A simple check back in your records can give you a pretty good idea of whether your summer cow cooling practices are adequate, says Bill Thatcher, a dairy reproductive specialist with the University of Florida.
He says Israeli dairy scientists examined winter and summer reproduction records of 48 herds in their country. Herd size averaged 400 cows, which means nearly 20,000 cows were involved in the study. Most of the Israeli herds use highly intensive cooling systems.
The Israelis compared their top 24 herds for economically corrected milk to their bottom 24 herds. The wintertime milk production was identical, at 87 lb./cow/day. In summer, however, the high herds averaged 85 lb. while the low herds averaged 76 lb.
In winter, the high herds had an average conception rate of 40%, the low herds 36%. But in summer, the high herds dipped to a 27% conception rate compared to 19% for the low herds.
In other words, the high herds were achieving two-thirds of their winter conception rate in summer. But the low herds were maintaining only 50% of their winter conception rate in summer.
The above data suggest a number of conclusions for dairy producers:
- Calculating the ratio of winter to summer conception rates can offer clues as to how well your cooling system is working. A drop of 45% to 50% suggests cooling is not adequate.
- Well-maintained cooling systems allow cows to produce high volumes of milk during summer.
- Well-maintained cooling systems allow cows to produce nearly 1,500 lb. more milk per year.
- No cooling system can likely cool cows enough to sustain a high rate of reproduction during the summer.
- Improperly maintained cooling systems have a detrimental effect on milk production levels and a devastating effect on reproduction rates.
Interrelationships of heat stress and reproduction