Crossbreeding systems for beef production

Commercial producers can improve productivity and efficiency by understanding and applying genetic principles. Improvement through genetics can be achieved using two different methods:

1. Selection
2. Crossbreeding

In order for commercial producers raising straightbred, single breed cattle to make genetic improvement, they must utilize selection, and provide an optimal environment for those cattle selected to express their genetic potential. Selection is an excellent tool with traits of moderate to high heritability such as growth rate and carcass traits. However, some of the most important traits related to beef cattle production, such as reproductive rate and calf survival, are of low heritability. This means the success of selection programs for these traits will be very limited.

Crossbreeding provides advantages from two main components, heterosis and complementarity. Heterosis (hybrid vigour) occurs when different breeds are mated together. One way to look at heterosis is that all purebred cattle are considered inbred as a result of breed formation and selection. Inbreeding leads to a reduction in performance, i.e. inbreeding depression. When different breeds are mated the crossbred progeny are less inbred than their parents. As a result the calves perform at a level above the average of their parents. This is heterosis, or hybrid vigour. Traits with lower heritability tend to exhibit high heterosis. Therefore, heterosis is more important for key traits relating to reproductive efficiency and calf survival, which have low heritabilities and do not respond well to selection (Table 1).

Each breed has it strengths and weaknesses. Complementarity results when desirable characteristics from different breeds are combined into a crossbred. Crossbreeding achieves a higher frequency of desirable characteristics among crossbreds than that found in either single parent breed. An example of complementarity would be mating a Charolais bull (growth and retail yield) to a Gelbvieh Angus cross cow. The result — the cow has the milk and the fertility, and the calf has more growth/retail yield. The characteristics gained from the mating complement each other. This effect of breed difference is powerful, but the choice of individuals from within a breed is also very important. Poor choices of breeds and animals from within a breed will have a lasting impact on the success of any crossbreeding plan.

Table 1. Heritability and Heterosis (Hybrid Vigour) Comparison

Heterosis in a sound crossbreeding program can increase productivity in the beef cow herd by 20%–25% over a comparable straight breeding program. To fully utilize the potential of a crossbreeding program, the cows themselves must be crossbred. Crossbred cows, when compared with straightbred cows, make better mothers. Crossbred cows wean approximately 15% more pounds of calf/cow exposed than straightbreds (Table 2). Another advantage is longevity and lifetime production. Research in Nebraska shows lifetime production and longevity of Hereford X Angus cows (3,258 lbs. weaned over 11 years) and Angus X Hereford cows (3,514 lbs. weaned over 10.6 years) was significantly greater than straightbred Angus (2,837 lbs. weaned over 9.4 years) or Herefords (2,405 lbs. weaned over 8.4 years).

The advantages of crossbred calves due to heterosis are also significant (Table 3). An optimum breeding system utilizes both methods of genetic improvement, with the mating of selected, genetically superior individuals in a well-planned crossbreeding program. This exploits both heterosis and complementarity.

Table 2. Heterosis Boost with Crossbred Cows

• 10% increase in conception rate
• 10% improvement in calving ease
• 7.5% increase in number of calves raised to weaning
• 5–10% increase in milk yield

Cumulative Effect = 15% increase in pounds weaned/cow exposed.

Table 3. Heterosis Advantage of Crossbred Calves

• 5% increase in number calves surviving to weaning.
• 5% heavier weaning weights
• 3% increase in postweaning gain

Combined Advantage = 10% more pounds weaned/calf born

Herd Level Production Improvements From Selection Or Crossbreeding

When calculating, at the herd level, the benefits from heterosis or selection over time, several factors have to be taken into account. Progress due to selection depends not only on the heritability of the trait, but also the intensity of selection, the genetic variation in the population, and the rate at which selected animals enter the herd (replacement rate). This makes the realization of benefits from selection a relatively slow process.

