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Biomedical subjects

J H Clark

Publications and source records attributed to J H Clark.

At least 55 records · Page 3Linked to original sources
PubMed1995

Influence of altering ruminal degradation of soybean meal protein on in situ ruminal fiber disappearance of forages and fibrous byproducts.

The objective was to determine the effects of altering ruminal CP degradation of soybean meal (SBM) by roasting (Exp. 1) on ruminal characteristics and extents of in situ disappearance of DM, OM, and fiber components (Exp. 2). A control diet (8.2% CP) containing oat hulls, corn silage, starch grits, ammoniated corn cobs, and molasses was supplemented to 17.1% CP with unroasted SBM (SBM-0) or SBM roasted at 165 degrees C for 75, 150, or 210 min (SBM-75, SBM-150, and SBM-210, respectively). In Exp. 1, SBM was incubated for 0, 2, 4, 8, 12, 16, and 24 h in the rumen of two steers that were fed the SBM-0 diet. Extents of ruminal CP degradation and rates of N disappearance decreased (P < .05) linearly with increasing roasting time of SBM. In Exp. 2, five ruminally cannulated steers were used in a 5 x 5 Latin square design and were fed the five diets listed above during five 11-d periods. On d 11, five substrates (alfalfa hay, orchardgrass hay, corn silage, soy hulls, and wheat straw) were incubated in the rumen for 24 h. Extents of in situ disappearance of DM, OM, and fiber (NDF, ADF, cellulose, hemicellulose, and total dietary fiber) were analyzed as a split-plot design. No substrate x diet interaction (P > .05) was observed for any of the measurements evaluated. Extents of in situ disappearance (24 h) of DM, OM, and fiber were highest (P < .05) when the control diet was fed and were lowest (P < .05) when the SBM-0 diet was fed. Decreasing the availability of SBM protein in the diet by roasting increased (P < or = .10) extents of in situ disappearance of DM, OM, and fiber linearly. These extents were similar for steers fed the control diet or the diet containing SBM-210. Ruminal concentrations of NH3 N, branched-chain VFA, and valerate were highest (P < .05) and ruminal pH lowest (P < .05) when the SBM-0 diet was fed. Results indicated a rapid ruminal fermentation of both protein and readily available carbohydrates of SBM (resulting in pH below 6.0) during the first 4.5 h after feeding the SBM-0 diet. Making both protein and readily available carbohydrates of SBM more slowly fermentable by roasting slowed early fermentation processes, maintained higher ruminal pH, and encouraged earlier and faster ruminal fiber digestion.

Animal Feed↗
PubMed1995

High oil corn as silage or grain for dairy cows during an entire lactation.

Forty-five multiparous Holstein cows were used to compare the effects of diets that contained high oil corn grain, high oil corn silage, or a combination of both. At wk 4 after calving, cows were assigned to one of four treatment in a 2 (silage type) x 2 (grain type) factorial arrangement: 1) control silage and control grain, 2) high oil silage and control grain, 3) control silage and high oil grain, or 4) high oil silage and high oil grain. Diets contained haylage, corn silage, and concentrate (25:25:50, DM basis); corn grain was 27% of dietary DM. Data were analyzed for wk 4 to 17 and wk 4 to 43 of lactation and adjusted for covariate measurements made during wk 3. During wk 4 to 43, DMI increased when high oil grain was included in the diet, but was unaffected by type of silage. During wk 4 to 43 of lactation, yields of milk, CP, and fat; percentages and yields of N components in milk; body condition score; BW; and concentrations of NEFA, glucose, BHBA, and urea N in plasma were not affected by type of silage or corn grain fed. Results were similar for wk 4 to 17, except that milk yield tended to be higher for cows fed the high oil grain, and CP content of milk was lower when high oil corn silage was in the diet. Compared with corn grain from typical hybrids, high oil grain may improve DMI and milk yield of dairy cows during early lactation.

