Achieving high conception rate is one of the conditions for achieving efficient production of milk at farm level. For many years the Israeli dairy industry suffered, like other farms in warm areas, a significant decline in the ability to pregnant the cows during summer months, causing seasonality in milk production throughout the year, and hence, to a seasonality of milk supply to the industry and market.
Unlike the effect of heat on cow's production which is largely depends on the cow's food consumption and less sensitive to short-term changes in the thermal comfort of the cows, the effect on cow's fertility in the summer is much more complex and spread out over a longer period around the time of insemination. Studies conducted recently by Israeli researchers from the Hebrew University in Jerusalem, showed that cow's fertility is sensible to heat stress conditions for a wide period, starting in the beginning of the development of the ovulating follicle till the implantation of the fertilized egg in the uterus (a period of around 50 days). Hence for the purpose of obtaining normal fertility levels in the summer, inseminated cows must be in normal body temperature, at least along this period, not an easy task!
A large scale research with the aim to improve cow's fertility in the summer was carried out in Israel in the mid-eighties. The research tested, for the first time in Israel the effect of intensive cooling the cows through a combination of wetting and forced ventilation on the performance of high yielding cows in the summer. The experiment was conducted over two consecutive summers in the experimental dairy farm of the Israeli ministry of agriculture. For the first time in Israel, we managed, through intensively cooling the cows during all summer days and day time, to completely avoid the increase in cow's body temperature of treated cows, as compared to the not cooled cows, where, body temperature was above the threshold of normality, in most of the day, along all the summer days. As a result of this situation, we were able, for the first time, to completely prevent the decline in summer conception rate of the cooled cows. The results of this study are presented in table 1.
Table 1 - reproductive performance of cows receiving intensive cooling in the summer in comparison to cows without any cooling during the same period.
The results of the experiment shoes that, by intensively cooling the cows throughout the summer, to get conception rated which are more than double of those obtained in cows without cooling, and almost the same conception rates reached in the winter months, in commercial dairy farms in Israel.
Based on data from the Israeli "herd book" data base and published at the end of each year, we found that, despite the findings described above, and over the years, some improvement in summer conception was detected, but was substantially lower than the results obtained in our study, probably due to the fact that cooling could not be as intensive and along all summer period, as that given to the cows in experimental conditions.
In recent years, with the development of the "summer-winter ratio" index and its publication by the Israeli "herd book", we were able, for the first time, subjectively characterize the different Israeli dairy farms, in terms of their ability to cope with the summer heat.
In order to examine the effect of the intensive cooling the cows, we sorted the data report for the summer / winter ration in 2015, choosing the ten farms in Israel with the highest milk production ratio ("successful farms") and compared them to the ten dairy farms with the lower ratio ("failing farms"). Besides these two groups, we also present the average ratio for milk production in dairy farm in Israel. The fertility traits of cows in successful and failing farms in Israel, as well as national averages are shown in table 2.
Table 2 - Average summer conception rates in cows from farms with high and low summer to winter milk production ratio in 2015.
From the presented in table 2, it was shown that there is great difference in cow's performance in the summer season in both in terms of milk production and conception rates. Conception rate of cows with the highest summer to winter milk production ratio declined during the summer months by only 10.6 percentage units, as compared to that obtained in the winter, but decreased by 22.7 and 28.7 percentage units, in all Israeli farms and in those with low summer to winter milk production ratio, respectively.
The knowledge and experience we have gained in Israel over the years, help dairy farmers in warm regions of the world to better dealing with heat stress.
Recently I started consulting large scale dairy farms in northern Mexico with cow cooling practices. As part of the project, fifteen dairy farms with nearly 40,000 cows, fully apply the principles of intensive cooling, as were implemented in "successful" Israeli dairy farms.
Monthly conception rate in inseminations given in the summer of 2015, in farms intensively cooling the cows was significantly higher in all the dairy farms in the project, as compared to those obtained in 2011-2014, without cooling. Summer and winter conception rates in five dairy farms, intensively cooling the cows in summer 2015 and in same farms without any cooling in 2011-2014, are shown in Figure 1. The summer to winter conception rate ratio of these farms was 0.43 in 2011 and rose to 0.87 in 2015, the year when intensive cooling started.
Figure 1 - The average conception rate of inseminations given during the winter months (January - March) and summer (June - August), in five dairy farms in north Mexico in 2015, with intensive cooling and in 2011 - 2014 without cooling.
Conception Rate (%)
If we compare the results obtained in the summer of 2015 dairy farms in Israel to those in northern Mexico, we can find a great similarity. Unlike years without any cooling in north Mexico, or alternatively, farms who tried to cool their cows but failed doing it in Israel, the summer conception rate was around 15%. On the other hand, conception rate of intensively cooled cows in the summer was more than double (34% and 30% in Israel and Mexico), respectively. The summer to winter conception rate ratio was 0.72 and 0.40 in farms with and without intensive cooling in Mexico, very similar to the corresponding ratio of 0.76 and 0.30 in Israel.
To summarize the data presented in this article, I concentrate in one table the findings of the three studies presented above and shown in table 3.
Table 3 - conception rates obtained in winter and summer in farms with different intensities of cooling, as compared to farms without any cooling.
* - Average national conception rate in same years
Based on what is shown in table 3, we can better understand the following:
- Overall conception rates during the winter months was decreased from levels around 50-60% in the eighties to values ranging between 35 and 45% today, (probably as a result of the increase in level of milk production of the cows?).
- There was no difference in conception rate in inseminations given in the summer, summer between cows from farms without any cooling and those who try but fail to cool the cows properly.
- The summer conception rate of cows without any cooling in the summer was 20% in the study carried out in the eighties, as compared to levels around 15%, in inseminations given these days, probably also, to the higher milk yields in these days (approximately 3000 kg/year more).
- Very intensive cooling (under experimental conditions), ensuring cows being in thermal comfort conditions throughout the entire day along all the summer, allow achieving summer conception rates similar to those reached in the winter.
- Intensive cooling the cows in commercial farms, doubles the summer conception rate, as compared to no cooled cows, although, not reaching the winter levels.
In conclusion, we can achieve good fertility of cows in the summer, with conception rates in the summer close to those obtained in the winter. This can be achieved through intensive cooling the cows in commercial dairy farms, where the goal of cows being in thermal comfort status throughout the day and the entire summer is achieved