Mike Van Amburgh at Cornell University reports that calves born in winter produce about 1,200 lb. less milk during their first lactation than calves born at temperatures of 60° to 75°F.
Several factors cause this, but reduced gain during winter months is a major reason. His research shows for every 1 lb. of daily gain prior to weaning, heifers will produce 937 lb. more milk during first lactation.
Cold stress in calves starts at 50°F. For every 1° drop in temperature below 50°F, a calf requires 1% more energy. Growth rate decreases about 0.2 lb. per day for every 10°F drop in temperature from 50°F. At 30°, a calf needs 30% more energy (calories) for maintenance and growth than at a more moderate 50°F.
For calves under 3 weeks of age, the extra energy needed in cold weather will have to come through feeding additional amounts of milk replacer, pasteurized milk or adding a fat supplement to the liquid diet. (See the milk replacer table.) For calves 3 weeks and older, additional energy intake should come from starter and the increase in milk or milk replacer.
The best way to increase the amount of milk replacer or milk fed in winter is to add a third feeding. If the feeding is from milk replacer, the third feeding is mixed the same as the other two feedings.
Don’t just increase the amount of milk replacer powder or solids in the same volume of water used for two feedings. Such a high level of solids can cause scours. A good guideline is not to exceed 15% solids in liquids fed to calves, whether from milk replacer or supplemented pasteurized milk.
How you mix milk replacer and water can have a significant effect on solids content of the final mix. As an example, if you add 10 oz. of milk replacer on top of 2 qts. of water, the solids content will be about 13.1%. If you add milk replacer first and then add water to make a 2-qt. mix, the milk replacer displaces some of the water, and the final solids mix will be about 15.2%. When adding 2 oz. more milk replacer
(12 oz. total) and then adding water to make exactly 2 qts., the solids content increases to 18.2%.
The importance of getting calves to eat starter to maintain growth during cold weather is illustrated in the daily gain table. Milk is used in the example, but the same principle holds for using milk replacer.
Below 0°F, milk alone supports no growth, but with 0.5 lb. of starter intake, calves will consume enough energy for some growth. In addition, the body heat produced from the digestion of solid feed will help the calf feel warmer than consuming only liquids.
Keep your calves growing this winter by getting them off to a good start with adequate amounts of high-quality colostrum right after birth. Follow with extra energy through the liquid diet for young calves and then starter in older calves up to weaning.
For your herd’s future, it is important to keep calves healthy and growing during all months of the year.
JIM LINN is a dairy nutrition consultant and retired Extension nutrition specialist at the University of Minnesota–St. Paul. Contact him at firstname.lastname@example.org.