Treating mastitis: Balancing cure, money, welfare and resistance

When evaluating the optimal mastitis treatment it is important to balance the welfare of the cow, the use of antibiotics, the economics and the cure rate. The importance of these factors varies according to dairy production system, and choosing the correct treatment approach is therefore an act of balancing.

Summary of presentation by Henk Hogeveen at the 53rd NMC annual meeting, Feb 2014

Take home message

  • When making decisions on mastitis treatment the herd manager has the difficult task of balancing cure rate (basically equal to animal welfare), the money and the risk of antibiotic resistance.
     
  • The largest part of the cost of treating a cow is not in the antibiotics, nor in the labour, it’s in the discarded milk.
     
  • Type of mastitis treatment can differ, depending on cow factors such as parity, stage of lactation and somatic cell count history, and the mastitis causal pathogen influence the probability of cure after treatment with antibiotics. Therefore cow-specific treatment of clinical mastitis is often recommended.
     
  • A review on clinical mastitis treatment was made to determine if cow-specific treatment was beneficial. The bacteriological cure depended on the antimicrobial treatment regime, the casual pathogen, and cow factors such as parity, stage of lactation, SCC history, history of clinical mastitis and whether the cows was systematically ill or not.
     
  • Total costs depended on treatment cost of the initial case of clinical mastitis (including costs for antibiotics, labor and milk withdrawal), treatment costs for follow-up cases of clinical mastitis, costs for milk production losses and costs for culling.
     
  • On average the total cost of a case by streptococci and treated with a standard 3 day IMM antimicrobial was $US 211 (€ 154), while the total costs if the casual pathogen was Staphylococcus aureus and treated with same regime was $US 274 (€ 199).
     
  • Transmission of mastitis caused approximately one third of total costs of a case of clinical mastitis ($US 547 (€ 749) per case when treated for IMM3).
     
  • Mild to moderate clinical mastitis caused by Gram-negative pathogens does not need to be treated with antimicrobials.
     
  • Using a mastitis severity score and bacteriological culture to determine the choice of treatment therefore allows for a justified and judicious use of antibiotics. Protocols using an on-farm culturing system in combination with a delay of the treatment decision have been developed to improve the quality of the treatments and to reduce treatments to cows that do not need it.
     
  • Such a protocol has been able to reduce the use of antibiotics with half without differences in cure rates, new intramammary infections and treatment failure risk, nor in recurrence of clinical mastitis, SCC, milk production and survival.
     
  • It seems that lactational treatment of subclinical mastitis increases welfare (measured by fewer cases of clinical mastitis), reduces the use of antibiotics and saves money. The most important cause of these very positive results is the expected effect of a reduction in transmission of mastitis.
     
  • Due to discussions on antimicrobial resistance in humans, in relation to the use of antibiotics in animal husbandry, a substantial reduction of antibiotic use has been agreed upon. The recommendation for blanket DCT has been changed towards a recommendation of selective DCT.
     
  • It has been essential to develop a new method to detect cows with mastitis for robotic milking.
     
  • A review on the performance of robotic mastitis detection models showed that these systems still generate a relatively large number of false positive alerts.
     
  • This review demonstrates that  not all cows with clinical mastitis are diagnosed and treated immediately on farms that milk robotically. The results also suggest that the cow’s own immune system is capable to clear (mild) cases of mastitis.
     
  • This observation, in addition to the presence of mastitis causal pathogens that are resistant to antimicrobials, is a strong incentive to develop alternative mastitis treatment protocols for robotic farms.
     
  • The decision to treat animals is important but still a routine decision. Farmers should together with the their veterinarian make a farm-specific treatment plan that can be routinely used for every mastitis case. The use of on-farm or off-farm culturing should be considered, as well as type and duration of treatment. The plan should balance the welfare of the animals, the economics and duration of treatment and disease and the use of antibiotics.

Introduction

Mastitis is an animal welfare problem and an economic problem. It is a production disease found on dairy farms around the world, and an important cause of a less efficient milk production. It can also be a food safety problem, affecting the milk quality, which creates problem for the dairy industry. Mastitis management should therefore have the goal of improving milk quality and the efficiency of milk production, and thus make milk production more sustainable.

Optimizing treatment

Mastitis treatment decisions are important to control the disease, and the most important factor in a treatment decision is the expected cure rate of the chosen treatment for the mastitis case at hand. But there is more to treating animals than cure rate, there is also the animal welfare aspect. Clinical mastitis gives pain (Kemp et al. 2008 VetRec), and cow behavior is also affected. (Medrano-Galarza et al, 2012 JDairySci). So better cure also gives better welfare.

Something that is currently subject to much debate, maybe more so in Europe than in the US, is antibiotic resistance. There are two parts in this; first, the resistance of mastitis pathogens, and it is in the interest of the dairy industry to keep this under control. If this increases there will be huge problems for the dairy industry. However, resistance of mastitis pathogens does not seem to be increasing; there is a good IDF fact sheet on this by Hogan.

