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Sulfur Supplementation of Urea-containing Silages and Concentrates. II. Ration Digestibility, Nitrogen, and Sulfur Balances
Sulfur Supplementation of Urea-containing Silages and Concentrates. II. Ration Digestibility, Nitrogen, and Sulfur Balances D. G. GRIEVE1, W. G. MERRILL, and C. E. COPPOCK Department of Animal Science Cornell University, Ithaca, New York 14850 Abstract
others (7, 11, 14). Lower nitrogen retention values were reported when urea was included in the corn silage portion of the ration (14) or in concentrates in some trials (10, 14) but not others (7, 11, 14). Factors which may influence utilization of urea include dietary nitrogen, amount of urea, digestible carbohydrate availability, and length of trial. An additional factor limiting urea utilization may be dietary sulfur. Using lambs fed purified diets containing urea, Thomas et al. (18) demonstrated improved growth, wool growth, and nitrogen and sulfur balances from supplemental sulfate sulfur. However, with practical diets containing urea, Jacobsen et al. (13) found supplemental sulfur to have no effect on nitrogen utilization. Our objectives were to determine effect of urea additions to corn silage and concentrate rations on ration digestibility and nitrogen utilization by dairy cows and to study effect of sulfur supplementation on urea nitrogen utilization.
Metabolism trials were conducted on 16 cows at three stages of lactation to evaluate effect of sulfur supplementation on utilization of urea in corn silage and concentrate portions of ration and on digestibility and nitrogen and sulfur balance. Treatments arranged in a 2 x 2 x 9. factorial consisted of: .5% urea-treated or 3.5% soybean meal-treated corn silage; 0 or .8~ urea-containing 18% crude protein concentrates; and 0 or .8% concentrate anhydrous sodittrn sulfate. Treatments did not affect digestibility of ration dry matter, cell walls, acid detergent fiber, or crude protein. Sulfur digestibility was improved by sulfur supplementation. Cows fed urea-treated corn silage had lower nitrogen balances ( - 14.0 vs. 4.2 grams per day) than cows fed soy-treated corn silage. Neither concentrate nitrogen source, sulfur supplementation, nor treatment interactions affected nitrogen utilization. Urea was better utilized when included in the concentrate rather than corn silage portion of the ration, and on a low sulfur ration sodium sulfate supplementation did not affect nitrogen utilization. Sulfur balances were not affected by treatments although absorbed sulfur and urinary sulfur were increased by sulfur supplementation.
Experimental Procedure
Introduction
Urea has provided an economical source of nitrogen in dairy cattle rations based on corn silage with little or no effect on milk yield when fed at moderate percents (.5% in corn silage and/or 1.0~ of concentrate) (9). However, concerning ration digestibility and nitrogen balances, reduction in dry matter digestibility was reported by one author (11) but not Received for publication August 18, 1972. 1Present address: Department of Animal and Poultry Science, University of Guelph, Guelph, Ontario, Canada.
A total of 44 7-day collections and balance trials were conducted on 16 Holstein cows at three stages of lactation, approximately 6, 20, and 34 wk postpartum. Treatments described under Experiment II (9) included silage nitrogen additive (.5% urea vs. 3.5% soybean meal), concentrate urea (0 vs..8%), and concentrate sulfur (0 vs..8~; sodium sulfate), all values as fed. Treatments were arranged in a 2 x 2 x 2 factorial and fed to cows for a complete lactation. There were 16, 15, and 13 collections at the three respective stages of lactation; fewer during second and third collection periods were due to removal of cows from trial as reported (9). Only animals in their second or later lactation (two per treatment combination) were used in metabolism studies. Feed offered was reduced to actual intake 1 wk before collection to minimize orts and maintain constant consumption throughout the collection. We processed and analyzed samples of feeds and orts as reported (9) and cell wall components (19). One percent aliquots of urine were collected for analysis of nitrogen
224
SULFUR
SUPPLEMENT
TABLE 1. Analysis of variance model for metabolism trial data. Source
-- M E T A B O L I S M
20__5
TABLE 2. Least squares adjusted daily means by periods, metabolism trial data.
