Department of Animal Science Florida Agricultural
Mimeograph Series No. 61-7 Experiment Station
April, 1961 Gainesville, Florida
Nutrient Composition and Digestibility of Chopped Oat
Silage Preserved With and Without Zinc Bacitracin j/
R. A. Alexander, J. T. McCall 2/, J. F. Hentges, Jr.,
P. E. Loggins and G. K. Davis 2/
Preservation of forage is probably the weakest link in feed production
program for livestock enterprises. Losses in making hay regularly range
from 15 to 30% under good conditions and often are 40 to 60% under adverse
weather conditions. Preservation in the silo permit better retention of
nutrients provided proper ensiling conditions can be established during
the first 72 hours.
The objective of this study was to compare the effect of ensiling
chopped oats with no preservative (control) and with Silotracin (zinc
bacitracin) on the nutrient composition and digestibility of nutrients
by cattle and by sheep.
Oat silage was made from Floriland oats grown on a fine sandy soil
and cut at the pre-bloom stage of maturity. They were ensiled in up-
right type polyvinyl experimental silos 4 ft. high and 4 ft. 8 in. in
diameter. One silage with no preservative (control) was compared with
another silage treated with 5 g. of Silotracin per ton of fresh chopped
oat silage. The oats remained ensiled for a period of 53 days.
One digestion trial was conducted with four crossbred Native-Rambouillet
wethers one-year-old of similar weight which were fed in expanded-metal
collection racks. In a second triat, four non pregnant four-year-old Here-
ford cows of similar weight were fed in stanchion-type stalls and feces
were collected as described by Gorski et al. (1957).
Digestion trials were of a conventional total collection type
and consisted of a 7-day adjustment period, a 10-day preliminary period
and a 7-day collection period. Animals were fed oat silage (ad libitum)
during a 7-day adjustment period to determine the quantity of silage
1/ Project supported in part and zinc bacitracin furnished as Silo-
tracin by Commercial Solvents Corporation, Terre Haute, Indiana...
2/ Present address, Department of Animal Science, Iboa State;,Ames, iowa
3/ Research Assistant, Assistant Chemist, Associate Animal Husbandman,
Assistant Animal Husbandman and Animal Nutritionist,.respectively.
they would consume. During the preliminary and collection periods, the
animals were fed oat silage at a constant rate. Trace mineralized salt and
defluorinated phosphate were fed to meet the requirements of the animals and
water was available at all times. Feed and feces were weighed twice daily
and aliquot samples were dried in a forced air oven at 650'. for 72 hours.
Samples were allowed to equilibrate to air-dry conditions at room temperature
for three-days then they were weighed for dry matter, ground and smaller
samples weighed for chemical analyses.
Proximate analyses were made as outlined by the A.O.A.C. (1955).
Nitrogen-free-extract was determined empirically by difference and
gross energy was measured with an adiabatic oxygen bomb calorimeter.
Analysis of variance was conducted as described by Snedecor (1956).
RESULTS AND DISCUSSION
Average chemical composition and gross energy content of the chopped
oat silages are summarized in table I. Percentage dry matter, protein,
nitrogen-free-extract and ash were higher in the Silotracin-treated silage
than in the control silage. However, the percentage ether extract, crude
fiber and calories of gross energy were lower in the Silotracin-treated
silage than in the control silage. Similar results have been reported by
Andrews and Stob (1958) who used 4 g. of Silotracin plus 40 lb. of molasses
per ton of oat silage.
Table I. Average chemical composition and gross energy
chopped oat silage in plastic silos
Dry Crude Ether Crude Gross
matter protein extract fiber NFE Ash energy
Preservative in silage Kcal./g.
Treatment % % %
Silotracin I.a 13.4 17.5 6.1 30.3 36.1 10.1 4.3
5 g./ton l.b 13.7 17.0 7.1 30.3 35.6 10.0 4.4
Av. 13.5 17.2 6.6 30.3 35.9 10.0 4.4
None I. 11.6 13.8 6.6 35.3 37.0 7.4 4,3
(Control) II. 12.7 16.3 7.4 32.8 33.9 9.6 4.7
Av. 12.2 15.1 7.0 34.0 35.4 8.5 4.5
Per cent 1. 13.3 20.9 -8.0c -14.2 2,4 26.8 -0.2
Increase of II. 7.1 3.7 -3.7 7.5 4.8 3.4 -6.3
treated over Av. 10.1 12.4 -5.7 -11.0 1.4 15.2 -3.3
Represents a composite sample of the
Represents a composite sample of the
top half of the plastic silos.
bottom half of the plastic silos.
Minus sign indicates an increase in the control silage over the Silotracin-
treated oat silage.
Siloiracin-treated oat silage contained 12% more crude protein than
the untreated silage. This increase may be due to the prevention of
loss of nitrogen as ammonia due to putrefaction of proteins and amino acids,
as indicated by less ammonium odor in the Silotracin-treated silo.
Since a total weight of the silage was not taken before or after
ensiling, it would be impossible to determine the reason for the 11%
decrease in crude fiber content of the Silotracin-treated silage as
compared to the control.
