Effect of precalving and postcalving dietary energy level on performance and blood metabolite concentrations of dairy cows throughout lactation.

The effects of the level of energy intake (high E and low E) offered before and after calving on body condition score at calving, production performance, and energy status in the first 250 d of lactation were evaluated in a 2 × 2 factorial design experiment involving 80 Holstein-Friesian dairy animals (40 primiparous and 40 multiparous). From d 80 until d 21 precalving, primiparous animals were offered either high or low pasture allowances. Thereafter, these animals were housed and had ad libitum access to a high energy density diet (high E) or restricted access [6 kg of dry matter (DM) per d] to a low energy density diet (low E), respectively, until calving. From d 100 until d 42 precalving, multiparous animals were offered either ad libitum or restricted (10 kg of DM/d) access to a late lactation diet, and thereafter, had ad libitum access to a high E diet or restricted access (7 kg of DM complete diet/d) to a low E diet, respectively, until calving. The forage to concentrate (F:C) ratios (DM basis) of these high E and low E diets [d 42 (d 21 in primiparous animals) until calving] were 64:36 and 83:17, respectively. Cows offered high E and low E precalving diets were allocated to either a high E or low E postcalving diet [F:C ratio (DM basis) of 30:70 and 70:30, respectively] and remained on these diets until d 250 of lactation. Multiparous animals offered a high E diet precalving had a significantly higher body condition score at calving than those offered the low E diet precalving. This effect was not evident in primiparous animals. Precalving diet had no significant effect on plasma nonesterified fatty acid concentrations during the last 3 wk precalving in primi- or multiparous animals. Primiparous animals offered a high E diet precalving had significantly higher postcalving plasma concentrations of nonesterified fatty acid, suggesting greater mobilization of body reserves. Primi- and multiparous animals offered a high E diet postcalving had a significantly higher dry matter intake, milk yield, and energy status postcalving compared with animals offered a low E diet postcalving. Milk yields of primiparous animals offered high E and low E diets postcalving were 29.7 and 24.8 kg/d, respectively, and milk yield of multiparous animals offered high E and low E diets postcalving were 33.5 and 28.2 kg/d, respectively. It is concluded that altering body condition score during the dry period is difficult but that specific dietary regimens applied precalving can have a significant influence on postcalving production and energy-related parameters.

Effects of breed and production system on lameness parameters in dairy cattle.

The aim of the present study was to assess the effects of Holstein-Friesian (HF) and Norwegian (N) dairy cattle genotypes on lameness parameters in dairy cattle within different production systems over the first 2 lactations. Following calving, HF (n = 39) and N (n = 45) heifers were allocated to 1 of 3 systems of production (high level of concentrate, low level of concentrate, and grass-based). High- and low-concentrate animals were continuously housed indoors on a rotational system so that they spent similar amounts of time on slatted and solid concrete floors. Animals on the grass treatment grazed from spring to autumn in both years of the study, so that most animals on this treatment grazed from around peak to late lactation. Claw health was recorded in both hind claws of each animal at 4 observation periods during each lactation as follows: 1) -8 to 70 d postcalving, 2) 71 to 150 d postcalving, 3) 151 to 225 d postcalving, and 4) 226 to 364 d postcalving. Sole lesions, heel erosion, axial wall deviation, sole length of the right lateral hind claw (claw length), right heel width, and right lateral hind heel height were recorded as well as the presence of digital dermatitis. The N cows had lower (better) white line and total lesion scores than HF cows. Cows on the high- and low-concentrate treatments had better sole and total lesion scores than cows on the grass treatment. The HF cows had better locomotion scores than N cows. Breed and production system differences were observed with respect to claw conformation, including claw length, heel width, and heel height. Digital dermatitis was associated with worse sole lesion scores and interacted with production system to influence white line lesion scores and maximum heel erosion scores. This study shows that genetic, environmental, and infectious factors are associated with hoof pathologies in dairy cows.

Effect of supplementation with barium selenate on the fertility, prolificacy and lambing performance of hill sheep.