Degrees of freedom
Total Blocks Treatments Error A Periods Blocks x periods Treatment x periods Error B
43 1 7 7 2 2 14 10
Period Item
(1) and sulfur as described (9). Feces samples were processed similar to feed sampies. Milk nitrogen was determined by Kjeldahl procedures (1) and milk sulfur estimated from nitrogen by assuming its presence in proportion of 6.25?0 of nitrogen (17). Data were analyzed by least squares analysis of variance of a fixed model. Collection periods were included in analysis as a split plot in time after Federer (8) (Table 1). Interaction of blocks (age group) and treatments (Error A) was assumed to be true error and was used for testing significance of treatment differences while Error B was used to test significance of treatment period interactions. Results and Discussion
Ration Digestibility. Mean values for daffy dry matter intake, ration digestibility, and milk yield b y collection period (6, 20, and 34 wk postpartum for periods 1, 2, and 3) are in Table 2. Highest dry matter intake occurred during the second period and was significantly greater (P < .05) than during period 3. Digestibility of cell wall and acid detergent fiber fractions of dry matter were higher and crude protein digestibility lower during second and third periods than during the first (P < .05). Milk yield reflected stage of lactation. Since
1
Dry matter intake (kg) Digestibility (~) Dry matter Organie matter Cell walls Acid detergent fiber Crude protein Milk yield (kg)
2
3
14.8 "b 15.7 ~ 13.2 b 68.5 69.5 C39.7" 35.0" 68.2 ~ 28.7"
67.9 69.0 47.6 b 43.0 b 65.8 b 21.2 b
~67.1 68.5 47.P 45.4 b 64.2 b 10A"
~.b.c Means bearing the same superscript are not significantly different (P < .05).
no concentrate was fed during period 3, digestibility values represent corn silage only and agree with other reported values (6). Effect of treatments on ration digestibility across all periods is in Table 3. Neither silage or concentrate nitrogen treatments nor sulfur supplementation affected any measures of ration digestibility (P < .05), excepting digestibility of ration sulfur which was improved (P < .01) by adding supplemental sulfur. This agrees with Jaeobson et al. (13). While differences between silage nitrogen treatment on digestibility were nonsignificant, soy-treated corn silage tended to be more digestible in all components than urea-treated silage. There was a significant interaction with silage nitrogen source by period for apparent crude protein digestibility. Nature of this interaction is in Table 4. Nitrogen was more highly digested from soy-treated silage in period 2 but not in periods 1 or 3. Only the differences in sulfur digestibility between silages approached significance (.10 > P > .05). Sulfur
TABLE 3. Main effects of corn silage and concentrate nitrogen sources and sulfur supplementation on digestibility of total ration components. Silage
Concentrate
Item
Urea
Soy
Urea
Soy
Dry matter Organic matter Cell wall constituents Acid detergent fiber Crude protein Sulfur
66.8 68.0 43.4 38.0 65.8 49.0
68.9 70.4 46.3 44.3 66.4 53.6
67.4 68.5 43.4 40.3 66.0 51.6
68.3 69.5 46.3 41.9 66.2 52.0
Sulfur -67.8 69.1 44.9 40.8 66.6 45.4 ~
+ 67.8 68.9 44.7 41.4 65.6 57.2 ~
SE .40 .36 .72 .84 .34 .92
" Means are significantly different (P <.01 ). JOURNAL OF DAIRY SCIENCE VOL,
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G R I E V E E T AL
TABLE 4. Interaction between silage nitrogen source and periods for apparent digestibility of ration nitrogen.
TABLE 6. Interaction between silage nitrogen source and periods for urine nitrogen as a percent of absorbed nitrogen. Silage N additive
Silage N additive Period
Urea
Soy
Period
Urea
Soy %
1 2 3
68.4 ~ 63.6b 65.3 ab
1 2 3
68.1" 68.0" 63.2b
44.7 ~ 63.9 °a 71.80
49.3 ~b 57.3 '~bc 57.9b°
~'b Values bearing common superscripts are not significantly different (P < .05) according to hsd test.
~,b,c.dValues bearing common superscripts are not significantly different (P < .05).
supplementation did not affect fiber digestibility as found in vitro by Barton et al. (2) and in vivo with sheep by Bray and Hemsley (3). Dietary sulfur as a percent of ration dry matter in our study was increased from .11 to .18 by addition of anhydrous sodium sulfate having the same range as those values in earlier studies (2, 3). Nitrogen utilization. Data on utilization of nitrogen by main treatment effects are in Table 5. Cows fed soy-treated corn silage were in positive nitrogen balances while those fed urea-treated silage were in negative balance (P < .05). Although there were no reports of a similar comparison, decreased efficiency of nitrogen utilization by cows fed urea-treated corn silage compared to untreated silage has been reported by some (5, 14) but not others (7, 12). The difference in nitrogen balance in our study was not, however, associated with any difference in milk yield (9), nor was there a treatment difference in milk nitrogen as a percent of absorbed nitrogen (Table 5). There was significant interaction with silage nitrogen source by period for urinary nitrogen expressed as a percent of absorbed nitrogen (Table 6). As silage became a greater part of the ration
