bination with showing the value of clover pastures, contributed
to a dramatic improvement in forage production, quality of man-
agement, and beef cattle production in Florida and throughout
the southeastern United States. The achievement of a 90% calf
crop and 500 pound calves at the research unit, along with other
projects at Ona and Belle Glade, had a demonstration value of
great impact on the beef cattle industry. Production levels of this
magnitude had been undreamed of in Florida during the early
1950's. In the planning stages of the project, even leading scien-
tists among reviewers held that the maximum calf crop attain-
able in Florida could not exceed 70% because of a semitropical
environment!
 The genetic basis for the progressive improvement in animal
performance may be stated as follows. The foundation females
generally had low fertility (being alternate-year producers) and
poor growth rate but moderately good maternal ability. Their
first-generation crossbred progeny had good growth potential
(average genotypic value plus hybrid vigor), and thus, showed
a highly significant advantage over typical Brahman-native
calves. The first generation crossbred females had excellent ma-
ternal ability, good fertility, and intermediate breeding value
for growth. Their second-generation progeny had genes for good
growth rate from two top crosses of selected bulls and a high
level of hybrid vigor. This combined with excellent maternal
ability in the first-generation crossbred dams resulted in a sec-
ond striking improvement in weaning weights. Further improve-
ment in either maternal ability or growth potential would be ex-
pected to be slow with improvement derived only from additive
breeding value of sires for maternal ability, growth rate, and
adaptability to the area. The full potential for improvement
through hybrid vigor had been achieved in the second generation
crossbred calf nursing the first-generation crossbred dam. The
results realized during the remainder of the trial were in agree-
ment with these expectations.
 Highly significant differences in size and growth rate were
obtained in cattle from the different breeding programs com-
pared. In total efficiency of production performance differences
were non-significant. The results from this trial differ from those
of other crossbreeding trials in that crossbreds were compared
with grades which descended from a crossbred foundation. For
the first two generations, animals in the upgrading systems were
similar both genotypically and phenotypically to the crossbreds.
Intense selection for fertility, maternal ability, and growth re-