Effects of manipulating dietary cation-anion balance on macromineral balance in sheep

Graduate Student Literature Review: Serotonin and calcium metabolism: A story unfolding

The peripartum period is characterized by dynamic shifts in metabolic, mineral, and immune metabolism as the dairy cow adapts to the demands of lactation. Emphasis over the past decade has been placed on understanding the biology of the large shift in calcium metabolism in particular. Moreover, research has also focused on exploring the role of serotonin during the transition period and lactation and further unraveling its relationship with calcium. This review aimed to demonstrate the integration of calcium physiology during the peripartal period and throughout lactation. More specifically, we sought to discuss the knowledge gained in recent years on calcium metabolism, mammary calcium transport, serotonin metabolism, and the serotonin-calcium axis. Herein we also discuss the challenges and limitations of current research and where that leaves the present understanding of the serotonin-calcium axis as we seek to move forward and continue exploring this interesting relationship.

Feeding a Negative Dietary Cation-Anion Difference to Female Goats Is Feasible, as Indicated by the Non-Deleterious Effect on Rumen Fermentation and Rumen Microbial Population and Increased Plasma Calcium Level

Simple Summary

Diets with a lower dietary cation-anion difference could prevent hypocalcemia, enhance health, and extend the economic life of transition mammary animals. However, there is less information on rumen fermentation, cellulolytic bacteria populations, and microbiota for female goats fed a negative dietary cation-anion difference diet. We speculate that a negative dietary cation-anion difference would not affect the rumen fermentation parameters. Therefore, the present study was conducted to evaluate the effect of a negative dietary cation-anion difference diet on rumen pH, buffering capability, volatile fatty acids of acetic acid, propionic acid, butyric acid, total volatile fatty acid and acetic acid/propionic acid profiles, ruminal cellulolytic bacteria populations, and microbiota. These results provide a further evaluation on the feasibility of feeding a negative dietary cation-anion difference diet to goats.

Abstract

The dietary cation-anion difference (DCAD) has been receiving increased attention in recent years; however, information on rumen fermentation, cellulolytic bacteria populations, and microbiota of female goats fed a negative DCAD diet is less. This study aimed to evaluate the feasibility of feeding a negative DCAD diet for goats with emphasis on rumen fermentation parameters, cellulolytic bacteria populations, and microbiota. Eighteen female goats were randomly blocked to 3 treatments of 6 replicates with 1 goat per replicate. Animals were fed diets with varying DCAD levels at +338 (high DCAD; HD), +152 (control; CON), and −181 (low DCAD; LD). This study lasted 45 days with a 30-d adaption and 15-d trial period. The results showed that the different DCAD levels did not affect the rumen fermentation parameters including pH, buffering capability, acetic acid, propionic acid, butyric acid, sum of acetic acid, propionic acid, and butyric acid, or the ratio of acetic acid/propionic acid (p > 0.05). The 4 main ruminal cellulolytic bacteria populations containing Fibrobacter succinogenes, Ruminococcus flavefaciens, Butyrivibrio fibrisolvens, and Ruminococcus albus did not differ from DCAD treatments (p > 0.05). There was no difference in bacterial richness and diversity indicated by the indices Chao, Abundance Coverage-based Estimator (Ace), or Simpson and Shannon, respectively (p > 0.05), among 3 DCAD levels. Both principal coordinate analysis (PCoA) weighted UniFrac distance and unweighted UniFrac distance showed no difference in the composition of rumen microbiota for CON, HD, and LD (p > 0.05). At the phylum level, Bacteroidetes was the predominant phylum followed by Firmicutes, Synergistetes, Proteobacteria, Spirochaetae, and Tenericutes, and they showed no difference (p > 0.05) in relative abundances except for Firmicutes, which was higher in HD and LD compared to CON (p < 0.05). At the genus level, the relative abundances of 11 genera were not affected by DCAD treatments (p > 0.05). The level of DCAD had no effect (p > 0.05) on growth performance (p > 0.05). Urine pH in LD was lower than HD and CON (p < 0.05). Goats fed LD had higher plasma calcium over HD and CON (p < 0.05). In summary, we conclude that feeding a negative DCAD has no deleterious effects on rumen fermentation and rumen microbiota and can increase the blood calcium level, and is therefore feasible for female goats.