from periods 1 through 3, this value increased more rapidly for cows on urea-silage treatment than for those fed soy silage till the period 3 treatment difference was significant (P < .05). This supports the nitrogen balance data, indicating less efficient metabolic utilization of nitrogen from urea-treated silage. Concentrate nitrogen treatment did not significantly affect any measures of nitrogen utilization (P < .05). Cows fed urea-containing concentrate tended to retain more nitrogen which also agrees with results of Huber et al. (11). On the other hand, Holter et aI. (10) have reported decreased nitrogen retention by cows fed ureacontaining concentrates, and this observation is supported by Knott et al. (14) in one trial but not in a second. In our study there was no statistical evidence for interaction between silage and concentrate nitrogen source treatments on nitrogen utilization. Urea intakes and corresponding nitrogen balances for all nitrogen treatments by periods are in Table 7. A broad range of urea intakes (from 0 to 208 g per day) is shown, but there is no association with nitrogen balance data except all values for urea silage fed animals are negative and those for animals fed soy-treated silage are
TABLE 5. Main effects of corn silage and concentrate nitrogen sources and sulfur supplementation on mean daily nitrogen balance data. Silage Item Intake (g/24 hr) Feces (g/24 hr) Urine (g/24 hr) Milk (g/24 hr) Balance (g/24 hr) Urinary/absorbed (%) Milk/absorbed (%)
Urea 311.3 105.9 119.9 99.5 --14.060.1 47.7
Concentrate
Sulfur
Soy
Urea
Soy
--
+
324.3 108.1 116.4 96.2 4.2" 54.8 43.5
327.7 110.2 118.9 98.6 .1 56.1 44.3
307.9 103.8 117.4 97.1 --9.8 58.7 46.9
323.1 107.0 121.7 97.9 --3.0 58.1 44.5
312.5 107.0 114.6 97.8 --6.7 56.7 46.7
Means are significantly different (P < .05). JOURNAL OF DAIRY SCIENCE VOL. 56, NO. 2
$E 6.94 2.22 3.10 1.73 4.43 1.34 1.11
SULFUR SUPPLEMENT -
227
METABOLISM
TABLE 7. Mean daily intakes of urea and nitrogen balances by nitrogen treatment and period. Period Silage
Concentrate
1
2
3
Treatment means
Urea
Urea
I82 ( -- 10.0)
208 ( - 18.8)
194 (-7.3)
I95 ( - 12,1 )
Urea
Soy
64 (-- 1.0)
170 (--38.8)
197 (--8.0)
144 (--15.9)
Soy
Urea
121
( Soy
Soy
59
3.2)
(
0 (--13.7)
Period means
0
6.4)
0 (-- 5.6)
60
(27.3)
(12.2)
0 (7.8)
0 (-- 3.7)
92
109
98
100
(-- 5.4)
(--14.2)
(4.9,)
(-- 3.7)
predominantly positive. Thus, it appears that the effect of ensiling urea is more important than dietary urea in determining efficiency of urea nitrogen utilization by the animal. Urea was more effectively utilized when added to the concentrate portion of the ration at feeding time than adding it to chopped corn before ensiling. Sulfur supplementation with anhydrous sodium sulfate had no effect on measures of nitrogen utilization (Table 5), nor was there interaction between nitrogen source and sulfur. Amount and source of sulfur in these trials had no effect on utilization of urea nitrogen which agrees with other reports (4, 13). Though it has been suggested that dietary nitrogen to sulfur ratios should be in the range of 10:1 (15) for best utilization of nitrogen, decreasing nitrogen to sulfur ratio in our experiment from 21:1 to 13:1 over all periods and from 19:1 to 11:1 during period 1 had no effect on nitrogen utilization. Either sulfur was not first limiting
in the diet, or the source of supplemental sulfur was not well utilized as indicated by Jacobson et al. (13). Sul[ur balance data. Effects of treatments on sulfur balance data are in Table 8. In genoral, cows were in slight negative sulfur balance on all treatments and during all periods. Nitrogen sources had no effect on these data, except cows fed urea silage excreted more urinary sulfur (P < .01). Of primary interest are comparisons between unsupplemented and sulfur supplemented groups when treatment differences occurred for sulfur intake, urinary sulfur, milk sulfur as a percent of absorbed sulfur (P < .01), and urinary sulfur as a percent of absorbed sulhtr (P < .05). No differences occurred in fecal sulfur, milk sulfur, or sulfur balance. Supplemental sulfur was highly absorbed (79.6$) as found by Jacobson et al. (13), who reported 72.2~; absorption of supplemental sulfur. However, absorbed sulfur was
T~a3LE 8. Main effects of corn silage and concentrate nitrogen source and sulfur supplementation on mean daily sulfur balance data. Silage Item Intake (g/24 hr) Feces (g/24 hr) Urine (g/24 hr) Milk (g/24 hr) Balance (g/24 hr) Urinary/absorbed ($) Milk/absorbed ($)
Concentrate
Urea
Soy
18.96 8.88 7.60 ~ 6.26 -- 3.76 73.0 74.0
21.76 9.01 10.47 ~ 6.01 -- 3.70 78.1 60.1
Urea 20.55 9.32 8.82 6.17 -- 3.74 72.4 65.6
Soy 20.17 8.57 9.26 6.10 -- 3.73 78.7 68.4
Sulfur --
q-
16.00~ 8.60 4.45 ~ 6.14 -- 3.19 64.5b 85.2 a
24.73" 9.29 13.69.~ 6.12 - 4.28 86.6b 48.8 a
sE .61 .21 .36 .12 .41 2.80 3.90
Means are significantly different (P < .01). b Means are significantly different (P < .05). JOURNAL OF DAIRY SCIENCE V O L . . 5 6 ,
NO.
