This is the time of year when most sheep and goat producers are entering the lambing and kidding season. However, I want to jump ahead and discuss replacement selection, because most of you will be selling young lambs and kids off into the early spring holiday markets. You don't want to sell off animals you should be keeping for replacements because you didn't incorporate data into a more thoughtful decision making process. Selecting your replacement males and females is one of the most important management decisions that you make. The decisions you make this year affect the gene pool and genetic improvement of your flock and herd for many years.
A wise old man once told me that the most important tool on a livestock farm is a scale to weigh your animals. I have often tried to refute that, but have never been quite able to do so. Certainly, whoever invented fencing pliers was the Einstein of Agriculture. Likewise, there are times I would doubt the quality of life without duct tape. But, I have to support the fact that a scale is our most important tool. The scale enables us to evaluate rate and efficiency of weight gain. Performance is the basis of our livestock industry.
There are other important criteria besides weight to consider when selecting which lambs and kids you will keep to enter your flock and herd. You should visually evaluate structural and muscular conformation, correctness of feet and legs, breed characteristics for purebreds and fleece quality for fiber types. But, how do evaluate rate of gain? Do you simply weigh them and the biggest ones are the best? The answer would be an emphatic NO! The scale weight only gives you a starting reference point to begin the selection process.
If you were to weigh your lambs and kids and simply select the biggest ones in the pen for replacements, you would probably pick a lot of singles born in the first week or two of your birthing season. Although these may be lambs and kids that look the best (phenotype), these are not necessarily your best offspring genetically. It is the lambs and kids with the best genetics (genotype) that you want to keep for replacements to improve your flock and herd. There will be lambs and kids that scale weigh lighter, but when you adjust their weights using the following factors, they will be genetically heavier than those that scale weigh higher.
Adjustment Factors That Affect Scale Weights
- Age of the Lamb or Kid - Assuming that you weigh them at one time to minimize labor; the offspring will be different ages on the weigh day and this must be adjusted for. A 14-20 day difference in age on 30-60 day weights is huge. Selecting heavier female replacements because they were born in the beginning of the season, and assuming their mothers were more fertile, would also be a questionable decision. Reproductive traits have a low heritability. Also, you may have turned the ram or buck in a day after certain females were in heat. Therefore, a whole heat cycle on a quality female was simply missed. Additionally, choose an average age in days to adjust to that is closest to the weigh date. The usual adjustments are to 30, 60, 90, or 120 days of age. Selecting replacements on post-weaning adjusted weights (90-120 day) will result in greater genetic improvement reliability in your flock than selecting on 30-60 day weights, because the heritability of post-weaning weights is higher than those of pre-weaning weights.
- Age of the Dam - The age of the mother is a reflection on potential milk production for the offspring. One year olds, or yearlings, have the greatest adjustment factors. Their udders are not fully developed, and they may not be fully grown out themselves. Two year olds and over six are considered to be similar in that they are just entering or leaving their prime. Females 3-6 years of age are in their prime and have the least adjustments.
- Gender - Intact males usually grow faster than wethers, which usually grow faster than females.
- Type of Birth - Record if the lamb or kid was born a single, twin, or triplet. The number delivered affects birth weights.
- How it was Reared - This is a reflection on the available milk. It may be born a twin, but raised as a single. This would allow for more milk for the one(s) left.
These are several factors that greatly influence scale weights and need to be considered and calculated into your growth performance records. To do this, record keeping is a necessity. There are adjustment factor tables that you can easily find online which evaluate these parameters and allow you to correctly evaluate the genetics of your animals. Example calculations are usually with the adjustment factor tables. The calculations are easy to do and only a pocket calculator is needed. (Another good tool!!)
Now, we all know selecting livestock replacements is not an exact science. We all have seen those lambs/kids that were show stoppers at 6 months of age, but as yearlings we can't remember why we kept them. Similarly, there were the ones you kept off the truck by a coin toss, and now you hope for twin females out of her every year. However, by collecting accurate records and using the adjustment factor tables, you will be able to select your replacements with greater precision using accurate data in conjunction with visual appraisal. Evaluate your potential replacement animals on a level genetic basis. The genetic improvement of your animal operation depends on it.
If you don't have access to a livestock scale, you can use a bathroom scale. Have a person stand on the scale. Take their weight. Have them hold a lamb/kid while on the scale and subtract the two weights.
Let's get a scale and weigh those lambs and kids! But keep some duct tape handy too!