A costly, but extremely important, feature of the cow-calf herd is the selection and development of replacement heifers. As described by Freking (2000), the heifer is a long-term investment whose costs must be supported by the rest of the cow herd for up to three years. Additionally, replacement heifers are the source of new genetics for the herd.
Objectives of selection
The first step in selection of heifers is to define their purpose in the herd. Generally, the following criteria must be used:
- They must get pregnant at 12 to 15 months of age and wean a calf. We know from extensive studies that the most profitable cow herds are those that wean a high percentage of calves compared to cows exposed for breeding. Secondly, breeding the yearling heifer will result in one more calf in her lifetime compared to a first breeding at 2 years of age.
- They must rebreed and continue to produce a calf every year. The cost of replacing cows with heifers is both in nonproductive time and in lower weight and growth of calves from first-calf heifers. Sustainability in the cow herd is a significant economic issue.
- Be a source of genetic improvement to the collective herd by introducing positive economic improvements in fertility, progeny growth and progeny market value.
Standards for selection
The following practices in selecting heifers will help the breeder reach the objectives in the herd:
- Select heifers at weaning that are bigger. Absent a sire or other genetic effect, selecting the biggest heifers at weaning will identify the heifers born earlier in the breeding season. Studies from Lesmeister et al (1974) showed heifers that calve early in the calving season were more sustainable in the herd and weaned heavier claves than heifers that calved later. Bigger heifers also grew faster before weaning. This faster growth was probably a combination of higher milk production from the dam and better genetics for growth - both of which are positive contributions to the next generation of females in the herd.
- Use genetic prediction tools such as expected progeny differences (EPDs) to define the traits that best match the environment for the heifers. An important feature of a cow herd is that it should be selected to match the environment they must live in. Traits such as milk production and mature size reach an optimum level based on the environment for the cow. For example, a +20 pounds EPD for milk may fit Pennsylvania, but could seriously reduce sustainability in Montana. Alternatively, carcass traits in progeny would not be affected by the environment of the cow.
- Identify heifers that have enough condition to be healthy, but are neither overfat or very thin, regardless of weight. Heifers that are overly fat at weaning may have reduced milk production, particularly for smaller-framed cattle. Heifers that are much thinner than the rest of the calves may experience fertility issues later in life because of higher maintenance needs.
- Use docility as one factor of selection. In addition to the safety and ease of handling over their lifetime, docility (or lack of it) is partially a learned experience. Progeny that have docility issues will not perform in the feedlot or pasture as well.
Development to breeding
The nutrition and management of heifers postweaning should be a planned and precise process. The critical breeding weight (CBW) at breeding is usually defined as 65 percent of the mature weight. The CBW is a function of weaning weight and frame size. For example, a heifer that weighs 500 pounds in October, is a frame size 5 and has an expected mature size of 1,200 pounds should weigh at least 800 pounds at breeding in May with a daily gain postweaning of about 1.4 pounds per day. That same heifer that is a frame size 6 will have a mature weight of about 1,300 pounds, a CBW of 850 pounds and a daily gain of 1.7 pounds per day. In practice, breeders usually underestimate the weight of their mature cows, so often will not feed heifers appropriately. The other extreme is feeding heifers like they are in a feedlot, which is expensive and detrimental to future production. In the Pennsylvania Heifer Development Program now underway, we have found free-choice good quality baleage has been acceptable in growing heifers at about 1.8 pounds per day, and these 5 and 6-frame heifers have all met or exceeded their CBW without being overfat. Results of a Purdue study in Table 1 show how vital proper development can be to future production.
If natural service is used, the selection of bulls will be an important step. There is significant information now available on beef cattle that sires can be selected that can be used safely with heifers and without inducing calving difficulty. Birth weight and calving ease EPDs are available for most breeds, and these tools can be used effectively to reduce calving difficulty in first-calf heifers - the single biggest loss of calves with these young cows. Additionally, AI can be used with synchronization tools now available to further improve genetic reach in the next generation. This practice is particularly helpful when low birth weight bulls are not available or separate breeding herds for heifers cannot be maintained.
An important practice in breeding heifers is to breed them 30 to 60 days ahead of the mature cow herd. In single-sire herds, this can extend the use of the bull in a breeding season. The most important feature is that the first-calf heifer will have this extra time to regain condition, continue to grow, and care for a calf before being asked to get bred for the second calf and get on schedule with the mature cow herd.
The bred yearling is still a young, growing cow. Nutrition is still an important part of her management. In addition to the weight gain from the calf in utero, most average-sized heifers will also add another 150 pounds of body weight during this period. One practice is to restrict feed intake in late gestation to reduce calf birth weight. Research shows this is not a good idea. First, birth weight can be controlled at breeding with the right bull. Secondly, restricted nutrition also restricts normal growth of the heifer, the ability to maintain condition, and her ability to rebreed. All of these factors are a costly mistake. Some studies have shown this restriction can lead to more calving difficulty because of the debilitated condition of the heifer. Sensible management will get more live calves than less feed to heifers.
Monitoring body condition, particularly in the last 60 days before calving, will result in more heifers getting rebred on time. Between breeding and calving, these heifers should gain about 250 pounds and still be in good condition when they calve. Supplemental feed may be needed to maintain this condition and can be supplied by a number of feeds that supply both energy (about 10 pounds of TDN per day) and protein (about 1.5 pounds per day). Whole soybeans and distillers grains are effective supplements for these nutrients.
Replacement heifers are a necessary part of the cow herd, but they require special selection and management to be successful.
Dr. John Comerford is associate professor of dairy and animal science at the Pennsylvania State University. Comment or question? Visit www.farmingforumsite.com and join in the discussions.