Biomedical subjects

M E Tumbleson

Publications and source records attributed to M E Tumbleson.

At least 19 recordsLinked to original sources

PubMed2006

Improvement in fermentation characteristics of degermed ground corn by lipid supplementation.

With rapid growth of fuel ethanol industry, and concomitant increase in distillers dried grains with solubles (DDGS), new corn fractionation technologies that reduce DDGS volume and produce higher value coproducts in dry grind ethanol process have been developed. One of the technologies, a dry degerm, defiber (3D) process (similar to conventional corn dry milling) was used to separate germ and pericarp fiber prior to the endosperm fraction fermentation. Recovery of germ and pericarp fiber in the 3D process results in removal of lipids from the fermentation medium. Biosynthesis of lipids, which is important for cell growth and viability, cannot proceed in strictly anaerobic fermentations. The effects of ten different lipid supplements on improving fermentation rates and ethanol yields were studied and compared to the conventional dry grind process. Endosperm fraction (from the 3D process) was mixed with water and liquefied by enzymatic hydrolysis and was fermented using simultaneous saccharification and fermentation. The highest ethanol concentration (13.7% v/v) was achieved with conventional dry grind process. Control treatment (endosperm fraction from 3D process without lipid supplementation) produced the lowest ethanol concentration (11.2% v/v). Three lipid treatments (fatty acid ester, alkylphenol, and ethoxylated sorbitan ester 1836) were most effective in improving final ethanol concentrations. Fatty acid ester treatment produced the highest final ethanol concentration (12.3% v/v) among all lipid supplementation treatments. Mean final ethanol concentrations of alkylphenol and ethoxylated sorbitan ester 1836 supplemented samples were 12.3 and 12.0% v/v, respectively.

Culture Media↗

PubMed2006

Element concentrations of dry-grind corn-processing streams.

The dry-grind corn process is one of two technologies used to convert corn into ethanol. In this process, all kernel components are processed through several sequential steps, including fermentation. Only one coproduct (distillers' dried grains with solubles [DDGS]) is available for marketing. DDGS provide income to offset costs of processing; issues that affect marketing have implications in the economic viability of dry-grind plants. Two issues relate to elements in DDGS: high concentrations and excessive variation. Data on element concentrations in dry-grind processing streams could be helpful in addressing these concerns. The objective of this study was to determine element concentrations in primary process streams from dry-grind plants. Samples of corn, ground corn, beer, wet grains, syrup, and DDGS were obtained from nine dry-grind plants, and element concentrations were determined. The concentrations of most elements in corn were not different among processing plants and were similar to published data. However, for the processing streams, there were differences in several element concentrations among processing plants. The concentrations of most elements in beer were about three times those of corn, due to the disappearance of starch during fermentation. Syrup had the highest element concentrations. Variations in element contents of DDGS and parent streams were due to processing conditions and not corn. Appropriate processing of thin stillage (the parent stream of syrup) could reduce the element content of DDGS.

Beer↗

PubMed2005

Membrane separation of solids from corn processing streams.

Corn processing streams are characterized by high water content. Removal of water and recovery of solids are major economic and logistical challenges. New technologies are needed to modify processing streams and to reduce variability and improve quality of coproducts. The objective was to determine the effectiveness of microfiltration and ultrafiltration systems in altering water, solids (protein) and ash contents of corn processing streams. Corn was either steeped with SO(2) (STW) or soaked (SKW) in water; STW contained more solids than SKW. Ultrafiltration of STW and SKW had little effect on water removal or solids recovery. Corn was processed by a conventional wet milling process and a wet milling process that used enzymes to eliminate use of SO(2) steeping. Protein streams from the conventional process (CG) and the enzymatic process (EG) were processed by microfiltration. Permeate streams from EG and CG had higher total solids and ash concentrations than retentate streams; much of the ash was recovered in permeate (67% and 83%, respectively). For CG, proteins were largely recovered in retentate, whereas for EG, proteins were recovered in permeate. SDS-PAGE data indicated a decrease in size of proteins in the EG process stream. Permeate streams from microfiltration were subject to ultrafiltration; there was little effect on solids and nutrient separations.

Chemical Fractionation↗

PubMed2005

Microfiltration of gluten processing streams from corn wet milling.