In contrast, benefits from heterosis are expressed at maximum value in each crossbred animal. This means that the payback from starting a crossbreeding system occurs much more quickly than from starting a selection program. For calf traits, maximum herd level heterosis benefits can be realized in the first year of a crossbreeding program, if all calves are crosses.

Figure 1 shows the expected economic benefits due to either selection or crossbreeding over a 5 year period, for the trait of calf livability (calves weaned/calves born). This trait has low heritability, but high heterosis potential. This example illustrates the difficulty in improving traits of low heritability through selection. Even after 5 years, the value of improvement from selection is very low (<$500 per herd), compared with benefits from heterosis (>$13,500). This represents a 34% increase in productivity due to heterosis, compared with the base straightbred herd. The economic benefit from increased calf livability in this case is 41 times greater for a crossbreeding program than for a selection program, over the first 5 years.

Figure 2 shows the anticipated benefits over time when these two different genetic strategies are used to increase weaning weight. This trait has moderate heritability and moderate heterosis potential. It is typically featured in selection programs in the industry. Although improvement in weaning weight through selection is significant, crossbreeding will result in twice the amount of economic benefit over the initial 5 years.

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Figure 1. Value of Additional Production Due to Selection or Crossbreeding to Improve Calf Livability ^(1,2,3)

¹ Accounts for heritability, selection intensity, genetic variation, cow replacement rate (20%), and parental contributions of sires and dams. Sires selected from top 10 % of population and replacement females from top 40% of heifer calves, for the trait of interest.

² Heterosis from implementation of a 3 breed rotational crossing program in a straightbred herd. Combination of heterosis due to crossbred calves and retention of crossbred replacement heifers in the herd

³ Calves valued at $1.00/lb, base straightbred herd of 100 cows with 90% conception rate, 90% calf liveability and 500lb weaning weight. Base herd production value of $40,500 per year.

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Figure 2. Value of Additional Weaning Weight Due to Selection or Crossbreeding ⁽¹⁾

¹ Accounts for heritability, selection intensity, genetic variation, cow replacement rate (20%), and parental contributions of sires and dams. Sires selected from top 10 % of population and replacement females from top 40% of heifer calves, for the trait of interest.

Three of the key production traits in cow-calf systems are conception rate, calf livability and weaning weight. The cumulative combined impact of heterosis for these traits, over an initial 5–year period, would be an improvement of 16% in value of production, relative to a base straightbred herd. In contrast, a selection program would be expected to increase value of production by only 3%, relative to the base herd (assuming that selection for multiple traits was as efficient as for a single trait).

This demonstrates the very large potential benefits of crossbreeding in cow-calf production. If the option of purchasing hybrid females as a means of initiating a crossbreeding program were considered, the benefits from heterosis would accumulate even more quickly. It is important to note that both selection and crossbreeding may be practiced at the same time. A strategic plan which utilized both crossbreeding and selection would optimize the use of genetics in the beef herd.

Crossbreeding Systems

Crossbreeding is an effective method of improving efficiency of production in commercial cow-calf herds. However, commercial cattle producers should study crossbreeding systems and evaluate them before deciding which one is suitable for their environment and resources. Table 4 outlines basic properties of crossbreeding systems to keep in mind when considering a program.

Table 4. Criteria for Evaluating Crossbreeding Systems

• Level of hybrid vigour (heterosis)
• Merit of component breeds
• Complementarity
• Consistency of performance
• Deals with genetic antagonisms
• Meets end-product target

In general, crossbreeding systems fall into 2 categories, those that produce replacement females as well as market cattle (rotational & composite systems), and those that produce only market cattle (terminal cross). In rotational (or composite) systems, bulls must be selected with maternal traits in mind as well as growth and carcass traits, since replacement heifers are retained from within the herd.

Terminal systems allow for greater emphasis on selection for growth and carcass traits in bulls since female replacements are supplied from outside the herd. The genetic merit of a terminal bull for maternal traits is of no consequence since his female progeny will not be bred. Calving ease must be considered regardless of the type of crossing system.

