Dept. Animal Science Mimeo. Series No. 63-12 Florida Agricultural
Defteitaryc-ience Mimeo. Series No. 63-5- Experiment Station
February, 1963 Gainesville, Florida
Physical Breakdown of Whole Citrus Seeds and
Digestibility of Rations High in Citrus Seeds by Ruminants.l/
C. B. Ammerman and J. M. Wing2J
Dried citrus pulp is an important carbohydrate feedstuff particularly in
the southeast. The dried pulp normally contains whole or cracked citrus seeds
but the quantity may vary because of variety of fruit or the type of citrus
product being prepared. Twenty-five samples of dried citrus pulp examined by
Ammerman and Arrington (1961) contained 1.8 to 8.3% seeds with an average seed
content of 4.8%. Citrus seeds are high in protein and fat and thus may repre-
sent an important source of feed nutrients if physically degraded and digested
within the alimentary tract. The present study was conducted to determine the
physical breakdown of dried, whole citrus seeds and the nutrient digestibility
of rations containing 8 to 105 whole citrus seeds by ruminants.
Ten mature milking cows (8 Jersey and 2 Guernsey) were fed daily 0.7 Ib.
of dried whole grapefruit seeds, 6.3 lb. of dried citrus pulp (approximately
5% whole orange seeds) and clover pasture ad libitum. Also, 8 dairy heifer
calves (5 Jersey and 3 Guernsey) approximately 6 mo. of age were fed dried
grapefruit seeds along with dried citrus pulp and green, leafy alfalfa hay.
The average daily intake for two of the calves was 1.7 lb. of pulp and 0.3 lb.
of seeds while the average daily intake for the other six calves was 3.6 Ib.
of pulp plus 0.4 Ib. of seeds. The daily intake of the alfalfa hay was either
2 or 3 Ib. depending upon the appetite of the calf. The nutrient composition
of the ration components is shown in Table 1.
Table 1. Composition of ration components/
Dry Crude Ether Fner
Matter Protein Extract rTs/.
Alfalfa hay 91.5 18.9 2.2 186 ,
Citrus pulp 90.6 6.7 7.1 .92
Citrus seeds 94.1 14.9 39.2
i_ Other than dry matter content, all values expressed on a
moisture free basis.
2~ This study was supported in part by funds from the Citrus Processors Asso-
ciation, Winter Haven, Florida.
Ammerman, Assistant Animal Nutritionist, Department of Animal Science;
Wing, Associate Dairy Husbandman, Department of Dairy Science. The
assistance of J. P. Boggs, M. C. Jayaswal, H. L. Somers and R. W. Banks
is gratefully acknowledged.
All animals had been receiving citrus pulp prior to the time of the experi-
ment and the additional whole seeds were fed for an 8-day preliminary period.
To determine digestion coefficients with the calves, and total seeds excreted,
chromic oxide was given twice daily by capsule beginning with the preliminary
period and continued throughout the experiment. The daily chromic oxide intake
was 20 g. for the mature cows and 8 g. for the calves. Following the prelimi-
nary period, fecal grab samples of approximately 200 g. each were obtained
twice daily for 4 days. The fecal samples from each animal were composite and
a portion washed through a series of sieves to recover seeds or seed particles
and to determine fecal particle size. The remainder of the composite sample
for each calf was dried for chemical analyses.
Chemical analyses for dry matter, protein and ether extract were made
according to the methods of A.O.A.C. (1960) and chromic oxide in the feces was
determined by the procedure of Christian and Coup (1954). Gross energy was
measured with an adiabatic oxygen bomb calorimeter. Nutrient digestion coeffi-
cients were calculated from the data obtained with calves using the ratio tech-
nique. Since the mature cows were grazing and thus total nutrient intake was
unknown, nutrient digestion coefficients were not determined with this group of
Results and Discussion
The data for fecal particle size are shown in Table 2.