2
228
GRIEVE El" AL
apparently inefficiently utilized by the animal and largely excreted in urine. Difference in amount of urinary sulfur between sulfur treatments closely parallels difference in sulfur intake, both values being approximately 9 g. Though it has not been demonstrated that sttlfur was limiting in our experiment, nitrogen:sulfur ratios were wider than considered optim u m in unsupplemented diets. Consequently, we agree with Jacobson et al. (13) in concluding that supplemental sulfur from anhydrous sodium sulfate was inefficiently utilized by animals and it had no effect on nitrogen utilization.
(8) (9)
(10)
(11) Acknowledgments The authors express appreciation to Dr. W. I-I. Allaway and Mr. V. Lazar, U. S. Plant, Soil and Nutrition Laboratory, Ithaca, New York, for assistance in sulfur determinations and to Messrs. L. Bernholz and T. Kuntz for their technical assistance.
12 )
13)
References (1) A.O.A.C. 1965. Official Methods of Analysis, 10th ed. Association of Official Agricultural Chemists. Washington, D.C. (2) Barton, J. S., L. S. Bull, and R. W. Hemken. 1971. Effects of various levels of sulfur upon cellulose digestion in purified diets and lignocellulose digestion in corn fodder pellets in vitro. J. Anita. Sei., 33:682. (3) Bray, A. C., and J. A. Hemsley. 1969. Sulfur metabolism of sheep. IV. The effect of varied dietary sulfur content on some body fluid sulfate levels and on the utilization of urea supplemented roughage by sheep. Australian J. Agr. Res., 20:759. (4) Burgess, P. L., and J. W. G. Nicbolson. 1971. Effect of sulfur supplementation on the performance of lactating dairy cows fed urea-containing diets. Can. J. Anita. Sci., 51:711. (5) Conrad, H. R., and J. W. Hibbs. I961. Urea treatment affects utilization of corn silage. Ohio Farm and Home Res., 46:13. (6) Coppoek, C. E., and J. B. Stone. 1968. Corn silage in the ration of dairy cattle. A review. Cornell Misc. Bull., 89. (7) Da]rymple, J. M. 1969. Adaptation to urea by the lactating cow. M. So. Thesis, Uni-
JOURNAL OF DAIRY SCIENCE VOL. 56, NO. 2
14)
(15)
(16)
(17)
(is)
(19)
versity of Guelph, Guelph, Ontario, Canada. Federer, W. T. 1967. Experimental Design, Theory and Application. Oxford and IBH t~ublishing Co., Calcutta. Grieve, D. G., C. E. Coppock, W. G. Merrill, and H. F. Tyrrell. 1973. Sulfur supplementation of urea-containing sflages and concentrates. I. Feed intake and lactation performance. J. Dairy Sci., 56:218. Holter, J. B., N. F. Colovos, H. A. Davis, and W. E. Urban, Jr. 1968. Urea for lactating dairy cattle. III. Nutritive value of rations of corn silage plus concentrate containing various levels of urea. J. Dairy Sci., 51:1243. Huber, J. T., R. A. Sandy, C. E. Polan, H. T. Bryant, and R. E. Blaser. 1967. Varying levels of urea for dairy cows fed corn silage as the only forage. J. Dairy Sei., 50:1241. Huber, J. T., and J. W. Thomas. 1969. Ureatreated corn silage in low protein rations for lactating cows. J. Dairy Sci., 52:944. ( Abstr. ) Jacobson, D. R., B. Soewardi, J. W. Barnett, R. H. Hatton, and S. B. Cart. 1969. Sulfur, nitrogen, and amino acid balance, and digestibility of low-sulfur and sulfur-supplemented diets fed to lactating cows. J. Dairy Sci., 52:472. Knott, F. N., C. E. Polan, and J. T. Huber. 1972. Further observations on utilization of ~area by lactating cows. J. Dairy Sci., 55: 466. Moir, tL J., M. Somers, and A. C. Bray. 1968. Utilization of dietary sulfur and nitrogen by ruminants. The Sulfur Inst. J., 3:15. Schmutz, W. G., L. D. Brown, and J. W. Thomas. 1969. Nutritive value of corn silages treated with chemical additives for lactation. J. Dairy Sci., 52:1408. Sherman, H. C. 1938. Chemistry of Food and Nutrition, 4th ed. The MacMillan Co., New York. Thomas, W. E., ]. K. Loosli, H. H. Williams, and L. A. Maynard. 1951. The utilization of inorganic sulfates and urea nitrogen by lambs. J. Nutrition, 43:515. Van Soest, P. J., and R. H. Wine. 1967. The use of detergents in the analysis of fibrous feeds. IV. Determination of plant cell wall constituents. J. Ass. Offlc. Anal. Chem., 50:50.
