This is a stressful period for calves and heifers. We are on pace for one of the warmest average March temperatures in several years, yet most mornings still require a hat and gloves. Increasing ambient temperatures during the day, increased humidity and cooler nights have clear impacts on heifer performance and health.
    The thermal neutral zone is the ambient temperature range in which calves do not expend additional energy to stay warm or cool off. The thermal neutral zone for calves is between 50 and 78 degrees Fahrenheit at birth, and between 32 and 73 degrees for weaned heifers.
    Managing ventilation is challenging in the spring and fall with fluctuating temperatures. The goal of any calf or heifer ventilation system is to provide enough air exchanges per hour without creating a chilling draft.
    The minimum winter ventilation rate is four air changes per hour (ACH), often achieved utilizing a positive pressure tube system for calves and younger heifers. As the temperature increases so does the required ventilation rate. In mild spring and fall weather, a target rate of 15 to 20 ACH is recommended. In summer months, it rises to 40 to 50 ACH. This can be achieved by opening the sidewall curtains in stages in naturally ventilated barns.
    Early spring is also a good time of year to perform regular maintenance on your curtains, fans and positive pressure tubes. Also check eaves, soffits and weatherhoods for debris.
    Cold temperatures generally increase intakes. Conversely, intakes will often decrease when warmer temperatures follow a cold spell. Fluctuating temperatures and humidity often lead to variable intake, making it difficult to evaluate the feed bunk and predict intakes.
    Variation in energy intake and nutrient supply impacts feed conversion efficiency. In heifer systems where grain and hay are fed separately, producers are likely to see lower forage and higher concentrate intakes since heifers that are marginally hungry will typically have lower voluntary intakes.
    Changes in feeding behavior and feed intake are typically the first signs heifers are feeling the stress of environmental change. Decreased or variable intakes may increase coccidial shedding which can lead to exposure to other calves, especially in high-risk environments like wet bedding. Disease challenges in the digestive tract have been linked to higher risk for decreased respiratory health.
    Higher daytime temperatures in the spring result in thawing of bedding packs and increased bedding moisture. With plenty of moisture and organic matter, microbial activity accelerates and ammonia concentration increases. This change can irritate the respiratory tract and increase risk of respiratory disease, especially in enclosed facilities where ventilation is not adjusted. Increased humidity also increases the risk for airborne pathogen transfer as pathogens can travel further on moist air.
    All of these factors make spring a good time to work with your veterinarian to review vaccination protocols to make sure heifers have optimal protection from respiratory disease-causing organisms.
    Although this past winter was significantly milder than the previous year, heifers still developed a thick winter hair coat. It may not be practical to remove this winter coat, but some farms have installed brushes to assist with long hair removal in the spring. This may also help clean up heifers after external parasites, such as lice, seemed to thrive this winter.
    Heifers with wet, dirty and matted hair coats will require significantly more energy to stay warm than animals with clean, dry coats. Increase bedding frequency and amount to maintain a clean and dry bedding pack. Box-scraping outside lots can also be helpful through the spring mud season.
    Managing calf and heifer environments can go a long way in promoting youngstock health and performance. Finally, remember that energy demands increase when environmental quality decreases. Work with your nutritionist to ensure diets meet nutrient requirements.
    Barry Visser is a nutritionist for Vita Plus.