Pathophysiology of grass tetany and other hypomagnesemias. Implications for clinical management

Periparturient Mineral Metabolism: Implications to Health and Productivity

Mineral metabolism, in particular Ca, and to a lesser extent phosphorus (P) and magnesium (Mg), is altered with the onset of lactation because of extensive irreversible loss to synthesize colostrum and milk. The transient reduction in the concentration of Ca in blood, particularly when it lasts days, increases the risk of mineral-related disorders such as hypocalcemia and, to a lesser extent, hypophosphatemia. Although the incidence of clinical hypocalcemia can be reduced by prepartum dietary interventions, subclinical hypocalcemia remains prevalent, affecting up to 60% of the dairy cows in the first 3 d postpartum. More importantly, strong associations exist between hypocalcemia and increased susceptibility to other peripartum diseases and impaired reproductive performance. Mechanistic experiments have demonstrated the role of Ca on innate immune response in dairy cows, which presumably predisposes them to other diseases. Hypocalcemia is not related to inadequate Ca intake as prepartum diets marginal to deficient in Ca reduce the risk of the disease. Therefore, the understanding of how Ca homeostasis is regulated, in particular how calciotropic hormones such as parathyroid hormone and 1,25-dihydroxyvitamin D3, affect blood Ca concentrations, gastrointestinal Ca absorption, bone remodeling, and renal excretion of Ca become critical to develop novel strategies to prevent mineral imbalances either by nutritional or pharmacological interventions. A common method to reduce the risk of hypocalcemia is the manipulation of the prepartum dietary cation-anion difference. Feeding acidogenic diets not only improves Ca homeostasis and reduces hypocalcemia, but also reduces the risk of uterine diseases and improves productive performance. Feeding diets that induce a negative Ca balance in the last weeks of gestation also reduce the risk of clinical hypocalcemia, and recent work shows that the incorporation of mineral sequestering agents, presumably by reducing the absorption of P and Ca prepartum, increases blood Ca at calving, although benefits to production and health remain to be shown. Alternative strategies to minimize subclinical hypocalcemia with the use of vitamin D metabolites either fed prepartum or as a pharmacological agent administered immediately after calving have shown promising results in reducing hypocalcemia and altering immune cell function, which might prove efficacious to prevent diseases in early lactation. This review summarizes the current understanding of Ca homeostasis around parturition, the limited knowledge of the exact mechanisms for gastrointestinal Ca absorption in bovine, the implications of hypocalcemia on the health of dairy cows, and discusses the methods to minimize the risk of hypocalcemia and their impacts on productive performance and health in dairy cows.

Metabolic Diseases in Beef Cattle

Beef cattle are less prone to metabolic diseases as compared with dairy cattle; however, there are disease entities of concern in feedlot and cow-calf beef cattle operations. In one study, a prevalence of 2% was found for ruminant acidosis in a feedlot; however, there is little prevalence information published with regard to metabolic diseases in beef cattle.1 Metabolic diseases covered in this article are hypomagnesemia, ruminal acidosis, and all of the common sequelae, polioencephalomalacia, manganese deficiency, and protein-energy malnutrition (PEM).

The Contribution of Dietary Magnesium in Farm Animals and Human Nutrition

Magnesium (Mg) is a mineral that plays an essential role as cofactor of more than 300 enzymes. Mg in farm animals' and human nutrition is recommended to avoid Mg deficiency, ensure adequate growth and health maintenance. Mg supplementation above the estimated minimum requirements is the best practice to improve farm animals' performances (fertility and yield) and food products' quality, since the performance of farm animals has grown in recent decades. Mg supplementation in pigs increases meat quality and sows' fertility; in poultry, it helps to avoid deficiency-related health conditions and to improve meat quality and egg production by laying hens; in dairy cows, it serves to avoid grass tetany and milk fever, two conditions related to hypomagnesaemia, and to support their growth. Thus, Mg supplementation increases food products' quality and prevents Mg deficiency in farm animals, ensuring an adequate Mg content in animal-source food. These latter are excellent Mg sources in human diets. Sub-optimal Mg intake by humans has several implications in bone development, muscle function, and health maintenance. This review summarizes the main knowledge about Mg in farm animals and in human nutrition.

