Biomedical subjects

J W West

Publications and source records attributed to J W West.

At least 19 recordsLinked to original sources

PubMed2007

Performance of lactating dairy cows fed whole cottonseed coated with gelatinized starch plus urea or yeast culture.

Thirty lactating Holstein cows were used in an 8-wk randomized design trial to test the viability of select additives included in the gelatinized corn starch coating applied to whole cottonseed (WCS) on nutrient intake and digestibility and milk yield and composition. Treatments included WCS coated with 2.5% gelatinized corn starch (control); control plus 0.5% urea; or control plus 2.0% yeast culture. The treated WCS represented 12.6% of the dietary dry matter. Cellulose intake was lower for the control coating compared with either the urea or yeast coating because of slightly lower cellulose concentrations in the control treatment. Intake of all other nutrients was similar for all treatments. Whole-tract nutrient apparent digestibility was not altered by treatment. Dry matter intake and milk yield were similar among treatments. Percentage solids-not-fat was lower for the yeast treatment compared with control, but no other differences were observed in milk composition among treatments. Efficiency of milk production (energy-corrected milk yield per unit of dry matter intake) was higher for the urea and yeast treatments compared with control because of slightly higher yield of milk fat and energy-corrected milk. No differences were observed in body weight change during the trial between treatments. Results of this trial indicate that including urea or yeast culture in the gelatinized starch coating does not change whole tract digestibility, but does improve milk production efficiency.

Animal Feed↗

PubMed2006

Effect of prepartum dietary calcium on intake and serum and urinary mineral concentrations of cows.

Nine multiparous and 12 primiparous cows were fed diets containing an anionic salt supplement and moderate Ca (0.99%) or high Ca (1.50%) concentrations for 21 d prepartum to determine the effects of dietary Ca concentration on serum and urine electrolytes and on postpartum intake and milk yield. Blood samples were collected during 21 to 1 d prepartum, 0 to 2 d postpartum, and 3 to 21 d postpartum. Dietary cation-anion difference (DCAD) for prepartum diets was approximately -6 mEq/100 g of dry matter (Na + K - Cl - S). Immediately postpartum, cows were fed diets with positive DCAD with greater than 1.00% Ca concentration. Mean serum Ca concentrations 21 to 1 d prepartum, 0 to 2 d postpartum, and 3 to 21 d postpartum were 9.62, 8.41, and 9.38 mg/dL. There were no treatment effects on serum Ca concentration. Mean serum Ca concentration was higher for primiparous than multiparous cows (9.34 vs. 8.93 mg/dL) for the trial and at calving (8.77 vs. 8.13 mg/dL). Mean serum HCO(3)(-) and urinary pH, respectively, were 20.32 mEq/L and 5.67 prepartum, 25.82 mEq/L and 7.62 at calving, and 26.08 mEq/L and 8.25 postpartum. No differences due to treatment were observed for serum and urinary concentrations of HCO(3)(-), pH, Mg, Na, K, and Cl. Milk yield was similar for 0.99 and 1.50% Ca treatments (22.8 and 20.7 kg/d). Diets containing 0.99 or 1.5% Ca maintained serum Ca at adequate levels around parturition and resulted in similar dry matter intake and postpartum milk yield.

Animal Nutritional Physiological Phenomena↗

PubMed2005

Effects of dietary cation-anion difference on intake, milk yield, and blood components of the early lactation cow.