In corn wet milling, dry matter can be separated from liquids in process streams with centrifuges or vacuum belt filtration (VBF). Because separations usually are not complete, dry matter can be lost in the liquid streams (overflow from the gluten thickener centrifuge and filtrate from VBF). This represents a loss of nutrients, especially protein, to low valued coproducts and reduces quality of water for recycling within the process. The objective was to compare microfiltration of light and heavy gluten process streams to conventional separation methods. Batches of light and heavy gluten were obtained from a wet mill plant and processed by microfiltration. Samples of permeate and concentrate from microfiltration were analyzed and compared to corresponding streams from wet milling. Microfiltration of light gluten resulted in concentrate and permeate streams similar in composition to conventionally processed light gluten using a centrifuge, suggesting that microfiltration is as effective as centrifugation in partitioning solids and water in light gluten. Dewatering of heavy gluten found that conventional VBF caused dry matter concentrations in gluten cake to be higher than concentrate from microfiltration. Permeate from microfiltration of heavy gluten had higher concentrations of ash and lower soluble nitrogen than filtrate from VBF. Microfiltration was able to remove more ash from concentrate, which may improve the value of wet milling coproducts. These data demonstrated microfiltration has potential for separation of light and heavy gluten streams, but more data are needed on effectiveness and practicality.

Centrifugation↗

PubMed2004

Composition of corn and distillers dried grains with solubles from dry grind ethanol processing.

Increase in the demand for ethanol has resulted in growth in the dry grind (DG) ethanol industry. In DG processing, the whole corn kernel is fermented, resulting in two main coproducts, ethanol and distillers dried grains with solubles (DDGS). Marketing of DDGS is critical to the economic stability of DG plants. The composition of DDGS can vary considerably; this reduces market value. Factors that cause variation in composition need to be evaluated. The objective was to determine the relationship between composition of corn and composition of DDGS. Samples of corn and DDGS were obtained from a DG ethanol plant and analyzed for protein, fat, starch and other nutrients. Concentrations of protein, fiber and starch were similar to published data for corn but were higher for DDGS. Coefficients of variation for protein fat and fiber concentrations were similar for corn and DDGS. There were no significant correlations between concentrations of components in corn and those in DDGS. Variation in the composition of DDGS was not related to variation in corn composition and probably was due to variation in processing streams or processing techniques. This implies that reducing the variation in composition of DDG will require modification of processing strategies.

Biotechnology↗

PubMed2003

Characterization of gluten processing streams.

Corn gluten meal (CGM) is a major coproduct of corn wet milling; it has value because of high protein. However, variation in composition and high P content reduce market value. Data that characterize gluten streams would be helpful in identifying key processing steps that could be modified to improve the quality of CGM and increase processing efficiency. Few data are published in the literature on the detailed composition of gluten processing streams. The objective was to characterize the gluten process streams in a corn wet milling plant. Samples were obtained from one plant over a six month period and analyzed for dry matter (DM), total N (protein), ash and elements. DM and macroelement content of the streams were increased significantly during processing. Ash, priority pollutant elements and microelement concentrations were low and of little concern. About 38% of the N (protein) in light gluten was not recovered in the CGM; most of this was lost at the gluten thickener step into the gluten thickener overflow. Much of the P also was removed at this step. Modification of the gluten thickener overflow to increase N and reduce P could make CGM a more valuable coproduct and improve processing efficiency.

Conservation of Natural Resources↗

PubMed2003

Characterization of light gluten and light steep water from a corn wet milling plant.

The primary commodity of corn wet milling is starch, but two coproducts (corn gluten feed, CGF and corn gluten meal, CGM) also are produced. CGM and CGF are marketed as animal foodstuffs and are important economically; however, variation in composition reduces quality. There are few data on the effect of composition of the parent process streams, light steep water (LSW) and light gluten (LG), respectively, on composition of CGF and CGM. The objective was to characterize LG and LSW. Samples of LG and LSW were collected: (1) hourly for one day, (2) every 3 h for 3 days, and (3) daily for 3 weeks. Dry matter, N and ash were determined. Variation in composition of LG and LSW was greatest during longer periods of time (days and weeks) rather than shorter (hourly or every 3 h). There was significant variation in DM (solids) content, which directly affected the concentration of other components. Variation in N (protein) of LG and LSW accounted for much of the variation in CGF and CG. Processes that modify processing and reduce variation could increase the quality of CGF and CGM.

Agriculture↗

PubMed2001

Fumonisin B(1) increases serum sphinganine concentration but does not alter serum sphingosine concentration or induce cardiovascular changes in milk-fed calves.

