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Net flux of nutrients across splanchnic tissues in wethers consuming bermudagrass or ryegrass—wheat hay supplemented with rumen undegradable protein
Small Ruminant Research ELSEVIER
Small Ruminant Research 25 (1997) 119-128
Net flux of nutrients across splanchnic tissues in wethers consuming bermudagrass or ryegrass-wheat hay supplemented with rumen undegradable protein A.L. Goetsch a,*, A.R. Patil b, Z.S. Wang b, K.K. Park b, D.L. Galloway, Sr b, J.E. Rossi b, B. Kouakou b a Dale Bumpers Smdl Furms Research Center. Agriculturnl Rrseorch Service, USDA, Booneuillr, AR 72927-9214, USA ’ Depurtment ofAnimal
Science, University of’Arkan.ws, Fuyettruille,
AR 72701, USA
Accepted 2 October 1996
Abstract Crossbred wethers (14, 37 + 1.5 kg BW and 10 months old) were used in a 21-day experiment (2 X 2 factorial) to determine effects of dietary grass source (tropical vs temperate) on response to rumen undegradable protein supplementation in oxygen consumption by, and net flux of N fractions across, the portal-drained viscera and liver. Bermudagrass (B; 73.1% NDF and 6.2% CP) or ryegrass-wheat (RW; 65.9% NDF and 8.9% CP) hay was supplemented with 53 g clay- ’ (DM) of soybean meal (S) or 53 g day-’ (DM) of soybean meal plus 70 g day -’ (DM) of a mixture of feedstuffs high in rumen undegradable protein (SR; 46.6% corn gluten, 26.7% feather and 26.7% blood meals). Digestible energy intake (9.1, 10.0, 11.3 and 12.1 MJ day-‘) was greater (P < 0.01) for RW than for B, and N intake was 12.5, 21.5, 16.5 and 25.3 g day-’ (SE 1.08) for B-S, B-SR, RW-S and RW-SR, respectively. Splanchnic energy use as a percentage of DE intake was less (P = 0.03) for RW vs B (21.4 vs 27.8%). Supplementation with SR increased (P = 0.04) alpha-amino N release by the portal-drained viscera (6.6, 22.0, 9.8 and 20.6 mmol h- ‘) and hepatic uptake (10.9, 25.6, It .2 and 14.3 mmol h- ’ for B-S, B-SR, RW-S and RW-SR, respectively; SE 2.29). Supplementation with SR increased (P < 0.01) hepatic urea N release (26.7, 48.4, 29.0 and 41.8 mmol hK’) and ammonia N uptake (17.3, 29.7, 23.3 and 26.6 mmol hK’ for B-S, B-SR, RW-S and RW-SR, respectively) more (interaction; P = 0.09 and 0.08, respectively) with B than with RW. In conclusion, these results indicate that DE intake and splanchnic energy consumption for tropical and temperate grasses may influence metabolic fate of rumen undegradable protein N and, thus, impact potential performance benefits of supplementation. Also, unless forage intake is changed, any improvements in animal performance with rumen undegradable protein supplementation would be through increased N absorption without change in energy available to peripheral tissues, regardless of grass source. 0 1997 Elsevier Science B.V. Keywords: Sheep; Metabolism; Rumen undegradable protein; Forage
1. Introduction
* Corresponding author. Tel.: 501/675-3834; fax: 501/6752940.
Digestible energy intake temperate than for tropical
00921.4488/97/$17.00 0 1997 Elscvier Science B.V. All rights reserved. PII SO921 -4488(96)0098 I-9
is usually grass diets
greater because
for of
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Ruminant Research 25 (1997) 119-128
greater digestibility and sometimes greater intake (Minson, 1990). Also, the proportion of DE attributable to splanchnic tissue energy use is greater for tropical than for temperate grasses (Patil et al., 1995a,b,c, 1996; Goetsch et al., 1997). Therefore, energy available to extra-splanchnic tissues can differ between tropical and temperate grasses more than expected based on DE intake. Redfearn et al. (1995) postulated that bundle sheath cells of tropical grasses slow ruminal microbial degradation of some protein, thereby increasing passage to the postruminal tract of intact protein compared with temperate grasses. Thus, it was suggested that relatively high escape of tropical grass protein from rumen microbial attack explains observations in some experiments of little or no response in ADG by ruminants consuming tropical grasses to supplementation with rumen undegradable protein sources (Blasi et al., 1991; Hafley et al., 1993). In addition to differences in ruminal degradation of protein among forage sources, it is possible that DE intake and splanchnic energy use with various forage sources, as influencing metabolic fate of N from rumen undegradable protein supplements, could impact ruminant performance. Therefore, objectives of this experiment were to determine effects of grass source on response to supplementation with rumen undegradable protein in oxygen consumption by, and net flux of N fractions across, the portal-drained viscera (PDV) and liver in wethers.
2. Materials
and methods
2.2. Diets Sheep consumed ad libitum (offered at 105 to 110% of consumption on the preceding few days) coarsely chopped bermudagrass ((B grass source treatment) Cynodon dactylon; vegetative growth stage) or ryegrass (Lolium multijlorum; post-anthesis) and wheat ((RW grass source treatment) Triticum aestiuum; post-anthesis) hay. In addition, sheep were fed soybean meal (S supplement treatment; 53 g day- ’ , DM) or soybean meal (53 g day- ’ ; DM) plus a mixture of rumen undegradable protein (RUP) sources ((SR supplement treatment) 70 g day-‘, DM; 46.6% corn gluten, 26.7% feather and 26.7% blood meals). Protein supplements were top-dressed on hay and completely consumed. Equal-sized meals were fed at 14:00, 22:00 and 06:OO h; at 14:00 h, sheep received 3.5 g day-’ of a mineral source mixture of 20% trace mineral premix (12% Zn, 10% Mn, 5% K, 2.5% Mg, 1.5% Cu, 0.3% I, 0.1% Co and 0.02% Se) and 80% NaCl. Three wethers were allotted to B-S and RW-SR treatments and four to B-SR and RW-S treatments. Of primary interest in this experiment were changes in net fluxes of N fractions in absolute quantities rather than relative to intake of different diet constituents (e.g. total N). Therefore, the same quantities of S and RUP sources were provided with both sources of grass. This was felt desirable compared with confounding from supplementing with different quantities of protein sources to achieve similar total N intake or dietary N concentration, which also would have necessitated daily changes in offered quantities of supplemental feedstuffs.
2.1. Animals
2.3. Sampling and analyses
Crossbred (Suffolk X Rambouillet-Dorset) wethers (14, 37 &- 1.5 kg BW, 10 months old) were surgically fitted with chronic indwelling catheters in a hepatic vein, the portal vein and a mesenteric vein and artery (Ferrell et al., 1992) 8 weeks before the experiment. Catheters were filled with heparinized (100 U ml-‘) saline (0.85%; w/v> solution at surgery. Sheep were individually maintained in 1.l X 1.5-m elevated pens with expanded metal flooring and had free access to water. Sheep were cared for in accordance with guidelines of Consortium (1988).
The experiment was 21 days in length. Feed was sampled daily on Days 11 through 21 to form a composite. Feces were collected in canvas bags on Days 14 through 17, and a composite sample was formed from 10% aliquots of daily excretion. Ruminal fluid was obtained by stomach tube on Day 16 at 09:OO h, strained through cheesecloth, acidified with 7.2 N H,SO,, frozen and later analyzed for VFA (Goetsch and Galyean, 1983) and ammonia N (AMN; Broderick and Kang, 1980). Metabolism crates were used to house sheep dur-
A.L. Gortsch et ul./Small Table 1 Composition
(DM basis) of feedstuffs
consumed
Item
Bermudagrass
Ash (%I CP (o/o) NDF (%) ADF (%) ADL (%) Cellulose (%) HemicelluIose (%)
6.1 6.2 73.1 37.0 4.8 29.5 36.0
hay
by wethers Ryegrass-wheat
hay
1.2 8.9 65.9 38.2 3.9 30.3 27.7
protein supplementation
Soybean meal
Rumen undegradable
7.1 49.0 9.5
4.5 66.1 8.7
para-aminohippuric through a sterile mesenteric vein infusion (0.8 ml was determined was obtained.
ing blood collections, with four sheep sampled daily (one per treatment) on Days 18, 19 and 20, and two were sampled on Day 21. Sheep were accustomed to metabolism crates because of prior exposure to these conditions and displayed normal intake and other activities while in crates. A priming dose (15 ml) of
Table 2 Effects of rumen undegradable
121
Ruminant Research 25 (1997) 119-128
on feed intake and digestion
protein mix
acid (22.5 g 1-l > was given 0.2-p,rn filter at 07:30 h into the catheter, followed by continuous min-‘) until 15:25 h. Body weight immediately after the last sample
by wethers consuming
bermudagrass
or ryegrass-wheat
hay Bermudagrass
Item
Ryegrass-wheat
SE
Effect a
Sb
SR ’
s
SR
841 53 895
860 123 983
869 53 922
865 123 988
79.9
839
925
856
920
74.3
54.7 459
54.0 501
68.0 581
68.4 622
2.27 44.9
G G
9.1
10.0
11.3
12.1
0.89
G
12.5
21.5
16.5
25.3
1.08
G, T
55.4
68.5
57.6
68.4
2.99
T
6.9
14.8
9.5
17.2
0.66
G. T
DM intuke (g day- ‘) Hay Supplement Total
79.9
OM Intake (g dayDigestion
’)
% g day-’ DE intake (MJ day - t) N
Intake (g dayDigestion
’)
% g day-’ NDF Intake (g dayDigestion % .g day-’
’)
620
639
578
581
53.8
53.8 333
49.9 320
69.9 403
68.5 393
2.62 33.8
G z
a Effect: Cl and g = grass source (bermudagrass vs ryegrass-wheat; P < 0.05 and 0.10, respectively); T = supplement treatment (S vs SR; P < 0.05). b S = 53 g day- ’ (DM) of soybean meal. ’ SR = 53 g day- ’ (DM) of soybean meal plus 70 g day- ’ (DM) of a mixture of rumen undegradable protein sources (46.6% corn gluten, 26.7% feather and 26.7% blood meals).
