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A cranial mesenteric vein preparation for measurement of amino acid uptake by lambs
- S. A. Neutze, V. H. Oddy, J. M. Gooden
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- Journal:
- The Journal of Agricultural Science / Volume 122 / Issue 2 / April 1994
- Published online by Cambridge University Press:
- 27 March 2009, pp. 309-314
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A surgical preparation was developed to measure uptake of amino acids from the small intestine into the cranial mesenteric vein (CMV) of lambs. Results from this preparation were compared with those from the traditional hepatic portal vein (PV) preparation in the same lambs. Necropsy revealed that, in contrast to the PV preparation which included all portal-drained viscera, the CMV preparation drained primarily small intestine (0·84–0·92 small intestinal mass). The CMV preparation contributed 0·238 of blood flow from and 0·307 of oxygen consumption by the PV preparation. Venous-arterial differences for alpha-amino nitrogen (AAN), phenylalanine (Phe) and tyrosine (Tyr) were three- to fourfold greater in the CMV than in the PV preparation, indicating that the CMV preparation is more sensitive for measuring amino acid uptake. The ratio CMV/PV for uptake of AAN was 0·61 (P< 0·001), but this ratio was much closer to unity (mean 0·84) for Phe and Tyr. Since the CMV preparation drains primarily the small intestine, through which all amino acid absorption occurs, it should prove to be extremely valuable for studying absorption from and metabolism within this organ using a combination of arteriovenous and isotopic tracer techniques.
Uptake of labelled phenylalanine into different blood fractions in the portal vein and cranial mesenteric vein of lambs
- S. A. Neutze, J. M. Gooden, V. H. Oddy
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- Journal:
- The Journal of Agricultural Science / Volume 126 / Issue 4 / June 1996
- Published online by Cambridge University Press:
- 27 March 2009, pp. 511-518
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Four lambs (mean 27 kg liveweight) offered 900 g/day lucerne chaff were prepared with catheters in the portal vein (PV), cranial mesenteric vein (CMV), femoral artery (FA) and abomasum. L-[2,6-3H]phenylalanine (Phe) and 14C-(Phe)casein were infused into the abomasum in separate experiments. Concurrent samples of blood from the PV, CMV and FA were prepared as four fractions: plasma, deproteinized whole blood, free Phe in deproteinized whole blood, and whole blood. Ratios of net label uptakes in different blood fractions indicated that red blood cells and blood proteins were unlikely to contribute to net Phe uptake into the PV or CMV. Small peptides may have contributed up to 20% to total appearance of Phe in the PV and CMV. However, net uptake of peptides from the lumen was probably zero. It was concluded that the Phe uptake and, by implication, total amino acid uptake from the lumen of the small intestine into the PV and CMV were as free amino acids.
Effects of protein and energy supply on the growth and carcass composition of lambs from differing nutritional histories
- R. S. HEGARTY, S. A. NEUTZE, V. H. ODDY
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- Journal:
- The Journal of Agricultural Science / Volume 132 / Issue 3 / May 1999
- Published online by Cambridge University Press:
- 01 May 1999, pp. 361-375
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Effects of dietary energy and protein supply on liveweight (LW) gain and gain of protein, fat and ash in the carcass, and weight and gain of non-carcass organs were determined in 118 weaned crossbred lambs from two nutritional histories at Camden, NSW in 1991. Half of the lambs were fed to achieve and maintain LW at 35 kg (LOW group) and half of the lambs were fed ad libitum until they attained 50 kg LW (HIGH group), during a preliminary period of 126 days. In the subsequent experimental period, lambs were allocated to treatments providing 500, 800, 1200 or 1500 g/day of pelleted diets (123 g crude protein, 10 MJ ME/kg dry matter). Diets at each intake contained either 0, 30, 60 or 90 g of formaldehyde-treated casein (rumen escape protein, REP). This resulted in an experiment comparing LOW and HIGH group lambs at four energy intakes, within which were four rates of inclusion of REP. During the 90-day experimental period, LOW group lambs had higher rates of gain of LW, carcass weight and all non-carcass components than did HIGH lambs (P<0·001). At any rate of carcass gain, LOW lambs contained a significantly lower proportion of fat in carcass gain than did HIGH lambs (P<0·05). After adjustment to a common carcass weight, the carcass of LOW lambs contained a significantly lower mass of fat than did that of HIGH lambs at slaughter (P<0·05).
