Directory UMM :Data Elmu:jurnal:S:Small Ruminant Research:Vol35.Issue3.Jun2000:
Small Ruminant Research 35 (2000) 225±233
In¯uence of undegraded intake protein on intake, digestion, serum
hormones and metabolites, and nitrogen balance in sheep
K.C. Swansona, J.S. Catonb,*, D.A. Redmerb, V.I. Burkeb, L.P. Reynoldsb
a
b
Department of Animal Science, University of Kentucky, Lexington, KY 40546, USA
Department of Animal and Range Sciences, North Dakota State University, Fargo, ND 58105, USA
Accepted 30 June 1999
Abstract
In Exp. 1, 20 ewes of mixed breeding were fed grass hay : straw mixtures, assigned to one of four supplemental treatments
and evaluated during six collection periods. Supplemental treatments were control (no supplement), and low, medium, and
high levels (5.2%, 22.1%, and 41.3% of DM, respectively) of undegraded intake protein (UIP). Supplements were formulated
to be similar in degraded intake protein (DIP; 21%). Digestibilities of DM, OM, and CP were increased (P < 0.10) with protein
supplementation and in medium and high compared with low UIP supplemented ewes. Digestibility of CP also was increased
(P < 0.10) in ewes on high compared with medium treatments. Serum insulin was not in¯uenced (P > 0.10) by UIP treatment,
except in collection period four. In contrast, serum glucose and growth hormone were not in¯uenced (P > 0.10) by UIP
treatment. In Exp. 2, four wether lambs fed the same treatments as in Exp. 1, were used in two 4 4 Latin squares trials. In
trial 1 lambs received a grass hay diet (6.7% CP) and in trial 2 lambs were fed 40 : 60 blend (6.6% CP) of grass hay and spring
wheat straw. In both trials, N intake, urinary N, N digestion, apparent N absorption, and N retention were increased (P < 0.10)
with protein supplementation. In addition, in trial 1, urinary N, N digestion, and apparent N absorption were increased
(P < 0.10) in medium and high compared with low UIP and also in high compared with medium UIP treatments. In trial 2 of
Exp. 2, total feed intake (g/kg BW), digestibility of DM and OM, BW, and fecal N were increased (P < 0.10) with protein
supplementation. Organic matter digestion, BW, N intake, and N retention were increased by medium and high compared with
low UIP. Fecal N, BW, N intake, and N retention were increased (P < 0.10) in high compared with medium UIP. These data
indicate that increasing levels of UIP supplementation increases DM, OM, and CP (N) digestibility, serum urea N
concentration, and N retention in sheep fed low quality forage. # 2000 Elsevier Science B.V. All rights reserved.
Keywords: Sheep; Protein supplements; Intake; Nitrogen balance; Growth hormone; Insulin
1. Introduction
Supplemental CP often increases performance of
ruminants fed or grazing low quality (low CP) forages
*
Corresponding author. Tel.: 1-701-231-7653; fax: 1-701231-7590.
E-mail address: [email protected] (J.S. Caton).
(Owens et al., 1991). Research has shown that protein
supplementation can increase intake (Church and
Santos, 1981; Kartchner, 1981; McCollum and
Galyean, 1985) and (or) digestibility (Church and
Santos, 1981; Kartchner, 1981) of low-quality forage.
Egan (1965) showed that duodenally infused casein
increased intake of low quality forage indicating that
there may be regulators of intake which are indepen-
0921-4488/00/$ ± see front matter # 2000 Elsevier Science B.V. All rights reserved.
PII: S 0 9 2 1 - 4 4 8 8 ( 9 9 ) 0 0 0 9 1 - 7
226
K.C. Swanson et al. / Small Ruminant Research 35 (2000) 225±233
dent of the rumen. These data led to the hypothesis that
undegraded intake protein (UIP) supplementation of
ruminants fed or grazing low quality forage may
increase performance. Von Keyserlingk and Mathison
(1993) reported an increase in DM digestibility in ®sh
meal and canola supplemented compared with nonsupplemented lambs fed barley straw. However, they
reported no difference in digestibility between ®sh
meal and canola meal supplemented treatment groups
and no differences in intake among all three treatment
groups. Donaldson et al. (1991) reported increases in
total and forage intake in steers grazing high quality
(CP 27.4±28.5%) winter annuals and receiving protein supplements with low or high amounts of UIP
protein compared with steers supplemented with corn.
In addition, work with increasing level of CP supplementation has resulted in higher intake, lower growth
hormone and higher insulin concentrations (Cheema
et al., 1991a,b). In the previous studies these results
could not be attributed to either DIP or UIP levels as
both increased with increasing supplemental CP level.
Therefore, our objectives were to evaluate the in¯uence of increasing levels of supplemental UIP, while
holding degraded intake protein (DIP) relatively constant, on intake, digestion, serum hormones and metabolites, and nitrogen balance in sheep fed low quality
forage.
2. Materials and methods
2.1. Experiment 1
20 mature ewes of mixed breeding (63 5.4 kg),
housed inside the small animal research center
(SARC) in individual pens, were offered low quality
forage ad libitum and subjected to six 7-day collection
periods following 14-day dietary adjustments. Mature,
cool season, grass hay : straw blends (chopped
15.2 cm) were used as forage with 100 : 0, 60 : 40,
and 40 : 60 grass hay:straw mixes for periods 1 and 2,
3 and 4, and 5 and 6, respectively (Table 1). Straw was
added to the forage base as periods advanced to ensure
a low quality forage and to keep total forage CP as low
as possible. Ewes were also assigned randomly to one
of four supplement treatments. Supplements were
control (no supplement), low, medium, and high
UIP (Table 2). Supplements, fed to provide 100%,
120%, and 140% of recommendations (NRC, 1985),
were formulated to be similar in DIP (21%) and
energy (1.77 Mcal NEm/kg). Supplements were fed
daily 08:30 hours at 119, 179, and 193 g/d (DM basis)
for periods 1 and 2 (100%, grass hay), 3 and 4 (60 : 40,
grass hay : straw), and 5 and 6 (40 : 60, grass hay : straw), respectively. Level of supplement offered
increased with each straw addition because forage
intake declined. Therefore, in order to maintain similar CP intakes across period, supplementation level
needed to be increased. Water was offered ad libitum.
During each collection period, BW were measured
on the ®rst and last day. Individual intakes were
recorded and diet samples were collected daily and
composited across days within period. Fecal grab
samples were taken at 08:00 hours and 16:00 hours
daily during each collection period. Diet and fecal
samples were dried and ground to pass a 2 mm screen
and fecal samples were composited within animal
across sampling day for each period. Diet and fecal
samples were analyzed for DM, ash, CP, and ADF by
standard procedures (AOAC, 1990). Analysis of NDF
was conducted by the method of Robertson and Van
Soest (1982). Digestibilities were estimated using acid
Table 1
Composition of forages fed to ewes (% of DM)
Item
100% hay
Ash
CP
DIPa
UIPa
NDF
ADF
a
60% hay, 40% straw
40% hay, 60% straw
Period 1
Period 2
Period 3
Period 4
Period 5
Period 6
9.4
6.7
3.9
2.8
75
45
7.8
6.7
3.6
3.1
73.1
44.0
9.9
6.7
3.6
3.1
77.3
49.0
11.6
7.1
4.1
3.0
76.8
48.1
9.8
6.6
3.3
3.3
80.8
53.4
9.1
6.5
3.2
3.3
83.1
53.9
Based on 16 h dacron bag degradabilities conducted in a fistulated cow.