others (7, 11, 14). Lower nitrogen retention values were reported when urea was included in the corn silage portion of the ration (14) or in concentrates in some trials (10, 14) but not others (7, 11, 14). Factors which may influence utilization of urea include dietary nitrogen, amount of urea, digestible carbohydrate availability, and length of trial. An additional factor limiting urea utilization may be dietary sulfur. Using lambs fed purified diets containing urea, Thomas et al. (18) demonstrated improved growth, wool growth, and nitrogen and sulfur balances from supplemental sulfate sulfur. However, with practical diets containing urea, Jacobsen et al. (13) found supplemental sulfur to have no effect on nitrogen utilization. Our objectives were to determine effect of urea additions to corn silage and concentrate rations on ration digestibility and nitrogen utilization by dairy cows and to study effect of sulfur supplementation on urea nitrogen utilization.
Metabolism trials were conducted on 16 cows at three stages of lactation to evaluate effect of sulfur supplementation on utilization of urea in corn silage and concentrate portions of ration and on digestibility and nitrogen and sulfur balance. Treatments arranged in a 2 x 2 x 9. factorial consisted of: .5% urea-treated or 3.5% soybean meal-treated corn silage; 0 or .8~ urea-containing 18% crude protein concentrates; and 0 or .8% concentrate anhydrous sodittrn sulfate. Treatments did not affect digestibility of ration dry matter, cell walls, acid detergent fiber, or crude protein. Sulfur digestibility was improved by sulfur supplementation. Cows fed urea-treated corn silage had lower nitrogen balances ( - 14.0 vs. 4.2 grams per day) than cows fed soy-treated corn silage. Neither concentrate nitrogen source, sulfur supplementation, nor treatment interactions affected nitrogen utilization. Urea was better utilized when included in the concentrate rather than corn silage portion of the ration, and on a low sulfur ration sodium sulfate supplementation did not affect nitrogen utilization. Sulfur balances were not affected by treatments although absorbed sulfur and urinary sulfur were increased by sulfur supplementation.
Experimental Procedure
Introduction
Urea has provided an economical source of nitrogen in dairy cattle rations based on corn silage with little or no effect on milk yield when fed at moderate percents (.5% in corn silage and/or 1.0~ of concentrate) (9). However, concerning ration digestibility and nitrogen balances, reduction in dry matter digestibility was reported by one author (11) but not Received for publication August 18, 1972. 1Present address: Department of Animal and Poultry Science, University of Guelph, Guelph, Ontario, Canada.
A total of 44 7-day collections and balance trials were conducted on 16 Holstein cows at three stages of lactation, approximately 6, 20, and 34 wk postpartum. Treatments described under Experiment II (9) included silage nitrogen additive (.5% urea vs. 3.5% soybean meal), concentrate urea (0 vs..8%), and concentrate sulfur (0 vs..8~; sodium sulfate), all values as fed. Treatments were arranged in a 2 x 2 x 2 factorial and fed to cows for a complete lactation. There were 16, 15, and 13 collections at the three respective stages of lactation; fewer during second and third collection periods were due to removal of cows from trial as reported (9). Only animals in their second or later lactation (two per treatment combination) were used in metabolism studies. Feed offered was reduced to actual intake 1 wk before collection to minimize orts and maintain constant consumption throughout the collection. We processed and analyzed samples of feeds and orts as reported (9) and cell wall components (19). One percent aliquots of urine were collected for analysis of nitrogen
224
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SUPPLEMENT
TABLE 1. Analysis of variance model for metabolism trial data. Source
-- M E T A B O L I S M
20__5
TABLE 2. Least squares adjusted daily means by periods, metabolism trial data.
Degrees of freedom
Total Blocks Treatments Error A Periods Blocks x periods Treatment x periods Error B
43 1 7 7 2 2 14 10
Period Item
(1) and sulfur as described (9). Feces samples were processed similar to feed sampies. Milk nitrogen was determined by Kjeldahl procedures (1) and milk sulfur estimated from nitrogen by assuming its presence in proportion of 6.25?0 of nitrogen (17). Data were analyzed by least squares analysis of variance of a fixed model. Collection periods were included in analysis as a split plot in time after Federer (8) (Table 1). Interaction of blocks (age group) and treatments (Error A) was assumed to be true error and was used for testing significance of treatment differences while Error B was used to test significance of treatment period interactions. Results and Discussion
Ration Digestibility. Mean values for daffy dry matter intake, ration digestibility, and milk yield b y collection period (6, 20, and 34 wk postpartum for periods 1, 2, and 3) are in Table 2. Highest dry matter intake occurred during the second period and was significantly greater (P < .05) than during period 3. Digestibility of cell wall and acid detergent fiber fractions of dry matter were higher and crude protein digestibility lower during second and third periods than during the first (P < .05). Milk yield reflected stage of lactation. Since
1
Dry matter intake (kg) Digestibility (~) Dry matter Organie matter Cell walls Acid detergent fiber Crude protein Milk yield (kg)
2
3
14.8 "b 15.7 ~ 13.2 b 68.5 69.5 C39.7" 35.0" 68.2 ~ 28.7"
67.9 69.0 47.6 b 43.0 b 65.8 b 21.2 b
~67.1 68.5 47.P 45.4 b 64.2 b 10A"
~.b.c Means bearing the same superscript are not significantly different (P < .05).
