In the last 40 years, Israeli researchers realized comparative studies in order to define the negative effect of heat stress in dairy cows and the effect of using cooling methods to mitigate the heat and reduce the losses in the productivity and fertility of the cows during summer.
Recently, an index called "summer to winter ratio" was developed in the Israeli dairy sector. This index allows to evaluate the effectiveness of using methods to alleviate heat stress in each dairy farm in Israel, by evaluating the performance in the 3 summer months (July – September), to that of 3 months of winter (January – March), taking into account the winter results as a base. The summer to winter ratio index is included in an annual report, presented to each "participating farm" in the official milk control system, called "Israeli Herd book", and managed by the Israel Cattle Breeders Association" (ICBA). The index analyzes data about milk production, fat, protein and Somatic Cell Count (SCC) content in the milk, as well as the conception rate, to inseminations given in winter and summer.
Based on this report technical assistance services priorities are determined, concentrating and focusing efforts in dairy farms with poor results.
Tables 1, 2 and 3 present data from Israeli Herd Book database in 2015., where summer to winter ratio is compared between small (family farms), milking cows twice a day to large scale (cooperative farms), milking cows 3 times per day (Table 1), dairy farms with different level of production, low, medium and high (Table 2) and farms, located in different climatic zones (Table 3).
Table 1 - The summer to winter ratio index in small (family) and large (cooperative) farms.
Table 2 - The summer to winter ratio index in farms of different production level.
Table 3 - The summer to winter ratio index in farms located in different climatic zones.
From the information presented in Tables 1, 2 and 3 we can see that, cows in small and large scale farms, manage to get a summer to winter milk production ratio of 95% and both lose about 5% of milk fat and protein in the summer months.
Differently to milk production, the conception rate in winter is in both types of farms was over 40%, but, in the summer, the rate is further reduced in the family farms, as compared to cooperative farms (17% and 20%, respectively), possibly due to better management practices realized in large scale farms.
Comparing the different farms according to the annual production level, we find that the summer to winter milk production ratio was much higher in the farms of high production level, as compared to medium and low production farms. This is possibly due to better management practices in general, and above all, the better use of cooling systems in these herds. Comparing the results in different climatic zones of the country, we see that except for the mountainous area, in the other regions, being characterized by different climatic conditions during the summer, the achievements are almost similar, when measuring the summer decline in milk production and fertility traits.
We assume that, the intensive use of cooling methods has the potential to eliminate much of the negative effect of summer heat stress on the cows. In order to confirm this assumption, we realized a comparison of the summer to winter ratio index in 2015, for the different parameters, between farms implementing and intensively operating the cooling system ("successful farms") to those who didn't cool the cows at all, or did it extensively ("failing farms"). For reference, we added the average results of all the cooperative, large scale farms in Israel. Data from this comparison is presented in Table 4.
Table 4 - The summer to winter ratio index in cooperative, large scale farms successfully implementing cooling systems ("successful farms") and those who do not cool their cows, or do it extensively ("failing farms").
It has been demonstrated in this study that, intensive cooling the cows at different stages of lactation, when it occurs in the summer, can significantly reduce the expected summer decline in cow's performance. The declines in milk production from winter to summer in "successful" and "failing" farms was 1.5 and 5.8 kg / day, respectively, and the decline in the conception rate was 11 and 29 percentage units, respectively.
There is no doubt that, in order to obtain "good results" in the summer, cows must receive "good quality" cooling, throughout the entire summer time. When speaking about "good quality" cooling, I mean providing the cows with good wetting treatment and adequate air speed (forced ventilation). We must assure that cows have enough space in the "cooling site" and enjoy the good cooling treatment for long enough throughout the day. Cows need the cooling treatment being distributed by many times a day and in a frequency of at least every 4 hours, including night time. Cooling at night is extremely important for high producing cows in the summer.