Quantitation of alpha-linked glucose polymers passing to the small intestine in cattle

Effects of feeding stockpiled tall fescue versus summer-baled tall fescue-based hay to late gestation beef cows: I. Cow performance, maternal metabolic status, and fetal growth

We hypothesized that cows grazing stockpiled tall fescue (STF) during late gestation would have increased nutrient intake, resulting in improved metabolic status and fetal growth compared with cows consuming summer-baled tall fescue hay. Multiparous, spring-calving, crossbred beef cows (year 1: n = 48, year 2: n = 56) were allocated by body weight (BW), body condition score (BCS), age, service sire, and expected calving date to 1 of 2 forage systems (4 rep/system) in mid-November on day 188 of gestation: strip-graze endophyte-infected STF in 4.05 ha pastures or consume ad libitum endophyte-infected summer-baled tall fescue-based hay in uncovered dry lots. Treatments were terminated 1 wk postpartum, and cow-calf pairs were managed together until weaning. Data were analyzed with forage system, year, and their interaction as fixed effects. Sampling day was a repeated effect for cow metabolites and hormones. Calf date of birth was in the model when P < 0.25; pasture or pen was the experimental unit. Cow prepartum BW was not affected (P ≥ 0.424) by forage system, but cows grazing STF tended (P = 0.09) to have greater BCS at day 35 and had greater (P = 0.03) final precalving BCS than hay-fed cows. Additionally, final precalving 12th rib fat thickness tended (P = 0.09) to be greater for STF than hay-fed cows. Calves born to cows fed hay only weighed 10.2% less (P = 0.03) at birth than calves born to cows consuming STF, indicating reduced fetal growth. Postpartum cow BW, BCS, first service conception rate, and overall pregnancy rate were not affected (P ≥ 0.15) by late gestational forage system. After day 0, serum urea N was greater (P < 0.001) in cows consuming STF on all days measured. Cows grazing STF also tended (P = 0.08) to have greater plasma glucose than cows consuming hay. Serum nonesterified fatty acids (NEFA) were greater (P < 0.001) in cows grazing STF on day 56 in year 1 and on day 77 and 99 in year 2. Serum triiodothyronine was less (P = 0.03) on day 0, but greater (P = 0.004) on day 99, in cows grazing STF. Cows grazing STF tended (P = 0.06) to have greater thyroxine on day 77 in year 1. Serum cortisol was greater (P = 0.003) on day 35 and tended (P = 0.10) to be greater on day 99 in cows grazing STF. Calf birth weight was positively correlated with prepartum maternal serum urea N (r = 0.31, P = 0.002) and NEFA (r = 0.12, P = 0.005). In this study, cows grazing STF had increased nutrient intake during late gestation, resulting in greater fetal growth.

Glutamate is the major anaplerotic substrate in the tricarboxylic acid cycle of isolated rumen epithelial and duodenal mucosal cells from beef cattle

In this study, we aimed to determine the contribution of substrates to tricarboxylic acid (TCA) cycle fluxes in rumen epithelial cells (REC) and duodenal mucosal cells (DMC) isolated from Angus bulls (n = 6) fed either a 75% forage (HF) or 75% concentrate (HC) diet. In separate incubations, [(13)C(6)]glucose, [(13)C(5)]glutamate, [(13)C(5)]glutamine, [(13)C(6)]leucine, or [(13)C(5)]valine were added in increasing concentrations to basal media containing SCFA and a complete mixture of amino acids. Lactate, pyruvate, and TCA cycle intermediates were analyzed by GC-MS followed by (13)C-mass isotopomer distribution analysis. Glucose metabolism accounted for 10-19% of lactate flux in REC from HF-fed bulls compared with 27-39% in REC from HC and in DMC from bulls fed both diets (P < 0.05). For both cell types, as concentration increased, an increasing proportion (3-63%) of alpha-ketoglutarate flux derived from glutamate, whereas glutamine contributed <3% (P < 0.05). Although leucine and valine were catabolized to their respective keto-acids, these were not further metabolized to TCA cycle intermediates. Glucose, glutamine, leucine, and valine catabolism by ruminant gastrointestinal tract cells has been previously demonstrated, but in this study, their catabolism via the TCA cycle was limited. Further, although glutamate's contribution to TCA cycle fluxes was considerable, it was apparent that other substrates available in the media also contributed to the maintenance of TCA fluxes. Lastly, the results suggest that diet composition alters glucose, glutamate, and leucine catabolism by the TCA cycle of REC and DMC.