K.C. Swanson et al. / Small Ruminant Research 35 (2000) 225±233
Table 2
Components and chemical composition of supplements fed to ewes
(% of DM)
Components
UIP treatment
Low
Medium
High
Wheat mids
Casein
Corn starch
Beet molasses
Fata
Dicalcium phosphate
Soybean meal
Corn gluten meal
Blood meal
70.0
13.0
9.0
5.0
1.0
2.0
±
±
±
40.3
±
±
5.0
±
2.0
30.0
7.6
15.1
21.0
±
±
5.0
±
3.3
15.0
18.7
37.0
Chemical composition
Ash
CP
DIPb
UIPb
NDF
ADF
7.0
25.6
20.4
5.2
28.3
8.5
6.1
42.9
20.8
22.1
23.9
8.0
5.8
62.4
21.1
41.3
22.4
5.0
a
Alifet USA, Cincinnati, OH.
Formulated to contain 21% DIP across supplements and to
have 5.3, 22.3, and 41.2% UIP for low, medium, and high UIP
treatments, respectively.
b
insoluble ash (Van Keulin and Young, 1977) and the
marker ratio technique (Merchen, 1988).
Bloods samples were collected via jugular venipuncture prior to feeding on the ®rst 3 days of each
collection period in serum separator tubes (Becton
Dickinson Vacutainer Systems, Rutherford, NJ),
allowed to clot for a minimum of 30 min, and centrifuged at 1560 g for 30 min. Serum was then
decanted and stored at ÿ208C until analyzed.
Blood serum (500 ml) was analyzed for growth
hormone (GH) using radioimmunoassay (RIA) as
previously described for cattle (Reynolds et al.,
1990). The GH assay utilized NIDDK-oGH-I-4 (biopotency 1.5 IU/mg) as the radioiodination preparation, USDA-bGH-B-1 (biopotency 1.9 IU/mg) as
the reference standard, NIDDK-oGH-2 as the primary
antiserum, and sheep anti-rabbit gamma globulin as
the secondary antiserum (Swanson, 1996). All samples were run in a single assay, and intra-assay variation was determined by assaying replicates (n 6) of
a pool of lamb plasma in the same assay. The resulting
mean SE concentration of GH in the lamb plasma
pool was 1.02 0.09 ng/ml. To further validate the
227
GH assay, a pool of lamb plasma was assayed at
sample volumes of 200, 300, 400, 500, 600, and
700 ml, which yielded an inhibition curve that was
parallel to that of the reference standard.
Blood serum was analyzed for insulin concentrations using a commercially available RIA procedure
(Coat-A-Count, Diagnostic products corporation, Los
Angeles, CA) and procedures similar to those by
Reynolds et al. (1990). A glucose oxidase kit (Procedure no. 510, Sigma diagnostics, St. Louis, MO) was
used to determine serum glucose levels. Serum urea
nitrogen was measured using a urea nitrogen kit
(Procedure no. 640, Sigma diagnostics, St. Louis,
MO). We have reported similar procedures for measuring glucose and urea nitrogen in serum of cattle
(Reynolds et al., 1985, 1990).
Data were analyzed with the GLM procedures of
SAS (1988) and were subjected to repeated measures
analysis (Gill and Hafs, 1971). The model for analysis
of BW, intake, digestibility, and serum hormones and
metabolites included effects of treatment, sampling
period, animal within treatment, and sampling period
by treatment interactions with animal within treatment
being used as the error term for treatment effects. A
sampling period treatment interaction (P < 0.10)
was present for serum insulin concentrations; therefore, these data were analyzed for treatment effects
within each sampling period. Serum urea nitrogen and
BW also showed a signi®cant sampling period treatment interaction (P < 0.10); however, the interaction
appeared to be due to differences in magnitude
between treatment groups; therefore, treatment effects
on urea nitrogen and BW data are reported across
periods.
When signi®cant F-tests were observed (P < 0.10),
means were compared using contrast statements.
Treatment contrasts were control vs. protein (low,
medium, and high UIP), low UIP vs. medium and
high UIP, and medium UIP vs. high UIP.
2.2. Experiment 2
Two trials were conducted to determine the in¯uence of increasing supplemental UIP on digestibility
and nitrogen balance. Four wether lambs (62.2
2.4 kg) were housed in metabolism crates at SARC
and were fed the same supplemental treatments as
described above in a 4 4 Latin square design. Lambs
228
K.C. Swanson et al. / Small Ruminant Research 35 (2000) 225±233
were offered 100 : 0 and 40 : 60 grass hay : straw
blends in trials 1 and 2, respectively. Wethers were
allowed a 10-day period to adapt to the feed and
metabolism crates prior to each collection period.
Forage and supplement were offered at 07:00 hours
daily, with additional forage offered at 16:00 hours.
Forage and water consumption were measured daily
and feces and urine were collected on days 10±17 of
each period. Diet, feces, and urine samples were
analyzed for DM, ash, total N, and ADF by standard
procedures (AOAC, 1990). Analysis of NDF was
conducted by the method of Robertson and Van Soest
(1982).
Data were analyzed as 4 4 Latin square using the
GLM procedure of SAS (1988). The model included
effects of animal, period, and treatment. When signi®cant F-tests (P < 0.10) were observed means were
compared using contrast statements. The contrast
statements used were the same as those used in
Exp. 1.
3. Results and discussion
3.1. Experiment 1
Body weight of ewes was not affected (P > 0.10) by
treatment (data not shown). Forage and total intake
also were not in¯uenced (P > 0.10) by treatment
(Table 3). Rittenhouse et al. (1970) and Branine
et al. (1985) reported no change in forage intake
due to protein supplementation. Other investigators
have shown an increase in low quality forage intake
as a result of protein supplementation (Church and
Santos, 1981; McCollum and Galyean, 1985; Krysl
et al., 1987; Cheema et al., 1991a).
Forage fed in this study averaged 6.7% CP which
may not have been low enough to result in an intake
response to supplemental CP. However, other investigations (Cheema et al., 1991a) with oat hay containing 6.25% CP yielded linear increases in forage intake
with increasing level of cotton seed meal supplementation. Alternatively, forage DIP present in our study
(average 3.7%; 49 g/head daily for control ewes) may
have been adequate for ruminal fermentation, resulting in no forage intake response from additional DIP
(low UIP) supplementation. If this were the case,
additional levels of UIP supplementation when DIP
was adequate failed to alter forage intake. This concept is supported by recent work with cows fed a 5.7%
CP cool season hay and supplemented with increasing
levels of UIP (Sletmoen-Olson et al., 1999a). In the
present study, increasing DIP levels by almost twofold
had no effect on forage intake.
