Over the past few weeks we have certainly seen some extreme weather conditions around the world.  Those on the east coast of North America have been hit by record cold temperatures.  At the same time, those in Australia have been experiencing record hot temperatures.  These extreme weather conditions have many wondering what effects “Global Warming” will have on the dairy cattle  There has been lots of coverage in the media about  dairy cattle and their alleged contribution to greenhouse gases and how that is contributing to Global Warming.  Very little has been addressed about the effects extreme weather conditions have on the dairy cattle themselves.  One thing appears certain.  Extreme heat waves and cold fronts are the new ‘normal’.

As producers know, cow and calf comfort is one of the most important factors in milk production and growth.  As more and more producers are experiencing extreme temperatures, keeping their animals comfortable is becoming harder.  Drastic increases or decreases in ambient temperature affects animal production systems by affecting the health, reproduction, nutrition etc. of the animals and thereby results in poor performance, inferior product quality, outbreak of novel diseases, etc.  Dairy cattle are   more susceptible to increased ambient temperature than other ruminants, because of their high metabolic rate and the poor water retention mechanism of their kidney and gastrointestinal tracts.  Young stock are not immune to these weather stresses either.

Greater temperature shifts and shifts that are more frequent seem to be the most obvious weather changes that will have effects on dairy cattle.  It is forecasted that we can expect even greater atmospheric temperature changes.  Therefore these issues are going to come to the forefront.  The following are the five major impacts   that global warming will have on dairy cattle.

  1. Ambient temperature’s effect on Dry Matter Intake (DMI)
    When cows are stressed their Dry Matter Intake (DMI) decreases.  As the heat rises DMI decreases.  Feed consumption by dairy cattle starts to decline when average daily temperature reaches 25 to 27 Centigrade  (77 to 81 Fahrenheit) and voluntary feed intake can be decreased by 10-35% when ambient temperature reaches 35 C (95 Fahrenheit) and above.  Conversely, cows that are experiencing extreme cold weather conditions increase their DMI intake drastically, but instead of the consumption being converted in to milk production, a much larger portion of their energy is committed to their maintenance energy requirements.  Thermal cold stress conditions result in 20-30% more maintenance energy requirement and an ensuing reduction in the amount of net energy available for growth and production.
  2. Increased respiratory rate
    When dairy cows experience increased thermal stress, their heart rate rises.  The heart rate of the animal under thermal heat stress is higher to ensure more blood flow towards peripheral tissue to dissipate heat from the body core to the skin.  This increased effort takes much needed energy away from milk production.  Respiration rate of the animal can be used as an indicator of the severity of thermal load but several other factors such as animal condition, prior exposures to high temperature etcetera should be considered to interpret the observed respiration rate.
  3. Decreased conception rates
    As weather stress increases, dairy reproduction function decreases, resulting in decreased conception rates.  This is a result of thermal stress that causes imbalance in secretion of reproductive hormones.  High ambient temperature has also been reported to increase incidence of ovarian cysts.  Plasma progesterone levels in animals under high ambient temperatures are low compared to animals that are experiencing thermal comfort.  It has also been reported that high ambient temperature causes poor quality of ovarian follicles resulting in poor reproductive performance in cattle.  Fertility of cattle is also reduced due to low intensity and duration of estrus caused by reduced luteinizing hormone (LH) and estradiol secretion during thermal stress.  In addition, thermal stress also causes decreased reproductive efficiency by increasing the calving interval. Calves born from dams under thermal stress were found to be of lower body weight than those from normal cows.  Additionally the dams had reduced lactation performance due to the carryover effects of thermal stress which occurred during the prepartum period.
  4. Decreased Metabolic Responses
    Under heat stress metabolism is reduced, which is associated with reduced thyroid hormone secretion and gut motility, resulting in increased gut fill.  Plasma growth hormone concentration and secretion rates decline with high temperature (35 ºC / 95 ºF).  Ruminal pH is typically lower in heat stressed cattle
  5. Decreased Milk Production
    Reduction in milk production is one of the major economic impacts of climatic stress upon dairy cattle.  Decrease in milk yield due to thermal heat stress is more prominent in Holstein than in Jersey cattle (Read more…).  Decreased synthesis of hepatic glucose and lower non esterified fatty acid (NEFA) levels in blood during thermal stress causes reduced glucose supply to the mammary glands and results in low lactose synthesis, which in turn leads to low milk yield.  As mentioned earlier, reduction in milk yield is further intensified by decrease in feed consumption by the animals to compensate for high environmental temperature.  Actually 35% of reduced milk production is due to decreased feed intake while the remaining 65% is attributable directly to the thermal stress.  Other factors resulting in reduced milk production during thermal stress are decreased nutrient absorption, negative effects on rumen function and hormonal status and increased maintenance requirements.  These all mean that there is reduced net energy available for production.

To combat heat stress check out these articles (Read more: Are you feeling the heat?  and Heat Stress on Dairy Cattle) and to combat cold stress (Read more: COMMON SENSE, COWS and the UN-COMMON COLD of 2014!“COLD CALVES” – The Next Drama Coming to a Calf Pen Near You! and Cold Weather Effects on Dairy Cattle)

The Bullvine Bottom Line

There is no question that the world’s temperatures are changing because of atmospheric pressure changes caused by Global Warming.  Warming or cooling of the climate system of the earth has multifaceted effects on animals.  Intensification and increased frequency of thermal stress due to global warming has the most prominent impact on dairy cattle and causes   different physiological, metabolic and production disturbances.  The importance of responding to thermal stress has been increased for dairy farmers in tropical, subtropical and even in temperate regions of the world due to atmospheric warming.  As these effects increase, it will be increasingly urgent for the milk producers of the world to provide environments that are able to combat these effects and offer the greatest comfort for their cattle.  Global Warming is actually Global Warning for the dairy industry.


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