Characteristics of developmental changes in the kinetics of glucose and urea in Japanese Black calves: Comparison with Holstein calves1

The current study was conducted to clarify the characteristics of glucose and urea kinetics in male Japanese Black calves, using a glucose and urea dilution method with stable isotopes, at preweaning (3 wk of age) and postweaning (13 and 26 wk of age) stages, in comparison with the kinetics of glucose and urea in male Holstein calves. Six Japanese Black and 6 Holstein calves were arranged in a 2 (breed) x 3 (stage) factorial block design. These 12 suckling calves were fed only whole milk, offered concentrate and or chardgrass hay after 3 wk of age, and weaned at 6 wk of age. Under steady-state conditions, glucose challenges (1.0 mg/kg of BW; [U-13C]d-glucose) and urea challenges (both 2.2 mg/kg of BW; [13C]urea and [15N2]urea) were performed at the 3 stages examined. There were no significant differences in plasma glucose concentrations between Japanese Black and Holstein calves at any stage, but the glucose concentrations at 3 wk of age were greater (P <0.05) than those at 13 wk of age in both breeds. The glucose pool size in Japanese Black calves was smaller (P <0.05) than that in Holstein calves at all stages. Within each breed, there were no significant differences between the glucose pool sizes at 3 and 13 wk of age, but the glucose pool size was larger (P <0.05) at 26 wk of age. Moreover, Japanese Black calves had greater glucose irreversible loss rates (P <0.01) than Holstein calves at 3 wk of age, and the glucose irreversible loss rates were less (P <0.05) on and after 13 wk of age in both breeds. Japanese Black calves had greater plasma urea N concentrations (P <0.05) than Holstein calves at all stages, and in both breeds, the urea N concentrations increased (P <0.05) with age. The urea pool size was smaller (P <0.01) in Japanese Black calves than in Holstein calves at all stages, and in both breeds, the urea pool size increased (P <0.05) with age. In comparison with Holstein calves, Japanese Black calves had greater urea irreversible loss rates (P <0.05) on and after 13 wk of age and greater urea recycling rates (P <0.05) at 26 wk of age. In addition, in both breeds, urea irreversible loss rates and urea recycling rates increased (P <0.05) with age. We conclude that Japanese Black calves have partially different glucose and urea kinetics from Holstein calves and that the kinetics of these metabolites in both Japanese Black and Holstein calves are strongly influenced by weaning.

Effects on nutrient and hormonal profile of long-term infusions of glucose or insulin plus glucose in cows treated with recombinant bovine somatotropin before peak milk yield