There was an interesting relationship between the condition and the
chemical composition (table 1) of the silage in the top half and bottom
half of each silo. The silage in the bottom half of the untreated silo was
of better quality than that in the top half. This was not the case in
the Silotracin-treated silo in which the chemical composition was rela-
tively constant throughout. This may indicate that in the top half of
this silo, the fermentation process was enhanced by the Silotracin pre-
servative. From these data, it would appear that the top portion of
the silo would be the logical place to concentrate the preservative.
While both the treated and untreated silages were lacking in palat-
ability, the Silotracin-treated silage was more palatable than the con-
trol silage as measured by animal acceptance and consumption. It took
the animals a few days to become accustomed to eating the silage; how-
ever, the sheep consumed the silage more readily than did the cows.
Silotracin-treated silage had a more desirable color and odor than the
control silage. The pH of composite samples from the bottom half of
each silo was 5.6 for the control and 5.3 for the Silotracin treatment.
Other workers have reported that silage made with Silotracin as
a preservative was of good color and odor and that the palatability was
enhanced (Andrews and Stob, 1958; Dexter, 1957; Rusoff, 1959). However,
Becker et al. (1960) fed oat forage from the same source as reported
herein and found that large dairy heifers consumed less Silotracin-treated
oat silage than control oat silage. Average amounts of oat silage con-
sumed per day per helfer were: no preservative 98 Ib., Silotracin 87 Ib.
and ground snapped corn 81 Ib.
Results of the digestion trials are given in table 2. There was
a highly significant increase (P<0.01) in protein digestibility of the
Silotracin-treated silage over the control silage. Although there
were no other statistically significant treatment differences in nutrient
digestibility, there were trends indicating advantages for the Silo-
One explanation for the increased digestibility of nutrients may be
a more favorable environment in the rumen for cellulose breakdown and
volatile fatty acid production when the Silotracin-tr'ated silage was fed.
This is logical because Rusoff (1959) reported that lactic and pro-
pionic acid content of oat silage dry matter was greater in a Silotracin-
treated silage than in a control oat silage.
Ramsey et al. (1960) reported no significant difference in the di-
gestibility of nutrients in oat silage preserved with Silotracin from
that of a control oat silage without a preservative. Work with other
forages (Chapman et al., 1959; Ransey et al., 1959; Rusoff et al., 1959a;
Rusoff et al., 1959b; Wing and Wilcox, 1960) has not shown any signifi-
cant advantage in digestibility or fat corrected milk (FCM) production
when Silotracin was used as a preservative.
Data presented in table 2 indicated that the crude fiber fraction
was more digestible than the nitrogen-free-extract (NFE). Similar find-
ings are reported in the composition tables published by Morrison (1956)
and Schneider (1947), The indigestible lignin fraction of feed is usually
in the crude fiber fraction while the readily digestible carbohydrates
are usually in the NFE fraction; however, Moxon and Bentley (1953) have
reported that lignin is often found in larger amounts in the NFE fraction
than in the crude fiber fraction. Thus, the conventional Weende method
(AOAC) of forage analyses often may provide misleading information
relative to the nutritive value of the crude fiber content of some forages.
These studies indicate that Silotracin can be used to advantage as
a preservative of oat silage cut at a very early stage of maturity.
Table 2. Average apparent digestion coefficients, digestible energy,
and total digestible nutrients for chopped oat
silage by cattle and by sheep
Dry Crude Ether Crude Energy
matter protein extract fiber NFE TDN
Treatment % % % % _
Silotracin Sheep 58,0a 63.1 53.1 77.7 60.2 62.1 63.6
5 g./ton Cows 55.9a 61.0 51.3 77.2 52.7 56.0 60.5
Av. 57.0b 62.1** 52.2 77.5 56.5 59.1 62.1
None Sheep 54.6 54.9 52.8 74.4 55.7 58.6 61.7
(Control Cows 51.8 50.2 42.7 76.7 53.7 54.3 59.6
Av. 53.2 52.6 47.8 75.6 54.7 56.5 60.7
Per cent Sheep 5.9 13.0 0.6 4,3 7.5 5.6 3.0
Increase of Cows 7.3 17.7 16.8 0.7 1.9c 3.0 1.4
treated Av. 6,7 15.3** 8.4 2.5 3.2 4.4 2.3
./ Represents an average of four observations.
b/ Represents an average of eight observations.
_/ Minus sign indicates an increase in the control silage over the Silotracin-
treated oat silage.
d/ (P <0.01)
Chopped oat silage preserved with Silotracin (zinc bacitracin) was
compared to a control oat silage without a preservative in a conventional
total collection digestion trial using both cattle and sheep. Per-
centage dry matter, protein, NFE, and ash content were higher in the
Silotracin-treated silage than in the control silage while the per-
centage ether extract, crude fiber, and calories of gross energy content
were lower. Silotracin-treated oat silage contained 12% more crude protein
and 11% less crude fiber than the untreated silage. Protein digestibility
was significantly greater (PO0.01) in the Silotracin-treated oat silage
than in the control. Although there were no other statistically
significant treatment differences in digestibility, there were increases
in all digestion coefficients for the Silotracin-treated oat silage.
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