For many spring-calving herds, cows are well into the last three months of gestation. Ken Olson, associate professor and extension beef specialist at South Dakota State University (SDSU), highlights some key questions to ask yourself during this last trimester.

What body condition are the cows in?

“Depending on weather and feed conditions since weaning, some cows may now be in a less than desirable body condition score,” Olson starts in a recent iGrow newsletter post. According to Olson, the ideal body condition score (BCS) is around 5 or 6. These cows will have some rib cover but the last rib will still be defined, and they should have some fat around their tail head.

Cows who go into their last trimester of pregnancy in good condition will be easier to maintain than cows with a BCS of 4 or lower, since it is harder to improve BCS in late pregnancy or postcalving.

Olson also notes that it is important to consider the energy demand of cold stress. “Two weeks of 20 below zero temperature will take off one point in BCS if the diet isn’t adjusted for cold stress,” Olson explains. This is even more pronounced in thin cows.

Is there enough forage available for them to graze?

If there is not enough grass or hay for cattle to meet their energy needs, supplementation will be required. Late-gestation cows need a ration testing 50 to 56 percent TDN (total digestible nutrients).

To meet this TDN requirement, by-product feeds can be supplemented. If there is sufficient forage but with a low-protein content, a protein supplement is needed. Most low-quality forages have a protein content of 3 to 4 percent, while a cow in late-gestation needs a diet that has around 7 to 9 percent protein.

Does protein and energy need to be supplemented?

“A mature cow on winter range during her last trimester without supplement will lose a BCS point in about 40 to 50 days,” Olson says. “Both protein and energy are deficient in dormant-standing forages,” he adds.

To overcome these deficiencies, Olson recommends adding 4 pounds of a 20 percent commercial cake-type of supplement to winter range-fed cattle to maintain BCS.

Other options include providing a by-product feed like distillers grains or use homegrown, harvested forages instead of a purchased supplement. Adding 12 pounds of a 10 percent crude protein hay to winter range or crop residue diets will help maintain BCS.

If you need to supplement energy, high-fiber energy sources such as soy hulls, sugar beet pulp, and corn gluten feed are your best options. If protein is needed in conjunction with energy, feeds associated with oilseeds, oilseed meals, and by-product feeds such as fishmeal and distillers grains are options.

“When feeding by-products, palatability must be taken into consideration,” Olson elaborates. With distillers grains, sulfur toxicity can also be an issue.

Given that there are several options for supplements, what you decide to use should be driven 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 improve body condition,” Olson explains.

While a BCS of 5 or more in late pregnancy is desired, if adverse weather causes BCS to be less than ideal, feed management to improve BCS by the time of calving will be critical for calf health and cow fertility in future breeding seasons.

Kassidy Buse

Kassidy Buse was the 2018 Hay & Forage Grower summer editorial intern. She is from Bridgewater, S.D., and graduated from Iowa State University with a degree in animal science. Buse is currently attending the University of Nebraska-Lincoln pursuing a master’s degree in ruminant nutrition.