An animal's genetics determine its potential. This is a simple assertion with big ramifications.
They're big because we can apply management practices to influence an animal's growth, carcass quality and reproductive performance. But, regardless of what we do, a particular animal won't outperform another animal that has better genetics if the two are managed the same way.
That's why the objective is to apply our knowledge of genetics in a way that ensures we have the best possible potential in each conception. In other words, actively determine best potential through genetics.
What are the tools, or genetic "arrows," we can use to achieve this? What are the obstacles? Let's look at some of the genetic arrows in a systematic way, then relate them to obstacles we face in applying them to traits.
Animal Breeding Conventional animal breeding tools can be divided into two components: selection and mating systems. Each component has a very precise objective. We use selection to change frequencies of beneficial genes in the population. We use mating systems to optimize gene combinations.
The two are not mutually exclusive. The outcome of a mating system can be enhanced by the selection of superior animals going into the program. Likewise, the potential impact of superior animals can be enhanced by a well-designed mating system.
Once we define objectives of our breeding program, then the search begins for animals that best meet the criteria set in those objectives. First, we need data and a system to transform that data into information. Although we lack data on many traits, we can rank animals based on the information we have. We can then choose individuals closest to our breeding objectives.
Breeding objectives can be simple or complex. For simple objectives, such as single trait selection, EPDs are important information. EPDs represent a synthesis of data from a wide range of sources. That is why they're valuable.
Consider the weaning weight EPD of a bull. Data supporting that EPD can consist of pedigree information, individual performance and progeny data, all combined in an optimum way. In many of the evaluation systems used today, an EPD also contains information derived from correlated traits.
For complex breeding objectives, such as multiple-trait selection, we can combine EPDs into selection indices. Accuracy numbers help our decision making by conveying EPD reliability.
Mating systems exist to optimize gene combinations, either by increasing or decreasing heterozygosity. In increasing homozygosity, inbreeding makes progeny more uniform - a production goal in some species.
On the other hand, crossbreeding increases heterozygosity in progeny. This gives progeny the advantage of hybrid vigor, especially in characteristics like viability and reproductive performance.
Carcass Merit Carcass merit characteristics have attracted much attention the last several years. In his article on page 4, Harlan Ritchie cites a survey of feedyard operators, ranking their top three traits of interest: quality grade, yield grade and muscling.
But, while some data are available through carcass data collection programs, the genetic programs to improve these characteristics have suffered from lack of data. The total number of animals with the required information is limited, as is the accuracy of genetic evaluations achieved from use of existing information.
To address the problem, several breed associations are now running carcass data collection programs. These programs are designed to provide information for use in genetic evaluation systems.
Strict attention needs to be paid to creating and sustaining contemporary groups and generating enough progeny to achieve reasonable accuracy in the evaluation. The programs are expensive, time consuming and limited in the number of animals impacted. As such, they're only a substitute for open, industry-wide programs of routine data collection on large numbers of animals.
An expansive, open program can use measures of traits correlated to those of direct interest. For carcass traits, the use of ultrasound is one such measure. Ultrasound has the distinct advantage of providing the opportunity to take measures directly on breeding animals as well as their progeny in slaughter programs.
The American Angus Association will publish ultrasound evaluations in the near future. The real value of ultrasound information lies not in producing ultrasound evaluations themselves, but combining that data with the carcass data in multiple trait evaluations to enhance the carcass merit EPDs.
In his article, Dr. Ritchie also comments that beef for the upscale domestic market must have exceptional eating qualities reflecting tenderness, juiciness and flavor. Data retrieval systems for routinely measuring these characteristics currently don't exist.
We do have, however, a program that will help the industry measurably in this area: the National Cattlemen's Beef Association Carcass Merit Program (CMP). Data collected in this project will consist not only of carcass measurements but also shear force measurements and sensory panel assessments on bulls from several breeds.
In this project, EPDs will be produced for all traits measured. For the first time there will be EPDs for tenderness and sensory panel data on a small number of bulls in each breed.
An exciting opportunity also exists in the carcass merit area: the use of DNA information to aid selection decisions. As part of the CMP, biological material from 10 sires in each breed and their progeny are assessed for segregation of important genes. If successful, DNA testing for segregation of these genes is on the very near horizon.
Maternal Ability And Reproductive Performance Currently, we have no program for direct selection against bulls whose daughters have poor reproductive performance. The obstacle is lack of information.
The solution is to move data recording systems to a total herd enrollment (recording) program, as some breeds already have done. Total herd enrollment, linked with documented reasons for removing breeding animals from the herd, can provide the data-collection framework needed to establish evaluations for reproductive performance.
>From the perspective of cow productivity, there are evaluations on >maternal ability, perhaps the most misunderstood and most often debated >genetic evaluations published. How good and how useful are these?
First, we must recognize that maternal ability is a prediction of how much growth (occurring in the progeny of a bull's daughters) will differ from expected, given her growth genes.
Two females with identical total maternal evaluations can be quite different in how each achieves the total. Consideration of how growth was achieved may be important in environments where higher yield cannot be adequately supported, and might translate into lower subsequent reproductive success.
However, in an environment where that is not the case, it can be argued that most attention should be placed on the total evaluation, not the component.
Growth Traits Very successful programs for selection for growth characteristics exist. As Dr. Ritchie notes, Colorado State University's Tom Field asks, "How many pounds can we generate at what cost?" Two factors influence the answer: growth potential and efficiency.
Data on growth traits to yearling age are abundant. Evaluation systems exist for all breeds. Successful selection for changing growth is well documented in the genetic trends published by breed associations.
These trends show the occurrence of very sophisticated selection. Substantial trends for increased postnatal growth have resulted in marginal corresponding increases in birth weight in several breeds.
This demonstrates sophisticated selection in that birth weight is positively correlated to weaning and yearling weights. For such an event to occur, parents that break the rule (higher growth equal larger birth weights) must be found. Unfortunately, efficiency - a factor determining cost - is not a trait for which we have the same luxury of data.
Multibreed evaluations are a new tool now available for calculations of growth EPDs. The American Simmental Association's (ASA) multibreed system allows joint evaluation of animals from different breeds simultaneously in one system.
The evaluation provides reliable genetic information on composite breeds and on crossbred breeding stock. Predictive models can be constructed from these evaluations to choose sires for matings to particular breeds of females.
These selection aids may enhance the sophistication of our crossbreeding programs in the commercial sector. Other breed associations are planning for the development of similar programs for growth. Similar evaluations for other traits will follow.
Selection Indices Thus far, I haven't distinguished between breeding programs that emphasize one trait as compared to those emphasizing two or more traits. For multiple trait selection, we may use selection indices.
Selection indices provide a vehicle for multiple trait selection that maximizes progress, given relative economic values of the traits in the index. For many years, the dairy industry has provided producers with an index of evaluations for net dollar value of production based on a combination of yield and composition of milk.
The prediction reflects the difference in income generating potential in the lactation of daughters of different bulls. The dairy industry also calculates a total performance index (TPI) that includes production characteristics along with type characteristics.
Selection index theory has been around for over 50 years, but it has found little use in the beef industry. This may be due to the difficulty in accurately assessing the relative economic weights or to the segmented nature of the beef industry. In production systems where there is integration, indices including growth and carcass characteristics seem possible and reasonable. In the last few years, there has been increased discussion of index selection in beef cattle, but not much has occurred. This may be a missed opportunity.