51. Question 8, cont. Terminal crosses = you mate all F1 generation heifers to meat sires; keep no replacements. Rotation-terminal combination = you mate young and desirable cows to produce replacements and breed all others to produce calves for slaughter.
52.
Editor's Notes
In this chapter, beginning on page 12-1 of your manual, we will be looking at sire selection for a beef herd.
Through A.I. you have access to the best bulls in the world; putting the small breeders and large breeders on a even field. Using bulls that have hundreds, even thousands, of recorded offspring reduces risks.
The same genetic principles apply to beef cattle that apply to dairy cattle, even though the traits emphasized are a bit different.
We can impact selection. We don’t control gestation length, age at puberty, etc.
Here are the heritability estimates for some of the traits beef cattle are selected for.
This is the only factor that we can impact.
We want to measure genetic differences only, not who is better with the feed scoop.
If you want to keep 20 replacements and have 60 to pick from you can make faster progress than if you had 20 to pick from. The average natural service sire can cover 30 to 50 cows a year versus an A.I. bull breeding thousands. We don’t need too many to get the job done, so they really have to be good.
Without genetic variation we couldn’t make progress.
Concentrate on traits that have economic value, and reasonable heritability, allowing selection to work.
Still takes 9 months to get a calf, 15 months before we can breed that heifer to calve at 24 months of age.
The old bell curve again.
These are some of the sources for data used in progeny testing bulls.
The resulting EPDs have increased selection options and pressure.
These factors are considered in EPDs
Traits to consider when breeding heifers, or producing calving ease bulls.
If you sell calves this is important, it relates to the product you sell.
This factor is important to the feedlot, an extra .1 lb per day adds up.
How the bull performs himself is one indicator of his transmitting ability.
Simply said.
The object is to produce a consistent and predictable end product.
More scores relating to the end product.
A bull with daughters in production is going to be at least 4-years-old before we know for sure. Because of the years of records, pedigrees can predict it with a moderate degree of accuracy.
If you look at 100 calves of a bull which ones will you likely remember, the average or the extremes? Will you be able to take the time to go look for the offspring? GTS does this for us. It gives us a picture of what the average offspring will look like.
This program can help you put it all together. Your goals, your criteria for breeding, and mating each cow individually using all the information each time.
Let's go to the pages listed and look at the information.
You will get many more calves from any given bull in your herd than from any given cow; therefore, the emphasis needs to be on the sires.
Many desirable traits in a commercial operation are enhanced by cross-breeding. Heterosis is free.
Low heritability traits are impacted more by hybrid vigor than high heritability traits.
The more breeds the more hyrid vigor.
Maternal and terminal. Identify the kind of cows you need for your environment and select the breeds that meet those needs.
This cross will net about 2/3 of the potential hybrid vigor.
This system nets nearly 90%. The system is difficult to manage with natural service, but easily managed using A.I. because all the cows can be in one pasture and the different breeds of bulls are in the refrigerator.
Used to maximize hybrid vigor. Can be utilized best by using A.I.
A system where every calf is sold.
A system allowing for replacement development and maximizing growth in the rest.
Expensive and labor demanding.
A live, small calf is better than a dead, large calf or a ruined heifer.
Actual calvings are reported and summarized.
Using bulls that are proven to improve the traits selected reduces set backs. Knowing when cows were bred and are due to calve helps increase the chances of saving calves. Today you can use the directory to look at how the bull performed as an individual, and using his EPD’s how he will transmit those things to your herd.
Simple but efficient facilities need not be expensive, and allow you to use the most powerful genetic tools available in your herd.
![CHAPTER 12 ,[object Object]](https://image.slidesharecdn.com/aimanualchapter12-100917103719-phpapp01/85/Ai-manual-chapter-12-1-320.jpg)
![Why Beef A.I.? ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)