January in New England means two things: well wishes for a happy and prosperous new year to all of you who read Farming, and the inevitable freezing temperatures. Maybe 2013 will be the year that global warming really kicks in and the winter temps will only just get down to around freezing or so, but I'm not holding my breath.
Cold weather takes more of a toll on livestock than we realize. While we spend a lot of time concerning ourselves about heat stress for dairy animals during the summer months and trying to keep them cool, we also need to recognize that the extreme cold of winter sucks the heat from nearly everything in the barnyard. Animals that are exposed to cold temperatures must use more energy to stay warm - energy that in warmer weather would be used for growth or milk production. Cows, heifers and calves that are exposed to long periods of extreme cold with no adjustments to diet or environment will not be able to maintain body condition, and eventually their health and milk production will be negatively affected.
In the U.S. we measure energy in calories, and in ruminant nutrition we refer to energy as kilocalories (kcal) or megacalories (mcal). Calories are funny things. We all need them, but when we consume too many relative to the work we do, we'll get fat. The opposite is also true. Cows are the same. Massive amounts of calories are required to meet a cow's energy needs for maintenance and to produce milk. Extremely cold weather requires more calories in the diet to generate more heat, keeping the metabolism functioning properly.
Cows naturally try to compensate for colder temperatures by increasing feed intakes. Given the opportunity, cows will eat more when it's cold. Grains and commodity byproducts offer more energy per pound than forages. In fact, when temperatures become extremely cold, forages alone will not supply enough calories to keep cows warm and productive. If cows - as well as heifers and calves - are not fed enough to compensate for cold temperatures, they will begin using their body fat reserves to meet energy requirements. As more calories are used for a milk cow's body maintenance, less energy is available for milk production. In the extreme condition, cows that go into the winter with marginal body conditions and then proceed to lose more weight during the winter are hardly in a position to make milk when they freshen in the spring.
A typical feed ration that's been balanced in the fall when daytime temperatures are in the mid-60s calls for a cow to consume about 47 pounds of dry matter to support 70 pounds of milk production. Later in January, when the daytime temperature doesn't climb above 20 and nights are well below freezing, that same cow must eat another 4 pounds of dry matter to compensate for her increased energy needs, and none of that additional dry matter is going into milk production.
Cold weather has a way of sneaking up on us, and reformulating a diet is often done after the fact and ends up being too little, too late. We should be thinking about cold weather already in December and adding some bypass fat to the ration for added energy long before the real cold sets in. This will help keep body condition losses to a minimum. Cows that freshen in March and April after being subjected to extreme cold as a dry cow will often have metabolic issues that slow them down or, worse, shut them down.
Reformulating your dairy cow diets to increase energy density is usually the most cost-effective means of getting more nutrients into your cows during the winter months. Every dairy farmer should be formulating cows' diets with the aid of computerized ration models that incorporate lowest-cost routines. Nutrition modeling software such as CPM and CNCPS do an amazingly accurate job of formulating rations that meet nutritional needs for a wide range of temperature and humidity combinations.
Young calves are particularly vulnerable when exposed to cold temperatures. Preweaned baby calves that are not yet consuming a lot of grain starter will quickly descend into a negative energy balance. They will stop growing and even lose weight if milk solids and overall nutrition are not adjusted to compensate for the insufficiency in energy caused by the cold. When temperatures in the housing environment get down below freezing night after night, the metabolizable energy requirement can double. That means if you're feeding a calf a gallon of milk per day, you have to feed it two, just to keep it at a maintenance level and prevent weight loss.
The feeding directions on most commercial milk replacers are designed for thermoneutral conditions and do not offer any suggestions as to how much more solids should be added in cold conditions. Table 1 should be helpful in determining how much extra milk powder should be offered to a calf at different ambient temperatures.
In the table it's clear to see that a Holstein calf that's about a month old and weighs 120 pounds needs an additional 1.5 pounds or more of milk replacer (depending on how much starter it's eating) to maintain an aggressive daily gain when the ambient temperature in its housing area drops below freezing for all or part of the day. Even during the fall months, when temperatures drop into the 40s and 50s, baby calves will be using more calories to stay warm.
Trying to stay ahead of the energy curve during the winter can be a challenge, especially with soaring feed prices. Work with your nutritional consultant or feed company representative as you plan for the upcoming cold weather and keeping your herd healthy.
The author is a dairy nutritional consultant and works for Central Connecticut Cooperative Farmers Association in Manchester, Conn.