Production losses in dairy cattle due to mycotoxin contamination are subject to a number of factors and uncertainties. Here we delve deeper into the effects of these toxins and the best practical way to control them.
This year an interesting situation is being faced of identifying whether mycotoxins are a real threat to animal producers worldwide or not. The dairy industry is usually under constant mycotoxin attack due to the very high dry matter intake (DMI) per cow per day. Since 1989, the population of dairy cows has significantly dropped, while milk production has remained relatively constant. These days, dairy cows produce a lot more milk than decades ago as a result of higher DMI. Higher DMI has led to increased intake of mycotoxins and their negative effects in ruminants (Oltenacu and Broom, 2010). At the same time, it is extremely difficult to identify when mycotoxins are causing poor health and performance.
Maize harvested in Argentina in 2016. This corn was intended for export but was contaminated with mycotoxins. [Photo: Newton Padovani, Nutriad International]
Some mycotoxins such as zearalenone predominantly affect reproduction and are relatively easy to identify. Mycotoxins that can cause acute intoxications and dramatic changes in milk production and animal health status at high levels can be identified much more easily. Unfortunately, the most common and most difficult mycotoxins to identify occur when rations contain low levels of the mycotoxins and the health effects are subclinical. The presence of mycotoxins in feed is often connected with an increase in the incidence of metabolic disorders such as ketosis, retained placentas, displaced abomasums, mastitis, metritis, lameness, elevated somatic cell counts (SCC) and consequently slightly decreased milk production. Subclinical mycotoxicoses reduces profitability by lowering milk production and increasing expenses from necessary veterinary therapies.
Contributing factor to chronic conditions
Mycotoxins can be the primary agent causing acute health or production problems in a dairy herd, but are more likely to be a contributing factor to chronic problems including a higher incidence of disease, poor reproductive performance, or suboptimal milk production. Mycotoxins exert their effects through 4 primary mechanisms:
- intake reduction or feed refusal,
- reduced nutrient absorption and impaired metabolism,
- alterations in the endocrine and exocrine systems, and
- suppression of the immune system.
Recognition of the impact of mycotoxins on animal production has been limited by the difficulty in diagnosis. Symptoms are often non-specific and can be the result of a progression of effects, making a diagnosis difficult or impossible because of the complex clinical results with a wide range of symptoms.
Mycotoxins can be the primary agent causing acute health or production problems in a dairy herd, but are more likely to be a contributing factor to chronic problems including a higher incidence of disease, poor reproductive performance, or suboptimal milk production. [Photo: Jan Willem Schouten]
Link mastitis and mycotoxins
Mastitis is a multi-factorial disease which is defined as an inflammation of the mammary gland. Mastitis usually occurs primarily in response to intramammary bacterial infection, but also to intramammary mycoplasmal or fungal infections. Mechanical trauma, thermal trauma, and chemical insult predispose the gland to intramammary infection. The occurrence of mastitis depends on the interaction of host, agent, and environmental factors (Zhao and Lacasse, 2007). The cow, the bacteria, the management, and the environment all play a role in the risk of mastitis, and hence in the prevention and control of mastitis. Some bacteria have adapted to long-term survival in the host without severe disease symptoms. These bacteria usually spread in a contagious manner from cow-to-cow, and identification and removal of infected cows is the key to control this type of mastitis. Other bacteria have adapted to environmental survival and cause opportunistic infections, sometimes with severe clinical symptoms when they are present in large numbers, or when the host is immuno-compromised. SCC taken on bulk tank milk are a good indicator of the general state of udder health in the dairy herd. Somatic cells in milk consist mainly of white blood cells produced by the cow to destroy bacteria which cause mastitis that enter the udder and to repair damaged udder tissue. These cells are always present in milk but when an infectious agent enters the udder or when the udder is damaged, the number of somatic cells shed by the individual cow increases. Tissue damage and the increased SCC resulting from mastitis infection can block the tiny milk ducts in the udder, resulting in lower production when the milk secreting cells above the blockage are dried off. An estimate of milk production loss as predicted from bulk tank SCC is given in Table 1.