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Ruminant Research 25 (1997) 119-128
Blood was withdrawn starting at O&00, 09:00, lO:OO,ll:OO, 12:00, 13:00, 1400 and 15:OOh, with a IO-mm interval between sheep and representing an entire 8-h feeding interval. The treatment order for sampling differed among days. A I-ml sample was obtained anaerobically into a heparinized syringe and placed in ice. Oxygen saturation and hemoglobin concentration (OSM 2; Radiometer Corporation, Copenhagen, Denmark) were measured immediately; oxygen concentration was calculated as described by Eisemann and Nienaber (1990). Another sample was taken in a tube with potassium oxalate and sodium fluoride and placed in ice. On the day of sampling, a 1.5ml aliquot was diluted with deionized water (4.5 ml) and subjected to automated procedures for paraaminohippuric acid, alpha-amino nitrogen (AAN), urea nitrogen (UN) and AMN, as described by Eisemann and Nienaber (1990). Concentrations of paraaminohippuric acid, AAN, UN and AMN were averaged across time for calculation of blood flows and metabolite fluxes. Net metabolite fluxes were calculated based on venoarterial concentration differences and whole blood flows (Burrin et al., 1991), with some values being extrapolated from this 8-h feeding interval to a 24-h basis for comparison with daily feed intake. Park et al. (1997) utilized similar methodology with wethers consuming alfalfa, B or RW ad libitum, although hourly samples were com-
Table 3 Effects of rumen undegradable bermudagrass or ryegrass-wheat Item
protein hay
supplementation Bermudagrass Sb
Ammonia N (mmol I- ‘)
on ruminal
posites of three consecutive samples taken at 20-min intervals. Very similar temporal patterns in net fluxes across splanchnic tissues were observed for B and RW. Fecal composites were at dried 55°C and allowed to air-equilibrate. Hay and fecal samples were ground to pass a l-mm screen. Hay, supplement and fecal samples were analyzed for DM, ash, Kjeldahl N, energy (AOAC, 1984) and NDF (Goering and Van Soest, 1970; without sodium sulfite, decalin or ethoxyethanol). For supplement NDF analysis samples were ground to pass a 0.6-mm screen and treated with amylase (Chemey et al., 1989). Hay samples also were analyzed for ADF and ADL (Goering and Van Soest, 1970). Cellulose was estimated as loss in weight upon H2S0, treatment and hemicellulose as the difference between NDF and ADF. The average of feed intake on Day 12 through the day of blood sampling was used to calculate digestibilities. Data were analyzed by the general linear models procedure of SAS (1990), with a model consisting of grass source, rumen undegradable protein inclusion in the diet and their interaction. Portal-drained viscera and hepatic net fluxes were not estimated for two wethers (B-SR and RW-S treatments) because of non-patent portal vein catheters. Therefore, the number of observations was 14 for feed intake,
fluid ammonia
N and VFA concentrations
Ryegrass-wheat SR ’
in wethers
SE
S
SR
9.5
8.8
10.4
11.0
2.35
63 70.5 17.1 1.00 8.9
59 69.1 18.2 1.1 I 8.8 I .36 I .42 3.80
54 70.1 17.7 1.32 7.5 1.44
63 68.3 20.8 0.83 7.8 0.94 1.32 3.29
110.0
consuming
Effect a
VFA
Total (mmol I- ’ ) Acetate (mot per 100 mol) Propionate (mol per 100 mol) Isobutyrate (mol per 100 mol) Butyrate (mol per 100 mol) Isovalerate (mot per 100 mol) Valerate (mol per 100mol) Acetate:urouionate
1.23 1.16 4.19
a Effect: g = grass source (bermudagrass vs ryegrass-wheat; b S = 53 g day- ’ (DM) of soybean meal. ’ SR = 53 g day- ’ (DM) of soybean meal plus 70 g day26.7% feather and 26.7% blood meals).
1.82 4.02 P < 0.10); t = supplement
0.99 I .04 0.395 0.56 0.455 0.354 0.253
t g
t
treatment (S vs SR; P < 0.10).
’ (DM) of a mixture of rumen undegradable
protein sources (46.6% corn gluten,
A.L. Goetsch et al./Small Table 4 Effects of rumen undegradable protein supplementation in wethers consuming bermudagrass or ryegrass-wheat Item
Blood flow(1h- ‘) Portal vein Hepatic vein Hepatic artery
Ammonia N Whole blood concentration Portal vein Hepatic vein Artery Net flux (mmol hh’) Portal-drained viscera Hepatic Splanchnic
(mmol l-
3.33 2.16 4.57 114 99 213
N, urea N and ammonia
N measures
SE
Effect a
12.8 11.5 3.2
i
SR
89 118 29
89 108 19
3.24 2.76 4.65 135 145 269
3.43 2.76 4.69 120 106 228
3.68 2.96 5.00 114 102 216
0.250 0.266 0.242 14.8 16.2 24.7
’)
6.6 - 10.9
(mmol l-
112 142 28
S
123
’)
4.38 4.27 4.3 I
(mm01 l-
Ryegrass-wheat SR ’
93 119 26
oxygen Whole blood concentration (mmol lPortal vein Hepatic vein Artery Consumption (mmol h- ‘) Portal-drained viscera Hepatic Splanchnic
Urea N Whole blood concentration Portal vein Hepatic vein Artery Net flux (mmol h- ’ ) Portal-drained viscera Hepatic Splanchnic
on whole blood flow and oxygen, alpha-amino hay
Bermudagrass Sb
Alpha-amino N Whole blood concentration Portal vein Hepatic vein Artery Net flux (mm01 h- ’ ) Portal-drained viscera Hepatic Splanchnic
Ruminant Reseurch 25 (1997) 119-128
4.86 4.62 4.64
4.30 4.26 4.28
4.65 4.49 4.44
0.356 0.433 0.283
9.8 - 11.2 - 2.5
20.6 - 14.3 6.3
5.25 3.72 2.11
T T
- 4.2
22.0 - 25.6 - 2.3
5.4 5.7 5.7
Il.1 11.1 10.9
7.8 8.0 7.8
10.1 10.6 10.4
0.71 0.64 0.65
T, 1 T, i T, i
- 17.9 26.7 8.8
- 17.8 48.4 26.8
- 20.2 29.0 14.1
- 20.2 41.8 21.6
5.19 2.29 5.93
T, i t
C, T
’)
’) 0.660 0.466 0.474 16.4 - 17.3 -0.9
0.682 0.422 0.443 26.7 - 29.7 -3.1
0.675 0.470 0.496 20.7 -23.3 -3.0
0.746 0.445 0.460 25.0 - 26.6 - 1.7
0.0412 0.0384 0.0399 2.32 2.23 0.12
T T, i I
a Effect: G = grass source (bermudagrass vs ryegrass-wheat; P < 0.05); T and t = supplement treatment (S vs SR; P < 0.05 and 0.10, respectively); I and i = interaction between grass source and supplement treatment (P < 0.05 and 0.10, respectively). b S = 53 g day- ’ (DM) of soybean meal. ’ SR = 53 g day- ’ (DM) of soybean meal plus 70 g day- ’ (DM) of a mixture of mmen undegradable protein sources (46.6% corn gluten, 26.7% feather and 26.7% blood meals).
124
A.L. Goetsch et al./Smail
Ruminant Research 25 (1997) 119-128
digestibility, ruminal fluid concentrations of VFA and AMN, metabolite concentrations in arterial and hepatic venous blood and splanchnic net fluxes; 12 observations (three per treatment) were derived for portal venous blood concentrations of metabolites and PDV and hepatic net fluxes.
