With the madness of Spring calvings and lambings well and truly over and Summer marching on past the longest day, we are back at that time of year to reflect on the previous breeding season and start looking ahead to the next one.

At the time of writing, Southern Europe is set for record-breaking temperatures to be reached this week and we are certainly noticing the effects of a hot, dry June on dairy cattle conception rates. Whilst it is unlikely that we will be experiencing such extreme temperatures in the UK, it is worth considering the impact of heat stress on Spring calving beef cattle – who are predominantly grazed outside – with little control over the effects of the weather during the service period. It is inevitable that we need to be prepared in the future for prolonged periods of uncharacteristically hot Summers on the national beef suckler herd.

Cows have a lower comfortable body temperature than humans, with the upper limit at around 25°C. Once the temperature goes outside of their ideal range, they will change their behaviour in order to keep their core body temperature normal. This is ‘heat stress’ which can range from mild to severe depending on many factors. Humidity also plays a big part in this; as the relative humidity rises, the less they can tolerate temperature increases. Animal’s that are likely to show signs first are bulls; cattle that are darker coloured, heavier or thicker coated; as well as those that have had previous pneumonia challenges.

Heat stress will negatively impact cattle performance in several ways:

  • Feed intakes
  • Reproductive performance in cows and heifers
  • Growth Rates
  • Bull Fertility

Tips to optimise fertility for grass fed beef cows in hot Summers:

  • In a ‘normal’ year the spring grass should provide enough energy for a cow to maintain condition, produce milk for the calf and to achieve good daily live weight gain in the calves, as long as it is not grazed below 4cm tall. Below this the grass in unlikely to be providing the energy requirements needed and the grass growth will take longer to recover for future grazing.
  • Increased temperatures cause a decrease in appetites and therefore dry matter intakes. For some animals, in particular in-calf and first calved heifers, this will mean that they cannot successfully grow a calf and maintain a good enough body condition to maintain a pregnancy. During dry periods place bales of straw in fields for additional feed. If straw intake exceeds 2kg per head per day, supplementary feeding will be needed to maintain condition and performance. (Source: BRP+ managing cattle and sheep during extreme weather conditions, AHDB)
  • Fertility in beef cattle is highly correlated to nutrition and body condition score. Consider weaning calves from thin cows/heifers earlier (around 6 months) to allow more time for improvement of body condition for the next pregnancy.
  • Consider creep feeding calves to increase grass availability for the cows and prevent loss of condition in the cows during the early breeding season. Feed Conversion Efficiency is greatest in younger animals, so this is often more economic than having to feed additional forage to adult cattle once the grass runs out!

Table 1: Average consumption of water for different classes of livestock

Source: AHDB managing-cattle-and-sheep-during-extreme-weather-events

  • Reserve your best grazing for 1st calved heifers who have been rearing calves whilst not having reached their mature bodyweight themselves, and for thinner/poorer conditioned cows.
  • Reserve your best grazing for 1st calved heifers who have been rearing calves whilst not having reached their mature bodyweight themselves, and for thinner/poorer conditioned cows.
  • Semen quality can be affected for up to 8 weeks after as little as 12hours exposure to acute heat stress in bulls. Extreme heat will also alter bull behaviour e.g. more lying down, seeking shade etc which will impact on the number of cows served.
  • Oestrus activity in cows and heifers can be affected by hot weather so cattle which are returning may not be as easily detected.
  • Extreme heat can also influence hormones involved in the oestrus cycle which can favour multiple simultaneous ovulations and can result in an increased twinning rate. If you are seeing an unusual number of twins born in a short space of time (with no change in sire genetics) it is often interesting to look back at the weather during the previous service period!

You should be aiming for around 2/3 of your herd to calve within the first three weeks of the breeding period. This means that any influence on fertility can have a noticeable impact on the calving pattern. If there is much variation around this at scanning time, it will at least allow for planning around expected calving dates and also pinpoint where there may have been issues during the service block which may warrant further investigation. Scanning your beef cattle early (at least 5 weeks after bull removal) is a worthwhile investment to pick up any barreners to avoid having to house and feed these ‘freeloaders’ over winter.