Fecal particle size expressed as percent of total sample
+10 +20 +30 +40 -40
Average 2.5 9.2 8.4 7.5 72.4i/
Range 0.1-6.1 1.0-15.7 4.8-11.3 5.2-9.7 66.6-78.1
Average 5.1 7.6 6.5 5.7 75.1
Range 3.1-7.2 4.4-10.0 4.7-9.4 3.3-9.1 71.3-79.2
Y U. S. Bureau of Standards.
2/ Values represent percent retained by each sieve.
3/ Percent passing No 40 sieve.
The size of fecal particles remaining following digestive processes was similar
for both calves and mature cows. Over 705 of the total fecal dry material for
both groups passed through a No 40 sieve and the distribution of the larger
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particles was similar.
There were approximately 2,900 seeds per lb. in the grapefruit seed sample.
In addition, the citrus pulp contained an average of 182 whole seeds per Ib.
Thus the mature cows consumed approximately 3,200 whole citrus seeds daily while
the calves consumed either 1,200 or 1,800 whole seeds daily depending on the
level of feed intake. No intact whole seeds or recognizable particles of citrus
seeds were recovered in the fecal samples from either the calves or the cows
indicating that rather complete physical disintegration had occurred.
Average digestion coefficients of 74, 67, 86, and 72 for dry matter, protein,
ether extract, and energy, respectively, were obtained for the total ration fed
to calves (Table 3).
Table 3. Digestion coefficients obtained with calvesl'
Dry Crude Ether
Matter Protein Extract Energy
Total ration 73.51+4.2/ 67.316.7 85.514.4 72.014.2
SEach figure represents an average of 8 values.
The coefficient of digestibility obtained for protein was significantly in-
fluenced (P<0.05) by the difference in alfalfa hay intake. Average protein
digestion coefficients of 62.8 and 71.7 were obtained with calves consuming 2
and 3 lb. of hay respectively. These coefficients may be compared with values
of 73 reported by Morrison (1957) for very leafy alfalfa hay and 50 found by
Ammerman and Arrington (1961) for dried citrus pulp. However, only 8 to 13%
of the total ration protein was from the seeds, and the effect of this pro-
portion on the digestibility coefficient of the total protein would be small.
The ether extract of the total ration was approximately 86% digestible. This
value may be compared with digestion coefficients of 80, essentially 100 and
79 found by others (Ammerman and Arrington, 1961; Keener et al., 1957; and
Neal et al., 1935) for dried citrus pulp. Morrison (1957Treported the ether
extract in very leafy alfalfa hay to be 31% digestible. From 50 to 56% of the
ether extract in the complete ration was contributed by citrus seeds and the
data suggest that this fraction was highly digestible.
When whole citrus seeds were fed to calves and cows, no whole seeds or
seed particles were recovered in the feces. Digestion coefficients obtained
with calves for dry matter, protein, ether extract and energy for rations con-
taining 8 to 1056 whole citrus seeds were 73.5, 67.3, 85.5 and 72.0, respec-
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Association of Official Agricultural Chemists. Official Methods of Analysis.
9th Ed. Washington, D. C. 1960.
Ammerman, C. D. and L. R. Arrington. Re-evaluation of Citrus Pulp as a Feed.
Proceedings Florida Nutrition Conference. 1961.
Christian, K. R. and M. R. Coup. Measurement of Feed Intake by Grazing Cattle
and Sheep. VI. The Determination of Chromic Oxide in Faeces. New Zealand J.
Sci. Tech. A, 36: 328. 1954.
Keener, H. A., N. F. Colovos and R. B. Eckberg. The Nutritive Value of Dried
Citrus Pulp for Dairy Cattle. New Hampshire Agr. Expt. Sta. Bull. 438. 1957.
Morrison, F. B. Feeds and Feeding. 22nd Ed. The Morrison Publishing Company,
Ithaca, N. Y. 1957.
Neal, W. M., R. B. Becker and P. T. Dix Arnold. The Feeding Value and Nutri-
tive Properties of Citrus By-Products. I. The Digestible Nutrients of Dried
Grapefruit and Orange Cannery Pefuses and the Feeding Value of the Grapefruit
Refuse for Growing Heifers. Flo.r.Cia Agr. Expt. Sta. Bull. 275. 1935.