Low performance of vitamin C compared to ammonium chloride as an urinary acidifier in feedlot lambs

Abstract Obstructive urolithiasis is highly prevalent disease in feedlot sheep. Urinary acidification is effective for disease prevention. Forty-five healthy 3-4 month-old male Santa Inês crossbred feedlot lambs were distributed into three groups of 15 animals each. Ammonium chloride (GA) at 400 mg/kg/day/animal, vitamin C (GC) at 4 mg/kg/day/animal, and a combination of the two (GAC) were administered orally for 21 d. Blood and urine samples were taken 7 d before beginning treatment (M0), immediately before (M1), and weekly for 21 d (M2, M3, and M4) for renal function tests, levels of Ca, P, and Mg in serum and urine, urinalysis, and fractional excretion (FE) analysis in these minerals. In groups GA and GAC, pH decreased in M2 and remained acidic throughout the experiment. A significant decrease in serum P and a urinary increase in Ca and Mg occurred in GA. The FE of Ca increased during treatments, but there was no interference with Mg. The FE of P was significantly lower in GA. Ammonium chloride was an effective urinary acidifier in sheep, but vitamin C administered orally did not provide stable results. Thus, based on our results, vitamin C supplementation may not effective for urinary acidification to prevent obstructive urolithiasis.

Mineral supplements improve the calcium status of pregnant ewes grazing vegetative cereals

Grazing vegetative wheat, barley and oats (both dual-purpose and traditional spring varieties) is becoming an important strategic and tactical grazing option on farms where crops and livestock coexist. However, metabolic disorders have been reported and many producers avoid grazing these crops with reproducing ewes because of the risk. A recent survey of 18 farms grazing crops with pregnant ewes indicated a high proportion of grazed crops had forage calcium (Ca), sodium (Na) and magnesium (Mg) below published requirements and potassium (K) above the published maximum tolerable level. Many ewes grazing these crops had concentrations of Ca in plasma and urine indicative of a low or marginal Ca status. The aims of the present study were to further investigate the changes in mineral status that occur in ewes grazing vegetative crops during late pregnancy and to measure the effectiveness of mineral supplements for improving Ca and Mg status. On each of six farms, a paddock growing cereals in the vegetative stage was subdivided into three plots. Three groups of 30 pregnant ewes were selected and each group allocated to one plot. Forage was provided as wheat on four farms, barley on one farm and oats on one farm. Ewes were mature (3–7 years), in the last third of pregnancy (between 108 and 129 days after the start of mating) and were mostly twin-bearing. They grazed the crops for 21 days. One group of ewes was given no supplement (Control), a second was provided with an industry standard supplement (Standard) [Causmag (MgO):limestone (CaCO3):salt (NaCl), 40:40:20] at 30 g/day, whereas the third group was provided with a low dietary cation-anion difference (DCAD) supplement (New) (MgCl2.6H2O:CaSO4.2H2O:NaCl, 12.5:32.5:55.0) also at 30 g/day. Both Ca supplements improved Ca and, to a lesser extent, Mg status. The supplemented ewes showed significant increases in Ca concentration in urine, plasma and Ca fractional excretion on all but one of the six farms. There were no consistent differences between the two supplemented groups of ewes. It is concluded that the Ca status of ewes grazing vegetative cereal crops in late pregnancy can be improved by providing supplements containing Ca, Mg and Na. As the literature indicates the relationship between Ca status and susceptibility to hypocalcaemia is still inconclusive, additional research on a commercial scale is required to determine if supplements decrease the incidence of metabolic disorders when pregnant ewes graze cereal crops.