Aflatoxicosis in cattle: clinical findings and biochemical alterations

Aflatoxicosis is a serious health condition resulted from aflatoxin (AF)-producing fungi. Major health threats resulted from AFs and reflect on the livestock industry with great economic losses. There are limited scientific evidences concerning the AFs in ruminant, therefore it is important to evaluate AFs health hazards in cattle. Here, we investigate biochemical, oxidative stress, and postmortem changes associated with unexpected acute bovine aflatoxicosis. Seventy-two cattle were suffered from aflatoxisocis. Depression and inappetence were predominant clinical findings of the diseased animals. Analysis of feedstuffs revealed presence of aflatoxin B1 (AFB1). The AF-intoxicated animals showed a significant increase in alanine amino transferase (ALT), aspartate amino transferase (AST), alkaline phosphatase (ALP), serum creatinine (SCr), catalase (CAT), and malondialdehyde (MDA) levels. Moreover, a significant decrease in total protein (TP), magnesium (Mg), and reduced glutathione (GSH) were also seen. Hepatomegaly, enlarged gallbladder as well as congestion of the intestine and kidney were observed. This study elucidates the critical and constructive measurements needed for the prevention of the AFs hazardous effects to livestock for the future control of AF outbreaks. Conducting series of diagnostic assays reflect the marked health condition alterations in the biochemical and antioxidant status of the AF-intoxicated cattle.

Do calcium and magnesium deficiencies in reproducing ewes contribute to high lamb mortality?

High lamb mortality continues to be a significant economic and welfare problem within the Australian sheep industry, with 20–30% of lambs born in commercial flocks dying mostly within 3 days of birth. Clinical hypocalcaemia and hypomagnesaemia cause ewe mortality, and, subsequently, either fetal or lamb death, but it is not known whether subclinical deficiencies of calcium (Ca) and magnesium (Mg) compromise lamb survival. This review considers the potential mechanisms through which Ca and Mg deficiencies may influence lamb survival, and factors influencing the risk of deficiency. Pastures grazed by lambing ewes may be marginal in calcium (Ca; <4 g/kg DM) and magnesium (Mg; <0.9 g/kg DM) but also have a high dietary cation–anion difference (>12 meq/100 g DM) and high concentrations of potassium (K; >30 g/kg DM) and nitrogen. In young cereal crops, sodium concentrations are also often low (<0.9 g/kg DM). This combination of minerals and other nutrients creates an imbalance in supply and increases susceptibility to acute Ca (hypocalcaemia) and Mg (hypomagnesaemia) deficiency. Calcium is required for smooth muscle function and has a direct role in uterine contraction, so may influence the duration of parturition. Low Ca and Mg intake both influence insulin release and sensitivity, low Mg results in poor glycaemic control and insulin resistance by impairing both insulin secretion and its action on peripheral tissues, also potentially altering the duration of parturition as well as risk of metabolic disease. Magnesium is also a neuroprotectant that slows the neuronal damage during hypoxia and has been linked with thermogenesis in offspring and increased immunoglobulins in colostrum. These functions indicate potential importance in improving the ease of parturition and improved ability of the newborn lamb to thermoregulate and survive after birth. Subclinical Ca and Mg deficiencies commonly occur in 20% of lambing ewes grazing temperate pastures, so further studies are warranted to investigate whether correction of these deficiencies can improve lamb survival.

A reconnaissance survey of farmers' awareness of hypomagnesaemic tetany in UK cattle and sheep farms

Hypomagnesaemic tetany (HypoMgT) in ruminants is a physiological disorder caused by inadequate intake or impaired absorption of magnesium (Mg) in the gut. If it is not detected and treated in time, HypoMgT can cause the death of the affected animal. A semi-structured questionnaire survey was conducted from July 2016–2017 to assess farmers’ awareness of HypoMgT in cattle and sheep in the UK. The questionnaire was distributed to farmers at farm business events and agricultural shows, and through a collaborative group of independent veterinary practices to their clients. Farmers were asked about (i) the incidence of presumed HypoMgT (PHT); (ii) their strategies to treat or prevent HypoMgT; (iii) mineral tests on animals, forage and soil, and (iv) farm enterprise type. A total of 285 responses were received from 82 cattle, 157 mixed cattle and sheep, and 46 sheep farmers, of whom 39% reported HypoMgT in their livestock, affecting 1–30 animals. Treatment and/or prevention against HypoMgT was reported by 96% respondents with PHT and 79% of those without. Mineral tests on animal, forage, and soil was conducted by 24%, 53%, and 66% of the respondents, respectively, regardless of PHT. There was a highly significant association between the use of interventions to tackle HypoMgT and the incidence of PHT (p < 0.01). The top three treatment/prevention strategies used were reported as being free access supplementation (149), in feed supplementation (59) and direct to animal treatments (drenches, boluses and injections) (45) although these did vary by farm type. Although some (9) reported using Mg-lime, no other pasture management interventions were reported (e.g., Mg-fertilisation or sward composition). Generally, the results indicate that UK farmers are aware of the risks of HypoMgT. A more integrated soil-forage-animal assessment may improve the effectiveness of tackling HypoMgT and help highlight the root causes of the problem.

