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MANAGEMENT MATTERS


KEEPING COWS COOL... ...SOME HOT TIPS


It’s summer and we’ve already had some hot weather. While frequent weather checks were made before silage making, when did you last look at the forecast for temperature and humidity levels that will impact on cow stress levels?


C


Bryn Davies ows’ ideal


temperature range is between -40 180


C, by the 200 to 260


C and C


C mark then


potential heat stress situations occur. At 320


C you will notice dramatic effects – feed intakes fall and consequently milk production. High levels of humidity, 80% or above, can compound the stress levels, and it’s the high yielding cows that are the most sensitive.


Why? Because the rumen generates heat in its normal mode of action, much like a furnace. The more feed


you put in, the more heat it produces. So as we strive to maximize dry matter intakes, we are also maximizing heat output. Feed passage rates and gut motility slow down and, in turn, dry matter intakes fall, by up to 33% in severe conditions, yields start to drop, acidosis creeps in and butterfats start to tail off.


What to look out for: •


Excessive respiration - 80 to 100 breaths per minute, panting and salivating


• Increased body fl uid loss - water intakes may increase by up to 33%


• Raised body temperature Reduced forage intakes





• Reduced immune function, leading to greater risk of exposure to mastitis pathogens


What to do: •





• Check the weather forecast and be prepared for heat. Clean all water troughs in readiness, inspect and clean daily


throughout high temperatures; ideally make 7.5cm of linear water trough space available per cow, add water to the TMR if it allows.


Install fans the full length of the collecting yard – the main area


of increased stress where cows are in close proximity of each other. Introduce a misting spray at the parlour entrance. • Aim for cool air moving across the cows when resting; open up shed sides, remove Yorkshire boarding and replace with netting or Galebreaker material


• Install fans in sheds to move air wherever possible.


• •


If necessary, cover skylights if an excessive


number of them are south facing. Feeding high quality forage, it’s imperative


to counter the reduced intakes. Also remember poorer forages take more chewing, which increases heat production and adds to the work load. • Include more rumen protected fat to increase the energy density of the diet; specifi c fats will allow us to go up to 1 kg per cow per day.


• Balance the diet with less grain to be more sympathetic towards rumen function. Potentially keep starch and sugar levels to 20% of DMI.


• Increase potassium to 1.5% and sodium to 0.5% of the total diet DMI. These minerals must be replenished because potassium is lost with sweating and sodium with increased urine production. Both these minerals will effect the animals base DCAB level - we talk about potential minus DCAB levels in dry cows, well we need to have positive DCAB levels in high yielding milk cows.


Some more hot points


• When cows get stressed and their core temperature rises, it can take four hours after milking before it falls to normal. • Cows sweat at only 10% of the human rate so are slower to cool down. • Although cows do not have many sweat glands, they will sweat a certain amount during hot weather and lose electrolytes. Heat-stressed cows can become potassium defi cient, which in turn increases blood acidity. These cows can also increase blood pH by increasing the dietary cation- anion difference (DCAD), according to latest research fi ndings. This is the difference between the amounts of positively charged cations, in particular sodium and potassium, in the diet and the negatively charged anions, especially chloride and sulphur, in the diet. Raising DCAD increases the ability of the cow’s blood to buffer acids and this raises blood pH and reduces acidity. A target fi gure of +350 mEq/kgDM is recommended. Keeping cows cool requires more attention to detail, however it will enable them to maintain overall performance, as well as their dignity.


THE JOURNAL AUGUST 2010 83


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