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.