Hypomagnesemia in dairy cattle in Uruguay

ABSTRACT: An outbreak of hypomagnesemia is reported in Holstein dairy cattle grazing lush oat (Avena sativa) pasture in Uruguay. Nine of 270 (3.3%) cows died in May-July (autumn-winter) 2017. These nine cows were from 2 to 9-years-old (1st-6th lactation), with 22 to 194 days of lactation and 15.8 to 31.4L of daily milk production. Two cows with acute sialorrhea, muscle spasms, lateral recumbency, weakness, opisthotonos, and coma, were euthanized and necropsied. No significant macroscopic or histological lesions were found. One untreated clinically-affected cow and eight out of 14 clinically healthy cows of the same group under similar management and production conditions had low serum levels of Mg (lower than 0.7mmol/L). Secondarily, both clinically affected cows and six out of 14 healthy cows had low serum Ca levels. The K/(Ca+Mg) ratio of two oat forages, corn silage, and ration was 5.10, 7.73, 2.45, and 0.85, respectively. A K/(Ca+Mg) ratio lower than 2.2 represents a risk for hypomagnesemia. The difference between the contribution-requirement of minerals in the diet was established and a daily deficiency of Mg (-0.36g/day), Na (-25.2g/day) and Ca (-9.27g/day) was found, while K (184.42g/day) and P (12.81g/day) were in excess. The diet was reformulated to correct the deficiencies and the disease was controlled by the daily administration of 80g of magnesium oxide, 80g of calcium carbonate and 30g sodium chloride per cow. It is concluded that hypomagnesemia is a cause of mortality in dairy cattle in Uruguay, and that the condition can be prevented by appropriate diet formulation.

The Use of Biochemical Measurements to Identify Pre-Slaughter Stress in Pasture Finished Beef Cattle

This study considered the relationship between pre-slaughter stressors and plasma biomarkers in 488 pasture-raised cattle across two experiments. The design aimed to test groups consisting of steer only, heifer only, and mixed sex cattle under direct kill versus rested (14 days in abattoir holding paddocks) protocols. In Experiment One, cattle were sourced from four farms, and transported by trucks and ships on the same day. In Experiment Two, cattle were sourced from four farms where a comparison was made between marketing via two commercial saleyards or direct farm gate consignment to abattoir. Blood samples were collected at exsanguination for subsequent analyses and relation to meat quality attributes. Muscle damage, as indicated by creatine kinase, is the biomarker most correlated to ultimate pH and muscle glycogen concentrations. A two-week rest period is effective for lowering this enzyme and improving muscle glycogen concentration. Although the cattle was subjected to a range of stress inducing treatments, we found that plasma biomarkers alone appeared insufficient for use as diagnostic stress indicators.

Assessment of magnesium intake according to requirement in dairy cows

To date, no specific hormonal regulation system has been identified for homoeostatic control of the essential mineral Mg. In cattle, the maintenance of physiological plasma Mg concentration depends on gastrointestinal absorption, primarily from the rumen, which serves as a pool for covering the requirement. Whereas a possible surplus (absorption greater than requirement) is rapidly excreted by the kidneys, a shortage (absorption lower than requirement) cannot be compensated for by mobilization from the large Mg pool in bones or soft tissue, so that the maintenance of the necessary physiological Mg concentration in plasma relies on continuous and sufficient absorption. Our knowledge concerning the site and mechanisms of Mg absorption has improved during the last few decades, and meta-analyses of the absorption of Mg in dairy cows have shown that the K content has a pronounced negative effect on Mg digestibility. The current recommendations of Mg intake propose a constant percentage of Mg and emphasize the depressive effect of high potassium (K) intake on Mg absorption. The current knowledge about the antagonism between K intake and Mg absorption allows a more flexible solution which includes the K content of the diet. An assessment of Mg intake is proposed that incorporates the improved knowledge of Mg absorption, metabolism and requirement. Within this framework, an equation is derived that allows a prediction of the amount of Mg required to compensate for dietary K content, the goal being to avoid both possible undernutrition or an unnecessary surplus of dietary Mg.

