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Heifer Reproductive Management Strategies: Selection, Rearing And Breeding

published: August 24th 2007
by: Bruce B. Carpenter Associate Professor a

Introduction

The selection and development of replacement beef females is critical to the performance of the entire beef operation. Selection of replacements at weaning, and the subsequent management given to yearlings and two-year-olds, can affect performance well into their years as mature cows.

It may be helpful to conceptualize, or manage, the replacement heifer enterprise within the context of “Strategic Planning.” This well known model for business planning consists of three components which are developed from the top-down, and implemented from the bottom-up.

1. “Strategic goals”: These are typically long-term. i.e. Why am I doing this? Will I raise or purchase replacements? Etc.

2. “Tactical goals”: These are things that must happen year-in, year-out for strategic goals to be met. They may include targets for production such as pregnancy rate or conception patterns, type of early breeding program, etc. Other examples might include identifying the type of replacements to be purchased, or the kind(s) of bulls to be used.

3. “Operational activities”: These are activities that happen daily, weekly or seasonally in order for long-term plans and goals to be realized. They might include things like feeding (how much and how often), check-weighing animals for target weights or average daily gain, obtaining reproductive tract scores, scoring animals for body condition, estrous synchronization, implementation of pasture and forage monitoring, and perhaps most important - contingency plans and readjustments.

The remainder of this discussion will focus on operational activities and how they relate to given targets for production (tactical goals) in the replacement heifer enterprise.

Overview

Both first and second calf heifers have higher nutrient requirements than do mature cows and management systems must account for this. Further-more, the overall productivity for all ages of heifers is substantially lower than for mature cows. These factors interact to make the replacement heifer enterprise the most expensive of all beef enterprises on most ranches. However, because these animals represent a large part of the genetic future of the beef herd, and because properly developed heifers usually go on to make good, productive cows, extra care and attention is certainly warranted.

Key Points in Selection and Development of Heifers are:

•At weaning, select the oldest, heavier (within breed type) heifers.

•These types of heifers are themselves out of early calving cows.

•Manage them to gain 1.0 to 1.25 pounds per day from weaning to first breeding. This allows them to be at 65% of expected mature weight at 12 - 16 months of age.

•Breed yearling heifers 30 days before the mature cow herd.

•Feed and manage yearlings, two-year-old, and mature cows separately.

•Likewise, keep the financial information on these groups separate. This allows each management group to be evaluated for strengths and weaknesses.

Maximum reproductive rates may not equate with economically “optimum” reproductive rates.

Nevertheless, all ranches have financial break-even points and at some point, production revenue must cover

certain costs.

Feeding Heifers to Reach

Biological End-Points

A good procedure for developing yearling heifers to insure that a high percentage have reached puberty by first breeding, is to use actual weaning weights to select replacements. In addition, it is recommended to select heifers that are born in the first 60 days of the calving season. This allows managers to begin with animals that are physiologically more mature. Keep about 20% in excess of what the anticipated replacement rate is. Establish a target weight (65% of mature weight). Establish a target age (12 - 16 months according to breed type). Calculate needed average daily gain. Weigh animals individually during the growth phase. Remember that averages, or averages on group weigh-ups can be misleading since a large number of heifers may weigh  below the group average.

Information on weight gain can be used in several ways. First, it will indicate if heifers are growing sufficiently and if not, then it will afford managers a chance to implement contingency plans. For example, light-weight heifers can be sorted and fed separately, or sold to prevent further losses. Also, information on weight gains can be used to plan anticipated calf crops, budgets, and cash flow. For example, weight gain data can give a rough idea of anticipated calf crops. That estimate could be 7-8 months ahead of information on calf crop projections derived from a post-breeding pregnancy test. For example, if all heifers reach target weight, then their calf crops would likely be in the 80-90 % range; whereas, if only 70% reach target weight, then anticipated calf crops might be in the 50 to 60% range. Planning budgets could be adjusted accordingly.

Adequate body condition, especially just prior to calving is critical for pregnant heifers. Heifers should have a body condition score (BCS) of 5-6, meaning that no ribs are showing and that they have a smooth appearance with slight fat deposition. Heifers should be fed to maintain good condition throughout the breeding season. Thin (BCS 4 or less) first and second calf heifers have low rebreeding rates compared to heifers with higher BCS.

