Brady Campbell, Program Coordinator, OSU Sheep Team
Data collection. 
Seems pretty simple right? Most of you are probably reading this and thinking, “we already collect data on our flock, what else could he be talking about?” As any good shepherd would do, you are probably recording the basic information such as sex, birth date, birth type, dam, sire, and individual identification on each newborn in your flock. Some of you may even be collecting birth and weaning weights to gather a better understand on the performance of your flock in the short term. However, I will venture to say that not many are collecting additional information that will benefit your flock in the long term such additional body weight measurements, fat depth measurements, or loin eye muscle depth measurements to mention a few.
Today, genetic selection, whether you are considering to buy a male or female to add to your flock, is no longer solely determined by physical appearance and the information found within the individuals pedigree. Genetic parameters estimated by collecting and recording information with the National Sheep Improvement Program (NSIP) in the form of Estimated Breeding Values (EBV’s) have changed the game. Estimated Breeding Values are used to quantify the genetic merit of breeding sheep, based on phenotypic traits, by evaluating an individuals genetics in conjunction with the environment in which it is raised.
Founded in 1986, NSIP is not a new program that shepherds are being exposed too, but it is a program that has shown a significant amount of growth and value being added to sheep over the past decade. NSIP focuses on combining genetic assessments and visual observations as a means to select for the most desired breeding stock for the producers specific needs. Understanding the genetic history of an individual animal provides valuable insight for future breeding plans and offspring.
So now that we have a basic understanding of NSIP, you may be thinking, what EBV’s should I be measuring or looking for when selecting animals to add to my flock. This is a difficult question to answer as everyone has a different goal in mind. From a commercial standpoint, some may want to focus on fat depth, while others are more concerned about maternal characteristics to improve their ewe base. All are great parameters to focus on, but remember, do not focus on just one selection criteria. When we become extremely focused on one parameter that we desire, we lose focus on other important features. For example, if we are only focused on increased weaning weight, this may result in heavy birth weights. This isn’t always bad, but this intense selection criteria may lead you to having more issues with dystocia amongst your ewe flock and in the long run require more labor to assist your ewes. Every decision that is made has trade-offs and it is up to you to decide which is worth the investment for both the welfare of your animals and you.
For the purpose of our discussion today, let us focus on parameters that may be of interest to you when purchasing a new ram for your commercial flock. Of course, those that are related to weight traits and are applicable to all sheep breeds are Birth Weight (BWT), Maternal Birth Weight (MBWT), Weaning Weight (WWT), Maternal Weaning Weight (MWWT), Postweaning Weight (PWWT). Birth Weight and Weaning Weight makes the most sense here as it estimates the weight of the offspring at birth and weaning. As we discussed earlier, if you were interested in decreasing issues associated with dystocia and changing your feeding program did not help, perhaps negatively selecting for birth weight (smaller birth weight) could aid in this management decision. Postweaning Weight is an additional weight that can be collected after weaning weight in which is used to describe the performance of lambs without the influence of their dam.
The other two remaining weight parameters are a bit different from what you may expect for a terminal breed of sheep, but nonetheless are important as we considered the longevity and performance of our ewes, if you choose to retain replacements. Maternal Birth Weight estimates the effects of the ewe on the lamb(s) growth potential. Ewes with a positive Maternal Birth Weight estimate would be more favorable for producing lambs. In the same regard, Maternal Weaning Weight estimates overall mothering ability, such as ewe behavior and milk production.
In addition, other beneficial parameters to consider include those that are directly related to body composition such as Postweaning Fat Depth (CF), Postweaning Loin Eye Muscle Depth (EMD), and Carcass Plus. Simply stated, Postweaning Fat Depth is an indicator of genetic differences in carcass fat depth whereas Loin Eye Muscle Depth is an indicator of genetic differences in muscling. Both of these parameters are important in monitoring and identifying those individuals that are heavy muscled with a lean carcass. These measurements are adjusted to a standard weight of 110 lbs. In addition, Carcass Plus, which is a combination of Postweaning Weight, Postweaning Fat Depth, and Postweaning Loin Eye Muscle Depth, provides a nice estimate for terminal sires. This EBV is beneficial as it encompasses three different EBV’s and allows for you to compare one EBV rather than three. In the sense of comparing sires, this makes the process a bit easier.
Although you may not initially consider this with a terminal breed, collecting data on reproductive performance may also be beneficial to your operation. Number of Lambs Born (NLB) and Number of Lambs Weaned (NLW) are great estimates used to determine the overall reproductive performance of your ewes. Although not currently available for terminal breeds, Scrotal Circumference (SC) is an important measurement to take. Regardless if you are recording data for NSIP or not, I would highly recommend taking several Scrotal Circumference measurements on your males. These measurements can help identify rams that have the potential to be more reproductively sound and be used to identify ewe lambs that should be retained in the flock from specific males as it may also influence their reproductive performance.
I realize that all of this information can be a bit daunting at first, but trust me, its well worth the investment. Having a better understanding of the genetic potential of your flock and those that you intend on purchasing from will allow you to make the soundest buying and breeding decisions. Adding value to your flock by recording the genetic potential of your animals seems like a win-win situation to me.
Do note that our discussion focused on selecting terminal sires, however, there are also EBV’s available for maternal characteristics if you are interested in producing replacement females. For the purpose of this discussion I wanted to illustrate that spending a bit more on a quality ram that is supported by data as compared to a ram that does not will certainly pay for itself when it comes to sale day when marketing your lambs.
Yes, there are still and always will be sheep purchased based on their physical appearance, but when it comes to consistent performance and gaining the greatest return on investment, I’ll leave that to science and the data collected through NSIP.For those that are interested in learning more about NSIP, feel free to visit their website, contact a producer that actively participates in the program, or myself and we will get you set up. Until then, happy shepherding!
Editor’s Note: Explanations for the description of EBV’s comes from the NSIP EBV Notebook written by Dr. David Notter. This notebook is available online.