Invited review: Mineral absorption mechanisms, mineral interactions that affect acid-base and antioxidant status, and diet considerations to improve mineral status

Several minerals are required for life to exist. In animals, 7 elements (Ca, P, Mg, Na, K, Cl, and S) are required to be present in the diet in fairly large amounts (grams to tens of grams each day for the dairy cow) and are termed macrominerals. Several other elements are termed microminerals or trace minerals because they are required in much smaller amounts (milligrams to micrograms each day). In most cases the mineral in the diet must be absorbed across the gastrointestinal mucosa and enter the blood if it is to be of value to the animal. The bulk of this review discusses the paracellular and transcellular mechanisms used by the gastrointestinal tract to absorb each of the various minerals needed. Unfortunately, particularly in ruminants, interactions between minerals and other substances within the diet can occur within the digestive tract that impair mineral absorption. The attributes of organic or chelated minerals that might permit diet minerals to circumvent factors that inhibit absorption of more traditional inorganic forms of these minerals are discussed. Once absorbed, minerals are used in many ways. One focus of this review is the effect macrominerals have on the acid-base status of the animal. Manipulation of dietary cation and anion content is commonly used as a tool in the dry period and during lactation to improve performance. A section on how the strong ion theory can be used to understand these effects is included. Many microminerals play a role in the body as cofactors of enzymes involved in controlling free radicals within the body and are vital to antioxidant capabilities. Those same minerals, when consumed in excess, can become pro-oxidants in the body, generating destructive free radicals. Complex interactions between minerals can compromise the effectiveness of a diet in promoting health and productivity of the cow. The objective of this review is to provide insight into some of these mechanisms.

Practical implications of mineral and vitamin imbalance in grazing sheep

Rapid progress in research on mineral functions in biological systems over the past 20 years has provided new and unexplored implications for health and production in grazing livestock. The strong interaction among calcium (Ca), magnesium (Mg), phosphorus (P), sodium (Na), potassium (K) and vitamin D influences the absorption, utilisation and status of these nutrients, particularly Ca and Mg. An imbalanced intake of Ca, Mg, P, Na, K and vitamin D is common in ruminants grazing pastures and vegetative crops. The interaction may modify susceptibility to clinical hypocalcaemia, hypomagnesaemia and pregnancy toxaemia, or to subclinical and chronic deficiencies of Ca, Mg and Na. However, hypocalcaemia is also associated with endocrine failure. Whether this failure is susceptible to nutritional modulation or even whether supplements of Ca, Mg, Na and vitamin D reduce or exacerbate the risk of metabolic disease in sheep is unclear. Selenium, manganese, zinc, copper, sulfur, vitamin E and vitamin A play synergistic roles in the antioxidant defence mechanism and modulate the consequences of oxidative stress. In extensive grazing systems combined low intakes of these antioxidants are not unusual, particularly in seasonally dry environments and at a time coinciding with the increased oxidative stress that naturally occurs through the reproductive cycle. This oxidative stress is accentuated by heat stress and parasite infection. Oxidative stress in the short-term influences growth, reproduction, offspring survival and health. Long-term, oxidative damage to embryo DNA and changes in RNA expression, may influence lifetime performance of offspring. The high cost of providing mineral supplements to grazing sheep is a deterrence to addressing the implications of multiple mineral deficiencies. New herbaceous and shrub options to increase the botanical and nutritional diversity within pasture and crop-grazing systems may allow livestock to select a heterogeneous diet providing a more balanced mineral intake.

Biology and Diseases of Ruminants (Sheep, Goats, and Cattle)

Ruminants continue to be important in their traditional role in agricultural research and teaching. They are now also extensively used for studies in molecular biology; genetic engineering; and biotechnology for basic science, agricultural and clinical applications. Concern and interest for the welfare for these species and improved understanding of their biology and behavior have continued and are reflected in changing husbandry and management systems. This chapter addresses at high levels basic biology, husbandry, and the more common or important diseases of the three ruminant species used most commonly in the laboratory, namely sheep, goats and cattle.

