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The effects of stress on Reproductive performance

The banning of inductions has focused attention on a shortened mating period to prevent a prolonged calving season.

A reduced mating period has inevitably increased empty rates – mating cows with a 53 percent conception rate for only 10 weeks as opposed to 13 weeks will tend to double empty rates with all things being equal. Cows are being tail painted through September to detect cycling cows – identifying and reducing stress may be one thing to consider to increase future fertility and profitability. In both humans and animals some stress is probably good for performance – it helps humans get out of bed in the morning and drives us to achieve goals throughout the day. Sometimes life throws us more challenges than we can cope with and we get overly stressed – we try to compensate by working harder but often productivity and output declines and we succumb to health problems to which we would normally be resistant.

I see the same thing in dairy cows,which are incredibly productive and robust but sometimes struggle to cope with additional, unexpected challenges – and fertility is one of the casualties. Metabolic diseases like milk fever, disorders such as retained fetal membranes, infected or damaged uterus and diseases such as BVD may all work against them and lower conception rates. Seemingly small stresses like changes to the dairy shed, the pressure of backing gates, deterioration of raceways or increase in walking distance each day may be enough to make vulnerable animals such as first calvers, older cows and later calving cows less fertile. Good nutrition is essential to help animals cope when stresses rise. Cows below the ideal BCS at calving take longer before they start cycling and the better fed the cow is after calving the sooner she will start cycling.

Supplementing energy intake from around 6 weeks after calving may improve fertility in cows that would otherwise be underfed. Cows that are gaining weight over mating are more likely to get pregnant than cows that are losing weight. Cows should be regularly body scored to ensure targets are being met.

Wet and cloudy weather reduces the energy from pasture, so a poor late spring and early summer are likely to impact on submission rates. Replacing the energy lost in pasture may be possible if supplementary feed rates can be increased or higher energy feeds like rumen protected fats can be introduced to minimise weight loss through mating.


Some tips to reduce nutritional stress over mating:

  • Avoiding excess condition loss and changes in feed intake.
  • Monitor fat to protein rations in the milk as an indication of how cows are coping – a falling ratio may indicate weight loss.
  • Falling milk urea levels through mating could indicate sub-optimal protein levels in the diet related to changes in pasture quality.
  • Avoid additional challenges like salmonella by cleaning out feed troughs regularly.
  • Trace mineral deficiencies can cause anoestrous, increased risk of uterine infection and early embryonic death, so regular monitoring pre-mating can identify problems early.
  • Bovatec® can aid in the control of ketosis with subsequent improvement in immune function, which can aid in reducing the incidence of clinical mastitis in lactating dairy cows so may indirectly effect fertility.
  • Consider supplementary phosphorus if cows have had a hard winter.


For further information, contact your local Nutrition Specialist.

Article supplied by Dr. Rob Derrick, Nutritionist.