no concentrate was fed during period 3, digestibility values represent corn silage only and agree with other reported values (6). Effect of treatments on ration digestibility across all periods is in Table 3. Neither silage or concentrate nitrogen treatments nor sulfur supplementation affected any measures of ration digestibility (P < .05), excepting digestibility of ration sulfur which was improved (P < .01) by adding supplemental sulfur. This agrees with Jaeobson et al. (13). While differences between silage nitrogen treatment on digestibility were nonsignificant, soy-treated corn silage tended to be more digestible in all components than urea-treated silage. There was a significant interaction with silage nitrogen source by period for apparent crude protein digestibility. Nature of this interaction is in Table 4. Nitrogen was more highly digested from soy-treated silage in period 2 but not in periods 1 or 3. Only the differences in sulfur digestibility between silages approached significance (.10 > P > .05). Sulfur
TABLE 3. Main effects of corn silage and concentrate nitrogen sources and sulfur supplementation on digestibility of total ration components. Silage
Concentrate
Item
Urea
Soy
Urea
Soy
Dry matter Organic matter Cell wall constituents Acid detergent fiber Crude protein Sulfur
66.8 68.0 43.4 38.0 65.8 49.0
68.9 70.4 46.3 44.3 66.4 53.6
67.4 68.5 43.4 40.3 66.0 51.6
68.3 69.5 46.3 41.9 66.2 52.0
Sulfur -67.8 69.1 44.9 40.8 66.6 45.4 ~
+ 67.8 68.9 44.7 41.4 65.6 57.2 ~
SE .40 .36 .72 .84 .34 .92
" Means are significantly different (P <.01 ). JOURNAL OF DAIRY SCIENCE VOL,
56, N O . 2
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G R I E V E E T AL
TABLE 4. Interaction between silage nitrogen source and periods for apparent digestibility of ration nitrogen.
TABLE 6. Interaction between silage nitrogen source and periods for urine nitrogen as a percent of absorbed nitrogen. Silage N additive
Silage N additive Period
Urea
Soy
Period
Urea
Soy %
1 2 3
68.4 ~ 63.6b 65.3 ab
1 2 3
68.1" 68.0" 63.2b
44.7 ~ 63.9 °a 71.80
49.3 ~b 57.3 '~bc 57.9b°
~'b Values bearing common superscripts are not significantly different (P < .05) according to hsd test.
~,b,c.dValues bearing common superscripts are not significantly different (P < .05).
supplementation did not affect fiber digestibility as found in vitro by Barton et al. (2) and in vivo with sheep by Bray and Hemsley (3). Dietary sulfur as a percent of ration dry matter in our study was increased from .11 to .18 by addition of anhydrous sodium sulfate having the same range as those values in earlier studies (2, 3). Nitrogen utilization. Data on utilization of nitrogen by main treatment effects are in Table 5. Cows fed soy-treated corn silage were in positive nitrogen balances while those fed urea-treated silage were in negative balance (P < .05). Although there were no reports of a similar comparison, decreased efficiency of nitrogen utilization by cows fed urea-treated corn silage compared to untreated silage has been reported by some (5, 14) but not others (7, 12). The difference in nitrogen balance in our study was not, however, associated with any difference in milk yield (9), nor was there a treatment difference in milk nitrogen as a percent of absorbed nitrogen (Table 5). There was significant interaction with silage nitrogen source by period for urinary nitrogen expressed as a percent of absorbed nitrogen (Table 6). As silage became a greater part of the ration
from periods 1 through 3, this value increased more rapidly for cows on urea-silage treatment than for those fed soy silage till the period 3 treatment difference was significant (P < .05). This supports the nitrogen balance data, indicating less efficient metabolic utilization of nitrogen from urea-treated silage. Concentrate nitrogen treatment did not significantly affect any measures of nitrogen utilization (P < .05). Cows fed urea-containing concentrate tended to retain more nitrogen which also agrees with results of Huber et al. (11). On the other hand, Holter et aI. (10) have reported decreased nitrogen retention by cows fed ureacontaining concentrates, and this observation is supported by Knott et al. (14) in one trial but not in a second. In our study there was no statistical evidence for interaction between silage and concentrate nitrogen source treatments on nitrogen utilization. Urea intakes and corresponding nitrogen balances for all nitrogen treatments by periods are in Table 7. A broad range of urea intakes (from 0 to 208 g per day) is shown, but there is no association with nitrogen balance data except all values for urea silage fed animals are negative and those for animals fed soy-treated silage are