Early lactation Holsteins cows (15 primiparous and 18 multiparous) were offered rations with dietary cation-anion difference, calculated as mEq (Na + K - Cl - S)/100 g of feed dry matter (DCAD:S), of 20, 35, or 50 mEq from d 0 (calving) to 42 d postpartum (August 20, 2000 to January 9, 2001) to determine the effects of increasing DCAD:S on dry matter intake (DMI), milk yield, and blood metabolites. For DCAD:S of 20, 35, and 50, DMI was 3.30, 3.38, 2.96 kg/100 kg of body weight (BW); milk yield was 25.5, 24.2, and 22.4 kg/d, respectively. No differences were observed for concentration or yield of milk fat or milk protein. Serum Ca, P, Mg, Na, K, Cl, cation-anion difference, insulin, and glucose did not differ with DCAD. Serum HCO3- was 26.07, 25.88, and 27.64 mEq/L for 20, 35, and 50 DCAD:S. Serum Ca, Mg, Na, and K concentrations were greater for primiparous cows (9.52 mg/dL, 2.35 mg/dL, 140.03 mEq/L, 4.66 mEq/L, respectively) than for multiparous cows (9.27 mg/dL, 2.12 mg/dL, 137.63 mEq/L, 4.46 mEq/ L, respectively). A DCAD:S between 23 and 33 mEq/100 g of dry matter (DM) appears to be adequate during cool weather for the milk yield that occurred in the present study based on DMI (kg/100 kg of BW), whereas DCAD:S of 50 mEq/100 g of DM may be excessive and could be too alkaline or unpalatable, resulting in decreased DMI (kg/100 kg of BW).

Animals↗

PubMed2004

Influence of corn variety and cutting height on nutritive value of silage fed to lactating dairy cows.

Two corn varieties predicted to differ in digestibility were harvested at 2 cutting heights (10.2 or 30.5 cm) to determine effects on the nutrient content of the resulting silage, nutrient intake, nutrient digestibility, and production of lactating cows fed such corn silage originally harvested at two-thirds milk line. Acid detergent fiber (ADF) concentration was higher and in vitro true dry matter (DM) digestibility (IVTDMD) was lower for the variety predicted to have average digestibility. An interaction was observed between variety and cutting height because of decreased ADF and increased IVTDMD for the average digestibility variety cut at 30.5 vs. 10.2 cm; no differences were observed for the higher digestibility variety at each cutting height. When silages were fed to 32 Holstein cows in a 5-wk randomized design trial, DM intake, milk yield, and milk composition were similar. There was an interaction between variety and cutting height for DM intake and total tract apparent digestibility of DM, crude protein, and neutral detergent fiber because of lower intake and digestibility for the diets containing either the high cut, average quality variety or low cut, higher quality variety. These results suggest that increasing the cutting height to 30.5 cm does not improve silage quality or improve milk yield of cows. Although the 2 varieties selected for this trial were predicted to differ in digestibility, these differences were not great enough to influence milk yield or composition of lactating cows.

Agriculture↗

PubMed2004

Effect of supplemental L-lysine-HCL and corn source on rumen fermentation and amino acid flow to the small intestine.

Four lactating Jersey cows fitted with ruminal and duodenal cannulae were used in a 4 x 4 Latin square design trial to determine the effect of supplemental lysine in diets containing dry ground (GC) or steam-flaked (SFC, 360 g/L) corn on ruminal fermentation and amino acid (AA) flow to the duodenum. Supplemental L-lysine-HCL provided 10 g/d of additional Lys to the total mixed rations. There were no interactions between supplemental Lys and corn source. Supplemental Lys increased Lys intake, but did not alter nutrient intake and digestibility or N flow to the duodenum. Intake of dry matter (DM), organic matter (OM), and neutral detergent fiber (NDF) and ruminal digestibility of starch tended to be higher, whereas ruminal digestibility of DM, OM, acid detergent fiber, and NDF was lower for diets supplemented with SFC compared with GC. Whole-tract digestibility was similar for both corn supplements. Ruminal pH and molar proportions of volatile fatty acids were not affected by supplemental Lys or corn source; however, ruminal NH(3) concentrations were lowest when SFC was fed. Intake of N tended to be higher and the flow of total N and individual AA to the duodenum was higher for diets supplemented with SFC. There was a trend for increased flow of microbial N for diets supplemented with SFC. Supplemental L-lysine-HCL did not alter ruminal fermentation, flow of amino acid to the small intestine, or nutrient digestibility, but feeding SFC reduced ruminal fiber digestion and increased microbial protein synthesis and flow of amino acid to the duodenum.

Amino Acids↗

PubMed2003

Effects of hot, humid weather on milk temperature, dry matter intake, and milk yield of lactating dairy cows.