3. Results Bermudagrass hay was slightly lower than RW in CP concentration (Table 1). As typical with tropical and temperate grasses (Minson, 1990), B was higher than RW in concentrations of NDF, ADL and hemicellulose. Total DM and OM intakes were similar (P > 0.10) between grass sources and supplement treatments (Table 2). Supplement comprised 6.0, 12.7, 5.9 and 12.9% of DM intake, and 33.5, 60.6, 25.7 and 52.1% of nitrogen intake, for B-S, B-SR, RW-S and RW-SR, respectively. Digestible OM (P = 0.02) and DE (P = 0.03) intakes were greater for RW than for B because of greater (P < 0.01) OM and NDF digestibilities. The differences between B and RW in digestibilities of OM and NDF appear somewhat greater than implicated by concentrations of NDF and ADL, perhaps reflecting an impact of different proportions and unique arrangements of specific plant tissues on microbial fiber degradation (Wilson, 1993). Digestible N intake was greater (P < 0.01) for RW than for B because of greater N intake (P < O.Ol), although digestible N intake was greater for SR than for S as a result of both greater (P < 0.01) N intake and digestibility. Differences in digestible N intake between supplement treatments suggest nearly complete (i.e. 94%) total tract digestibility of protein in RUP sources added to the diet. Ruminal AMN concentration was similar (P > 0.10) among treatments (Table 3). The concentration of total VFA in ruminal fluid did not differ among treatments (P > 0.10). The molar proportion of acetate was not affected by treatment (P > O.lO), although that of propionate was greater (P = 0.07) for SR than for S diets. Likewise, the acetate to propionate ratio was less (P = 0.05) for SR than for S. Portal and hepatic venous blood flows were similar (P > 0.10) among treatments (Table 4). Hepatic arterial blood flow was affected (P = 0.09) by an
interaction between grass source and supplement treatment. Whole blood oxygen concentrations and net fluxes were not altered (P > 0.10) by treatment. Concentrations of AAN in whole blood were similar among treatments (P > 0.10; Table 4). Splanchnic net flux of AAN was greater (P = 0.03) for RW than for B, although net fluxes across the PDV and liver did not differ with forage source (P > 0.10). Supplementation with SR increased (P = 0.04) PDV release of AAN slightly more than it increased (P = 0.04) hepatic uptake. Thus, net flux of AAN across the splanchnic bed was greater (P = 0.03) for SR than for S diets. Assuming that the difference between S and SR diets in PDV AAN release was attributable to RUP sources, 59.5% of N in RUP sources reached the liver as AAN. Interactions between grass source and supplement treatment occurred in UN concentration in portal (P = 0.06), hepatic venous (P = 0.05) and arterial blood (P = 0.06). Uptake of UN by the PDV was similar among treatments (P > 0.101, although splanchnic release was greater (P = 0.06) for SR than for S. Grass source and supplement treatment interacted (P = 0.09) in hepatic UN release. Whole blood AMN concentrations were not altered (P > 0.10) by treatments (Table 4). Portaldrained viscera release of AMN was greater (P = 0.01) for SR than for S. Grass source and supplement treatment interacted in hepatic uptake (P = 0.08) and splanchnic net flux AMN (P = 0.03).
4. Discussion Assuming 0.46 MJ of heat per mol of oxygen consumed by splanchnic tissues (McLean, 1972), the difference between DE intake and splanchnic bed energy use was greater (P = 0.02) for RW than for B (9.3 vs 6.9 MJ day-‘; SE 0.61). The lack of difference between B and RW diets in total VFA and acetate and propionate concentrations suggest similar methane production. Therefore, it seems reasonable to assume that the difference between splanchnic energy use and DE intake related closely to energy metabolizable by extra-splanchnic tissues. As a proportion of DE intake, heat production was greater for B than for RW in the liver (P = 0.07; 13.5 vs 10.4%, SE 1.07) and splanchnic bed (P = 0.03; 27.8
A.L.
Goetsch
et ul./Smull
Ruminant
vs 21.4%, SE 1.841, although that for the PDV did not significantly differ between grass sources ((P = 0.20) 14.0 and 11.6% for B and RW, respectively; SE 1.19). Similar to results in the present experiment, Goetsch et al. (1994) did not alter the ratio of splanchnic energy consumption to DE intake by including a similar mixture of RUP sources in a bromegrass hay diet consumed by wethers. Thus, it appears that any increase in splanchnic energy consumption due to RUP addition to low- or moderatequality grasses is non-existent or small. Causal factors of, or physiological processes associated with, greater splanchnic energy use relative to DE intake for tropical vs temperate grass diets do not appear affected by increases in absorption, PDV release or hepatic uptake of amino acids elicited by dietary RUP addition. Examples of RUP concentrations in RUP sources used are 8 1, 65 and 82% for feather, corn gluten and blood meals, respectively (NRC, 1985a; Preston, 1987; Waltz et al., 1989). Barrio et al. (1986) noted similar in situ N disappearance for feather and corn gluten meals between ruminal incubation periods 12 and 24 h in length. Duff et al. (1995) observed slightly greater in situ N disappearance at 24 vs 12 h of ruminal incubation for feather and blood meals (37 vs 26% and 25 vs 15%, respectively) but similar values for corn gluten meal (25 and 28% at 12 and 24 h, respectively). Thus, with similar intake of grass sources in the present experiment, substantial effects of ruminal digesta retention time on extent of ruminal protein degradation are unlikely. The increase in PDV AMN release with RUP supplementation does not agree with the similar ruminal AMN concentration among treatments. However, only one sample of ruminal fluid was obtained at 3 h post-feeding. The increase in PDV AMN release averaged 33% of added RUP source N. This value, and the estimate of 59.5% of N in RUP sources accounted for by the increase in PDV AAN release with RUP addition, seem in accordance with expected ruminal degradability of the RUP source mixture and the assumption that some amino acids were metabolized by PDV tissues or released in peptides. Based on requirements of NRC (1985b) for medium mature weight lambs, these wethers required approximately 136 and 150 g day- ’ of CP for ADG
Research
25 (1997)
119-128
125
of 100 and 150 g, respectively. To estimate DE requirements, net energy for maintenance and gain requirements of NRC (1985b) were used. In addition, it was assumed that DE was 82% of ME (NRC, 1985b) and that energy used in maintenance plus gain was 60% of ME (Tolkamp and Ketelaars, 1994). By these procedures, DE required for 100 and 150 g ADG was 10.7 and 12.4 MJ day-‘, respectively. Actual feed intake resulted in 58 and 85% of CP and DE required for 100 g ADG with B-S, and 98 and 94%, respectively, with B-SR. The RW-S diet resulted in 69 and 9 1% of required CP and DE for 150 g ADG, and 106 and 97%, respectively, was supplied by RW-SR. Dietary addition of RUP increased CP intake so that it was similar to, or slightly greater than, the quantity required for ADG predicted based on DE intake. Actual ADG was similar between grass sources but greater (P = 0.01) for SR vs S (65, 238, 70 and 216 g day-’ for B-S, B-SR, RW-S and RW-SR, respectively; SE 52.4). Observed ADG was not greater for RW vs B diets, as was expected based on CP and DE intakes. This disparity may relate in part to differences among diets in gut digesta fill and the relatively short period of time during which treatments were imposed. For example, gastrointestinal tract digesta fill typically is greater with tropical than with temperate grass diets (Reid et al., 1990; Sun et al., 1994; Kouakou et al., 1995a,b). Live weight gain for B-SR and RW-SR treatments in the present experiment was appreciably greater than predicted, perhaps in part because of compensatory growth. Between weaning and surgery, wethers consumed ad libitum moderate-quality grass hay. Live weight gain during the 6-week period before the experiment, following a 2-week period after surgery, was low and averaged 69 g day- ‘. Dry matter intake during that time averaged 2.9% BW, and average dietary concentrations of CP and DE were 9.7% and 11.3 MJ kg- ’ DM, respectively. The BW, moderate frame size of these wethers and the previous low to moderate plane of nutrition reflect considerable potential for protein accretion (ARC, 1980). Greater hepatic uptake of AAN for SR vs S diets agrees with results of other studies. For example, Guerino et al. (1991) noted greater hepatic AAN uptake with than without abomasal casein infusion with restricted feed intake. Also, a diet of chopped
126
A.L. Goetsch et al./Small
Ruminant Research 25 (1997) 119-128
alfalfa hay with greater N intake than with a highconcentrate diet elicited greater hepatic AAN uptake (Huntington, 1989). These effects appear the result of increased liver protein synthesis (Guerino et al., 1991) and(or) greater removal of amino acids in excess of the potential for use in protein synthesis by peripheral tissues. In regards to the first factor, because of little change in DE intake with RUP addition and that less than 10% of whole body protein synthesis is attributable to the liver (Lobley, 19941, it seems doubtful that an increase in hepatic protein synthesis in the present experiment could have accounted for all of the observed change in hepatic AAN uptake with RUP supplementation. If the second factor was important, then because level of supplemented RUP and the increase in PDV AAN release were similar for RUP addition to B and RW, but the difference between splanchnic energy use and DE intake was less for B-SR than for RW-SR, greater hepatic AAN uptake was expected for B-SR. There is some but not conclusive evidence for this. Rumen undegradable protein supplementation had a numerically (P = 0.16) greater effect on hepatic AAN uptake with B than RW, despite lower N intake for B than for RW diets. Other measures supporting effect of a difference between grass sources in peripheral energy availability on amino acid uptake by the liver are the greater difference in hepatic UN release between B-S and B-SR than between RW-S and RW-SR; comparable but nonsignificant interaction in splanchnic UN release; and tendency for greater effect of RUP addition on splanchnic net flux of AAN for RW than for B (interaction; P = 0.13). These results seem to reflect how differences in peripheral energy supply between grasses can impact whether amino acids of RUP sources give rise to urea synthesized by the liver or are used by peripheral tissues for protein synthesis. Ammonia N release by the PDV and uptake by the liver were correlated (r = 0.97; P < 0.011, although the interaction between grass source and supplement treatment was noted only for hepatic uptake. Greater DE intake for RW than for B diets may have facilitated greater microbial AMN capture with RW and partially contributed to the interaction between grass source and supplement treatment in hepatic UN release. Thus, the interaction between grass source and supplement treatment in hepatic UN
release appears due to hepatic uptake of both AMN and AAN.