TABLE 5. Main effects of corn silage and concentrate nitrogen sources and sulfur supplementation on mean daily nitrogen balance data. Silage Item Intake (g/24 hr) Feces (g/24 hr) Urine (g/24 hr) Milk (g/24 hr) Balance (g/24 hr) Urinary/absorbed (%) Milk/absorbed (%)
Urea 311.3 105.9 119.9 99.5 --14.060.1 47.7
Concentrate
Sulfur
Soy
Urea
Soy
--
+
324.3 108.1 116.4 96.2 4.2" 54.8 43.5
327.7 110.2 118.9 98.6 .1 56.1 44.3
307.9 103.8 117.4 97.1 --9.8 58.7 46.9
323.1 107.0 121.7 97.9 --3.0 58.1 44.5
312.5 107.0 114.6 97.8 --6.7 56.7 46.7
Means are significantly different (P < .05). JOURNAL OF DAIRY SCIENCE VOL. 56, NO. 2
$E 6.94 2.22 3.10 1.73 4.43 1.34 1.11
SULFUR SUPPLEMENT -
227
METABOLISM
TABLE 7. Mean daily intakes of urea and nitrogen balances by nitrogen treatment and period. Period Silage
Concentrate
1
2
3
Treatment means
Urea
Urea
I82 ( -- 10.0)
208 ( - 18.8)
194 (-7.3)
I95 ( - 12,1 )
Urea
Soy
64 (-- 1.0)
170 (--38.8)
197 (--8.0)
144 (--15.9)
Soy
Urea
121
( Soy
Soy
59
3.2)
(
0 (--13.7)
Period means
0
6.4)
0 (-- 5.6)
60
(27.3)
(12.2)
0 (7.8)
0 (-- 3.7)
92
109
98
100
(-- 5.4)
(--14.2)
(4.9,)
(-- 3.7)
predominantly positive. Thus, it appears that the effect of ensiling urea is more important than dietary urea in determining efficiency of urea nitrogen utilization by the animal. Urea was more effectively utilized when added to the concentrate portion of the ration at feeding time than adding it to chopped corn before ensiling. Sulfur supplementation with anhydrous sodium sulfate had no effect on measures of nitrogen utilization (Table 5), nor was there interaction between nitrogen source and sulfur. Amount and source of sulfur in these trials had no effect on utilization of urea nitrogen which agrees with other reports (4, 13). Though it has been suggested that dietary nitrogen to sulfur ratios should be in the range of 10:1 (15) for best utilization of nitrogen, decreasing nitrogen to sulfur ratio in our experiment from 21:1 to 13:1 over all periods and from 19:1 to 11:1 during period 1 had no effect on nitrogen utilization. Either sulfur was not first limiting
in the diet, or the source of supplemental sulfur was not well utilized as indicated by Jacobson et al. (13). Sul[ur balance data. Effects of treatments on sulfur balance data are in Table 8. In genoral, cows were in slight negative sulfur balance on all treatments and during all periods. Nitrogen sources had no effect on these data, except cows fed urea silage excreted more urinary sulfur (P < .01). Of primary interest are comparisons between unsupplemented and sulfur supplemented groups when treatment differences occurred for sulfur intake, urinary sulfur, milk sulfur as a percent of absorbed sulfur (P < .01), and urinary sulfur as a percent of absorbed sulhtr (P < .05). No differences occurred in fecal sulfur, milk sulfur, or sulfur balance. Supplemental sulfur was highly absorbed (79.6$) as found by Jacobson et al. (13), who reported 72.2~; absorption of supplemental sulfur. However, absorbed sulfur was
T~a3LE 8. Main effects of corn silage and concentrate nitrogen source and sulfur supplementation on mean daily sulfur balance data. Silage Item Intake (g/24 hr) Feces (g/24 hr) Urine (g/24 hr) Milk (g/24 hr) Balance (g/24 hr) Urinary/absorbed ($) Milk/absorbed ($)
Concentrate
Urea
Soy
18.96 8.88 7.60 ~ 6.26 -- 3.76 73.0 74.0
21.76 9.01 10.47 ~ 6.01 -- 3.70 78.1 60.1
Urea 20.55 9.32 8.82 6.17 -- 3.74 72.4 65.6
Soy 20.17 8.57 9.26 6.10 -- 3.73 78.7 68.4
Sulfur --
q-
16.00~ 8.60 4.45 ~ 6.14 -- 3.19 64.5b 85.2 a
24.73" 9.29 13.69.~ 6.12 - 4.28 86.6b 48.8 a
sE .61 .21 .36 .12 .41 2.80 3.90
Means are significantly different (P < .01). b Means are significantly different (P < .05). JOURNAL OF DAIRY SCIENCE V O L . . 5 6 ,
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apparently inefficiently utilized by the animal and largely excreted in urine. Difference in amount of urinary sulfur between sulfur treatments closely parallels difference in sulfur intake, both values being approximately 9 g. Though it has not been demonstrated that sttlfur was limiting in our experiment, nitrogen:sulfur ratios were wider than considered optim u m in unsupplemented diets. Consequently, we agree with Jacobson et al. (13) in concluding that supplemental sulfur from anhydrous sodium sulfate was inefficiently utilized by animals and it had no effect on nitrogen utilization.