3-Hydroxybutyric Acid↗
PubMed1995

Ruminal fermentation and passage of nutrients to the duodenum of lactating cows fed mixtures of corn and barley.

Five Holstein cows were used in a 5 x 5 Latin square design and fed diets containing five different ratios of starch from ground shelled corn and steam-rolled barley. The DMI decreased and both the proportions of OM and starch digested in the rumen increased as barley starch increased in the diet. Corn and barley starches fed in a ratio of 75:25 maximized the proportions of ADF and NDF digested in the rumen. Replacement of 25% of the corn starch with barley starch resulted in the largest increase in the molar percentage of propionate and the largest decrease in the molar percentage of acetate in ruminal fluid. Passage of NAN to the duodenum was not affected by treatment; however, the percentage of nonammonia nonmicrobial N in NAN decreased as barley starch increased. Passage of AA to the duodenum was largest when corn and barley starches were fed in ratios of 100: 0 and 0:100 because of the influence of DMI and microbial protein synthesis. Production of Milk, CP, and SNF was similar when cows were fed diets containing corn and barley starches in ratios of 100:0, 75:25, and 50:50 but was decreased when the ratios were 25:75 and 0:100. Increased production responses of cows when diets contained larger amounts of starch from ground shelled corn were probably due to increased DMI.

Amino Acids↗
PubMed1994

Convergent pathways for steroid hormone- and neurotransmitter-induced rat sexual behavior.

Estrogen and progesterone modulate gene expression in rodents by activation of intracellular receptors in the hypothalamus, which regulate neuronal networks that control female sexual behavior. However, the neurotransmitter dopamine has been shown to activate certain steroid receptors in a ligand-independent manner. A dopamine receptor stimulant and a D1 receptor agonist, but not a D2 receptor agonist, mimicked the effects of progesterone in facilitating sexual behavior in female rats. The facilitory effect of the neurotransmitter was blocked by progesterone receptor antagonists, a D1 receptor antagonist, or antisense oligonucleotides to the progesterone receptor. The results suggest that in rodents neurotransmitters may regulate in vivo gene expression and behavior by means of cross-talk with steroid receptors in the brain.

Adrenal Glands↗
PubMed1994

Nitric oxide mediates sexual behavior in female rats.

Nitric oxide (NO), an active free radical formed during the conversion of arginine to citrulline by the enzyme NO synthase (NOS), mediates vasorelaxation, cytotoxicity, and neurotransmission. Neurons containing NOS (NOergic) are located in the hypothalamus. These NOergic neurons control the release of several hypothalamic peptides. Release of NO from these NOergic neurons stimulates pulsatile release of luteinizing hormone-releasing hormone (LHRH) in vivo and LHRH release in vitro. LHRH not only induces LH release, which induces ovulation, but also facilitates female sexual behavior. Sexual behavior can be induced reliably in estrogen-primed ovariectomized female rats by progesterone (P). This behavior consists of proceptive behavior to attract the male and the assumption of a clear characteristic posture, lordosis, when mounted by the male. To ascertain the role of NO in the control of sexual behavior in female rats, an inhibitor of NOS, NG-monomethyl-L-arginine was microinjected into the third cerebral ventricle (3V) of conscious, ovariectomized, estrogen-primed rats with indwelling cannulae. NG-Monomethyl-L-arginine (10-1000 micrograms) prevented P-facilitated lordosis when administered intracerebroventricularly into the 3V, 20 min prior to the 3V injection of P. NG-Monomethyl-D-arginine, which does not inhibit NOS, did not inhibit lordosis under the same experimental conditions. Microinjection into the 3V of sodium nitroprusside (SNP), which spontaneously releases NO, facilitated lordosis in estrogen-primed rats in the absence of P. The facilitation of lordosis induced by either P or SNP was prevented by intracerebroventricular injection of hemoglobin, which binds NO. Lordosis facilitated by P or SNP was blocked by injection of LHRH antiserum into the 3V. The results are interpreted to mean that the P-facilitated lordosis response is mediated by LHRH release. Furthermore, since NO release from SNP also facilitates lordosis in the absence of P and this response could be blocked by LHRH antiserum, we conclude that P brings about the release of NO, which stimulates LHRH release that facilitates lordosis. Thus, the results indicate that NO induces LHRH release and that LHRH then plays a crucial role in mediation of sexual behavior in the female rats.