5. Conclusion In ten month-old wetbers with ad libitum consumption, splanchnic energy use as a percentage of DE intake was greater for B than for RW diets. This difference was not affected by supplementation with RUP. Furthermore, RUP supplementation increased PDV AAN release similarly regardless of grass source. Interactions occurred between dietary inclusion of RUP and grass source in hepatic release of UN and uptake of AMN; tendencies for interactions also were noted in hepatic uptake and splanchnic net flux of AAN. Factors responsible for these interactions cannot be conclusively stated. Nonetheless, it is suggested that greater DE intake for RW vs B minimized PDV release and hepatic uptake of AMN when RUP was supplemented through effects on rumen microbial AMN incorporation. Also, the greater difference between DE intake and energy consumption by the splanchnic bed for RW than for B presumably resulted in greater amino acid use in peripheral tissue protein synthesis and, thus, relatively low hepatic AAN uptake with supplemental RUP. In conclusion, unless forage intake is changed, any effects on animal performance of RUP supplementation should occur through increased N absorption without change in energy available to peripheral tissues, regardless of grass source.
Acknowledgements Published with the approval of the Director of the Arkansas Agricultural Experiment Station, Manuscript Number 96043. Mention of a trademark or proprietary product in this paper does not constitute a guarantee or warranty of the product by the USDA and does not imply its approval to the exclusion of other products that also may be suitable. Appreciation is expressed to the NRI Competitive Grants Program/USDA (Award No. 92-37208-8 18.5) and Arkansas Science and Technology Authority (Award No. 94-B-02) for partial financial support.
A.L. Goeach
et (11./Small
Ruminant
References AOAC, 1984. Official Methods of Analysis. 14th edn., Association of Official Analytical Chemists, Washington, DC, pp. 129- 130. ARC, 1980. The Nutrient Requirements of Ruminant Livestock. Agricultural Research Council, Commonwealth Agricultural Bureaux, Famham Royal Slough, UK, pp. 1-58. Barrio, J.R., Goetsch, A.L. and Owens, F.N., 1986. Effect of dietary concentrate level on in situ dry matter and nitrogen disappearance of a variety of feedstuffs. J. Dairy Sci., 69: 420-430. Blasi, D.A., Ward, J.K., Klopfenstein, T.J. and Britton, R.A., 1991. Escape protein for beef cows: III. Performance of lactating beef cows grazing smooth brome or big bluestem. J. Anim. Sci., 69: 2294-2302. Broderick, G.A. and Kang, J.H., 1980. Automated simultaneous determination of ammonia and total amino acids in ruminal fluid and in uitro media. J. Dairy Sci., 63: 64-75. Burrin, D.G., Ferrell, C.L., Eisemann, J.H. and B&ton, R.A., 1991. Level of nutrition and splanchnic metabolite flux in young lambs. J. Anim. Sci., 69: 1082-1091. Chemey, D.J.R., Patterson, J.A. and Chemey, J.H., 1989. Use of 2-ethoxyethanol and alpha-amylase in the neutral detergent fiber method of feed analysis. J. Dairy Sci., 72: 3079-3084. Consortium, 1988. Guide for the Care and Use of Agricultural Animals in Agricultural Research and Teaching. Editorial Production Services, Association Headquarters, Champaign, IL, pp. 6-22, 47-49. Duff, G.C., Goetsch, A.L., Park, K.K., Galloway, D.L., Sr, Rinne, M. and Patil, A.R., 1995. Feed intake and digestion by Holstein steers consuming low-protein forage supplemented with different nitrogen sources. J. Appl. Res., 7: 115-128. Eisemann, J.H. and Nienaber, J.A., 1990. Tissue and whole-body oxygen uptake in fed and fasted steers. Br. J. Nutr., 54: 399-411. Ferrell, C.L., B&ton, R.A. and Freetly, H.C., 1992. Chronic catheterization of hepatic and portal veins of sheep. In: P. Dziuk and M. Wheeler (Editors), Handbook of Methods for Study of Reproductive Physiology in Domestic Animals. University of Illinois, Urbana, IL, Sections VIII and F. Goering, H.K. and Van Soest, P.J., 1970. Forage Fiber Analyses. Apparatus, Reagents, Procedures and Some Applications. ARS, USDA, Agricultural Handbook No. 379, pp. 1- 12. Goetsch, A.L. and Galyean, M.L., 1983. Influence of frequency of feeding on passage of fluid and particulate markers and rumen fermentation in steers fed a concentrate diet. Can. J. Anim. Sci., 63: 727-730. Goetsch, A.L., Ferrell, CL. and Freetly, H.C., 1994. Effects of different supplements on splanchnil oxygen consumption and net flux of nutrients in sheep consuming bromegrass hay ad libitum. Br. J. Nutr., 72: 701-712. Goetsch, A.L., Patil, A.R., Galloway, D.L., Sr, Wang, Z.S., Kouakou, B., Park, K.K. and Rossi, J.E., 1997. Oxygen consumption by splanchnic tissues in wethers consuming ad libitum different proportions of bermudagrass and ryegraswheat. Arch. Anim. Nutr., 50: I-11.
Reseurch 25 (I 997) I 19-128
127
Guerino, F., Huntington, G.B. and Erdman, R.A., 1991. The net portal and hepatic flux of metabolites and oxygen consumption in growing beef steers given postruminal casein. J. Anim. Sci., 69: 387-395. Hafley, J.L., Anderson, B.E. and Klopfenstein, T.J., 1993. Supplementation of growing cattle grazing warm-season grass with proteins of various ruminal degradabilities. J. Anim. Sci., 71: 522-529. Huntington, G.B., 1989. Hepatic urea synthesis and site and rate of urea removal from blood of beef steers fed alfalfa hay or a high concentrate diet. Can. J. Anim. Sci., 69: 215-223. Kouakou, B., Goetsch, A.L., Patil, A.R., Galloway, D.L., Sr and Park, K.K., 1995a. Effects of forage source and grain level on performance and visceral organ mass of growing wethers. J. Anim. Sci., 73(Suppl. 1): 169 (abstract). Kouakou, B., Goetsch, A.L., Patil, A.R., Galloway, D.L., Sr, Park, K.K. and West, C.P., 1995b. Effects of grass source and maturity on performance and visceral organ mass or growing wethers. J. Anim. Sci., 73(Suppl. 1): 261 (abstract). Lobley, G.E., 1994. Amino acid and protein metabolism in the whole body and individual tissues of ruminants. In: J.M. Asplund (Editor), Principles of Protein Nutrition of Ruminants. CRC Press, Boca Raton, FL, pp. 147-177. McLean, J.A., 1972. On the calculation of heat production from open-circuit calorimetric measurements, Br. J. Nutr., 27: 597600. Minson, D.J., 1990. Forage in Ruminant Nutrition. Academic Press, San Diego, CA, pp. 9-149. NRC, 1985a. Ruminant Nitrogen Usage. National Research Council, National Academy Press, Washington, DC, p. 33. NRC, 1985b. Nutrient Requirements of Sheep. 6th revised edn., National Research Council, National Academy Press, Washington, DC, pp. 2-7, 49-50. Park, K.K., Goetsch, A.L., Johnson, Z.B. and Rossi, J.E., 1997. Temporal pattern of net flux of nutrients across splanchnic tissues in wethers consuming different forages. Small Rum. Res., in press. Patil, A.R., Goetsch, A.L., Galloway, D.L., Sr, Kouakou, B., Wang, Z.S., Park, K.K. and Rossi, J.E., 1995a. Effects of grass source and physical form on net flux of nutrients across splanchnic tissues in sheep. J. Anim. Sci., 73(Suppl. I): 260 (abstract). Patil, A.R., Goetsch, A.L., Park, K.K., Kouakou, B., Galloway, D.L., Sr and Johnson, Z.B., 1995b. Influences of grass source on net flux of nutrients across splanchnic tissues in sheep with restricted intake. Arch. Anim. Nutr., 48: 257-269. Patil, A.R., Goetsch, A.L., Park, K.K., Kouakou, B., Galloway, D.L., Sr, West, C.P. and Johnson, Z.B., 1995~. Net flux of nutrients across splanchnic tissues in sheep fed tropical vs. temperate grass hay of moderate or low qualities. Livest. Prod. Sci., 43: 49-61. Patil, A.R., Goetsch, A.L., Park, K.K., Kouakou, B., Galloway, D.L., Sr and Johnson, Z.B., 1996. Influences of grass source and legume level on net flux of nutrients across splanchnic tissues in sheep. Small Rum. Res., 22: I1 l- 122. Preston, R.L., 1987. Ingredient table helps balance rations. Feedstuffs, 59(42): 18.
