Progress Report Series No. 76 U 
August, 1959
AGRICU LTU RAL EXPERI 
STATION
of The Alabama Polytechnic Institute, 
Auburn, Ala.
E. V. SMITH, Director
Roughages for Dairy Cows
L. A. Smith,' W. B. Kelley,' and George E. Hawkins'
Tracy sorghum produces good yields of forage and has
created much interest as a silage crop for dairy cattle.
Also, Johnsongrass, a commonly grown forage in the
Black Belt area of Alabama is used extensively as a hay
for dairy cows.
To determine the comparative values of these crops to
alfalfa as a roughage for dairy cows a test was conducted
by the API Agricultural Experiment Station.
The objectives of the test were: (a) to determine the
chemical composition, the digestibility, and the intake of
alfalfa and Johnsongrass hays and of Tracy sorghum
silage, and (b) to deteraminethea-ount of iiilk produced
by cows fed these three forages.
EXPERIMENTAL PROCEDURE
The forges used in this study were cut at the stage of
maturity recommended for each crop. Alfalfa was in
approximately one-tenth bloom at cutting, whereas, the
Johnsongrass was cut at the pre-bloom stage. Both for-
ages were passed through a stem-crusher after cutting
to speed up the field curing process. Tracy sorghum was
cut with a forage harvester in the dough 
stage of matur-
ity and ensiled in an upright silo. The silage was greenish
in color and had a pleasant aroma.
Twenty-four dairy cows that had been in production 2
to 5 months and producing an average of 30.5 pounds of
milk daily were used for this 5-week test. During the 2
weeks before the test all cows were fed all the alfalfa and
Johnsongrass hays and Tracy sorghum silage they would
eat. In addition they were fed 1 pound of concentrate for
each 3 pounds of 4 per cent FCM (fat corrected milk)
produced. At the start of the test the cows were placed
in 8 groups of 3 each according to the level of milk pro-
'Superintendent Black Belt Substation.
2Deceased, former 
Superintendent, 
Black Belt
Substation.
'Associate dairy husbandman.
duction. Within these production groups the cows were
assigned at random to 1 of the 3 test rations: (a) alfalfa
hay and ground oat grain containing 1 per cent salt; (b)
Johnsongrass hay and a concentrate mixture, and (c)
Johnsongrass hay plus Tracy sorghum silage and a con-
centrate mixture. The concentrate mixture was 82.5 per
cent ground oat grain, 16.5 per cent cottonseed meal,
(41 per cent protein grade), and 1 per cent salt. During
the experimental period the concentrate mixture and the
oat grain salt mixture were fed at the same rate as during
the pre-experimental period.
Cows were fed approximately 10 per cent more of their
assigned roughage than they would eat. Thus, they 
had
some selectivity in the forage consumed. As a result the
refused Johnsongrass was mostly stems.
During the test, all cows on test were housed 
and fed
in individual tie stalls. Water was available twice daily
during exercise periods on a concrete-paved paddock.
Body weights were determined on two successive days
at the start and end of the test.
Digestibility of the experimental forges was 
deter-
mined by a digestion trial with steers. In addition, 
com-
position of the forages was determined.
RESULTS
Alfalfa hay was superior to Johnsongrass hay and to
Tracy sorghum silage in composition as indicated by crude
protein and crude fiber contents, Table 
1. However, on
the dry matter basis, the TDN (total digestible 
nutrients)
content of the Johnsongrass hay that 
was eaten was 6.5
per cent higher than that of alfalfa hay 
and 19.0 per cent
higher than that of Tracy sorghum 
silage. During the
digestion trial, steers on Johnsongrass 
hay refused 24.6
per cent of the amount fed, whereas, 
those on alfalfa
hay refused 1.0 per cent of the 
amount fed. The re-
fused Johnsongrass was mostly stems 
showing that the
steers selectively ate the leaves. Therefore, 
the TDN
value given for Johnsongrass hay 
is essentially the TDN
value for Johnsongrass leaves. Also, 
the Johnsongrass hay
fed in this test was green and leafy 
in appearance.
