Biomedical subjects

D O'Callaghan

Publications and source records attributed to D O'Callaghan.

At least 19 recordsLinked to original sources

PubMed2006

Report of the equine herpesvirus-1 Havermeyer Workshop, San Gimignano, Tuscany, June 2004.

Amongst the infectious diseases that threaten equine health, herpesviral infections remain a world wide cause of serious morbidity and mortality. Equine herpesvirus-1 infection is the most important pathogen, causing an array of disorders including epidemic respiratory disease abortion, neonatal foal death, myeloencephalopathy and chorioretinopathy. Despite intense scientific investigation, extensive use of vaccination, and established codes of practice for control of disease outbreaks, infection and disease remain common. While equine herpesvirus-1 infection remains a daunting challenge for immunoprophylaxis, many critical advances in equine immunology have resulted in studies of this virus, particularly related to MHC-restricted cytotoxicity in the horse. A workshop was convened in San Gimignano, Tuscany, Italy in June 2004, to bring together clinical and basic researchers in the field of equine herpesvirus-1 study to discuss the latest advances and future prospects for improving our understanding of these diseases, and equine immunity to herpesviral infection. This report highlights the new information that was the focus of this workshop, and is intended to summarize this material and identify the critical questions in the field.

Animals↗

PubMed2006

[Type IV secretion system and their effectors: an update].

Subversion of eukaryotic hosts by bacterial pathogens requires specialized macromolecules secretion systems delivering virulence factors either into the environment or directly into host cells. Transport of molecules across bacterial and eukaryotic membranes is a process requiring multi-component machineries called secretion systems. This review focuses on the Type IV secretion system. This complex is required for genetic exchange (DNA transport) and secretion of effectors (proteins, macromolecules, DNA-proteins complex) into target cells. They transport a wide variety of substrates including large DNA/protein complexes, multi protein toxins, or individual proteins. We describe recent advances on the structure and the function of this secretion system, their effectors and their effects on the functions of eukaryotic cell.

Bacteria↗

PubMed2005

Effects of diets fed to dairy cows before and after calving on their plasma progesterone profiles after calving.

Four weeks before their predicted mean second lactation calving date, 60 spring-calving Holstein-Friesian cows were blocked into groups of six on the basis of their predicted calving date and body condition score, and allocated at random to one of six dietary treatments in a factorial design: ad libitum grass silage, ad libitum grass silage plus barley straw or ad libitum grass silage plus 3 kg of concentrates, was offered for four weeks before the expected calving date, and after calving they were offered either 4 kg or 8 kg of concentrates plus ad libitum grass silage for eight weeks. On average, the first luteal activity occurred in all the groups at 29 days after calving. Seventeen of the cows had an atypical first plasma progesterone profile; 12 were anovulatory, three had prolonged luteal phases and two became anovulatory after having been cyclic. The cows offered grass silage only before calving had a significantly shorter mean (se) interval between calving and second luteal activity (44.9 [2.1] days), than the cows offered grass silage and straw (53.5 [1.9] days) or grass silage and concentrates (51.5 [3.2] days) (P<0.05). After calving none of the 28 cows offered grass silage and 4 kg of concentrates started cycling before day 21, whereas five of the 30 cows offered grass silage and 8 kg of concentrates cycled before day 21 (P<0.05).

Animal Feed↗

PubMed2004

[Strategies for bacterial virulence genes identification].

One of the recent preoccupations of medical microbiology has been to characterise the mechanisms of virulence of bacterial pathogens at the molecular level. One hundred years after Koch, Stanley Falkow proposed a new, molecular version of Koch's postulates to define avirulence gene: (a) the gene confers a certain phenotype to the studied bacteria, (b) inactivation of the gene abolishes the phenotype, (c)reintroduction of the gene restores the wild type to the mutant. Although this strategy, based upon mutagenesis and the use of experimental models, allows the identification of many genes, it is not comprehensive. Other methods can be used to complete the identification of virulence factors such as differential expression, either at the level of transcription (transcriptome) or at the level of protein expression (proteome). All these techniques are now supported by the data from complete genome sequencing projects. The pool of information obtained from these approaches allows the definition of the 'virulome', which is the assembly of factors a pathogen requires for virulence. Understanding the virulome will open the way to the development of new strategies for vaccination or the development of new generation of antimicrobials.

