Badlands said:
I am aware of what the EPD was for, and selecting against gut mass wasn't it.
Badlands
Researchers at Colorado State University and the USDA-ARS Fort Keogh Livestock and Range Research Laboratory in Miles City have proposed that an EPD could be developed for maintenance energy requirements using genetic predictions for mature weight and milk. Drs. Rick Bourdon and Bruce Golden at Colorado State University have also proposed other indicators which could be used in this genetic prediction that would add accuracy to the EPD. Measurements of cow body condition and gut weight would help explain even more of the variation in mature cows energy requirements. Mature weight, milk indicators, and body condition scores are all relatively inexpensive to collect, and breed associations have a great deal of data already collected for these traits. Gut weight, on the other hand, is an expensive and difficult measurement to collect, but offers a great deal of information in explaining the variation in maintenance energy requirements of mature cows of the same mature weight.
Visceral organs (i.e. gut mass) have the largest impact on maintenance energy requirements out of all the tissue in the body. The liver and intestinal tract alone use about 40 to 50 percent of the energy supplied for maintenance. Visceral organs as a whole consume approximately 73 percent of maintenance energy.
Using some measure of gut mass would seem to be a very good gauge to getting at the actual trait, instead of using indicators of indicator traits. Currently, milk indicators are responsible for the gut mass component, because there is a relatively strong correlation between milking ability and visceral organ mass. The problem with using just milk indicators is not all cattle with larger gut mass have higher milking potential.
There are several problems with measuring visceral organs. First of all, to weigh the organs of an animal, it has to be slaughtered and all of the fat and connective tissue must be stripped off the organs to acquire this measure. Obviously, no one wants to slaughter their best cow to find out how much her organs weigh. Neither do they want to pay someone to prepare the organs to be weighed. This is a very impractical and costly process to find out which animal is the most efficient.
Instead of slaughtering the animals we want to propagate, we could use ultrasound to acquire a measurement of one of the organs that is a major source of consuming energy for maintenance. The liver seems to be the best candidate for this task. It is one of the most accessible organs for ultrasonic examination, and is the largest user of maintenance energy of all the organs of the body.
Measuring the liver with ultrasound is not quite as simple as measuring rib eye area. The liver is much larger and is deeper in the body cavity of the animal than the rib eye. It is not possible with current technology to get a cross section image of the liver as is done for rib eye area. Research by Braun from the University of Zurich, Switzerland demonstrated a method of using ultrasonic measurements of the veins associated with the liver to estimate the weight of the liver. He found a moderately strong correlation between the depth from the exterior surface of the liver to the caudal vena cava and portal vein to liver weight in mature non-lactating dairy cows.
Researchers from Colorado State University and CSU Veterinary Teaching Hospital investigated the relation of ultrasonic measurements of venous depths in the liver with liver weight of Red Angus slaughter steers and heifers. The findings from this study were that a relationship does not exist between ultrasonic measurements of the liver and liver weight in Red Angus fat cattle. This is likely due to the aggressive feeding of these cattle. Compared to range cattle, the liver of feedlot cattle function at an abnormally accelerated metabolic rate. Although ultrasonic liver measures may not immediately be used to enhance the accuracy of maintenance EPDs, future potential exists.
The development of this new EPD raises questions on how to make this genetic prediction more accurate.
As researchers continue to prefect the maintenance energy EPD, more research will go into economically incorporating data describing gut mass. Much of the variation between cow's maintenance energy requirements can be described with the current prediction indicators of mature weight and milk, but gut mass has the potential to add even more reliability to the prediction.
Having an EPD for maintenance energy requirements will give cattle producers a powerful selection tool to produce the type of cattle that best fit their environment and production scheme. The ability to make informed decisions during selection allows producers to optimize their production practices, while hopefully maximizing profit. The development of Economically Relevant Traits (ERTs) such as the maintenance energy requirement EPD is one more step the Red Angus Association has taken to more accurately describe Red Angus cattle to make them the most predictable and profitable cattle available.
http://old.redangus.org/newredsite/themagazine/feb02/magazine.html