Gerald Lobley - Academia.edu (original) (raw)
Papers by Gerald Lobley
Clinical Science, May 1, 2002
Obesity is commonly associated with a high incidence and prevalence of dyslipidaemia, cardiovascu... more Obesity is commonly associated with a high incidence and prevalence of dyslipidaemia, cardiovascular disease and Type II diabetes. Interestingly, studies have also reported decreased antioxidant levels in obese subjects. This may constitute an independent risk factor in the pathogenesis of coronary artery disease as obese subjects would have a decreased capacity to prevent the oxidative modification of low-density lipoproteins, which is a mechanism suggested as central to the development of atherogenesis. As part of a study to investigate responses to weight loss, we have assessed the effects on GSH status of a decrease in body mass of 5 %, either after 6 days of complete starvation or 11 days of a very low calorie diet (2.55 MJ/day). There were significant differences between the two groups in the synthesis rate of erythrocyte GSH in response to weight loss. Both the fractional and the erythrocyte synthesis rate of GSH decreased significantly (P 0.01) in the starvation group by 22 % and 16 % respectively. In contrast, no change in synthesis rates was observed in the very low calorie diet group (P 0.05). Total erythrocyte concentration of GSH was unaffected by the weight loss within both groups. These results suggest that erythrocyte GSH synthesis is depressed in response to a very rapid weight loss induced by fasting. An acute reduction in GSH synthesis in response to a rapid weight loss may constitute a risk factor during periods of increased GSH demands.
Journal of Dairy Science, 2001
Movements of N across the gut can be more than double N intake and thus have major effects on N m... more Movements of N across the gut can be more than double N intake and thus have major effects on N metabolism of the ruminant. These movements may be associated with net losses, as occurs with production of ammonia or irreversible loss of secreted proteins, or as a means by which N products can be salvaged and used for anabolic purposes, e.g., use of urea-N as a source for microbial protein synthesis. Understanding the conditions and mechanisms that underlie these movements should enhance our ability to manipulate feed and husbandry to improve production efficiency. Between 40 and 80% of urea-N synthesized by the liver is returned to the gut, and 35 to 55% of this is converted to further anabolic use in both cattle and sheep. While some of this anabolic use may occur in the small intestine, most involves the rumen, a process that is dependent on energy supply under conditions in which the efficiency of conversion of digested N to amino acids is low. Current data would suggest that sheep are more efficient (P < 0.001) than cattle in such conversions. Dairy cattle are also more efficient than steers (P < 0.05), and this may be related to the nature of the rations studied experimentally (type and quality of the forage). The proportion of digestible N lost as ammonia is greater (P < 0.001) for steers fed forages than concentrates. As much as 40% of ammonia absorbed from the gut is derived from endogenous urea-N and forms part of a cycle that conserves N within the body. Loss of N also occurs from intrarumen recycling due to the presence of proteolytic bacteria and protozoa. Their removal, or inhibition, can lead to marked improvements in protein flow to the duodenum. Net inflows due to endogenous protein secretions amount to 30 to 40% of apparent absorption across the small intestine, and 30 to 70% of this may be lost through oxidation. The relative profiles of most amino acids are unchanged during the absorptive process, but disproportional losses can occur for threonine, valine, and cysteine, probably due to poor reabsorption from secretions such as the mucins. Preferred strategies to enhance anabolic performance involves increasing conversion of urea-N to anabolic products and reducing secretory losses due to the presence of environmental or dietary factors.
Leanness in Domestic Birds, 1988
Publisher Summary Alterations in partition of nutrients between fat and protein can result from t... more Publisher Summary Alterations in partition of nutrients between fat and protein can result from three types of interactions. The first involves the removal of fat with no alteration in the rate of protein gain. The second involves a similar amount of total energy deposition but with emphasis shifted toward protein, the rate of fat gain will fall as a passive consequence. The third involves a combination of the first two in which increases in the deposition of protein energy are accompanied by an active reduction in rates of lipid accretion. The chapter also discusses the dynamic aspects of protein metabolism and examines some of the controls exerted over the fates of amino acids. It also discusses the hormonal influences which, in concert or in opposition, dictate whether amino acids are retained as new protein, used as energy sources, or provide carbon for either carbohydrate or fat synthesis. The chapter also explains how these may differ between lean and fat strains of various mammalian species.
