Effects of growth potential and growth path on tenderness of beef
longissimus muscle from bulls and steers
R.
W. Purchas*, D.
L. Burnham†, and
S. T. Morris†
*Institute of Food, Nutrition,
and Human Health and †Institute
of Veterinary, Animal, and Biomedical Sciences, Massey University,
Palmerston North, New Zealand
ABSTRACT The influence of growth potential or growth
path on the tenderness of the longissimus muscle was investigated
using 117 Angus and Angus-cross bulls and steers raised on pasture
over two successive years. Growth rate for a period of 100 d from
a weight of about 200 kg was used to identify the faster-growing
two-thirds of cattle within the gender groups, half of which were
grown fast to a slaughter weight of 530 kg at 16 to 18 mo of age
(the Fast group), whereas the other half were restricted in growth
(the Restricted group) so they attained a similar final weight as
the slower-growing third (the Slow group) at about 26 mo of age.
The Restricted group was included to determine whether the tougher
meat expected from the Slow group relative to the Fast group (based
on previous results) was due to the greater age of the Slow group
or to their slower early growth rate. Beef from the Fast group was
tenderer than that from both the Slow and Restricted groups based
on sensory panels (P < 0.05) and objective measures (P < 0.05),
indicating that the early growth-rate potential was less important
than the differences in age or the patterns of growth for the Slow
and Restricted groups. Improved tenderness for the Fast group was
associated with more intramuscular fat (P < 0.05) and higher
myofibrillar fragmentation indexes (P < 0.05). Patterns of tenderness
differences between treatment groups were similar for bulls and
steers, but beef from bulls was tougher (P < 0.001) than that
from steers. The more tender beef from steers was associated with
a slightly lower ultimate pH (P < 0.001), higher myofibrillar
fragmentation indexes (P < 0.001), and more intramuscular fat
(P < 0.001). Ultimate pH affected beef tenderness (P < 0.01),
but adjustments to a constant pH did not decrease differences between
treatment and gender groups. The higher growth rates (P < 0.01)
and leaner carcasses (P < 0.01) of bulls compared with steers
were consistent with other studies. Increases in age of 8 to 10
mo may be associated with less tender beef for cattle finished on
pasture, and beef from bulls is likely to be less tender than that
from steers.
Implications
This study sought to determine whether the greater tenderness of
the longissimus muscle from cattle that reached a finished weight
sooner was attributable mainly to their higher growth potential
or their younger age at slaughter. The results, which were obtained
by limiting the feed for a group with a high growth potential so
they reached a slaughter weight at the same time as cattle with
a lower growth potential, showed that tenderness of beef from this
restricted group was lower than that of the fast-growing group and
very similar to the slow group. This suggests that beef tenderness
is determined more by the age at slaughter than by early growth
rates, although in this study it was not possible to separate age
effects from effects of different nutritional levels and seasons
of slaughter. These growth-pattern effects on tenderness were similar
for beef from steers and bulls, but beef from bulls was less tender
than that from steers for all groups.
Keywords: organic beef production; Japan; New Zealand; beef market
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