One of the most time-honored traditions in putting together a quality cow herd has been retaining and developing heifers from within the herd itself. While many heifers are required to replace cull cows which no longer have a place in the herd, additional females may be retained to build numbers. Also, quality heifer calves from outside the herd may also be purchased and developed. It is estimated that about 30 percent of the heifer calves produced in the U. S. are retained and developed for cow herd replacements. Costs associated with heifer development represent a significant up-front investment. Additionally, management of the heifer during the development period can significantly affect her lifetime productivity and must be carefully planned. Much of the following text was taken from a paper by Dhuyvetter and Lardy, ND State (1999).
Research has shown us that heifers that calve early in their first calving season continue to calve early in subsequent calving seasons and wean heavier calves throughout their lifetime compared to heifers that calve later in their first calving season. Therefore, it is very important that heifers are managed to enhance productivity and control costs.
The period from the time the heifer calf is weaned to the time she is bred is critically important in replacement heifer development. As a producer, your goals should include getting heifers bred early, minimizing calving difficulties, weaning acceptable calves, and having the heifer stay in the herd for a long, productive life.
As with any growing calf, prior to weaning, the replacement heifer is largely dependent on the dam to provide nourishment and care. However, there are some management practices which can impact the future productivity of heifers during this period. If possible, heifers should be individually identified to allow producers to base selection upon actual records of birth weight and weaning weight. Other considerations include:
1) Creep feeding. Data regarding creep feeding replacement heifers is controversial. In some instances, creep feeding replacement heifers can result in reduced performance when those heifers enter the cow herd. The problem is more prevalent when the cows are good milkers and creep feed is consumed at a rate of 3 to 6 pounds per day. Apparently, excess fat can be deposited in the mammary tissue, resulting in lower milk production potential and lower productivity when heifers enter the cow herd.
In contrast, an extensive survey conducted by the American Simmental Association and Montana State University indicated no reduction in subsequent performance when creep fed heifers were compared to non-creep fed heifers.
2) Selection. Traditionally, the biggest heifers at weaning have been retained for replacements. This method is simple and straightforward. This selection method is not necessarily bad, since older heifers from earlier calving, heavier milking dams with good growth potential would be selected. However, care must be taken to avoid selecting heifers which may be overly fat. This can lead to reduced milk production, or may have some endocrine imbalance leading to reduced fertility. This method may also result in the gradual increase in mature cow size, which at some point leads to herd production inefficiencies.
A strict selection process should be developed to select replacement heifers. This process should use available weight and performance records as well as visual appraisal. Select heifers from sires that transmit desired milk production and mature size and have demonstrated early sexual maturity. From this pool keep those heifers of desired body type and frame size which are most likely to breed early, calve without difficulty, and remain sound with minimal inputs.
Age at Puberty
In order for a heifer to calve at 22 to 24 months of age, she must reach puberty by 12 to 14 months of age. Table 1 shows the breed group averages for age and weight at puberty based on data from the US Meat Animal Research Center.
Breeds and breed types vary with respect to age at puberty. In addition, sire selection within a breed also plays a role in determining age and weight at puberty. Age and weight at puberty are moderately to highly heritable traits. This means that producers can use selection to improve these traits within a given herd.
An easy method of selection for age at puberty in replacement heifers is to select daughters of bulls with large scrotal circumference. An interesting correlation, in general, bulls with larger scrotal circumferences have daughters that reach puberty earlier.
Another related study at the University of Nebraska indicates that exposing heifers (from weaning to breeding) to surgically altered (gomer) bulls can reduce age at puberty by 40 days and increase the number of heifers bred during the first 21 days of the breeding season.
Target Breeding Weights
Heifers that breed and calve early their first year have been shown to have an advantage in lifetime production. This is in addition to a reduction in overall production costs to the initial calving. For early breeding to occur, heifers must be cycling at the start of the breeding season. Furthermore, conception is greatly improved by breeding after several heat cycles compared to the first estrus. Therefore, heifers should be cycling 60 days prior to breeding or by about 12 months of age.
The level of nutrition the heifer receives the first winter following weaning will influence her rate of development, weight gain, and the age and weight at which she reaches puberty. Heifers fed for a higher rate of gain will be heavier and younger at puberty. Low rates of gain will delay puberty, but heifers will reach puberty at a lower weight. The fact that weight has such an important impact on sexual development allows use of a simple nutritional management concept known as target weight. A heifer's target weight is the minimum weight she should achieve by the time she is exposed for breeding.
Current target weight recommendations call for heifers to weigh 65 percent of their estimated mature weight at the time of breeding. Mature weight of heifers can be estimated from frame scores determined by measuring height at the hip or from weights of similar cows in the herd.
Feeding management is especially important at this time. In addition to greater feed costs, overfeeding heifers may also contribute to decreased productivity. The period from about three to nine months of age is critical to mammary growth in heifers. Both inadequate nutrition and overfeeding in this period have been shown to result in reduced milk production.
Target gains will vary depending on weaning weights, frame size, breed type, and length of the backgrounding feeding period. Typical gain targets from weaning to breeding are 1.25 to 1.5 lbs per day for British breed type heifers and 1.5 to 1.75 lbs per day for Continental breed types. Research suggests that the rate of gain in the development period does not need to be constant as long as the target weight is reached. In fact, some research identifies advantages to developing heifers in stages of reduced energy and gain followed by periods of compensatory growth. A slight reduction in feed expenses has been shown for heifers developed at fairly slow rates of gain early followed by a period of accelerated growth just prior to breeding.
Feeding and Nutrition
It is relatively easy to feed heifers from weaning to breeding to accomplish targeted moderate rates of gain with fairly simple rations. Replacement heifers have nutrient requirements which differ from the rest of the cow herd; consequently, they should be fed and managed separately.
Heifers are commonly developed most economically on high forage rations supplemented with grains and grain by-products, protein concentrates, and minerals as needed to meet their needs and gain target. Modest levels of gain can be achieved solely on high quality roughage fed on a free-choice basis.
In addition, it is important to understand the composition and quality of feeds to be fed. Forages, in particular, vary considerably in level of protein and energy and should be analyzed in order to accurately balance rations. High quality hays are those with over 12 percent crude protein and 58 percent TDN. Hays with crude protein values between 8 and 11 percent and TDN in the mid 50s would be considered average quality hays. Hay with less than 8 percent crude protein and 52 percent TDN would be considered low quality forage.
Insufficient energy intake which results in poor growth can have negative effects on breeding performance of heifers as yearlings and on their subsequent performance in the cowherd.
If large groups of heifers will be developed, producers should consider splitting the heifers into two or more feeding groups (based on weight). This will allow more precise feeding of each group based on necessary target breeding weights and daily gains.
Proper feeding and nutrition of developing heifers is crucial. What are the costs of nutritional mismanagement? Here are a few of the implications:
· increased age at puberty
· Lower conception rates
· Greater degree of calving difficulty
· Increased calf morbidity and mortality
· Calves born later in the calving season
· Lighter weaning weights
· First calf heifers with poor reproductive performance during rebreeding
· Later rebreeding of first calf heifers
· Reductions in lifetime productivity
· Increased rate of culling
Building a quality cow herd requires significant investments of time, money and above all, dedication. It is up to the producer to determine which methods he wishes to follow and implement the appropriate strategies to achieve the desired goals which is a cow herd that is profitable today and tomorrow.
Dr. Steve Blezinger is a nutrition and management consultant with an office in Sulphur Springs, TX. He can be reached at P. O. Box 653 Sulphur Springs, TX 75483, by phone at (903) 885-7992 or by e-mail at firstname.lastname@example.org.