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Biomedical subjects

T C Jenkins

Publications and source records attributed to T C Jenkins.

At least 19 recordsLinked to original sources
PubMed2006

Major advances in nutrition: impact on milk composition.

A number of major scientific advances have been realized in the last 25 yr in determining the opportunities and limitations of altering milk composition through nutritional manipulation. Because of the greater sensitivity of milk fat to dietary manipulation than either protein or lactose, nutritional control of milk fat content and fatty acid composition received a great deal of attention. New information emerged linking ruminal production of trans fatty acid isomers with milk fat depression. As a result, research on fatty acid biohydrogenation intensified yielding new insight on the origin of specific trans fatty acid isomers originating from ruminal biohydrogenation and how these isomers were modified by the action of mammary enzymes. The discovery of conjugated linoleic acid (CLA) as a potent anticarcinogen also led to extensive work on enhancing its concentration in milk through nutritional manipulation and discovering the physiological effects of specific CLA isomers. New protected fats were developed in recent years that were designed to resist biohydrogenation and enhance the concentration of unsaturated fatty acids in milk. The nutritional factors receiving the most attention during the last 25 yr for their influence on milk protein content were forage-to-concentrate ratio, the amount and source of dietary protein, and the amount and source of dietary fat. New insights were tested on modes of action whereby fat supplements caused a decline in protein concentration. Changes in milk lactose concentration occur only in extreme and unusual feeding situations, but the basic biology of lactose synthesis and regulation are still being explored using modern molecular techniques. This paper highlights the major advances in controlling milk composition by dietary manipulation and how it influences the entire animal system from practical feeding studies to basic cellular work on mammary tissue metabolism.

Animal Feed↗
PubMed2006

The effect of carbohydrate source on nitrogen capture in dairy cows on pasture.

The objective of this study was to determine if feeding carbohydrate supplements with faster degradation rates than corn to dairy cows grazing ryegrass would improve nitrogen capture, milk production, and components. Treatments were grain supplements based on: 1) corn (CORN), 2) barley and molasses (BM), or 3) citrus pulp and molasses (CM). For BM and CM, the diet composition was the same as that of CORN except that a portion of the corn was replaced with barley and molasses or citrus pulp and molasses, respectively, on a dry matter basis. Cows grazed ryegrass (Lolium multiflorum Lam.) pasture. Yield of milk, 3.5% fat-corrected milk, energy-corrected milk, and milk fat, as well as milk fat percentage, were not different among treatments. True milk protein percentage was higher for CORN (2.81%) compared with CM (2.70%), but was not different for BM (2.77%). However, true milk protein yield was not different among treatments. Milk urea N was higher for BM (11.43 mg/dL) compared with both CORN and CM (average: 9.95 mg/dL). There were no differences among CORN, BM, and CM treatments for overall BUN (average: 10.60 mg/dL). At 0400 h, however, cows on CORN had higher BUN than cows on CM (11.43 vs. 9.96 mg/dL), but there were no differences between CORN and BM (average: 11.21 mg/dL) or BM and CM (average: 10.48 mg/dL), and there were no differences among treatments at other time points. The CM diet might have shown more advantage if the pasture crude protein content was higher. Partial replacement of corn with citrus pulp for grazing cows should be further studied using pasture with higher crude protein content. Although cows receiving CM and BM did not produce more milk than cows on CORN, if barley or citrus pulp is less expensive than corn, they may be viable replacements for a portion of the corn supplement for grazing cows.

Animal Nutritional Physiological Phenomena↗
PubMed2005

Nutrient content of whole cottonseed.

The objective of this study was to determine if the nutrient and gossypol contents and in vitro digestibility of 3 types of genetically modified whole cottonseed differed from traditional whole cottonseed. Samples of seed from traditional (no genetic modifications) and genetically modified varieties of cotton grown in 1999 and 2000 were analyzed. Genetic modifications included the insertion of genes to protect cotton from insect pests (Bt), and damage from glyphosate herbicides (RR), and from both (Bt/RR). Year effects were significant for in vitro dry matter (DM) digestibility, gossypol, DM, crude protein (CP), fat, neutral detergent fiber (NDF), acid detergent fiber (ADF), and ash. Higher rainfall resulted in higher CP, fat, and ash and lower NDF and gossypol. There were no differences among seed types for ground or whole seed digestibility, DM, CP, fat, NDF, ADF, ash, lignin, net energy for lactation, amino acids, total fatty acids, or seed index. Overall, the nutrient content and digestibility of varieties of genetically modified seed were similar to that of varieties of traditional whole cottonseed.