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Redfearn, D.D., Moser, L.E., Walk, S.S. and Klopfenstein, T.J., 1995. Ruminal degradation of switchgrass, big bluestem, and smooth bromegrass leaf proteins. J. Anim. Sci., 73: 598-605. Reid, R.L., Jung, G.A., Cox-Gamer, J.M., Rybeck, B.F. and Townsend, E.C., 1990. Comparative utilization of warm- and cool-season forages by cattle, sheep and goats. J. Anim. Sci., 68: 2986-2994. SAS, 1990. SAS/STAT User’s Guide. Version 6. Vol. 2, 4th edn., Statistical Analysis System Inst., Gary, NC, pp. 891-996. Sun, W., Goetsch, A.L., Forster, L.A., Jr, Galloway, D.L., Sr and Lewis, P.K., Jr, 1994. Forage and splanchnic tissue mass in growing lambs: effects of dietary forage levels and source on splanchnic tissue mass in growing lambs. Br. J. Nutr., 71: 141-151.
Research 25 (1997) 119-128 Tolkamp, B.J. and Ketelaars, J.J.M.H., 1994. Efficiency of energy utilization in cattle given food ad libitum: predictions according to the ARC system and practical consequences. Anim. Prod., 59: 43-47. Waltz, D.M., Stem, M.D. and Illg, D.J., 1989. Effect on ruminal protein degradation on the intestinal amino acid supply to lactating cows. J. Dairy Sci., 72: 1509- 1528. Wilson, J.R., 1993. Organization of forage plant tissues. In: H.G. Jung, D.R. Buxton, R.D. Hatfield and J. Ralph (Editors), Forage Cell Wall Structure and Digestibility. American Society of Agronomy, Crop Science Society of America, Soil Science Society of America, Madison, WI, pp. I-32.
Small Ruminant Research 25 (1997) 119-128
Net flux of nutrients across splanchnic tissues in wethers consuming bermudagrass or ryegrass-wheat hay supplemented with rumen undegradable protein A.L. Goetsch a,*, A.R. Patil b, Z.S. Wang b, K.K. Park b, D.L. Galloway, Sr b, J.E. Rossi b, B. Kouakou b a Dale Bumpers Smdl Furms Research Center. Agriculturnl Rrseorch Service, USDA, Booneuillr, AR 72927-9214, USA ’ Depurtment ofAnimal
Science, University of’Arkan.ws, Fuyettruille,
AR 72701, USA
Accepted 2 October 1996
Abstract Crossbred wethers (14, 37 + 1.5 kg BW and 10 months old) were used in a 21-day experiment (2 X 2 factorial) to determine effects of dietary grass source (tropical vs temperate) on response to rumen undegradable protein supplementation in oxygen consumption by, and net flux of N fractions across, the portal-drained viscera and liver. Bermudagrass (B; 73.1% NDF and 6.2% CP) or ryegrass-wheat (RW; 65.9% NDF and 8.9% CP) hay was supplemented with 53 g clay- ’ (DM) of soybean meal (S) or 53 g day-’ (DM) of soybean meal plus 70 g day -’ (DM) of a mixture of feedstuffs high in rumen undegradable protein (SR; 46.6% corn gluten, 26.7% feather and 26.7% blood meals). Digestible energy intake (9.1, 10.0, 11.3 and 12.1 MJ day-‘) was greater (P < 0.01) for RW than for B, and N intake was 12.5, 21.5, 16.5 and 25.3 g day-’ (SE 1.08) for B-S, B-SR, RW-S and RW-SR, respectively. Splanchnic energy use as a percentage of DE intake was less (P = 0.03) for RW vs B (21.4 vs 27.8%). Supplementation with SR increased (P = 0.04) alpha-amino N release by the portal-drained viscera (6.6, 22.0, 9.8 and 20.6 mmol h- ‘) and hepatic uptake (10.9, 25.6, It .2 and 14.3 mmol h- ’ for B-S, B-SR, RW-S and RW-SR, respectively; SE 2.29). Supplementation with SR increased (P < 0.01) hepatic urea N release (26.7, 48.4, 29.0 and 41.8 mmol hK’) and ammonia N uptake (17.3, 29.7, 23.3 and 26.6 mmol hK’ for B-S, B-SR, RW-S and RW-SR, respectively) more (interaction; P = 0.09 and 0.08, respectively) with B than with RW. In conclusion, these results indicate that DE intake and splanchnic energy consumption for tropical and temperate grasses may influence metabolic fate of rumen undegradable protein N and, thus, impact potential performance benefits of supplementation. Also, unless forage intake is changed, any improvements in animal performance with rumen undegradable protein supplementation would be through increased N absorption without change in energy available to peripheral tissues, regardless of grass source. 0 1997 Elsevier Science B.V. Keywords: Sheep; Metabolism; Rumen undegradable protein; Forage
1. Introduction
* Corresponding author. Tel.: 501/675-3834; fax: 501/6752940.
Digestible energy intake temperate than for tropical
00921.4488/97/$17.00 0 1997 Elscvier Science B.V. All rights reserved. PII SO921 -4488(96)0098 I-9
is usually grass diets
greater because
for of
120
A.L. Goetsch et ul./SmdI
Ruminant Research 25 (1997) 119-128
greater digestibility and sometimes greater intake (Minson, 1990). Also, the proportion of DE attributable to splanchnic tissue energy use is greater for tropical than for temperate grasses (Patil et al., 1995a,b,c, 1996; Goetsch et al., 1997). Therefore, energy available to extra-splanchnic tissues can differ between tropical and temperate grasses more than expected based on DE intake. Redfearn et al. (1995) postulated that bundle sheath cells of tropical grasses slow ruminal microbial degradation of some protein, thereby increasing passage to the postruminal tract of intact protein compared with temperate grasses. Thus, it was suggested that relatively high escape of tropical grass protein from rumen microbial attack explains observations in some experiments of little or no response in ADG by ruminants consuming tropical grasses to supplementation with rumen undegradable protein sources (Blasi et al., 1991; Hafley et al., 1993). In addition to differences in ruminal degradation of protein among forage sources, it is possible that DE intake and splanchnic energy use with various forage sources, as influencing metabolic fate of N from rumen undegradable protein supplements, could impact ruminant performance. Therefore, objectives of this experiment were to determine effects of grass source on response to supplementation with rumen undegradable protein in oxygen consumption by, and net flux of N fractions across, the portal-drained viscera (PDV) and liver in wethers.
2. Materials
and methods
2.2. Diets Sheep consumed ad libitum (offered at 105 to 110% of consumption on the preceding few days) coarsely chopped bermudagrass ((B grass source treatment) Cynodon dactylon; vegetative growth stage) or ryegrass (Lolium multijlorum; post-anthesis) and wheat ((RW grass source treatment) Triticum aestiuum; post-anthesis) hay. In addition, sheep were fed soybean meal (S supplement treatment; 53 g day- ’ , DM) or soybean meal (53 g day- ’ ; DM) plus a mixture of rumen undegradable protein (RUP) sources ((SR supplement treatment) 70 g day-‘, DM; 46.6% corn gluten, 26.7% feather and 26.7% blood meals). Protein supplements were top-dressed on hay and completely consumed. Equal-sized meals were fed at 14:00, 22:00 and 06:OO h; at 14:00 h, sheep received 3.5 g day-’ of a mineral source mixture of 20% trace mineral premix (12% Zn, 10% Mn, 5% K, 2.5% Mg, 1.5% Cu, 0.3% I, 0.1% Co and 0.02% Se) and 80% NaCl. Three wethers were allotted to B-S and RW-SR treatments and four to B-SR and RW-S treatments. Of primary interest in this experiment were changes in net fluxes of N fractions in absolute quantities rather than relative to intake of different diet constituents (e.g. total N). Therefore, the same quantities of S and RUP sources were provided with both sources of grass. This was felt desirable compared with confounding from supplementing with different quantities of protein sources to achieve similar total N intake or dietary N concentration, which also would have necessitated daily changes in offered quantities of supplemental feedstuffs.
