Summer is over... But not the problems linked to heat stress

Arianna Zanella, DVM

We are now in September and the long, hot summer 2022 is drawing to a close. And as the season comes to an end, you would also like to forget the major heat stress issues that every dairy herd has faced over the past 3 or 4 months. In truth, the summer heat, despite milder temperatures and shorter days, is still affecting the performance and health of dairy herds.

The main problems encountered on the farm during late summer and autumn can be divided into 3 main areas:

  • inadequate milk production, especially in relation to the herd’s average days in milk;
  • low fertility;
  • increased incidence of podiatric diseases.

With reference to milk production, a syndrome of low milk production in autumn (or SBPLA) has now been identified.
This problem is now well known in all parts of the world and classified as a multifactorial syndrome on a genetic, but mainly management basis.
AIA controls done in Italy in recent years have clearly shown a significantly lower average production than in spring, despite the very similar climatic conditions during the two periods.
As already mentioned, the causes of this situation are to be found at least in part in the genetics of the animals themselves. Despite long selection, our cows are still very much influenced by the photoperiod.

Specifically, cows that spend the dry period during the warmer months, in addition to suffering the consequences of a very high THI, also have to deal with exposure to many hours of light, an aspect that negatively influences their subsequent lactation performances and thus also the peak milk in the fall period.
The most conspicuous part of SBPLA prevention, however, is carried out by paying attention to all those aspects that contribute to reducing the influence of heat stress on our herds, both in the lactating and dry group of animals. In particular, the drop in production that occurs in the summer months is not fully recovered at the end of the warm season and reduces the production averages of the following months as well.

Regarding fertility, the conception rate still remains low during fall despite the significant drop in ambient temperatures. In most cases this is a delayed effect of herd exposure to heat stress during the summer months.

The latter influences the outcome of fertilizations made during the warmer season, but the problem lingers into the following months. This is explained by the fact that the development of follicles that should be fertilized during autumn started 40 to 50 days earlier, thus exactly during the summer period. Several studies have shown a lower quality of follicles collected in late summer/early fall to which a reduced rate of conception has been correlated.

The fall period is also often characterized by a high incidence of podiatric diseases in the barn. The origin of this issue can vary, but in most cases the increased number of hours spent standing during the summer is the main cause. To combat heat stress, cows drastically reduce their hours of rest in cubicles to increase their ability to dissipate heat. In the long run, this type of behavior takes its toll on hoof health, and the effects become clearly evident at the conclusion of the season.


For many years now we have known the immediate consequences of exposure to heat stress on both the productive and reproductive performance of our herds. To all this, however, we must also add the long-term effects of this condition, which do not end with the drop in temperature and the change of season.

For this reason, the adoption of all those systems that allow us to alleviate summer problems becomes even more essential.

Intervention must concern both the managerial part, adjusting rationing and avoiding overcrowding situations in the different groups, and above all the structural part with the adoption of ventilation and cooling systems that remain the most effective way to drastically reduce immediate and long-term problems.