Animal Feed↗
PubMed2005

Effect of grazing and fat supplementation on production and reproduction of Holstein cows.

The objective of this trial was to investigate the effects of feeding a soybean oil refining by-product (SORB), made up mainly of sodium salts of long-chain fatty acids, on reproductive performance and productivity of 36 early lactation Holstein cows managed in a free-stall barn or on annual rye-ryegrass pasture. In this 2 x 2 factorial arrangement of treatments, cows consumed 0 or 0.5 kg/d of SORB as part of a total mixed ration for barn cows or as part of a grain supplement fed to cows on intensively, rotationally stocked pasture. Blood was sampled 3 times weekly and plasma was measured for progesterone to assess ovarian activity. Estrus activity was recorded using the HeatWatch estrus detection system. Although average 14-wk milk production (37.2 kg/d) was not different among treatments, barn cows had more persistent lactations than did grazing cows. Cows housed in the barn lost less body weight and returned to initial body weight sooner and had lower mean concentrations of plasma nonesterified fatty acids (464 vs. 261 mEq/L) than those managed on pasture. The milk fat of cows on pasture contained greater proportions of conjugated linoleic acid and linolenic acid but a corresponding 0.22 percentage unit decrease in milk fat concentration (3.39 vs. 3.16%). Cows managed on pasture had greater peak concentrations of plasma progesterone during the first estrous cycle. Cows managed on pasture and fed SORB had the greatest accumulation of plasma progesterone over the 14 wk of the study (SORB x housing interaction). These cows experienced the most mounts during their first estrus (9.3) and pregnancy rate was also greatest for this treatment (62.5%). Feeding SORB did not affect production of milk, fat, or protein. Loss of body condition was less in cows fed SORB. Ruminal fluid concentration of propionate increased and ruminal pH decreased in cows fed SORB. A lower proportion of fatty acids less than 18 carbons in length was found in the milk fat of cows fed SORB, thus indicating lower de novo synthesis of fatty acids. Higher proportions of C18:2n-6 and conjugated C18:2 were found in the milk fat of cows fed SORB. Based on concentrations of plasma progesterone, cows fed SORB experienced their first ovulation earlier (26.7 vs. 42.4 d postpartum) than did cows not supplemented with SORB. Neither housing system nor SORB supplementation influenced detection of first estrus (50.5 d) or the mean length of each estrus period (447 min).

Animals↗
PubMed2005

Dilution rate and pH effects on the conversion of oleic acid to trans C18:1 positional isomers in continuous culture.

In a previous in vitro study, mixed ruminal microorganisms converted oleic acid to a variety of trans monenes when grown in batch cultures under constant environmental conditions. To determine whether a similar conversion occurs under environmental conditions more typical of the rumen, conversion of 13C-labeled oleic acid to biohydrogenation intermediates was determined in ruminal microorganisms grown in continuous culture at two pH (5.5 and 6.5) and liquid dilution rates (0.05 and 0.10/h) arranged factorially. After each morning feeding of the dual-flow continuous cultures, 250 mg of oleic acid in 5 mL of ethanol were injected into each culture. On d 10, 250 mg of oleic-1-(13C) replaced the unlabelled oleic acid in ethanol. Trans fatty acids were isolated from culture samples by solid phase extraction, and 13C enrichment and identity of double bond position was determined by gas chromatography-mass spectroscopy. At pH 6.5 and 0.10/h dilution rate, 13C enrichment was detected in all trans-C18:1 isomers having double bond positions from C6 through C16 in the acyl chain. However, when pH or dilution rate in fermentors was lowered, no 13C enrichment was detected in any trans isomer with a double bond position beyond C10. Enrichment in stearic acid increased by reducing culture pH from 6.5 to 5.5, but decreased when dilution rate dropped from 0.10 to 0.05/h. The stearic acid carbons that originated from oleic acid biohydrogenation increased from 30 to 72% when pH dropped from 6.5 to 5.5. The 13C enrichment of trans-10 was reduced under low pH and dilution rate conditions. The results of this study confirm that ruminal microorganisms are capable of converting oleic acid to a wide variety of trans-C18:1 positional isomers when ruminal conditions are favorable (such as the pH 6.5 and 0.10/h dilution rate treatment). However, at low pH and dilution rate, the conversion of oleic acid to trans-C18:1 still occurs, but positional isomers produced are restricted to double bond positions from C6 to C10. Low pH conditions also increased the conversion of oleic acid to stearic acid.