The other part is antibiotic resistance in humans. Use of antibiotics in dairy cattle has shown to be a contribution to this, although a minor one. Still, prudent use of antibiotics should be advocated. In the Netherlands there is a lot of concern about antibiotics, and the dairy industry has therefore decided to reduce the amount of antibiotics used.

Economics

Farming is a business and decisions have to be economically valid. There is the cost of antibiotics versus benefits of higher cure rates or better prevention. The herd manager has the difficult task of balancing cure rate (basically equal to animal welfare), the money and the risk of antibiotic resistance.

Available papers on cure rates are using averages, and these are general and not farm specific. So it does not fit the individual farm. But it is possible to do a calculation spread sheet. Link to slide show that shows the spreadsheet calculation.

(Take a look at Henk Hogeveen’s presentation on Slideshare, the spreadsheet explanation starts at Slide 12.)

In this calculation you enter the cost of:

  • Antibiotics
  • Discarded milk
  • Treatment (labour)
  • Milk production losses
  • Culling

The largest part of the cost of treating a cow is not in the antibiotics, nor in the labour, it’s in the discarded milk.

Treatment of clinical mastitis

Clinical mastitis is treated with a standard intramammary antimicrobial treatment in many countries. Antimicrobial treatments can vary in antimicrobial compound, route of application, duration and cost. In some countries, e.g in Scandinavia, there are strict rules with regards to the use of antimicrobial treatment of clinical mastitis, whereas in other countries, like the USA, rules are more liberal and approximately 90% of all cases of clinical mastitis are treated with antibiotics. Type of treatment can differ, depending on cow factors such as parity, stage of lactation and somatic cell count history, and the mastitis causal pathogen influence the probability of cure after treatment with antibiotics. Therefore cow-specific treatment of clinical mastitis is often recommended.

A review on clinical mastitis treatment was made by Steeneveld, (2011 JDairySci.), to determine if cow-specific treatment was beneficial. The bacteriological cure for each simulated case of clinical mastitis depended on the antimicrobial treatment regime, the casual pathogen, and cow factors such as parity, stage of lactation, SCC history, history of clinical mastitis and whether the cows was systematically ill or not.

Total costs of for each of these depended on treatment cost of the initial case of clinical mastitis (including costs for antibiotics, labor and milk withdrawal), treatment costs for follow-up cases of clinical mastitis, costs for milk production losses and costs for culling.

The different treatment regimes used in the simulation, and their average costs were (exchange rate from Dec 1, 2013, 1$=€1.37):

• IMM3 - standard 3 day intramammary, $US 242 (€ 177)

• IMM5 - extended 5 day intramammary, $US 272 (€ 191)

• IMM3_S - combination of 3 day intramammary plus systemic, $US 271 (€ 198)

• IMM3_S_NSAID_S - combination of 3 day intramammary plus systemic plus one day non-steroid anti-inflammatory drugs, $US 275 (€ 201)

• IMM5_S - 5 day intramammary plus systemic. $US 295 (€ 212)

Average probabilities of bacteriological cure for the five treatment regimes were 0.53, 0.67, 0.67, 0.72, 0.81 respectively.

The casual pathogen and several other cow characteristics influenced the total costs of CM treated with different treatment regimes. On average the total cost of a case by streptococci and treated with a standard 3 day IMM antimicrobial was $US 211 (€ 154), while the total costs if the casual pathogen was Staphylococcus aureus and treated with same regime was $US 274 (€ 199).

The cost of CM increased with increasing daily milk production at the onset of the CM. It also increased with increasing relative production value, increasing parity number, and decreasing month in milk. Costs were also higher for repeated cases of CM as well as for CM in systematically ill cows.

For all different treatments the standard 3 day IMM had the lowest cost, but also the lowest probability of bacteriological cure.

In a follow-up study Halasa (2012) used the same treatment possibilities but included transmission of pathogens. This altered the order of optimal treatment options.

Total costs (per 100 cows per year) for mastitis were:

• IMM3: $US 10,885 (€ 14,910)

• IMM5: $US 8,621 (€ 11,810)

• IMM3_S: $US 10,885 (€ 14,910)

• IMM3_S_NSAID_S: $US 10,885 (€ 14,910)

• IMM5_S: $US 8,841 (€11,560)

Extended treatment did not provide better economical results (although they did provide better cure rates and thus a better animal welfare). When taking the use of antibiotics into account, the balance tips towards short duration treatment with antibiotics.

The important role of transmission was confirmed in another study by Down et al (2013). Approximately one third of total costs of a case of clinical mastitis ($US 547 (€ 749) per case when treated for IMM3) was due to transmission of mastitis. In this study the 3 day intermammary treatment IMM3 was the most cost-effective.

Reducing the use of antibiotics by half

There seems to be general consensus among scientists that mild to moderate clinical mastitis caused by Gram-negative pathogens does not need to be treated with antimicrobials (Roberson, 2012). Using a mastitis severity score and bacteriological culture to determine the choice of treatment therefore allows for a justified and judicious use of antibiotics. Protocols using an on-farm culturing system (e.g. Cameron et al, 2013) in combination with a delay of the treatment decision have been developed to improve the quality of the treatments and to reduce treatments to cows that do not need it. Such a protocol has been able to reduce the use of antibiotics with half without differences in cure rates, new intramammary infections and treatment failure risk (Lago et al, 2011a), nor in recurrence of clinical mastitis, SCC, milk production and survival. (Lago et al, 2011b).