Six weeks before mating, the ewes on six hill farms were randomly assigned to receive either a subcutaneous injection of a long-acting supplement containing 50 mg/ml selenium as barium selenate, or no injected selenium. Before the treatment, the mean activity of glutathione peroxidase (GSHPx) in the ewes on the six farms ranged from 166 to 592 U/g haemoglobin (Hb) and their plasma selenium concentrations ranged from 0.60 to 1.61 micromol/l. Treated ewes had higher plasma selenium concentrations and higher GSHPx activities than control ewes during the study. Conception rates were higher in the treated ewes than in the control ewes. At six weeks, the lambs born to the treated ewes had higher plasma selenium and GSHPx levels than the controls. The treated ewes reared 9 per cent more lambs than the control ewes. The treated ewes had lower abortion rates, and higher liveweights and body condition scores than the controls. There were weak but positive associations between the plasma selenium and GSHPx levels of the ewes and their reproductive performance.

Solution structure and dynamics of the single-chain hepatitis C virus NS3 protease NS4A cofactor complex.

The backbone assignments, secondary structure, topology, and dynamics of the single-chain hepatitis C virus NS3 protease NS4A cofactor complex have been determined by NMR spectroscopy. Residues I34 to S181 of NS3 and the central three residues of the NS4A cofactor were assigned and the secondary structure was verified for these residues. In several X-ray structures of NS4A-bound NS3 protease, residues 1 to 28 are stabilized by crystal packing, which allows for the formation of the A0 strand and alpha0 helix. In solution, these N-terminal residues are largely unassigned and no evidence of a well-structured A0 strand or alpha0 helix was detected. NOEs between residues in the E1-F1 loop (containing D81) and the alpha1 helix (containing H57) together with the detection of a D81-H57 hydrogen bond indicate that in solution the catalytic triad (D81, H57, S139) of the protease is better ordered in the presence of the NS4A cofactor. This is consistent with the earlier crystallographic results and may explain the observed increase in catalytic activity of the enzyme due to NS4A binding. A model-free analysis of our relaxation data indicates substantial exchange rates for residues V51-D81, which comprise the upper part of the N-terminal beta-barrel. A comparison of chemical-shift differences between NS3 protease and the NS3 protease-NS4A complex shows extensive chemical-shift changes for residues V51-D81 indicating that non-local structural changes occur upon NS4A binding to the NS3 protease that are propagated well beyond the protease-cofactor interaction site. This is consistent with crystallographic data that reveal large structural rearrangements of the strand and loop regions formed by residues V51-D81 as a result of NS4A binding. The coincidence of large exchange rates for the NS3 protease-NS4A complex with chemical-shift differences due to NS4A binding suggests that residues V51-D81 of the NS3 protease NS4A complex are in slow exchange with a NS4A-free conformation of NS3 protease.

Routine withholding of digitalis for heart rate below 60 beats per minute: widespread nursing misconceptions.

OBJECTIVE: To describe the nursing practice of withholding digitalis solely on the basis of a heart rate less than 60 beats/min and to determine the rationale for this practice. DESIGN: Non-randomized survey. SETTING: Five hospitals in a midwestern metropolitan area, ranging from affiliates of a university medical center to a private community-based hospital. SUBJECTS: Two hundred twelve nurses, 53% from critical care units, 19% from step-down units, and 28% from nonmonitored units). RESULTS: Eighty-one percent of respondents either withheld digitalis unnecessarily or administered the drug without correctly indicating why they did so. Nurses with CCRN certification were more likely to answer correctly than those who were not certified (p = 0.0001). Categories for incorrect rationale were (1) incorrect understanding of the drug's mechanism of action (46%), (2) deference to physician's decision-making (28%), (3) adherence to hospital policy (18%), and (4) adherence to guidelines taught in nursing school (6%). CONCLUSIONS: The results document the need to correct widespread misconceptions regarding the mechanism of action for digitalis and subsequent nursing practice.

Density and breaking strength of bones of mortalities among caged layers.

The incidence of deaths attributable to cage layer osteoporosis (CLO) and the associated parameters of bone strength were studied in a flock of 5000 commercial laying hens over one laying cycle. Of the 9.7 per cent mortality rate, 35 per cent were attributed to CLO, and the mean age of death of the CLO hens (45.5 weeks) was significantly earlier than that of the non-CLO hens (51.6 weeks). There was a significant linear relationship between the density and breaking strength of whole bones with no difference between the CLO and non-CLO hens. However, the density and breaking strength of the bones of the non-CLO hens were consistently greater than those of the CLO hens. The density and breaking strength of the bones of both groups of birds increased with age.

