Influence of D r y M a t t e r and N i t r o g e n Intakes on Fecal N i t r o g e n Losses in Cattle 1 O. T. STALLCUP, G. V. DAVIS, and L. SHIELDS Department of Animal Science University of Arkansas, Fayetteville 72701 ABSTRACT Dietary factors influencing loss of fecal nitrogen in Holstein steers have been examined in data on metabolism from forage diets. Two factors, total nitrogen and dry matter intake, accounted for a large part of the variation in fecal nitrogen. Nitrogen intake expressed as grams per kilogram dry matter intake more accurately accounted for variability in total fecal nitrogen than did nitrogen intake expressed as grams per animal per day. Data were from trials on 68 forages covering a range of nitrogen intakes and of nitrogen concentration in dry matter of forage. Correlations were .93 between total fecal nitrogen and dry matter intake, .90 between total fecal nitrogen and total nitrogen intake, and .95 between total fecal nitrogen and total fecal dry matter. However, at high and low nitrogen intake there was evidence of departure from a linear relationship. The relative usefulness of three regression analyses to estimate metabolic fecal nitrogen is discussed. I NTRODUCTION Fecal nitrogen (FN) represents an important loss of nitrogen (N) in cattle. The early work of Blaxter and Mitchell (2) suggests that the content of metabolic fecal nitrogen (MFN) in feces is high. In ruminants, MFN is complex due to the added influence of rumen microorganisms. Mason (8) concluded that 57 to 81% of the nondietary N was associated with bacterial material. Two methods have been proposed for calculating MFN. They are a direct approach measuring MFN output on nitrogen-free diets (3, 4, 15, 17, 21) and an indirect method based on extrapolation to zero of losses of FN
Received October 22, 1974. 1Published with the approval of the Director, Arkansas Agricultural Experiment Station.
from diets containing varying amounts of N (2, 14, 20). Titus (20) recommended that the latter method not be used due to lack of accuracy at low intake of N. Hutchinson (6) observed that two factors, intakes of total N and dry matter (DM), accounted for a large part of the variation in FN. He observed high correlations between total FN excreted and intake of DM in sheep. However, at high and low intake of total N, he found evidence of departure from a linear relationship due to positive effect of N. Kehar and Mukherjee (7) and Hironaka et al. (5) observed that FN was related more closely to excretion of fecal DM than to intake of DM. In experiments with steers, Titus (20) observed that excretion of MFN was related to intake of apparent digestible DM. Blaxter and Mitchell (2) reported that N in MFN is of endogenous origin and should be included in maintenance requirements of ruminants. This is true for animals on nitrogen-free rations. When animals are on rations containing N, microorganisms also obtain N from two other s o u r c e s : digested but unabsorbed dietary N and excess N which has been incorporated into urea in the liver and then recycled via saliva into the rumen or hind gut. As a result of these sources of N, the porportion of endogenous N in microbial residues and MFN excreted probably decreases as intake of dietary N increases (9). Mason (9) further observed that when roughage diets of medium to high quality were given to steers and adult sheep, excretion of nondietary FN was related positively to intake of truly digestible DM. No relationships were significant between nondietary FN and intake of either truly digestible N or truly digestible DM. The main objective of this study was to examine influences of intakes of DM and N of steers fed forage diets on output of FN. Further objectives were to estimate excretion of MFN from indirect methods based on extrapolation to zero of FN losses from varying intakes of N and to measure the relationship of FN to excretion of fecal DM.
1301
.= Fo
t~
TABLE 1. Intake o f forage and fecal concentration of nitrogen and dry m a t t e r and the nutritive value of forages used in nitrogen metabolism trials. Sudan and sorghum-sudan forage (6)
All forages (68) a
Crude protein in DM b (%) Nitrogen (g/kg DM) Dry matter intake (kg/day) Crude protein intake (g/day) Nitrogen intake (g/day) Dry matter in feces (kg/day) Nitrogen in feces (g/day) Crude protein in feces (g/100 g DM intake) T D N c in DM (%) Apparent dig d of crude protein (%) Dig energy in DM (k cal/kg)
CTotal digestible nutrients. dDigestible.