Animals↗

PubMed2003

Influence of nutrition on the effectiveness of superovulation programmes in ewes: effect on oocyte quality and post-fertilization development.

Two experiments were carried out to study the effect of nutrition on embryo development in two periods in superovulated ewes (Expt 1) and on oocyte developmental capacity during the late follicular phase (Expt 2). In Expt 1, a lower superovulation response in terms of animals ovulating (P < 0.05), ovulation rate per ewe ovulating (P = 0.1) and number of good quality embryos per animal treated (P < 0.07) was noted in ewes fed an ad libitum diet compared with ewes offered control (1.5 times the daily maintenance energy requirements, 1.5 x M) or low energy (0.5 x M) diets. Nutrition also modified the morphological and functional quality of the oocytes and embryos recovered. Thus, 92% of day 4 embryos recovered from ewes offered the control diet were classified as good embryos, compared with 70 and 82% of those recovered from ewes offered the ad libitum and low diets, respectively (P < 0.05). Ewes offered the ad libitum diet had a greater percentage of poorly developed embryos compared with ewes offered the control or low diets (P < 0.05). Ewes fed the low diet tended to have more non-fertilized oocytes than ewes offered the control diet (P = 0.09). Diet of recipient ewes to which good quality embryos were transferred on day 4 did not affect embryo quality, when assessed 12 days later (day 16 of pregnancy). However, recipient diet affected prostaglandin F(2alpha) (PGF(2alpha)) production in vitro, and uterine tissue that originated from recipient ewes on the low diet secreted more PGF(2alpha) relative to uterine tissue that originated from recipients on the control diet (P < 0.05). In Expt 2, fewer total (P < 0.05) and good quality (P < 0.01) oocytes and a lower percentage of good quality oocytes (P < 0.01) were obtained from superovulated ewes offered the ad libitum diet compared with ewes offered the low diet. In addition, cleavage rate tended to be higher (51 versus 35%, P = 0.09) in ewes offered the low diet compared with ewes offered the ad libitum diet. In conclusion, changes in diet can affect the quality of the oocyte and embryo in superovulated sheep. A lower superovulation response and a decrease in the quality of oocytes and embryos indicate that ad libitum diets are highly detrimental for superovulatory programmes when compared with low and control diets. In addition, the results from the present study indicate that a low energy diet during early embryo development increased the uterine production in vitro of PGF(2alpha) which could lead to a poor uterine environment thereby compromising the development of the embryo.

Animal Nutritional Physiological Phenomena↗

PubMed2002

Effects of calcium salts of fatty acids and calcium salt of methionine hydroxy analogue on plasma prostaglandin F2alpha metabolite and milk fatty acid profiles in late lactation Holstein-Friesian cows.

Effects of a dietary lipid supplement containing calcium salts of fatty acids and methionine hydroxy analogue on plasma prostaglandin F2alpha (PGF2alpha) metabolite (PGFM) and milk fatty acid profiles were examined in 40 late lactation, nonpregnant, Holstein-Friesian cows for a period of 70 days. Effects on milk production, milk composition, and blood metabolites were also examined. Cows were paired on the basis of lactation number (first lactation, n = 8; second lactation, n = 32) and randomly assigned from within pairs to one of two dietary treatments: unsupplemented control (C) or 400 g per cow per day of the lipid supplement (S). Cows receiving the supplement had higher (P < 0.05) total milk production, total fat production (kg), and total lactose production (kg). Plasma cholesterol was significantly higher (P < 0.01) after 30 days of treatment in cows receiving the supplement. Cows receiving the supplement had lower (P < 0.01) concentrations of short chain milk fatty acids (C4:0 to C14:1) and higher concentrations of long chain fatty acids (C18:1 and C18:2; P < 0.01) than control animals. Oxytocin-induced prostaglandin release on Day 16 postovulation was increased (P < 0.01) in cows receiving the supplement. In conclusion, supplementation with calcium salts of fatty acids and methionine hydroxy analogue significantly increased milk yield and plasma PGFM.