Nutrient Requirements. It is impossible to accurately supplement growing or pregnant yearlings along-side dry cows, lactating cows or lactating two-year-olds. All four classes of females have different nutrient requirements. For example, when lactating two-year-olds are compared to lactating cows, the cows actually require slightly more TOTAL crude protein and energy. But because mature cows are larger in body size, actual forage intake is higher. Consequently, they consume more total nutrients. Because of forage intake limitations, and additional requirements for growth, both two-year-olds, and growing and pregnant yearlings, need a more nutrient-dense, higher quality diet. Dry cows in early and mid gestation have the lowest requirements for diet quality. Clearly, the amount of forage should never be limiting for any class of beef animal.

Deficiencies in any nutrient (water, minerals, vitamins, protein or energy) can limit production. Often, supplement costs can be reduced by managing the relationships between dietary protein and energy. Briefly, energy is critical for growth and the pubertal process in heifers, and under range and pasture conditions, forage typically supplies the bulk of energy in the diet. Yet during the winter supplementation period, it is protein that is most often the limiting nutrient in the grazing diet. Protein is required for growth and milk, but it is also required for rumen function. A 60-70 % ruminally degradable protein supplement can stimulate forage intake and thus dietary energy. Supplemental energy can come from fat, or starch (grain), or digestible fiber. Caution should be used with high starch supplements because they are capable of depressing forage intake and sometimes animal production. Often, high starch supplements are not as efficient or effective as supplements high in natural protein (Table 1; adapted Wallace and Parker, 1992). Also, depending on the amount fed, they often must be provided more frequently: daily or every other day, as compared to once or twice per week for a high protein supplements (Wallace and Parker, 1992).

Generally supplements high in non-protein nitrogen (NPN) are not as effective as natural protein supplements. This is due to a need for higher quality protein by heifers. NPN is best used in animals that may be only slightly protein deficient, and with low protein requirements (i.e. dry cows).

In order for protein supplements to work to increase forage intake, and thus dietary energy intake, it is imperative that there is an adequate supply of pasture forage (or hay). Cattle must be able to “fill up” daily. This requires eating about 2.5 % of their body weight per day in roughage. There may be specific situations where forage quantity is, or will become limiting. In these cases, energy supplements may be used to extend or replace the forage supply (See McCollum). However, because of supplement efficiency and expense, these are typically short-term propositions.

The relationship of forage standing crop to protein and energy supplementation is clear. Management of the forage standing crop through proper stocking rates will be a prime determinant of animal performance and supplemental feeding expenses. Also, moderate to light stocking under native range conditions, will allow animals more plant selectivity, meaning that a higher quality diet can be obtained. Again, this is something that replacement heifers require. In situations where hay is used as a winter supplement, the use of forage testing on hay can indicate what levels of additional nutrients will need to be provided as a supplement. Knowing this can control costs. For example, 6% protein hay would require twice as much actual protein in the supplement as a 12% protein hay.

Assessing forage Supply and Stocking Rate. Pastures, like cattle should be continually monitored. Projecting animal demand as it relates to forage supply (until the next growth phase) can help animal performance by ensuring their supply of forage - or with planning for contingencies - like hay requirements for the period. Assessment of pasture forage supplies should be done during times when forage will be dormant (winter, summer dry season, etc.). This technique works best in environments where winter annuals are not abundant. Forage supply can be calculated with actual sampling techniques, which usually are the most accurate, or by visual estimates with a trained eye (See White and Richardson). Remember that under native range conditions, only about 25% of standing forage production should be counted on for livestock use. This is because 1/2 should be left to protect soil and plants and 25% of what remains after that is unavailable to livestock. Some improved pastures may be grazed a little heavier, but never to the point where forage quantity limits animal dry matter requirements.

On improved warm season pastures such as coastal bermuda grass, hay is often provided in the winter. The cultivation of winter annuals such as ryegrass or clover can reduce hay and other supplement costs, and can compliment many heifer development programs.

How Do You Know if Nutrient Requirements Are Being Met? Weight gain in growing heifers is the best indicator. Weight gain associated with pregnancy can sometimes obscure true growth. So in pregnant heifers, body condition scoring is probably best. Again, if body condition is poor or declining, then supplemental energy and/or protein will be required. Study “cow pies.” Manure that is hard and “stacks up” may indicate a protein deficiency. Use of forage sampling can indicate diet quality. Similar procedures can be used with animal fecal analysis (NIRS; see GAN Lab). Always monitor body condition in all animals.

Rearing Strategies

Performance among all beef enterprises - yearling, two-year-old, and mature cows, is interdependent. Early calving cows produce older, heavier heifers. Older, heavier heifers breed and calve early. If managed properly as two-year-olds, they will go on to make productive, early calving brood cows.