Ten Holstein cows were treated with 30.9 mg.d-1 of recombinant bST from 15 to 41 d of lactation. The Latin square design included three infusion periods of 6 d each with 3 d of rest between infusion periods. Infusions were physiological saline, glucose (50 g.h-1), and insulin plus glucose (12.5 IU.h-1 + 50 g.h-1). Blood was collected continuously during the last 24 h of each infusion period. Statistical analyses of data for energy balance, milk yield, and DMI were performed on the last 3 d of each infusion period. Production data before and after infusions (i.e., no recombinant bST) estimated that recombinant bST increased milk yield of cows infused with glucose and saline by 3.1 and 3.6 kg.d-1, respectively. Net energy intake was not affected by infusion, but glucose infusion resulted in higher BW loss than did saline infusion (2.33 vs. 0.08 kg.d-1, respectively), and insulin plus glucose infusion resulted in BW gain (0.65 kg.d-1). Milk yield was 39.9, 39.6, and 37.6 kg.d-1 for cows infused with saline, glucose, and insulin plus glucose, respectively. The insulin plus glucose infusion increased milk protein 11 and 14% compared with response to saline and glucose infusions, respectively; no change occurred in the proportion of casein and whey proteins. Serum bST was increased 109% with exogenous recombinant bST. Serum IGF-I was lower for cows infused with glucose than for those infused with saline (21.03 vs. 27.44 ng.ml-1) and increased to 46.55 ng.ml-1 for cows infused with insulin plus glucose. Serum concentrations of insulin and glucose were 13.7 and 56.7, 18.5 and 61.9, and 30.5 muIU.ml-1 and 39.4 mg.dl-1 for cows infused with saline, glucose, and insulin plus glucose, respectively. The results of this study suggest that low concentrations of plasma insulin in early lactation may limit the IGF-I response to recombinant bST (uncoupling). Despite higher IGF-I, milk yield was lower, probably as a result of low blood glucose. These results suggest that, in early lactation, insulin is still anabolic because the BW gain of cows increased. However, milk yield was still higher than that for cows in late lactation with similar insulin concentrations.

Metabolism of propionate, glucose, and carbon dioxide as affected by exogenous glucose in dairy cows at energy equilibrium

In vivo kinetic techniques were used to quantify changes in metabolism of propionate, glucose, and blood CO2 when glucose was infused intravenously at 0, 342, or 737 g/d into four lactating cows. Neither production of milk or milk fat nor composition of milk was changed. Production of milk protein increased for the high glucose treatment. Isotope dilution data were used to calculate irreversible losses of rumen propionate, plasma glucose, and blood CO2 and to determine a unique solution for flux of C in this three-pool system. Irreversible losses of propionate and CO2 were not changed. Infusions of glucose increased irreversible loss of glucose in proportion to amounts infused, thus indicating there was no change in endogenous production of glucose. For the control, 52% of the C flux of blood glucose was derived directly from rumen propionate and another 26% came from other gluconeogenic substrates. Flux of C into glucose from exogenous sources increased in proportion to amounts of glucose infused. Flux of C from rumen propionate remained constant. The rate of C leaving the glucose pool, other than as CO2, tended to increase with infusion of glucose, and oxidation of glucose tended to increase for the high glucose treatment. High producing cows adjusted to increased exogenous glucose by increasing glucose utilization and without decreasing endogenous glucose production.

Net absorption of glucose, L-lactate, volatile fatty acids, and nitrogenous compounds by bovine given abomasal infusions of starch or glucose

Three experiments were conducted to evaluate effects of abomasal infusion of glucose or starch on absorption of metabolites (glucose, L-lactate, volatile fatty acids, and nitrogenous compounds) from portal-drained viscera of a nonlactating Holstein cow and two Hereford X Angus heifers. Portal blood and plasma flow were determined by dilution of para-aminohippuric acid. Net absorption was portal-arterial concentration difference times portal plasma flow. Plasma concentration and portal-arterial difference of glucose increased rapidly and directly in response to increased rates of abomasal glucose infusion in the cow (Experiment 1). In the cow (Experiment 2), net absorption of L-lactate was greater with carbohydrate than with water infusion; net absorption of L-lactate was greater and of n-butyrate was less with starch than with glucose infusion. These responses were not evident in the heifers (Experiment 3). Net absorption of alpha-amino-N in the heifers was greater with starch than with glucose infusion. Increased concentrate intake by the heifers did not interact with responses to abomasal infusions. Recovery of infused glucose as absorbed glucose was similar for the cow and the heifers (65%). However, heifers absorbed (as glucose) 35% of infused starch and the cow only 8%.