Lactating cows were exposed to moderate and hot, humid weather to determine the effect of increasing ambient temperature, relative humidity, or temperature-humidity index (THI) on intake, milk yield, and milk temperature. Minimum and maximum temperatures averaged 17.9 and 29.5 degrees C (cool period) and 22.5 and 34.4 degrees C (hot period), and minimum and maximum THI averaged 63.8 and 76.6 (cool period) and 72.1 and 83.6 (hot period). Environmental conditions had minor effects on intake and milk yield during the cool period. During the hot period, the THI 2 d earlier and mean air temperature 2 d earlier had the greatest impact on milk yield and DMI, respectively. Both breeds maintained milk temperature within normal ranges during the cool period, but Holstein and Jersey p.m. milk temperatures averaged 39.6 and 39.2 degrees C during the hot period. Current day mean air temperature during the hot period had the greatest impact on cow p.m. milk temperature, and minimum air temperature had the greatest influence on a.m. milk temperature. Dry matter intake and milk yield declined linearly with respective increases in air temperature or THI during the hot period and milk temperature increased linearly with increasing air temperature. Dry matter intake and milk yield both exhibited a curvilinear relationship with milk temperature. Environmental modifications should target the effects of high temperatures on cow body temperature and should modify the environment at critical times during the day when cows are stressed, including morning hours when ambient temperatures are typically cooler and cows are not assumed to be stressed.

Animals↗

PubMed2003

Effects of heat-stress on production in dairy cattle.

The southeastern United States is characterized as humid subtropical and is subject to extended periods of high ambient temperature and relative humidity. Because the primary nonevaporative means of cooling for the cow (radiation, conduction, convection) become less effective with rising ambient temperature, the cow becomes increasingly reliant upon evaporative cooling in the form of sweating and panting. High relative humidity compromises evaporative cooling, so that under hot, humid conditions common to the Southeast in summer the dairy cow cannot dissipate sufficient body heat to prevent a rise in body temperature. Increasing air temperature, temperature-humidity index and rising rectal temperature above critical thresholds are related to decreased dry matter intake (DMI) and milk yield and to reduced efficiency of milk yield. Modifications including shade, barns which enhance passive ventilation, and the addition of fans and sprinklers increase body heat loss, lowering body temperature and improving DMI. New technologies including tunnel ventilation are being investigated to determine if they offer cooling advantages. Genetic selection for heat tolerance may be possible, but continued selection for greater performance in the absence of consideration for heat tolerance will result in greater susceptibility to heat stress. The nutritional needs of the cow change during heat stress, and ration reformulation to account for decreased DMI, the need to increase nutrient density, changing nutrient requirements, avoiding nutrient excesses and maintenance of normal rumen function is necessary. Maintaining cow performance in hot, humid climatic conditions in the future will likely require improved cooling capability, continued advances in nutritional formulation, and the need for genetic advancement which includes selection for heat tolerance or the identification of genetic traits which enhance heat tolerance.

Animal Nutritional Physiological Phenomena↗

PubMed2003

Ruminal fermentation and bacterial protein synthesis of whole cottonseed coated with combinations of gelatinized corn starch and urea.

Four ruminally and duodenally cannulated Jersey cows were used in a 4 x 5 incomplete Latin square study to determine the effects of including urea in the gelatinized corn starch coating applied to whole cottonseed (WCS) on ruminal fermentation, fiber digestion, and bacterial protein synthesis. Treatments included uncoated WCS (control) and four coated WCS treatments. The coatings provided two concentrations each of gelatinized corn starch (2.5 [2S] or 5% [5S]) and feed grade urea (0.25 [2U] or 0.5% [5U]). Treated WCS comprised 15% of the ration dry matter that was fed as a total mixed ration once daily. Ruminal pH and molar proportions of isobutyrate was higher and NH3-N concentrations lower for control compared with coated WCS. Molar proportions of propionate tended to be higher and valerate was lower with 2S compared with 5S. Molar proportions of acetate tended to be lower, whereas butyrate was higher for 5U than 2U. Nutrient intake was lower for WCS coated with 5S5U compared with 2S5U. Ruminal NDF digestibility of NDF tended to be higher with 5U compared with 2U, but no differences were observed in ruminal or total tract apparent digestibility of nutrients. No differences were observed in the flow of total N or bacterial N to the duodenum, but the flow of nonbacterial N tended to be higher for WCS coated with 5U. Coating WCS appears to slightly alter ruminal metabolism while providing similar amounts of N flowing to the duodenum without altering fiber digestion.

