I was puzzled to read the statement I have highlighted in orange in the following article about the value of heterosis. Doesn't this contradict the results we are always talking about with the Shoshone pool of cattle - the number of exceptionally long lived cows and the good fertility in a population of cattle where the heterosis has been reduced through close breeding?
This brings me to one of the most interesting topics discussed at the RBCS that
could not be any more timely. “Crossbreeding: The Forgotten Tool”,
presented by soon-to-retire Dr. Jim Gosey, University of Nebraska Beef
Extension Specialist, that has emerged as the “voice of common sense” in
today’s beef production era characterized by commercial straight-bred Angus
production. Jim has devoted his professional career to helping beef cattle
producers make money largely through a clearer understanding of genetic
application principles. You can access his entire presentation at
http://www.rangebeefcow.com/speakers/Gosey.htlm.Quotes from his presentation follow:
"Many commercial cowherds have drifted towards straight bred Angus in an
attempt to achieve management simplicity, greater uniformity and to pursue a
premium, non-commodity product."
"The result is the loss of most of the heterosis that once existed in many of our
commercial cowherds."
“Heterosis and breed complementarity are powerful forces that combine to
produce the total advantage of beef cattle crossbreeding systems.”
“Heterosis, or hybrid vigor, is measured as the performance advantage of
crossbreds over the average of their straight bred parents. Maximum heterosis is
realized in the first cross of distinctly different parents.”
"Most ranchers know crossbreeding can increase output, but perhaps don't
appreciate the potential advantage in lifetime productivity of crossbred cows."
“This crossbred advantage can amount to as much as 25% greater lifetime
productivity (pounds of calf weaned per cow exposed) for crossbred cows as
compared to straight bred cows.
“
Lost maternal heterosis shows up in the same lowly heritable traits that would be
associated with the inbreeding depression, namely reproductive, fitness and
longevity traits."Thus, the price paid for loss of heterosis occurs as a number of very small
losses that when added up can amount to a substantial sacrifice in lifetime
productivity."
"Ranchers would be wise to crossbreed even if heterosis were zero, due to the
complementary effects of matching strengths of one breed to offset the
weaknesses of another breed.”
“Heterosis can impact many traits, but is especially useful in improving
performance in lowly heritable traits, such as reproduction, early growth and
fitness or lifetime productivity as shown in Table 1. On the other hand, highly
heritable traits (above 40% heritability) like carcass traits respond to direct
selection within breed.”
Table 1 Average Heterosis in Beef cattle Traits
Trait % Heterosis
Calf Crop Weaned 8
Weaning Weight 13
Yearling Weight 4
Carcass Traits 3
Lifetime Productivity 25
“This huge increase in lifetime productivity of the crossbred cow is driven by the
reproductive performance through earlier puberty, higher conception rate, faster
breed back, greater longevity and the maternal impact on calf performance.”