Animals↗
PubMed2004

Disappearance of docosahexaenoic and eicosapentaenoic acids from cultures of mixed ruminal microorganisms.

Previous studies showed conflicting results regarding the ability of ruminal microorganisms to hydrogenate docosahexaenoic acid (C22:6, DHA) and eicosapentaenoic acid (C20:5, EPA). To determine the disappearance of DHA and EPA from mixed ruminal cultures, 2 ruminal in vitro experiments were conducted using graded levels of DHA and EPA. The first experiment examined DHA added at 0, 5, 10, 15, and 20 mg per culture flask. In the second experiment, EPA was added at 0, 5, 10, and 15 mg per culture flask. Docosahexaenoic acid and EPA were incubated in triplicate in 125-mL flasks, and 5 mL of culture contents was taken at 0, 12, and 24 h for fatty acid analysis by gas liquid chromatography. After 24 h of incubation, 4.1, 4.1, 4.0, and 3.3 mg of DHA disappeared from the 5, 10, 15, and 20 mg of DHA cultures, respectively. In the second experiment, 5, 8.3, and 7.1 mg of EPA disappeared after 24 h of incubation for the 5-, 10-, and 15-mg EPA cultures, respectively. Addition of DHA to cultures increased trans-C18:1 fatty acid accumulation by 105, 91, 82, and 74% for the 5, 10-, 15-, and 20-mg cultures, respectively, compared with control. The addition of EPA increased trans-C18:1 fatty acid accumulation by 56, 64, and 55% for the 5-, 10-, and 15-mg EPA cultures, respectively, compared with control. Addition of DHA and EPA to cultures caused a reduction in C18:1 n-9 and C18:2 n-6 biohydrogenation compared with control. Results from these experiments clearly demonstrate the ability of ruminal microorganism to transform DHA and EPA to other fatty acids causing their disappearance from cultures.

Animals↗
PubMed2004

Performance of lactating dairy cows fed whole cottonseed with elevated concentrations of free fatty acids in the oil.

Twenty-four multiparous cows were used in a 10-wk randomized block design trial to evaluate the effects of feeding whole cottonseed (WCS) containing increasing concentrations of free fatty acids (FFA) in the oil on nutrient intake and digestibility, milk yield and composition, and select plasma metabolites. Two lots of WCS containing either 3 or 12% FFA were blended to provide WCS with 3, 6, 9, and 12% FFA. Cottonseeds were included in the wheat silage-based total mixed ration at 12.5% of dry matter (DM). There was no difference in intakes of DM, crude protein (CP), or neutral detergent fiber; yield of milk; or percentages of milk protein, lactose, or SNF. Milk fat percentage was lowest for the diet containing WCS with 6% FFA. Concentrations of individual milk fatty acids C6:0 decreased and C16:1 increased linearly as FFA in WCS increased. A cubic response was observed for concentrations of C8:0, C10:0, and C12:0 because of higher concentrations when diets contained WCS with 6% FFA than 3 and 12% FFA, which were higher than 9% FFA. Intake and apparent total tract digestibility of acid detergent fiber increased linearly as FFA concentration in WCS increased. Apparent NDF digestibility was highest for diets containing WCS with 3 and 6% FFA; CP digestibility was highest with WCS containing 3 and 9% FFA. Differences in milk fatty acid concentration and nutrient digestibility suggest minor changes in rumen fermentation; however, feeding WCS with up to 12% FFA did not negatively impact nutrient intake and digestibility or milk yield or composition.

Animal Nutritional Physiological Phenomena↗
PubMed2004

The effects of feeding fish oil on uterine secretion of PGF2alpha, milk composition, and metabolic status of periparturient Holstein cows.

