Summertime stressors like high heat and humidity can reduce a calf's response to vaccines. Sam Leadley, calf-care specialist with Attica (N.Y.) Veterinary Associates offers these tips for vaccinating in the summer: 

1. Vaccinate early in the morning when heat stress is lowest.  

2. Keep vaccines out of direct sunlight. 

3. Keep vaccines cool by putting them on cold packs or in insulated boxes.  

4. Put killed vaccines back in the refrigerator. 

5. Use modified live vaccines within three to four hours of reconstituting them.