Animals↗

PubMed2001

Effect of nutrition on endocrine parameters, ovarian physiology, and oocyte and embryo development.

Reproductive efficiency in high yielding dairy cows has decreased over the past 50 years, despite significant gains in genetic selection for increased milk output. One possible reason for this decline has been a change in the nutritional intake to meet the increased energy and protein demands for higher milk production. Excess energy intake in sheep will lead to significant reductions in progesterone concentrations; the effects in cattle are not so clear. Nutrition, unless radically changed, will have little effect on gonadotropin concentrations in ruminants, and this is in contrast to the situation for pigs and for primates, where very short-term nutritional changes manifest themselves in altered gonadotropin secretion. Cattle with reduced energy intake have smaller dominant follicles and more three-wave cycles, compared with animals on higher feed intakes. One of the main areas where nutrition influences reproductive efficiency is at the level of embryo production. Several studies indicate that excess energy intake reduces the response to superovulation and also decrease the yield of embryos and alters expression of some gene constructs within the developing embryo. The mechanism of this effect is not clear but indications are that the quality of the oocytes may be compromised. Indeed recent data indicate that nutritional changes around the time of mating may have detrimental effects on the establishment of pregnancy in heifers. Thus, nutritional balancing is critical for high-yielding dairy cows, in particular. The challenge remains to modify nutritional and management strategies in such cows to maintain the levels of production made possible by genetic selection and still maintain an acceptable level of fertility.

Animal Nutritional Physiological Phenomena↗

PubMed2001

Effect of diet quantity and urea supplementation on oocyte and embryo quality in sheep.

The objective was to investigate the effects of dietary energy and urea supplementation on oocyte and embryo quality in sheep using in vivo and in vitro experimental models. Sixty-three ewes were fed grass meal at 0.5 or 2.0 times maintenance energy requirements (MER). The diet was supplemented with feed grade urea (U) for half of the ewes on each energy treatment. Ewes were stimulated with 1000 IU eCG and either slaughtered on the day of pessary withdrawal, for in vitro embryo production, or mated and slaughtered on Day 5 for embryo recovery. Urea decreased cleavage rate (48.3 vs 39.7%) and consequently blastocyst rate (41.6 vs 36.8%) but the differences were not significant. Oocytes from animals on 2.0 MER had a lower cleavage rate (54.9 vs 36.0%) and blastocyst yield (49.3 vs 31.4%) than those on 0.5 MER. However, there was an interaction between urea and energy for cleavage (P = 0.04) and blastocyst yield (P = 0.03) indicating a variable response to urea in the presence of high energy. This was manifested by a decrease in cleavage rate in the presence of urea and high energy (22%, 8 of 36), and a reduction in blastocyst development (19%, 7 of 36). When blastocyst development rate was expressed as a proportion of cleaved oocytes there was no difference between groups; in addition, there was no difference between groups in terms of blastocyst hatching rate (overall mean 66.1%) or blastocyst cell number on Day 8 (overall mean +/- SEM, 138.4 +/- 9.0, n=61). The effect of urea on cleavage rate in vivo was more severe. Urea supplementation reduced (P<0.001) the cleavage rate (93 vs 62%). Despite this, the yield of blastocysts was unaffected. Oocytes from ewes on 0.5 MER exhibited a lower (P<0.05) cleavage rate than those on 2.0 MER (66 vs 87%). This effect was also apparent at the blastocyst stage (40.0 vs 50.9%), although the difference was no longer significant. There were no differences in hatching rate (overall mean 70.7%) or blastocyst cell numbers (overall mean +/- SEM, 166.3 +/- 15.6, n=40). Collectively, these results suggest that both high dietary energy and urea content influence subsequent embryo development in vitro, and the deleterious effects of urea are likely influenced by concomitant energy intake.

