As spring approaches, so does calving for most beef cattle producers. Spring also begins the most critical part of the journey for the replacement heifer becoming a cow.

A spring calving replacement heifer with a target mature weight of 1,200 pounds is likely weighing about 950 pounds entering the last trimester of pregnancy and would need to gain about 2 pounds per day prior to calving even if she was in a moderate body condition. In the last trimester, at least half of that weight gain will be related to fetal growth and not to the growth of the heifer. Feeding an ad libitum amount of hay containing 52% total digestible nutrient (TDN) and 8% crude protein (CP), along with 3.4 pounds of distillers grains would meet the crude protein needs of this heifer and her rumen undegradable protein needs.

However, this diet is still slightly short on the energy this heifer needs. This could be concerning if the heifer is thinner than desired and weather conditions are particularly harsh. Blending in some higher-quality hay or adding other energy feeds could improve her energy balance.

Once the heifer calves and lactation starts, both her protein and energy needs will increase substantially. The early-spring calving heifer (February or March) will likely not have access to any green grass for a few months in most of Nebraska and the upper Midwest. If this lactating heifer were fed the previously mentioned hay and 3.4 pounds of distillers grains, she would be well below the energy she requires. This is a critical situation for the cow, and even more concerning if turnout to green grass is delayed or the new mother is thinner than desired.

Sometimes during calving, producers will have green grass become available to the cows. Assuming this lactating heifer can find enough green grass to make up half of her diet and the producer feeds the hay containing 52% TDN and 8% CP to make up the difference, this heifer is still slightly short on her energy needs. Supplying 2.2 pounds of distillers grains would help ensure this heifer’s needs were met. Additionally, supplying more nutrient-dense supplemental forage would be sufficient. If enough green grass were available, she could meet her needs with grass alone.

Shortly after peak lactation, when nutrient needs are the highest, this heifer is asked to rebreed. Therefore, making sure her nutrient needs are being met just before calving through breeding is critical for her to remain in the herd. Checking feed resources for nutrient content before late gestation will help producers determine if the nutrient needs of these heifers are met. Assessing body condition score frequently will also allow producers to make necessary changes to the ration in a timely manner. For more information on the nutrient needs of beef cows, see NebGuide 2268 Supplementation Needs for Gestating and Lactating Beef Cows and Comparing the Prices of Supplement Sources. University of Nebraska Extension educators and specialists are available to help with ration balancing.

Jenkins is a Nebraska Extension cow-calf range management specialist. This report comes from UNL BeefWatch.