Digestibility of ADF and NDF were not affected
(P > 10) by treatment (Table 3). In contrast, DM, OM,
and, CP apparent digestibility increased (P < 10) in
protein supplemented ewes compared with controls. In
Table 3
Influence of increasing levels of supplemental UIP on DM intake and digestibility in ewes fed low quality forage
Item
Intake
Forage, g
Total, g
Forage, g/kg BW
Total, g/kg BW
Digestibility,%
DMb,c
OMb,c
CPb,c,d
ADF
NDF
a
UIP treatment
Control
Low
Medium
High
SE
Pa
1319
1319
21.4
21.4
1266
1430
18.4
20.8
1225
1389
18.5
21.0
1239
1403
18.3
20.7
86
86
1.1
1.1
0.87
0.82
0.15
0.97
46.1
50.5
36.7
46.2
54.6
48.7
53.3
54.3
45.4
54.6
50.7
56.2
60.8
47.8
57.0
51.3
56.1
66.9
47.6
57.2
P equals observed significance for main effect of treatment.
Control vs. low, medium, and high (P < 0.10).
c
Low vs. medium and high (P < 0.10).
d
Medium vs. high (P < 0.10).
b
1.45
1.65
1.10
1.65
1.91
0.08
0.08
0.01
0.67
0.63
229
K.C. Swanson et al. / Small Ruminant Research 35 (2000) 225±233
Table 4
Influence of increasing levels of supplemental UIP on serum hormones and metabolites in ewes fed low quality forage
Item
Glucose, mg/dl
Urea N, mg/dlb,c,d
Growth Hormone, ng/ml
UIP treatment
Control
Low
Medium
High
SE
Pa
58.4
11.1
3.23
56.4
14.3
2.41
57.3
18.4
2.97
58.8
21.2
2.55
1.19
1.12
.58
0.50
0.01
0.73
a
P equals observed significance for main effect of treatment.
Control vs. low, medium, and high (P < 0.10).
c
Low vs. medium and high (P < 0.10).
d
Medium vs. high (P < 0.10).
b
addition, digestibility of DM, OM, and CP were
increased (P < 10) in ewes supplemented with medium and high levels compared with low levels of UIP.
An increase (P < 10) in CP digestibility also was
observed in ewes supplemented with high compared
with medium UIP. In agreement with these observations, Church and Santos (1981), Kartchner (1981),
and Caton et al. (1988a) reported an increase in
digestibility in response to protein supplementation.
In the present study, increases in DM, OM, and CP
digestibility due to protein supplementation likely
resulted from the high digestibility of the supplement
provided.
Serum glucose and growth hormone concentrations
were not in¯uenced (P > 0.10) by treatment (Table 4).
Other investigators have also shown no effect due to
protein supplementation on blood glucose in ruminants (Krysl et al., 1987; Cheema et al., 1991b;
Shetaewi and Ross, 1991; Caton et al., 1994). Recent
work (Sletmoen-Olson et al., 1999b) has suggested
that plasma glucose concentrations in gestating beef
cows are increased by DIP based supplements (natural
sources) when compared with either non-supplemented controls or medium and high levels of UIP supplementation. Our data, in conjunction with others
suggests that, in non-pregnant, non-lactating ruminants, protein supplements usually do not effect serum
glucose levels. Serum growth hormone has been
shown to decrease (Krysl et al., 1987; Caton et al.,
1988b; Cheema et al., 1991b) or not change (Caton
et al., 1994; Sainz et al., 1994) with protein supplementation in ruminants. Sletmoen-Olson et al. (1999b)
has demonstrated that lactating cows have reduced
plasma growth hormone concentrations in response to
increasing UIP supplementation. Reasons for the lack
of response in serum growth hormone in the present
study are unclear, but may be related to basal forage
CP levels. In studies where growth hormone has
decreased with protein supplementation, it appears
that growth hormone may be responding to plane of
nutrition, resulting in lower growth hormone concentrations in ruminants on higher planes of nutrition.
Alternatively, other unde®ned mechanisms related to
source of supplemental protein may be present.
As expected, serum urea nitrogen increased
(P < 10) in protein supplemented vs. control ewes
(Table 4) which agree with previous reports by Caton
et al. (1988b, 1994), Cheema et al. (1991b), Sainz
et al. (1994) and Sletmoen-Olson et al. (1999b). Serum
urea nitrogen also was increased (P < 10) in ewes fed
medium and high UIP compared with those fed low
UIP and in those fed high UIP compared with medium
UIP, which agrees with the observations of Caton et al.
(1994) and Sletmoen-Olson et al. (1999b). These data
demonstrate that increasing supplemental UIP
increases serum urea nitrogen concentrations suggesting that at least a portion of the UIP is not only
absorbed but also catabolized.
Analysis of serum insulin resulted in a sampling
period treatment interaction (P < 0.10) so data are
presented by period (Table 5). Insulin was not affected
by treatment, except in period four, in which serum
insulin was increased (P < 0.10) in ewes fed high
compared with those fed medium UIP. Caton et al.
(1988b, 1994), Krysl et al. (1987), and Cheema et al.
(1991b) showed increases in serum insulin due to
protein supplementation of ruminants and others
(Caton et al., 1994; Sletmoen-Olson et al. (1999b))
demonstrated an increase in insulin in steers fed
increasing levels of UIP. These data are inconsistent
230
K.C. Swanson et al. / Small Ruminant Research 35 (2000) 225±233
Table 5
Influence of increasing levels of supplemental UIP on serum insulin concentrations (mu/ml) in ewes fed low quality forage
Period
1
2
3
4b
5
6
a
b
UIP treatment
Control
Low
Medium
High
SE
Pa
3.75
5.41
10.77
7.46
7.95
5.52
5.86
4.91
5.80
9.45
6.69
6.45
8.50
5.92
8.43
5.33
5.08
7.24
6.00
4.86
10.45
14.55
6.83
4.65
1.38
1.35
2.91
2.19
2.59
2.88
0.14
0.91
0.55
0.05
0.89
0.81
P equals observed significance for main effect of treatment.
Medium vs. high (P < 0.10).
with our current ®ndings, except for one sampling
period.
3.2. Experiment 2
In trial 1, water intake was increased (P < 0.10) in
protein supplemented wethers compared with controls
(Table 6). However, forage intake, total feed intake,
and apparent digestibility of DM, NDF, and ADF were
not in¯uenced (P > 0.10) by protein supplementation.
In contrast, digestibility of OM increased (P < 0.10) in
protein supplemented wethers compared with control
wethers (Table 6). In addition, total N intake, urinary
N, N digestion, N absorption, and N retention all were
increased (P < 0.10) in protein supplemented wethers
compared with control wethers (Table 7). In similar
studies evaluating CP levels, Cheema et al. (1991a)
also observed increased N intake, urinary N, N absorp-
tion, and N retention, and Caton et al. (1988a) showed
increased N intake, urinary N, and N retention in
response to protein supplementation. In the present
studies, urinary N, N digestion, and N absorption also
were increased (P < 0.10) in medium and high UIP
treatments compared with the low UIP treatment and
in high compared with medium treatments indicating
that the additional UIP protein was being metabolized.