Carcass fat gain in the experimental period was not affected by LW at the start of that period or by nutritional history once initial LW was accounted for as a covariate. Data were consistent with fat deposition being principally controlled by energy intake over the immediate pre-slaughter period. In contrast, responses to energy intake in the rate of gain of carcass muscles, ash, liver, head and feet and gut tissue were significantly greater in lambs of LOW compared to HIGH nutritional history. A significant component of this effect of nutritional history was attributable to LW differences between LOW and HIGH lambs; however, nutritional history still had a significant effect on these parameters once initial LW was accounted for as a covariate. Nutritional history may also have modified carcass composition by changing the partial efficiency of use of available energy for protein deposition without changing the partial energetic efficiency of fat deposition.
Measurement of protein turnover in the small intestine of lambs. 2. Effects of feed intake
- S. A. NEUTZE, J. M. GOODEN, V. H. ODDY
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- Journal:
- The Journal of Agricultural Science / Volume 128 / Issue 2 / March 1997
- Published online by Cambridge University Press:
- 01 March 1997, pp. 233-246
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This study used an experimental model, described in a companion paper, to examine the effects of feed intake on protein turnover in the small intestine of lambs. Ten male castrate lambs (∼ 10 months old) were offered, via continuous feeders, either 400 (n = 5) or 1200 (n = 5) g/day lucerne chaff, and mean experimental liveweights were 28 and 33 kg respectively. All lambs were prepared with catheters in the cranial mesenteric vein (CMV), femoral artery (FA), jugular vein and abomasum, and a blood flow probe around the CMV. Cr-EDTA (0·139 mg Cr/ml, ∼ 0·2 ml/min) was infused abomasally for 24 h and L-[2,6-3H]phenylalanine (Phe) (420±9·35 μCi into the abomasum) and L-[U-14C]phenylalanine (49·6±3·59 μCi into the jugular vein) were also infused during the last 8 h. Blood from the CMV and FA was sampled during the isotope infusions. At the end of infusions, lambs were killed and tissue (n = 4) and digesta (n = 2) samples removed from the small intestine (SI) of each animal. Transfers of labelled and unlabelled Phe were measured between SI tissue, its lumen and blood, enabling both fractional and absolute rates of protein synthesis and gain to be estimated.
Total SI mass increased significantly with feed intake (P < 0·05), although not on a liveweight basis. Fractional rates of protein gain in the SI tended to increase (P = 0·12) with feed intake; these rates were −16·2 (±13·7) and 23·3 (±15·2) % per day in lambs offered 400 and 1200 g/day respectively. Mean protein synthesis and fractional synthesis rates (FSR), calculated from the mean retention of 14C and 3H in SI tissue, were both positively affected by feed intake (0·01 < P < 0·05). The choice of free Phe pool for estimating precursor specific radioactivity (SRA) for protein synthesis had a major effect on FSR. Assuming that tissue free Phe SRA represented precursor SRA, mean FSR were 81 (±15) and 145 (±24) % per day in lambs offered 400 and 1200 g/day respectively. Corresponding estimates for free Phe SRA in the FA and CMV were 28 (±2·9) and 42 (±3·5) % per day on 400 g/day, and 61 (±2·9) and 94 (±6·0) on 1200 g/day. The correct value for protein synthesis was therefore in doubt, although indirect evidence suggested that blood SRA (either FA or CMV) may be closest to true precursor SRA. This evidence included (i) comparison with flooding dose estimates of FSR, (ii) comparison of 3H[ratio ]14C Phe SRA in free Phe pools with this ratio in SI protein, and (iii) the proportion of SI energy use associated with protein synthesis.
Using the experimental model, the proportion of small intestinal protein synthesis exported was estimated as 0·13–0·27 (depending on the choice of precursor) and was unaffected by feed intake. The contribution of the small intestine to whole body protein synthesis tended to be higher in lambs offered 1200 g/day (0·21) than in those offered 400 g/day (0·13). The data obtained in this study suggested a role for the small intestine in modulating amino acid supply with changes in feed intake. At high intake (1200 g/day), the small intestine increases in mass and CMV uptake of amino acids is less than absorption from the lumen, while at low intake (400 g/day), this organ loses mass and CMV uptake of amino acids exceeds that absorbed. The implications of these findings are discussed.