Biochemical Journal, 1980
1. A method is described by which, from analysis of terminal samples, the rate constants that def... more 1. A method is described by which, from analysis of terminal samples, the rate constants that define the changes in specific radioactivity of free amino acids during continuous infusions can be estimated. The method involves the infusion of 3H-labelled and 14C-labelled forms of an amino acid for different, but overlapping, periods. 2. The procedure was developed for infusions of proline and tyrosine into New Zealand White rabbits and the rate constants were determined for blood and muscle. 3. The rate constant for equilibrium of radioactive free proline was much lower in muscle than in blood, and indicated that a plateau condition may not be attained in muscle by the end of a 6 h infusion. 4. Comparison of the ratio of areas under the curves of estimated specific radioactivity plotted versus time with the 3H/14C ratio of bound amino acid in muscle protein suggested that radioactive proline and tyrosine may be incorporated preferentially from an extracellular rather than an intracell...
The Proceedings of the Nutrition Society, 1978
![Research paper thumbnail of Tissue sequestration of C-labelled bicarbonate [HCO3−] in fed and fasted young sheep](https://attachments.academia-assets.com/100930983/thumbnails/1.jpg)
](Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology, 1999
Carbon dioxide entry rates (CER) based on isotopic activities in either expired air or blood foll... more Carbon dioxide entry rates (CER) based on isotopic activities in either expired air or blood following a 24-h intravenous infusion of [ 13 C]-and [ 14 C] sodium bicarbonate were compared with CO 2 production quantified by respiration hood in young sheep (28-30 kg) either fed (three animals) or fasted (three animals). CO 2 production increased with intake (5.2 vs 10.3 mol/day; PB 0.001) as did CER values based on expired air (9.9 vs 18.6 mol/day; PB0.001) or blood (7.5 vs 16.5 mol/day; P B0.001). The differences between air and blood CER values were significant (PB0.001). There were no differences, however, when data were compared between [ 13 C] and [ 14 C] measurements. How much of these differences could be attributed to sequestration of label in body tissues was examined at the end of the infusion. The highest specific radioactivities (dpm/g dry matter) in acid-fast tissue material were observed for the more metabolically active tissues, liver, jejunum and kidney, with the lowest values for fat and muscle. When tissue mass was taken into account, however, the largest proportions of the dose sequestered were in bone muscle, skin and fat with significantly more retained for the former three (PB 0.01) during fasting. Separately, losses as urinary urea were also quantified. Total measured sequestration of label only accounted for approximately 24-44% of the difference between CER and CO 2 production.
Biochemical Society Transactions, 1977
Proceedings of the British Society of Animal Production (1972), 1992
With the failure of current nutritional schemes for dairy ruminants to predict yields of milk and... more With the failure of current nutritional schemes for dairy ruminants to predict yields of milk and milk components, and perceptions of milk's nutritional value following recommendations to reduce dietary fat intake, an integrated approach to feeding and metabolism needs to be developed. Such a system must therefore be ‘metabolite’ based.An ability to predict changes in milk constituent output in response to alterations in nutrition requires, in the first instance, the identification of specific precursors for milk component synthesis in the lactating mammary gland. Arteriovenous differences across the mammary gland indicate that blood free amino acids (AA) are either taken-up by the gland in excess, equal to, or in insufficient amounts compared to their output in milk (1). Isotope labelling experiments have indicated that, in addition to AA free in blood, the mammary gland utilises a substantial amount of AA derived from constitutive mammary gland protein breakdown (2). The prese...
Proceedings of the British Society of Animal Production (1972), 1994
Amino acid requirements for energy metabolism and protein turnover within the gastrointestinal tr... more Amino acid requirements for energy metabolism and protein turnover within the gastrointestinal tract are substantial and may be met from luminal and arterial pools of amino acids. Several studies have demonstrated that the quantity of amino acids appearing in the portal blood does not balance apparent disappearance from the intestinal lumen and that changing diet or the availability of energy-yielding substrates to the gut tissues may influence the uptake of amino acids into the portal blood (Seal & Reynolds, 1993). For example, increased net absorption of amino acids was observed in animals receiving exogenous intraruminal propionate (Seal & Parker, 1991) and this was accompanied by changes in glucose utilisation by the gut tissues. In contrast, there was no apparent change in net uptake of [l-13C]-leucine into the portal vein of sheep receiving short term intraduodenal infusions of glucose (Piccioli Cappelli et al, 1993). This experiment was designed to further investigate the eff...