Fecal N and BW were not in¯uenced (P > 0.10) by
protein supplementation in wethers fed grass hay
(Table 7).
In trial 2, water intake was unaltered in protein
supplemented wethers compared with controls (Table
8). When expressed as g/d or g/kg BW, forage intake
was not in¯uenced (P > 0.10) by treatment; however,
total intake was increased with protein supplementation. Digestibility of DM and OM also were increased
(P < 0.10) in protein supplemented wethers compared
Table 6
Influence of increasing levels of supplemental UIP on intake and digestibility in wethers fed grass hay (Trial 1)
Item
UIP treatment
Total water Intake, g/db
Total feed Intake, g/d
Forage intake, g/d
Total feed Intake, g/kg BW
Forage intake, g/kg BW
Digestibility
DM
OMb
NDF
ADF
a
b
Control
Low
Medium
High
SE
Pa
1733
1346
1346
20.9
20.9
2146
1494
1375
23.2
21.3
2100
1493
1373
23.3
21.4
2133
1511
1392
23.5
21.6
95.5
63.6
63.6
1.05
1.04
0.06
0.31
0.96
0.34
0.96
48.8
52.6
56.3
50.7
49.3
53.5
55.0
47.9
50.0
54.2
56.0
48.7
52.1
55.9
58.0
51.2
0.9
0.75
1.05
1.45
0.15
0.09
0.32
0.38
P equals observed significance for main effect of treatment.
Control vs. low, medium, and high (P < 0.10).
231
K.C. Swanson et al. / Small Ruminant Research 35 (2000) 225±233
Table 7
Influence of increasing levels of supplemental UIP on nitrogen retention in wethers fed grass hay (Trial 1)
Item
BW, kg
N Intake, g/db
Fecal N, g/d
Urinary N, g/db,c,d
N Digestion, %b,c,d
Apparent N Absorption, g/db,c,d
N Retention, g/db
UIP treatment
Control
Low
Medium
High
SE
Pa
64.4
16.2
8.9
5.2
45.0
7.2
2.0
64.4
21.3
10
7.6
53.2
11.4
3.8
64.2
24.8
10.4
10.0
58.1
14.4
4.4
64.5
28.6
10.6
12.6
62.9
18.0
5.3
0.28
0.75
0.46
0.33
0.95
0.38
0.54
0.89
0.01
0.14
0.01
0.01
0.01
0.02
a
P equals observed significance for main effect of treatment.
Control vs. low, medium, and high (P < 0.10).
c
Low vs. medium and high (P < 0.10).
d
Medium vs. high (P < 0.10).
b
with controls and OM digestibility was increased
(P < 0.10) in medium and high UIP treatments compared with the low UIP group. However, NDF and
ADF digestibility were not in¯uenced (P > 0.10) by
treatment. Body weight, N intake, fecal N, urinary N,
N digestion, N absorption, and N retention all were
increased (P < 0.10) in protein supplemented wethers
compared with control wethers (Table 9). Body
weight, N intake, urinary N, N digestion, N absorption, and N retention also were increased (P < 0.10) in
medium and high compared with the low UIP group,
and were increased (P < 0.10) in the high UIP compared with medium UIP treatment group. If anything,
the increasing levels of UIP in¯uenced nitrogen meta-
bolism to a greater extent in trial 2 than in trial 1,
perhaps because of the decreased forage quality in trial
2. This suggestion is supported by the negative N
balance of control wethers in trial 2 compared with the
positive N balance of controls in trial 1.
4. Conclusions
In summary, results indicate that protein supplementing sheep fed a 6.5±7.0% CP forage with increasing levels of UIP increases DM, OM, and CP
digestibility and serum urea N concentrations, but
does not affect forage intake, ADF and NDF digest-
Table 8
Influence of increasing levels of supplemental UIP on intake and digestibility in wethers fed 40 : 60 grass : hay straw blend (Trial 2)
Item
Total water Intake, g/d
Total feed Intake, g/db
Forage intake, g/d
Total feed Intake, g/kg BWb
Forage intake, g/kg BW
Digestibility
DMb
OMb,c
NDF
ADF
a
UIP treatment
Control
Low
Medium
High
SE
Pa
2013
851
851
14.2
14.2
2210
1037
844
17.3
14.0
2566
1000
807
16.5
13.4
2513
1055
862
16.9
13.8
173.6
42.3
42.3
0.65
0.65
0.18
0.05
0.81
0.05
0.83
46.4
50.5
53.6
46
51.4
55.7
54.0
44.0
53.4
57.5
55.2
45.9
52.2
57.4
55.0
43.8
0.67
0.48
1.04
0.90
0.01
0.01
0.66
0.26
P equals observed significance for main effect of treatment.
Control vs. low, medium, and high (P < 0.10).
c
Low vs. medium and high (P < 0.10).
b
232
K.C. Swanson et al. / Small Ruminant Research 35 (2000) 225±233
Table 9
Influence of increasing levels of supplemental UIP on nitrogen retention in wethers fed 40 : 60 grass hay : straw blend (Trial 2)
Item
BW, kgb,c,d
N Intake, g/db,c,d
Fecal N, g/db,d
Urinary N, g/db,c,d
N Digestion, %b,c
Apparent N Absorption, g/db,c,d
N Retention, g/db,c,d
UIP treatment
Control
Low
Medium
High
SE
Pa
60.0
8.6
5.3
4.8
38.5
3.4
ÿ1.5
60.2
16.5
6.4
8.9
61.0
10.1
1.1
60.6
21.4
6.2
12.8
70.8
15.2
2.4
62.7
28.1
7.1
17.3
74.8
21.0
3.7
0.50
0.45
0.21
0.30
1.48
0.26
0.33
0.03
0.01
0.01
0.01
0.01
0.01
0.01
a
P equals observed significance for main effect of treatment.
Control vs. low, medium, and high (P < 0.10).
c
Low vs. medium and high (P < 0.10).
d
Medium vs. high (P < 0.10).
b
ibilities, or serum growth hormone and glucose concentrations. Nitrogen digestibility, absorption, and
retention also are increased with protein supplementation. Increasing levels of UIP also appear to increase N
digestibility, absorption, and retention, especially
when lower quality forages are fed.
In conclusion, it appears that providing additional
UIP, while holding DIP constant can alter digestion
and nitrogen metabolism. Increases observed in nitrogen retention resulting from providing additional protein can be explained, at least in part, by increasing
UIP levels. Growth hormone and insulin concentrations in serum appear unresponsive when sheep consuming 6.5±7.0% CP cool season forages are
supplemented with DIP or increasing UIP level.
Acknowledgements
The authors appreciate Tim Johnson for animal
care, Ruth Weis for laboratory assistance and Julie
Berg for clerical assistance. This project was partially
supported by USDA special grant No. 92-34243-8312
and regional research funds NC-189.