Amino Acid Oxidoreductases↗
PubMed1994

Estrogen affinity crosslinking to tyrosinase-like immunoreactive proteins of rat uterine nuclear extracts.

We have previously described tyrosinase-like proteins of rat uterine nuclear extracts with type II estrogen binding characteristics. In this paper we have been able to affinity label these polypeptides with radio-iodinated estradiol. The major label at approximately 33-38 kDa comigrates with a approximately 36 kDa tyrosinase immunoreactive band assessed by autoradiograms and Western blots following electrophoresis. A minor label was also detected at approximately 45 kDa. The label is attenuated by excess quercetin hence these proteins are believed to represent putative type II estrogen binding sites that bind this bioflavonoid. These estrogen binding proteins are distinct from the estrogen receptor as judged by immunoblotting. The affinity crosslinking will be a useful approach in the purification of tyrosinase like proteins.

Animals↗
PubMed1994

Hormonal regulation of hypothalamic gene expression: identification of multiple novel estrogen induced genes.

Estrogen (E) has been shown to play a major role in hypothalamic function and is a prerequisite for progesterone (P) induced sexual behavior in female rats. In the course of studies in search of steroid induced hypothalamic genes, we discovered a surprisingly large number of E-induced genes (21 mRNAs in total). This is the largest number of E-induced genes ever identified in a single organ. Many of these mRNAs exhibit considerable magnitudes of induction and their levels were maintained typically during subsequent P treatment. Among the induced genes, several encode metabolic enzymes and may account for some of the morphological changes observed in hypothalamic neurons in response to E. Since E appears to play a major role in defining the pattern of hypothalamic gene expression in conjunction with its capacity for behavioral modulation, these newly identified cDNAs may serve as genetic markers for correlative studies of E-induced central nervous system behavior.

Animals↗
PubMed1994

Inhibition of rat sexual behavior by antisense oligonucleotides to the progesterone receptor.

To test further the idea that sexual behavior in rodents is mediated via the progesterone receptor (PR) in the ventromedial nucleus of the hypothalamus, antisense and sense oligonucleotides to progesterone receptor were administered intracerebroventricularly into the third cerebral ventricle of ovariectomized estrogen-primed animals. Progesterone-facilitated sexual behavior was inhibited in animals treated with antisense oligonucleotides, with proceptive and receptive responses being minimal or completely suppressed. Sexual behavior was not altered by control sense oligonucleotides. In vitro binding assays of the cytosol progesterone receptors demonstrated a 52.2% reduction of PRs in the hypothalamus of animals that received antisense oligonucleotides, suggesting a reduction in PR synthesis. These data suggest that a threshold level of estrogen-induced hypothalamic PR is critical in the regulation of progesterone-facilitated sexual behavior in female rats.

Animals↗
PubMed1994

Infusion of four long-chain fatty acid mixtures into the abomasum of lactating dairy cows.

Five Holstein cows were utilized in a Latin square design to determine the effects of postruminal profile of fatty acids on DMI, milk yield and composition, nutrient digestibilities, and metabolites in blood. Treatments were abomasal infusions of 1) control, 169 to 180 g/d of meat solubles; 2) control plus 450 g/d of mostly saturated fatty acids; 3) canola fatty acids; 4) soybean fatty acids; or 5) sunflower fatty acids. Infusion of fatty acids decreased intakes of DM, CP, and gross energy; yields of milk, FCM, SNF, total solids, CP, NPN, true protein, whey protein, and casein; and percentages of SNF, CP, NPN, true protein, and casein in milk. Cows infused with mostly saturated fatty acids consumed more CP and digestible energy; yielded more milk, FCM, fat, SNF, total solids, CP, true protein, and casein; and had greater percentages of SNF and total solids in milk than cows infused with unsaturated fatty acids. Milk fatty acids reflected the profile of the infused fatty acid mixture. Ruminal characteristics and apparent digestibilities of DM, NDF, energy, and fatty acids generally were not different among treatments. The profile of fatty acids reaching the small intestine may influence responses when supplemental fats are fed to lactating dairy cows.