2.1. Animals
2.3. Sampling and analyses
Crossbred (Suffolk X Rambouillet-Dorset) wethers (14, 37 &- 1.5 kg BW, 10 months old) were surgically fitted with chronic indwelling catheters in a hepatic vein, the portal vein and a mesenteric vein and artery (Ferrell et al., 1992) 8 weeks before the experiment. Catheters were filled with heparinized (100 U ml-‘) saline (0.85%; w/v> solution at surgery. Sheep were individually maintained in 1.l X 1.5-m elevated pens with expanded metal flooring and had free access to water. Sheep were cared for in accordance with guidelines of Consortium (1988).
The experiment was 21 days in length. Feed was sampled daily on Days 11 through 21 to form a composite. Feces were collected in canvas bags on Days 14 through 17, and a composite sample was formed from 10% aliquots of daily excretion. Ruminal fluid was obtained by stomach tube on Day 16 at 09:OO h, strained through cheesecloth, acidified with 7.2 N H,SO,, frozen and later analyzed for VFA (Goetsch and Galyean, 1983) and ammonia N (AMN; Broderick and Kang, 1980). Metabolism crates were used to house sheep dur-
A.L. Gortsch et ul./Small Table 1 Composition
(DM basis) of feedstuffs
consumed
Item
Bermudagrass
Ash (%I CP (o/o) NDF (%) ADF (%) ADL (%) Cellulose (%) HemicelluIose (%)
6.1 6.2 73.1 37.0 4.8 29.5 36.0
hay
by wethers Ryegrass-wheat
hay
1.2 8.9 65.9 38.2 3.9 30.3 27.7
protein supplementation
Soybean meal
Rumen undegradable
7.1 49.0 9.5
4.5 66.1 8.7
para-aminohippuric through a sterile mesenteric vein infusion (0.8 ml was determined was obtained.
ing blood collections, with four sheep sampled daily (one per treatment) on Days 18, 19 and 20, and two were sampled on Day 21. Sheep were accustomed to metabolism crates because of prior exposure to these conditions and displayed normal intake and other activities while in crates. A priming dose (15 ml) of
Table 2 Effects of rumen undegradable
121
Ruminant Research 25 (1997) 119-128
on feed intake and digestion
protein mix
acid (22.5 g 1-l > was given 0.2-p,rn filter at 07:30 h into the catheter, followed by continuous min-‘) until 15:25 h. Body weight immediately after the last sample
by wethers consuming
bermudagrass
or ryegrass-wheat
hay Bermudagrass
Item
Ryegrass-wheat
SE
Effect a
Sb
SR ’
s
SR
841 53 895
860 123 983
869 53 922
865 123 988
79.9
839
925
856
920
74.3
54.7 459
54.0 501
68.0 581
68.4 622
2.27 44.9
G G
9.1
10.0
11.3
12.1
0.89
G
12.5
21.5
16.5
25.3
1.08
G, T
55.4
68.5
57.6
68.4
2.99
T
6.9
14.8
9.5
17.2
0.66
G. T
DM intuke (g day- ‘) Hay Supplement Total
79.9
OM Intake (g dayDigestion
’)
% g day-’ DE intake (MJ day - t) N
Intake (g dayDigestion
’)
% g day-’ NDF Intake (g dayDigestion % .g day-’
’)
620
639
578
581
53.8
53.8 333
49.9 320
69.9 403
68.5 393
2.62 33.8
G z
a Effect: Cl and g = grass source (bermudagrass vs ryegrass-wheat; P < 0.05 and 0.10, respectively); T = supplement treatment (S vs SR; P < 0.05). b S = 53 g day- ’ (DM) of soybean meal. ’ SR = 53 g day- ’ (DM) of soybean meal plus 70 g day- ’ (DM) of a mixture of rumen undegradable protein sources (46.6% corn gluten, 26.7% feather and 26.7% blood meals).
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Ruminant Research 25 (1997) 119-128
Blood was withdrawn starting at O&00, 09:00, lO:OO,ll:OO, 12:00, 13:00, 1400 and 15:OOh, with a IO-mm interval between sheep and representing an entire 8-h feeding interval. The treatment order for sampling differed among days. A I-ml sample was obtained anaerobically into a heparinized syringe and placed in ice. Oxygen saturation and hemoglobin concentration (OSM 2; Radiometer Corporation, Copenhagen, Denmark) were measured immediately; oxygen concentration was calculated as described by Eisemann and Nienaber (1990). Another sample was taken in a tube with potassium oxalate and sodium fluoride and placed in ice. On the day of sampling, a 1.5ml aliquot was diluted with deionized water (4.5 ml) and subjected to automated procedures for paraaminohippuric acid, alpha-amino nitrogen (AAN), urea nitrogen (UN) and AMN, as described by Eisemann and Nienaber (1990). Concentrations of paraaminohippuric acid, AAN, UN and AMN were averaged across time for calculation of blood flows and metabolite fluxes. Net metabolite fluxes were calculated based on venoarterial concentration differences and whole blood flows (Burrin et al., 1991), with some values being extrapolated from this 8-h feeding interval to a 24-h basis for comparison with daily feed intake. Park et al. (1997) utilized similar methodology with wethers consuming alfalfa, B or RW ad libitum, although hourly samples were com-
Table 3 Effects of rumen undegradable bermudagrass or ryegrass-wheat Item
protein hay
supplementation Bermudagrass Sb
Ammonia N (mmol I- ‘)
on ruminal
posites of three consecutive samples taken at 20-min intervals. Very similar temporal patterns in net fluxes across splanchnic tissues were observed for B and RW. Fecal composites were at dried 55°C and allowed to air-equilibrate. Hay and fecal samples were ground to pass a l-mm screen. Hay, supplement and fecal samples were analyzed for DM, ash, Kjeldahl N, energy (AOAC, 1984) and NDF (Goering and Van Soest, 1970; without sodium sulfite, decalin or ethoxyethanol). For supplement NDF analysis samples were ground to pass a 0.6-mm screen and treated with amylase (Chemey et al., 1989). Hay samples also were analyzed for ADF and ADL (Goering and Van Soest, 1970). Cellulose was estimated as loss in weight upon H2S0, treatment and hemicellulose as the difference between NDF and ADF. The average of feed intake on Day 12 through the day of blood sampling was used to calculate digestibilities. Data were analyzed by the general linear models procedure of SAS (1990), with a model consisting of grass source, rumen undegradable protein inclusion in the diet and their interaction. Portal-drained viscera and hepatic net fluxes were not estimated for two wethers (B-SR and RW-S treatments) because of non-patent portal vein catheters. Therefore, the number of observations was 14 for feed intake,
fluid ammonia
N and VFA concentrations
Ryegrass-wheat SR ’
in wethers
SE
S
SR
9.5
8.8
10.4
11.0
2.35
63 70.5 17.1 1.00 8.9
59 69.1 18.2 1.1 I 8.8 I .36 I .42 3.80
54 70.1 17.7 1.32 7.5 1.44
63 68.3 20.8 0.83 7.8 0.94 1.32 3.29
110.0
consuming
Effect a
VFA
Total (mmol I- ’ ) Acetate (mot per 100 mol) Propionate (mol per 100 mol) Isobutyrate (mol per 100 mol) Butyrate (mol per 100 mol) Isovalerate (mot per 100 mol) Valerate (mol per 100mol) Acetate:urouionate
1.23 1.16 4.19
a Effect: g = grass source (bermudagrass vs ryegrass-wheat; b S = 53 g day- ’ (DM) of soybean meal. ’ SR = 53 g day- ’ (DM) of soybean meal plus 70 g day26.7% feather and 26.7% blood meals).
1.82 4.02 P < 0.10); t = supplement
0.99 I .04 0.395 0.56 0.455 0.354 0.253
t g
t
treatment (S vs SR; P < 0.10).