Fumonisin B(1) is the most toxic and commonly occurring form of a group of mycotoxins that alter sphingolipid biosynthesis and induce leukoencephalomalacia in horses and pulmonary edema in pigs. Purified fumonisin B(1) (1 mg/kg, iv, daily) increased serum sphinganine and sphingosine concentrations and decreased cardiovascular function in pigs within 5 days. We therefore examined whether the same dosage schedule of fumonisin B(1) produced a similar effect in calves. Ten milk-fed male Holstein calves were instrumented to obtain blood and cardiovascular measurements. Treated calves (n = 5) were administered purified fumonisin B(1) at 1 mg/kg, iv, daily for 7 days and controls (n = 5) were administered 10 ml 0.9% NaCl, iv, daily. Each calf was euthanized on day 7. In treated calves, serum sphinganine concentration increased from day 3 onward (day 7, 0.237 +/- 0.388 micromol/l; baseline, 0.010 +/- 0.007 micromol/l; mean +/- SD), whereas, serum sphingosine concentration was unchanged (day 7, 0.044 +/- 0.065 micromol/l; baseline, 0.021 +/- 0.025 micromol/l). Heart rate, cardiac output, stroke volume, mean arterial pressure, mean pulmonary artery pressure, pulmonary artery wedge pressure, central venous pressure, plasma volume, base-apex electrocardiogram, arterial Po(2), and systemic oxygen delivery were unchanged in treated and control calves. Fumonisin-treated calves developed metabolic acidosis (arterial blood pH, 7.27 +/- 0.11; base excess, -9.1 +/- 7.6 mEq/l), but all survived for 7 days. We conclude that calves are more resistant to fumonisin B(1) cardiovascular toxicity than pigs.

Acidosis, Respiratory↗

PubMed2001

Fumonisin B(1) is hepatotoxic and nephrotoxic in milk-fed calves.

Fumonisins are a group of mycotoxins that alter sphingolipid biosynthesis and induce leukoencephalomalacia in horses and pulmonary edema in pigs. Experimental administration of fumonisin induces hepatotoxicity in all species, including cattle, as well as nephrotoxicity in rats, rabbits, and sheep. We investigated the hepatotoxicity and nephrotoxicity of fumonisin B(1) to calves. Ten milk-fed male Holstein calves aged 7 to 14 days were instrumented to obtain blood and urine. Treated calves (n = 5) were administered fumonisin B(1) at 1 mg/kg, iv, daily and controls (n = 5) 10 ml 0.9% NaCl, iv, daily until euthanized on day 7. Fumonisin B(1)-treated calves were lethargic and had decreased appetite from day 4 onward, serum biochemical evidence of severe liver and bile duct injury, and impaired hepatic function. Treated calves also had biochemical evidence of renal injury that functionally involved the proximal convoluted tubules. Sphinganine and sphingosine concentrations in liver, kidney, lung, heart, and skeletal muscle were increased in treated calves. Sphinganine, but not sphingosine, concentration was increased in brains of treated calves. In fumonisin B(1)-treated calves, hepatic lesions were characterized by disorganized hepatic cords, varying severity of hepatocyte apoptosis, hepatocyte proliferation, and proliferation of bile ductular cells. Renal lesions in treated calves consisted of vacuolar change, apoptosis, karyomegaly, and proliferation of proximal renal tubular cells, as well as dilation of proximal renal tubules, which contained cellular debris and protein. This is the first report of fumonisin B(1)-induced renal injury and organ sphingolipid alterations in cattle.

Animals↗

PubMed2001

Fumonisin toxicosis in swine: an overview of porcine pulmonary edema and current perspectives.