Mineral status of reproducing ewes grazing vegetative cereal crops

Grazing vegetative wheat, barley and oats (both dual-purpose and traditional spring varieties) is becoming an important strategic and tactical grazing option on farms where crops and livestock co-exist. The high winter growth rates of the crops offer an opportunity to fill the winter feed gap and the high nutritive value (metabolisable energy and crude protein) makes them well suited to meet the requirements of reproducing ewes. However, metabolic disorders have been reported and many producers avoid grazing these crops with reproducing ewes because of the risk. The present study aimed to establish the mineral status of both forage and of reproducing ewes grazing wheat, oats or barley. On each of 18 farms, a group of 50 pregnant ewes was monitored. The farms were located in Western Australia (6 farms) southern New South Wales (7 farms) and central New South Wales (5 farms). The average start of grazing was 118 days (range 97–133 days) after the start of mating. Crops grazed were wheat (8 farms), barley (4 farms) or oats (6 farms) and the average period of grazing was 20 days (range 14–24 days). Samples of blood and urine were collected pre- and post-grazing from 11 to 17 ewes and samples of crop and soils were also collected for mineral analysis. A high proportion of farms had forage calcium (Ca, 70%), sodium (Na, 70%) and magnesium (Mg, 18%) below published requirements and potassium (K, 70%) above the published maximum tolerable level. Strong negative correlations were found between soil Colwell K and forage Ca, Mg and Na. Analysis of samples collected from the ewes at the end of the grazing period indicated that ewes on 94% of farms had alkaline urine and on 88% of farms Ca concentrations in the urine were in the marginal range. None of the flock-average Ca concentrations in plasma was in the deficient range, but 59% of the flocks contained some individual ewes with plasma Ca in the deficient range. A small proportion of flock-average concentrations of Mg (6%) and Na (18%) in plasma were in the deficient range. In conclusion, the forages had a complex mineral composition meaning that grazing ewes may have an increased risk of direct or induced Ca (hypocalcaemia) or Mg (hypomagnesaemia) deficiency. The low Na and high K concentrations of these crops may also pose a direct risk to livestock production. Preliminary analysis indicated higher risks from grazing wheat and from grazing crops grown on high-K soils.

Acidogenic mineral additions increased Ca mobilization in prepartum sows

Increased sow milk production is associated with an increase in unexplained sow mortality during prepartum and early postpartum periods. This association has led to purported claims of hypocalcemic disorders. Assuming similar responses as dairy cows, feeding anionic mineral salts in late gestation and early lactation may reduce potential hypocalcemia related disorders in sows. Two experiments using CAD-MATE (Granco Minerals, Petersburg, VA), an acidogenic mineral supplement (AMS), were designed to determine the amount required to increase urinary Ca excretion and to identify renal compensatory responses to acid loads in sows. In Exp. 1, 30 multiparous gestating sows (Landrace × Large White) were fed 1 of 6 diets with either 0, 0.5, 1.0, 1.5, 2.0, or 2.5% AMS additions for 14 d. Diets provided a range (33 to -216 mEq/kg) of cation-anion balance, calculated as Na + K - Cl - S. Two 24-h urine samples were collected via bladder catheters for mineral analysis. One venous blood sample was drawn from 2 sows per diet on d 14. In Exp. 2, twelve sows were fed 1 of 3 diets to provide either 0, 1.5, or 2.5% AMS. Three 24-h composites of urine and fecal excreta were collected and analyses were used to calculate apparent mineral retention. Venous blood pH (range 7.41 to 7.33) and base excess (range 5.4 to 0.5 mmol/L) decreased (linear, < 0.10), but blood ionized Ca (range 1.28 to 1.37 mmol/L) increased (linear, < 0.05) proportionally to dietary AMS additions. Blood anion gap was not affected by diet. Urine pH decreased (linear, < 0.10) with additions of AMS (range 7.47 to 5.52). In Exp. 2, urinary SO (range 134 to 396 mEq/d) and NH (range 84 to 323 mEq/d) excretion increased ( < 0.05) with AMS additions. Urinary Mg, Na, and K excretion did not differ among treatments. Fecal excretion of Ca, Mg, and P increased ( < 0.05) in sows fed diets with 2.5% AMS. Fecal K, Na, and Cl excretion did not differ among treatments. Apparent Ca retention decreased ( < 0.05) with AMS additions, but apparent Mg and Cl retention increased ( < 0.05). In conclusion, AMS induced a renal compensated acid load as exhibited by urinary ion excretion patterns and maintenance of blood gas values within physiological ranges. Feeding diets with 1.5 or 2.5% AMS increased urinary and fecal Ca excretion and decreased apparent Ca retention implying an increase in mobilization of body Ca pools in prepartum sows.

Júnior N, Araújo V, Silva Filho A, Gomes D, Barbosa A, Farias C, Magalhães A, Lima M, Melo S, Oliveira D. Avaliação dos perfis minerais séricos, urinários e sedimentares de ovinos recebendo dieta calculogênica

RESUMO A urolitíase obstrutiva em pequenos ruminantes é uma doença metabólica de etiologia multifatorial com distribuição mundial. A elevação da concentração urinária de solutos, minerais ionizados (cristaloides) que formam cristais insolúveis é citada por alguns autores como o fator mais importante. Assim, o conhecimento do perfil mineral dos animais submetidos a dietas calculogênicas e a composição química dos urólitos tornam-se ferramentas eficazes na prevenção da doença. Neste estudo, foram utilizados 14 ovinos hígidos, machos (não castrados), da raça Santa Inês, com idade aproximada de 90 dias, distribuídos em dois grupos (G1 - sem vitamina C e G2 - com vitamina C) e alimentados com dieta calculogênica. A análise dos perfis minerais, séricos e urinários revelou completo desbalanceamento na relação entre concentrações de cálcio, fósforo e magnésio, havendo elevação expressiva do fósforo e do magnésio e diminuição substancial do cálcio. Com isso, a análise bioquímica dos urólitos demonstrou que o cálcio esteve presente em 50% das amostras analisadas.