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In¯uence of undegraded intake protein on intake, digestion, serum
hormones and metabolites, and nitrogen balance in sheep
K.C. Swansona, J.S. Catonb,*, D.A. Redmerb, V.I. Burkeb, L.P. Reynoldsb
a
b
Department of Animal Science, University of Kentucky, Lexington, KY 40546, USA
Department of Animal and Range Sciences, North Dakota State University, Fargo, ND 58105, USA
Accepted 30 June 1999
Abstract
In Exp. 1, 20 ewes of mixed breeding were fed grass hay : straw mixtures, assigned to one of four supplemental treatments
and evaluated during six collection periods. Supplemental treatments were control (no supplement), and low, medium, and
high levels (5.2%, 22.1%, and 41.3% of DM, respectively) of undegraded intake protein (UIP). Supplements were formulated
to be similar in degraded intake protein (DIP; 21%). Digestibilities of DM, OM, and CP were increased (P < 0.10) with protein
supplementation and in medium and high compared with low UIP supplemented ewes. Digestibility of CP also was increased
(P < 0.10) in ewes on high compared with medium treatments. Serum insulin was not in¯uenced (P > 0.10) by UIP treatment,
except in collection period four. In contrast, serum glucose and growth hormone were not in¯uenced (P > 0.10) by UIP
treatment. In Exp. 2, four wether lambs fed the same treatments as in Exp. 1, were used in two 4 4 Latin squares trials. In
trial 1 lambs received a grass hay diet (6.7% CP) and in trial 2 lambs were fed 40 : 60 blend (6.6% CP) of grass hay and spring
wheat straw. In both trials, N intake, urinary N, N digestion, apparent N absorption, and N retention were increased (P < 0.10)
with protein supplementation. In addition, in trial 1, urinary N, N digestion, and apparent N absorption were increased
(P < 0.10) in medium and high compared with low UIP and also in high compared with medium UIP treatments. In trial 2 of
Exp. 2, total feed intake (g/kg BW), digestibility of DM and OM, BW, and fecal N were increased (P < 0.10) with protein
supplementation. Organic matter digestion, BW, N intake, and N retention were increased by medium and high compared with
low UIP. Fecal N, BW, N intake, and N retention were increased (P < 0.10) in high compared with medium UIP. These data
indicate that increasing levels of UIP supplementation increases DM, OM, and CP (N) digestibility, serum urea N
concentration, and N retention in sheep fed low quality forage. # 2000 Elsevier Science B.V. All rights reserved.
Keywords: Sheep; Protein supplements; Intake; Nitrogen balance; Growth hormone; Insulin
1. Introduction
Supplemental CP often increases performance of
ruminants fed or grazing low quality (low CP) forages
*
Corresponding author. Tel.: 1-701-231-7653; fax: 1-701231-7590.
E-mail address: [email protected] (J.S. Caton).
(Owens et al., 1991). Research has shown that protein
supplementation can increase intake (Church and
Santos, 1981; Kartchner, 1981; McCollum and
Galyean, 1985) and (or) digestibility (Church and
Santos, 1981; Kartchner, 1981) of low-quality forage.
Egan (1965) showed that duodenally infused casein
increased intake of low quality forage indicating that
there may be regulators of intake which are indepen-
0921-4488/00/$ ± see front matter # 2000 Elsevier Science B.V. All rights reserved.
PII: S 0 9 2 1 - 4 4 8 8 ( 9 9 ) 0 0 0 9 1 - 7
226
K.C. Swanson et al. / Small Ruminant Research 35 (2000) 225±233
dent of the rumen. These data led to the hypothesis that
undegraded intake protein (UIP) supplementation of
ruminants fed or grazing low quality forage may
increase performance. Von Keyserlingk and Mathison
(1993) reported an increase in DM digestibility in ®sh
meal and canola supplemented compared with nonsupplemented lambs fed barley straw. However, they
reported no difference in digestibility between ®sh
meal and canola meal supplemented treatment groups
and no differences in intake among all three treatment
groups. Donaldson et al. (1991) reported increases in
total and forage intake in steers grazing high quality
(CP 27.4±28.5%) winter annuals and receiving protein supplements with low or high amounts of UIP
protein compared with steers supplemented with corn.
In addition, work with increasing level of CP supplementation has resulted in higher intake, lower growth
hormone and higher insulin concentrations (Cheema
et al., 1991a,b). In the previous studies these results
could not be attributed to either DIP or UIP levels as
both increased with increasing supplemental CP level.
Therefore, our objectives were to evaluate the in¯uence of increasing levels of supplemental UIP, while
holding degraded intake protein (DIP) relatively constant, on intake, digestion, serum hormones and metabolites, and nitrogen balance in sheep fed low quality
forage.
2. Materials and methods
2.1. Experiment 1
20 mature ewes of mixed breeding (63 5.4 kg),
housed inside the small animal research center
(SARC) in individual pens, were offered low quality
forage ad libitum and subjected to six 7-day collection
periods following 14-day dietary adjustments. Mature,
cool season, grass hay : straw blends (chopped
15.2 cm) were used as forage with 100 : 0, 60 : 40,
and 40 : 60 grass hay:straw mixes for periods 1 and 2,
3 and 4, and 5 and 6, respectively (Table 1). Straw was
added to the forage base as periods advanced to ensure
a low quality forage and to keep total forage CP as low
as possible. Ewes were also assigned randomly to one
of four supplement treatments. Supplements were
control (no supplement), low, medium, and high
UIP (Table 2). Supplements, fed to provide 100%,
120%, and 140% of recommendations (NRC, 1985),
were formulated to be similar in DIP (21%) and
energy (1.77 Mcal NEm/kg). Supplements were fed
daily 08:30 hours at 119, 179, and 193 g/d (DM basis)
for periods 1 and 2 (100%, grass hay), 3 and 4 (60 : 40,
grass hay : straw), and 5 and 6 (40 : 60, grass hay : straw), respectively. Level of supplement offered
increased with each straw addition because forage
intake declined. Therefore, in order to maintain similar CP intakes across period, supplementation level
needed to be increased. Water was offered ad libitum.
During each collection period, BW were measured
on the ®rst and last day. Individual intakes were
recorded and diet samples were collected daily and
composited across days within period. Fecal grab
samples were taken at 08:00 hours and 16:00 hours
daily during each collection period. Diet and fecal
samples were dried and ground to pass a 2 mm screen
and fecal samples were composited within animal
across sampling day for each period. Diet and fecal
samples were analyzed for DM, ash, CP, and ADF by
standard procedures (AOAC, 1990). Analysis of NDF
was conducted by the method of Robertson and Van
Soest (1982). Digestibilities were estimated using acid
Table 1
Composition of forages fed to ewes (% of DM)
Item
100% hay
Ash
CP
DIPa
UIPa
NDF
ADF
a
60% hay, 40% straw
40% hay, 60% straw
Period 1
Period 2
Period 3
Period 4
Period 5
Period 6
9.4
6.7
3.9
2.8
75
45
7.8
6.7
3.6
3.1
73.1
44.0
9.9
6.7
3.6
3.1
77.3
49.0
11.6
7.1
4.1
3.0
76.8
48.1
9.8
6.6
3.3
3.3
80.8
53.4
9.1
6.5
3.2
3.3
83.1
53.9
Based on 16 h dacron bag degradabilities conducted in a fistulated cow.