Rotational Systems

The rotational system requires establishing two or more breeding herds. In a two-breed rotational system, two groups of crossbred cows are established. Cows sired by Breed A are mated to males of Breed B, and females sired by Breed B are mated to males of Breed A. In a three-breed rotation, a third breed is added to the sequence (Figure 3). In rotational systems heterosis is retained at high levels, 66% in two–breed rotation, 86% in three–breed rotation. However, fluctuation in breed composition between generations can result in considerable variation in level of performance among cows and calves, unless breeds used in the rotation are similar in performance characteristics. Use of breeds with similar performance characteristics restricts the use that can be made of breed differences to optimize breed complementarity.

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Figure 3. Rotational System (3-breed)

Crossbred (Hybrid) Bulls

Hybrid bulls offer an alternative method of rotational crossbreeding. Using F1 bulls or composite bulls in rotational systems can significantly reduce intergenerational variance, especially if breeds chosen to produce F1 bulls optimize performance levels (ie. breed complementarity) in their crosses (i.e. continental X British). Using F1 bulls consisting of the same two breeds as the crossbred cow– herd but unrelated can result in retention of 50% of maximum possible heterosis. Supply of performance tested F1 bulls from selected and proven purebred parents may be limited.

Rotate Sire Breed

The rotation of sire breeds every 2 to 4 years provides similar benefits to a rotational breeding system for producers with small herds and limited breeding pastures. The result is simplified management, and individual and maternal heterosis. Disadvantages are the increased intergenerational variation and reduction in heterosis as breed makeup of females' swings more toward one breed and back again. This can be minimized if the breeds utilized are similar.

Rotating F1 males every 2 to 4 years can help reduce intergenerational variation but maintain complementarity if appropriate breed crosses are selected. By rotating different breeds of F1 bulls (AB, CD, EF, etc.) every 4 years, you can avoid wide intergenerational swings in biological type, if breeds A, C and E are similar in type as are breeds B, D and F.

Terminal System

In a terminal system (Figure 4) all calves are marketed and replacement females are purchased from outside the herd. This allows for more intensive selection for specific traits in the male and female lines used in the cross. Cows are usually selected for moderate frame, good milking and mothering ability. High growth potential and good carcass characteristics are important in the male line.

Heterosis benefits will be maximized when a crossbred cow (F1 female) is mated to a sire of a third breed. In a terminal system females are selected to match environment and resources while males are selected to meet end product targets (i.e. growth and carcass). High degree of complementarity and consistency of progeny is possible. Replacements need to be purchased and are price and availability dependent.

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Figure 4. Terminal System

Rotational Terminal

Figure 5 demonstrates a rotational terminal system. This system combines the best parts from the traditional rotational systems and the static terminal sire systems. The rotational part of the system provides replacement females while the terminal sire part of the system allows most of the marketed calves to be sired by growth carcass type sires. Cows remain in the rotational part of the system until they reach 4 years of age and then they move to the terminal part of the system. However a large herd size is required (at least 100 cows).

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Figure 5. Rotational-Terminal

Composites

Definition:

"A population made up of two or more component breeds, designed to retain heterosis (hybrid vigour) in future generations without crossbreeding with other breeds."

Composite cattle are hybrid cattle that breed to their own kind, retaining a level of hybrid vigour we normally associate with traditional crossbreeding. Management requirement of a composite herd is similar to a straightbred herd, substantial heterosis can be maintained in composite populations so long as adequate number of sires are used in each generation to avoid inbreeding.

Heterosis will vary depending on the number of breeds that were used to form the composite. It can range from 50% of maximum possible heterosis for a 2–breed composite to 87.5% for an 8–breed composite. Selection of breeds going into the composite is also critical. Breed differences should be fully exploited so as to match the composite with the environment in which it will be used and to match it with market specifications.

