2.7. Protein quality measurements
Body weight gain was determined by the difference in body
weight between the start and end of the experiment. Empty body
weight at the start of the experiment was measured after 12 h of
fasting, and the empty body weight at the end of the experiment
was measured by euthanasia of each animal without fasting,
removing the intestinal contents, and measuring the weight of
the animal. The feed/gain ratio of each animal was obtained by
dividing the feed intake of the animal by its empty body weight
gain.
Protein efficiency ratio (PER) was determined by the following
equation (Henry, 1965), which related to protein intake and empty
body weight gain:
PER ¼ Body weight gain
Protein intake :
Net Protein Ratio (NPR) was calculated from the body weight
loss of the N-free diet group according to the method of Bender
and Doell (1957):
NPR ¼ Weight gain on protein diet Weight loss on N-free diet
Protein intake :
Net protein utilisation (NPU) was measured by analysing the
carcass of each animal and measuring protein retention at the
end of the experiment. Protein loss of the N-free diet group was
calculated as follows:
NPU ¼ Body N of protein diet Body N of N-free diet
Nitrogen intake
True digestibility of each feed protein was determined by measuring
the amount of metabolic fecal N from the N-free diet feed
and performing the following equation according to the method
of Schneider and Flatt (1975):
TD ð%Þ ¼ N intake ðfecal N endogenous fecal NÞ
N intake 100:
The biological value (BV) of each feed was calculated from the
relationship between NPU and true digestibility as described by
Hackler (1977):
BV ð%Þ ¼ NPU true digestibility ð%Þ
Tabl