By Gary Sliworsky, Ag rep, Emo
The goals of a cross-breeding program can be twofold. First, capitalize on traits that can be improved through heterosis and then select breeds with the strengths needed to make those improvements.
First let’s understand some of the terminology:
•F1–The first generation offspring as a result of cross-breeding
The F1 contains 50 percent of the genes of the two parental breeds and expresses 100 percent of the heterosis. Ideally, the whole herd should be made up of F1s, but such a herd can’t produce its own replacements.
•F2–The second generation, which is made up of intermating F1s.
For example, if a Hereford-Angus sire is bred to Hereford-Angus cows, the resulting offspring will have characteristics that range all the way from pure Hereford to pure Angus.
This is too much variation for most herd breeding programs.
•Rotational Crossing–Some form of rotational cross-breeding usually is used to take advantage of heterosis, but also have relatively consistent results.
A two-breed rotation where the offspring are bred back successively to one of the parent breeds maintains 67 percent of the heterosis expressed as F1s.
A third breed could be introduced to make a three-way rotational cross that maintains 86 percent of the possible heterosis. As well, a fourth breed can be included.
A three- or four-way cross could have a downside. If the additional breed or breeds are of lower merit than the first two breeds, you might give up more value than you gain.
In theory, the three- and four-way crosses should be the best performers. However, few trials have been able to distinguish a large difference in merit between two-way and three-way crosses.
Reproductive traits and factors affecting length of productive life appear to be improved regardless of the specific crossing program employed.
Heterosis also is a factor in maintaining the yield traits in crossbred F1s and F2s to remain competitive with the higher yielding purebreds.
As in purebred selection, the most common advice is to set goals for your herd. When choosing genetic material to add to it (usually sires), select the highest merit bulls available from the breed you select.
Dates to remember
•Feb. 24-25–Large animal clinic dates for Dr. Dan Matyasovszky (call 1-807-475-3837 to book an appointment).