Hipocalcemia não puerperal em vacas leiteiras sob pastejo de aveia e azevém: estudo de fatores predisponentes

A Hipocalcemia Não Puerperal (HNP) é uma condição rara e pouco compreendida. Não há estudos que expliquem a sua relação com a ingestão de pastagens de inverno como base da alimentação volumosa. Os objetivos deste trabalho foram descrever aspectos clínicos de dois casos naturais de HNP, e estudar o balanço mineral e eletrolítico de vacas leiteiras de alta e de média produção alimentadas em pastagem de inverno em diferentes estágios de evolução. Foram acompanhados dois casos de HNP em vacas leiteiras, mantidas em pastagens de aveia ou de azevém no município de Francisco Beltrão, PR. De três propriedades localizadas no mesmo município, foram selecionadas vacas lactantes hígidas de alta produção da raça Holandesa (n=11) e de média produção das raças Holandesa (n=8) e Jersey (n=9), mantidas em pastagem mista de aveia e azevém, de junho a outubro de 2011, e complementadas com silagem de milho. Amostras de sangue, de urina e dos alimentos ingeridos foram colhidas antes do ingresso na pastagem (maio), e nos estágios inicial (junho), intermediário (julho) e final (setembro) do ciclo de maturação da forragem. Foram determinadas as concentrações séricas e urinárias de Ca, P, Mg, Na+, K+, Cl- e creatinina e calculada as excreções fracionadas. Nas amostras de alimento foram determinadas a matéria seca (MS) e as concentrações de Ca, P, Mg, Na, K, Cl e S, e calculou-se a diferença entre cátions e ânions da dieta (DCAD) nos diferentes momentos. Com base nas evidências pode-se afirmar que vacas leiteiras em lactação mantidas em pastagem de aveia e/ou de azevém nos meses de inverno podem desenvolver hipocalcemia e exibir sinais clínicos e resposta ao tratamento similares aos da hipocalcemia puerperal clássica, mesmo não sendo recém paridas. A ingestão de aveia e azevém, substituindo parcialmente a silagem de milho como volumoso da dieta, não provoca desequilíbrio eletrolítico e não interfere com a calcemia, a fosfatemia ou a magnesemia de vacas lactantes de alta e de média produção. A utilização das forrageiras de inverno como a única ou principal fonte de volumoso da dieta parece ser o fator desencadeante da doença e pode estar relacionada com o excesso de cátions ingeridos devido à elevada concentração de K, principalmente, quando a planta é jovem.

Mineral status in cattle fed rice straw and para grass combined with different levels of protein derived from cassava foliage

Eight male cattle of the Local Yellow breed with an average live weight of 121 kg and an average age of 18 months were used to evaluate the effects of different levels of sun-dried cassava (Manihot esculenta) foliage supplementation on mineral metabolism in growing cattle fed rice straw and para grass as basal diet. Rice straw ad libitum and para grass (Brachiaria mutica) at 1% DM of BW comprised the basal diet. The study was arranged as a 4×4 double Latin square design, with cassava foliage contributing 0, 0.8, 1.6 or 2.4 g CP/kg BW. The cassava foliage intake was lower than the planned levels. DM consumption was significantly affected by cassava foliage supplementation, with the largest intake observed at the two highest levels of cassava foliage supplementation. Rice straw intake showed the opposite pattern, with lower intake at higher cassava foliage supplementation. No refusals occurred for para grass in any of the treatments. Ca, P, Mg, K, S and Mn intake increased significantly with increasing intake of cassava foliage, but Na intake was not affected by treatment. Faecal excretion of Ca, Mg, S and Mn increased significantly with increasing cassava foliage intake. There were no differences between P, K and Na excretion in faeces. There was a significant diet effect on Mg, S and Mn digestibility. Mg and Mn digestibility increased with increasing cassava foliage supplementation, while S digestibility decreased. Ca, P, K and Na digestibility was not affected by diet. There was a significant effect of treatment on P retention, with the highest value observed for supplementation with 1.6 g CP/kg BW cassava foliage. Ca and Mg showed similar trends, with the highest retention again for supplementation with 1.6 g CP/kg BW cassava foliage. There were weak but significant positive correlations between nitrogen retention and the macro minerals Ca, P and Mg. Furthermore, retention of all these minerals was positively correlated. Mineral losses in urine were not affected by dietary treatment with the exception of P excretion, which was affected by treatment. In conclusion, cassava foliage is a good Ca source which compensates for the low Ca content in rice straw and para grass, but P deficiency appears to be exaggerated in cattle with higher cassava intake. The results suggest that under these conditions growing cattle on a high cassava intake would benefit from P and S supplementation.