TABLE 1. COMPOSITION AND DIGESTIBILITY OF TEST
FORAGES, DRY MATTER BASIS
Johnson- Tracy
Component Alfalfa grass sorghum
Per cent Per cent Per cent
TDN .......---------------- 58.8 65.0 46.0
DP ----------------- 14.9 7.4 0.0
Crude prot. --------- 20.4 11.7 6.6
Crude fiber ---------- 28.9 34.0 29.7
Ether ext. ------------ 1.3 1.4 2.9
NFE .......---------------- 42.6 45.6 55.4
Ash .....---------------------. 6.8 7.3 5.4
The average intakes of hay or hay equivalent in the
form of silage per 100 pounds of body weight by cows in
the roughage groups were: (a) alfalfa hay, 2.55 pounds;
(b) Johnsongrass hay, 2.34 pounds; and (c) Johnsongrass
hay-Tracy sorghum silage, 2.16 pounds (Johnsongrass hay,
1.33 pounds and Tracy sorghum silage, 0.83 pounds).
Average amounts of dry forage eaten by each group
differed significantly. An evaluation of digestible 
nutri-
ents eaten showed that cows on alfalfa ate 12.8 per cent
more TDN than needed for body maintenance and milk
production. In comparison, cows on Johnsongrass hay
ate 22.7 per cent more TDN than needed, however, 
cows
that received a combination of Johnsongrass hay and Tracy
sorghum silage ate only 10 .per cent more TDN than
needed. Further evaluation of the nutrient intake data
revealed that the digestible protein intake of 
cows fed the
Johnsongrass and Tracy sorghum silage ration 
was only
95 per cent of the recommended allowance. In contrast,
the digestible protein intakes of cows on 
the alfalfa hay
ration and of those on the Johnsongrass 
hay ration were
187.6 and 125.4 per cent respectively of 
the recommend-
ed allowances.
Daily milk production (4 per cent fat 
corrected milk)
of cows fed the alfalfa hay ration was 
0.8 and 1.8 pounds
higher than that of cows fed the Johnsongrass 
hay or the
Johnsongrass hay-Tracy sorghum silage 
rations, respec-
tively, Table 2. The 1.8 pounds difference 
in daily milk
production per cow on the alfalfa hay 
and Johnsongrass
hay-Tracy sorghum silage rations was 
significant and
probably resulted from the shortage 
of the digestible pro-
tein itake (-0.095 pound per cow 
per day) by cows on
the latter ration. Since cows require 
about 0.049 pound
of digestible protein to produce 
a pound of 4 per cent fat
corrected milk the protein shortage 
seems to account for
the differences in milk production 
of the alfalfa hay ration
and the Johnsongrass hay-Tracy 
sorghum silage ration
groups.
TABLE 2. AVERAGE DAILY 4 PER CENT FAT CORRECTED
MILK BY ROUGHAGE GROUPS
Milk
production
Roughage
Lb.
Alfalfa hay ------- 27.6
Johnsongrass hay --------------------
26.8
Johnsongrass hay-
Tracy sorghum silage ----- 25.8
Cows on the alfalfa hay ration utilized 30.3 per cent of
their digestible nutrients intake for milk production 
as
compared to 26.5 and 29.9 per cent for cows on the John-
songrass hay and those on Johnsongrass hay-Tracy 
sor-
ghum silage rations, respectively. Therefore, 
the efficiency
of utilization of digestible nutrients for milk production
was slightly lower for 
cows fed the Johnsongrass 
hay
ration than for those fed the other ration.
There were no differences 
in the body weight changes
that could be attributed to the roughages fed.
SUMMARY
Johnsongrass hay fed in this study was about equal to
alfalfa hay as a source of roughage 
for dairy cows as in-
dicated by milk production of 
cows fed these forages.
Milk production of cows on Johnsongrass 
hay as the only
roughage was 97.1 per cent as much 
as that of cows on
alfalfa hay. However, cows that were 
fed both Johnson-
grass hay and Tracy sorghum silage roughages 
produced
6.5 per cent less milk than cows fed alfalfa 
and 4.0 per
cent less than those fed Johnsongrass 
hay as the only
roughage.
The portion of Johnsongrass hay 
consumed, which was
mostly leaves, was more digestible 
than the alfalfa hay.
However, when the refused Johnsongrass 
hay is taken in-
to account it would be necessary 
to feed 20 per cent
more Johnsongrass than alfalfa 
to obtain the same TDN
intake. Also, alfalfa hay had a 
higher digestible protein
content than the Johnsongrass 
hay. For this reason it
was not necessary to use a protein 
supplement with alfalfa
hay. Since Johnsongrass hay 
usually is low in digestible
protein the concentrate mixture 
fed with this forage
should include a protein supplement. 
Johnsongrass like
most other forages drops 
in quality as it matures. 
There-
fore, the results of this test 
would not be applicable 
to
Johnsongrass cut after blooms 
appear.
Tracy sorghum silage was 
low in TDN content and 
the
protein content of this forage 
was not digested to a meas-
urable extent.