Journal of dairy science, 2011
The objectives of the current study were to determine the fate and contribution to Met kinetics o... more The objectives of the current study were to determine the fate and contribution to Met kinetics of 2-hydroxy-4-(methylthio)butanoate (HMTBA) at the whole-body, splanchnic, and mammary levels. Four multicatheterized cows (31.3 kg of milk/d; 17.7 kg of DMI/d) were used in a crossover design, with two 1-wk periods, to determine the metabolic fate of HMTBA and its effect on Met metabolism. Over the last 2 d of each period, cows were infused, via a jugular vein, with saline or HMTBA (Alimet, Novus International Inc., St. Louis, Mo) at the rate of 36 g/d. During the last 8h, the HMTBA infusion was substituted by equimolar [1-(13)C]HMTBA (8.79 mmol/h) and l[methyl-(2)H(3)]Met (1.31 mmol/h) was infused in all cows. During the last 5h, hourly samples (n=6) were collected to determine plasma flows plus the isotopic enrichments (IE) and concentrations of HMTBA ((13)C) and Met (both (13)C and (2)H(3)) in plasma from an artery plus portal, hepatic, and mammary veins. The IE of [(13)C] and [(2)H(...
Journal of Animal Science, 2012
Although in dairy cows the mammary gland (MG) is the major net user of essential AA (EAA) supply,... more Although in dairy cows the mammary gland (MG) is the major net user of essential AA (EAA) supply, milk protein synthesis from absorbed EAA is not a straightforward process. Early studies identified 2 groups of EAA based on different pattern of mammary utilization: group 1 [Met, Phe (+Tyr), Trp], where MG uptake was similar to secretion in milk protein, and group 2 (Arg, Ile, Leu, Lys, Thr, and Val), where uptake exceeded milk protein output. This review examines the validity of this classification under variable protein supply through a meta-analysis, with the outcomes then explained with studies in which the fates of individual EAA were monitored using isotope approaches. For the meta-analysis, the Fick principle, based on stoichiometric transfer of Phe+Tyr uptake to milk protein, was used to estimate mammary plasma flow across all studies. This approach was judged acceptable because doubling Phe supply did not result in mammary oxidation of Phe+Tyr and either limited or no contribution of peptides to Phe and Tyr mammary supply could be detected. The AA content of proteins synthesized by the MG was estimated from milk protein composition, and the uptake-to-output ratio (U:O) for individual AA was re-calculated based on these assumptions. Analysis of individual samples by isotopic dilution resulted in reduced variance compared with analysis on pooled samples performed with an AA analyzer. Globally, the U:O of His and Met is maintained close to unity under variable protein supply. The group 2 AA could be subdivided. First, the U:O for group "2v" AA (Ile, Leu, Val, and Lys) is greater than 1 and varied with protein supply. Accordingly, the increased U:O of Leu, induced by duodenal casein infusion, led to extra-mammary Leu oxidation. Decreasing Lys supply decreased Lys U:O and the associated transfer of N to non-EAA, mainly to Glx, Asx, Ser, and Ala. Second, the U:O of group "2nv" AA, Arg and Thr, does not vary with protein supply. The Arg U:O averages 2.5, whereas the Thr U:O, albeit averaging 1.2, does not differ from unity. Excess of both these AA is probably directed toward the synthesis of non-EAA rather than energy supply. Overall, the ability of the MG to use excess EAA-N supply offers alternative sources of N and C for energy provision, lactose synthesis and non-EAA synthesis. The latter function spares dietary non-EAA for other necessary processes, such as gluconeogenesis and energy supply, in other tissues to support lactation.
