Stress - health and productivity

Stress in dairy cattle

Like humans, the chronic effects of stress from poor welfare levels can lead to adverse metabolic changes in the dairy cow and can have significant effects on their health and productivity. Cattle are susceptible to a variety of psychological stress factors; rough handling can cause them to become apprehensive of people and to be stressed in their presence, and poor housing conditions can lead to illnesses which may be directly linked to stress.

Stress causes the release of various hormones, which are part of the cow's natural 'fight or flight' mechanism, evolved over time as a response to dangerous situations. These hormones, such as cortisol (hydrocortisone) and adrenalin help to prepare the cow's metabolism for the dangers it may have had to face, by, for example, increasing its heart rate and breathing, to help it to escape a predator. Acute stress at milking time, for instance, is most obviously apparent in a reduced milk yield resulting from the release of adrenalin, leading to incomplete milk let-down and increased residual milk.

Other times when animals regularly experience these metabolic changes through stress can occur when in oestrus, at calving time, when being transported, when being moved from one building or cow group to another, or when cows are being handled in out-of-routine situations.

Chronic stress, where poor environmental conditions have a longer-term effect, can lead to various metabolic systems such as the immune and reproductive systems being adversely affected by the production of cortisol. This suppression of the immune system can lead to an increased incidence of mastitis and higher Somatic Cell Counts. Chronically-stressed cows become more prone to infections, and because their yield may decrease - caused by poor milk let down as well as reduced appetite - the presence of larger numbers of white blood cells is further concentrated in the milk.

Improving the handling of livestock, livestock housing and general animal welfare can help to reduce the negative effects of stress in dairy cattle. Some key aims are:

  • Reducing apprehension in the herd by minimising rough handling practices, such as shouting, slapping, punching, hitting with the hand or stick and tail twisting. The increased gentle handling of younger cattle has been shown to reduce the fearfulness of cattle towards people.
  • Reducing stress levels that may be caused by poorly-devised routines or situations that can lead to adverse and overly-aggressive handling of livestock, including frustration and impatience with animals, difficulties in moving cattle due to poor building layout, time pressures and equipment not working properly.
  • Recognising that the quiet, empathic handling of cows at milking times can lead to shorter let-down times, shorter milking times, more efficient milking and reduced potential of teat end damage.
  • Recognising that cows can be bullied by other herd members when housed, resulting in them not being able to get sufficient food or water. Attention to adequate loafing areas, numbers of cubicles and stocking densities is important in this respect, as well as understanding the social hierarchy of the herd.
  • Being aware of how a poor housing environment can affect stress levels, from poor ventilation and heat stress in particular.

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