Abomasum↗
PubMed1994

Secretion of oleic acid in milk fat in response to abomasal infusions of canola or high oleic sunflower fatty acids.

The feasibility of dietary strategies to increase oleic acid content of milk fat is unclear. Four Holstein cows were infused abomasally with free long-chain fatty acids from canola (62.5% C18:1) or high oleic sunflowers (86% C18:1). Each fatty acid mixture was infused for 3 d at 0, 133, 267, 400, 267, 133, and 0 g/d for a total of 21 d; cows then were changed to the opposite fatty acid mixture, and the infusion sequence was repeated. The DMI and percentages of casein and whey N in milk were decreased by infusion of fatty acids, but milk yield and percentages of fat and NPN in milk were increased. Contents of short- and medium-chain fatty acids and C16:0 in milk fat decreased, and contents of C18:1, C18:2, and C18:3 increased, as fatty acid infusion increased. Contents of C16:0 and C18:0 in plasma triglyceride were decreased, and content of C18:1 was increased, by increasing infusion of fatty acids. All changes reversed when the amount of fatty acid infused was decreased. Within the range of amounts of fatty acids infused, the relationship between yield of C18:1 in milk fat and the amount of C18:1 infused into the abomasum was linear, and transfer efficiency was 54.1%. Increased concentration and yield of C18:1 in milk were attributable mostly to the increased exogenous supply of C18:1.

Abomasum↗
PubMed1994

Effects of amount of protein and ruminally protected amino acids in the diet of dairy cows fed supplemental fat.

The objectives of this experiment were to investigate the effects of amount of dietary CP and ruminally protected AA supplementation on production of milk and milk components, ruminal fermentation, and nutrient digestibilities by cows fed diets containing high oil corn and tallow. Holstein cows in midlactation producing 22 to 25 kg/d of milk were used in a 5 x 5 Latin square design. Treatments were 1) control (16.8% CP, no added fat); 2) 14.2% CP, no AA; 3) 14.2% CP, with AA; 4) 17.5% CP, no AA; and 5) 17.5% CP, with AA. Diets 2 to 5 contained supplemental fat from high oil corn and tallow. Diets consisted of 33% alfalfa haylage, 17% corn silage, and 50% concentrate DM. Intake of DM was not different among treatments. Dietary fat increased yields of milk, fat, SNF, and total solids and percentages of fat and total solids. Increasing CP from 14.2 to 17.5% did not alter production or composition of milk. Supplemental AA increased yields of 4% FCM, milk fat, milk CP, true protein, and casein protein and percentages of CP, true protein, and casein protein in milk when either 14.2 or 17.5% CP was in the diet. Supplemental fat did not alter ruminal fermentation, but increases in dietary CP increased total VFA concentration in the rumen without affecting proportions of individual VFA. Apparent digestibilities of DM, OM, CP, starch, and energy in the total tract were greater for cows fed the 17.5% CP diets. Addition of AA to the 14.2% CP diet increased apparent digestibilities of DM, OM, ADF, NDF, and energy in the total tract but decreased digestibilities for cows fed the 17.5% CP diets. Feeding AA to midlactation cows in diets containing supplemental fat may alleviate the decrease in milk protein percentage associated with fat supplementation; this response was similar for cows fed diets that contained either 14.2 or 17.5% CP.

Amino Acids↗
PubMed1994

Evaluation of chemical and physical properties of feeds that affect protein metabolism in the rumen.