K.C. Swanson et al. / Small Ruminant Research 35 (2000) 225±233
Table 2
Components and chemical composition of supplements fed to ewes
(% of DM)
Components
UIP treatment
Low
Medium
High
Wheat mids
Casein
Corn starch
Beet molasses
Fata
Dicalcium phosphate
Soybean meal
Corn gluten meal
Blood meal
70.0
13.0
9.0
5.0
1.0
2.0
±
±
±
40.3
±
±
5.0
±
2.0
30.0
7.6
15.1
21.0
±
±
5.0
±
3.3
15.0
18.7
37.0
Chemical composition
Ash
CP
DIPb
UIPb
NDF
ADF
7.0
25.6
20.4
5.2
28.3
8.5
6.1
42.9
20.8
22.1
23.9
8.0
5.8
62.4
21.1
41.3
22.4
5.0
a
Alifet USA, Cincinnati, OH.
Formulated to contain 21% DIP across supplements and to
have 5.3, 22.3, and 41.2% UIP for low, medium, and high UIP
treatments, respectively.
b
insoluble ash (Van Keulin and Young, 1977) and the
marker ratio technique (Merchen, 1988).
Bloods samples were collected via jugular venipuncture prior to feeding on the ®rst 3 days of each
collection period in serum separator tubes (Becton
Dickinson Vacutainer Systems, Rutherford, NJ),
allowed to clot for a minimum of 30 min, and centrifuged at 1560 g for 30 min. Serum was then
decanted and stored at ÿ208C until analyzed.
Blood serum (500 ml) was analyzed for growth
hormone (GH) using radioimmunoassay (RIA) as
previously described for cattle (Reynolds et al.,
1990). The GH assay utilized NIDDK-oGH-I-4 (biopotency 1.5 IU/mg) as the radioiodination preparation, USDA-bGH-B-1 (biopotency 1.9 IU/mg) as
the reference standard, NIDDK-oGH-2 as the primary
antiserum, and sheep anti-rabbit gamma globulin as
the secondary antiserum (Swanson, 1996). All samples were run in a single assay, and intra-assay variation was determined by assaying replicates (n 6) of
a pool of lamb plasma in the same assay. The resulting
mean SE concentration of GH in the lamb plasma
pool was 1.02 0.09 ng/ml. To further validate the
227
GH assay, a pool of lamb plasma was assayed at
sample volumes of 200, 300, 400, 500, 600, and
700 ml, which yielded an inhibition curve that was
parallel to that of the reference standard.
Blood serum was analyzed for insulin concentrations using a commercially available RIA procedure
(Coat-A-Count, Diagnostic products corporation, Los
Angeles, CA) and procedures similar to those by
Reynolds et al. (1990). A glucose oxidase kit (Procedure no. 510, Sigma diagnostics, St. Louis, MO) was
used to determine serum glucose levels. Serum urea
nitrogen was measured using a urea nitrogen kit
(Procedure no. 640, Sigma diagnostics, St. Louis,
MO). We have reported similar procedures for measuring glucose and urea nitrogen in serum of cattle
(Reynolds et al., 1985, 1990).
Data were analyzed with the GLM procedures of
SAS (1988) and were subjected to repeated measures
analysis (Gill and Hafs, 1971). The model for analysis
of BW, intake, digestibility, and serum hormones and
metabolites included effects of treatment, sampling
period, animal within treatment, and sampling period
by treatment interactions with animal within treatment
being used as the error term for treatment effects. A
sampling period treatment interaction (P < 0.10)
was present for serum insulin concentrations; therefore, these data were analyzed for treatment effects
within each sampling period. Serum urea nitrogen and
BW also showed a signi®cant sampling period treatment interaction (P < 0.10); however, the interaction
appeared to be due to differences in magnitude
between treatment groups; therefore, treatment effects
on urea nitrogen and BW data are reported across
periods.
When signi®cant F-tests were observed (P < 0.10),
means were compared using contrast statements.
Treatment contrasts were control vs. protein (low,
medium, and high UIP), low UIP vs. medium and
high UIP, and medium UIP vs. high UIP.
2.2. Experiment 2
Two trials were conducted to determine the in¯uence of increasing supplemental UIP on digestibility
and nitrogen balance. Four wether lambs (62.2
2.4 kg) were housed in metabolism crates at SARC
and were fed the same supplemental treatments as
described above in a 4 4 Latin square design. Lambs
228
K.C. Swanson et al. / Small Ruminant Research 35 (2000) 225±233
were offered 100 : 0 and 40 : 60 grass hay : straw
blends in trials 1 and 2, respectively. Wethers were
allowed a 10-day period to adapt to the feed and
metabolism crates prior to each collection period.
Forage and supplement were offered at 07:00 hours
daily, with additional forage offered at 16:00 hours.
Forage and water consumption were measured daily
and feces and urine were collected on days 10±17 of
each period. Diet, feces, and urine samples were
analyzed for DM, ash, total N, and ADF by standard
procedures (AOAC, 1990). Analysis of NDF was
conducted by the method of Robertson and Van Soest
(1982).
Data were analyzed as 4 4 Latin square using the
GLM procedure of SAS (1988). The model included
effects of animal, period, and treatment. When signi®cant F-tests (P < 0.10) were observed means were
compared using contrast statements. The contrast
statements used were the same as those used in
Exp. 1.
3. Results and discussion
3.1. Experiment 1
Body weight of ewes was not affected (P > 0.10) by
treatment (data not shown). Forage and total intake
also were not in¯uenced (P > 0.10) by treatment
(Table 3). Rittenhouse et al. (1970) and Branine
et al. (1985) reported no change in forage intake
due to protein supplementation. Other investigators
have shown an increase in low quality forage intake
as a result of protein supplementation (Church and
Santos, 1981; McCollum and Galyean, 1985; Krysl
et al., 1987; Cheema et al., 1991a).
Forage fed in this study averaged 6.7% CP which
may not have been low enough to result in an intake
response to supplemental CP. However, other investigations (Cheema et al., 1991a) with oat hay containing 6.25% CP yielded linear increases in forage intake
with increasing level of cotton seed meal supplementation. Alternatively, forage DIP present in our study
(average 3.7%; 49 g/head daily for control ewes) may
have been adequate for ruminal fermentation, resulting in no forage intake response from additional DIP
(low UIP) supplementation. If this were the case,
additional levels of UIP supplementation when DIP
was adequate failed to alter forage intake. This concept is supported by recent work with cows fed a 5.7%
CP cool season hay and supplemented with increasing
levels of UIP (Sletmoen-Olson et al., 1999a). In the
present study, increasing DIP levels by almost twofold
had no effect on forage intake.