Animals↗

PubMed2001

Genetic merit for milk production and reproductive success in dairy cows.

The effect of genetic merit for milk production traits - fat, protein and milk yield - in dairy cows on milk production, body condition, blood metabolites, reproductive hormones, feed intake and reproductive performance was studied over a period of 2 years. Cows were grouped into two categories, based on calculated pedigree indices using multiple-trait across country evaluation (MACE). Cows of high genetic merit (HGM, n = 48 in year 1 and n = 46 in year 2) had a mean predicted difference +/- standard deviation for milk production of 475 +/- 76kg. The cows of medium genetic merit (MGM, n = 48 in both years) had a mean predicted difference for milk production of 140 +/- 68kg. The cows calved between January and April, and were offered grass silage ad libitum plus 9kg concentrates per cow per day, irrespective genetic merit, from calving to turnout in March, when they were subjected to one of three grazing systems. Cows were available for rebreeding from late April until late July of each year.High genetic merit cows had higher milk production, incurred greater body condition loss between calving and first service and had lower plasma glucose and insulin-like growth factor-1 (IGF-1) concentrations than medium genetic merit cows. Furthermore, HGM cows had lower first and second service and overall conception rates, and required more services per conception than the MGM cows. Cows that did not conceive to first service were retrospectively compared to those that conceived to first service within each genetic merit group. There were no significant differences between the HGM cows that did not conceive to first service and those that conceived to this service in terms of milk production, body condition score change between calving and first service, feed intake at first service, or in plasma concentrations of glucose, non-esterified fatty acids (NEFA) or IGF-1. Medium genetic merit cows that did not conceive to first service lost more body condition between calving and first service than did those that conceived to this service. In the present study, HGM cows had higher milk production and reduced reproductive performance in comparison with MGM cows. However, reproductive performance was not associated with milk production, feed intake or plasma concentrations of glucose, NEFA or IGF-1 between calving and first service, since there were no significant differences in these variates between high or medium genetic merit cows that did not conceive to first service and those that conceived to this service. Therefore, these variates are unlikely to be useful predictors of reproductive performance, under the conditions of the present study.

Animals↗

PubMed2001

Brucellosis: a worldwide zoonosis.

Brucella is one of the world's major zoonotic pathogens, and is responsible for enormous economic losses as well as considerable human morbidity in endemic areas. Control of brucellosis requires practical solutions that can be easily applied to the field. Rapid DNA-based diagnostic tests for both humans and livestock have now proved themselves on an experimental level. Data on the virulence of Brucella suggest common mechanisms shared with plant pathogens and endosymbionts of the alpha-proteobacteria. Understanding virulence will have practical repercussions in the realms of vaccine development and, perhaps, development of new antibiotics. The first complete Brucella genome sequence will be released soon, and this will help greatly in our understanding of the biology and evolution of this pathogen.

Animals↗

PubMed2001

Aromatic compound-dependent Brucella suis is attenuated in both cultured cells and mouse models.

The aroC gene of the facultative intracellular pathogen Brucella suis was cloned and sequenced. The cloned aroC gene complements Escherichia coli and Salmonella enterica serovar Typhimurium aroC mutants. A B. suis aroC mutant was found to be unable to grow in a defined medium without aromatic compounds. The mutant was highly attenuated in tissue culture (THP1 macrophages and HeLa cells) and murine virulence models.

Animals↗

PubMed2001

Epithelial calcium transporter expression in human duodenum.

Calcium absorption in intestine and kidney involves transport through the apical membrane, cytoplasm, and basolateral membrane of the epithelial cells. Apical membrane calcium influx channels have recently been described in rabbit (epithelial calcium channel, ECaC) and rat (calcium transport protein, CaT1). We amplified from human duodenum a 446-base partial cDNA probe (ECAC2) having a predicted amino acid similarity of 97% to rat CaT1. Duodenum, but not ileum, colon, or kidney, expressed a 3-kb transcript. A larger transcript was also found in placenta and pancreas, and a different, faint transcript was found in brain. In duodenal biopsies from 20 normal volunteers, expression varied considerably but was not significantly correlated with vitamin D metabolites. This signal correlated with calbindin-D(9k) (r = 0.48, P < 0.05) and more strongly with the plasma membrane calcium ATPase PMCA1 (r = 0.83, P < 0.001). These data show that although individual variations in calcium channel transcripts are not vitamin D dependent, expression of genes governing apical entry and basolateral extrusion are tightly linked. This may account for some of the unexplained variability in calcium absorption.

