Heat stress is extremely costly for the dairy industry due to the immediate impact on farm incomes resulting from depressed milk yields, and the longer term financial burdens caused by follow-on health and breeding issues.
A major financial assessment of the impact of heat stress on livestock returns in the United States has put the all-species cost of the condition at up to US$2.36 billion a year.
The same study recorded an annual dairy sector loss of up to US$1500 million, followed by beef on US$370m, swine on US$316m and poultry on US$165m.
These are massive cost figures. Even allowing for the scale of the US industry, they illustrate the extent to which rising global temperatures are imposing a high price on dairy farmers around the world.
Immediate economic damage, caused by heat stress, is due to falling milk yields which, in the most severe cases, can be reduced by as much as 40%. This is in response to cows not eating normally during heat stress, a reaction which cuts milk output rapidly, while also triggering subsequent energy and rumen concerns. Apart from reduced feed intake, there is also a change in cow’s eating behaviour that increases the risk of ruminal acidosis, leading to lower energy intake from the diet.
Recovery from heat stress is also an issue. Restoring pre-stress yields will depend on a number of factors, such as the stage of lactation at which heat stress strikes and the age of the affected cow. There is also evidence that different breeds suffer more than others from heat stress and can take longer to return to normal once temperatures become more manageable.
Another observed negative impact of heat stress is that it can reduce the cow’s expression of oestrus behaviour, changing follicular development and affecting the cow’s productive cycle. This obviously has implications for an affected herd’s calving index and cow replacement costs.
Increased lameness is another high-cost result of heat stress. This is linked to cows spending as much as 60% of the day standing, in an attempt to cool themselves by maximising their exposure to available air flows. This can be a serious problem, as cows which spend more than 45% of their time standing are more likely to suffer subsequent lameness than animals which rest normally.
Measures taken by farmers to counter heat stress also impose additional costs, with at-risk dairy farms needing to make higher protective investments than units in lower temperature areas. The challenge is to decide how much to invest in cooling systems, such as fans and sprinklers, knowing that heat stress is weather-induced and will vary from year to year.
However, when the heat rises there is clear evidence that cooling systems deliver positive results. According to research based on dairy herds in northeast Kansas, cooled cows produced 5% more milk during heat stress than non-cooled cows faced with the same conditions.
As for cost-effectiveness, the same research found that the expense of installing fans and sprinklers would be covered within 2-3 years by production increases of 5-10%.
In addition, cooling-induced milk production benefits might carry forward into periods when heat stress is not at its highest level. Only considering the impact of cooling systems during high heat stress conditions may therefore underestimate the economic value of reducing stress during less intense periods.
The same Kansas study reached the conclusion that while heat stress management strategies can generate large economic returns with second or higher lactation cows, the benefit attached to reducing stress in first lactation cows could be considerably less, due to their lower productivity.
Feed treatment cost-benefits also warrant high priority consideration. For example, the inclusion of Actisaf, from Phileo Lesaffre Animal Care, France, as a yeast probiotic for dairy cows during a summer trial in Israel, produced a 10:1 return on investment.
One of three yeast-based products developed by Phileo for use in relation to heat stress, Actisaf has shown improved fibre digestion in trials with affected dairy cows, helping to stabilise the rumen and reduce respiratory rates.
During the product’s use in Israel, carried out over a 13-week period, the maximum daily temperature averaged 31.2°C with relative humidity averaging 83.6. In the face of such conditions, the performance difference between cows receiving Actisaf and cows in a non-supplement control group, was considerable.
Results for the Actisaf cows showed 2.5% higher performance than the control for dry matter intake, 3.7% higher for feed efficiency, 4% higher for milk yield and 7% higher for milk fat.
The way Actisaf helps to counter the negative effect of heat stress is by optimising the rumen fermentation, reducing the risk of acidosis, and improving the digestibility of the diet. Having better rumen comfort, cows eat more often and receive more energy from the feed.
References are available from the author on request