrawal times in place to reflect the strict requirements that define organic products and enough consumer education, the organic market should recognize and accept the benefits of this policy change. Livestock would benefit by receiving more aggressive medical intervention as financial pressure not to treat animals could be alleviated as it has been in the EU (Ruegg, 2009), and having prescription antibiotics available as a treatment option could encourage more contact with veterinarians instead of neighbors to discuss animal health. Additional research is needed to support this position that could come from data determining if financial and public pressure are enough to encourage farmers to withhold treatments. In that case, additional actions such as stricter enforcement of the law may be necessary to promote a higher standard of care for organic animals.

New Research: Do organic animal operations encourage management decisions that negatively impact animal welfare? Part 1

For my senior ethics class, I chose to write about an issue everyone has an opinion on, from granola folks at the co-op telling me to watch Food Inc. to farmers complaining about the outbreak of upper respiratory disease from those untreated organic herds sneezing over the fence. I actually ended up changing my own views quite a bit following the extensive research I did, and I really enjoyed writing the paper. I wanted to evaluate the claims often made to me by professors in my land grant school (Oregon State) about the misleading advertizing and hidden evils of organic production, and I wanted to see if there was anything to back up the fanaticism and devotion sometimes projected by organic devotees. This paper is by NO MEANS an exhaustive review of the literature, and I am not qualified to make any official judgement, and is simply meant to be a personal commentary from a recent graduate.

So rather than sit here blathering, the first portion is below, and you can read the full paper here.

_____________________________________________________________

Few agricultural debates come close to generating the same passionate and heated responses that organic farming seems to elicit. The discussion surpasses the interests of producers with conflicting ideologies to be hotly debated by assertive consumers as well; people who highlight the paradox created by their interest in the safe and responsible production of their food, while avoiding all involvement in its creation. The originally proposed Organic Foods Production Act of 1990 received nearly 300,000 comments on the proposed requirements, more than any other piece of legislation in history (Vos, 2000). Clearly this indicated that the role organic farming played in food production was extremely important to U.S. citizens then, and continues to be a relevant topic as organic operations have grown by 40-50% every five years since 1992 (USDA, 2010).

The general public also has a strong interest in the way animals are managed, especially when management techniques play a role in the health or well-being of the animals prior to their use for meat, milk, or eggs. Humane management is often brought up when discussing the merits or flaws of organic operations, and is extremely important to producers due to the important role animal welfare plays when consumers make purchasing decisions. Prickett et al. (2010) found through the use of a telephone survey that 49% of consumers consider the well-being of farm animals when purchasing meat, and 83% of consumers disagree that lower prices are more important than the well-being of the animals used. These numbers become critical when organic producers need to justify the increased cost of their products and conventional producers are forced to avoid the alternate impression that their animals are treated poorly.
Marketing pressure placed on both groups leads to a vicious back and forth of both valid questions and vague accusations, among which is the suggestion that organic farms can act as reservoirs of disease (Kijlstra and Eijck, 2006). One mechanism for this accusation could be the avoidance of chemical or synthetic intervention for pest control and treatment of disease. This paper seeks to evaluate organic farming ideologies and legal constraints that create ethical dilemmas surrounding animal welfare, and determine whether organic management encourages decisions that are detrimental to the animals involved.

Animal Welfare and the Organic Movement
Early organic movements were created with the goal that a more sustainable and environmentally friendly farming system could be created that would benefit not only farmers and consumers of organic products, but also the animals within this system (Lund, 2006). These ideals have persevered and are a common talking point in promotional materials that market organically raised animals as drug and chemical free, and much closer to a “natural” condition (Riddle, 2005). This concept of “natural” is commonly used to differentiate organically produced animal products from conventional ones.

Utilizing the word “natural” creates an issue of perception; while the public widely accepts “natural” as a product descriptor, the word itself has no legal definition when used in food advertizing or packaging in the U.S. However, consumers have been shown to associate descriptions of “naturalness” not only with animal welfare but sustainability and care for the environment (Verhoog et al., 2003). While this may imply a scheme to sway consumer loyalty, the word is widely accepted by organic producers as an accurate descriptor to differentiate organic methods from conventional. While “natural” can have broad definitions like including the entire universe or everything untouched by man (thus either removing agriculture or providing no distinctions in practice), Verhoog et al. (2004) were able to show that organic producers feel organic can be classified as more natural than conventional agriculture as its aim is to be harmoniously integrated into nature. In this way nature is seen as a teacher or model for sustainable and humane agriculture. This ethos pushes organic farmers into an ecocentric approach when making management decisions. From this perspective, we begin to see how organic farmers may view welfare differently than conventional farmers or veterinarians.

Read the rest of the paper here.