Animal Feed↗

PubMed2002

Effect of replacing corn silage with annual ryegrass silage on nutrient digestibility, intake, and milk yield for lactating dairy cows.

Twenty Holstein cows were used in an 8-wk randomized block design study to determine the effects of replacing corn silage with ryegrass silage on nutrient intake, apparent digestion, milk yield, and milk composition. The 8-wk trial consisted of a 2-wk preliminary period followed by a 6-wk collection period. Experimental diets were formulated to provide 55.5% of the total dry matter (DM) as forage. Ryegrass silage was substituted for 0, 35, 65, and 100% of DM provided by corn silage. Dietary concentrations of neutral detergent fiber (NDF) and acid detergent fiber (ADF) increased as ryegrass silage replaced corn silage. Intake of DM and crude protein (CP) was similar for all treatments, but intake of NDF and ADF increased linearly as ryegrass silage replaced corn silage. Apparent digestibility of DM declined linearly, whereas digestibility of CP increased linearly as ryegrass silage replaced corn silage. Apparent digestibility of NDF and ADF was highest for the diets in which ryegrass or corn silages provided all of the forage, resulting in a quadratic response. Dry matter intake was not different among treatments. Yield of milk, fat, and protein increased as ryegrass silage replaced corn silage. No differences were observed for body weight change, body condition score, and serum urea nitrogen concentration, but serum glucose concentration increased with increasing dietary proportion of ryegrass silage. These results indicate that substituting ryegrass silage for a portion or all of the corn silage in diets fed to lactating dairy cows can improve yield of milk and components.

Animal Nutritional Physiological Phenomena↗

PubMed2001

Platelet-derived growth factor C (PDGF-C), a novel growth factor that binds to PDGF alpha and beta receptor.

We have characterized platelet-derived growth factor (PDGF) C, a novel growth factor belonging to the PDGF family. PDGF-C is a multidomain protein with the N-terminal region homologous to the extracellular CUB domain of neuropilin-1, and the C-terminal region consists of a growth factor domain (GFD) with homology to vascular endothelial growth factor (25%) and PDGF A-chain (23%). A serum-sensitive cleavage site between the two domains allows release of the GFD from the CUB domain. Competition binding and immunoprecipitation studies on cells bearing both PDGF alpha and beta receptors reveal a high affinity binding of recombinant GFD (PDGF-CC) to PDGF receptor-alpha homodimers and PDGF receptor-alpha/beta heterodimers. PDGF-CC exhibits greater mitogenic potency than PDGF-AA and comparable or greater mitogenic activity than PDGF-AB and PDGF-BB on several mesenchymal cell types. Analysis of PDGF-CC in vivo in a diabetic mouse model of delayed wound healing showed that PDGF-CC significantly enhanced repair of a full-thickness skin excision. Together, these studies describe a third member of the PDGF family (PDGF-C) as a potent mitogen for cells of mesenchymal origin in in vitro and in vivo systems with a binding pattern similar to PDGF-AB.

Amino Acid Sequence↗

PubMed2000

Detection of Glu-Glu-tagged proteins in mammalian cell culture media by dot immunoblotting.

A dot immunoblotting technique has been developed to estimate the relative expression levels of tagged recombinant human proteins in mammalian cell culture media. Variations in sample denaturation, blocking agents and membrane composition and treatment were used to optimize the signal-to-noise ratio of the defined procedure. The method is rapid, with sensitivity extending to the low nanomolar range for a number of recombinant proteins. This technique should have general utility for antibody-based measurements of other tagged and non-tagged proteins in cell culture media or in biological fluids.