Digestibility of ADF and NDF were not affected
(P > 10) by treatment (Table 3). In contrast, DM, OM,
and, CP apparent digestibility increased (P < 10) in
protein supplemented ewes compared with controls. In
Table 3
Influence of increasing levels of supplemental UIP on DM intake and digestibility in ewes fed low quality forage
Item
Intake
Forage, g
Total, g
Forage, g/kg BW
Total, g/kg BW
Digestibility,%
DMb,c
OMb,c
CPb,c,d
ADF
NDF
a
UIP treatment
Control
Low
Medium
High
SE
Pa
1319
1319
21.4
21.4
1266
1430
18.4
20.8
1225
1389
18.5
21.0
1239
1403
18.3
20.7
86
86
1.1
1.1
0.87
0.82
0.15
0.97
46.1
50.5
36.7
46.2
54.6
48.7
53.3
54.3
45.4
54.6
50.7
56.2
60.8
47.8
57.0
51.3
56.1
66.9
47.6
57.2
P equals observed significance for main effect of treatment.
Control vs. low, medium, and high (P < 0.10).
c
Low vs. medium and high (P < 0.10).
d
Medium vs. high (P < 0.10).
b
1.45
1.65
1.10
1.65
1.91
0.08
0.08
0.01
0.67
0.63
229
K.C. Swanson et al. / Small Ruminant Research 35 (2000) 225±233
Table 4
Influence of increasing levels of supplemental UIP on serum hormones and metabolites in ewes fed low quality forage
Item
Glucose, mg/dl
Urea N, mg/dlb,c,d
Growth Hormone, ng/ml
UIP treatment
Control
Low
Medium
High
SE
Pa
58.4
11.1
3.23
56.4
14.3
2.41
57.3
18.4
2.97
58.8
21.2
2.55
1.19
1.12
.58
0.50
0.01
0.73
a
P equals observed significance for main effect of treatment.
Control vs. low, medium, and high (P < 0.10).
c
Low vs. medium and high (P < 0.10).
d
Medium vs. high (P < 0.10).
b
addition, digestibility of DM, OM, and CP were
increased (P < 10) in ewes supplemented with medium and high levels compared with low levels of UIP.
An increase (P < 10) in CP digestibility also was
observed in ewes supplemented with high compared
with medium UIP. In agreement with these observations, Church and Santos (1981), Kartchner (1981),
and Caton et al. (1988a) reported an increase in
digestibility in response to protein supplementation.
In the present study, increases in DM, OM, and CP
digestibility due to protein supplementation likely
resulted from the high digestibility of the supplement
provided.
Serum glucose and growth hormone concentrations
were not in¯uenced (P > 0.10) by treatment (Table 4).
Other investigators have also shown no effect due to
protein supplementation on blood glucose in ruminants (Krysl et al., 1987; Cheema et al., 1991b;
Shetaewi and Ross, 1991; Caton et al., 1994). Recent
work (Sletmoen-Olson et al., 1999b) has suggested
that plasma glucose concentrations in gestating beef
cows are increased by DIP based supplements (natural
sources) when compared with either non-supplemented controls or medium and high levels of UIP supplementation. Our data, in conjunction with others
suggests that, in non-pregnant, non-lactating ruminants, protein supplements usually do not effect serum
glucose levels. Serum growth hormone has been
shown to decrease (Krysl et al., 1987; Caton et al.,
1988b; Cheema et al., 1991b) or not change (Caton
et al., 1994; Sainz et al., 1994) with protein supplementation in ruminants. Sletmoen-Olson et al. (1999b)
has demonstrated that lactating cows have reduced
plasma growth hormone concentrations in response to
increasing UIP supplementation. Reasons for the lack
of response in serum growth hormone in the present
study are unclear, but may be related to basal forage
CP levels. In studies where growth hormone has
decreased with protein supplementation, it appears
that growth hormone may be responding to plane of
nutrition, resulting in lower growth hormone concentrations in ruminants on higher planes of nutrition.
Alternatively, other unde®ned mechanisms related to
source of supplemental protein may be present.
As expected, serum urea nitrogen increased
(P < 10) in protein supplemented vs. control ewes
(Table 4) which agree with previous reports by Caton
et al. (1988b, 1994), Cheema et al. (1991b), Sainz
et al. (1994) and Sletmoen-Olson et al. (1999b). Serum
urea nitrogen also was increased (P < 10) in ewes fed
medium and high UIP compared with those fed low
UIP and in those fed high UIP compared with medium
UIP, which agrees with the observations of Caton et al.
(1994) and Sletmoen-Olson et al. (1999b). These data
demonstrate that increasing supplemental UIP
increases serum urea nitrogen concentrations suggesting that at least a portion of the UIP is not only
absorbed but also catabolized.
Analysis of serum insulin resulted in a sampling
period treatment interaction (P < 0.10) so data are
presented by period (Table 5). Insulin was not affected
by treatment, except in period four, in which serum
insulin was increased (P < 0.10) in ewes fed high
compared with those fed medium UIP. Caton et al.
(1988b, 1994), Krysl et al. (1987), and Cheema et al.
(1991b) showed increases in serum insulin due to
protein supplementation of ruminants and others
(Caton et al., 1994; Sletmoen-Olson et al. (1999b))
demonstrated an increase in insulin in steers fed
increasing levels of UIP. These data are inconsistent
230
K.C. Swanson et al. / Small Ruminant Research 35 (2000) 225±233
Table 5
Influence of increasing levels of supplemental UIP on serum insulin concentrations (mu/ml) in ewes fed low quality forage
Period
1
2
3
4b
5
6
a
b
UIP treatment
Control
Low
Medium
High
SE
Pa
3.75
5.41
10.77
7.46
7.95
5.52
5.86
4.91
5.80
9.45
6.69
6.45
8.50
5.92
8.43
5.33
5.08
7.24
6.00
4.86
10.45
14.55
6.83
4.65
1.38
1.35
2.91
2.19
2.59
2.88
0.14
0.91
0.55
0.05
0.89
0.81
P equals observed significance for main effect of treatment.
Medium vs. high (P < 0.10).
with our current ®ndings, except for one sampling
period.
3.2. Experiment 2
In trial 1, water intake was increased (P < 0.10) in
protein supplemented wethers compared with controls
(Table 6). However, forage intake, total feed intake,
and apparent digestibility of DM, NDF, and ADF were
not in¯uenced (P > 0.10) by protein supplementation.
In contrast, digestibility of OM increased (P < 0.10) in
protein supplemented wethers compared with control
wethers (Table 6). In addition, total N intake, urinary
N, N digestion, N absorption, and N retention all were
increased (P < 0.10) in protein supplemented wethers
compared with control wethers (Table 7). In similar
studies evaluating CP levels, Cheema et al. (1991a)
also observed increased N intake, urinary N, N absorp-
tion, and N retention, and Caton et al. (1988a) showed
increased N intake, urinary N, and N retention in
response to protein supplementation. In the present
studies, urinary N, N digestion, and N absorption also
were increased (P < 0.10) in medium and high UIP
treatments compared with the low UIP treatment and
in high compared with medium treatments indicating
that the additional UIP protein was being metabolized.
