Responses in carcass composition and meat quality after seven generations o
f selection for components of lean growth rate were examined in a populatio
n of large White pigs. There were four selection groups in the study, with
divergent selection for lean growth rate on ad-libitum (LGA) or restricted
(LGS) feeding regimes, lean food conversion ratio (LFC) and daily food inta
ke (DFI). In generations six and seven, two offspring from each of 10 sires
, within each selection line, were to be allocated for half-carcass dissect
ion and measurement of meat quality. There were 320 animals in the study, w
ith 40 animals from each of the high and low selection lines and, within ea
ch selection line, two offspring per sire.
Responses in carcass composition were similar in the three selection groups
given food ad libitum, but rates of lean and fat growth rate differed betw
een selection lines. Intramuscular fat content was reduced with selection f
or high LGA and high LFC but was increased with selection for low DFI (-1.7
and -3.2 v. 2.7 (s.e.d. 0.7) mg/g), which was unexpected given the higher
carcass fat content of the low DFI line, relative to the high line (249 v.
190 (s.e.d. 7) g/kg). Muscle colour was darker, as measured by trained sens
ory panel assessment, in selection lines which reduced the rate of fat depo
sition to achieve a leaner carcass thigh LFC and low DFI) but there was no
response in muscle colour with selection for LGA (0.4 and 0.3 v. 0.0 (s.e.d
. 0.1)). Responses in muscle shear force (5.3 v. 4.4 (s.e.d. 0.4) kg) and f
lavour liking (4.0 v. 4.3 (s.e.d. 0.12)) were limited to the LGA and LFC se
lection groups, respectively. There were no significant responses in muscle
moisture content, muscle pH or myofibrillar fragmentation inner, nor were
there any responses in meat quality with selection on LGS. Therefore, decre
asing the rate of fat deposition was associated with darker meat and increa
sing the rate of lean growth was associated with higher shear force. There
were selection strategy specific responses in the fatty acid composition of
intramuscular fat, which may have contributed to the responses in eating q
uality.
In general, responses in meat quality were small, such that incorporation o
f meat quality traits in selection objectives, which ave primarily focused
on increasing the efficiency of lean meat production, may not be necessary.
However, it would be pertinent to evaluate periodically genotypes of breed
ing companies for muscle quality traits.