Cereal (8) silages
S o r g h u m (32) silages
Mean
SD
Mean
SD
Mean
SD
Mean
SD
Mean
SD
Mean
9.1 14.3 3.5 347.5 54.5 1.3 25.3
3.4 5.3 1.6 281.2 44.1 .7 14.5
10.9 17.1 4.8 525.7 82.4 1.4 28.0
3.2 5.0 .7 165.1 25.9 .4 6.7
11.7 18.4 5.4 712.2 111.6 2.4 45.3
4.7 7.4 2.4 536.2 84.0 1.3 26.0
7.8 12.2 3.4 259.5 40.7 1.2 23.9
1.8 2.8 1.3 105.7 16.6 .5 10.3
13.3 20.9 3.7 482.2 75.6 1.3 28.2
1.9 2.9 1.7 229.1 35.9 .7 11.7
7.5 11.8 2.7 213.2 33.4 1.1 19.0
2.1 3.4 .8 86.6 13.6 .3 6.5
4.5 45.6
.9 18.9
3.7 71.5
.5 4.6
5.1 56.5
1.1 5.0
4.4 66.6
.8 8.5
5.1 66.2
1.0 4.7
4.5 62.1
.9 7.2
63.5
7.7
64.0
9.4
54.6
11.0
39.7
19.3
61.3
5.5
38.2
18.7
2613
339
3025
229
aNumber in parenthesis indicates n u m b e r of forages in each group. bDry matter.
Corn (13) silages
Hays (9)
2382
240
2681
364
2814
329
2524
SD
284
.W
NITROGEN METABOLISM ON FORAGE EXPERIMENTAL PROCEDURES
Data on digestibility were from feeding 32 sorghum sitages, 13 corn silages, 9 hays, 8 cereal silages, and 6 lots of sundan and sorghum-sundan hybrid forage. Each forage was fed to three steers for a 14-day preliminary and a 7-day collection period. Data on intakes of N and DM and of amounts of N and DM in forages and feces are in Table 1. The steers were confined in metabolism stalls in a room at 21 C and 50% relative humidity. Animals in the various trials were growing Holstein steers that averaged 228.4 -+ 74.4 kg body weight. In view of the trends of influences of N intake reported (6), we decided to investigate separate effects of intakes of N and DM on losses of FN. The following statistical approach was adopted: 1) Relationships between intakes of N and DM and losses of FN were examined within four ranges of N intake (g/day) as in Table 2. 2) Relationships between the same three variables were analyzed within three ranges of intake of N when intake of N was expressed as g/kg of DM. 3) Linear partial regression analysis (16) was considered adequate. RESULTS A N D DISCUSSION
A preliminary analysis revealed high correlation coefficients between intake of DM and total FN (.93), between intake of N and total
1 303
FN (.90), and between FN and fecal DM (.95). Multiple correlation coefficients are in Table 2 for four quantities of total N intake. Variations in total FN were accounted for satisfactorily by intakes of total DM and N at two intakes (B and D) but less satisfactorily at an extremely low N intake (A) and within the approximate NRC requirement for N for maintenance (C). A comparison of the standard partial regression coefficients reveals the relative importance of N and DM in determining losses of FN. In group B, intake of DM was nearly 2.5 times and in group D, more than twice as important as intake of N. Both correlation coefficients were significant (Table 2). In groups A and C intake of DM was of primary importance. One of the factors influencing relative contributions of intakes of N and DM on FN may have been the wide variation in N and digestibilities of the forages at a given intake of N. Means, standard deviations, and ranges of crude protein (DM basis) of forages in each group were: (A) 5.7 +- 1.3, 3.8 to 7.4; (B) 8.4 -+ 2.5, 3.7 to 16.2; (C) 9.0 -+ 2.2, 6.6 to 14.3; (D) 12.7 i 3.3, 7.3 to 19.9. Within those intakes of N where the partial correlation for intake of N was not significant (A and C), there is a much narrower range in percent of crude protein (N X 6.38) than in those intakes associated with significant partial correlations (B and D). Full regression equations based on intake of N (g/day) were:
TABLE 2. Multiple correlation (R), standard measure coefficients (b t) and partial regression coefficients (b) of fecal nitrogen (Y) on dry matter intake (X 1) ; and nitrogen intake (X=) within selected ranges of nitrogen intake.