Regional brain monoamine concentrations and their alterations in bovine hypomagnesaemic tetany experimentally induced by a magnesium-deficient diet.

Monoamines are important brain neurotransmitters. An investigation was carried out to determine if hypomagnesaemic tetany was associated with alterations in regional brain monoamine concentrations in bovines. The results, established in cows with normal magnesium status, demonstrated that regional differences existed in the distribution and concentration of brain monoamines in the adult bovine, which were similar to those in other species. In magnesium-deficient cows, severe hypomagnesaemia and lowered cerebrospinal fluid (CSF) magnesium concentrations were associated with significant alterations in monoamine concentrations in some brain regions. Alterations in 3,4-dihydroxyphenylalanine (DOPA) and dihydroxyphenylacetic acid (DOPAC) concentrations in the corpus striatum, and dopamine (DA) in the cerebral cortex and cerebellum were recorded. These regions play an important role in both voluntary and involuntary motor function, and therefore these alterations may play a role in the aetiology of hypomagnesaemic tetany. However, there was no significant change in DA concentrations in the corpus striatum (the main dopaminergic region in the brain) associated with hypomagnesaemia. In addition, a significantly lower norepinephrine (NE) concentration in the corpus striatum of hypomagnesaemic animals was also recorded. Norephinephrine is generally excitatory and therefore lowered NE concentrations would be expected to result in depression rather than stimulation of motor function.

Iodine deficiency in cattle: compensatory changes in thyroidal selenoenzymes.

The trace elements selenium and iodine are both essential for normal thyroid hormone metabolism. To investigate the relationships between these functions, heifers were maintained on iodine-deficient or iodine-sufficient diets from mid pregnancy to term. In these heifers and their offspring the interrelationship between iodine and selenium was apparent with the preferential 10- to 12-fold induction of the selenoenzyme, thyroidal type I, selenium-containing iodothyronine deiodinase activity by iodine deficiency. This was accompanied by two- to four-fold increases in cytosolic glutathione peroxidase activity, probably reflecting increased oxidative activity and metabolism in the thyroid gland in response to iodine deficiency. The above selenoenzyme activities were not affected in liver, kidney, pituitary and brain by iodine deficiency. The results are consistent with a critical role for selenium in both the normal function of cattle thyroid and key enzymes to compensate for the effects of iodine deficiency.

Postmortem biochemical markers of experimentally induced hypomagnesaemic tetany in cattle.

Severe hypomagnesaemia and tetany were induced in 10 lactating cows by feeding them semi-synthetic low magnesium diets and the animals were used to study the stability of postmortem markers of hypomagnesaemic tetany. There were significant relationships between the concentrations of magnesium in either cerebrospinal fluid (CSF) or plasma and either aqueous or vitreous humour. The onset of hypomagnesamic tetany was also associated with low magnesium concentrations in plasma, CSF and aqueous and vitreous humour. Magnesium concentrations less than 0.25 mmol/litre in fresh aqueous humour may be indicative of severe hypomagnesaemia and possible tetany in lactating cows, but the concentration of magnesium in aqueous humour was unstable postmortem. The concentration of magnesium in vitreous humour was relatively stable and a concentration of less than 0.55 mmol/litre could be used as a diagnostic marker of tetany in cattle for up to at least 48 hours postmortem, at ambient temperatures typical of Northern Ireland.

Clinical and laboratory findings in cases of toxic mastitis in cows in Northern Ireland.