Measurement of protein turnover in the small intestine of lambs. 1. Development of an experimental model
- S. A. NEUTZE, J. M. GOODEN, V. H. ODDY
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- Journal:
- The Journal of Agricultural Science / Volume 128 / Issue 2 / March 1997
- Published online by Cambridge University Press:
- 01 March 1997, pp. 217-231
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The objective of this study was to develop an experimental model to measure both fractional and absolute rates of protein synthesis in the small intestine of lambs. Six male castrate lambs (∼6 months old, mean liveweight 26 kg) were offered, via continuous feeders, 900 g/day lucerne chaff. They were prepared with catheters in the cranial mesenteric vein (CMV), femoral artery (FA), jugular vein and abomasum, and a blood flow probe around the CMV. Cr-EDTA (0·139 mg Cr/ml, ∼0·2 ml/min) was infused abomasally for 24 h and L-[2,6-3H]phenylalanine (Phe) (441±33·8 μCi into the abomasum) and L-[U-14C]phenylalanine (43·9±4·08 μCi into the jugular) were also infused during the last 8 h. Blood from the CMV and FA was sampled during isotope infusions. At the end of infusions, lambs were killed and tissue and digesta samples removed from four sites along the small intestine (SI). Transfers of labelled and unlabelled Phe were measured between SI tissue, its lumen and blood, enabling both fractional and absolute rates of protein synthesis and gain to be estimated. The total SI protein pool was 84 (±1·7) g and fractional gain rate was 7·5 (±5·5)% per day. Mean protein synthesis and fractional synthesis rates (FSR) were calculated from the mean retention of 14C and 3H in SI tissue. FSR tended to increase caudally along the SI (although P > 0·05). The choice of free Phe pool for estimating precursor specific radioactivity (SRA) for protein synthesis had a significant effect on FSR. Assuming that tissue free Phe SRA represented precursor SRA gave a mean FSR of 129 (±24)% per day. Corresponding estimates for free Phe SRA in the FA and CMV were 20 (±1·8) and 30 (±3·1)% per day respectively. The correct value for protein synthesis was therefore in doubt, although indirect evidence suggested that blood SRA (either FA or CMV) may be closest to true precursor SRA. This evidence included (i) comparison with flooding dose estimates of FSR, (ii) comparison of 3H[ratio ]14C Phe SRA in free Phe pools with this ratio in SI protein, and (iii) the proportion of SI energy use associated with protein synthesis. Advantages of the present experimental model compared to other methods included (i) measurements of both protein synthesis and gain, and hence, all components of turnover, (ii) measurement of absolute as well as fractional rates of synthesis and gain, (iii) inclusion of proteins which are synthesised and exported, and (iv) concurrent measurement of protein synthesis and energy utilization by the small intestine.
Interrelationships between amino acid and glucose metabolism in lambs of different dietary history supplemented with rumen escape protein
- V. H. ODDY, S. R. EDWARDS, H. M. WARREN, P. A. SPECK, P. J. NICHOLLS, S. A. NEUTZE
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- Journal:
- The Journal of Agricultural Science / Volume 128 / Issue 1 / February 1997
- Published online by Cambridge University Press:
- 01 February 1997, pp. 105-116
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Changes in amino acid and glucose metabolism in response to increments of rumen escape protein (REP) were studied in groups of lambs of three differing dietary histories and consequent weights, but similar ages. Crossbred wether lambs (Merino × (Border Leicester × Merino)) were fed to obtain three distinct growth patterns. The LW group (n = 15) were offered a low quality roughage diet throughout the experiment. The MW group (n = 19) were offered a high quality mixed diet followed by the same low quality diet as LW lambs. The HW group (n = 8) were offered a high quality mixed diet throughout. All diets were offered once daily ad libitum. The LW, MW and HW groups had liveweights of 18, 32 and 41 kg respectively at the commencement of supplementation, and were 33±0·1 weeks of age. REP supplements (formaldehyde-treated casein) were offered at 0, 20, 40, 60 or 80 g/day to MW and LW lambs and at 0 or 40 g/day to HW lambs.