Amino Acid Sequence↗

PubMed2000

Effect of genetic merit, milk yield, body condition and lactation number on in vitro oocyte development in dairy cows.

The effects of milk yield, body condition score (BCS) and lactation number on the number of oocytes recovered and blastocysts formed were studied following in vitro maturation, fertilization and culture of bovine oocytes collected from 48 high and 46 medium genetic merit dairy cows in their first and third lactation. The cows were slaughtered between 125 and 229 d post partum. Ovaries were recovered, and 2- to 10-mm follicles were aspirated. Cleavage rate and number of blastocysts were determined at 44 h and 7 d after insemination, respectively. Oocytes from high genetic merit cows formed fewer blastocysts and had lower cleavage and blastocyst formation rates than those from medium genetic merit cows (0.36 +/- 0.19, 70.4 and 6.8% vs 0.85 +/- 0.22, 77.4 and 11.4%, respectively). The effect of milk production was tested by grouping cows in their third lactation into high and low groups. There was no difference in number of oocytes recovered and subsequent development into blastocysts between the cows in the high milk production group (4559 to 5114 kg, n = 20) and cows in the low yield (3162 to 3972 kg, n = 20) group (6.9 +/- 1.34 vs 8.9 +/- 1.32, respectively). The effect of BCS was tested by grouping cows in their first or third lactation into high and low groups. Cleavage and blastocyst formation rates were greater for oocytes from cows with a high BCS (3.3 to 4.0, n = 20) than a low BCS (1.5 to 2.5, n = 20) (75.7 vs 61.9% and 9.9 vs 3.0%, respectively). Cows in the first lactation yielded fewer oocytes (5.7 +/- 1.24) than cows in the third lactation (7.8 +/- 0.79). Thus, the quality of oocytes probably contributes to reduced fertility, often evident in high genetic merit dairy cows.

Animals↗

PubMed2000

Identification of Brucella suis genes affecting intracellular survival in an in vitro human macrophage infection model by signature-tagged transposon mutagenesis.

Bacteria of the genus Brucella are facultative intracellular pathogens which have developed the capacity to survive and multiply in professional and nonprofessional phagocytes. The genetic basis of this aspect of Brucella virulence is still poorly understood. To identify new virulence factors, we have adapted signature-tagged transposon mutagenesis, which has been used essentially in animal models, to an in vitro human macrophage infection model. A library of 1,152 Brucella suis 1330 tagged mini-Tn5 Km2 mutants, in 12 pools, was screened for intracellular survival and multiplication in vitamin D(3)-differentiated THP1 cells. Eighteen mutants were identified, and their attenuation was confirmed in THP1 macrophages and HeLa cells. For each avirulent mutant, a genomic fragment containing the transposon was cloned. The genomic DNA sequence flanking the transposon allowed us to assign functions to all of the inactivated genes. Transposon integration had occurred in 14 different genes, some of which were known virulence genes involved in intracellular survival or biosynthesis of smooth lipopolysaccharide (the virB operon and manB), thus validating the model. Other genes identified encoded factors involved in the regulation of gene expression and enzymes involved in biosynthetic or metabolic pathways. Possible roles in the virulence of Brucella for the different factors identified are discussed.

Brucella↗

PubMed2000

Effects of superovulated heifer diet type and quantity on relative mRNA abundances and pyruvate metabolism in recovered embryos.

