SUMMARY
Effect of genotype and dietary lysine content during the
grower phase on growth performance, serum urea N, and carcass
and meat quality.
Fabian, J., L. I. Chiba, D. L. Kuhlers, L. T. Frobish,
C. R. Kerth, K. Nadarajah, W. H. McElhenny, and B. L. Anderson.
A total of 32 select line (SL) and 32 control line (CL) Duroc
pigs were used in two trials to determine the effect of selection
for lean growth efficiency and dietary lysine content during
the grower phase on pig performance. In each trial, pigs weighing
20 kg were assigned to 16 pens with two gilts or two barrows
per pen, and pens were randomly assigned within genetic lines
to one of the four grower (G) diets (0.5, 0.7, 0.9, or 1.1
g lysine/kg diet). After 50 kg, all pigs were fed finisher
1 (50-80 kg) and finisher 2 (80-105 kg) diets formulated to
meet the NRC nutrient requirements. Pigs were allowed ad libitum
access to feed and water. Blood samples were taken from each
pig at 20, 50, and 105 kg. Pigs were subjected to ultrasound
backfat (UBF) measurement at 50 and 105 kg. The initial statistical
analyses revealed that variances between the two trials were
homogeneous, thus the data were combined.
During the G phase, pigs fed the high-lysine
diets consumed less feed [linear (Ln), P < 0.001] and grew faster (Ln, P < 0.05)
and more efficiently (Ln, P < 0.001) as the dietary lysine
level increased. With the increasing dietary lysine content,
pigs had lower ultrasound backfat (Ln, P < 0.001)and higher
serum urea N (Ln, P < 0.001) at the end of the G phase. However,
during the F1 and F2 phases, pigs grew faster (Ln, P < 0.01
and P = 0.07, respectively) and more efficiently (Ln, P < 0.05)
as the lysine content of the G diets decreased, resulting in
no differences in overall growth performance or carcass and
meat characteristics. The SL pigs grew faster (P < 0.01), and
had lower 10th rib backfat ( P < 0.001) and larger longissimus
muscle area (P = 0.08) than the CL pigs, which were reflected
in higher estimated daily lean gain (P < 0.001). The SL pigs
had lower meat color ( P < 0.05) and firmness (P = 0.07) scores.
These results indicate that pigs exhibited compensatory growth
after dietary lysine restrictions during the G phase, and were
able to compensate fully. Although the SL pigs had superior
growth rate and body composition, both genetic lines responded
similarly to the restrictions.
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