CROSSBREEDING SYSTEMS for BEEF CATTLEByDavid R. HawkinsMichigan State University

CROSSBREEDINGMost 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 vigorBreed 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 HeterosisIndividual 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 ComplementarityBreeds 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 SystemProvide heterosisMatch cows to environmental resourcesProvides uniformity within the cow herdYields a consistent productDeals with genetic antagonismsMeets the end product target

Key Factors To ConsiderNatural 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 pastureAll calves go to feedlot, so what is the source of herd replacements?

Two Breed RotationalTwo 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 RotationalNeed 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 RotationalMore complex to manage than 2 or 3 breed rotational systems.Are comparable sires available for natural service?Record keeping increases dramatically.

Static Terminal SireCow 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 SireYounger 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 SystemsRotate sire breed every 4 years.Save replacement heifers the last 2 years to avoid inbreeding (sire x daughter matings).CompositesTwo or more component breeds designed to retain heterosis without crossbreeding and maintained like a pure breed.Rotate crossbred F1 bulls.