The goal of the NC-185 Cooperative Regional Research Project is to provide the information needed to improve the nutrition and feeding of dairy cattle, a major factor determining composition of milk and cost of milk yield. Emphasis is placed on understanding how energy and protein nutrition of lactating cows can be manipulated to increase the quantity and improve the profile of AA passing to the small intestine and to improve yield of milk and milk protein. To achieve this goal, one of the major objectives of this project has been to evaluate quantitatively the chemical and physical properties of protein and energy sources that determine AA availability to lactating cows. Reliable measurements of microbial protein synthesis and protein degradation in the rumen are critical in the evaluation process. Therefore, one of the ongoing areas of investigation of this research project has been to determine the most appropriate methods for estimating microbial protein synthesis and dietary protein degradation in the rumen. Other areas have been investigated, using continuous culture fermenters and ruminally and duodenally cannulated cows, including factors that alter microbial metabolism of N in the rumen and subsequently protein supply to the small intestine, such as sources of carbohydrate, protein, and fat and interrelationships of protein and carbohydrate. Findings of the NC-185 Cooperative Regional Research Project Committee and other investigators are summarized in this review.

Animal Feed↗
PubMed1993

Variants of somatotropin in cattle: gene frequencies in major dairy breeds and associated milk production.

The amino acid sequence of bovine somatotropin (bST) varies at position 127 where either valine or leucine is found. The frequencies of leucine127 and valine127 bST gene alleles in cows (n = 302) and sires (n = 70) from major dairy breeds (Holstein, Brown Swiss, Guernsey, Jersey, and Ayrshire) were determined using DNA extracted from whole blood or spermatozoa. A 428 base pair fragment of the bST gene was amplified using polymerase chain reaction (PCR) and variants of the bST gene were detected as polymorphisms by Alu I restriction endonuclease digestion of PCR products. Restriction enzyme DNA fragments for the leucine127 variant were 265, 96, 51, and 16 base pair and for the valine127 variant were 265, 147, and 16 base pair as a polymorphism of bST was present in the 147 base pair DNA fragment. Frequencies of leucine127 and valine127 alleles for cows (n = 302) were 1.0 and 0 for Brown Swiss, .93 and .07 for Holstein, .92 and .08 for Guernsey, .79 and .21 for Ayrshire, and .56 and .44 for Jersey, respectively. In Holstein sires used for artificial insemination (n = 70), the frequency of leucine127 and valine127 alleles was .96 and .04. Estimates of transmitting ability for milk production tended to be greater for Holstein cows that were homozygous for leucine127 bST and Jersey cows that were homozygous for valine127 bST whereas Holstein sires with different bST genotypes were similar. In summary, frequencies of alleles for the bST gene were not similar in different dairy breeds and estimates of milk production were correlated with bST gene variant in cows but not sires.

Alleles↗
PubMed1993

Proposal of Quinella ovalis gen. nov., sp. nov., based on phylogenetic analysis.

Quin's oval is a relatively large bacterium often seen in the rumens of sheep fed diets containing some readily fermented carbohydrates. It has not been obtained in axenic cultures, but a number of its features have been determined by various methods, such as studying cell suspensions purified from rumen fluid by differential centrifugation. We obtained similarly purified suspensions from a sheep fed a diet containing a large amount of molasses. Nearly complete 16S rRNA sequence analysis of these cells as well as cells as Selenomonas ruminantium subsp. ruminantium GA192 (ATCC 12561; type strain) and S. ruminantium subsp. lactilytica HD4 (ATCC 27209) was done. These sequences were compared with those of other bacteria. Evolutionary distance estimates indicated that Quin's oval was most closely related to the Selenomonas-Megasphaera-Sporomusa group in the gram-positive phylum but that it belongs in a new genus. We propose the name Quinella ovalis gen. nov., sp. nov., with its description based on previously known features.

Animals↗
PubMed1993

Dose titration of sustained-release recombinant bovine somatotropin in lactating dairy cows.