Animals↗

PubMed1999

Nutritional strategies for managing the heat-stressed dairy cow.

Heat stress results from the animal's inability to dissipate sufficient heat to maintain homeothermy. Environmental factors, including ambient temperature, radiant energy, relative humidity, and metabolic heat associated with maintenance and productive processes, contribute to heat stress. The focus of this article is to identify environmental and metabolic factors that contribute to excessive heat load, describe how disruption of homeothermy alters physiologic systems of the cow, and discuss nutritional modifications that help to maintain homeostasis or prevent nutrient deficiencies that result from heat stress. Changes in diet are needed during hot weather to maintain nutrient intake, increase dietary nutrient density, or to reestablish homeostasis. Formulation for adequate nutrient intake is challenging because of the competition between nutrient density and other needs for the cow, including energy density and adequate dietary fiber. Lower DMI during hot weather reduces nutrients available for absorption, and absorbed nutrients are used less efficiently. An excess of degradable dietary protein is undesirable because of energy costs to metabolize and excrete excess N as urea. Optimizing ruminally undegraded protein improves milk yield in hot climates. Mineral losses via sweating (primarily K) and changes in blood acid-base chemistry resulting from hyperventilation reduce blood bicarbonate and blood buffering capacity and increase urinary excretion of electrolytes. Theoretical heat production favors feed ingredients with a lower heat increment, such as concentrates and fats, whereas forages have a greater heat increment. Improved dietary energy density and the lower heat increment associated with the inclusion of dietary fat must be coupled with limitations to fat feeding to avoid ruminal and metabolic disorders. Numerous nutritional modifications are used for hot weather feeding; however, many need further investigation to achieve specific recommendations.

Animal Nutritional Physiological Phenomena↗

PubMed1999

Comparison of Tifton 85 and Coastal bermudagrasses for yield, nutrient traits, intake, and digestion by growing beef steers.

A study was undertaken to compare Tifton 85 (T85) and Coastal (CBG) bermudagrasses for effects of cultivar and age at harvest on yields of DM and digestible DM, in vitro digestion, nutrient content, cell wall composition, in situ digestion kinetics, and feed intake and digestion by growing beef steers. In Exp. 1, T85 and CBG forages staged for growth in May or July of 1993 were harvested at 3, 4, 5, 6, 7, and 8 wk from subplots. Tifton 85 bermudagrass had 7.1% greater DM yield, 18.2% higher (P < .05) digestible DM yield, and 7.1% greater IVDMD than CBG, and, after 5 wk of forage growth, IVDMD of both T85 and CBG decreased with increased age at harvest (P < .05). In Exp. 2, T85 and CBG forages staged for growth in July 1997 were harvested at 2, 3, 4, 5, 6, and 7 wk from subplots. Even though T85 had higher concentrations of NDF and ADF than CBG, T85 had 34.1% higher DM yield, 47.9% higher digestible DM, 55.0% higher digestible NDF, 91.7% higher digestible ADF, greater IVDMD, in vitro NDF and ADF disappearances, and higher in situ DM and NDF digestion (P < .05). Coastal bermudagrass had higher concentrations of lignin and lower concentrations of total neutral sugars, arabinose, glucose, and xylose than T85 (P < .05). In vitro digestibilities of DM, NDF, and ADF were lower and concentrations of ADF and lignin were greater for 7- vs 6-wk harvests of both T85 and CBG (P < .05). In Exp. 3, T85 and CBG forages staged for growth in July 1997 were harvested as hay at 3, 5, and 7 wk from .8-ha pastures and fed to 36 individually penned growing beef steers (initial BW = 244 kg) to quantify ad libitum intake without supplementation. Tifton 85 bermudagrass had lower concentrations of lignin and ether-linked ferulic acid and greater concentrations of NDF, ADF, hemicellulose, and cellulose than CBG (P < .05). Steers fed T85 had higher (P < .05) digestion of DM, OM, NDF, ADF, hemicellulose, and cellulose than steers fed CBG. Digestion of NDF, ADF, hemicellulose, and cellulose decreased (P < .05) with increased age at harvest for both cultivars. In conclusion, T85 produced more DM and had more digestible nutrients in vitro, in situ, and in vivo than CBG, and 3 and 5 wk of growth would be recommended ages to harvest either cultivar.