Group a
Nitrogen intake range (g/day)
No. of observations
R
A
12.3 - 25.4
11
.74
B
25.5 - 45.0
27
.90
C
45.1 - 65.0
14
.59
D
65.1 -- 237.2
16
.94
Independent variate
bt
b
tbN-3
X1 X2 X1 X~ Xa X: Xt X2
.8265 -.1766 .7803 .3145 .5921 -.2719 .6701 .3154
22.7477 -.5733 33.7596 2.5616 30.1801 -1.5917 51.6343 .6516
2.79 -.60 8.48**** 3.42*** 2.38** -1.09 4.34*** 2.04*
*P
Received October 22, 1974. 1Published with the approval of the Director, Arkansas Agricultural Experiment Station.
from diets containing varying amounts of N (2, 14, 20). Titus (20) recommended that the latter method not be used due to lack of accuracy at low intake of N. Hutchinson (6) observed that two factors, intakes of total N and dry matter (DM), accounted for a large part of the variation in FN. He observed high correlations between total FN excreted and intake of DM in sheep. However, at high and low intake of total N, he found evidence of departure from a linear relationship due to positive effect of N. Kehar and Mukherjee (7) and Hironaka et al. (5) observed that FN was related more closely to excretion of fecal DM than to intake of DM. In experiments with steers, Titus (20) observed that excretion of MFN was related to intake of apparent digestible DM. Blaxter and Mitchell (2) reported that N in MFN is of endogenous origin and should be included in maintenance requirements of ruminants. This is true for animals on nitrogen-free rations. When animals are on rations containing N, microorganisms also obtain N from two other s o u r c e s : digested but unabsorbed dietary N and excess N which has been incorporated into urea in the liver and then recycled via saliva into the rumen or hind gut. As a result of these sources of N, the porportion of endogenous N in microbial residues and MFN excreted probably decreases as intake of dietary N increases (9). Mason (9) further observed that when roughage diets of medium to high quality were given to steers and adult sheep, excretion of nondietary FN was related positively to intake of truly digestible DM. No relationships were significant between nondietary FN and intake of either truly digestible N or truly digestible DM. The main objective of this study was to examine influences of intakes of DM and N of steers fed forage diets on output of FN. Further objectives were to estimate excretion of MFN from indirect methods based on extrapolation to zero of FN losses from varying intakes of N and to measure the relationship of FN to excretion of fecal DM.
1301
.= Fo
t~
TABLE 1. Intake o f forage and fecal concentration of nitrogen and dry m a t t e r and the nutritive value of forages used in nitrogen metabolism trials. Sudan and sorghum-sudan forage (6)
All forages (68) a
Crude protein in DM b (%) Nitrogen (g/kg DM) Dry matter intake (kg/day) Crude protein intake (g/day) Nitrogen intake (g/day) Dry matter in feces (kg/day) Nitrogen in feces (g/day) Crude protein in feces (g/100 g DM intake) T D N c in DM (%) Apparent dig d of crude protein (%) Dig energy in DM (k cal/kg)
CTotal digestible nutrients. dDigestible.
Cereal (8) silages
S o r g h u m (32) silages
Mean
SD
Mean
SD
Mean
SD
Mean
SD
Mean
SD
Mean
9.1 14.3 3.5 347.5 54.5 1.3 25.3
3.4 5.3 1.6 281.2 44.1 .7 14.5
10.9 17.1 4.8 525.7 82.4 1.4 28.0
3.2 5.0 .7 165.1 25.9 .4 6.7
11.7 18.4 5.4 712.2 111.6 2.4 45.3
4.7 7.4 2.4 536.2 84.0 1.3 26.0
7.8 12.2 3.4 259.5 40.7 1.2 23.9
1.8 2.8 1.3 105.7 16.6 .5 10.3
13.3 20.9 3.7 482.2 75.6 1.3 28.2
1.9 2.9 1.7 229.1 35.9 .7 11.7
7.5 11.8 2.7 213.2 33.4 1.1 19.0
2.1 3.4 .8 86.6 13.6 .3 6.5
4.5 45.6
.9 18.9
3.7 71.5
.5 4.6
5.1 56.5
1.1 5.0
4.4 66.6
.8 8.5
5.1 66.2
1.0 4.7
4.5 62.1
.9 7.2
63.5
7.7
64.0
9.4
54.6
11.0
39.7
19.3
61.3
5.5
38.2
18.7
2613
339
3025
229
aNumber in parenthesis indicates n u m b e r of forages in each group. bDry matter.