Composites have the potential for "standardizing" commercial cattle, thus reducing the variation we currently see in market animals. Problem cattle today, from the feedlot and carcass perspective, are biologically extreme breeds. These extremes in market cattle are due to purebreds, high percentage animals from extreme breeds or crosses of similar extreme breeds. Often the result of poor crossbreeding decisions. With a composite breed, crossbreeding decisions are made when the breed is formed. Commercial producers just need to choose what composite breed to use. Composites are expected to be complete and balanced in performance and only those composites that fulfill this expectation are expected to survive.

Which Breeds To Use?

The environments and the resources available to raise beef cattle are as varied as the breeds themselves (Table 5). Notice the tremendous variability in the available breeds. Another factor to consider is the large degree of variability that exists within a breed. Breeding decisions involve individual animals, not breed averages, so selection of the right individuals within a breed is critical. Breed differences like these can be blamed for product inconsistency, but they can also be exploited to produce adapted animals and a consistent product.

Great variation in the seed stock and commercial cow–calf sectors of the industry is important to ensure you are positioned to match biological types of cows to environments and resources. The challenge is to design effective crossbreeding systems that allow for diversity in the cow-calf sector and that deliver consistency of end product.

A number of factors must be considered when choosing breeds to use in a crossbreeding system. Among these are:

• individual breeding goals
• environment
• quantity and quality of feeds available
• cost and availability of good seed stock
• how breeds will complement each other in the crossing program; and
• market-specific breed combinations may command market premiums.

Table 5. Breeds Grouped into Biological Types for Four Criteria (a,b)

^a From Cundiff et al., 1993 BIF Proceeding

^b Increasing number of X's indicate relatively higher values.

Ideal Mix Of Biological Types

Scientists involved in breed evaluation research generally agree a mix of British and Continental breeding of about 50/50 for the cow herd would be optimal for most of North America, excluding the subtropical areas. Limited feed resources indicates a higher percentage of British breeding. Where abundant feed resources are available and/or maximum lean yield is desired, a higher percentage of Continental breeding is recommended. To maximize heterosis, do not over use any one particular breed.

Summary

Crossbreeding can increase productivity in the cow herd by 20%–25% over a comparable straight breeding program, due to heterosis. Heterosis improves performance in key traits that are of low heritability. Levels of expected heterosis for the various mating systems outlined above are in Table 6. This increase can be achieved without increasing cow size and maintenance requirements. Crossbreeding can also produce benefits from complementarity.

Crossbreeding is an effective method of improving efficiency of production in commercial cow–calf herds. However, study the crossbreeding systems available and weigh the advantages and disadvantages before deciding which one suits your environment and production resources. While it is important to use crossbred cows, it is even more important that these crossbred cows match your production environment and feed resources.

Focusing on end-product targets is the next step but should only take place when the cow type is optimized for the production environment. Table 7 is an attempt to characterize production environments and lists likely ranges for optimal levels of several important traits within those environments. To maximize the benefits of crossbreeding, a strong selection system must be utilized to identify breeding animals with superior genetic merit for heritable, economically important traits. Poor selection of breeds or bulls within a breed, will have a lasting impact on the crossbreeding program.

Table 6. Levels of Expected Heterosis for Various Mating Systems

Rotate Sire Breed Every 4 Years

Rotating F1 Bulls

Composites

* Relative to F1 @ 100%

Table 7. Matching Genetic Potential for Different Traits in Varying Production Environments(1)

Breed Role in Terminal Crossbreeding System

⁽¹⁾ L = Low; M = Medium; H = High; N=None

⁽²⁾ Heat, cold, parasites, disease, mud, altitude, etc.

⁽³⁾ Ability to store fat and regulate energy requirements with changing (seasonal) availability of feed.

⁽⁴⁾ Physiologic tolerance to heat, cold, internal and external parasites, disease, mud and other stress.

* adapted from Beef Improvement Federation. 1996. Guidelines for Uniform Beef Improvement Programs.