Effect Of Mixing Uniformity On
Uneven ingredient dispersion feeds may lead to
reduced bird performance. In order for birds to
reach their genetic potential for growth and meat
yield, levels of protein, energy vitamins and minerals
must be provided in their proper ratio. Duncan
(1989) reported that as protein variation increased
in feeds, growth rate and feed conversion were depressed (Table 1). A 10% variation in the feed quality
significantly reduced both weight gain and increased feed conversion. When the coefficient of variation
(CV) of the feed was increased to 20%, another significant increase was observed in feed/gain (F/G).
A recent study on the effect of mixing uniformity
on day one old broilers was conducted by McCoy
et al. (1994). Feed was formulated to meet or
exceed NRC requirements for all nutrients for
broiler chicks from 0 to 3 week of age. However,
in experiment 2, feeds were formulated to 80%
of NRC recommendations for crude protein (CP),
lysine, methionine, Ca, and P. The purpose of
using deficient diet in this study was to accentuate
any difference in growth performance that might
result from diet nonuniformity.
In experiment 1, feeds were collected from mixer
after 20, 40 and 80 revolutions of mixing (20 =
highly non-uniformity mixing, 40 = moderate nonuniformity
mixing and 80 = uniform mixing).
Variability of feed decreased sharply between 20
and 40 revolutions and no further reduction
occured between 40 and 80 revolutions (Table
2). The CV values from analyses of salt
concentrations were 43, 11 and 13% for 20, 40
and 80 revolutions, respectively. No difference
occured among treatment for average daily gain
(ADG), average daily feed intake (ADFI), bone
strength, bone ash, carcass crude protein, carcass
fat, or carcass ash. However, there was a trend
for a linear increase in gain:feed (G/F) ratio when
mixer revolutions were increased.
In experiment 2, feeds were collected after 5, 20,
and 80 revolutions. The salt test CV % decreased
from 40.5% to 12.1% when mixing was increased
from 5 to 20 revolutions, but there was no further
reduction of CV % from 20 to 80 revolutions (Table
3). ADG, ADFI and G/F improved when CV %
decreased from 40.5 to 12.1%. However, mortality
was not affected by treatment.
The effect of poorly mixed feed on pig performances
was reported by Traylor at el. (1994). In this
experiment the effect of mix time on diet uniformity
and growth performance was evaluated in nursery
and finishing pigs on a double-ribbon mixer.
For the nursery experiment, increasing mix time
from 0 to 0.5 min decreased the CV % from 106.5
to 28.4% (Table 4). Increasing mix time to 4 min
reduced CV value to 12.3%. ADG, F/G and ADFI
was increased by 49, 19 and 20 %, respectively
as the CV for marker concentration decreased
from 106.5 to 12.3%.
For the finishing experiment, increasing mix time
reduced the CV for diet uniformity from 54 to less
than 10 % (Table 5). The mix time had no statistically significant effects on ADG, ADFI, F/G and bone strength. However, rate and efficiency of gain had
numerical increases of 4 and 5 %, respectively, as mix time increased from 0 to 0.5 min.
They concluded that that increased mix time improved diet uniformity and performance of nursery pigs.
Finishing pigs were less sensitive to diet nonuniformity, with growth performance being affected only
slightly as mix time was increased from 0 to 4 min. The finishing pigs were quite tolerant of CVs of at
least 15% and even up to 54%. However, caution is warranted when using a medicated feed article.