Journal of dairy science, 2012
Rumen-protected forms of Met contain an equimolar mixture of the D- and L-isomers. Only L-Met can... more Rumen-protected forms of Met contain an equimolar mixture of the D- and L-isomers. Only L-Met can be directly used for protein synthesis, but it is unclear how much of the D-isomer can be transformed into L-Met in ruminants. Four lactating dairy cows, with an average milk yield of 32.4 kg/d, received a basal diet (12.5% crude protein, supplying 1,718 g/d of metabolizable protein) in 12 equal meals per day plus an abomasal infusion of amino acids (590 g/d, casein profile without Met). They were used in 3 consecutive studies to determine utilization of D-Met. First, the cows each received portal vein infusions for d of 5, 10, or 15 g/d of DL-Met in a Youden square. On the last day of each period, 6 arterial samples were collected at 45-min intervals. Concentrations of L- and D-Met were determined on a chiral column by gas chromatography-mass spectrometry. Portal infusion of 5, 10, and 15 g/d of DL-Met increased plasma total Met concentrations (19.7, 25.0, and 34.4±0.6 μM) and the prop...
British Journal of Nutrition, 2000
Eighteen pure-bred steers (live weight 350 kg) from each of two breeds, Aberdeen Angus (AA) and C... more Eighteen pure-bred steers (live weight 350 kg) from each of two breeds, Aberdeen Angus (AA) and Charolais (CH), were split into three equal groups (six animals each) and offered three planes of nutrition during a 20-week period. The same ration formulation was offered to all animals with amounts adjusted at 3-week intervals to give predicted average weight gains of either 1·0 kg/d (M/M group) or 1·4 kg/d (H/H group). The remaining group (M/H) were offered the same amount of ration as the M/M group until 10 weeks before slaughter when the ration was increased to H. Data on animal performance, carcass characteristics and fibre-type composition in skeletal muscle are presented elsewhere (; ). On three occasions (17, 10 and 2 weeks before slaughter) the animals were transferred to metabolism stalls for 1 week, during which total urine collection for quantification of Nτ-methylhistidine (Nτ-MeH) elimination was performed for 4 d. On the last day, animals were infused for 11 h with [2H5] ...
British Journal of Nutrition, 2020
Journal of Animal and Feed Sciences, 2004
Urea metabolism was estimated in dairy cows fed forage conserved as hay, formic acidtreated silag... more Urea metabolism was estimated in dairy cows fed forage conserved as hay, formic acidtreated silage or microbial inoculated silage. Use of [ 15 N 15 N]urea kinetics indicated that urea-N production was greatest (P<0.05) with inoculated silage. Gut entry rate of urea-N was not affected by treatments. Urea-N recycled to ornithine cycle tended to be greater (P<0.08) when cows received inoculated silage compared to when fed acid-treated silage. The proportion of recycled urea-N lost in faeces was greater (P<0.05) when cows were fed forage conserved as hay as opposed to when fed inoculated silage. Overall, urea metabolism was similar between cows fed formic acid-treated silage or hay. Inoculated silage, however, increases urea production and recycling to the ornithine cycle.
Journal of dairy science, 2007
The objective of this study was to measure net portal absorption of 2-hydroxy-4-methylthiobutanoa... more The objective of this study was to measure net portal absorption of 2-hydroxy-4-methylthiobutanoate (HMTBA) in dairy cows. Four multicatheterized lactating cows were used in a cross-over design with 7-d experimental periods. They were fed every other hour a total mixed ration and received, in addition, twice a day, 12.5 or 25 g/meal of HMTBA. On the last day of treatment, net portal absorption of HMTBA was numerically greater after the 25-g compared with the 12.5-g bolus meal of HMTBA, and the amount absorbed relative to the dose ingested was unchanged between treatments averaging 11.2 +/- 4.7% of the dose. This represents a minimum value of HMTBA availability because it does not take into account any HMTBA metabolized to Met by gut tissues (in sheep this amounted to another 5% of the dose). A rapid method to estimate net portal absorption based on temporal variations of the peripheral plasma HMTBA concentrations following the HMTBA meal is also presented. Based on the good relation...
Journal of Dairy Science, 2007
pothesis that supplemental Gln would reduce glucose utilization across the gut or increase liver ... more pothesis that supplemental Gln would reduce glucose utilization across the gut or increase liver gluconeogenesis or mammary glutamine uptake to increase milk protein synthesis.