Based on this table, herds with cell counts over 500,000 SCC could be producing from 8 to 18% below potential because of the presence of sub-clinical mastitis infections (www.omafra.gov, 2011). The maximum legally allowed SCC in the US is 750,000/ml. This limit is high compared to many other international standards. Most of Europe, New Zealand, and Australia have a limit of 400,000/ml and Canada has a limit of 500,000/ml. Mycotoxins are also known to be responsible for immune system functions modulation. It is known that mycotoxins decrease the resistance of different animal species to diseases and increase the incidence of metabolic disorders in ruminants.
Economic evaluation of mycotoxin management
Production losses due to mycotoxin contamination are subject to a number of factors and uncertainties. The losses are hugely variable in time and difficult to estimate. However, the effects of the contamination are often significant and can be long lasting.
The economic impact of mycotoxins is difficult to estimate even after an outbreak of mycotoxicosis. The most important losses are probably those associated with long-term under-performance. Estimates of this can be made on the basis of the information provided earlier. Thus a simple simulation model was developed that allows for the estimation of production and financial losses due to the long-term sub-clinical impact of mycotoxins in dairy cattle.
The following assumptions were made:
- No change in DMI or loss in milk production volume. A decrease of 0.4 %-point in milk fat and 0.1 %-point in milk protein.
- No penalising change in SCC, thus assuming almost ideal sanitary conditions of cows.
- An increase in calving interval of 60 days and an increase in inseminations by 10% along with an increase in veterinary cost of 10%.
- Application of an efficient mycotoxin deactivator restores losses by 80%.
Under these assumptions the model predicts that on a herd-basis mycotoxin contamination will cause losses in milk income of approximately 12% and that the addition of an efficient mycotoxin deactivator will restore losses to just 3% under the income level achieved in the absence of mycotoxins. Total farm revenue changed with similar percentages but variable costs or the operation costs increased by 3% in the presence of mycotoxins. The annual return over variable costs decreased from 14.5 to 7.6% due to the presence of mycotoxins. The cost of the mycotoxin deactivator for a continuous treatment throughout lactation and dry period was estimated at US$ 28/cow. The application of this mycotoxin treatment lead to an improvement in returns over variable cost to 12.3% due to an improvement in revenue of US$ 225/cow. Consequently, the return on investment (ROI) of the use of a mycotoxin treatment is approximately 7:1.
The assumptions associated with these simulations are considered to be rather close to the current US operational conditions. The model can be adapted to other economic situations; for instance those applicable to the EU, Middle East or Latin America. However, following a number of simulations, it appears that the economic returns of mycotoxin deactivators under conditions where contamination is suspected will easily be equal or superior to the rather conservative estimates obtained with these analyses.
Strategies to control mycotoxins
The best practical way to control mycotoxin levels is to use rapid test kit systems for the analysis of mycotoxins in raw ingredients which are not yet in silos. Different rapid test kit systems are validated for different mycotoxins and commodities offering a very quick and effective way of raw material screening before they enter the feed mill.Once the levels are known, every feed mill can estimate the quality of its raw ingredients in terms of mycotoxin contamination and can effectively and more precisely (by dosage adjustment) apply feed additives during feed production.
Another strategy of mycotoxin risk management is to test for the presence of mycotoxins in finished feeds including TMR (total mixed ration) and silages. This method has some advantages and disadvantages. Since each raw ingredient can bring its own mycotoxins into the finished feed, the most important advantage is that the presence of raw ingredients with a low inclusion rate (5-10%) which can still cause significant contamination of the finished feed but can be inadvertently overlooked if not tested can be identified by testing the finished feed. The most important disadvantage is that analysis of finished feed takes quite a long time such that the tested feed is likely to have been fed to the animals by the time tshe results from the analysis are known.
Storage mycotoxin contamination (ochratoxins, aflatoxins) can be prevented by keeping temperature and moisture content in silos low whilst aerating the grain regularly. In cases where perfect storage conditions cannot be guaranteed, the use of mould inhibitors and silage inoculants is highly recommended. The application of specific feed additives (mycotoxin deactivators) which are able to help reduce the negative effects of different mycotoxins in dairy cows is highly recommended.