Remember Energy Needs During the Last Trimester

For most spring calving beef herds, energy needs in winter become more important as the cow fights harsh weather conditions and approaches (or is in) her last trimester before calving. During this time, she is preparing herself for both birth and lactation, in addition to rapid calf growth and development. Diets lacking sufficient amounts of energy during this time can result in loss of cow body condition (BCS) regardless of environmental conditions. This can lead to lighter calves at calving and weaning, decreased milk production from the cow, longer post-partum interval, delayed rebreeding for the cow, and can negatively impact a calf’s lifetime performance. Wind, wet weather, and poor housing conditions can magnify this issue as well. By understanding the importance of adequate energy and clean hair coats have on cows during the latter portion of winter, beef producers can prepare a plan to deliver appropriate amounts of energy to help cows and their future calves. 

A major factor in determining increased energy needs for cows during extreme weather conditions is being aware of what is called the thermoneutral zone. The thermoneutral zone is the temperature range where cattle do not need to expend additional energy to maintain their core body temperature. When temperatures fall below the thermoneutral zone, cattle will need to use additional energy to maintain their core body temperature; this area is called the lower critical temperature. Hair coat, wind, and moisture conditions impact the lower critical temperature. 

Cows adapted to cold climates will grow a heavy winter coat. Heavy winter coats work by trapping air to create insulation and allow the lower critical temperature to decrease if the cow’s body condition score is sufficient. Cows with heavy winter coats will have a lower critical temperature of around 18 degrees Fahrenheit under normal coat conditions (minimal wind, clean, dry coats). Under these normal conditions, a rule of thumb is to increase energy in the ration by 1% for every degree below the lower critical temperature. It is important to remember that during the last trimester, the cow’s rumen capacity is reduced due to the calf’s rapid growth. This reduces the cows’ voluntary feed intake and emphasizes the need for producers to test forages to be sure nutrient-dense; high-quality feedstuffs are being delivered to meet cow needs. 

The lower critical temperature of cows will increase when they are exposed to wind, precipitation, and muddy conditions. This change in lower critical temperature will also increase their energy needs more than the 1% recommendation. Table 1 compares the energy needed during winter weather conditions in Wisconsin for a 1400 lb. cow with a body condition score of 5.5 during the second and third of pregnancy in a spring calving cow herd. 

Table 1

It is a general rule of thumb that 1.0 Mcal of NEm/day is equal to 1 lb. of corn. This illustrates the impact extreme weather and/or wet haircoats have on energy requirements for cows during their middle and third trimester. Keeping cows out of the wind, keeping them dry, and out of deep mud (less than ankle deep) can help cows stay on a healthy path as they reach calving. By helping cows stay clean and dry, especially during their last trimester, beef producers can expect better and more productive cow-calf pairs this spring. 

Author

 

Adam Hartfiel

Regional Livestock Educator – Adam Hartfiel is Regional Livestock Educator for Adams, Green Lake, Waushara Counties. His educational programming has focused on beef cattle production and management.

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