The Proceedings of the Nutrition Society, 1978
Clinical Science, May 1, 2002
Obesity is commonly associated with a high incidence and prevalence of dyslipidaemia, cardiovascu... more Obesity is commonly associated with a high incidence and prevalence of dyslipidaemia, cardiovascular disease and Type II diabetes. Interestingly, studies have also reported decreased antioxidant levels in obese subjects. This may constitute an independent risk factor in the pathogenesis of coronary artery disease as obese subjects would have a decreased capacity to prevent the oxidative modification of low-density lipoproteins, which is a mechanism suggested as central to the development of atherogenesis. As part of a study to investigate responses to weight loss, we have assessed the effects on GSH status of a decrease in body mass of 5 %, either after 6 days of complete starvation or 11 days of a very low calorie diet (2.55 MJ/day). There were significant differences between the two groups in the synthesis rate of erythrocyte GSH in response to weight loss. Both the fractional and the erythrocyte synthesis rate of GSH decreased significantly (P 0.01) in the starvation group by 22 % and 16 % respectively. In contrast, no change in synthesis rates was observed in the very low calorie diet group (P 0.05). Total erythrocyte concentration of GSH was unaffected by the weight loss within both groups. These results suggest that erythrocyte GSH synthesis is depressed in response to a very rapid weight loss induced by fasting. An acute reduction in GSH synthesis in response to a rapid weight loss may constitute a risk factor during periods of increased GSH demands.
Journal of Dairy Science, 2001
Movements of N across the gut can be more than double N intake and thus have major effects on N m... more Movements of N across the gut can be more than double N intake and thus have major effects on N metabolism of the ruminant. These movements may be associated with net losses, as occurs with production of ammonia or irreversible loss of secreted proteins, or as a means by which N products can be salvaged and used for anabolic purposes, e.g., use of urea-N as a source for microbial protein synthesis. Understanding the conditions and mechanisms that underlie these movements should enhance our ability to manipulate feed and husbandry to improve production efficiency. Between 40 and 80% of urea-N synthesized by the liver is returned to the gut, and 35 to 55% of this is converted to further anabolic use in both cattle and sheep. While some of this anabolic use may occur in the small intestine, most involves the rumen, a process that is dependent on energy supply under conditions in which the efficiency of conversion of digested N to amino acids is low. Current data would suggest that sheep are more efficient (P < 0.001) than cattle in such conversions. Dairy cattle are also more efficient than steers (P < 0.05), and this may be related to the nature of the rations studied experimentally (type and quality of the forage). The proportion of digestible N lost as ammonia is greater (P < 0.001) for steers fed forages than concentrates. As much as 40% of ammonia absorbed from the gut is derived from endogenous urea-N and forms part of a cycle that conserves N within the body. Loss of N also occurs from intrarumen recycling due to the presence of proteolytic bacteria and protozoa. Their removal, or inhibition, can lead to marked improvements in protein flow to the duodenum. Net inflows due to endogenous protein secretions amount to 30 to 40% of apparent absorption across the small intestine, and 30 to 70% of this may be lost through oxidation. The relative profiles of most amino acids are unchanged during the absorptive process, but disproportional losses can occur for threonine, valine, and cysteine, probably due to poor reabsorption from secretions such as the mucins. Preferred strategies to enhance anabolic performance involves increasing conversion of urea-N to anabolic products and reducing secretory losses due to the presence of environmental or dietary factors.
Leanness in Domestic Birds, 1988
Publisher Summary Alterations in partition of nutrients between fat and protein can result from t... more Publisher Summary Alterations in partition of nutrients between fat and protein can result from three types of interactions. The first involves the removal of fat with no alteration in the rate of protein gain. The second involves a similar amount of total energy deposition but with emphasis shifted toward protein, the rate of fat gain will fall as a passive consequence. The third involves a combination of the first two in which increases in the deposition of protein energy are accompanied by an active reduction in rates of lipid accretion. The chapter also discusses the dynamic aspects of protein metabolism and examines some of the controls exerted over the fates of amino acids. It also discusses the hormonal influences which, in concert or in opposition, dictate whether amino acids are retained as new protein, used as energy sources, or provide carbon for either carbohydrate or fat synthesis. The chapter also explains how these may differ between lean and fat strains of various mammalian species.
