Summer is coming and before long we might be wishing we had some of the cool weather we experienced this past winter. In a typical Midwestern summer, 60 to 70% of the days will have a temperature-humidity index (THI) value above 68 which is when our cows begin experiencing heat stress. Because of the tremendous drop in milk production and dramatic drop in conception, most producers have done a great job of installing cooling systems for their milking cows. Based on research, most dairy farmers would also benefit from a cooling strategy for their dry cows.
A growing body of research shows a large benefit for cooling dry cows. There have been at least nine research trials done on cooling dry cows and all have shown an improvement in milk production the subsequent calving, ranging from a couple of pounds per day up to 11 pounds per day. The lowest responses were when cows were only cooled with shade and only cooled during the close up dry period. Higher responses were observed when cooling cows during the entire dry period using fans and sprinklers.
Research at the University of Florida shows cows cooled during the entire dry period in June, July and August (average THI = 78) had improved production that lasted at least 40 weeks into lactation (Figure 1). This increase is likely due to the increased regeneration of mammary tissue during the dry period. All cows were cooled after calving. They also observed that cooled cows had improved immune system function. Cooled cows had lower somatic cell counts after calving. Cows with improved immune function also are likely have fewer pneumonia and uterine disorders after calving.
This Florida research also evaluated and tracked the calves that were born to these two groups of cows. Gestation length was 4 days longer for cows cooled during the dry period and their calves averaged 14 pounds heavier at birth. This difference in weight was maintained through weaning. Those calves also had better colostrum absorption and improved immune system function through weaning.
The calves that were cooled or not cooled in utero were all raised together after birth and were followed through their first lactation. Heifers who were cooled in utero averaged nearly one service per conception less to become pregnant than heifers that were not cooled (1.8 vs 2.6). The heifers cooled in utero also averaged 6 pounds more milk per day for the first 35 weeks of lactation. This trial should be repeated, but these results are intriguing.