Subclinical mastitis

Bio-economic models have been used to calculate the costs of mastitis. It seems that lactational treatment of subclinical mastitis increases welfare (measured by fewer cases of clinical mastitis), reduces the use of antibiotics and saves money. The most important cause of these very positive results is the expected effect of a reduction in transmission of mastitis. However, more studies on transmission are needed before advising this broadly.

A recent study (Bexiga et al. 2013) calculated the economic efficiency of lactational treatment of subclinical mastitis caused by CNS (coagulase-negative staphylococci), the most frequently isolated bacteria from milk samples in several studies worldwide. It concluded that lactational treatment of subclinical mastitis caused by CNS was not financially justifiable in most cases.

Dry cow therapy

For most countries there is not much difference in economic efficiency between blanket and selective dry cow therapy (DCT). Therefore, until recently, in the Netherlands, the balance was held in favor of blanket DCT. There was a little more use of antibiotics, approximately equal costs and better animal welfare though reduction of the use of antibiotics. Due to discussions on antimicrobial resistance in humans, in relation to the use of antibiotics in animal husbandry, a substantial reduction of antibiotic use has been agreed upon. The recommendation for blanket DCT has been changed towards a recommendation of selective DCT. See Theo Lam's article on Dry Cow Therapy

Automatic milking

Automatic milking has gained worldwide acceptance since its introduction in the 1990s, and today more than 10 000 farms globally milk automatically. Since the concept is based on the system operating on its own without human presence, it has been essential to develop a new method to detect cows with mastitis. This new method involves two tests; one is a mastitis detection model in the robotic system that uses sensor data (e.g. electrical conductivity, milk yield) as input to generate mastitis alerts. To find all cases of CM, farmers are advised to visually check all mastitis alerts.

A review on the performance of these detection models showed that these systems still generate a relatively large number of false positive alerts. (Hogeveen et al, 2010, Rutten et al., 2013).

Checking all mastitis cases is time-consuming and frustrating task, as in most cases the alerted cow will not show any signs of clinical mastitis.

Robotic milking farmers have indicated that they prefer a detection model that focuses only on severe cases of clinical mastitis and that generate very few false alerts at the same time. (Mollenhorst et al.,2010). They are eager to minimize the additional time and nuisance of checking large numbers of false alerts even at the expense of missing cows with (mild or moderate) clinical mastitis. (Claycomb et al., 2009). This is in line with a small practical experiment that demonstrated that the majority of mastitis alerts are not associated with mastitis and that farmers use their own rules to decide which mastitis alerts to check visually. (Hogeveen et al., 2013)

Main reasons for farmers to check a mastitis alert visually were: a spike in electrical conductivity, a drop in milk production, presence of clots on the filter sock, when the robot failed to milk a cow, or a combination of these reasons.

Main reasons for farmers not to visually check a mastitis alert were: the absence of flakes or clots on the milk filter (28%), the decline in milk yield was not sufficient or alarming (19%), the cow has a high electrical conductivity but keeps re-appearing on the mastitis alert list (10%), lack of time (10%). The decision making process of the farmers to check or not check mastitis alerts resulted in a <3% of all mastitis alerts that were confirmed visually, and it was estimated that approximately 75% of cows with clinical mastitis that had been correctly identified by the detection model were missed. It can be concluded that on robotic milking farms a large proportion of cows with clinical mastitis do not receive antimicrobial treatment.

This data demonstrates that not all cows with clinical mastitis are diagnosed and treated immediately on farms that milk robotically. The question arises whether this is a problem since farmers that milk robotically are still able to produce milk of such quality sufficient for human consumption. Moreover, results suggest that the cow’s own immune system is capable to clear (mild) cases of mastitis (Erskine, 1992).

This observation, in addition to the presence of mastitis causal pathogens that are resistant to antimicrobials, is a strong incentive to develop alternative mastitis treatment protocols for robotic farms. Such an alternative treatment paradigm does not exist (yet) and may address today’s increasing public concern regarding animal welfare and the development of (multi)resistant pathogens in human health and in the animal production sector (Van Werven, 2013).

Farm-specific treatment

The decision to treat animals is important but still a routine decision. Farmers should together with the experts, their veterinarian, think about a farm-specific treatment plan that can be routinely used for every mastitis case. The use of on-farm or off-farm culturing should be considered, as well as type and duration of treatment. The plan should balance the welfare of the animals, the economics and duration of treatment and disease and the use of antibiotics. A final weighing is dependent on the preferences of the farmer and the constraints of society.

Henk Hogeveen's presentation on Slideshare

Henk Hogeveen's blog Animal Health Management

IDF fact sheet on antimicrobial resistance

IDF guide to prudent use of antibiotics

Theo Lam's presentation on dry cow therapy

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Monica Wadsworth

Monica Wadsworth
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Source

Summary of presentation by Henk Hogeveen at the 53rd NMC annual meeting, Feb 2014

NMC online