Forty six barrows were fed a common diet after completing a 35 d growth trial in
which 50% received 5 mg/d of pST and the
other 50% a placebo injection. At the conclusion of the growing trial (130 lb), the
pST-injected pigs were leaner (22%) and
yielded carcasses with larger longissimus
muscle area (21 %). However, pigs fed to a
slaughter weight of 225 lb yielded carcasses
that were not different from control pigs in
length, longissimus muscle area, or belly
weights. Pigs administered pST during the
growing phase continued to have 10% less
backfat, which resulted in a 1.6% greater
yield of lean cuts. Postinjection growth rate
of pST-treated pigs was significantly reduced
for the initial 2 wk to cause an overall reduced ADG during the finishing period.
Days to reach slaughter did not differ with
treatment because those pigs previously
receiving pST were heavier initially. There
is no advantage to injecting pigs with pST
during the growing phase to improve overall
growth. However, pST administration during
the growing phase appears to have a sustained
effect on carcass fat thickness of pigs
slaughtered at 225 lb.