This study investigated the effects of quantity and type of diet fed to superovulated donor heifers on molecular and metabolic indices of embryonic development. These effects included the relative abundances of mRNAs for the alpha 1 subunit of Na/K-ATPase and the antioxidant enzyme Cu/Zn-SOD, as well as pyruvate utilization in bovine morulae and blastocysts developed in vivo. Heifers were fed a daily ration of either grass silage and a citrus-beet pulp-based concentrate or grass silage and a barley-based concentrate for 116 days, both at 3 kg per day or ad libitum. In embryos derived from heifers fed the pulp-based diets, the relative abundances of the transcripts were not affected by either day of collection or quantity of diet. In embryos derived from heifers fed the barley-based diets, the relative abundances of the Na/K-ATPase transcripts were also not changed by these main effects, while the relative abundances of the Cu/Zn-SOD transcripts were affected by day of collection and by the quantity of diet. Pyruvate metabolism was affected by day of collection, and was significantly increased in day 8 embryos compared with day 7 and day 6 embryos. Diet quantity did not affect pyruvate utilization, whereas diet type did increase pyruvate metabolism in the barley group when compared with the pulp group. The results of this study show for the first time that molecular and metabolic variations may exist in embryos derived in vivo and developed in donor heifers on nutritional regimens differing in type and quantity. Differences in embryos collected on different developmental days may be attributed to varying cell numbers. Alterations in the relative abundances of the Cu/Zn-SOD transcripts and pyruvate metabolism caused by the quantity of diet fed to the donor animal were likely to have been due to alterations in metabolic end products that accumulate in reproductive tract fluids, whereas differences in embryonic metabolism caused by type of diet are related to the composition of the diet. These findings characterize embryos produced in vivo at the molecular level, indicating that the molecular markers used in the present study can differentiate between populations of embryos produced under different nutritional regimens and determine conditions conductive to the production of good quality embryos.

Analysis of Variance↗

PubMed2000

Effect of nutrition and superovulation on oocyte morphology, follicular fluid composition and systemic hormone concentrations in ewes.

The objective was to determine the effect of dietary intake on follicle and oocyte morphology in unstimulated and superovulated ewes. Fifty-four ewes were fed grass meal at 0.5, 1.0 or 2.0 times maintenance energy requirements (M) for 32 days. Oestrous cycles were synchronized using progestagen pessaries and either unstimulated or superovulated with 200 mg pig FSH. The ewes were killed and ovaries were collected either 36 or 12 h before the anticipated LH surge. Serum progesterone concentrations in ewes on day 10 after withdrawal of the pessary were lower in ewes fed 2.0M than in ewes fed 0.5M or 1.0M (P < 0.05). LH pulse frequency tended to be higher in ewes fed 2M than 1M (1.0 +/- 0.3 versus 0.3 +/- 0.2 pulses per 8 h) on day 6 after removal of the pessary but the effect was not significant. In unstimulated ewes, more follicles (>/= 3 mm) were observed when the animals were killed in ewes fed 2.0M (3.5 +/- 0.3) than in ewes fed 0.5M (2.4 +/- 0.3) or 1.0M (2.4 +/- 0.5; P < 0. 05). Fewer follicles were observed in superovulated ewes on 0.5M (7. 5 +/- 1.2) than in ewes on 1.0M (12.0 +/- 0.5) or 2.0M (12.3 +/- 1. 4; P < 0.05). Follicular fluid progesterone concentrations were higher in ewes fed 0.5M compared with those fed 1M or 2M (P < 0.05). Insulin-like growth factor (IGF)-I concentrations were higher in follicular fluid from ewes on 1M compared with either those on 0.5M or 2M (P < 0.05), whereas IGF-II concentrations were lower in follicular fluid from ewes on 2M compared with those on 1M or 0.5M (P < 0.05). Superovulation increased follicular fluid progesterone, oestradiol, IGF-I and IGF-II concentrations (P < 0.01). Concentrations of the 34, 22 and 20 kDa IGF binding proteins were lower in follicles from superovulated ewes compared with unstimulated ewes (P < 0.05). Oocytes from superovulated ewes showed abnormalities such as premature activation of cumulus expansion and vacuolation of the nucleolus and increased frequency of detachment of interchromatin-like granules from the nucleolar remnant. Collectively, these results indicate that both high and low dietary intakes can alter systemic and follicular fluid hormone concentrations. Relative to dietary effects, the effects of superovulation were greater and involved substantial increases in follicular fluid hormone concentrations and abnormal oocyte morphology.

