Updated for April 2024:
The reproductive success of a beef cow-calf operation is built on its replacement heifer development and feeding programs.
In an optimal system, replacement heifers are selected as calves at weaning.
They must then grow at a minimal rate so they are ready to be bred and conceive by a time that permits them to calve about a month before the main herd, at less than two years of age.
They must then raise their own calf and be successfully bred again in time to calve with the first fifty percent of the main herd if they are to not adversely affect the overall herd calving interval, and calving distribution over time.
To achieve this, the nutritional program must be adequate to achieve some key growth and development milestones along the way.
Replacement Heifer Development:
Research has shown that first calf heifers take longer to recover from calving, and on average conceive 30 days later than the rest of the herd following calving.
Therefore, to fit into annual calving cycle of the herd, they must grow and develop at a rate that enables them to calve at 23 months of age.
This means, for optimal performance, they should reach 60-65% of mature body weight (MBW) by 14 months of age for breeding, and 80-85% of MBW at calving. With a cow MBW of 1350 lbs. (reasonable today), the target weights would be about 850 and 1150 lbs. respectively.
Assuming calves are born in March and weigh an average of 550 lbs. at weaning at 8 months of age, in November, the subsequent average growth rates would need to be 1.67 lbs/head/day during the first winter feeding period, prior to breeding, and about 1.30 lbs/head/day post-breeding during the heifer’s second winter feeding period (body weight gain is not expected during late gestation).
Replacement Heifer Nutritional Requirements:
The nutritional requirements for heifers at the different stages of development discussed above are compared with those for mature cows in the attached table. The forage used in the example (35% ADF, 58% TDN) would be approximately early bloom and generally considered high quality beef hay, , perhaps one step below good quality dairy hay.
The table illustrates that the highest quality ration is required by the growing heifer calves if they are to reach optimal breeding weight by 14 months of age.
The second highest nutrient requirement is for the first calf heifers during late gestation and post-calving, but note that the requirements for bred heifers are intermediate and comparable to that for the mature cows during calving.
Furthermore, with the exception of non-lactating (dry) beef cows in mid-gestation, all of the groups would require concentrate supplementation to achieve optimal performance and avoid excessive body-weight loss, and its adverse effects on colostrum and milk production and subsequent reproductive efficiency.
Lack of attention to the dietary requirements of heifers is why many herds experience poor reproductive performance with their heifers, as well as poor recovery and re-breeding post-calving.
Strategies for Feeding Replacement Heifers:
Achieving uniform heifer development and performance is difficult when forages are fed free-choice and grains are supplemented separately due to ingredient selection and competition between individuals.
This is where the use of a TMR mixer can be especially advantageous in that it permits the blending of forages, as well as the use of a range of cost-effective ingredients, including by-products, to achieve nutritional goals with minimal waste. The challenge is sometimes how to assemble and feed rations to avoid excessive batching requirements.
As is so often stated, the table shows why it’s generally recommended that bred heifers, and ultimately, 1st calf heifers, be fed separately from the rest of the herd, as their nutritional requirements are so much higher than mature cows in mid-gestation (dry cows).
If possible, running thin cows with the bred heifers during winter feeding can assist them to regain extra body weight prior to calving.
For most farms, and especially smaller farms, it should be adequate to formulate a calving ration based on the requirements of the 1st calf heifers (e.g. min. 62% TDN and 10% CP), and feed this to all the animals during late gestation and post-calving.
The same “calving” formulation can be fed to the bred heifers on a limited basis (e.g. 90-95% free-choice) when their grazing season is over, or a more precise formulation can be used until it is time for the “calving” ration to be started.
If sufficient numbers of heifer calves are kept for breeding, it may be practical to formulate a special mix for this group. With smaller numbers, as well as to save time, it may work simply add extra grain and/or protein supplement to a reserved amount of another ration, e.g. a bred heifer or calving ration, to bring its nutrient content up to the required level before being fed.
Regardless of the feeding method that is used, one can see that special attention needs to be given to the nutritional requirements of replacement heifers if one is to achieve optimal cow-calf performance over time …“Because Nutrition Matters™”.
Dr. Alan Vaage is a Ruminant Nutritionist with over 30 years of experience in the beef industry, and currently provides technical support for Jaylor Fabricating Inc., Orton, Ontario. Dr. Vaage can be contacted by email: nutrition@jaylor.com.