Corn (13) silages
Hays (9)
2382
240
2681
364
2814
329
2524
SD
284
.W
NITROGEN METABOLISM ON FORAGE EXPERIMENTAL PROCEDURES
Data on digestibility were from feeding 32 sorghum sitages, 13 corn silages, 9 hays, 8 cereal silages, and 6 lots of sundan and sorghum-sundan hybrid forage. Each forage was fed to three steers for a 14-day preliminary and a 7-day collection period. Data on intakes of N and DM and of amounts of N and DM in forages and feces are in Table 1. The steers were confined in metabolism stalls in a room at 21 C and 50% relative humidity. Animals in the various trials were growing Holstein steers that averaged 228.4 -+ 74.4 kg body weight. In view of the trends of influences of N intake reported (6), we decided to investigate separate effects of intakes of N and DM on losses of FN. The following statistical approach was adopted: 1) Relationships between intakes of N and DM and losses of FN were examined within four ranges of N intake (g/day) as in Table 2. 2) Relationships between the same three variables were analyzed within three ranges of intake of N when intake of N was expressed as g/kg of DM. 3) Linear partial regression analysis (16) was considered adequate. RESULTS A N D DISCUSSION
A preliminary analysis revealed high correlation coefficients between intake of DM and total FN (.93), between intake of N and total
1 303
FN (.90), and between FN and fecal DM (.95). Multiple correlation coefficients are in Table 2 for four quantities of total N intake. Variations in total FN were accounted for satisfactorily by intakes of total DM and N at two intakes (B and D) but less satisfactorily at an extremely low N intake (A) and within the approximate NRC requirement for N for maintenance (C). A comparison of the standard partial regression coefficients reveals the relative importance of N and DM in determining losses of FN. In group B, intake of DM was nearly 2.5 times and in group D, more than twice as important as intake of N. Both correlation coefficients were significant (Table 2). In groups A and C intake of DM was of primary importance. One of the factors influencing relative contributions of intakes of N and DM on FN may have been the wide variation in N and digestibilities of the forages at a given intake of N. Means, standard deviations, and ranges of crude protein (DM basis) of forages in each group were: (A) 5.7 +- 1.3, 3.8 to 7.4; (B) 8.4 -+ 2.5, 3.7 to 16.2; (C) 9.0 -+ 2.2, 6.6 to 14.3; (D) 12.7 i 3.3, 7.3 to 19.9. Within those intakes of N where the partial correlation for intake of N was not significant (A and C), there is a much narrower range in percent of crude protein (N X 6.38) than in those intakes associated with significant partial correlations (B and D). Full regression equations based on intake of N (g/day) were:
TABLE 2. Multiple correlation (R), standard measure coefficients (b t) and partial regression coefficients (b) of fecal nitrogen (Y) on dry matter intake (X 1) ; and nitrogen intake (X=) within selected ranges of nitrogen intake.
Group a
Nitrogen intake range (g/day)
No. of observations
R
A
12.3 - 25.4
11
.74
B
25.5 - 45.0
27
.90
C
45.1 - 65.0
14
.59
D
65.1 -- 237.2
16
.94
Independent variate
bt
b
tbN-3
X1 X2 X1 X~ Xa X: Xt X2
.8265 -.1766 .7803 .3145 .5921 -.2719 .6701 .3154
22.7477 -.5733 33.7596 2.5616 30.1801 -1.5917 51.6343 .6516
2.79 -.60 8.48**** 3.42*** 2.38** -1.09 4.34*** 2.04*
*P