REP increased basal digestible organic matter intake (DOMI), liveweight gain (LWG) and urinary N excretion and tended to increase N balance in LW and MW lambs. DOMI, N intake, N balance and LWG were all higher (P < 0·05) in HW compared to MW and LW lambs. REP tended (P < 0·10) to increase LWG in each dietary history group.
Blood glucose concentration was higher (P < 0·01) in HW than in other lambs but was not significantly altered by REP supplementation. Irreversible loss of glucose was greater (P < 0·01) in HW lambs and increased (P < 0·001) with REP for LW and MW lambs. REP increased (P < 0·05) phenylalanine (Phe) concentration in blood, Phe flux and oxidation and whole body rates of protein synthesis and degradation. HW lambs had higher (P < 0·05) values for all these parameters than did MW and LW lambs.
REP increased (P < 0·05) plasma concentrations of insulin-like growth factor-1, and plasma insulin increased (P < 0·05) in MW but not in LW or HW lambs. REP had no effect on plasma growth hormone (GH) concentration. Plasma concentration of insulin was higher (P < 0·05) in HW than in MW or LW lambs, while GH was not significantly affected by dietary history.
The results show that supplementation of ruminant diets with REP increases the rate of flux and oxidation of amino acids, and the rate of glucose utilization. Amino acid supply appears to influence glucose utilization more through oxidation rate than supply, and this relationship is affected by previous dietary history (weight for age) and energy availability, either from the diet or from body stores.
Kinetics of nitrogen transfer across the rumen wall of sheep given a low-protein roughage
- S. A. Neutze, R. C. Kellaway, G. J. Faichney
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- Journal:
- British Journal of Nutrition / Volume 56 / Issue 2 / September 1986
- Published online by Cambridge University Press:
- 09 March 2007, pp. 497-507
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- September 1986
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1. The significance of blood urea-nitrogen transfer to the rumen was examined in sheep given alkali-treated wheat straw supplemented with 3.5 (diet A), 5.9 (diet B) and 11.6 (diet C) g urea-N/kg dry matter (DM).
2. Mean voluntary intakes of DM (g/d) were 897, 1149 and 1225 for diets A, B and C respectively, indicating significant (P < 0.05) intake responses to urea supplementation. Digestion studies were conducted at 90% of voluntary intake. Dietary N intakes (g/d) were 7.1, 11.5 and 18.6 for diets A, B and C respectively.
3. Absorption of ammonia-N from the rumen (g/d) was 3.5, 6.7 and 8.9 for diets A, B and C respectively, with all dietary differences being significantly different (P < 0.05).
4. Non-ammonia-N (NAN) leaving the abomasum (g/d) was 9.6, 12.7 and 14.8 for diets A, B and C respectively. Microbial N leaving the abomdsum (g/d) was 6.8, 9.6 and 10.7 for diets A, B and C respectively. Hence, significantly (P < 0.05) more N was provided to the intestines with increased urea supplementation. Net efficiencies of microbial protein synthesis (g N/kg organic matter apparently digested in the rumen), estimated from 16N incorporation, were 24.2, 23.7 and 25.3 for diets A, B and C respectively, and were not significantly different (P > 0.05).
5. Calculated proportions of microbial N derived from rumen NH2-N were 1.05, 0.95 and 0.91 for diets A, B and C respectively, reflecting the high proportion of total N as urea-N in the diets. Proportions of microbial N derived from blood urea-N were 0.31, 0.21 and 0.12 for diets A, B and C respectively, indicating a decreasing significance of blood urea as a source of microbial N as dietary urea increased (P < 0.05).
6. Transfer of blood urea-N to the rumen (g/d) was 3.8, 4.7 and 2.6 for diets A, B and C respectively, being significantly (P < 0.05) lower on diet C. Using an estimate, of the salivary contribution of urea-N to the rumen, it was concluded that there was a significant though not large transfer of blood urea-N across the rumen wall on all diets.
7. Net transfer of blood urea-N to the rumen was estimated from a two-pool model and was +0.4 g/d for diet A, though this was not significantly different from zero. Net transfers for diets B and C were -2.0 and - 6.3 g N/d respectively.
8. Significant intake responses to exogenous urea supplementation were observed because of a limited capacity to recycle N to the rumen under the conditions of low dietary N supply imposed.