Seventy-two high-lean growth gilts (initially
75.5 lb BW) were used to determine the influence of dietary lysine on carcass
characteristics at 120 and 160 lb. Gilts
were randomly selected for slaughter when
the average weight of pigs in the pen
equaled or exceeded 120 and 160 lb. The
experiment was designed as a randomized
complete block, with initial weight serving
as the blocking factor. Six dietary treatments were included, ranging from .54 to
1.04% digestible lysine (.69 to 1.25% total
dietary lysine). At 120 lb, hot carcass weight decreased and then increased as did
dressing percentage for gilts fed increased
dietary lysine. Average backfat thickness
and 10th rib fat depth were not influenced
by dietary treatment. However, longissimus
muscle area (loineye) was increased for
gilts fed greater dietary lysine. Kidney fat
and total carcass lipid decreased but carcass
moisture increased as dietary lysine increased. The decreased carcass lipid content resulted in reduced longissimus muscle marbling at 120 lb. For gilts fed to 160 lb, hot and chilled carcass weight decreased and then increased as dietary lysine increased. Dressing percentage followed a similar pattern because of the difference in carcass weight. Backfat thickness, 10th rib fat thickness, and kidney fat decreased for gilts fed increased dietary lysine. Carcass moisture and crude protein increased and then decreased as dietary lysine increased. The moisture content was maximal for gilts fed .94% digestible lysine, whereas carcass crude protein was maximal for gilts fed .74% digestible lysine. However, carcass lipid followed an opposite pattern, decreasing
and then increasing as dietary lysine increased. Carcass muscle score improved
but longissimus muscle marbling decreased
for gilts fed greater dietary lysine. The
data from this experiment suggest that the
high-lean growth gilt requires at least 18
and 22 g/d lysine intakes from 80 to 120
and from 120 to 160 lb, respectively, to
optimize longissimus muscle area and minimize carcass lipid content.
