DURING periods of cold weather calves must be supplied with enough energy to maintain core body temperature as well as growth and immune function, writes Dr Jessica Cooke, Volac International.
If calves are not fed enough milk, they will start to expend their internal energy reserves simply to keep warm, diverting energy away from body weight gain.
Calves, like all mammals, keep their body temperature constant generating metabolic heat and continuously exchanging heat with the environment. The amount of metabolizable energy (ME) required under normal conditions is the sum of the ME requirement for maintenance (amount of energy used for normal body functions such as digestion, respiration and heat production) plus the ME requirement for growth.
The thermoneutral zone is the range of ambient temperatures in which an animal is not required to elicit specific heat-conserving or heat-dissipating mechanisms to maintain body temperature, and for young calves it ranges from 15 to 25°C. The lower critical temperature (LCT) is the temperature at which animals require additional ME for maintenance (i.e. to maintain body temperature): for a young calf (0 to 3 weeks) the LCT is 10 to 15°C, and for calves older than 3 weeks it is 6 to 10°C.
Young calves are prone to heat loss because of their high surface area to body weight ratio and they also have poor insulation (i.e. thin skin and subcutaneous fat). Furthermore, they cannot rely on heat production by ruminal fermentation. Older calves are more likely to be eating calf starter, driving rumen development and a functional rumen produces its own heat which helps to keep the calf warm.
How much extra energy is needed?
At temperatures of 15°C a young calf (0-3 weeks) needs an extra 1.06MJ of ME/d to maintain the same growth rate as when it’s 15 to 25°C, but at 0°C it needs an additional 4.23MJ of ME/d. Older calves (assuming they are eating starter) require additional ME to maintain growth when temperatures drop below 10°C: at 0°C an additional 2.11MJ of ME/d is needed.
Supplying calves with extra energy:
During the first three weeks of life, when starter intake is minimal, the energy available to the calf is directly proportionate to the supply of milk or milk replacer.
Based on a milk replacer containing 19.8ME MJ/kg DM, a calf (0-3 weeks) requires an extra 55g of milk powder per day for each 5°C drop in ambient temperature below 20°C, to maintain the same growth rate as when its warmer. For example, at 0°C an extra 4.23MJ/d is needed which is supplied in 220g of milk powder (19.8ME MJ/kg DM x 97.5% [assume 2.5% moisture] x 220g = 4.25MJ of ME). Thus if a calf is normally fed 750g milk powder per day, it will need a total of 750 + 220 g = 970g per day to continue to grow at the same rate as when it is 15 to 25°C.
For older calves (>3 weeks) an extra 55g of milk replacer per day is needed for each 5°C drop in temperature below 10°C. Increase the level of milk solids offered per calf per day by either increasing the concentration of the milk replacer (e.g. from 125g/L to 150g/L) or by offering a higher volume of milk per day.
Provide dry, clean, draught-free housing:
Calf housing with high moisture levels and draughts will dramatically increase the calves’ susceptibility to cold stress. Reducing cold air draughts (whilst maintaining ventilation) and providing insulation in the calf shed will help to reduce body heat loss:
n Provide effective barriers to draughts at calf level and provide places for the calf to shelter (e.g. use whole bales in the shed). Plastic and timber are better insulating materials than concrete and steel.
n Provide plenty of deep straw bedding to give calves a place to ‘nest’.
n Keep bedding clean and dry – much of the insulation value of bedding is lost when it is wet. Calves that rise from laying on wet bedding will have wet hair and skin – this moisture will evaporate taking energy from the calf.
n Use calf coats – coats should be dry and cleaned regularly
Cold weather is yet another challenge that calves can face, but by ensuring calves are well nourished and properly housed will help to ensure they can continue to grow well and remain healthy.