 

ResearchBlogging.org
Vonne Lund, & Bo Algers (2003). Research on animal health and welfare in organic farming—a literature review Livestock Production Science, 80 (1-2), 55-68 : 10.1016/S0301-6226(02)00321-4

Article review: Effects of early pregnancy diagnosis by palpation per rectum on pregnancy loss in dairy cattle

Image from UPenn

Just a short one here today. Not too much interesting going on in a study that supports the null, but the methods are great.
This study looked at the affect that one or two rectal palpations to determine pregnancy had on embryo viability. I can see why there would be a question, it seems like a highly invasive procedure when you’re shoulder deep in cow rectum and feeling for an amnion several layers of membranes away. But we tend to anthropomorphize, and many dairy cattle require minimal restraint for the procedure. Nonetheless, it does seem likely that there could be a negative effect on the embryo, especially when rupturing or crushing the amnion via rectal palpation has been a historical method of terminating an unwanted pregnancy in cows (before we started using PGF2α) (Romano, 2011).
The study did a great job of identifying factors that have created conflicting results in the past. Whether that was sampling bias, uncontrolled treatments (multiple people and techniques for palpation), or a lack of a true control. They took the time to show how each one of those shortcomings was corrected in this study, and I think they did a great job designing the experiment.
In the end it was surprising to see that there was no difference between the cows subjected to rectal palpation once or twice compared to the control. I didn’t expect to see a significant difference, but potentially a small one. The authors did warn that because this experiment was so controlled, the results may not be similar to every situation. Inexperienced personnel or different techniques could change the pregnancy rates in practice (the study employed a single veterinarian with >25 years experience). One difference they took time to note was the much lower pregnancy rate in dairy cows as opposed to primiparous heifers. The exact etiology of this is unknown, but is commonly found in dairy. The authors mention it as it played a role in their analysis of the two farms involved (other factors affecting rates between the farms were geographic area, rate of twinning, and breed of cattle).

Not especially exciting, but it’s always great seeing researchers identify a conflicted area and tackle it with strict methods/controls and a large sample size.

ResearchBlogging.orgRomano JE, Thompson JA, Kraemer DC, Westhusin ME, Tomaszweski MA, & Forrest DW (2011). Effects of early pregnancy diagnosis by palpation per rectum on pregnancy loss in dairy cattle. Journal of the American Veterinary Medical Association, 239 (5), 668-73 PMID: 21879969

Article Review: A review of the causes of poor fertility in high milk producing dairy cows

The more I read, the more I’m extremely grateful for the rigor that my reproduction class required. None of this would have made sense to me last year, and it’s amazing how many of the details I’ve been able to keep in my conscious memory. I’m sad that I’m missing the advanced repro course offered in the fall, but hopefully the experience I’m gaining here will be just as valuable, and I can continue applying what I’ve learned so that I don’t lose the knowledge.

I was extremely impressed with this article. It felt like a lecture rather than a textbook, and as a reader it was easy to finish, but still full of great content. The focus is on how while our dairy cows have been engineered to crank out milk, we’ve seen a dramatic drop in their reproductive success which hurts the efficiency of dairy operations.

Pretty amazing what selective breeding can do. But we knew that, we managed to make dachsunds from wolves.

The article explains that rather than a minimalist approach that looks at only one factor (such as inadvertent selection for poor reproductive fitness) to correct the problem, a more inclusive or holistic approach is needed. I learned a lot more about common problems such as lameness, mastitis, metritis, and poor BCS and how they relate specifically to resumption of estrus after parturition and zygote viability. I’m always amazed how farmers can actually succeed at maintaining herd numbers when conception and birth rates are so low.

There was a lot written about heat stress, and that always seems obvious when it gets over any comfortable temperature. But heat and other environmental stressors are actually a lot more dangerous to reproductive health than I was aware. According to the article, “exposure of ovarian oocytes to unfavorable physiological events during follicle development from primadorial to pre-ovulatory stage may result in the ovulation of defective oocytes up to three months after the insult (Britt, 1992; Fair, 2010).” When you have 60-90 days to breed your cattle to stay on schedule, this is extremely influential to your breeding program. This also makes the situation down in Texas more dangerous in that, with the dry weather during their normal wet season, any excess stress surrounding parturition could delay or destroy what’s left of their breeding program. Once they can’t even breed replacement heifers, its all over.

So, after looking at multiple conditions that hurt reproductive efficiency and discussing their prevention. The article sums itself up with a nice poster identifying the key areas they covered.

(Walsh, 2011)

For the causes and preventative measures covering these you can check out the article. It finishes up by making the point that we can’t just develop a new antibiotic for metritis or mastitis, but we need to reevaluate our genetic selection and more importantly, our management strategies to ensure as many of these factors are met as possible.

Walsh SW, Williams EJ, & Evans AC (2011). A review of the causes of poor fertility in high milk producing dairy cows. Animal reproduction science, 123 (3-4), 127-38 PMID: 21255947

Reference: University of Illinois lactation biology website

In searching for information on mastitis, I came across this treasure trove of information. It was too good for me not to post here. It’s got great summaries, information, and a large collection of case studies. I almost wish the site itself was a book I could keep on the shelf, but for now I’ll just add it to my favorites. I want to recommend the page covering mastitis treatment and control for some light reading. It gives a really quick dirty rundown on industry methods and research. I was especially interested in the attempts to make vaccines, specifically ones for Staphylococcus Aureus, which can cause chronic infections that force dairy farmers to cull cows.

If you want to learn more about lactation biology, or are a student studying milk production, you need to visit this site and use it as a resource. Thank you to Dr. Walton Hurley for making your teaching materials available to everyone.