Insulin and gastric inhibitory polypeptide secretion in young milk-fed and adult goats

Plasma concentrations of glucose, immunoreactive insulin (IRI), and immunoreactive gastric inhibitory polypeptide (IR-GIP) were studied in six adult and five young milk-fed goats after intravenous or intraduodenal infusions of glucose. Glucose concentrations after intraduodenal infusions were elevated from 3.5 to 4.7 mmol/liter on the average in adult and from 4 to 7 mmol/liter in young goats. Intravenous infusions were given at rates adjusted to mimic very closely the plasma glucose curves after intraduodenal infusions. Plasma IRI increased from 250 to 600 pmol/liter in adult and from 180 to 500-600 pmol/liter in young goats, but no significant differences were observed between intravenous and intraduodenal infusions. Duodenal infusions of glucose did not stimulate the release of IR-GIP in adult or young goats. It is concluded that the goat is lacking the incretin system for rapid disposal of oral glucose loads and that IR-GIP does not participate in regulation of glucose-stimulated insulin release in this species.

Estimation of the proportion of non-ammonia-nitrogen reaching the lower gut of the ruminant derived from bacterial and protozoal nitrogen

1. A method for estimating the proportions of bacterial- and protozoal-N in the total non-ammonia-N reaching the lower gut of the ruminant under steady-state conditions was evaluated. Three trials using two different diets were conducted with a Holstein steer equipped with a rumen cannula and duodenal re-entrant cannulas. 2. An intraruminal primed infusion of (15NH4)2SO4 was administered for 68 h during each trial. Bacteria and protozoa samples were isolated from rumen fluid at approximately 6 h intervals during each infusion period. Total non-ammonia-N was isolated from duodenal digesta samples taken at approximately the same times. All of these samples were analysed for 15N enrichment. A computer program was used to fit equations to the 15N-enrichment curves of bacterial- and protozoal-N. Models of both bacterial- and protozoal-N kinetics consisted of a small pool which equilibrated rapidly with rumen NH3 and a large pool with a fractional turnover rate of 0.045-0.070/h for bacterial-N and 0.056-0.069/h for protozoal-N. 3. Abomasal fluid turnover was estimated by a single injection of polyethylene glycol (molecular weight 4000) into the rumen followed by sampling of rumen fluid and duodenal digesta. 4. Estimates of abomasal fluid turnover, bacterial-N turnover, and protozoal-N turnover were entered into an equation which was adjusted by computer iteration to fit the 15N-enrichment curve of duodenal digesta non-NH3-N generated from each (15NH4)2SO4 infusion period. The computer fit of this equation to the observed results gave estimates of 0:39-0.45 and 0.22-0.41 for the proportion of duodenal non-NH3-N derived from bacterial-N and protozoal-N respectively. 5. This method is potentially useful in estimating microbial protein passage to the lower gut in ruminants. Sampling digesta from the omasum rather than the duodenum would simplify the method and possibly increase the reliability of the estimates.

[Dependence of rumen fatty acid production on the composition of rations]