(8) (9)
(10)
(11) Acknowledgments The authors express appreciation to Dr. W. I-I. Allaway and Mr. V. Lazar, U. S. Plant, Soil and Nutrition Laboratory, Ithaca, New York, for assistance in sulfur determinations and to Messrs. L. Bernholz and T. Kuntz for their technical assistance.
12 )
13)
References (1) A.O.A.C. 1965. Official Methods of Analysis, 10th ed. Association of Official Agricultural Chemists. Washington, D.C. (2) Barton, J. S., L. S. Bull, and R. W. Hemken. 1971. Effects of various levels of sulfur upon cellulose digestion in purified diets and lignocellulose digestion in corn fodder pellets in vitro. J. Anita. Sei., 33:682. (3) Bray, A. C., and J. A. Hemsley. 1969. Sulfur metabolism of sheep. IV. The effect of varied dietary sulfur content on some body fluid sulfate levels and on the utilization of urea supplemented roughage by sheep. Australian J. Agr. Res., 20:759. (4) Burgess, P. L., and J. W. G. Nicbolson. 1971. Effect of sulfur supplementation on the performance of lactating dairy cows fed urea-containing diets. Can. J. Anita. Sci., 51:711. (5) Conrad, H. R., and J. W. Hibbs. I961. Urea treatment affects utilization of corn silage. Ohio Farm and Home Res., 46:13. (6) Coppoek, C. E., and J. B. Stone. 1968. Corn silage in the ration of dairy cattle. A review. Cornell Misc. Bull., 89. (7) Da]rymple, J. M. 1969. Adaptation to urea by the lactating cow. M. So. Thesis, Uni-
JOURNAL OF DAIRY SCIENCE VOL. 56, NO. 2
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versity of Guelph, Guelph, Ontario, Canada. Federer, W. T. 1967. Experimental Design, Theory and Application. Oxford and IBH t~ublishing Co., Calcutta. Grieve, D. G., C. E. Coppock, W. G. Merrill, and H. F. Tyrrell. 1973. Sulfur supplementation of urea-containing sflages and concentrates. I. Feed intake and lactation performance. J. Dairy Sci., 56:218. Holter, J. B., N. F. Colovos, H. A. Davis, and W. E. Urban, Jr. 1968. Urea for lactating dairy cattle. III. Nutritive value of rations of corn silage plus concentrate containing various levels of urea. J. Dairy Sci., 51:1243. Huber, J. T., R. A. Sandy, C. E. Polan, H. T. Bryant, and R. E. Blaser. 1967. Varying levels of urea for dairy cows fed corn silage as the only forage. J. Dairy Sei., 50:1241. Huber, J. T., and J. W. Thomas. 1969. Ureatreated corn silage in low protein rations for lactating cows. J. Dairy Sci., 52:944. ( Abstr. ) Jacobson, D. R., B. Soewardi, J. W. Barnett, R. H. Hatton, and S. B. Cart. 1969. Sulfur, nitrogen, and amino acid balance, and digestibility of low-sulfur and sulfur-supplemented diets fed to lactating cows. J. Dairy Sci., 52:472. Knott, F. N., C. E. Polan, and J. T. Huber. 1972. Further observations on utilization of ~area by lactating cows. J. Dairy Sci., 55: 466. Moir, tL J., M. Somers, and A. C. Bray. 1968. Utilization of dietary sulfur and nitrogen by ruminants. The Sulfur Inst. J., 3:15. Schmutz, W. G., L. D. Brown, and J. W. Thomas. 1969. Nutritive value of corn silages treated with chemical additives for lactation. J. Dairy Sci., 52:1408. Sherman, H. C. 1938. Chemistry of Food and Nutrition, 4th ed. The MacMillan Co., New York. Thomas, W. E., ]. K. Loosli, H. H. Williams, and L. A. Maynard. 1951. The utilization of inorganic sulfates and urea nitrogen by lambs. J. Nutrition, 43:515. Van Soest, P. J., and R. H. Wine. 1967. The use of detergents in the analysis of fibrous feeds. IV. Determination of plant cell wall constituents. J. Ass. Offlc. Anal. Chem., 50:50.