This paper describes the clinical and laboratory findings from 264 cases of toxic mastitis in cows in Northern Ireland between October 1995 and May 1997. Nearly all the cases occurred during the winter housing period, with 84 per cent occurring between November and March inclusive, and 30 per cent in March. Sixty per cent of the cases occurred within one month of calving, and 29 per cent within four days of calving. The most common clinical signs were lethargy (92 per cent), discoloured milk (90 per cent), anorexia (72 per cent), tachypnoea (23 per cent), diarrhoea (23 per cent), recumbency (18 per cent) and staggering (15 per cent). Severe pyrexia (18 per cent) and clinical dehydration (44 per cent) were relatively common findings. Pure growths of Escherichia coli were isolated from 50 per cent of the milk samples, but 11 per cent yielded no bacterial growth. In vitro sensitivity tests indicated that enrofloxacin was effective against 98 per cent of the bacteria isolated, and framycetin and amoxycillin/clavulanic acid against 91 per cent. Abnormally high blood urea levels were observed in 31 per cent of cases, high blood creatinine levels in 42 per cent, and severe leucopenia in 56 per cent. Of the cases which were followed up, 14 per cent died, 21 per cent were culled early and a further 22 per cent lost milk production from the affected quarter.

Stillbirth/perinatal weak calf syndrome: a study of calves with an abnormal thyroid gland.

Data collected from 365 calves dead from stillbirth/perinatal weak calf syndrome were analysed to determine the predictive value of thyroid gland weight as an indicator of abnormality of the thyroid gland, and to examine the relationships between abnormality of the thyroid gland and other findings in the calves and also the parity of the dam. There was a significant relationship (P < 0.001) between the thyroid gland weight and bodyweight for the calves with a histologically normal thyroid gland, but there was no such relationship for calves with an abnormal thyroid gland. Only 1.1 per cent of the histologically normal thyroid glands weighed more than 30 g, indicating that there is a very high probability that glands weighing more than 30 g are abnormal. However, 76.0 per cent of moderately to severely affected glands weighed less than 30 g. The following significant differences between calves with an abnormal and those with a normal thyroid gland were established. Abnormal thyroid glands were significantly heavier (P < 0.01), constituted a significantly greater percentage of the calf's bodyweight (P < 0.01) and had a significantly lower iodine concentration (P < 0.001). A significantly higher proportion of calves with an abnormal thyroid gland had uninflated lungs (P < 0.01), and a significantly higher proportion had pneumonia (P < 0.01). Abnormal thyroid glands were associated with a low selenium concentration in the kidneys. There were no associations between abnormalities of the thyroid gland and the parity of the dam, the presence of skeletal fractures, the weight or sex of the calf, infection with leptospira, Salmonella dublin, Bacillus species, Actinomyces pyogenes or Aspergillus species, the quantities of hepatic iron pigment, liver vitamin E concentration or serum cholesterol concentration.

Experimental reproduction of iodine deficiency in cattle.

The role of iodine deficiency in stillbirth/perinatal weak calf syndrome was investigated in pregnant heifers. Five heifers were fed an iodine deficient diet (mean [sd] iodine concentration 0.06 [0.01] mg/kg dry matter [DM]) and six received an iodine sufficient diet (mean [sd] iodine concentration 1.45 [0.27] mg/kg DM). The diets consisted of wheat and soyabean meal with added minerals and vitamins (with or without iodine) and were fed to the heifers over the final four to five months of pregnancy. The iodine deficient diet produced clinicopathological changes and pathological changes in the thyroid glands of both the heifers and their offspring. However, all the calves in the iodine deficient group were born clinically normal.

Postmortem biochemical markers of experimentally induced hypomagnesaemic tetany in sheep.

Hypomagnesaemic tetany was induced in non-lactating and lactating ewes by feeding them semi-synthetic low magnesium diets containing additional potassium chloride and citric acid. Aqueous and vitreous humour were sampled from one eye at the time of death (fresh) and from the second eye after the head had been stored at ambient temperature for 24 hours (24-hour). There were significant relationships between the concentrations of magnesium in cerebrospinal fluid and plasma and its concentrations in fresh aqueous humour and fresh vitreous humour. Magnesium concentrations of < 0.33 mmol/litre in fresh aqueous humour and < 0.50 mmol/litre in 24-hour aqueous humour were associated with severe hypomagnesaemia and tetany. However, the concentration of magnesium in aqueous humour is relatively unstable and, unless the time of death was known accurately, its interpretation would be difficult. Magnesium concentrations of < 0.60 mmol/litre in fresh vitreous humour and < 0.65 mmol/litre in 24-hour vitreous humour were associated with severe hypomagnesaemia and tetany in adult sheep. The concentration of magnesium in vitreous humour was relatively stable for up to 48 hours postmortem.