Animal Nutritional Physiological Phenomena↗

PubMed1999

Effect of roughage type and concentrate supplementation on follicle numbers and in vitro fertilisation and development of oocytes recovered from beef heifers.

Increasing dietary energy tends to decrease the ovulatory response and produce fewer viable embryos following superovulation of beef cattle. Data in sheep indicate that high energy intake can decrease progesterone concentrations (P4), although effects in cattle are not as clear. The objectives were to evaluate the effects of roughage type and concentrate supplementation on P4 concentrations, follicle growth and subsequent oocyte fertilisation and embryo development in vitro. Forty-two beef heifers were allocated to 3 treatment groups: (i) silage ad libitum plus 6 kg concentrates (silage + conc.; n = 14); (ii) silage ad libitum (silage; n = 14) or (iii) hay ad libitum (hay; n = 14) for 40 days. Oestrus was synchronised using a controlled intravaginal progesterone releasing device (CIDR) for 7 days plus prostaglandin F2 alpha (15 mg luprostiol) administered 2 days before CIDR withdrawal. Ovaries were stimulated with 600 i.u. of follicle stimulating hormone (pFSH) administered in 6 equal doses at 12-h intervals, starting 12 days after CIDR withdrawal. Daily blood samples were collected from 3 days after CIDR insertion until CIDR withdrawal, and for another 3 days prior to pFSH, for P4 determination. Oocytes were recovered postmortem 12 h after the last pFSH injection, matured, fertilised and cultured in vitro. There was no overall effect of diet (P > 0.05) on P4 concentrations. The number of follicles grown in heifers on silage + conc (18.8 +/- 3.3), silage (23.5 +/- 3.4) or hay (18.1 +/- 2.6) were not affected by the dietary treatment (P > 0.05). The percentage of oocytes fertilised from heifers on hay (88%) was higher compared to oocytes from heifers on silage (79%; P < 0.05), but was not different (P > 0.05) compared to the proportion of oocytes from heifers on silage + conc. (86%). The percentage of fertilised oocytes that cleaved was higher from heifers on silage (94%; P < 0.01) compared with oocytes from heifers on hay (82%) or silage + conc. (86%). The proportion of embryos that developed to blastocyst was not different (P > 0.05) between groups of oocytes from heifers on silage + conc. (8%), silage (14%) or hay (15%). Heifers on silage produced numerically more blastocysts (silage: 19 from 14 heifers; silage + conc.: 8 from 14 heifers; hay: 12 from 14 heifers). These results suggest that dietary treatment used prior to oocyte recovery did not significantly influence the developmental competence of the oocytes in vitro.

Ammonia↗

PubMed1999

Investigation into the role of the response regulator NtrC in the metabolism and virulence of Brucella suis.

During infection, Brucella species have to adapt to a range of different environments. Environmental sensing in bacteria often involves the concerted action of two-component regulatory systems consisting of sensor and response regulator components. In this study, we identified, cloned and sequenced four independent response regulator gene fragments from Brucella melitensis. One amplified gene fragment showed nearly 90% identity to the response regulator subfamily of NtrC transcriptional activators, and further analysis revealed the presence of an adjacent gene encoding the sensor protein NtrB. The NtrBC two-component regulatory system has been shown to play varying roles in nitrogen metabolism and potentially in virulence in other bacterial species. A B. suis ntrC isogenic mutant was constructed which showed no significant differences in growth rates compared to the wild-type strain when grown at different temperatures in vitro. However, the mutant exhibited a reduction in metabolic activity in the presence of many amino acids. The mutation did not affect survival or multiplication of B. suis in macrophages, but during the initial stages of infection in the murine brucellosis model, the ntrC mutant showed a reduced ability to multiply rapidly in splenic tissue.

Amino Acid Sequence↗