Fumonisin toxicosis in swine was named porcine pulmonary edema (PPE) after outbreaks of a fatal disease in pigs fed Fusarium verticillioides (F. moniliforme)-contaminated corn screenings from the 1989 corn crop in Iowa, Illinois, and Georgia. Pigs that died had severe pulmonary edema, which has not been identified in other species after exposure to fumonisins. The disease has been reproduced experimentally by feeding of naturally contaminated corn, F. verticillioides culture material, and by intravenous administration of fumonisin B1 (FB1). Hepatic lesions consisting of apoptosis, necrosis, and hepatocyte proliferation also are observed. As in other species, alterations in clinical pathology reflect hepatic injury as well as elevated serum cholesterol concentration. In chronic studies, esophageal plaques, hyperplastic hepatic nodules, and right ventricular hypertrophy were found. In pigs, as in other species, fumonisin alters sphingolipid biosynthesis, with the greatest alterations in sphingosine and sphinganine concentrations in kidney, liver, lung, and heart. Our recent studies on fumonisin toxicosis in pigs have focused on immune effects and the pathogenesis of pulmonary edema. The specific immune system was not affected; however, FB1 inhibited phagocytosis and sphingolipid biosynthesis in pulmonary macrophages. Fumonisin induced an accumulation of membranous material in pulmonary capillary endothelial cells; this change appears specific to this cell type and to swine. In short-term cardiovascular studies, fumonisin decreased left ventricular dP/dt(max) (an index of cardiac contractility), mean systemic arterial pressure, heart rate, and cardiac output, and increased mean pulmonary artery pressure and pulmonary artery wedge pressure. These changes are compatible with the inhibition of L-type calcium channels by increased sphingosine and/or sphinganine concentration. Therefore, fumonisin-induced pulmonary edema in swine appears to result from acute left-sided heart failure mediated by altered sphingolipid biosynthesis.

Animals↗

PubMed2000

Purified fumonisin B(1) decreases cardiovascular function but does not alter pulmonary capillary permeability in swine.

Fumonisins are mycotoxins produced by Fusarium verticillioides, which induce acute pulmonary edema in swine. We previously reported that ingestion of fumonisin-containing culture material decreases cardiovascular function in swine (1996,a,b; Fundam. Appl. Toxicol. 31, 169-172; 33, 140-148; 1999, Am. J Vet. Res. 60, 1291-1300). The main purpose of this study was to confirm that fumonisin B(1) was responsible for the observed cardiovascular changes. Treated pigs (n = 6) were given daily intravenous injections of purified fumonisin B(1) at 1 mg/kg for 4 days, while controls (n = 6) were injected with equal volumes of saline. On day 5, pigs were anesthetized with butorphanol-chloralose and instrumented for hemodynamic studies. Terminally, bronchoalveolar lavage was performed on each pig to determine the relative permeability index of the pulmonary endothelium. Fumonisin B(1)-treated pigs had marked decreases in the maximal rate of change of left ventricular pressure (dP/dt(max)), mean aortic pressure, cardiac output, and arterial pO(2), accompanied by increases in mean pulmonary artery pressure, oxygen extraction ratio, and blood hemoglobin concentration. Plasma and left ventricular sphingosine and sphinganine concentrations were markedly increased in treated pigs at day 5; however, there was no difference in the relative permeability index between groups. Serum cholesterol concentrations and activities of hepatic-derived enzymes were increased, and hepatocyte apoptosis and mitoses were present in the livers of fumonisin-treated pigs. In the lungs of treated pigs, there was proteinaceous edema and membranous accumulations in capillary endothelial cells. These results indicate that cardiovascular function is altered by fumonisin B(1), and that fumonisin-induced pulmonary edema is caused by left-sided heart failure and not by altered endothelial permeability. Because of the potential for contamination of human foodstuffs by fumonisins, the cardiovascular toxicity of these compounds must be taken into consideration.

Animals↗

PubMed1999

Sequence of cardiovascular changes leading to pulmonary edema in swine fed culture material containing fumonisin.

OBJECTIVES: To determine the sequence of cardiovascular and blood gas changes induced by ingestion of fumonisin-containing culture material in swine and to examine the temporal relationship of these changes to plasma sphinganine and sphingosine concentrations. ANIMALS: 12 healthy castrated pigs (38 to 50 kg). PROCEDURE: Pigs were instrumented to permit cardiovascular monitoring and collection of blood samples. Baseline values were obtained, and pigs were randomly assigned to 1 of 2 groups. Control pigs (n = 6) were fed a standard grower diet, whereas culture material that contained 20 mg of fumonisin B1/kg of body weight was added to the feed of treated pigs (n = 6) each day. Hemodynamic data, results of arterial and mixed venous blood gas analyses, and plasma sphinganine and sphingosine concentrations were recorded every 12 hours until treated pigs were euthanatized because of impending death from pulmonary edema. RESULTS: Sphinganine and sphingosine concentrations were increased in plasma of treated pigs within 24 hours of initial fumonisin exposure and continued to increase dramatically until euthanasia. Fumonisin-treated pigs had increased respiratory rate, mean pulmonary artery pressure, and pulmonary artery wedge pressure, along with decreased heart rate and cardiac output in the 12-hour period before euthanasia. Fumonisin-treated pigs also had systemic arterial hypotension, arterial and mixed venous hypoxemia, metabolic acidosis, decreased oxygen delivery, and increased oxygen consumption immediately before euthanasia. CONCLUSIONS AND CLINICAL RELEVANCE: Fumonisin-induced pulmonary edema in swine is probably caused by acute left-sided heart failure. Onset of hemodynamic changes was associated with plasma sphinganine concentration > or = 2.2 microM/L and plasma sphingosine concentration > or = 1 microM/L.