Biochemical changes induced by hypomagnesaemia in lactating cows and ewes.

Severe hypomagnesaemia was induced in lactating cows and lactating sheep by feeding them magnesium-deficient diets for 17 and 14 days, respectively. Hypomagnesaemia in cows was associated with abnormally high rates of change in the numbers of leucocytes, neutrophils, monocytes and platelets. There were increases in the concentration of iron in the liver of the hypomagnesaemic ewes and in the heart of the hypomagnesaemic cows, which were not associated with a haemolytic process. The percentage of some of the peroxidisable fatty acids was lower in the heart tissue of hypomagnesaemic cows, but the reduction was not associated with significant lipid peroxidation.

Fertility of dairy cows in Northern Ireland.

A comprehensive database was established on the milk production and reproductive performance of dairy cows in 19 selected herds in Northern Ireland, varying in size, management system and genetic merit. Data were obtained for 2471 cows, 1775 of which calved in a second year, and 693 were culled from the herd for specific reasons. The estimated mean rate of heat detection (assessed by the interheat interval during the main breeding season) in all the herds was 71 per cent, with a range from 53 to 92 per cent The average conception rate to first insemination was 37.1 per cent (range 21 to 66 per cent). The average calving interval for the retained cows was 407.2 days (range 359 to 448 days). Twenty-eight per cent of the cows that calved were culled, with infertility being the largest single reason (26.8 per cent of the cows culled). There were major differences in reproductive performance between the herds, but heat detection rate, conception rate and calving interval did not appear to be affeded by a herd's genetic merit. The herds with shorter calving intervals were characterised by better heat detection efficiency (83 v 61 per cent, P<0.01), a shorter interval from calving to first insemination (74 v 97 days; P<0.05), a higher conception rate to first insemination (45 v 34 per cent, P>0.10) and a lower removal rate (23 v 37 per cent, P<0.01). Furthermore, the cows in these herds had lower body condition scores (BCS) in the dry period (3.0 v 3.3; P<0.05) but lost less body condition in early lactation (0.3 v 0.6 BCS units, P<0.05). These results show that dairy herd fertility in Northern Ireland is generally low and similar to that previously reported for England and the USA, but that in some herds changes in herd management practices improved the cows' fertility.

Hypomagnesaemia and new data on vitreous humour magnesium concentration as a post-mortem marker in ruminants.

Magnesium deficit has been associated with many sub-clinical and clinical conditions in humans and animals. The incidence of hypomagnesaemia is high in lactating cows grazing spring pastures, occasionally resulting in the often fatal condition known as grass tetany. While plasma magnesium concentrations can be used to assess magnesium status in the live animal, post-mortem diagnosis of clinical grass tetany is difficult. Recent studies have investigated the potential of eye fluid magnesium concentration as a post-mortem marker of hypomagnesaemic tetany. In tetany induction studies carried out in adult ewes and lactating cows significant relationships were found to exist between the concentrations of magnesium in either cerebrospinal fluid or plasma and either aqueous or vitreous humour. In freshly dead animals aqueous humour magnesium concentrations of < 0.33 mmol/L in adult sheep and < 0.25 mmol/L in adult cattle were associated with severe hypomagnesaemia and tetany. However, aqueous humour was found to be unstable post-mortem. Vitreous humour was considerably more stable and a vitreous humour magnesium concentration in adult sheep of < 0.65 mmol/L for up to 24 hours post-mortem or < 0.55 mmol/L in adult cows for up to 48 hours was associated with severe hypomagnesaemia and tetany. Provided clear-fluid samples are taken from appropriate animals and processed correctly in the laboratory, the concentration of magnesium in vitreous humour is a useful and practical marker in the post-mortem diagnosis of hypomagnesaemic tetany in ruminants.

Effect of offering dairy cows diets differing in phosphorus concentration over four successive lactations: 1. Food intake, milk production, tissue changes and blood metabolites.