Magnesium disorders in horses

Magnesium (Mg) is an essential macroelement that is required for cellular energy-dependent reactions involving adenosine triphosphate and for the regulation of calcium channel function. Subclinical hypomagnesemia is common in critically ill humans and animals and increases the severity of the systemic inflammatory response syndrome; worsens the systemic response to endotoxins; and can lead to ileus, cardiac arrhythmias, refractory hypokalemia, and hypocalcemia. This article discusses the clinical signs, consequences, and treatment of hypomagnesemia in horses and describes the association of Mg and endotoxemia, insulin resistance, and brain injury.

Effect of different potassium levels in hay on acid-base status and mineral balance in periparturient dairy cows

Forages commonly used in dry cow rations contain high K concentrations. This results in a high dietary cation-anion difference (DCAD), which can compromise the calcium homeostasis of periparturient cows. The aim of this study was to determine the effect of 2 types of hay, fed during the prepartum period and differing in their K concentrations, on the peripartum acid-base status and mineral balance of dairy cows. During the prepartum period, the cows of group K(33) (n = 6) received a diet based on hay with a high K concentration (33 g/kg of DM), whereas the cows of group K(13) (n = 6) received a diet based on hay with a low K concentration (13 g/kg of DM). Both experimental diets were formulated to be isoenergetic and isonitrogenous. After calving, all cows received the same diet based on hay K(33). Blood and urine samples were taken on d 14, 7, and 3 before parturition, at parturition, and then daily during the first 8 d after calving. Concentrations of minerals were analyzed in both blood and urine. Creatinine was also measured in urine for the calculation of the mineral:creatinine ratio. The acid-base parameters in blood (pH and HCO(3)(-) concentration) and urine (pH, net acid-base excretion, and base-acid quotient) were determined on d 14, 7, and 3 before parturition, at parturition, and on d 1 after parturition. The use of hay K(13) reduced the DCAD value of the prepartum diet by half (195 vs. 514 mEq/kg of DM). No significant differences between the 2 groups were observed for blood acid-base indicators or plasma minerals except for the Mg plasma concentration, which tended to be higher in group K(13) from d 3 prepartum to d 2 after calving. In group K(13), urinary Ca excretion tended to be higher from d 3 prepartum to d 1 after parturition than that in group K(33). On d 3 before parturition, urinary pH and net acid-base excretion were significantly lower in group K(13) than in group K(33). On d 14, 7, and 3 before parturition, base-acid quotient was significantly lower in group K(13) than in group K(33). In group K(13), daily feed intake and hence daily intake of Ca, P, and Mg during d 3 and 4 after parturition were higher than in group K(33). The decrease of the DCAD in positive ranges by feeding a low-K hay before parturition induced a reduction of the metabolic alkalotic charge, as observed in acid-base parameters in urine, and increased the availability of Ca and P as a result of higher feed intake at the onset of lactation.

Hypocalcemia in Dairy Cows: Meta-analysis and Dietary Cation Anion Difference Theory Revisited

Data from 137 published trials involving 2,545 calvings were analyzed using random effects normal logistic regression models to identify risk factors for clinical hypocalcemia in dairy cows. The aim of the study was to examine which form, if any, of the dietary cation anion difference (DCAD) equation provided the best estimate of milk fever risk and to clarify roles of calcium, magnesium, and phosphorus concentrations of prepartum diets in the pathogenesis of milk fever. Two statistically equivalent and biologically plausible models were developed that predict incidence of milk fever. These models were validated using data from 37 trials excluded from the original data used to generate the models; missing variables were replaced with mean values from the analyzed data. The preferred models differed slightly; Model 1 included prepartum DCAD, and Model 2 included prepartum dietary concentrations of potassium and sulfur alone, but not sodium and chloride. Other factors, included in both models were prepartum dietary concentrations of calcium, magnesium, phosphorus; days exposed to the prepartum diet; and breed. Jersey cows were at 2.25 times higher risk of milk fever than Holstein cows in Model 1. The results support the DCAD theory of greater risk of milk fever with higher prepartum dietary DCAD (odds ratio = 1.015). The only DCAD equation supported in statistical analyses was (Na(+) + K(+)) - (Cl(-) + S(2-)). This finding highlights the difference between developing equations to predict DCAD and those to predict milk fever. The results support a hypothesis of a quadratic role for Ca in the pathogenesis of milk fever (model 1, odds ratio = 0.131; Model 2, odds ratio = 0.115). Milk fever risk was highest with a prepartum dietary concentration of 1.35% calcium. Increasing prepartum dietary magnesium concentrations had the largest effect on decreasing incidence of milk fever in both Model 1 (odds ratio = 0.006) and Model 2 (odds ratio = 0.001). Increasing dietary phosphorus concentrations prepartum increased the risk of milk fever (Model 1, odds ratio = 6.376; Model 2, odds ratio = 9.872). The models presented provide the basis for the formulation of diets to reduce the risk of milk fever and strongly support the need to evaluate macro mineral nutrition apart from DCAD of the diet.