The objectives were to determine the effect of dietary fish oil (FO) on uterine secretion of PGF2alpha, milk production, milk composition, and metabolic status during the periparturient period. Holstein cows were assigned randomly to diets containing FO (n = 13) or olive oil (OO, n = 13). Cows were fed prepartum and postpartum diets that provided approximately 200 g/d from 21 d before the expected parturition until 21 d after parturition. The FO used contained 36% eicosapentaenoic acid (EPA, C20:5, n-3) and 28% docosahexaenoic acid (DHA, C22:6, n-3). Blood samples were obtained from 14 d before the due date until d 21 postpartum. A total of 6 FO and 8 OO cows without periparturient disorders were used in the statistical analyses of PGF2alpha-metabolite (PGFM) and metabolite concentrations. Length of prepartum feeding with OO or FO did not differ. Proportions of individual and total n-3 fatty acids were increased in caruncular tissue and milk of cows fed FO. The combined concentrations of EPA and DHA in caruncular tissue were correlated positively with the number of days supplemented with FO. Cows fed FO had reduced concentrations of plasma PGFM during the 60 h immediately after parturition compared with cows fed OO. Concentrations of prostaglandin H synthase-2 mRNA and protein in caruncular tissue were unaffected by diet. Production of milk and FCM were similar between cows fed the two oil diets. However, cows fed FO produced less milk fat. Feeding FO reduced plasma concentrations of glucose. Dietary fatty acids given during the periparturient period can reduce the uterine secretion of PGF2alpha in lactating dairy cows and alter the fatty acid profile of milk fat.

Animals↗
PubMed2004

Ruminal biohydrogenation in Holstein cows fed soybean fatty acids as amides or calcium salts.

Fatty amides of high oleate fats and calcium salts of palm oil were reported to resist biohydrogenation by ruminal microorganisms. This study was conducted to determine whether converting polyunsaturated fat sources to amides and calcium salts had equal ability to resist biohydrogenation. A total mixed ration consisting of forage and concentrate contained (dry basis): 1) 2.45% soybean oil (SBO), 2) 2.75% calcium salt of SBO, 3) 2.75% amide of SBO, or 4) 2.75% of a mixture of the calcium salt and amide (80:20, wt/wt) of SBO. The 4 diets were fed ad libitum to 4 multiparous lactating Holstein cows fitted with ruminal cannulas in a 4 x 4 Latin square with 21-d periods. Omasal samples were taken to measure postruminal fatty acid content and determine the extent of ruminal biohydrogenation. Adding SBO to the diets as either calcium salts or amides increased omasal flow of C18:2 (n-6) from 25 to 39 g/d. Omasal flow of C18:1 increased from 36 to 49 g/d when SBO was fed to cows as calcium salts, but increased to 86 g/d when SBO was fed as amides. Adding the soybean amide to the diet more than doubled the delivery of C18:1 (n-9) to the omasum of lactating cows, but it also increased trans fatty acid production in the rumen accompanied by milk fat depression. In this study, calcium salts and amide derivatives of fatty acids were both effective in enhancing omasal flow of unsaturataed fatty acids in lactating dairy cows. Amides were more effective than calcium salts for increasing the postruminal flow of oleic acid.

Amides↗
PubMed2004

Short communication: docosahexaenoic acid promotes vaccenic acid accumulation in mixed ruminal cultures when incubated with linoleic acid.

Previous studies found that feeding dairy cows a blend of fish and soybean oils enhanced milk vaccenic acid (VA) and conjugated linoleic acid (CLA) concentrations more than when the oils were fed separately. In these studies, the authors concluded that a component in fish oil was stimulating ruminal VA production from other sources of unsaturated fatty acids; however, that component was not identified. The objective of this study was to determine whether docosahexaenoic acid (DHA), an omega-3 fatty acid (FA) in fish oil, is the active component that promotes trans-C18:1 FA, VA in particular, accumulation using cultures of mixed ruminal microorganisms. Treatments consisted of control, control plus 5 mg of DHA (DH), control plus 30 mg of soybean oil (SBO), and control plus 5 mg of DHA and 30 mg of SBO (DHSBO). Treatments were incubated in triplicate in 125-mL flasks, and 5 mL of culture contents was taken at 0 and 24 h for fatty acid analysis by gas-liquid chromatography. After 24 h of incubation, the level of trans-C18:1 FA (14.1 and 11.7 mg/culture) and VA (13.0 and 10.2 mg/culture) increased more with added DHA than with added SBO, respectively. Combining DHA and SBO yielded higher quantities of trans-C18:1 FA (21.3 mg/culture) and VA (19.8 mg/culture) in the cultures than either fat source alone. These data suggest that DHA is the component in fish oil that promotes VA accumulation when incubated with linoleic acid.