Biochemical Journal, 1980
1. A method is described by which, from analysis of terminal samples, the rate constants that def... more 1. A method is described by which, from analysis of terminal samples, the rate constants that define the changes in specific radioactivity of free amino acids during continuous infusions can be estimated. The method involves the infusion of 3H-labelled and 14C-labelled forms of an amino acid for different, but overlapping, periods. 2. The procedure was developed for infusions of proline and tyrosine into New Zealand White rabbits and the rate constants were determined for blood and muscle. 3. The rate constant for equilibrium of radioactive free proline was much lower in muscle than in blood, and indicated that a plateau condition may not be attained in muscle by the end of a 6 h infusion. 4. Comparison of the ratio of areas under the curves of estimated specific radioactivity plotted versus time with the 3H/14C ratio of bound amino acid in muscle protein suggested that radioactive proline and tyrosine may be incorporated preferentially from an extracellular rather than an intracell...
The Proceedings of the Nutrition Society, 1978
Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology, 1999
Carbon dioxide entry rates (CER) based on isotopic activities in either expired air or blood foll... more Carbon dioxide entry rates (CER) based on isotopic activities in either expired air or blood following a 24-h intravenous infusion of [ 13 C]-and [ 14 C] sodium bicarbonate were compared with CO 2 production quantified by respiration hood in young sheep (28-30 kg) either fed (three animals) or fasted (three animals). CO 2 production increased with intake (5.2 vs 10.3 mol/day; PB 0.001) as did CER values based on expired air (9.9 vs 18.6 mol/day; PB0.001) or blood (7.5 vs 16.5 mol/day; P B0.001). The differences between air and blood CER values were significant (PB0.001). There were no differences, however, when data were compared between [ 13 C] and [ 14 C] measurements. How much of these differences could be attributed to sequestration of label in body tissues was examined at the end of the infusion. The highest specific radioactivities (dpm/g dry matter) in acid-fast tissue material were observed for the more metabolically active tissues, liver, jejunum and kidney, with the lowest values for fat and muscle. When tissue mass was taken into account, however, the largest proportions of the dose sequestered were in bone muscle, skin and fat with significantly more retained for the former three (PB 0.01) during fasting. Separately, losses as urinary urea were also quantified. Total measured sequestration of label only accounted for approximately 24-44% of the difference between CER and CO 2 production.
Biochemical Society Transactions, 1977
Proceedings of the British Society of Animal Production (1972), 1992
With the failure of current nutritional schemes for dairy ruminants to predict yields of milk and... more With the failure of current nutritional schemes for dairy ruminants to predict yields of milk and milk components, and perceptions of milk's nutritional value following recommendations to reduce dietary fat intake, an integrated approach to feeding and metabolism needs to be developed. Such a system must therefore be ‘metabolite’ based.An ability to predict changes in milk constituent output in response to alterations in nutrition requires, in the first instance, the identification of specific precursors for milk component synthesis in the lactating mammary gland. Arteriovenous differences across the mammary gland indicate that blood free amino acids (AA) are either taken-up by the gland in excess, equal to, or in insufficient amounts compared to their output in milk (1). Isotope labelling experiments have indicated that, in addition to AA free in blood, the mammary gland utilises a substantial amount of AA derived from constitutive mammary gland protein breakdown (2). The prese...
Proceedings of the British Society of Animal Production (1972), 1994
Amino acid requirements for energy metabolism and protein turnover within the gastrointestinal tr... more Amino acid requirements for energy metabolism and protein turnover within the gastrointestinal tract are substantial and may be met from luminal and arterial pools of amino acids. Several studies have demonstrated that the quantity of amino acids appearing in the portal blood does not balance apparent disappearance from the intestinal lumen and that changing diet or the availability of energy-yielding substrates to the gut tissues may influence the uptake of amino acids into the portal blood (Seal & Reynolds, 1993). For example, increased net absorption of amino acids was observed in animals receiving exogenous intraruminal propionate (Seal & Parker, 1991) and this was accompanied by changes in glucose utilisation by the gut tissues. In contrast, there was no apparent change in net uptake of [l-13C]-leucine into the portal vein of sheep receiving short term intraduodenal infusions of glucose (Piccioli Cappelli et al, 1993). This experiment was designed to further investigate the eff...
