Rise in milk production
Cows are genetically selected for efficiency, resulting in modern animals that are highly productive, but at the same time very fragile and demanding. Twenty-five years ago, the average dairy cow produced 6,029 kg of raw milk per year. Twice-a-day milking was the norm, and bovine growth hormones were an emerging topic of debate. Today’s modern dairy cow produces an average of 9,681 kg of milk each year, a 61% increase in a quarter of a century. That means the average modern dairy cow weighing 680 kg may produce close to 5% of its body weight in milk per day of lactation. Growth hormones and three-times-a-day milking are major factors in the increase in milk production, as are high-energy feed rations and genetic selection for animals with the highest milk outputs.
There is an increasing global thirst for milk and milk based products. The forecast is that milk production will increase considerably, driven by consumer demand in emerging markets. The International Farm Comparison Network (IFCN, 2016) forecasted an increase in milk production of 54% in India, 43% in Africa, 27% in China and 43% in Brazil (Figure 1).
Meeting this growing demand requires upgrading many aspects of dairy farm management. New feeding strategies have been developed and new additives have become available to effectively increase animal efficiency, control the rumen environment and prevent damage caused by the presence of anti-nutritional factors in the feed.
Figure 1. Forecasted increase in milk production around the world
Feedstuffs are variable in quality
Dairy cows rely on energy, protein, minerals and vitamins for milk production, making the quality and composition of feedstuffs essential. However, the nutritional composition of cereals and oilseeds is very variable and sometimes inadequate to satisfy a modern cow’s requirements, jeopardizing profitability. Variability can occur in protein content, mineral value and amino acid profile.
One of the main protein sources for dairy cows, soybean meal, fluctuates in its nutritional value depending on its source. García-Rebollar et al. (2016) tested 500 samples of soybean with three different origins (US, Argentina and Brazil) in a nine-year comprehensive study. As expected, the study showed a huge variation both between samples from the same area and between samples from different origins—a direct consequence of different cultivars, climate conditions and soil characteristics.
Preservation method and microbiological characteristics are important determinants for the nutritional quality of feedstuffs. For example, corn loses some of its nutritional value when infected with mold. The contaminated grains have a lower protein content (falling from 9% to 8%), lower fat content (from 4% to 1.5%) and consequently contain lower levels of energy (Tindall, 1983).
Representative forage sampling is a challenge
Forages are essential feedstuffs for dairy and ruminants in general. Roughage is a necessary component of the ruminant diet to maintain good rumen health and efficiency. Forages are much more variable than cereals, not only in their chemical composition, but also in terms of digestibility and their ability to stimulate rumination. However, forage sampling is complicated due to the inhomogeneous distribution of nutrients.
Given the double function of forage (nutritional and mechanical), mistakes in evaluating forage quality can have severe consequences. The dry matter of corn and grass silage varies considerably over time. Wet forage should be analyzed each week to prevent overestimation of dry matter intake. However, this analysis is often overlooked and, considering the high inclusion levels of wet silage in dairy rations, the risk of energy deficiency and lack of effective fiber can be severe, quickly compromising animal performance and health, and predisposing animals to ketosis and other metabolic diseases. The evaluation of neutral detergent fiber (NDF) and its digestibility can be crucial. Overestimating the NDF content can increase the risk of sub-acute ruminal acidosis (SARA) in high-producing and fresh cows, while underestimation can slow down the transit time of forage in the rumen and consequently limit feed intake. In this situation, the dairy cow will be at risk of falling into a negative energy balance. SARA is a pathology that can negatively influence production and health. It stems from an excess of fast fermenting carbohydrates in the diet, a common feeding technique to meet the high energy demands of modern lactating animals. Increasing chewing activity by providing effective sources of fiber is one of the most reliable strategies to control SARA. In this regard, wheat straw is a good and economically effective fiber source that is often widely available at farm level. Unfortunately, wheat straw is one of the forages more likely to be contaminated with mycotoxins (Figure 2).
Figure 2. Mycotoxin contamination in straw. The dark blue shading indicates the proportion of samples for which the mycotoxin level exceeded the risk threshold for ruminants (% value given in brackets).
The threat from anti-nutritional factors
Grains and forages are not only a source of nutrients; they can also hide many threats such as naturally occurring antinutritional factors. Some can be mitigated with technological treatments (e.g. antitrypsin factors) but some can persist or even increase during storage. Mycotoxins, secondary metabolites from fungi and molds, are one example of anti-nutritional factors that can survive storage and cause problems to animals.
A recent survey showed that the majority of the 170,000 known natural metabolites have fungal origins (Gruber- Dorninger et al., 2016). Some fungal metabolites have pharmaceutical uses like penicillin. Other components, such as ergot alkaloids, have both poisonous and pharmaceutical properties. Some mycotoxins, such as aflatoxins and trichothecenes, are potent poisons for dairy cows. A wide range of grain and forages can be contaminated by mycotoxins, of which more than 400 strains have been identified to date. The 2017 BIOMIN World Mycotoxin Survey, the broadest and most comprehensive analysis of global mycotoxin occurrence, showed that the risk of mycotoxin contamination remains high for fumonisins, with deoxynivalenol and other trichothecenes being the most commonly occurring mycotoxins globally.
The presence of mold on feedstuffs does not indicate mycotoxin contamination, but it does indicate that the potential for contamination exists. On the contrary, the risk of contamination in feedstuffs that appear clean or mold-free cannot be excluded. Mycotoxins themselves are invisible to the naked eye so visual detection is not possible.
The economic effects of mycotoxins on animal performance are clear. The rumen is the most important organ in dairy cow digestion, and the composition of feedstuffs affects its function and metabolic activity. The liver is another important organ for cow nutrition, and its efficiency and health can affect performance. Mycotoxins are perhaps the main anti-nutritional factors, having a direct negative effect on both the rumen and the liver as well as many other organs (Figure 3).
Many scientific articles have shown that mycotoxins pose a real risk. For example, Abeni et al., (2014) showed that a combination of aflatoxins and fumonisins was able to reduce the growth rate and increase the age of the first estrus in heifers. This delay was due to chronic liver toxicity, which reduced the liver’s ability to produce glucose.
Deoxynivalenol, the most frequently occurring mycotoxin worldwide, can reduce rumen function, microbial production, metabolizable protein availability and flux of essential amino acids to the intestine (Danicke et al., 2005). Therefore, in case of the presence of trichothecenes in feedstuffs, nutritionists seem obliged to increase protein levels in the diet in order to maintain milk production levels, which is an expensive proposition.
Figure 3. Effects of mycotoxins in ruminants
Mycotoxin management in three simple steps
Feedstuffs can sustain milk production and provide nutrients. However, feedstuffs have two main drawbacks: variability and high mycotoxin contamination. While it is not possible to eliminate either, these steps can help reduce the risks:
Step 1. Analyze feed regularly.
It is important to understand the risk associated with each feedstuff, and to assess them for anti-nutritional factors. Analysis of feedstuffs for the presence of mycotoxins is common practice and a high priority, especially in view of the worldwide prevalence of fungal metabolites.
Step 2. Store feed properly.
Ensure proper preservation of feedstuffs to achieve a more stable nutritional composition over time. It will also reduce the growth of storage mycotoxins.