Animal Nutrition

Cooling Pays, Even in First-Calf Heifers

Geoff Dahl
By Geoffrey Dahl, University of Florida

The pay back from cooling dry cows is well known, more milk in the next lactation. But what about first-calf heifers during late gestation? According to new research the answer is yes. 

In fact, three new studies in the Journal of Dairy Science, all from the University of Florida, demonstrate that cooling dry cows and first-calf heifers provides benefits to the cows and to their offspring. 

Davidson et al., 2021, was the first of its kind study to examine if cooling first-calf heifers during the last 60 days of gestation was beneficial. All 31 heifers were housed in a sand-bedded freestall barn. Cooled heifers also had soakers over the feedline and fans. Cooled heifers had significantly lower respiration rates; rectal, skin and vaginal temperatures; and sweating rates. In addition, during the first 15 weeks of lactation cooled heifers produced 8.6 lbs/day more milk than their non-cooled counterparts. Overall, our study demonstrated a strong and positive response of dairy heifers to active cooling with fans and soakers in late gestation. 

Laporta et al., 2020, examined 10 consecutive years of late gestation heat stress research. We selected 156 daughters and 45 granddaughters with 3 years of lactation data to determine the impact of in utero heat stress during their dams’ dry period. Management and environmental conditions for daughters and granddaughters were the same from birth through their third lactation. 

Results show that daughters and granddaughters of heat-stressed dams all had reduced milk production through 3 lactations compared to their counterparts born from dams cooled during the dry period. Milk production losses per day for daughters of heat-stressed cows was 4.8 lbs, first lactation; 5.1 lbs, second lactation; and 14.3 lbs, third lactation. In granddaughters the milk production loss per day was 2.9 lbs in the first lactation. Losses were greater in the second and third lactations, but granddaughter numbers were too small for statistical significance. We also evaluated the lifespan and productive life of daughters. Daughters born from heat-stressed cows had an 11.7-month shorter life span and a 4.9-month shorter productive life than heifers born from cooled cows. This study clearly shows that maternal heat stress during late gestation reduces daughter survivability and milk production for up to 3 lactations.

Fabris et al., 2020, evaluated the effect of heat stress or cooling on the involution of and the creation of mammary secretory cells during the dry period. By measuring gene expression and cellular microstructure we were able to determine that heat stress during the early dry period down regulates several genes which slows involution. And heat stress during the late dry period slowed the creation of new secretory cells. These two factors combined, provide evidence that heat stress impairs mammary gland turnover and subsequent milk production. 

In Laporta et al., 2020, we also estimated the annual economic loss of heat stress on heifers born from heat-stressed cows. In the United States, we estimated the additional cost of rearing heifers born from heat-stressed dry cows at $134 million ($157.49/heifer); the loss from a shortened productive life at $90 million ($9.61/cow/yr); and $371 million in lost milk production (264.5 lbs/daughter/year). We estimated the total loss from reduced milk production, survivability through first-calving and reduced productive life of daughters at $595 million year. This is just losses from daughters born to heat stressed dry cows. Previous research by Ferreira et al., 2016, estimated total annual milk production losses in multiparous cows not cooled in the dry period at $810 million in the U.S. These results show that cooling dry cows and heifers can enhance profitability.


Davidson et al., 2021. J. Dairy Sci. 104:2357-2368

Fabris et al., 2020. J. Dairy Sci. 103:8576-8586

Laporta et al., 2020. J. Dairy Sci. 103:7555-7568