Forty-eight 50-kg barrows ((Yorkshire x Landrace) x Duroc) were allocated to one
of six dietary treatments in a randomized block design with four blocks. Each block
represented a time period. Each experiment consisted of a 14-day adaptation period to
the diets, followed by a 7-day fecal and urine collection period. Pigs were penned
individually in metabolism pens (5′ x 5′) equipped with low-pressure water nipples
providing free access to water, and plastic flooring. Pigs were housed in an
environmentally controlled room maintained at 21ıC. Treatments consisted of six diets;
three diets containing 15.5, 12.5, 9.5 % protein, and corn and soybean meal as protein
sources, and three diets containing 12.5% protein with either added wheat middlings
(WM), sunflower hulls (SH), and corn distillers grains (CDG). Diets were formulated to
meet NRC (1998) recommended true digestible AA and energy requirement for the 50-kg
growing pig. Synthetic amino acids were added to the 12.5%, 9.5%, WM, SH, and CDG
diets. There were two feeding regimes in this experiment, feed restricted and ad libitum.
The feed restricted group was fed at 3.5% of each pig’s BW and divided into two
equivalent meals per day (8:00 a.m. and 4:00 p.m.). The ad libitum group was offered
5.0% of each pig’s BW and divided into two equivalent meals per day (8:00 a.m. and 4:00
p.m.). All feces and urine were collected for a duration of 6 to 7 days from each pig.
Feces were collected via bags directly attached on the skin surrounding the anus. Urinary
pH, nitrogen, ammonia, and urea, and fecal nitrogen and urease were determined.
Reducing dietary protein from 15.5 to 12.5% did not reduce nitrogen retention in either
feeding regimes (ad libitum or restricted) and reduced (P < .05) total daily nitrogen,
urinary nitrogen, and urinary ammonia output. Reducing dietary protein from 15.5 to
9.5% also reduced (P < .05) total daily nitrogen, urinary nitrogen, and urinary ammonia
output but decreased nitrogen retention independent of whether pigs we provided free
access or restricted access to feed. Addition of fiber source such as WM, SH, or CDG to
a 12.5% protein diet yielded similar nitrogen retention to that of a 12.5 or 15% protein diet
without fiber addition, but did not reduce urinary nitrogen or urea excretion when
compared to a 12.5% protein diet containing no fiber. Fecal urease enzyme activity was
reduced as dietary protein was reduced, but was not increased when fiber sources were
included. In conclusion, nitrogen retention is not compromised and urinary nitrogen in the
form of urea is decreased when pigs are fed diets containing 12.5% CP compared to that
of pigs fed diets containing 15.5% CP. Addition of fiber sources at 10% of the diet to a
12.5% CP diet does not further reduce urinary nitrogen or urea excretion, and does not
increase fecal urease enzyme activity. Feeding a diet containing 9.5% CP dramatically
reduced N excretion in the form of urinary urea, however, it decreases protein accretion
as measured by nitrogen retention.