In three experiments with two Black-and-White dairy cows the influence of soybean oil and coconut fat as well as that of rations rich in roughage and concentrated feed on the production of fatty acids were determined with the isotope dilution method. A change in the method of sampling from the rumen in the course of the investigations resulted in distinctly different absolute production quotas, which can presumably be traced back to the disproportionate mixing in of the isotope and/or different production quotas in various regions of the rumen. The relative differences between the production quotas dependent on the rations, however were approximately the same with both sampling methods, so that they make the comparison of the rations concerning rumen fermentation possible. The production of acetic acid and the total production of fatty acids (C2--C4) correlated closely both with the intake of digestible energy and the intake of digestible organic matter. There was also a highly significant correlation o that they make the comparison of the rations concerning rumen fermentation possible. The production of acetic acid and the total production of fatty acids (C2--C4) correlated closely both with the intake of digestible energy and the intake of digestible organic matter. There was also a highly significant correlation o that they make the comparison of the rations concerning rumen fermentation possible. The production of acetic acid and the total production of fatty acids (C2--C4) correlated closely both with the intake of digestible energy and the intake of digestible organic matter. There was also a highly significant correlation between the relation of acetic and propionic acid in the rumen fluid and the quotient from acetic and propionic acid produced. In contrast to this, a significant relation between the concentration of fatty acids and the production of fatty acids could not be ascertained. Soybean oil and coconut fat brought about a slightly better utilisation of the fat-free organic matter for the production of fatty acids in the rumen. This could mainly be traced back to the increased production of propionic acid. The production of acetic acid per kg fat-free organic matter was insignificantly reduced. A reduced quota of roughage in the ration as well as the use of feed fats resulted in a decrease in the production of acetic acid and an increase in the production of propionic acid. The influence of the quota of roughage, however, was bigger than that of the use of fats. When rations rich in roughage were given, the share the energy contained in the total fatty acids has in the total of the digested energy was, on an average of both animals, slightly lower in comparison to rations rich in concentrated feed. However, the reason for this is not to be found in a lower share the energy digested in the stomachs has in the total of digested energy but in a higher amount of fermentation losses with a nutrition rich in roughage.

Blood plasma magnesium, potassium, glucose, and immunoreactive insulin changes in cows moved abruptly from barn feeding to early spring pasture

Cations and immunoreactive insulin in plasma were measured in 35 lactating cows moved abruptly to early spring pasture. After change of cows from grass-clover hay to fescue-bluegrass pasture containing 22 to 31 g potassium/kg dry matter, immunoreactive insulin of 5 Holstein cows increased 30% in 5 days and averaged 45% above prepasture concentrations for 40 days. Magnesium averaged 44% below prepasture content of plasma during this period and was correlated negatively with potassium -.17 and immunoreactive insulin -.37. Thirty Herford cows were changed from corn silage and grass-clover hay to wheat-rye pasture containing 3.06% potassium in the dry matter. Each day on pasture, 10 cows each were fed 2.3 kg cornmeal, 10 were given 30 g magnesium oxide by capsule, and 10 were given no supplement. After unsupplemented cows were moved to pasture, immunoreactive insulin rose 51% in 8 days and plasma magnesium fell 24%. Both supplements reduced immunoreactive insulin, but magnesium was maintained higher by magnesium oxide than by cornmeal. Injection of two Holstein cows with insulin (2 IU/kg body weight) reduced plasma concentrations of both potassium and magnesium 20% below that of two cows injected with only physiological saline. Whether elevated plasma insulin may accelerate development of hypomagnesemia in cattle on spring pasture with relatively high potassium content has not been established.

Gluconeogenesis in cattle: significance and methodology

Gluconeogenesis is a continual process that is of great importance in ruminants because almost all dietary carbohydrates are fermented to volatile fatty acids in the rumen. In turn, propionate is the only major volatile fatty acid that contributes to gluconeogenesis. Many different techniques and analytical procedures are involved in studying ruminant gluconeogenesis. Glucose kinetics can be examined by single-injection or continuous-infusion isotope dilution techniques with a variety of glucose labels. Correcting for recycling of label is an important consideration. Absorption of glucose from the gut can be measured by combining arterial-venous differences and flow rates of portal blood or can be estimated by determining the amount of glucose plus alpha-glucose polymers passing into the small intestine. Production of propionate in the ruminoreticulum can be measured by isotope dilution techniques. Quantitating the conversion of propionate to glucose requires the use of [carbon-14]propionate with careful corrections for propionate carbon entering the citric acid cycle before incorporation into glucose; The same fundamental techniques used with propionate are required to quantitate the contributions of amino acids and other precursors to glucose. In vitro studies of gluconeogenic enzymes, and cellular, tissue, or organ preparations provide valuable insights into the gluconeogenic processes and controls but must be validated by in vivo experiments. Progress has been considerable in understanding some aspects of ruminant gluconeogenesis, but many more studies will be required to obtain a complete understanding.