Written with contributions by Adele Harty, former SDSU Extension Cow/Calf Field Specialist.
We are beginning to enter the last 3 months of gestation for the majority of spring-calving cows in South Dakota. Below are a few questions that each cattle owner should ask themselves as their cows enter the last trimester of pregnancy:
- What body condition are the cows in?
- Is there enough forage available for them to graze?
- If there is not enough forage to graze, is there hay available?
- What quality is the forage?
- Does protein or energy need to be supplemented?
- Which feeds are considered energy and/or protein sources?
First, what condition the cows are in is a critical question to ask. Depending on weather and feed conditions since weaning, some cows may now be in a less than desirable body condition score. The ideal body condition score is between 5 and 6. These cows will have some cover on their ribs, but you may still be able to make out the last rib or two. They should also have some fat around their tail head. If cows go into the last trimester in good condition, they will be easier to maintain than if they are in a BCS 4 or lower. It becomes more difficult to increase body condition score in late pregnancy or after calving. Additionally, an important issue to consider is the energy demand of winter cold stress. Two weeks of 20 below zero temperature will take off one BCS if the diet isn’t adjusted for cold stress. This is especially true for cows that are already thin (fat cover is a great insulator).
To consider the next questions, first, if you are short on grass or hay, you will have to supplement energy to make up for that deficiency. A cow in late gestation requires an adequate supply of a 50 to 56% TDN diet. This can be provided with a variety of byproduct feeds if adequate grass or hay are unavailable. If there is sufficient forage but the protein content is low, such as dormant winter range or crop residue, a protein supplement will be needed. To determine the amount of protein to add to the diet, it is important to know that cows in late-gestation need a diet containing approximately 7 to 9% protein. Most low-quality forages will be 3 to 5 % protein so they will require supplemental protein. Make sure to consider the protein from the forage and from any supplement to determine the amount of supplement that may be needed. On the other hand, good quality hay should have adequate protein content due to earlier harvest date.
A mature cow on winter range during her last trimester without supplement will lose a BCS in abut 40 to 50 days. Both protein and energy are deficient in dormant standing forage. To overcome these deficiencies, you could add 4 pounds of a 20% commercial cake type of supplement to the winter range to maintain BCS or provide a byproduct feed such as dried, modified, or wet distiller’s grains. Another option would be to use home-grown harvested forages instead of purchased supplement. You could add 12 pounds of a 10% CP hay along with grazing winter range or crop residue (such as corn stalks) to maintain BCS. What ration you choose depends on your feeds that are available.
If an energy supplement is needed, the best options are high fiber energy sources, such as soy hulls, sugar beet pulp, and corn gluten feed. If protein is needed, there are many options associated with oilseeds (soybeans, sunflowers), oilseed meals (soybean meal, sunflower meal, and cottonseed meal) and by-product feeds such as fishmeal and distiller’s grains. When feeding by-products, palatability must be taken into consideration. Additionally, sulfur toxicity can be a concern with distiller’s grains. There are several different options for the type of supplement to use, and which to use should partially be determined by the equipment that is available to deliver it.
It is best to start managing your cows’ BCS in the fall because this is the easiest and cheapest time to increase body condition. Strive to have your cows at a BCS of 5 or better in late pregnancy. However, if weather or other conditions cause BCS to be less than desired as they enter the last trimester of pregnancy, feed management to obtain a BCS of 5 or slightly better by the time they calve will be critical to calf health and cow fertility during the following breeding season.