Journal of dairy science, 2011
The objectives of the current study were to determine the fate and contribution to Met kinetics o... more The objectives of the current study were to determine the fate and contribution to Met kinetics of 2-hydroxy-4-(methylthio)butanoate (HMTBA) at the whole-body, splanchnic, and mammary levels. Four multicatheterized cows (31.3 kg of milk/d; 17.7 kg of DMI/d) were used in a crossover design, with two 1-wk periods, to determine the metabolic fate of HMTBA and its effect on Met metabolism. Over the last 2 d of each period, cows were infused, via a jugular vein, with saline or HMTBA (Alimet, Novus International Inc., St. Louis, Mo) at the rate of 36 g/d. During the last 8h, the HMTBA infusion was substituted by equimolar [1-(13)C]HMTBA (8.79 mmol/h) and l[methyl-(2)H(3)]Met (1.31 mmol/h) was infused in all cows. During the last 5h, hourly samples (n=6) were collected to determine plasma flows plus the isotopic enrichments (IE) and concentrations of HMTBA ((13)C) and Met (both (13)C and (2)H(3)) in plasma from an artery plus portal, hepatic, and mammary veins. The IE of [(13)C] and [(2)H(...
Journal of Animal Science, 2012
Although in dairy cows the mammary gland (MG) is the major net user of essential AA (EAA) supply,... more Although in dairy cows the mammary gland (MG) is the major net user of essential AA (EAA) supply, milk protein synthesis from absorbed EAA is not a straightforward process. Early studies identified 2 groups of EAA based on different pattern of mammary utilization: group 1 [Met, Phe (+Tyr), Trp], where MG uptake was similar to secretion in milk protein, and group 2 (Arg, Ile, Leu, Lys, Thr, and Val), where uptake exceeded milk protein output. This review examines the validity of this classification under variable protein supply through a meta-analysis, with the outcomes then explained with studies in which the fates of individual EAA were monitored using isotope approaches. For the meta-analysis, the Fick principle, based on stoichiometric transfer of Phe+Tyr uptake to milk protein, was used to estimate mammary plasma flow across all studies. This approach was judged acceptable because doubling Phe supply did not result in mammary oxidation of Phe+Tyr and either limited or no contribution of peptides to Phe and Tyr mammary supply could be detected. The AA content of proteins synthesized by the MG was estimated from milk protein composition, and the uptake-to-output ratio (U:O) for individual AA was re-calculated based on these assumptions. Analysis of individual samples by isotopic dilution resulted in reduced variance compared with analysis on pooled samples performed with an AA analyzer. Globally, the U:O of His and Met is maintained close to unity under variable protein supply. The group 2 AA could be subdivided. First, the U:O for group "2v" AA (Ile, Leu, Val, and Lys) is greater than 1 and varied with protein supply. Accordingly, the increased U:O of Leu, induced by duodenal casein infusion, led to extra-mammary Leu oxidation. Decreasing Lys supply decreased Lys U:O and the associated transfer of N to non-EAA, mainly to Glx, Asx, Ser, and Ala. Second, the U:O of group "2nv" AA, Arg and Thr, does not vary with protein supply. The Arg U:O averages 2.5, whereas the Thr U:O, albeit averaging 1.2, does not differ from unity. Excess of both these AA is probably directed toward the synthesis of non-EAA rather than energy supply. Overall, the ability of the MG to use excess EAA-N supply offers alternative sources of N and C for energy provision, lactose synthesis and non-EAA synthesis. The latter function spares dietary non-EAA for other necessary processes, such as gluconeogenesis and energy supply, in other tissues to support lactation.
