Winter is here! As I write this, we have had some snow and freezing temperatures, along with a healthy dose of mud, but the worst is yet to come. Some grazers may still be utilizing stockpiled forages but many of us have transitioned to feeding hay, baleage or silage.
Hopefully, we know the quality of our forage and the needs of the livestock that will be consuming it. Maybe we have even planned for supplemental energy sources when needed. This is all great until Mother Nature throws a monkey wrench into things. Rain, snow, wind and mud can destroy our best-laid plans.
There are charts that tell us the nutrient requirements of all types of livestock during different stages of their lives. These help us know which forages are best suited to which animals and when a supplement needs to be added to maintain performance and reach genetic potential. What we sometimes forget is that these tables do not account for non-typical weather conditions.
Energy needs
A sunny day with no wind and temperatures near zero are better tolerated than a muddy, 40-degree day with blowing rain. The temperature below which an animal’s body begins to lose its normal function is called lower critical temperature, or LCT. Below this temperature an animal needs to have additional energy to maintain body heat and normal body functions.
For cattle with a dry average winter hair coat, the LCT is 32 degrees Fahrenheit. If the hair coat is wet, the LCT increases to 59 degrees. Goats and horses have values similar to cattle. For sheep with 2.5 inches of wool, the LCT is 28 degrees. For freshly shorn sheep, the LCT is 50 degrees.
Due to the water shedding properties of wool, sheep are not as severely affected by rain as other livestock with wet hair coats.
A rule of thumb for the increase in energy need is, for each degree wind chill value below the LCT, the animal will need an additional 1% increase in total digestible nutrients, or TDN. With a wet hair coat this increases to a 2% increase in TDN.
Examples
For example, a cow with an average winter dry hair coat and 10-degree wind chill temperature would require an additional 22% TDN — 32 degrees LCT minus 10 degrees wind chill equals 22.
Now let us look at a wet hair coat with a 35-degree windchill. In this case, LCT 59 degrees – 35 degrees = 24. Now we need to multiply this by 2 due to the wet coat.
This cow will require an additional 48% TDN. So, even though the wind chill temperature is 25 degrees warmer than the previous example, this cow will require more than twice the additional energy that needed in the previous example.
Animals can eat more to compensate for increased energy needs. Cattle can increase consumption by nearly 30%, which would still not be enough for the example above.
There are two things to remember. First, we need to supply more feed. If not, they just run out of feed 30% sooner and go hungry waiting for more feed to arrive. Second, poor quality hay is slower to digest. Ruminants physically cannot eat as much poor quality hay as good hay.
Problems
The examples above show how easy it is for an animal’s energy needs to increase beyond the point where simply eating more will fix the problem. Bad things can happen when breeding animals are losing weight.
Reduced energy and weight loss during late pregnancy can lead to birthing difficulties, decreased milk production, reduced weaning weights and an increased length of time to breed back. These issues can have effects on future years performance.
The research evidence of how nutrition can affect future genetic expression of a fetus after it is born keeps building. Poor conditions during pregnancy can lead to multi-generational reductions in performance.
Prevention
There are ways to help prevent these problems. We need to test our forage, so we know if and how much supplementation is needed. Knowing what we have helps us feed forages so that we are not overfeeding or underfeeding.
We need to provide shelter to reduce wind chill issues. This can be a simple windbreak. While a dry inside location is great, a location that collects moisture and mud is not. Wet buildings with limited airflow can increase problems.
Feed late in the day, if possible. Maximum production of heat typically occurs 4-6 hours after consumption.
Finally, continue to feed energy at a higher level for a few days after the poor weather conditions end. Despite our best efforts the animals likely have to rely on their fat stores during the poor weather and need a little extra time to replace those stores so they will be ready for the next change in weather.