Lactating dairy cows (n = 264) were used in seven dose titration experiments at four geographic locations in the United States. A sustained-release formulation of recombinant bST was evaluated for a 30-wk treatment period that began 14 wk postpartum. The first series of four experiments evaluated doses of 0, 140, 350, or 700 mg of bST/14 d (series A); the second series evaluated doses of 0, 56, 140, or 350 mg of bST/14 d (series B). Milk yield, DMI, milk composition, body condition, health, and reproductive parameters were measured. Multiparous cows in series A that were administered 700 mg of bST/14 d yielded 3.0 kg/d more milk and 3.5% FCM than control cows. When all seven experiments were combined, multiparous cows that were administered 350 mg of bST/14 d yielded 2.7 and 2.6 kg/d more milk and 3.5% FCM than control cows. Dry matter intake was not significantly affected by bST administration. In series A, an increase in milk yield with no increase in DMI resulted in lower adequacy of dietary NEL and CP to meet maintenance and yield requirements among multiparous cows administered 700 mg of bST/14 d. Primiparous cows that were administered bST in series A and both parity groups in the combined seven experiments were not different from control cows in the adequacy of dietary NEL or CP to meet maintenance and yield requirements. No adverse effects of bST on health parameters were significant, and doses of 350 mg of bST/14 d or less caused no changes in reproductive parameters. Conception rate was decreased by administration of 700 mg of bST/14 d. These data suggest that 350 mg of bST/14 d increased yields of milk and FCM with no adverse effects on DMI, health, or reproduction in dairy cows.

Animals↗
PubMed1993

Influence of amount and degradability of protein on production of milk and milk components by lactating Holstein cows.

Forty-one multiparous cows were utilized in a completely randomized design with a 2 x 2 factorial arrangement of treatments to evaluate the amount and degradability of dietary CP on production of milk and milk components. The TMR contained 25% alfalfa haylage, 25% corn silage, and 50% concentrate to provide either 16.4 or 19.4% CP with a calculated ruminal degradability of 55 or 70%. Intakes of DM, ADF, and NDF and BW were not different among treatments. Production of milk, 4% FCM, fat, CP, and SNF was not affected by amount or degradability of dietary CP. Milk CP percentage was not affected significantly by amount or degradability of CP. Milk fat percentage was increased by the diet that was high in ruminally undegradable protein (2.90 and 3.12; low and high ruminally undegradable protein, respectively). These data suggest that synthesis of milk and milk components was not limited by a shortage of AA or that the different dietary sources of supplemental CP did not alter AA availability.

Animal Feed↗
PubMed1993

Influence of amount and degradability of dietary protein on nitrogen utilization by dairy cows.

Four Holstein cows fitted with ruminal and T-type duodenal cannulas were utilized in a 4 x 4 Latin square design with a 2 x 2 factorial arrangement of treatments. The TMR contained 25% alfalfa haylage, 25% corn silage, and 50% concentrate and provided either 16.4 or 19.6% CP, with ruminal degradability calculated to be 30 or 45%. Intakes of DM, OM, ADF, NDF, and N were not altered by either amount or degradability of CP. Intake and ruminal and postruminal digestibility of starch were greater when cows were fed diets high in undegradable CP but was not altered by amount of CP. Apparent total tract digestibilities for DM, OM, starch, ADF, and NDF were similar among treatments. Apparent total tract digestibility of N was 4.7 percentage units greater for diets low in ruminally degradable CP. Apparent digestibility of OM, ADF, and NDF and true digestibility of OM in the rumen were not altered by amount of CP or undegradable CP. Increasing the CP content of the diet and the proportion of undegradable CP in the diet increased NAN flow to the duodenum. Except for Met, flows of all AA to the duodenum were increased when CP was increased. Flow of Met to the duodenum was not altered by undegradable CP content of the diet. Production of milk, 4% FCM, and milk CP was not altered by amount of CP or undegradable CP. Milk fat content and yield were increased when diets high in undegradable CP were fed. Results suggest that all diets supplied adequate amounts of AA for these cows or that Met was deficient for all cows.

Amino Acids↗