Studies of the transition cow under a pasture-based milk production system: metabolic profiles

This study describes the effect of parity (multiparous versus primiparous) and body condition score (BCS) at calving (<3 or > or =3; scale 1-5) on variations of BCS, body weight (BW) and metabolic profiles in Holstein cows grazing on improved pastures. Forty-two cows were studied (21 multiparous and 21 primiparous) from 2 months before to 3 months after calving. BCS, BW and milk production were measured every 2 weeks. Blood samples were taken every 2 weeks to determine total protein, albumin, urea, non-esterified fatty acids (NEFA), beta-hydroxybutyrate (BHB), cholesterol, aspartate aminotransferase (AST), calcium, phosphorus and magnesium. Primiparous cows had lower BCS during the early postpartum (PP) period and produced less milk than multiparous. In primiparous cows NEFA concentrations were higher during the early postpartum period; BHB levels were similar in both categories during this period. Primiparous cows showed a more unbalanced metabolic profile than multiparous cows, reflecting that they are recovering from the loss of BCS after calving with less success.

Adrenoceptor heterogeneity in the ruminal epithelium of sheep

The pre-gastric rumen of sheep plays a crucial role in the fermentation of nutrients and in the absorption of nutrients and minerals. Adrenaline has been shown previously to increase ruminal absorption of glucose and water. The present study was intended to elucidate whether ruminal ion transport is also altered by adrenaline. In Ussing chambers, changes of I(sc) were recorded in isolated ovine ruminal epithelia after the serosal additions of adrenoceptor agonists or antagonists. I(sc) increased after the addition of adrenaline (10(-4) M) or clonidine (alpha2-agonist, 10(-4) M), but decreased after the addition of isoproterenol (beta-agonist, 10(-4) M) or terbutaline (beta2-agonist, 10(-5) M). The effect of adrenaline on I(sc) was augmented by the adrenoceptor antagonists prazosin (alpha(1), 10(-4) M) and bupranolol (beta, 10(-6) M), but inversed by yohimbine (alpha(2), 10(-5) M). Adrenaline induced an increase in Na+ net flux across the epithelium that was larger than the increase in equivalent current flow. It is concluded that adrenaline differentially regulates ion transport across the ruminal epithelium via alpha1-, alpha2-, and beta2-receptors. The main effect is a stimulation of electroneutral and electrogenic Na+ absorption. This stimulated Na+ absorption might be causative of increased water absorption from the rumen as described previously.

Macromineral disorders of the transition cow

Four macrominerals have the distinction of being involved in the "downer cow" syndrome, which is, unfortunately, often associated with parturition in cows. Inadequate blood calcium (Ca), phosphorus (P), magnesium (Mg), or potassium (K) concentrations can cause a cow to lose the ability to rise to her feet because these minerals are necessary for nerve and muscle function. Less severe disturbances in blood concentrations of these minerals can cause reduced feed intake, poor rumen and intestine motility, poor productivity, and increased susceptibility to other metabolic and infectious disease. Mechanisms for maintaining blood Ca, P, Mg, and K concentrations perform efficiently most of the time, but occasionally these homeostatic mechanisms fail and metabolic diseases such as milk fever occur. Understanding how and why these mechanisms fail may allow the practitioner to develop strategies to avoid these disorders.