The loss of phosphates from dairy farms contributes to the eutrophication of waterways. Whilst reducing the phosphorus (P) content of dairy cow diets has the potential to help reduce phosphate losses, diets containing inadequate dietary P may have a negative effect on cow health and performance. To address this issue, 100 winter-calving Holstein-Friesian dairy cows were offered diets containing either 'high' or 'low' levels of dietary P. The experiment was conducted over a 4-year period, with 80 primiparous cows commencing the study in year 1, while a further 20 primiparous cows commenced the study in year 2. Rations offered during the winter comprised grass silage, maize silage (70 : 30 dry matter (DM) basis, approximately) and concentrates (10.0 to 12.0 kg/cow per day). During the summer periods in years 1 and 2, half of the cows grazed both day and night, while the remaining cows grazed by day, and were housed by night and offered grass silage. During years 3 and 4, all cows grazed both day and night during the summer period. Concentrate feed levels during the summer periods were 3.0 to 4.0 kg/cow per day. Different dietary P levels were achieved by offering concentrates containing either high or low P levels during the winter period (approximately 7.0 or 4.4 g P/kg DM respectively), and during the summer period (approximately 6.8 or 3.6 g P/kg DM, respectively). Total ration P levels averaged 4.9 and 3.6 g P/kg DM for the 'high' and 'low' P winter diets respectively, and 4.2 and 3.6 g P/kg DM for the 'high' and 'low' P summer diets respectively. A total of 95, 70, 50 and 22 cows completed each of lactations 1 to 4 respectively. Dietary P level had no significant effect on food intake, milk output or milk composition (P > 0.05). Plasma P concentrations were significantly lower with cows offered the 'low' P diet in each of lactations 1 to 4 (P < 0.05). In each of lactations 3 and 4, cows offered the 'low' P diet tended to have lower condition scores and live weights than those offered the 'high' P diet. The results of this experiment highlight that the P content of dairy cow diets can be substantially reduced with no detrimental effect on dairy cow performance.

Effect of offering dairy cows diets differing in phosphorus concentration over four successive lactations: 2. Health, fertility, bone phosphorus reserves and nutrient utilisation.

This experiment examined the long-term effects of offering diets containing low levels of dietary phosphorus (P) on dairy cow health, fertility and bone composition, and the effect of dietary P level on nutrient utilisation. One hundred winter-calving Holstein-Friesian dairy cows were offered diets containing either 'high' or 'low' levels of dietary P over a 4-year period. Rations offered during the winter included grass silage, maize silage (70 : 30 dry matter (DM) basis, approximately) and concentrates (10.0 to 12.0 kg/cow per day). During the summer periods in years 1 and 2, half of the cows grazed both day and night, while the remaining cows grazed by day, and were housed by night and offered grass silage. During years 3 and 4, all cows grazed both day and night during the summer period. Concentrate feed levels during the summer periods were 3.0 to 4.0 kg/cow per day. Different dietary P levels were achieved by offering concentrates containing either high or low P levels during the winter period (approximately 7.0 or 4.4 g P/kg DM, respectively) and during the summer period (approximately 6.8 or 3.6 g P/kg DM, respectively). Total ration P levels averaged 4.9 and 3.6 g P/kg DM for the high and low P winter diets, respectively, and 4.2 and 3.6 g P/kg DM for the high and low P summer diets, respectively. A total of 95, 70, 50 and 22 cows completed each of lactations from 1 to 4, respectively. Neither the incidence of lameness or mastitis, or milk somatic cell count, were affected by dietary P level (P > 0.05), while none of the fertility parameters recorded in any of lactations from 1 to 4 was affected by the dietary P level (P > 0.05). Dietary P level had no effect on the specific gravity, ash or calcium content of rib cortical bone cores (n = 78 cows), while the P content of cortical bone (g/kg fresh, g/kg DM and mg/ml fresh bone) was lower with cows offered low P diets (P < 0.05). Dietary P level had no significant effect on the digestibility of either the DM, nitrogen, energy or acid detergent fibre fraction of the diet (P > 0.05), while faecal P excretions were reduced by a mean of 27 g/cow per day with cows offered the low P diets during the winter period. The results of this study indicate that dietary P levels can be reduced to proportionately 0.8 (approximately) of current UK feeding standards (Agricultural and Food Research Council, 1991), with no detrimental effect on dairy cow health or fertility, while having only minor effects on bone composition.