Crossbreeding- The Lost Art?: Part 3
Livestock Update, April 2001
Scott Greiner, Extension Animal Scientist, Beef, VA Tech
Note: This article is Part 3 in a three part series dealing with crossbreeding.
The fundamentals concerning the basic advantages of crossbreeding were outlined in Part 1 of this series. The primary advantages of crossbreeding beef cattle are heterosis (hybrid vigor) and breed complimentarity. Part 2 focused on the design and management of crossbreeding systems, with specific attention on the application for small herds. Additionally, tools such as the incorporation of artificial insemination, as well as purchasing replacement heifers were discussed as mechanisms to enhance the management ease of crossbreeding systems.
Crossbreeding systems have been abandoned by some producers who have cited problems maintaining uniformity in the cowherd as well as the calf crop with certain crossbreeding systems. Certainly, the potential for mongrelization of the herd exists if a crossbreeding program is not well designed and managed. This article will focus on the key aspects relative to individual sire selection that are important for maintaining a breeding system that will work over several generations.
As with any breeding system, sire selection is critical for genetic improvement. With crossbreeding systems, more than one breed of sire is typically used. As a result, the calf crop and female replacements are potentially sired by different breeds and individual bulls within those breeds. It is the differences between the breeds utilized, as well as differences in individual sires used, which are responsible for variation in a set of cows or a calf crop. Therefore, for a crossbreeding system to be viable, sire selection (both within and between breeds) is critical for maintaining uniformity from one generation to the next- while at the same time taking advantages of the strengths of the various breeds used in the system.
The most fundamental sire selection decision is the choice of breed. Choice of breeds to be used in the cross will be dependent on several factors, including the resources of the operation (the optimum level of milk production they can support) and the marketing program for the calf crop (specifically the targeted carcass merit endpoint). The following table has been created using across-breed EPD adjustments. The table is indicative of the genetic merit of the average bull in each breed listed for the primary growth and maternal traits. The breeds may be directly compared, as the EPDs have been adjusted to a common base. Certainly, considerable differences between breeds exist that may effectively be utilized by crossbreeding. As mentioned previously, optimum performance rather then maximum performance is desired for virtually all economically important traits. For this reason, _ to _ British x _ to _ Continental females tend to optimize mature size, milk production, and adaptability for many Virginia producers. Similarly, a tremendous amount of growth potential can be added through breed selection.
Breed Average EPDs Adjusted to a Common Base
|Breed||Breed Average EPD|
The breeds chosen, and the percentage of each breed represented in the calf crop also have a pronounced impact on carcass characteristics. Coupling the general superiority of the British breeds for marbling potential with the red meat yield advantages of the Continental breeds results in offspring that have desirable levels of both quality grade (marbling) and retail yield (yield grade). The specific end product target will dictate the combination/percentage of breeds that are most likely to generate cattle with the desired carcass traits. Utilizing breed differences for carcass traits to match marketing grids will be important for producers as more retained ownership and value-based marketing is practiced.
Selection of bull within breed is equally important. EPDs are a very useful and important tool in accomplishing this task. At the same time, breed strengths and weaknesses and the genetic merit of a breed as a whole for a particular trait also need to be considered when bulls are selected for use in a crossbreeding system. In other words, EPDs need to be considered on both a within and across-breed basis for effective bull selection in a crossbreeding program. Using the EPDs in this manner will assist the producer in minimizing large fluctuations in performance and production from one generation to the next when using more than one breed.
The following table can be used to compare the EPDs of bulls from two different breeds. To put the EPDs on a comparable basis, simple add or subtract the adjustment factor to the within-breed EPD of the bull. For example, consider a Simmental bull with a WW EPD of +35 and a Charolais bull with WW EPD of +15. To fairly compare the WW EPDs of these two bulls of different breeds, the EPDs must first be adjusted using the across-breed table. Using the table, the Simmental bull would have an across-breed WW EPD of +60.4 (35 + 25.4 = 60.4) and the Charolais bull an across-breed WW EPD of +59.8 (15 + 44.8 = 59.8). In this example, we would expect progeny of the Simmental bull and Charolais bull to be very similar on the average for weaning weight (across breeds EPDs of 60.4 vs. 59.8, for only .6 pound difference). Across-breed EPDs may be calculated for the growth and maternal traits of any breed listed in the table. They may be used to compare bulls of different breeds that are being used in the crossbreeding program for similar purposes (i.e. milk production in Gelbvieh and Simmental, or growth in Simmental and Charolais). They may also be useful in managing uniformity when breeds are rotated in a crossbreeding system to avoid large fluctuations in traits such as birth weight and milk.
2000 Adjustment Factors to Add to EPDs of Various Breeds to Estimate Across-Breed EPDs
|Breed||Birth Wt.||Weaning Wt.||Yearling Wt.||Milk|
The adjustment factors may also be useful in managing uniformity when breeds are rotated in a crossbreeding system to avoid large fluctuations in traits such as birth weight and milk. For example, using these adjustments, it can be demonstrated that a Gelbvieh bull with a milk EPD of +6 will add similar milk genetics to an Angus bull with a milk EPD of +20 (both the bulls would be +20 on an across-breed basis). This demonstrates the differences between the breeds that exist, as a Gelbvieh bull that is +6 for milk ranks in the lower 10% of the Gelbvieh breed while an Angus bull that is +20 for milk ranks in the top 20% of the Angus breed. With this in mind, a Gelbvieh bull can be selected to compliment an Angus cow base that will add a moderate amount of milk. Similar calculations can be made for birth weight and growth. The key is to recognize the basic genetic differences between breeds, and then select of bulls within those breeds with optimum genetics while avoiding extremes.
Another key factor for crossbreeding sire selection is the matching of frame score across the individual bulls selected. Frame score has a strong relationship with cow size. Therefore, minimizing differences in the frame scores of the bulls used to produce replacement females will assist in minimizing differences in mature size of the resulting cowherd. This coupled with avoiding large differences in milk production is the key to having a cowherd that is uniformly adapted to the resources of the operation even though several breeds are represented. Minimizing differences in frame score will also assist in minimizing differences in the calf crop.
For many feeder cattle producers, coat color is an economically important trait. Today's genetics offer the opportunity to stabilize coat color and still maintain a crossbreeding program. Technological advances such as DNA genotyping have made it possible to more easily manage coat color in several breeds. Therefore, coat color does not need to be a limiting factor to maintain a crossbreeding program.
In summary a well-designed, manageable crossbreeding system is an important aspect in making genetic progress in the various economically important traits that drive profitability in today's beef industry. To accomplish this task, bull selection must consider both within and across-breed differences to optimize genetic progress in these traits that influence reproductive efficiency, maternal performance, growth and feed efficiency, and end product merit.