Dairy calves need that extra special attention for the upcoming spring and summer months to maintain performance
A mild winter this year has been kind to our dairy calves with minimal milk solids and volume increases necessary at the University of Minnesota Southern Research and Outreach Center (SROC) to offset very cold winter days. As we move into warmer spring and summer months there are additional stressors and challenges that require attention to help support calf performance. The Dairy Calf and Heifer Association has established 'Gold Standards' for raising dairy calves from birth to 60 days of age with a goal of doubling calf body weight and 4 inches of frame growth during this period. Many calves have attained these standards at the SROC. Indeed calf performances at the SROC during spring and summer months should have the same goals as other times of the year, but typically calf performance is lower than during winter months (Table 1).
Table 1. Nursery Holstein calf performance by season when fed conventional milk feeding programs in naturally ventilated curtain side-wall frame-steel barns at U of M SROC, Wasecaa a
|Season||Body weight change ratio b||Hip height gain inches||Pre-weaning gain, days 1-42 lb/day||Nursery gain, days 1-56 lb/day||Starter intake, days 1-42 lb DM||Starter intake, days 1-56 lb DM|
- Summary from 8 selected studies conducted during Spring-Summer and 9 studies during Fall-Winter; calves fed 1.25 lb/day of 20:20 all milk protein milk replacer daily adjusted in cold weather at 0°F or below (14 studies medicated with 2:1 neomycin:oxytetracycline and 3 studies 1:1 for 14 days only) all with 18% crude protein texturized calf starter.
- Ratio of body weight at 56 days divided by initial body weight at 2 to 4 days of age.
- Calves born between late May and August have most depressed performance.
What can we do to alleviate calf stressors in the spring and summer months?
Routine stressors – Reduce stress variance by spreading out routine events such as dehorning, vaccinations, feed changes, tail docking when appropriate, and socialization/grouping. The morning hours are the best time to perform routine events especially in the warmer months.
Heat stress – Calves with increased respiratory rates, heavy breathing, increased body temperature, poor appetites, and general malaise are showing typical signs of heat stress. The Upper Critical Temperature (UCT) for calves is 78° F above which there is the potential for heat stress, but much depends on humidity and radiation. Heat stress occurs with high ambient temperature, high relative humidity (RH) and excessive radiant energy that prevents adequate heat loss by animals.
A good indicator of heat stress is the Temperature-Humidity Index (THI). For cows, when THI exceeds 72, signs of heat stress are indicated and they more pronounced at THI of 76 or greater (Table 2). The THI principle applies for calves but they may tolerate higher THI indices.
Table 2. Combinations of temperature and humidity that yield THI of 72 or 76a.
|Conditions for a THI of 72||Conditions for a THI of 76|
|72°F and 100% RH||76°F and 100% RH|
|74°F and 80% RH||78°F and 80% RH|
|76°F and 60% RH||80°F and 70% RH|
|80°F and 35% RH||84°F and 45% RH|
|84°F and 15% RH||88°F and 25% RH|
- Adapted from West, 2001, Proc., PDGHA National Conf., pp. 15-26.
- It is proposed that heat stress increases calf energy needs as panting and standing expend energy.
- Feed intake drops and maintenance energy is estimated to increase 20 to 30%.
- Water intake should be increased to prevent dehydration and perhaps increase starter intake. To prevent slopping water into the starter bucket, solid dividers between buckets or replacing soiled water frequently is suggested.
- Maternal factors have an influence on heat stressed calves. Heat stressed cows will have depressed intake, and often premature and light birth weight calves will result.
- Heat stress during late gestation can reduce colostrum quality causing calves to be smaller and less vigorous at birth.
- Hot weather can impair the calf's immune function and promote bacterial growth, which results in more infectious disease and secondary dehydration.
Managing heat stress –
- Reduce exposure to direct sunlight (such as turning hutches away from direct sunlight) and provide proper shade.
- Improving air flow is a basic need for all housing systems. Recent research found that using fans during the daytime in a naturally ventilated nursery cooled the calves very effectively.
- Elevating the rear of calf hutches improves airflow and reduces bacterial contamination.
- Guidelines for air flow rates for calves up to 2 months of age are 50 and 100 cfm housed under mild and hot conditions (40 air changes per hour), respectively.
- Consider bedding source for calf pens. Sand bedding is a poor insulator and does not retain heat but helps control flies. Sawdust is better than straw for summer bedding.
- Make sure calves are handled gently and properly.
- Implement good fly control practices that break up the life cycle to prevent build-up.
More research is indicated to clearly understand why calves do not do well in the summer months. For more information on calf management, go to the University of Minnesota Extension Dairy website at http://www.extension.umn.edu/dairy/calves-and-heifers.