Do we know the real cost of heat stress to the dairy industry?

Heat stress is considered one of the main causes of performance and economic losses in the world dairy sector. These losses are proportional to the degree of heat stress cows are subjected to (days or hours per year, cows are exposed to THI above threshold), as well as to the level of production and some nutritional and managerial practices. Do we really know to quantify the total losses? The answer for the moment is no!

The literature published until now deals with most of the potential areas, which can cause these losses, but no quantification and economic evaluation of the total losses, under different climates and types of farming conditions has been done yet.

I believe that it is of great importance to have these numbers in order to convince dairy farmers and institutions to take action and invest in the implementation of heat mitigation means, and cope with the heat stress problem. It is more effective to convince farmers to invest, by presenting them with the numbers related to the economic and environmental benefits they can have and how fast their investment can be paid back.

In this article, I will describe the already known pathways by which heat stress causes losses to the dairy farm and give details on those already known. I take part in these days in a special committee established by the International Dairy Federation (IDF), dealing with the heat stress in dairy farms topic. I expect that soon, as part of our work, an economic evaluation of the total losses will be completed and presented to the world dairy sector.

The first and most common parameter is the decrease in milk production. The best way to characterize it will be to present it in terms of Economical Corrected Milk (ECM), per cow annually. Based on research done in the US, annual milk production losses per cow ranged between 170 kg, in the “coolest” state, where only 6% of year time was above the cow’s threshold (THI 70), and more than 2,000 kg, in the “warmest” state, where 50% of year time is above that threshold. Today there are dairy farms located in regions experiencing conditions above threshold, close to 100% of year time, where we can expect high-yielding cows to lose more than 3,000 kg from their productive potential, unless they are properly cooled.

The negative impact of heat stress on milk production does not end by reducing milk volume but also by a decrease in milk fat and protein content. This occurs only in the hot period, with a “delay effect” on cows being dry at this time. Usually, we can expect a 0.35 – 0.40 percentage units in milk fat content and 0.30 – 0.35 percentage units in milk protein content, for the milk produced in the hot period.

Heat stress (as all kinds of stressors on the cow), causes also an Increase milk Somatic Cell Count (SCC). In most cases, this increase is not related to any kind of udder infection, and has no negative impact on milk quality. In this case too, the negative effect occurs only in the hot period, and can be characterized by an increase of 100,000 SCC units above that in the milk produced by a healthy cow in the cool period.

One of the negative effects of heat stress, which causes large economic losses but it's still very little known, is the decrease in feed efficiency, which also occurs only in the hot period.

When suffering from heat stress, cows utilize part of the energy they consume in order to activate body physiological means for heat dissipation. In most cases, these mechanisms are not capable to help the cow, but cause part of the feed consumed to be canalized to non-productive purposes. A research carried out at the University of Kansas showed that cows produced 1.4 kg of milk for each 1 kg of dry matter they consumed, when this happened in normal climate conditions (22°C), while in warm conditions (32°C), the cows produced only 1.2 kg of milk per 1 kg dry matter, a decrease in “feed efficiency” of 15%. Now, let's translate it into money. With a diet cost of 8 USD per cow/day, and 120 stressful days per year, annual losses per cow will reach almost 150 USD (much more than the cost of operating the cooling system in the farms). One more reason for the decrease in feed efficiency, when production is reduced under heat stress conditions, is the fact that, as feed cost for maintenance is the same in low and high yielding cows, then more feed is required to produce certain amount of milk in low producing cows, and so, more feed required per liter of milk produced.

One of the most known negative effects of heat stress on cows is the decreased fertility. This occurs in a wider period than the hot period (due to delayed effect on the fertility of cows inseminated in autumn and early winter, affected by summer negative impact on cow’s reproductive system). The decrease in summer fertility includes the failure to detect cows in heat, and the failure to pregnant the cows (low Conception Rate). The losses due to the decrease in cow’s fertility include also the elevated expenses for the use of hormonal treatment, and additional semen and man power in order to pregnant the cows. Low fertility increases average number of “days open” (prolongation of calving interval) above the optimal period for each cow. Not being able to properly cool the cows can easily increase the average open days by 20 days per cow, and with a value of 3 - 5 USD per additional “open day”, above optimum, it can increase farmer production cost by approximately 100 USD per cow. Low fertility in summer can also be translated into an increase in culling rate, due to infertility. As usually, high producing cows are those to be at higher risk of suffering infertility, mostly during the summer, then we can expect also a delay in herd genetic improvement , caused by an “obligatory culling” of high potential cows, just because they didn’t get pregnant. The reduction in cow fertility in the summer can also create seasonality in milk supply to the industries and markets throughout the year, which can be translated into economic losses to both, farmers and industry.

It is well known that being subjected to heat stress conditions, cows will experience reduced immunity status. This occurs only in the hot period and can be translated to the Increase rate of cows suffering diseases, mostly those occurring around time of calving, as well as an increase in the cases of clinical mastitis. The increase in the rate of diseases will increase farmer’s expenses in medicines and medical treatments. Still, there is no quantification and evaluation of the negative economic impact of heat stress on cow’s health and farm expenses for medicines. Anyhow, from my personal experience as a consultant to a 700-cow’s farm, located in the north east of Italy, I found that farm expenses for medicines dropped by almost 70% in the first year of implementing intensive cooling.

Calves born to cows experiencing heat stress in late pregnancy are expected to be born lighter and weaker and dam colostrum being of lower “quality”. These factors and the direct possible negative effect of heat stress on the newborn calf, have the potential to increase the rate of calf mortality, as well as a delay in their growth rate in the first stages of their life.

Literature talks about an increase of 10% in calf mortality, above normal, in those born under heat stress conditions.

The need to produce a certain amount of milk with higher number of cows means an increase GHG emission (mostly Methane). Methane emission per liter of milk produced is higher under heat stress conditions, due to the need to raise more cows and replacement heifers, to produce a certain amount of milk (like in the case of feed efficiency). There is no doubt that any additional “environmental tax” to be paid due to the increase in this emission “will be rolled” to the farmer.

As far as I know, being quite familiar with updated literature, there is still no work done, which quantifies all (or even a great part) of the economic losses presented in the list above. I expect that having the results of the work done these days by IDF scientific committee above mentioned will give the required information to the economists in this team, allowing them to calculate the total of economic losses caused by heat stress in different climate regions and farming systems. Not less important, making use of the updated literature, dealing with effectiveness of heat mitigation means in those conditions, allow these economists to calculate the expected economic benefit from their proper implementation. Transferring these numbers and operational instructions to farmers around the globe can help improve milk production efficiency as well as reduce its negative impact on the environment.