Q & A: Lower critical temperatures for newborn calves

Calving: what an exciting time of year! The “crop” for the next year is hitting the ground, the green grass is growing, and we are enjoying the season of new beginnings well-rested and enthusiastic about ranching, or at least this is how we see it playing out in our dreams! In reality, it is below zero, the tractor won’t start, you haven’t slept more than 3-hours-a-night in weeks, and there is a froze-down calf in the back porch. Don’t worry, you’re not alone. Previous estimates suggest that over 95,000 calves are lost annually due to cold stress, an industry loss of over $38 million. Below are a few of the most frequently asked questions regarding winter cold stress and its effects on newborn calves.

Q. First, what is a lower critical temperature?

A. This is the environmental temperature in which additional energy is not needed to maintain the thermoneutral status of the animal, or their regular body temperature. For a calf this is 102 to 102.5 °F.

Q. What is “cold” for a newborn calf?

A. Table 1. includes the lower critical temperatures for newborn calves based on their age. These temperatures are for a dry calf. Research has shown that at 25°F, in dry conditions, the energy requirements for a newborn calf will increase 30%.

Table 1. Lower Critical Temperatures¹ for Newborn Calves.

¹ Lower critical temperature: the environmental temperature at which the animal's nutrient requirements to maintain homeostasis are increased due to cold stress.

Q. How do newborn calves produce their body heat?

A. Thermogenesis (heat production) plays a key role in the survival of newborn calves. Half of the heat produced by a calf comes directly from shivering. It is critical for the calf to nurse as soon as possible when it is cold outside. The higher fat and lactose (milk sugar) content of colostrum plays a critical role in thermogenesis, and it is another reason that attention must be paid to colostrum intake in the newborn calf. Following birth, if the calf does not nurse within 30 to 60 minutes it will begin to deplete its blood glucose. Their body will try to compensate for this and replenish it from liver glycogen stores; however this supply will only last for 4 to 6 hours. Next the brown fat supplies will be mobilized. The rate of depletion is dependent of environmental temperature and calf health. Overall the 300-600 grams of fat and 180 grams of glycogen that a calf has available for mobilization will be exhausted within 18 hours of life in the absence of feed intake.

Q. What are causes of cold stress, besides temperature?

A. Evaporation is one of the major ways that heat is removed from a newborn calf’s body. The sooner a calf can get dry, the better chances they have. Shelter from the wind and other environmental factors is also needed. In addition, while calves are standing they have increased heat loss, therefore having dry, clean bedding will help calves fight off the cold and reduce the energy they need to stay warm.

Q What are the ramifications of cold stress for newborn calves?

A. As more energy is needed to maintain a calf’s body temperature, less is available for immune function and growth. In addition, the ability of the gastrointestinal (GI) tract to absorb nutrients will be reduced. There is a direct link between the suckling reflex and GI tract absorption, therefore when calves become chilled down and don’t suckle, this is hindered.

Q. Besides environmental influences, what can impact the calf’s ability to survive the cold?

A. The diet of the mother during the last trimester of gestation can also impact the calf’s ability to survive the cold. When the mother’s nutrient requirements are not being met prior to calving, there is an increased likelihood that her calf will be weak, have reduced glycogen and brown fat supplies, and her colostrum quality will be reduced. Feeding specific feedstuffs may also help. Research in 1999 from Miles City, MT showed that fat supplementation during late gestation increased calves’ cold tolerance. In addition, genetics can play a role in the mortality rate due to cold stress in newborn calves, with some breeds being more cold-tolerant than others.

Source: Kalyn Waters

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