’ (DM) of a mixture of rumen undegradable
protein sources (46.6% corn gluten,
A.L. Goetsch et al./Small Table 4 Effects of rumen undegradable protein supplementation in wethers consuming bermudagrass or ryegrass-wheat Item
Blood flow(1h- ‘) Portal vein Hepatic vein Hepatic artery
Ammonia N Whole blood concentration Portal vein Hepatic vein Artery Net flux (mmol hh’) Portal-drained viscera Hepatic Splanchnic
(mmol l-
3.33 2.16 4.57 114 99 213
N, urea N and ammonia
N measures
SE
Effect a
12.8 11.5 3.2
i
SR
89 118 29
89 108 19
3.24 2.76 4.65 135 145 269
3.43 2.76 4.69 120 106 228
3.68 2.96 5.00 114 102 216
0.250 0.266 0.242 14.8 16.2 24.7
’)
6.6 - 10.9
(mmol l-
112 142 28
S
123
’)
4.38 4.27 4.3 I
(mm01 l-
Ryegrass-wheat SR ’
93 119 26
oxygen Whole blood concentration (mmol lPortal vein Hepatic vein Artery Consumption (mmol h- ‘) Portal-drained viscera Hepatic Splanchnic
Urea N Whole blood concentration Portal vein Hepatic vein Artery Net flux (mmol h- ’ ) Portal-drained viscera Hepatic Splanchnic
on whole blood flow and oxygen, alpha-amino hay
Bermudagrass Sb
Alpha-amino N Whole blood concentration Portal vein Hepatic vein Artery Net flux (mm01 h- ’ ) Portal-drained viscera Hepatic Splanchnic
Ruminant Reseurch 25 (1997) 119-128
4.86 4.62 4.64
4.30 4.26 4.28
4.65 4.49 4.44
0.356 0.433 0.283
9.8 - 11.2 - 2.5
20.6 - 14.3 6.3
5.25 3.72 2.11
T T
- 4.2
22.0 - 25.6 - 2.3
5.4 5.7 5.7
Il.1 11.1 10.9
7.8 8.0 7.8
10.1 10.6 10.4
0.71 0.64 0.65
T, 1 T, i T, i
- 17.9 26.7 8.8
- 17.8 48.4 26.8
- 20.2 29.0 14.1
- 20.2 41.8 21.6
5.19 2.29 5.93
T, i t
C, T
’)
’) 0.660 0.466 0.474 16.4 - 17.3 -0.9
0.682 0.422 0.443 26.7 - 29.7 -3.1
0.675 0.470 0.496 20.7 -23.3 -3.0
0.746 0.445 0.460 25.0 - 26.6 - 1.7
0.0412 0.0384 0.0399 2.32 2.23 0.12
T T, i I
a Effect: G = grass source (bermudagrass vs ryegrass-wheat; P < 0.05); T and t = supplement treatment (S vs SR; P < 0.05 and 0.10, respectively); I and i = interaction between grass source and supplement treatment (P < 0.05 and 0.10, respectively). b S = 53 g day- ’ (DM) of soybean meal. ’ SR = 53 g day- ’ (DM) of soybean meal plus 70 g day- ’ (DM) of a mixture of mmen undegradable protein sources (46.6% corn gluten, 26.7% feather and 26.7% blood meals).
124
A.L. Goetsch et al./Smail
Ruminant Research 25 (1997) 119-128
digestibility, ruminal fluid concentrations of VFA and AMN, metabolite concentrations in arterial and hepatic venous blood and splanchnic net fluxes; 12 observations (three per treatment) were derived for portal venous blood concentrations of metabolites and PDV and hepatic net fluxes.
3. Results Bermudagrass hay was slightly lower than RW in CP concentration (Table 1). As typical with tropical and temperate grasses (Minson, 1990), B was higher than RW in concentrations of NDF, ADL and hemicellulose. Total DM and OM intakes were similar (P > 0.10) between grass sources and supplement treatments (Table 2). Supplement comprised 6.0, 12.7, 5.9 and 12.9% of DM intake, and 33.5, 60.6, 25.7 and 52.1% of nitrogen intake, for B-S, B-SR, RW-S and RW-SR, respectively. Digestible OM (P = 0.02) and DE (P = 0.03) intakes were greater for RW than for B because of greater (P < 0.01) OM and NDF digestibilities. The differences between B and RW in digestibilities of OM and NDF appear somewhat greater than implicated by concentrations of NDF and ADL, perhaps reflecting an impact of different proportions and unique arrangements of specific plant tissues on microbial fiber degradation (Wilson, 1993). Digestible N intake was greater (P < 0.01) for RW than for B because of greater N intake (P < O.Ol), although digestible N intake was greater for SR than for S as a result of both greater (P < 0.01) N intake and digestibility. Differences in digestible N intake between supplement treatments suggest nearly complete (i.e. 94%) total tract digestibility of protein in RUP sources added to the diet. Ruminal AMN concentration was similar (P > 0.10) among treatments (Table 3). The concentration of total VFA in ruminal fluid did not differ among treatments (P > 0.10). The molar proportion of acetate was not affected by treatment (P > O.lO), although that of propionate was greater (P = 0.07) for SR than for S diets. Likewise, the acetate to propionate ratio was less (P = 0.05) for SR than for S. Portal and hepatic venous blood flows were similar (P > 0.10) among treatments (Table 4). Hepatic arterial blood flow was affected (P = 0.09) by an
interaction between grass source and supplement treatment. Whole blood oxygen concentrations and net fluxes were not altered (P > 0.10) by treatment. Concentrations of AAN in whole blood were similar among treatments (P > 0.10; Table 4). Splanchnic net flux of AAN was greater (P = 0.03) for RW than for B, although net fluxes across the PDV and liver did not differ with forage source (P > 0.10). Supplementation with SR increased (P = 0.04) PDV release of AAN slightly more than it increased (P = 0.04) hepatic uptake. Thus, net flux of AAN across the splanchnic bed was greater (P = 0.03) for SR than for S diets. Assuming that the difference between S and SR diets in PDV AAN release was attributable to RUP sources, 59.5% of N in RUP sources reached the liver as AAN. Interactions between grass source and supplement treatment occurred in UN concentration in portal (P = 0.06), hepatic venous (P = 0.05) and arterial blood (P = 0.06). Uptake of UN by the PDV was similar among treatments (P > 0.101, although splanchnic release was greater (P = 0.06) for SR than for S. Grass source and supplement treatment interacted (P = 0.09) in hepatic UN release. Whole blood AMN concentrations were not altered (P > 0.10) by treatments (Table 4). Portaldrained viscera release of AMN was greater (P = 0.01) for SR than for S. Grass source and supplement treatment interacted in hepatic uptake (P = 0.08) and splanchnic net flux AMN (P = 0.03).
4. Discussion Assuming 0.46 MJ of heat per mol of oxygen consumed by splanchnic tissues (McLean, 1972), the difference between DE intake and splanchnic bed energy use was greater (P = 0.02) for RW than for B (9.3 vs 6.9 MJ day-‘; SE 0.61). The lack of difference between B and RW diets in total VFA and acetate and propionate concentrations suggest similar methane production. Therefore, it seems reasonable to assume that the difference between splanchnic energy use and DE intake related closely to energy metabolizable by extra-splanchnic tissues. As a proportion of DE intake, heat production was greater for B than for RW in the liver (P = 0.07; 13.5 vs 10.4%, SE 1.07) and splanchnic bed (P = 0.03; 27.8
A.L.
