“In hot conditions, cattle can become unproductive, overheat or die”.
Those words are from the opening line of a paper in the Journal of Agricultural Engineering Research published in 2000 by two colleagues - Rod McGovern and Jim Bruce. They had produced a model of the thermal balance for cattle in hot conditions and concluded that in hotter conditions, feed intake would be reduced, and production would fall.
Since then, we have also come to understand that there is an earlier negative impact of hotter conditions/heat stress. Namely, that is the reduction in fertility (RIDBA Journal 2021: Vol 22, Edition 1). Their thermal model included air temperature, humidity, wind speed and radiation, together with metabolic heat production from the animal.
Metabolic heat is lost from the body in a variety of ways. They include conduction from the body core to the skin, from the skin by convection, by long-wave heat transfer by radiation, and by latent heat loss via respiration and sweating.
Table 1 shows the results of instantaneous heat balance simulations at four different air temperatures.
| Example | 1 | 2 | 3 | 4 |
| Air temperature oC | -10 | 15 | 30 | 40 |
| Heat production W/m2 | 122 | 122 | 122 | 80 |
| Respiratory heat W/m2 | 47 | 12 | 74 | 73 |
| Stored heat W/m2 | 0 | 0 | 0 | 83.5 |
| Evaporation from skin W/m2 | 17 | 142 | 116 (max) | 181 (max) |
| Convective heat loss W/m2 | 15 | 59 | 45 | 28 |
| Heat flux through coat W/m2 | 102 | 11 | -24 | -75 |
| Respiration rate, breaths per minute | 12 | 12 | 59 | 86 (max) |
| Rise in body temperature oC | 0 | 0 | 0 | 1.2 |
Solar radiation can be added to the model to give results for the expected impact of solar gain (or shading) delivered at stated angles, wind speed, cloud cover, latitude, albedo, the emissivity of the animal and the reflectance. Many of these terms will be familiar to building engineers, but what is the result?
In cold weather - example 1 in Table 1 - convective heat losses are reduced by vasoconstriction but losses through the hair coat are high. In example 3, respiration rate increases to dump more energy as moisture and in example 4 the body starts to acquire heat and body temperature rises. In reality these cattle will already have adapted but with resultant losses to fertility, then feed intake, and then milk production. The impact of the summer which we’ve just experience in the UK on cattle was, and is, predictable.
The daily – or diurnal - pattern of air temperature can lead to a predictable pattern of heat stress in livestock, and a more recent study with young calves at Iowa State University (Appuhamy, et al. 2021 “The Effects of Diurnal Heat Stress in Dairy Heifer Calves”) describe further impacts.
The study shows that although feed intake increased at night to balance the reduced feed intake during the heat of the day, average daily liveweight gain and feed efficiency decreased significantly during periods of diurnal heat stress. They considered these effects are a likely consequence of nutrients being moved towards an activated immune system and away from productive processes. They also report that water intake per unit of feed consumed also increased significantly during diurnal heat stress.
We do need the science to inform us, and we don’t need the science to inform us. When it gets hot animals consume less food and drink more water and may have reduced immune competence. What a surprise! But heat and water are issues that have been tackled with different levels of precision around the world and this summer will have shaken UK livestock producers - hopefully into an acceptance that what is predictable can also be managed better. We have plenty of information on how to better manage heat and water in the UK’s livestock buildings, but we need to acknowledge the issues first, and work out what it costs to get it wrong.
A recent query involving a new build pig unit threw up the interesting detail that for the month of July 2022 the water consumption in the farrowing rooms increased by 20 litres per pig, per day, compared with the average of the previous three months. That is 37 m3 for the month on this particular site - from drinking water intake increasing to the smart pigs throwing water everywhere to keep cool. Of course, this also adds to slurry volumes. Dairy cows dramatically increase the volume of water intake in warm weather and pigs and poultry show clear preference for cooler drinking water in hot weather conditions. The main production and design questions for any farm - new or existing – are:
- Do we have the correct volumes and flow rates of decent water quality and temperature at the right height and with adequate space for expected competition?
That is no less than six design factors to get right… or wrong.
In food production processes, heat and moisture go hand in hand and the UK agricultural sector has plenty of potential to improve on the management of both factors. Potential gains have been mentioned before as something that need to go into any investment appraisal of our livestock systems. The example of poor fertility - the major reason for culling cows in the UK (NADIS 2022) - will be uppermost in UK dairy statistics this year of high air temperatures and low rainfall. The financial losses of poor fertility accrue from a range of variables (Table 2) and average £250 per cow in the UK herd.
Table 2. The cost of poor fertility.
- genetic gain
- ↓ milk production
- ↑veterinary costs
- ↑ number of heifers that need to be reared
- ↑ cost of AI (or the number of bulls needed)
- Disrupts the pattern of milk production
The chronic health issues linked in part to climate extremes are costing tens of thousands of pounds every year on individual UK livestock farms, which leads to significant potential benefits to offset investment in improved building design and higher specification materials.
And sell rainwater harvesting to the clients and the planners! It should be good business sense and will improve the sustainability image of our industry.
Jamie Robertson
RIDBA Livestock Consultant