Animals↗
PubMed2003

Challenges with fats and fatty acid methods.

The content and chemical nature of lipids in feedstuffs is heterogeneous. It has long been known that ether extraction by the Weende procedure inadequately characterizes the fat content of feedstuffs, yet it remains the official method. Diethyl ether (or hexanes that are often used) extracts significant amounts of nonnutritive, nonsaponifiable lipids from forages, and often incompletely extracts lipids of nutritional value, especially fatty acids present as salts of divalent cations. Preextraction hydrolysis of insoluble fatty acid salts with acid releases these fatty acids, and this step is included in the official procedure for certain feedstuffs in the United Kingdom; however, acid hydrolysis increases analysis time and decreases precision. Acid hydrolysis also causes confusion as to the proper definition of the fat content of feedstuffs. A preferred method of fat analysis determines the total fatty acid concentration in feed samples by converting fatty acid salts, as well as the acyl components in all lipid classes, such as triacylglycerols, phospholipids, and sphingolipids, to methyl esters using a simple, direct one-step esterification procedure. Fatty acid methyl esters are then quantified by GLC, which provides information on both fatty acid quantity and profile in a single analysis. Adjustments in conditions and reagents may be necessary to overcome difficulty in quantitatively preparing esters from certain types of fatty acids and their derivatives in commercial fat supplements. After correction for glycerol content, analysis of oils by this procedure provides information on the content of nonsaponifiable material, such as chlorophyll, waxes, and indigestible polymers formed from heat- or oxidatively damaged fats. The correct description of feedstuffs for energy value of fats is the content of total fatty acids.

Animal Feed↗
PubMed2003

Monensin by fat interactions on trans fatty acids in cultures of mixed ruminal microorganisms grown in continuous fermentors fed corn or barley.

In previous studies, monensin (M) and unsaturated plant oils independently increased trans fatty acid concentrations in cultures of mixed ruminal microorganisms. This study was conducted to determine if combining M with plant oil yielded interactions on trans fatty acid concentrations in cultures of mixed ruminal microorganisms or their effects were additive. Four continuous fermentors were fed 14 g of dry feed per day (divided equally between two feedings), consisting of alfalfa hay pellets (30% of DM) and either a high corn (HC) or a high barley (BB) concentrate (70% of DM) in each of two fermentors. Within each grain type, one fermentor was supplemented with M (25 ppm), and the other fermentor was supplemented with 5% soybean oil (SBO) during d 5 to 8. Monensin and SBO were added together in all fermentors during d 9 to 12. Samples were taken at 2 h after the morning feeding on the last day of each period and analyzed for fatty acids by gas-liquid chromatography. A second run of the fermentors followed the same treatment sequence to give additional replication. Average pH across all treatments was 6.15, which was reduced by M but not affected by SBO. Monensin reduced the ratio of acetate to propionate (A:P), which averaged 2.03 across all treatments; fat decreased A:P in cultures not receiving M but increased it in the presence of M. Monensin and SBO altered the concentration of several trans fatty acids, but the only interaction was a grain x M x SBO interaction for trans-10 C18:1. The increase in trans-10 C18:1 by the M and SBO combination exceeded the sum of increases in trans-10 C18:1 for each individual feed additive, but only for KB. For the HC diet, M increased trans-10 C18:1 more than fat alone and more than the M and SBO combination. The results of this study show that M and SBO effects are additive for all trans FA except for trans-10 C18:1. In the case of trans-10 C18:1, M and SBO interacted to give higher trans-10 C18:1 concentrations in ruminal contents than would be expected simply by adding their individual effects, but only for HB. Because some trans fatty acid isomers have been associated with milk fat depression in dairy cows, these results suggest more severe depressions in milk fat content when cows are fed M along with unsaturated plant oils.

Animal Feed↗
PubMed2002

Factors affecting conjugated linoleic acid and trans-C18:1 fatty acid production by mixed ruminal bacteria.