Goetsch
et ul./Smull
Ruminant
vs 21.4%, SE 1.841, although that for the PDV did not significantly differ between grass sources ((P = 0.20) 14.0 and 11.6% for B and RW, respectively; SE 1.19). Similar to results in the present experiment, Goetsch et al. (1994) did not alter the ratio of splanchnic energy consumption to DE intake by including a similar mixture of RUP sources in a bromegrass hay diet consumed by wethers. Thus, it appears that any increase in splanchnic energy consumption due to RUP addition to low- or moderatequality grasses is non-existent or small. Causal factors of, or physiological processes associated with, greater splanchnic energy use relative to DE intake for tropical vs temperate grass diets do not appear affected by increases in absorption, PDV release or hepatic uptake of amino acids elicited by dietary RUP addition. Examples of RUP concentrations in RUP sources used are 8 1, 65 and 82% for feather, corn gluten and blood meals, respectively (NRC, 1985a; Preston, 1987; Waltz et al., 1989). Barrio et al. (1986) noted similar in situ N disappearance for feather and corn gluten meals between ruminal incubation periods 12 and 24 h in length. Duff et al. (1995) observed slightly greater in situ N disappearance at 24 vs 12 h of ruminal incubation for feather and blood meals (37 vs 26% and 25 vs 15%, respectively) but similar values for corn gluten meal (25 and 28% at 12 and 24 h, respectively). Thus, with similar intake of grass sources in the present experiment, substantial effects of ruminal digesta retention time on extent of ruminal protein degradation are unlikely. The increase in PDV AMN release with RUP supplementation does not agree with the similar ruminal AMN concentration among treatments. However, only one sample of ruminal fluid was obtained at 3 h post-feeding. The increase in PDV AMN release averaged 33% of added RUP source N. This value, and the estimate of 59.5% of N in RUP sources accounted for by the increase in PDV AAN release with RUP addition, seem in accordance with expected ruminal degradability of the RUP source mixture and the assumption that some amino acids were metabolized by PDV tissues or released in peptides. Based on requirements of NRC (1985b) for medium mature weight lambs, these wethers required approximately 136 and 150 g day- ’ of CP for ADG
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of 100 and 150 g, respectively. To estimate DE requirements, net energy for maintenance and gain requirements of NRC (1985b) were used. In addition, it was assumed that DE was 82% of ME (NRC, 1985b) and that energy used in maintenance plus gain was 60% of ME (Tolkamp and Ketelaars, 1994). By these procedures, DE required for 100 and 150 g ADG was 10.7 and 12.4 MJ day-‘, respectively. Actual feed intake resulted in 58 and 85% of CP and DE required for 100 g ADG with B-S, and 98 and 94%, respectively, with B-SR. The RW-S diet resulted in 69 and 9 1% of required CP and DE for 150 g ADG, and 106 and 97%, respectively, was supplied by RW-SR. Dietary addition of RUP increased CP intake so that it was similar to, or slightly greater than, the quantity required for ADG predicted based on DE intake. Actual ADG was similar between grass sources but greater (P = 0.01) for SR vs S (65, 238, 70 and 216 g day-’ for B-S, B-SR, RW-S and RW-SR, respectively; SE 52.4). Observed ADG was not greater for RW vs B diets, as was expected based on CP and DE intakes. This disparity may relate in part to differences among diets in gut digesta fill and the relatively short period of time during which treatments were imposed. For example, gastrointestinal tract digesta fill typically is greater with tropical than with temperate grass diets (Reid et al., 1990; Sun et al., 1994; Kouakou et al., 1995a,b). Live weight gain for B-SR and RW-SR treatments in the present experiment was appreciably greater than predicted, perhaps in part because of compensatory growth. Between weaning and surgery, wethers consumed ad libitum moderate-quality grass hay. Live weight gain during the 6-week period before the experiment, following a 2-week period after surgery, was low and averaged 69 g day- ‘. Dry matter intake during that time averaged 2.9% BW, and average dietary concentrations of CP and DE were 9.7% and 11.3 MJ kg- ’ DM, respectively. The BW, moderate frame size of these wethers and the previous low to moderate plane of nutrition reflect considerable potential for protein accretion (ARC, 1980). Greater hepatic uptake of AAN for SR vs S diets agrees with results of other studies. For example, Guerino et al. (1991) noted greater hepatic AAN uptake with than without abomasal casein infusion with restricted feed intake. Also, a diet of chopped
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alfalfa hay with greater N intake than with a highconcentrate diet elicited greater hepatic AAN uptake (Huntington, 1989). These effects appear the result of increased liver protein synthesis (Guerino et al., 1991) and(or) greater removal of amino acids in excess of the potential for use in protein synthesis by peripheral tissues. In regards to the first factor, because of little change in DE intake with RUP addition and that less than 10% of whole body protein synthesis is attributable to the liver (Lobley, 19941, it seems doubtful that an increase in hepatic protein synthesis in the present experiment could have accounted for all of the observed change in hepatic AAN uptake with RUP supplementation. If the second factor was important, then because level of supplemented RUP and the increase in PDV AAN release were similar for RUP addition to B and RW, but the difference between splanchnic energy use and DE intake was less for B-SR than for RW-SR, greater hepatic AAN uptake was expected for B-SR. There is some but not conclusive evidence for this. Rumen undegradable protein supplementation had a numerically (P = 0.16) greater effect on hepatic AAN uptake with B than RW, despite lower N intake for B than for RW diets. Other measures supporting effect of a difference between grass sources in peripheral energy availability on amino acid uptake by the liver are the greater difference in hepatic UN release between B-S and B-SR than between RW-S and RW-SR; comparable but nonsignificant interaction in splanchnic UN release; and tendency for greater effect of RUP addition on splanchnic net flux of AAN for RW than for B (interaction; P = 0.13). These results seem to reflect how differences in peripheral energy supply between grasses can impact whether amino acids of RUP sources give rise to urea synthesized by the liver or are used by peripheral tissues for protein synthesis. Ammonia N release by the PDV and uptake by the liver were correlated (r = 0.97; P < 0.011, although the interaction between grass source and supplement treatment was noted only for hepatic uptake. Greater DE intake for RW than for B diets may have facilitated greater microbial AMN capture with RW and partially contributed to the interaction between grass source and supplement treatment in hepatic UN release. Thus, the interaction between grass source and supplement treatment in hepatic UN
release appears due to hepatic uptake of both AMN and AAN.
5. Conclusion In ten month-old wetbers with ad libitum consumption, splanchnic energy use as a percentage of DE intake was greater for B than for RW diets. This difference was not affected by supplementation with RUP. Furthermore, RUP supplementation increased PDV AAN release similarly regardless of grass source. Interactions occurred between dietary inclusion of RUP and grass source in hepatic release of UN and uptake of AMN; tendencies for interactions also were noted in hepatic uptake and splanchnic net flux of AAN. Factors responsible for these interactions cannot be conclusively stated. Nonetheless, it is suggested that greater DE intake for RW vs B minimized PDV release and hepatic uptake of AMN when RUP was supplemented through effects on rumen microbial AMN incorporation. Also, the greater difference between DE intake and energy consumption by the splanchnic bed for RW than for B presumably resulted in greater amino acid use in peripheral tissue protein synthesis and, thus, relatively low hepatic AAN uptake with supplemental RUP. In conclusion, unless forage intake is changed, any effects on animal performance of RUP supplementation should occur through increased N absorption without change in energy available to peripheral tissues, regardless of grass source.
Acknowledgements Published with the approval of the Director of the Arkansas Agricultural Experiment Station, Manuscript Number 96043. Mention of a trademark or proprietary product in this paper does not constitute a guarantee or warranty of the product by the USDA and does not imply its approval to the exclusion of other products that also may be suitable. Appreciation is expressed to the NRI Competitive Grants Program/USDA (Award No. 92-37208-8 18.5) and Arkansas Science and Technology Authority (Award No. 94-B-02) for partial financial support.
A.L. Goeach
et (11./Small
Ruminant
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Guerino, F., Huntington, G.B. and Erdman, R.A., 1991. The net portal and hepatic flux of metabolites and oxygen consumption in growing beef steers given postruminal casein. J. Anim. Sci., 69: 387-395. Hafley, J.L., Anderson, B.E. and Klopfenstein, T.J., 1993. Supplementation of growing cattle grazing warm-season grass with proteins of various ruminal degradabilities. J. Anim. Sci., 71: 522-529. Huntington, G.B., 1989. Hepatic urea synthesis and site and rate of urea removal from blood of beef steers fed alfalfa hay or a high concentrate diet. Can. J. Anim. Sci., 69: 215-223. Kouakou, B., Goetsch, A.L., Patil, A.R., Galloway, D.L., Sr and Park, K.K., 1995a. Effects of forage source and grain level on performance and visceral organ mass of growing wethers. J. Anim. Sci., 73(Suppl. 1): 169 (abstract). Kouakou, B., Goetsch, A.L., Patil, A.R., Galloway, D.L., Sr, Park, K.K. and West, C.P., 1995b. Effects of grass source and maturity on performance and visceral organ mass or growing wethers. J. Anim. Sci., 73(Suppl. 1): 261 (abstract). Lobley, G.E., 1994. Amino acid and protein metabolism in the whole body and individual tissues of ruminants. In: J.M. Asplund (Editor), Principles of Protein Nutrition of Ruminants. CRC Press, Boca Raton, FL, pp. 147-177. McLean, J.A., 1972. On the calculation of heat production from open-circuit calorimetric measurements, Br. J. Nutr., 27: 597600. Minson, D.J., 1990. Forage in Ruminant Nutrition. Academic Press, San Diego, CA, pp. 9-149. NRC, 1985a. Ruminant Nitrogen Usage. National Research Council, National Academy Press, Washington, DC, p. 33. NRC, 1985b. Nutrient Requirements of Sheep. 6th revised edn., National Research Council, National Academy Press, Washington, DC, pp. 2-7, 49-50. Park, K.K., Goetsch, A.L., Johnson, Z.B. and Rossi, J.E., 1997. Temporal pattern of net flux of nutrients across splanchnic tissues in wethers consuming different forages. Small Rum. Res., in press. Patil, A.R., Goetsch, A.L., Galloway, D.L., Sr, Kouakou, B., Wang, Z.S., Park, K.K. and Rossi, J.E., 1995a. Effects of grass source and physical form on net flux of nutrients across splanchnic tissues in sheep. J. Anim. Sci., 73(Suppl. I): 260 (abstract). Patil, A.R., Goetsch, A.L., Park, K.K., Kouakou, B., Galloway, D.L., Sr and Johnson, Z.B., 1995b. Influences of grass source on net flux of nutrients across splanchnic tissues in sheep with restricted intake. Arch. Anim. Nutr., 48: 257-269. Patil, A.R., Goetsch, A.L., Park, K.K., Kouakou, B., Galloway, D.L., Sr, West, C.P. and Johnson, Z.B., 1995~. Net flux of nutrients across splanchnic tissues in sheep fed tropical vs. temperate grass hay of moderate or low qualities. Livest. Prod. Sci., 43: 49-61. Patil, A.R., Goetsch, A.L., Park, K.K., Kouakou, B., Galloway, D.L., Sr and Johnson, Z.B., 1996. Influences of grass source and legume level on net flux of nutrients across splanchnic tissues in sheep. Small Rum. Res., 22: I1 l- 122. Preston, R.L., 1987. Ingredient table helps balance rations. Feedstuffs, 59(42): 18.
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