Controlled Breeding Seasons. Efficient management, selection, and development requires that cows and heifers be in controlled breeding and calving seasons of 90 days or less. Calving seasons longer that 80-90 days do not allow females to be on a true 12 month calving interval where they produce a calf every year. This is because pregnancy lasts 9 months, leaving only about 80 days in the calendar year for reproductive tract recovery and subsequent rebreeding. Controlled calving seasons will facilitate several things:

•Uniform age groups to select and grow replacements from.

•Accurate and economically efficient supplementation to meet the different nutrient requirements of the herd’s production cycles (dry animals, late pregnancy, lactation, etc.)

•Marketing of uniform calf crops.

It is well known that lactating two-year-olds are very often difficult to rebreed. One technique that can be used to manage this is to initiate their first breeding 30 days before the beginning of the regular breeding season for cows. This affords first-calf heifers some extra time to recover and rebreed as still growing two-year-olds. Heifers that start out as early calvers have a much better chance of establishing themselves as early calvers for the rest of their productive lives. It is nearly impossible to “back-up” late calving heifers or cows.

Replacement Rates Will Affect Costs. An adequate reproductive rate in the cow herd becomes a key to minimizing replacement heifer needs. Many times replacement heifer needs are underestimated. Typical ranges are from 10 - 30% and are affected by death loss and culling rate. Cows will be culled for nonbreeding, unsoundness, age, etc. For example (adapted; Fuentz, 1995), a herd with an 84% pregnancy rate, 3% annual death loss and other normal culling would require 80% of all heifers born to be kept as replacements; whereas with a 94% pregnancy rate, 1% death loss, and other normal culling, only 39% of the heifer calf crop would be needed as replacements.

Proper management and development of heifers will ensure their own reproductive performance and minimizes the numbers needed for replacements. Hence, costs are minimized.

Heifer Tests and Other Specialized Development Programs. Sometimes forage conditions and/or management limitations do not facilitate proper heifer development. In these cases, management may look to “off-ranch” heifer development programs based on either concentrate feeds or forages. If these development programs are structured properly, opportunities will exist to evaluate heifers in contemporary groups (heifer tests) in order to identify superior genetics for gain and/or other benchmarks for development. The importance of weight gain has been discussed. Other benchmarks that may be evaluated include reproductive tract score (RTS) and internal pelvic area. These measurements, while well-correlated with body weight, may add additional insight into pubertal status and the selection process. Both procedures require an experienced and qualified person. For TRS, heifers are palpated per rectum. Ovaries are evaluated for overall size and for the presence of structures (follicles, corpora lutea) which would indicate ovarian activity. Similarly, the size and tone of the uterus is evaluated. Heifers are subsequently given a RTS on 1 to 5 (RTS 1-2, not pubertal; RTS 3, almost pubertal; RTS 4, very likely pubertal; RTS 5, pubertal). At the same time that a RTS is conducted, heifers may be measured internally using a specialized instrument to determine internal pelvic area (height x width). While internal pelvic area by itself, is not an accurate predictor of calving difficulty, it may be integrated with other techniques to reduce calving difficulty. These may include selection and use of light birth weight EPD bulls, and culling heifers with age-adjusted yearling pelvic areas less than 140 cm2.

Breeding Strategies

Calving difficulty (dystocia) can never be completely eliminated because some cases are due to incorrect posture or presentation of the calf at the time of delivery. However, dystocia can be managed and greatly reduced by using the right kind of bulls on first-calf heifers. The most successful way to reduce calving difficulty in heifers is to breed them to bulls with high accuracy EPDs for low birth weight. That is: bulls that are genetically proven to sire calves with birth weights that are significantly lighter than the breed average.

If EPDs for birth weight are not available, then select bulls based on breed type: use a small breed of bull on heifers of a larger breed type. Often Longhorn, Jersey or Corriente bulls are used because of inherently low birth weights. Realize that calves sired by these breeds will likely be discounted at sale time because of light muscle, bone, or color patterns.

Simply using a small bull (within the same breed type as the heifer), or young bulls, WILL NOT reduce calving problems.

References

TCE publications listed below can be accessed at: http://tcebookstore.org/

Fuentz, D.M., 1995. The costs of raising replacement heifers and the value of purchased versus raised replacements. Cattlemen’s Satellite Short Course. Session #11.

GAN Lab (Grazing Animal Nutrition Laboratory) http:/cnrt.tamu. edu/ganlab

Hanselka, W. and McGinty A. How Much Forage Do You Have? TCE B-1646.

Hanselka, W. and McGinty. Photo Guide to Forage Supplies on Texas Rangelands. TCE L-5476.

McCollum, T., Supplementation Strategies for Beef Cattle. TCE B-1614.

Wallace, J.D. and Parker, E.E., 1992. Livestock Research Briefs and Cattle Growers Short Course. New Mexico State University.