Heifer Development Beginning at Weaning

By Steve Boyles

HEIFER SELECTION:  Heifers can be sold at weaning or anytime thereafter.  Select at least 20% excess and continue growing the heifers until breeding.  A second selection at yearling age is helpful.  Let the bull or artificial insemination program select the heifers you keep by maintaining a relatively short breeding season (45 days).  Pregnancy diagnosis after the breeding season provides another opportunity for culling.  A final selection can be made after heifers wean their first calf.  Weaning weight of the first calf is a fairly good, though not foolproof, indicator of future production.

EARLY GROWTH (weaning and yearling weight) AND FRAME:  The traditional method for choosing replacements is pick the big ones at weaning.  Traditional selection is simple and is not necessarily all bad.  If growth is needed, selection on size will provide it. The bigger heifers are generally older, and thus selection is from the earlier calving cows. It also may (or may not) select heifers of heavier milking cows.  Heavier and older heifers are more likely to cycle and breed early and be well on their way to having acceptable lifetime performance.

However, there are problems with the traditional method of selection.  Some of the heaviest heifers at weaning may be fat and offer the potential of poor lifetime milk production due to fat deposits in the udder.  Some big heifers are fast growing due to an endocrine imbalance and are subfertile at breeding.

The biggest problems traditional heifer selection is “frame creep”.  This is the gradual increase in mature cow size over time resulting from the use of larger frame bulls and retention of their daughters.  The larger, higher maintenance dams may be too big for the feed resources. If nutrition does not change, these cows may suffer reproductively.

Selecting heifers for larger actual weight will generally result in a more uniform group capable of reaching pubertal weight at about the same time.  So long as their sires and grandsires are not too big, there is little danger that selecting the larger heifers will cause significant “frame creep”.  Be careful not to mistake frame for weight.  Framey heifers with below average body condition may be “hard keepers” later in life.

FRAME SIZE:  Matching the development program with genotype: We know that most components of fertility that influence first calving and subsequent reproductive performance are not highly heritable. This suggests that management practices are most likely to influence the majority of factors related to reproductive performance. How we manage replacement heifer calves from the time they are weaned from their dams to the beginning of the first breeding period is extremely critical for their subsequent performance.

Studies indicate that puberty can be expected to occur at a genetically predetermined size among individual animals, and only when heifers reach target weights can high pregnancy rates be obtained. In other words, heifers with the genetic potential to reach a heavier mature weight must attain a heavier prebreeding weight before their first breeding season. Using the standard set by the Beef Improvement Federation for nine frame-size classifications for U.S. breeding cattle (Table 5), producers can estimate body composition and energy requirements per pound of gain at various weights during the feeding period.

Table 5.  Relationship of Frame Score and Hip Height to Estimated Mature Cow Weight^a

aHip height (in.) based on Beef Improvement Federation standards. Weights (lb) are expected averages for flesh condition (body condition score 5). Source: Fox, D. G., C. J. Sniffen, and J. D. O’Connor. 1988. Adjusting nutrient requirements of beef cattle for animal and environmental variations. Journal of Animal Science 66:1475.

Weaning weight and yearling weight are moderately to highly heritable traits (.25-.50).  As a rough guide, heifers that have within-herd weaning weight ratios below 90 (herd average 100) should be culled in a commercial herd.  One caution to keep in mind is watch for calves that have high adjusted weaning weights and low actual weaning weights.  These calves may come from heavy milking cows that are late calvers in the herd. In a purebred herd, the heifer’s EPDs for weaning and yearling weight should be used when making selection decisions on growth.  If seedstock producers are having trouble keeping their heaviest milking cows (high milk EPDs) in the early part of the calving season, they need to be aware of the impact that the some of these cows could have for their commercial bull buyers.

Yearling weights are a more accurate predictor of growth potential than weaning weights.  Yearling hip heights are more accurate for predicting mature size than weaning hip height.  Heifers with the heaviest yearling weights tend to be the largest framed.  Maximum acceptable frame scores may need to be established to match cow size with feed resources.  To remove your personal biases, it is suggested an unbiased 3^rd party measure your heifers and categorize them to frame and estimated mature size.

Growth is an important trait in heifer selection but there are other important traits.  What are those traits?

MATERNAL/PRODUCTION TRAITS:  The traits that are important in replacement heifers are the maternal traits: early puberty, fertility, calving ease, milk, soundness (longevity), temperament and efficiency.  Early puberty is highly heritable (H² = 50%) and related to early first pregnancy.  Calving ease is important because it affects the time required for rebreeding.  Soundness traits (feet, legs, udders, eye, etc.) are highly heritable and are related to longevity and productivity.  Genes for mastitis resistance have been identified; selection for bloat resistance have been accomplished; evidence has been developed indicating genetic differences in the incidence of fescue toxicity.

HEIFER SELECTION WITH CROSSBREEDING SYSTEMS:  Hybrid vigor is important but is not everything.  Producers should not overlook good replacement prospects just to gain a little more hybrid vigor.  Keeping heifers of terminal sires may cause “frame creep”.

TIME WHEN BORN:  Adjusted 205-day weights and ratios provide a better estimate of the true genetic differences in preweaning growth of the calves and milking ability of the cow than do actual weaning weights.  Late-born calves with light, actual weaning weights can still have excellent adjusted 205-day weights and ratios.

MILK PRODUCTION: Caution, some heavy milking cows may not meet nutritional requirements through the available forage.  The calving intervals for these cows will generally exceed 370 days.  Selecting replacement heifers out of these cows could eventually cause an increase in open cows.  Heifers with the heavier actual weaning weights are more likely to cycle early and calve early as 2-year-olds.  Therefore, actual weaning weights may do a better job of identifying the heifers and cows that will be the most productive.  Seldom should heifers be selected as replacements that have low actual weaning weights, but high adjusted weights and ratios.

Seedstock producers are selling the “genetics” for growth and milk.  The adjusted weights and other genetic indicators such as pedigree EPDs become more important.  However, seedstock operators should not produce cattle that are not adaptable to their customer’s resources.  If seedstock producers are having trouble keeping their heaviest milking cows in the early part of the calving season, they need to be aware of the impact that the some of these cows could have for their commercial bull buyers.

DISPOSITION:  Research has found differences in chute scores between heifer and steers.  It has been found that steers have a lower (more desirable) average temperament rating than heifers.  Cattle that are calmer have higher average daily gains than do cattle with excitable temperaments.