Fecal N and BW were not in¯uenced (P > 0.10) by
protein supplementation in wethers fed grass hay
(Table 7).
In trial 2, water intake was unaltered in protein
supplemented wethers compared with controls (Table
8). When expressed as g/d or g/kg BW, forage intake
was not in¯uenced (P > 0.10) by treatment; however,
total intake was increased with protein supplementation. Digestibility of DM and OM also were increased
(P < 0.10) in protein supplemented wethers compared
Table 6
Influence of increasing levels of supplemental UIP on intake and digestibility in wethers fed grass hay (Trial 1)
Item
UIP treatment
Total water Intake, g/db
Total feed Intake, g/d
Forage intake, g/d
Total feed Intake, g/kg BW
Forage intake, g/kg BW
Digestibility
DM
OMb
NDF
ADF
a
b
Control
Low
Medium
High
SE
Pa
1733
1346
1346
20.9
20.9
2146
1494
1375
23.2
21.3
2100
1493
1373
23.3
21.4
2133
1511
1392
23.5
21.6
95.5
63.6
63.6
1.05
1.04
0.06
0.31
0.96
0.34
0.96
48.8
52.6
56.3
50.7
49.3
53.5
55.0
47.9
50.0
54.2
56.0
48.7
52.1
55.9
58.0
51.2
0.9
0.75
1.05
1.45
0.15
0.09
0.32
0.38
P equals observed significance for main effect of treatment.
Control vs. low, medium, and high (P < 0.10).
231
K.C. Swanson et al. / Small Ruminant Research 35 (2000) 225±233
Table 7
Influence of increasing levels of supplemental UIP on nitrogen retention in wethers fed grass hay (Trial 1)
Item
BW, kg
N Intake, g/db
Fecal N, g/d
Urinary N, g/db,c,d
N Digestion, %b,c,d
Apparent N Absorption, g/db,c,d
N Retention, g/db
UIP treatment
Control
Low
Medium
High
SE
Pa
64.4
16.2
8.9
5.2
45.0
7.2
2.0
64.4
21.3
10
7.6
53.2
11.4
3.8
64.2
24.8
10.4
10.0
58.1
14.4
4.4
64.5
28.6
10.6
12.6
62.9
18.0
5.3
0.28
0.75
0.46
0.33
0.95
0.38
0.54
0.89
0.01
0.14
0.01
0.01
0.01
0.02
a
P equals observed significance for main effect of treatment.
Control vs. low, medium, and high (P < 0.10).
c
Low vs. medium and high (P < 0.10).
d
Medium vs. high (P < 0.10).
b
with controls and OM digestibility was increased
(P < 0.10) in medium and high UIP treatments compared with the low UIP group. However, NDF and
ADF digestibility were not in¯uenced (P > 0.10) by
treatment. Body weight, N intake, fecal N, urinary N,
N digestion, N absorption, and N retention all were
increased (P < 0.10) in protein supplemented wethers
compared with control wethers (Table 9). Body
weight, N intake, urinary N, N digestion, N absorption, and N retention also were increased (P < 0.10) in
medium and high compared with the low UIP group,
and were increased (P < 0.10) in the high UIP compared with medium UIP treatment group. If anything,
the increasing levels of UIP in¯uenced nitrogen meta-
bolism to a greater extent in trial 2 than in trial 1,
perhaps because of the decreased forage quality in trial
2. This suggestion is supported by the negative N
balance of control wethers in trial 2 compared with the
positive N balance of controls in trial 1.
4. Conclusions
In summary, results indicate that protein supplementing sheep fed a 6.5±7.0% CP forage with increasing levels of UIP increases DM, OM, and CP
digestibility and serum urea N concentrations, but
does not affect forage intake, ADF and NDF digest-
Table 8
Influence of increasing levels of supplemental UIP on intake and digestibility in wethers fed 40 : 60 grass : hay straw blend (Trial 2)
Item
Total water Intake, g/d
Total feed Intake, g/db
Forage intake, g/d
Total feed Intake, g/kg BWb
Forage intake, g/kg BW
Digestibility
DMb
OMb,c
NDF
ADF
a
UIP treatment
Control
Low
Medium
High
SE
Pa
2013
851
851
14.2
14.2
2210
1037
844
17.3
14.0
2566
1000
807
16.5
13.4
2513
1055
862
16.9
13.8
173.6
42.3
42.3
0.65
0.65
0.18
0.05
0.81
0.05
0.83
46.4
50.5
53.6
46
51.4
55.7
54.0
44.0
53.4
57.5
55.2
45.9
52.2
57.4
55.0
43.8
0.67
0.48
1.04
0.90
0.01
0.01
0.66
0.26
P equals observed significance for main effect of treatment.
Control vs. low, medium, and high (P < 0.10).
c
Low vs. medium and high (P < 0.10).
b
232
K.C. Swanson et al. / Small Ruminant Research 35 (2000) 225±233
Table 9
Influence of increasing levels of supplemental UIP on nitrogen retention in wethers fed 40 : 60 grass hay : straw blend (Trial 2)
Item
BW, kgb,c,d
N Intake, g/db,c,d
Fecal N, g/db,d
Urinary N, g/db,c,d
N Digestion, %b,c
Apparent N Absorption, g/db,c,d
N Retention, g/db,c,d
UIP treatment
Control
Low
Medium
High
SE
Pa
60.0
8.6
5.3
4.8
38.5
3.4
ÿ1.5
60.2
16.5
6.4
8.9
61.0
10.1
1.1
60.6
21.4
6.2
12.8
70.8
15.2
2.4
62.7
28.1
7.1
17.3
74.8
21.0
3.7
0.50
0.45
0.21
0.30
1.48
0.26
0.33
0.03
0.01
0.01
0.01
0.01
0.01
0.01
a
P equals observed significance for main effect of treatment.
Control vs. low, medium, and high (P < 0.10).
c
Low vs. medium and high (P < 0.10).
d
Medium vs. high (P < 0.10).
b
ibilities, or serum growth hormone and glucose concentrations. Nitrogen digestibility, absorption, and
retention also are increased with protein supplementation. Increasing levels of UIP also appear to increase N
digestibility, absorption, and retention, especially
when lower quality forages are fed.
In conclusion, it appears that providing additional
UIP, while holding DIP constant can alter digestion
and nitrogen metabolism. Increases observed in nitrogen retention resulting from providing additional protein can be explained, at least in part, by increasing
UIP levels. Growth hormone and insulin concentrations in serum appear unresponsive when sheep consuming 6.5±7.0% CP cool season forages are
supplemented with DIP or increasing UIP level.
Acknowledgements
The authors appreciate Tim Johnson for animal
care, Ruth Weis for laboratory assistance and Julie
Berg for clerical assistance. This project was partially
supported by USDA special grant No. 92-34243-8312
and regional research funds NC-189.
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