CROSSBREEDING SYSTEMS for BEEF CATTLE By David R. Hawkins Michigan State University
CROSSBREEDING • Most widely used mating system in commercial beef herds. • Can result in up to 23% increase in lbs. of calf weaned per cow exposed to breeding as compared to straight breeding. • Effective because of: • Heterosis or hybrid vigor • Breed Complementarity
HETEROSIS • % improvement observed over the average of two breeds when they are mated. Example: Breed A = 500 lb. weaning wt. Breed B = 450 lb. weaning wt. Expect 475 lb. progeny, observe 495 lb. progeny % Heterosis = [(495-475)/475]x100 = 4.2%
Types of Heterosis • Individual heterosis is observed in a crossbred calf. • Maternal heterosis is observed in a crossbred cow. • Heterosis tends to be highest in traits with low heritability (example = fertility) • Little if any heterosis is observed in traits of high heritability such as carcass traits.
Breed Complementarity • Breeds were developed in specific regions of the world & certain characteristics were fixed. • Combining breeds that differ in their strengths allows one to take advantage of these characteristics. • For example a breed that is high in maternal traits may lack muscling or carcass quality, while another breed excels in these traits.
Goals of an Effective Crossbreeding System • Provide heterosis • Match cows to environmental resources • Provides uniformity within the cow herd • Yields a consistent product • Deals with genetic antagonisms • Meets the end product target
Key Factors To Consider • Natural vs. A.I. Service? • Number of breeding pastures? • Will replacement heifers be raised or purchased? (Health & cost issues) • Are you willing to keep records? • Do you have the available labor, capital, facilities, etc.?
Two Breed Terminal • Cows are straightbred ( 0% maternal heterosis) • Obtain about 8.5% improvement in lbs. of calf weaned per cow exposed to mating. • Requires only one breeding pasture • All calves go to feedlot, so what is the source of herd replacements?
Two Breed Rotational • Two breeding pastures unless A.I. is used. • Minimum herd size of 50 cows (natural service) • Both breeds must possess some maternal ability since you will be keeping daughters in herd. • Heterosis stabilizes at 67% of maximum. • Expect about 16% improvement in lbs. of calf weaned per cow exposed.
Three Breed Rotational • Need 3 breeding pastures unless A.I. • Minimum of 75 cows. • Heterosis stabilizes at 86% of maximum. • Expect 205 improvement in lbs. of calf weaned per cow exposed. • Can utilize advantages of 3 breeds. • Management becomes more complex.
Four or Five Breed Rotational • More complex to manage than 2 or 3 breed rotational systems. • Are comparable sires available for natural service? • Record keeping increases dramatically.
Static Terminal Sire • Cow herd is crossbred (100% maternal heterosis). • Replacements purchased from another source. • Cows are mated to a “terminal sire” and resulting calves are marketed for slaughter. • Requires only 1 breeding pasture. • This system maximizes heterosis unless replacements are generated within the herd. • Up to 50% of the cows would be needed to do this.
Rotational Terminal Sire • Younger cows (1, 2, & 3 year olds) are mated to produce replacement females. • Mature cows are mated to “terminal sire”. • Expect 21% increase in lb. of calf weaned with 2 breed rotational – terminal sire. • Expect 24% increase in lb. of calf weaned with 3 breed rotational – terminal sire.
Less Complex Systems • Rotate sire breed every 4 years. • Save replacement heifers the last 2 years to avoid inbreeding (sire x daughter matings). • Composites • Two or more component breeds designed to retain heterosis without crossbreeding and maintained like a pure breed. • Rotate crossbred F1 bulls.