Journal of dairy science, 2012
Rumen-protected forms of Met contain an equimolar mixture of the D- and L-isomers. Only L-Met can... more Rumen-protected forms of Met contain an equimolar mixture of the D- and L-isomers. Only L-Met can be directly used for protein synthesis, but it is unclear how much of the D-isomer can be transformed into L-Met in ruminants. Four lactating dairy cows, with an average milk yield of 32.4 kg/d, received a basal diet (12.5% crude protein, supplying 1,718 g/d of metabolizable protein) in 12 equal meals per day plus an abomasal infusion of amino acids (590 g/d, casein profile without Met). They were used in 3 consecutive studies to determine utilization of D-Met. First, the cows each received portal vein infusions for d of 5, 10, or 15 g/d of DL-Met in a Youden square. On the last day of each period, 6 arterial samples were collected at 45-min intervals. Concentrations of L- and D-Met were determined on a chiral column by gas chromatography-mass spectrometry. Portal infusion of 5, 10, and 15 g/d of DL-Met increased plasma total Met concentrations (19.7, 25.0, and 34.4±0.6 μM) and the prop...
British Journal of Nutrition, 2000
Eighteen pure-bred steers (live weight 350 kg) from each of two breeds, Aberdeen Angus (AA) and C... more Eighteen pure-bred steers (live weight 350 kg) from each of two breeds, Aberdeen Angus (AA) and Charolais (CH), were split into three equal groups (six animals each) and offered three planes of nutrition during a 20-week period. The same ration formulation was offered to all animals with amounts adjusted at 3-week intervals to give predicted average weight gains of either 1·0 kg/d (M/M group) or 1·4 kg/d (H/H group). The remaining group (M/H) were offered the same amount of ration as the M/M group until 10 weeks before slaughter when the ration was increased to H. Data on animal performance, carcass characteristics and fibre-type composition in skeletal muscle are presented elsewhere (; ). On three occasions (17, 10 and 2 weeks before slaughter) the animals were transferred to metabolism stalls for 1 week, during which total urine collection for quantification of Nτ-methylhistidine (Nτ-MeH) elimination was performed for 4 d. On the last day, animals were infused for 11 h with [2H5] ...
British Journal of Nutrition, 2020
Journal of Animal and Feed Sciences, 2004
Urea metabolism was estimated in dairy cows fed forage conserved as hay, formic acidtreated silag... more Urea metabolism was estimated in dairy cows fed forage conserved as hay, formic acidtreated silage or microbial inoculated silage. Use of [ 15 N 15 N]urea kinetics indicated that urea-N production was greatest (P<0.05) with inoculated silage. Gut entry rate of urea-N was not affected by treatments. Urea-N recycled to ornithine cycle tended to be greater (P<0.08) when cows received inoculated silage compared to when fed acid-treated silage. The proportion of recycled urea-N lost in faeces was greater (P<0.05) when cows were fed forage conserved as hay as opposed to when fed inoculated silage. Overall, urea metabolism was similar between cows fed formic acid-treated silage or hay. Inoculated silage, however, increases urea production and recycling to the ornithine cycle.
Journal of dairy science, 2007
The objective of this study was to measure net portal absorption of 2-hydroxy-4-methylthiobutanoa... more The objective of this study was to measure net portal absorption of 2-hydroxy-4-methylthiobutanoate (HMTBA) in dairy cows. Four multicatheterized lactating cows were used in a cross-over design with 7-d experimental periods. They were fed every other hour a total mixed ration and received, in addition, twice a day, 12.5 or 25 g/meal of HMTBA. On the last day of treatment, net portal absorption of HMTBA was numerically greater after the 25-g compared with the 12.5-g bolus meal of HMTBA, and the amount absorbed relative to the dose ingested was unchanged between treatments averaging 11.2 +/- 4.7% of the dose. This represents a minimum value of HMTBA availability because it does not take into account any HMTBA metabolized to Met by gut tissues (in sheep this amounted to another 5% of the dose). A rapid method to estimate net portal absorption based on temporal variations of the peripheral plasma HMTBA concentrations following the HMTBA meal is also presented. Based on the good relation...
Journal of Dairy Science, 2007
pothesis that supplemental Gln would reduce glucose utilization across the gut or increase liver ... more pothesis that supplemental Gln would reduce glucose utilization across the gut or increase liver gluconeogenesis or mammary glutamine uptake to increase milk protein synthesis.
The Proceedings of the Nutrition Society, 1978