Animal Nutritional Physiological Phenomena↗

PubMed1999

Effects of dietary fiber on intake, milk yield, and digestion by lactating dairy cows during cool or hot, humid weather.

Lactating cows were offered diets with increasing neutral detergent fiber concentrations to determine the effects on intake, milk yield and composition, blood hormones, and nutrient digestion during cool or hot weather conditions. Tifton 85 bermudagrass hay was substituted for corn silage so that the forage portion of diets were: 1) 40% corn silage (control), 2) 32.4% corn silage, 7.6% bermudagrass, 3) 24.8% corn silage, 15.2% bermudagrass, or 4) 17.2% corn silage, 22.8% bermudagrass (dry basis). Dietary neutral detergent fiber concentrations (% dry matter) were 30.2, 33.8, 37.7, and 42.0, respectively. Intake of dry matter declined with increasing dietary neutral detergent fiber during cool and hot periods, but intake adjusted for cool weather treatment differences did not change further during hot weather. Milk yield declined linearly with increasing neutral detergent fiber during cool weather and changed quadratically during hot weather. Milk temperature declined with increasing dietary neutral detergent fiber for the p.m. milking during the cool period and declined with increasing dietary neutral detergent fiber for the a.m. and p.m. milkings during the hot period. Digestibility of neutral detergent fiber improved and ruminal turnover of particulate digesta was increased with greater dietary neutral detergent fiber content. No dietary fiber level by hot weather interaction was observed, suggesting that total energy intake may have and a greater effect on milk yield than dietary fiber content during hot, humid weather.

Animals↗

PubMed1998

Intake, milk yield, and digestion by dairy cows fed diets with increasing fiber content from bermudagrass hay of silage.

Lactating dairy cows were offered diets containing increasing quantities of Tifton 85 bermudagrass hay or silage and increasing dietary neutral detergent fiber (NDF) to determine effects of method of bermudagrass storage and dietary fiber content on intake, milk yield, and nutrient digestion. Bermudagrass was added as hay or silage at the rate of 8.5, 15.9, or 23.3% of dietary dry matter and was substituted for an equal quantity of corn silage. The method of bermudagrass storage did not affect intake [20.8 vs. 20.3 (+/- 0.3) kg/d for bermudagrass hay and silage diets; respectively], but an increase in the amount of bermudagrass and NDF in the diet did reduce intake. Dietary NDF concentration was well above minimum recommendations of the National Research Council. Milk yield was not altered by method of bermudagrass storage but declined as dietary NDF increased. Digestion of NDF tended to be lower for bermudagrass silage than for bermudagrass hay. An increase in the amount of bermudagrass in the diet improved digestion of dietary dry matter, acid detergent fiber, and NDF; however, milk yield declined because total intake declined. Improved NDF digestion caused by added bermudagrass hay or silage was confirmed by in vitro analyses. High quality bermudagrass hybrids could potentially be used in diets of lactating dairy cows because of the good digestion characteristics and relatively small effects on intake despite the high dietary fiber content. Tifton 85 bermudagrass may serve as a forage alternative for lactating dairy cows.

Animals↗

PubMed1997

Molecular analysis of the putative inactivation particle in the inactivation gate of brain type IIA Na+ channels.

