Genetic improvement programs are used to improve the quality and profitability of livestock. These programs involve 4 steps:
- Define breeding objectives
- Record pedigree data
- Perform EPD (Expected Progeny Difference) calculations
- Breed with the best based on EPD
The first step is to define the breeding objectives. The objective may be a single trait (antler size) or multiple traits. Multiple traits may include such things as velvet production, antler size, reproduction, growth rates, carcass traits and longevity. For example, bucks that reach full antler size in 3 years compared to five years will provide a better return on investment. Females that can reproduce for 20 years will be more profitable than does with shorter reproductive cycles. Does that bear triplets or twins consistently are significantly more profitable than animals with single off-spring. For venison markets, more weight and leanness are probably desirable traits.
Once breeding objectives have been identified, the next step is to determine the relative importance of each objective. These may differ with the deer species and the target markets for which the animals are being produced. Part of this exercise includes calculation and/or modeling of the costs and returns associated with each objective.
It is critical to differentiate between animal traits and characteristics that are due to genetics and those due to the environment. The higher the heritability factors the faster the genetic improvement. Based on a review of the research literature, Dr. Gallivan found the heritability of certain deer traits were as follows:
- Date of fawning (0-14%)
- Twinning of fawns (5-15%)
- Birth weight (0-18%) for white-tailed deer
- Birth weight (31-49%) for red deer
- Yearling body weight (58-64%) for white-tailed
- Later body weight (48-80%)
- Killing-out weight (68%)
- Velvet antler weight (43-85%)
- Hard antler weight (71-86%)
- Points (22-66%) for white-tailed
- Main beam length (47-70%) for white-tailed
- Antler spread (3-43%) for white-tailed
- Basal circumference (80-89%) for white-tailed.
The higher the percentages, the better the odds are that the trait will be passed on to the offspring. Notice that none of the traits is 100% and a few are pretty low. For example, if your buck has a 26 inch antler spread, the odds are only 3 to 43% that his sons will have the same spread. The odds for main beam length and basal circumference are a little better (47 to 89%). This data needs to be kept in mind when buying (and selling!) breeding stock.
Another important factor is genetic correlation. This is a measure of how selection for one trait will affect another trait. The correlation may be positive or negative. A good example of a negative correlation found in most livestock is between growth and reproduction. Animals that have been bred for fast growth rates tend to have lower reproduction rates.
According to Dr. Gallivan, the correlations in deer are favourable to genetic improvement programs. For example, high and positive correlations were found between a)birth and weaning weights; b)velvet antler weights in successive years; c)body weight and antler weight; and, d)body weight in females and velvet antler production in males (their sons).
The next step in the genetic improvement program is to measure and record the relevant traits. There are objective measurements e.g., obtained from scales, tape measures, ultrasound, lasers, etc. There are also subjective measures such as scoring or rating systems. Objective measures are preferred since they are more precise and usually are standardized.
The measurement of traits can come from several sources. They can come from the parents of the animal, from the animal itself, from the animal’s siblings. However, the most important source of measurement information is from the offspring, as this is what you are trying to predict.
There are several good reasons to record pedigree information. For certain livestock species, it is required to register the animal as being a “purebred.” Pedigree information is necessary to avoid inbreeding. Finally pedigree information is essential for genetic improvement programs. Having data on both sires and dams is preferred but can work with sires only. DNA testing can help identify parents in certain situations where that data is not known. It is important to have the date of birth as age affects many traits, e.g., weight, size, etc.
Once the data is collected, the next step is to calculate the EPD. The Expected Progeny Difference is “an estimate of the superiority of an animal’s offspring, relative to the offspring of an average animal in the population.” The advantage of using an EPD is that is offers an objective comparison of animals from different sexes, ages and herds. EPD is calculated from data on traits, pedigree information and genetic parameters. The complex calculations usually require a computer and appropriate statistical software.
EPDs for the relevant traits are combined into a single numerical index. The EPDs can then be used to rank bucks/bulls/stags from the best to the worst. The semen from animals with the highest EPDs are then used to improve the farmed deer species.
In summary, for a genetic performance program to be implemented in the deer industry, the following requirements must be met.
- Agree on the desirable traits of deer for specific markets, e.g., breeding, trophy, venison, etc.
- Collect trait and pedigree data. This means the industry has to agree on standardized data elements, have a significant number of deer farmers collect the data on their animals, and make the data available for analysis and calculation of EPDs.
- Publish the EPDs and use the best animals to improve specific herds and the industry in general.
This will take a significant amount of effort, work and cooperation. However, unless this initiative is undertaken, serious genetic improvements will only be wishful thinking.
Source: Dr. Cathy Gallivan