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Strategies for tackling summer challenges

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article image Trish Lewis facing summer challenges

Three key challenges faced by dairy farmers in summer are lower pasture quality and supply, heat stress, and mycotoxin issues, all of which have a negative impact on feed efficiency.

Pasture quality

Young leafy pasture has a low neutral detergent fibre (NDF) content which helps maximise feed intake, and a high content of rumen degradable protein (RDP). As pasture matures, the NDF percentage increases and the RDP percentage falls. If there is also less pasture available due to dry weather, this often results in an even lower amount of RDP in the diet.

Diet formulators are faced with the challenge of balancing the diet to ensure cows’ requirements are met, and feed intake and production are maintained. One tool in their armoury is to add a live yeast supplement to the diet to improve feed intake and increase fibre digestion when pasture NDF percentage rises. Another is to include protected urea in the diet to provide a steady supply of nitrogen (N) which rumen microbes can utilise for microbial protein production. Optigen II is a slow release non-protein supplement for cows. This will help to maintain a good supply of microbial protein for the cow even when pasture quality drops and feed intake falls. Both strategies can assist feed efficiency.

Heat stress

Even at low levels of humidity, temperatures above 26 °C can cause problems. Heat stress, even at a mild level, can have significant effects on productivity. Higher producing cows are more affected because they generate more heat while digesting the extra feed required for higher milk yields.

Heat stress also impacts overall health and fertility. As few as 10 percent of inseminations in heat stressed cattle result in pregnancies, and cows that are stressed in early lactation show poorer fertility two to three months later, due to impaired follicular development. Heat stress also lowers feed efficiency due to reduced feed intake and impaired rumen function.

 Nutritional strategies for tackling heat stress include:

  1. Ensuring a good water supply at all times
  2. Feeding more during cooler periods
  3. Increasing energy and protein density to counter lower feed intake
  4. Increasing fibre quality
Feeding lower NDF forages helps encourage feed intake and reduces heat production in the rumen, but it also increases the risk of sub-acute rumen acidosis (SARA). Heat stressed cows are also more prone to SARA due to reduced buffering from saliva, thus rumen buffers are important. Live yeast has been shown to improve the stability of rumen pH, reducing build-up of lactic acid. A proven product such as Yea-Sacc®1026 would suit this purpose.

When feed intake drops, it is also important to increase the density of minerals, trace elements and vitamins in the diet to ensure requirements are met. Sufficient potassium, sodium and magnesium are needed as unlike humans, cows sweat potassium more than sodium. Heat stressed cows also experience more oxidative damage to cells, so anti-oxidants such as vitamin E and selenium dependant enzymes have an important role to play in maintaining cow health. Sel-Plex® is a safe source of organic selenium and can help to maintain the immunity status of the cow.

Mycotoxins

Mycotoxins are microscopic poisons produced by moulds as part of their defence mechanism. Not all moulds produce mycotoxins, and those that do only do so sporadically, but where there is mould there is risk. Mycotoxins can be produced either by moulds growing out in the paddock or by those growing on silage or other stored feeds. When moulds die off their mycotoxins remain in the feed. Most moulds grow faster in warmer environmental temperatures which is why more mycotoxin issues are seen in summer.

Mycotoxins can produce a range of symptoms in dairy cows, the most common being reduced feed intake, reduced immunity (more infectious diseases seen), a drop in milk production and a rise in somatic cell count (SCC). Some mycotoxins cause swellings, behavioural changes or disrupted fertility. Mycotoxins invariably reduce feed efficiency. Rumen microbes can detoxify some mycotoxins, but this ability is impaired in high yielding or heat stressed cows or when silage mycotoxins are present.

Strategies for reducing the risk of mycotoxin issues include:

  1. Remove any contaminated feed from the diet.
  2. Where this is not possible, dilute it with clean feed. Calves, transition cows and high yielding cows are the groups most vulnerable to mycotoxins so they should be fed the cleanest feed. Good silage management, use of a proven silage inoculant and clean storage of feeds can all help. Care is needed to ensure purchased feeds are not contaminated, particularly in years with difficult harvest conditions.
  3. Another strategy is to add a mycotoxin binder to the diet. Mycotoxin binders adhere to mycotoxins in the digestive tract and prevent them from being absorbed into the bloodstream. It is important to select a product well proven to swiftly adhere to a wide range of mycotoxins. Yeast based products such as Mycosorb® can be fed at a lower feed rate than clay products and do not bind other nutrients in the diet.
  4. Testing for mycotoxins is expensive and can be unreliable due to the difficulty in getting a truly representative sample.  Mycotoxin binders are frequently used as a diagnostic tool to check whether mycotoxins are affecting performance.

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