Fast Na+ channel inactivation is thought to involve binding of phenylalanine 1489 in the hydrophobic cluster IFM in L(III-IV) of the rat brain type IIA Na+ channel. We have analyzed macroscopic and single channel currents from Na+ channels with mutations within and adjacent to hydrophobic clusters in L(III-IV). Substitution of F1489 by a series of amino acids disrupted inactivation to different extents. The degree of disruption was closely correlated with the hydrophilicity of the amino acid at position 1489. These mutations dramatically destabilized the inactivated state and also significantly slowed the entry into the inactivated state, consistent with the idea that F1489 forms a hydrophobic interaction with a putative receptor during the fast inactivation process. Substitution of a phe residue at position 1488 or 1490 in mutants lacking F1489 did not restore normal inactivation, indicating that precise location of F1489 is critical for its function. Mutations of T1491 disrupted inactivation substantially, with large effects on the stability of the inactivated state and smaller effects on the rate of entry into the inactivated state. Mutations of several other hydrophobic residues did not destabilize the inactivated state at depolarized potentials, indicating that the effects of mutations at F1489 and T1491 are specific. The double mutant YY1497/8QQ slowed macroscopic inactivation at all potentials and accelerated recovery from inactivation at negative membrane potentials. Some of these mutations in L(III-IV) also affected the latency to first opening, indicating coupling between L(III-IV) and channel activation. Our results show that the amino acid residues of the IFM hydrophobic cluster and the adjacent T1491 are unique in contributing to the stability of the inactivated state, consistent with the designation of these residues as components of the inactivation particle responsible for fast inactivation of Na+ channels.

Amino Acid Sequence↗

PubMed1997

Molecular analysis of potential hinge residues in the inactivation gate of brain type IIA Na+ channels.

During inactivation of Na+ channels, the intracellular loop connecting domains III and IV is thought to fold into the channel protein and occlude the pore through interaction of the hydrophobic motif isoleucine-phenylalanine-methionine (IFM) with a receptor site. We have searched for amino acid residues flanking the IFM motif which may contribute to formation of molecular hinges that allow this motion of the inactivation gate. Site-directed mutagenesis of proline and glycine residues, which often are components of molecular hinges in proteins, revealed that G1484, G1485, P1512, P1514, and P1516 are required for normal fast inactivation. Mutations of these residues slow the time course of macroscopic inactivation. Single channel analysis of mutations G1484A, G1485A, and P1512A showed that the slowing of macroscopic inactivation is produced by increases in open duration and latency to first opening. These mutant channels also show a higher probability of entering a slow gating mode in which their inactivation is further impaired. The effects on gating transitions in the pathway to open Na+ channels indicate conformational coupling of activation to transitions in the inactivation gate. The results are consistent with the hypothesis that these glycine and proline residues contribute to hinge regions which allow movement of the inactivation gate during the inactivation process of Na+ channels.

Amino Acid Sequence↗

PubMed1997

Effects of dietary forage source and amount of forage addition on intake, milk yield, and digestion for lactating dairy cows.

Lactating cows were used to determine the effects of increasing forage content from alfalfa (Medicago sativa L.) hay or Tifton 85 bermudagrass (Cynodon sp.) hay or Tifton 85 bermudagrass (Cynodon sp.) hay on dry matter intake (DMI), milk yield, and nutrient digestion. Forage proportions and neutral detergent fiber (NDF) content of diets were (dry basis) 1) 45% corn (Zea mays L.) silage (control), 33.5% NDF; 2) 15% bermudagrass hay and 30% corn silage, 39.5% NDF; 3) 30% bermudagrass hay and 15% corn silage, 46.6% NDF; 4) 15% alfalfa hay and 30% corn silage, 35.5% NDF; or 5) 30% alfalfa hay and 15% corn silage, 33.5% NDF. The DMI was greater with alfalfa diets than with bermudagrass diets, with low hay diets than with high hay diets, and with the control diet than with the hay diets. Digestibility of NDF in bermudagrass diets was greater than that in alfalfa diets, in high hay diets than in low hay diets, and in hay diets than in the control diet. In vitro NDF digestion was most rapid for bermudagrass hay, intermediate for corn silage, and slowest for alfalfa hay. Results suggest that NDF from bermudagrass was digested more completely and rapidly than was NDF from corn silage or alfalfa, which improved the rate of passage despite the high NDF content of diets containing bermudagrass. Milk yield followed trends for DMI. The control diet and diets containing alfalfa elicited the greatest DMI and milk yield, but DMI per 100 kg of body weight for Holsteins was equal for diets containing either bermudagrass or alfalfa. High quality bermudagrass can be used in rations for lactating dairy cows.

Animal Feed↗