Hypomagnesemia among cows in a confinement-housed dairy herd

Between January and March 2002, 55 cows in a 1,200-cow commercial dairy herd in south Florida died. Most of the cows that were found dead did not have any clinical signs of disease prior to death. Because of a history of a feed change, a bloom of blue-green algae in cow cooling ponds, and initial necropsy findings of moderate enteritis, the preliminary differential diagnosis included clostridial enteritis, blue-green algae toxicosis, and mycotoxicosis. Rumen acidosis, hypomagnesemia, and heavy metal toxicosis were included as secondary considerations. On the basis of physical examination and gross necropsy findings, results of clinicopathol ogic testing, and results of feed and water analyses, a diagnosis of hypomagnesemia was made. Control procedures that were implemented included changing the forage source and increasing the magnesium concentration in the diet.

Does high plant feed magnesium and potassium protect healthy ruminants from atherosclerosis? A review

The literature data were surveyed to clarify the role of magnesium and potassium in the development of atherosclerosis (AS) in cows and the findings were compared with human data. Special attention was paid to the eastern Finland where AS is very common in humans and absent in the cattle. A hypothesis is proposed that high magnesium and potassium intakes at plant feeding protect from severe AS processes at least in cows in the absence of chronic infections. In about 1500 necropsies in calves and cows on plant feeding, neither antemortem clinical AS symptoms nor postmortal macroscopical AS were detected in the endocardium or in aorta. Also, abattoiries in endemic selenium- and vitamin E-deficient areas report that no macroscopic AS have been found in the inspected more than 400000 slaughtered cattle. In vitamin D(3) poisoned cows AS is readily detected. The milk-fed calves in magnesium deficiency experiments regularly show AS after 3 months of age. Adult ruminating cattle get daily 150-300 g potassium while the need is 35 g. During the indoor feeding period the cows suffered in eastern Finland often from carotene, vitamin E and selenium deficiencies as well as also of energy, protein, phosphorus and zinc deficiencies before grass ensiling feeding started. Endemic goiter prevalence was about 30%. Still such cows did not have AS under such unfavorable conditions. The findings support the hypothesis that the high magnesium and potassium intakes protect cows from AS.

Dehydration in stressed ruminants may be the result of a cortisol-induced diuresis

The effect on water and electrolyte balance of stress, simulated by intravenous infusion of cortisol, was studied using 24 18-mo-old Merino wethers (37.0 +/- 0.94 kg mean body weight [BW]) over 72 h. The sheep were allocated to one of four groups: 1) no water/no cortisol (n = 6); 2) water/no cortisol (n = 4); 3) no water/cortisol (n = 6); and 4) water/cortisol (n = 4). Animals allocated to the two cortisol groups were given 0.1 mg x kg BW(-1) x h(-1) of hydrocortisone suspended in isotonic saline to simulate stress for the duration of the experiment. Total body water, plasma cortisol, osmolality and electrolytes, and urine electrolytes were determined at 24-h intervals for 72 h. In the presence of cortisol, total body water was maintained in the face of a water deprivation insult for 72 h. Water deprivation alone did not induce elevated plasma concentrations of cortisol, in spite of a 13% loss of total body water between 48 and 72 h. Infusion of cortisol was found to increase urine output (P = 0.003) and decrease total urinary sodium output (P = 0.032), but had no effect on plasma electrolyte levels or water intake. Water deprivation was found to increase plasma sodium concentrations (P = 0.037). These results indicate that sheep given cortisol to simulate stress suffer from a loss of body water in excess of that associated with a loss of electrolytes, and support the hypothesis that elevated physiological concentrations of cortisol induce a diuresis in ruminants that contributes to dehydration.

The use of blood analyses to evaluate mineral status in livestock

Animal responses are useful means of evaluating and assessing nutritional status. Blood mineral concentrations can be useful nutritional responses, although there are important limitations. The nutritional value in monitoring blood mineral concentrations varies with the specific mineral, being generally most valuable for those minerals in which homeostasis is regulated primarily by renal excretion, as opposed to regulation by variable absorptive efficiency. Examples of minerals for which blood concentrations are good measures of nutritional intake are selenium and magnesium. Blood mineral concentrations are affected by multiple variability factors. The strategy for use in mineral status assessment is to minimize non-nutritional variation by grouping animals for testing based on physiologic factors that affect, or are likely to affect, the concentration of the mineral or minerals being tested. Care should be taken to use the proper sampling protocol, so as not to cause artifactual variation. Removal of the serum from the clot within 2 hours of sample collection is an important step, among others. Sampling adequate numbers of animals and evaluating the herd mean and SD can minimize the effect of random variation on interpretation.