The objective of this study was to identify environmental factors that influence conjugated linoleic acid (CLA) and trans-C18:1 fatty acid production by mixed ruminal bacteria. Ruminal contents were collected from a 600-kg ruminally fistulated Hereford steer maintained on pasture. Mixed ruminal bacteria were obtained by differential centrifugation under anaerobic conditions and added to a basal medium that contained a commercial emulsified preparation of soybean oil and a mixture of soluble carbohydrates (cellobiose, glucose, maltose, and xylose). Culture samples were collected from batch culture incubations at 0, 2, 4, 6, 8, 12, 24, 26, 28, 30, 32, and 48 h. Continuous culture incubations were conducted at dilution rates of 0.05 and 0.10 h(-1) with extracellular pH values of 5.5 and 6.5, and 0.5 and 1.0 g/L of mixed soluble carbohydrates. Culture samples were obtained from the culture vessel once steady-state conditions had been achieved. In batch culture, trans-C18:1 concentrations increased over time and reached a maximum at 48 h. Little CLA was produced during the first 8 h, but cis-9, trans-11 CLA concentrations remained high between 24 and 30 h. When mixed ruminal bacteria were maintained in continuous culture on 0.5 g/L of mixed soluble carbohydrates, concentrations of trans-C18:1 and cis-9, trans-11 CLA were reduced (P < 0.05) at a dilution rate of 0.05 h(-1) and an extracellular pH of 5.5. Similar effects were also observed when 1.0 g/L of mixed soluble carbohydrates was used. When extracellular pH was lowered to 5.0, neither trans-C18:1 or CLA isomers were detected. In conclusion, our results suggest that culture pH appears to have the most influence on the production of trans-C18:1 and CLA isomers by mixed ruminal bacteria.

Animals↗
PubMed2002

The biohydrogenation of linoleamide in vitro and its effects on linoleic acid concentration in duodenal contents of sheep.

Previous studies showed that oleamide was protected from ruminal biohydrogenation and increased 18:1(n-9) concentration in milk when fed to lactating dairy cows. To appraise whether this protection extended to linoleamide, a rumen in vitro experiment was conducted to determine biohydrogenation of linoleamide followed by two sheep experiments to evaluate whether linoleamide could increase 18:2 (n-6) concentration in duodenal contents. Treatments for the in vitro and sheep studies consisted of three diets containing no added lipid (control), linoleic acid, or linoleamide. Lipids were added at 10% (DM basis) of the in vitro substrate (ground grass hay). The three substrates were incubated with mixed ruminal microbes in triplicate, and 5 mL of culture contents was taken at 0, 24, and 48 h for analysis of 18:2 (n-6) concentration by gas chromatography. The concentrations of 18:2 (n-6) (corrected for 18:2 (n-6) in the control cultures) at 0, 24, and 48 h were 2.51, 0.38, and 0.11 mg/5 mL for the linoleic acid cultures compared to 2.10, 1.35, and 1.08 mg/5 mL for the linoleamide cultures. Compared to linoleic acid, the cultures containing linoleamide had higher 18:1 (n-9) and lower concentrations of biohydrogenation products including trans-18:1 and 18:0. Three sheep with duodenal cannulas were fed the three diets in two separate 3 x 3 Latin squares each with 2-wk periods. The two squares only differed in the amount of added lipid (1.5 vs 5% of the ration DM). When the lipids were added at 1.5% of the ration DM, they had little effect on duodenal 18:2 (n-6) concentration (2.8, 3.6, and 4.3 mg/g DM for the control, linoleic acid, and linoleamide treatments, respectively). At 5% of the ration DM, both lipid supplements increased duodenal 18:2 (n-6) concentration over the control diet with a greater response observed for linoleamide (2.5, 12.2, and 16.8 mg/g DM for the control, linoleic acid, and linoleamide treatments, respectively). This study demonstrates reduced biohydrogenation of linoleamide based on its ability to maintain a higher concentration of 18:2 (n-6) in ruminal cultures and in duodenal contents of sheep compared to free linoleic acid.

Animals↗
PubMed2002

Effects of feeding time on nitrogen capture by lactating dairy cows grazing rye pasture.

