More than one summer is needed to cool cows properly

Summer heat stress has been considered in these days as one of the greatest causes for losses in the world dairy sector. Italian Breeders Association (A.I.A.), adopted the Summer to Winter ratio (S:W) index, a heat stress assessment tool based on the ratio between summer (July – September) and winter (January – March) farm performances. S:W ratio has been developed in Israel and adopted recently in Italy and other countries, as a tool for detecting performance pitfalls in summer due to excessive HS in dairy farms. The summer to winter ratio index (S:W), represents a highly effective synthesis of the negative impact of HS on cows, as it reflects the gap in the performances between different seasons, as well as evaluating individual farm capability to cope with the negative impact of the summer conditions, by using cow cooling means. The more the ratio value is below 1, the more the summer cow’s performance has been affected.

In this study, the S:W ratio has been calculated for the year 2020, in 2,400 dairy farms with Frisian cows, located in Lombardy region, north Italy. Calculation was based on official performance recording data, collected by AIA official technicians. The information collected included, per cow daily production of fat (4.0%) and protein (3.3%) corrected milk yield (FPCM), milk fat and protein (%), Linear score of somatic cell count (SCC), and conception rate (CR %), for all inseminations given in the summer and the winter of 2020. Also, we calculated the percentage of cows with production above certain level, in separate for first lactation and adult cows (high milk yield), as well as the ratios of peak lactations between two seasons.

In collaboration with the company Arienti, manufacturer and installer of cooling equipment for the dairy sector, I've been running in the last 5 years a consultancy support program to the farms, called “Element” program. We evaluated benefit arising from implementing intensive cooling program on cows' performance, by comparing S:W results in the year 2020, in all Lombardy farms, comparing it to 99 farms, participation in Arienti “Element” program. The Element program consists of the supply and proper installation of cooling means in the farm, and continuous consultancy service, provided to the farmers by the company's professional experts. The farms participating in this program can be considered homogeneous in their cooling management (cooling equipment and protocols). The cooling program started in 2017, and in summer 2020, 36 out of the 99 farms were at their second year of implementation of the cooling protocols, whereas the other 61 were in the first one.

The results obtained in the “cooling program” farms have been compared in summer 2020 to those of all Lombardy farms. The 2020 data of the 99 “Element program” farms was divided into two groups, those performing cooling in the first year in summer 2020, and those doing it for two years or more. The creation of these two groups and the idea to test them separately, arises from the assumption that the effect of cooling is expected to be improved, when being practiced for more than one year. This assumption has been based on the expected improvement in cow’s body condition, the reduction in average herd DIM (arising from the improvement in cow’s fertility), as well as continuous improvement in technical operation of the cooling system. The S:W ratio in 2020, for Lombardy farms and the two groups of “Element program” farms, are presented in the table 1.

Table 1 - The S:W ratio for different performance variables, in all dairy farms in Lombardy, and the farms practicing cooling for the first year, or for two years or more, in summer 2020.

As can be seen in table 1, cows from intensively cooled farms, have considerably higher S:W ratios, as compared to those from all Lombardy farms. All the performance variables tested are significantly different, when comparing intensively cooled farms (both, in first and multiple years of cooling operation), to all Lombardy farms, except for fat and protein percentages. It needs to be clarified that Lombardy farms might include also farms practicing in the “Element” cooling program, as well.

Not less important and interesting is the fact that a great part of the tested performance variables showed higher S:W ratios, in the farms practicing cooling for two consecutive summers or more, as compared to those who started cooling the cows in summer 2020. In order to study this point, we characterized cow’s monthly performance variables for 36 farms, where cooling in 2020 was practiced for two consecutive summers (started cooling in summer 2019). The data is presented in table 2.

Table 2 - Averages of tested variables in 36 “Element” program farms in three periods of time: “no cooling” (summer 2018), First year of cooling (summer 2019) and second year of cooling (summer 2020).

As can be clearly seen from table 2, there is a significant improvement in all tested variables, when cows are being cooled, and this improvement continues when cows are cooled for the second consecutive summer.

Monthly averages of milk production and conception rate in these tree tested years, for the cows in the 36 “Element” program farms are presented in figures (a) and (b). This data describes how cow’s performances evolve along this 3 years period.

Figure 1 - Monthly averages of (a) daily per cow corrected milk production (Kg), and (b) conception rate (%) to all insemination given every month.

From the data presented in figure (a), we can see a clear trend of continuous increase in per cow milk production. The winter average of daily milk production per cow increased from 35 Kg, in the year before intensive cooling has been implemented, to 38 Kg and more, when intensive cooling has been provided to the cows for two consecutive summers. It can be seen also that summer drop in milk production was reduced after cooling started, from 4-5 to 1-2 kg per day, in the summer before cooling started and in second summer of practicing intensive cooling, respectively. As can be seen in figure (b), summer conception rate dropped from 45% to 35%, in the year before cooling started (a drop of 10 percentage units), as compared to a decrease from 50% to 45% (a drop of 5 percentage units), in the year cooling was practiced for two consecutive summers, half the drop in the year before cooling started.

As can be seen in table 2, and in the two figures above, the improvements obtained after the first summer of performing intensive cooling is minor to that of the second summer (about half the improvement in S:W ratio), while the complete improvement in CR is reached already in first year of cooling.

The continuous improvement in summer milk production through the two years tested, although climate conditions in the three summers didn’t differ significantly, can be attributed to the fact that intensively cooling the cows in the summer help them eat more and, although producing more, they are also capable to accumulate more body reserves in late lactation and lose less of it in the first stages of lactation, when these periods occur in the summer, so cows maintain better body condition, positively influencing both, milk production and fertility in general, and in the summer months, in particular. The improvement in CR after one year of performing cooling helps reduce average herd DIM, a fact that helps reach higher milk averages and better udder health.

In conclusion – this article has been written, mainly, in order to encourage dairy farmers to implement and properly operate intensive cooling in their herds. Not less important is to teach those farmers that already installed cow cooling means, but still didn’t reach the desired and expected results, to be “patient”, as the beneficial effect of implementing cooling mean can’t be judged after just one summer of implementation, and cow’s performance keeps on improving in later years.