Management
An Inexpensive but Effective Method for Weaning More Total Pounds
By Justin Rhinehart , University of Tennessee
Since all food production is based on reproduction of the commodity , it stands to reason that a technology which positively impacts reproduction would be widely adopted . One of the major benefits of crossbreeding is realized through improved reproductive function . In fact , nearly all modern plant and livestock commodity production relies on heterosis ( trait improvement better than the average of the two parents ) from crossbreeding as one of their primary reproductive management technologies . But , for various market and convenience reasons , crossbreeding is not as widely used in commercial cow / calf production .
There seems to be several misconceptions about implementing a crossbreeding system in commercial cow herds . To dispel a couple of the major misconceptions before going further , it is important to note that crossbreeding does not necessarily mean introducing bos indicus (“ eared ”) genetics , although that might be a good option in several scenarios . Predominantly black hided feeder calves can be uniformly maintained in crossbreeding systems .
The “ no such thing as a free lunch ” principle still applies in this situation and , depending on the starting point , tradeoffs for some individual traits might have to be made when switching from a straightbred to crossbreeding approach . More intensive management of sire selection and / or rotation is necessary . Also , purchasing bulls from breeds with smaller registries can make
30 | AUGUST 2018 competition for a smaller population of high-quality sires more intense .
Heterosis can be broken down into three mating situations : individual , maternal and paternal . Individual heterosis is the advantage of the crossbred individual in relationship to the average of the purebred individuals . Maternal heterosis is expressed for traits measured on crossbred cows and is the advantage of the crossbred dam over the average of purebred dams . For example , a two-way-cross dam may wean heavier calves than the average of purebred dams from those two breeds . Paternal heterosis is the advantage of a crossbred sire over the average of the purebred sires ; generally , as an improvement in bull fertility .
Many studies have shown that traits high in heritability respond well to selection for improvement but show little response in heterosis . Traits that are lowly heritable show little response to selection for improvement but respond well in heterosis . Fortunately for the commercial cow-calf producer , those traits that respond well to crossbreeding are reproductive traits ( fertility , ability to recycle after calving , settling on first service , mothering ability , etc .).
Individual Heterosis
Using the results of crossbreeding , the cost of production could be lowered by a simple crossbreeding program of using a bull of a different breed than the cows . If a typical producer in a straightbred operation was producing 408 pounds of calf per cow exposed . An 8.5 percent increase from individual heterosis of crossbred calves over straightbred calves would be worth an extra 34 pounds of calf weaned per cow exposed ( 408 lb . x . 085 = 34.6 lb .) It is important to remember that indiscriminately selecting a bull based only on color or breed will not guarantee an improvement in production from crossbreeding . Selecting superior bulls in any system is still important .
Maternal Heterosis
Research has shown that crossbred cows have a higher conception rate at first service than straightbreds . All of these traits affect pounds of calf weaned per cow exposed in the herd . In a classic experiment involving three British breeds ( Angus , Hereford and Shorthorn ) conducted by USDA and Nebraska researchers , crossbred cows were compared to straightbred cows to determine the impact of heterosis on fertility . Crossbred cows were compared to straightbred cows when both were bred to produce crossbred calves by the same bulls of different breeds . Crossbred cows produced three-way-cross calves ( no more than 50 percent breed makeup of any breed ) and straightbred cows produced twoway-cross calves . The crossbred cows weaned a 6.5 percent larger calf crop that was 4.1 percent heavier than crossbred calves from straightbred cows . Combining these traits gave an advantage of 14.8 percent more pounds of calf weaned per cow exposed from crossbred cows over straightbred cows .
Since both types of cows were producing crossbred calves , this did not include the advantage of