The objective of this experiment was to determine whether varying times at which a partial mixed ration was fed, either before or after grazing, affected N utilization from rye pasture and thus affected milk yield and components. Sixteen Holstein cows were fed a partial mixed ration (PMR) either at 0700, 0830, or 1100 h. Cows were milked at 0900 h and turned out to graze at 0930 h. Treatments represented feeding times 2.5 h and 1 h before grazing and immediately after grazing. The study was conducted as a 3 x 3 Latin square with three 17-d periods. There were no significant differences among treatments for pasture intake or yield of milk or milk components. Milk yield, fat %, and protein % were 29.4, 29.6, and 29.3 kg, 3.5, 3.5, and 3.4%, and 3.4, 3.5, and 3.4% for treatments, respectively. The milk urea levels were 15.6, 15.1, and 15.5 mg/dl, and were not different among treatments. Blood samples were collected on the last day of each period at 0645, 0845, 1045, 1200, and 1400 h. Blood urea nitrogen (BUN) was measured as an indicator of ruminal N capture. Concentrations were not significantly different among diets before grazing; however, they were significantly different among all treatments approximately 1 h after cows were removed from pasture. Cows fed at 0700 h, 2 h before grazing, maintained lower BUN levels across the 7 h during which the blood samples were collected. Cows that ate the PMR immediately after grazing maintained the highest BUN. Feeding a PMR to cows that graze at different times before and after grazing affected the capture of ruminal N, as indicated by differences in the levels of BUN, but there was no effect on yield of milk or milk components.

Animal Nutritional Physiological Phenomena↗
PubMed2001

Synthesis of the first example of a C2-C3/C2'-C3'-endo unsaturated pyrrolo[2,1-c][1,4]benzodiazepine dimer.

We report the first example of a C2-C3/C2'-C3'-endo unsaturated pyrrolo[2,1-c][1,4]benzodiazepine (PBD) dimer 16 synthesised through a new and efficient route, thus establishing that C2-C3-endo unsaturation enhances both cytotoxicity and DNA-binding affinity in A-Ring-linked PBD dimers but to a lesser extent than C2/C2'-exo-unsaturation. This new route has allowed the preparation of multi-gram quantities of the related clinical candidate 1 and should lead to more structurally diverse PBD dimer analogues.

Azepines↗
PubMed2001

Design, synthesis, and evaluation of a novel pyrrolobenzodiazepine DNA-interactive agent with highly efficient cross-linking ability and potent cytotoxicity.

A novel sequence-selective pyrrolobenzodiazepine (PBD) dimer 5 (SJG-136) has been developed that comprises two C2-exo-methylene-substituted DC-81 (3) subunits tethered through their C8 positions via an inert propanedioxy linker. This symmetric molecule is a highly efficient minor groove interstrand DNA cross-linking agent (XL(50) = 0.045 microM) that is 440-fold more potent than melphalan. Thermal denaturation studies show that, after 18 h incubation with calf thymus DNA at a 5:1 DNA/ligand ratio, it increases the T(m) value by 33.6 degrees C, the highest value so far recorded in this assay. The analogous dimer 4 (DSB-120) that lacks substitution/unsaturation at the C2 position elevates melting by only 15.1 degrees C under the same conditions, illustrating the effect of introducing C2-exo-unsaturation which serves to flatten the C-rings and achieve a superior isohelical fit within the DNA minor groove. This behavior is supported by molecular modeling studies which indicate that (i) the PBD units are covalently bonded to guanines on opposite strands to form a cross-link, (ii) 5 has a greater binding energy compared to 4, and (iii) 4 and 5 have equivalent binding sites that span six base pairs. Dimer 5 is significantly more cytotoxic than 4 in a number of human ovarian cancer cell lines (e.g., IC(50) values of 0.0225 nM vs 7.2 nM, respectively, in A2780 cells). Furthermore, it retains full potency in the cisplatin-resistant cell line A2780cisR (0.024 nM), whereas 4 loses activity (0.21 microM) with a resistance factor of 29.2. This may be due to a lower level of inactivation of 5 by intracellular thiol-containing molecules. A dilactam analogue (21) of 5 that lacks the electrophilic N10-C11/N10'-C11' imine moieties has also been synthesized and evaluated. Although unable to interact covalently with DNA, 21 still stabilizes the helix (Delta T(m) = 0.78 degrees C) and has significant cytotoxicity in some cell lines (i.e., IC(50) = 0.57 microM in CH1 cells), presumably exerting its effect through noncovalent interaction with DNA.

Antineoplastic Agents↗