Animal Feed↗

PubMed1995

Effects of feeding wash-water solids on health and performance of ewes and lambs.

Diets containing 0, 10, or 20% dried wash-water solids (WWS) from a milk processing plant were fed to 48 Hampshire crossbred wews (average weight 58.1 kg) for 3 yr. Data were obtained on BW gains, hematology, tissue elements, and survival for ewes and BW gains, tissue elements and survival for their lambs. Ewes fed 20% WWS gained less (P < .05 ) BW during gestation and lactation in yr 1 and had lower BW (P < .05) in yr 2 and 3 than those fed 0 or 10% WWS. Lambs from ewes fed 20% WWS gained less (P < .05) BW in yr 2 and 3. Hematology variables of ewes, survival of ewes and survival of lambs were not effected by diet. Although WWS-containing diets contained high concentrations of Ca, P, Mn, and Fe and moderate concentrations of Mo, Mg, and Zn, diets had few effects on tissue elements in ewes and lambs. Concentrations of some tissue elements were less (P < .05) in lambs in yr 2 and 3 than in yr 1. Wash-water solids can be incorporated into ruminant diets, providing a disposal alternative that recycles and conserves nutrients. Long-term feeding posed only minor or negligible health of safety problems. Because fo low energy and N availability and high ash content, WWS probably should be limited to 10% or less of conventional diets.

Animal Feed↗

PubMed1992

Feeding wash water solids to sows during gestation and lactation: sow productivity, pig performance, and tissue compositions.

Diets containing 0, 10, or 20% dried wash water solids (WWS) from a milk processing plant were fed to 54 Yorkshire gilts (160 to 270 kg) for five parities. Feed intake, weight changes, and morbidity of sows were measured; number of pigs per litter, birth weight, and weight gain of pigs were also determined. Blood, tissue, and milk samples were taken from sows for hematological and mineral analyses, and tissue samples were taken from newborn pigs from each treatment per parity. Overall, initial sow weight, sow weight at weaning, and weight losses were not affected (P greater than .05) by treatment. At 107 d of gestation, overall weights decreased (P less than .05) linearly with level of WWS in the diet. The number of pigs per litter and weight of pigs were not affected (P greater than .10) by diet. Concentrations of NA (P less than .10) and Cd (P less than .05) were lower in kidney of sows fed 20% WWS, and concentrations of Zn were lower in bone and in kidney of sows fed the 20% WWS diet. The Sr and Ba concentrations increased (P less than .05, P less than .10) linearly in bone from sows with level of WWS in the diet. In pigs, concentrations of Mn in kidney and Zn in liver were lower for the 20% WWS treatment. In conclusion, feeding WWS to sows over five parities had minimal adverse effects on sow productivity and pig performance; the reduction in Zn concentrations in tissues of sows and pigs seemed to be related to the Ca content of WWS.

Animal Feed↗

PubMed1991

Evaluation of dairy food processing wash water solids as a protein source: II. Microbial protein synthesis, duodenal nitrogen flow, and small intestinal amino acid disappearance.

Twelve ruminally, duodenally, and ileally-cannulated Hereford heifers (average initial BW 313 +/- 20 kg) were used in a replicated experiment to evaluate dairy food processing wash water solids (WWS) as a protein source. Heifers were fed 2.8 kg of chopped (7.6 cm) hay and one of three supplements (1.5 kg/d, DM basis). Supplements were formulated to be similar in energy and contained 1.0 (control), 23.2 (WWS), and 21.6% (soybean meal; SBM) CP on an OM basis. Total N and nonammonia N entering the duodenum (g/d) were greater (P less than .10) for heifers fed WWS and SBM supplements than for controls. Bacterial N flow (g/d) at the duodenum was less (P less than .10) for controls (43.9) than for WWS- (63.9) and SBM- (69.9) supplemented heifers. Feed escape N (g/d) was greater (P less than .10) for WWS-fed heifers than for those fed SBM (32.1 vs 20.7 g/d, respectively). Total tract N digestion (g/d) was greatest (P less than .10) for SBM, intermediate for WWS, and least for control heifers. Microbial protein synthesis (g/kg of OM intake) was enhanced (P less than .10) by WWS and SBM supplementation, but efficiency of synthesis (g/kg of OM fermented) did not differ among treatments. Essential amino acid (AA) disappearance in the small intestine (g/d) was less (P less than .10) for control than for the other two treatments. Nonessential AA disappearance was greatest (P less than .10) for the WWS and least (P less than .10) for the control treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acids↗

PubMed1985

Metabolism of lysophosphatidylcholine by swine platelets.

