The author is a senior associate editor for Hoard’s Dairyman.

When temperatures are between 59°F and 82°F, a dairy calf can manage and control its body temperature with relative ease. “They are generating metabolic body heat and have normal exchange with environmental conditions,” explained Sarah Morrison, a research scientist at the William H. Miner Agricultural Research Institute.

Once temperatures dip below 59°F, it becomes more challenging for calves to maintain body temperature, and changes in humidity and wind speed are also contributing factors. This is the temperature threshold at which farms should be thinking about winter calf care strategies, Morrison recommended.

“Younger calves experience cold stress to a greater degree than other animals on the farm, and calves less than 3 weeks of age are most susceptible,” Morrison said during the December Hoard’s Dairyman webinar. She shared practices that farms can employ to help calves flourish during the winter months.

It starts at birth

Morrison said that newborn calves are going to be most vulnerable to cold temperatures. One reason is that a newborn calf has just 2% of its body weight as brown adipose, the fat that helps with nonshivering thermoregulation. Because they don’t have as much fat or as much hair, Morrison said they have relatively poor insulation. “It is harder for them to maintain body temperature,” she noted.

Additionally, a wet newborn calf is going to have a more difficult time staying warm. Using thermal images, Morrison showed that on a wet calf, the ears, nose, legs, and umbilical cord could be relatively cooler than the calf’s core body temperature because they are exchanging body heat with the environmental conditions. Meanwhile, a dry hair coat facilitates a calf’s ability to maintain body temperature.

Morrison said newborns from cows that had a difficult calving are more prone to heat loss due to impaired heat generating mechanisms. She noted that thermogenesis can be 36% less in these calves. Morrison emphasized that calves born to cows with dystocia may require extra attention after birth.

To help calves get off to a good start, Morrison said to minimize the time between when a calf is born and when it is dry. Calves born in cold take longer to stand, are slower to drink colostrum, and have greater loss of body heat when hair is wet. “You want to get that hair dry and warm, as this doubles the coat depth and helps provide extra protection,” she explained.

Colostrum can help with heat production, Morrison noted. “We talk about getting colostrum into calves from an immunoglobulin standpoint, but that colostrum has fat and protein, which help jump-start a calf’s metabolic capacity so they will start to increase their heat production potential,” she shared.

A solid meal plan

Morrison said that a goal of raising calves is to double birth weight by 56 days of age. However, calves have an order of operations when it comes to prioritizing the nutrients they consume, and when temperatures go down and calves are outside of their thermoneutral zone, Morrison said requirements for metabolizable energy go up.

In this case, the nutrients from milk or milk replacer are first going toward maintenance, which includes thermal regulation, the immune system, and stress response. “If we have increased maintenance requirements and are not addressing that through the nutrition program, we are not going to have anything left in the bank for growth,” Morrison asserted.

She shared that when temperatures fall from 59°F to 32°F, a calf’s metabolizable energy requirements go up 35%. When it goes down to 0°F, the requirement spikes 82%.

If feeding calves whole milk, at 59°F they need 2.2 quarts daily to simply meet maintenance requirements. At 5°F, that requirement climbs to 4.1 quarts.

“If you are not adjusting the ration, these calves won’t have anything left to grow,” she reiterated.

Morrison shared three ways to provide more nutrients to calves in cold weather. One method is to increase the solids fed per day. This can be done by feeding more milk or milk replacer per meal, adding another feeding, or increasing the solids concentration of the fluid diet.

Another option is to elevate the energy density of the ration, perhaps by switching to an “artic” or winter blend of milk replacer or adding fat supplementation.

The third way is to increase starter intake. Starter intake, in turn, promotes rumen development. When a calf’s rumen is functioning more like that of an adult cow, it is producing more metabolic heat, and the calf has a greater tolerance for extreme weather conditions, Morrison explained.

A key to encouraging starter intake is water consumption. While it can seem difficult — or almost impossible — to keep water in front of calves in cold weather without having to deal with frozen buckets, water serves an important function in rumen development.

Morrison shared a rule of thumb that calves should drink four parts of water for every one part of starter consumed. For example, a calf that is eating 1 pound of starter daily should drink 4 pounds or 1/2 gallon of water each day.

Calves’ water needs rise with age. Morrison shared that a preweaned calf should be drinking 1.3 to 2 gallons of water per day. By three months, water intake should be between 2.1 and 2.6 gallons per day, and at four months of age, a calf should be drinking 3 gallons or more a day.

Without water in the preweaning stage, calves will have slower rumen development. It also reduces their feed conversion rates. Morrison said, “If you can get water in front of calves a couple of times a day, that is a benefit.”

The micro-environment

The goal of calf housing, Morrison said, is to mitigate the effects of cold conditions. This starts with bedding, which must be clean and dry. Morrison recommended at least 3 inches of bedding between the calf and the floor, and possibly more on cold concrete floors.

She recommended doing a “kneel test,” either looking at calves’ knees or at your own knees after kneeling in a pen. If the knees are wet or dirty, it is an indication that more bedding is needed.

Morrison said wheat straw is a great bedding for calves, as it provides an area for the calf to create a microclimate for themselves. She also recommended a bedding score of 3, which means a calf’s legs are not visible when it is lying down.

“Bedding management is important to minimize heat losses to the calf,” she said. “It is also linked to a lower prevalence of respiratory disease.” Calf jackets and ear muffs can also be worn by calves to fend off cold temperatures.

Morrison emphasized the importance of keeping calves healthy and growing through the winter.

“We are putting a lot into these animals; we have a long-term investment in them,” she said. “What factors are holding your calves back from meeting your goals and reducing morbidity and mortality, while also promoting growth so that they enter lactation as productive members of the herd?”

She continued, “Identify what pieces of management can be implemented so that you can minimize the negative effects of environmental conditions.”