Maintain heifer health through temperature swings

By Dr. Noah Litherland
While we enjoy spring’s warmer weather, this is usually a stressful season for calves and heifers.  Increased ambient temperature during the day, increased humidity, and cooler nights have clear impacts on heifer intakes and health:

• Cold temperatures generally increase intake.  Intake will often noticeably decrease when warmer temperatures follow a cold spell.
• Warmer and wetter weather often leads to variable intake, making it difficult to evaluate the feedbunk and predict intake.
• Variation in energy intake and nutrient supply impacts feed conversion efficiency.  Heifers that are marginally hungry will typically have lower voluntary hay intake.  Heifer systems feeding grain and hay separately will be more susceptible to lower forage and higher concentrate intake.
• Decreased or variable intake may increase coccidial shedding, which can lead to exposure to other calves, especially in high-risk environments (wet bedding).
• A healthy GI tract tends to be associated with decreased respiratory health risk.  Changes in GI tract function associated with variable feed intake likely contribute to increased risk for compromised gut barrier function and may increase the risk for respiratory disease.
• Increased daytime temperature results in thawing of the bedding pack and increased bedding moisture.  Microbial activity in wet and nutrient-rich bedding results in increased air ammonia concentration (greater than 5 to 10 ppm), which can irritate the respiratory tract and increase the risk of respiratory disease.
• Increased humidity also increases risk for airborne pathogen transfer as pathogens can travel further on moisture-laden air.

Key things to watch
When evaluating heifers, key areas to observe include feed intake, manure consistency, hair coats, eye and nasal discharge, and ear placement.  Changes in feeding behavior and feed intake are typically the first signs heifers are feeling the stress of environmental change.  Loose manure and dirty tails is an indicator of inconsistent intake or digestive upset.  Evaluate eyes and noses for discharge.  Ear posture should be alert and balanced.

Strategies to minimize risk during damp weather

1. Work with your nutritionist to ensure diets meet nutrient requirements.  Remember that energy requirements increase when environmental quality decreases.
2. Maintain reasonable stocking density (at least 40 to 45 square feet of resting space per head for 200- to 400-pound heifers).
3. Provide access to roof cover for all heifers to protect them from rain and wind.
4. Increase bedding frequency and amount to maintain a clean and dry bedding pack.
5. Do not move compromised calves from individual to group housing.  Calves should remain in individual housing if:
   • Calves weigh less than 170 pounds
   • Calves are not eating at least 3 to 4 pounds of starter grain per day
6. Clean and sanitize waterers to decrease pathogen load.
7. Use a portable water trough for the first days at transition to help encourage water intake.  The trough can be used to dose Corid^® to aid in coccidiosis control.
8. Manage curtains and fans to provide at least 4 to 6 air changes per hour with air speeds targeted at 60 feet per minute.
9. Keep positive pressure tube fans running continuously.  These systems are designed to deliver fresh air without chilling calves.  Exterior and interior building temperature is not significantly altered by running positive pressure tubes.
10. Review herd vaccination procedures to make sure heifers have optimal protection from respiratory disease-causing organisms.

About the author:  Dr. Noah Litherland is the Vita Plus dairy youngstock technical specialist.  he grew up on a diversified livestock farm in central Illinois and was active in 4-H and FFA as a youth.  He earned his bachelor’s, master’s and Ph.D. from the University of Illinois, focusing on dairy cattle nutritional physiology.  He worked as a dairy extension specialist at Oklahoma State University from 2006 to 2008 and then as a dairy nutritionist at the University of Minnesota until 2014.  At Minnesota, Litherland served as the faculty supervisor of dairy research on the St. Paul campus.