Incubation of intact platelets from Sinclair(S-1) miniature swine with 32P-labeled lysophosphatidylcholine (lyso PC) indicated the presence of an active lysophospholipase with a pH optimum of 8.0 for hydrolysis of the substrate. However, lyso PC was incorporated into the membrane phosphatidylcholines by the acyltransferase pathway upon addition of ATP, Mg++ and CoA to the platelet suspension. These results suggest that intact platelets are able to resist the cytotoxic effects of lyso PC in plasma, and the phospholipids in platelet membranes are not readily affected by the lipid environment of the plasma. The acyltransfer reaction apparently is saturated with endogenous free fatty acids since arachidonic acid added exogenously did not further enhance the incorporation activity. Neither the acyltransferase nor the lysophospholipase activity was affected by Ca++, but divalent metal ions such as Zn++ inhibited the lysophospholipase activity. Cholesterol but not cholesteryl esters elicited a biphasic effect on both enzymes, stimulating at low concentration but inhibiting at a cholesterol to lyso PC ratio greater than 1. Serum albumin inhibited the lysophospholipase but gave a small biphasic effect to the acyltransferase.

1-Acylglycerophosphocholine O-Acyltransferase↗

PubMed1984

Ethanol consumption and serum lipid profiles in Sinclair(S-1) miniature swine.

Ethanol consumption was correlated with changes in acyl group profiles of phosphatidylcholine and triacylglycerols in serum of Sinclair(S-1) miniature boars. Serum triacylglycerols in the control pigs were high in linoleate (18:2) (48%) and low in stearate (18:0 (3%). Upon feeding with 10% (w/v) ethanol ad lib for two weeks, the proportion of 18:2 in serum triacylglycerols decreased to 12-15% with a concomitant increase in 16:0, 18:0 and 18:1. Similar, but less extensive, acyl group changes were observed in the serum phosphatidylcholine. In addition, there was a decrease in the proportion of 20:3(n-6), but a biphasic change was shown in 20:4(n-6) with respect to ethanol consumption. In general, the high ethanol consumers (7.0 g/kg/day) indicated a more rapid rate of acyl group change than the low consumers (3.8 g/kg/day). Upon withdrawal of ethanol, acyl groups of triacylglycerols rapidly returned towards the control values, whereas only small changes were observed for the recovery in phospholipids. In this situation, the low-consumer group indicated a more rapid recovery than the high-consumer group. Results indicate that with the swine model, serum lipid changes can be a useful parameter for correlating biological changes upon ethanol consumption.

Alcohol Drinking↗

PubMed1983

Sources of normal variation of plasma l-aspartate:2-oxoglutarate aminotransferase in Hereford range cattle.

1. Plasma levels of L-aspartate:2-oxoglutarate aminotransferase (AST) were estimated in Hereford cattle, 1 month to 12 years of age, kept under range conditions and in a group of Hereford x Angus cows kept on the same range. 2. Plasma levels of AST were estimated in a group of Crossbred cows and their calves fed a constant diet and kept in individual pens in the same geographic area as the Herefords. 3. Seasonal changes in mean plasma AST were observed in the Herefords corresponding with the change from dry winter grasses/hay and well water to fresh spring and summer grasses and slough water. No seasonal changes were observed in the Crossbreds given a constant dry diet and city water. 4. Plasma AST increased with age in calves 1 to 12 months of age in the Herefords but not in the Crossbreds. Mean plasma AST did not change with age in any of the adult cattle studied. 5. Small increases in plasma AST corresponding to increases in ambient temperature above - 12 degrees C were observed in the Crossbreds. 6. An increase in plasma AST was observed near the time of first ovulation in the confined cows. 7. No relationship could be demonstrated between plasma AST and sex, breed or time to parturition in the range cattle. Breed differences were observed in the Crossbred cows.

Aging↗