Effect of feeding sweet-potato condensed distillers solubles on intake and urinary excretion of minerals in Japanese Black steers

Four Japanese Black steers (16 months of age) were assigned to a 4 × 4 Latin square design to investigate the effect of graded levels of sweet-potato condensed distillers solubles (SCDS) in their diets on intake and urinary excretion of minerals. The four diets consisted of 0%, 10%, 20% and 30% (dry matter (DM) basis) SCDS, with SCDS replacing commercial concentrate (CC). Intake of K, Cl, S, P and Mg increased linearly with increasing SCDS content. Urinary pH increased linearly with increasing dietary SCDS content. SCDS feeding increased urinary K concentrations (linear and quadratic effects). Urinary concentrations of Cl increased linearly with increasing SCDS content. In contrast, urinary concentrations of Mg decreased with increasing SCDS content. Feeding of SCDS did not apparently affect urinary NH₃ ,P, Na or Ca concentrations. These results suggest that high SCDS feeding is not a risk for crystallization of minerals leading to the formation of magnesium-phosphate type calculi: although SCDS contains large amounts of P and Mg, high SCDS feeding decreased the Mg concentration and did not affect the P concentration in urine. Additionally, high SCDS feeding had no apparent effects on plasma concentrations of Na, K, Cl, Ca or inorganic P.

New perspectives on the mineral nutrition of livestock grazing cereal and canola crops

The grazing of cereal and canola crops during winter is an increasing component of grazing systems in southern Australia. The capacity of such crops to meet the requirements of young livestock and reproducing animals for sodium (Na), magnesium (Mg), calcium (Ca) and potassium (K) is reviewed. The growth responses of young stock to Na and/or Mg supplements when grazing wheat are discussed. These responses differ from ‘literature expectation’ in that they are rapid in onset and involve no clinical signs. We demonstrate that more insight about the variability in supplement response, both between and between crops species, is obtained when mineral contents are viewed from the perspective of their frequency distributions, rather than their mean values. The pivotal importance of high K concentration, low Na and the resultant K : Na ratio of forage is stressed, as is the interaction of these minerals in relation to Mg absorption. We also present frequency distributions for a range of mineral indices that ‘capture’ mineral interactions, including the ‘tetany index’, forage K :  (Na+Mg) ratio and dietary cation–anion difference. It is concluded that the last two indices warrant a much closer investigation. Possible effects of forage aluminium and organic acid contents are briefly discussed; these also deserve closer examination. As research in this area continues, it would be prudent to provide Na and/or Mg supplements for livestock grazing wheat and possibly oats and barley, and calcium supplements for livestock grazing oats or for reproducing animals grazing all three cereals.

Estudo retrospectivo de 66 casos de urolitíase obstrutiva em ovinos

Objetivou-se realizar um estudo retrospectivo dos principais achados epidemiológicos, clínicos, patológicos e laboratoriais de ovinos acometidos por urolitíase obstrutiva, atendidos na Clínica de Bovinos, Campus Garanhuns/ UFRPE. Para isso, foram analisadas 66 fichas clínicas de ovinos, todos machos não castrados, com idade entre dois meses e cinco anos. A maioria dos casos (79,63%) ocorreu na época chuvosa. A maioria dos animais (87,88%) era criada intensivamente e todos eram alimentados com concentrados. Os sinais clínicos mais importantes foram as manifestações de dor, congestão de mucosas, hipertermia e aumento da tensão abdominal associados a obstrução do trato urinário. Metade dos animais apresentou obstrução total da uretra. Destes, 69,70% morreram, enquanto nos casos de obstrução parcial, 30,30% morreram. Nos exames laboratoriais verificou-se neutrofilia e desvio à esquerda regenerativo, hiperfibrinogenemia e azotemia. Na urinálise constatou-se hematúria em 89,29% dos casos e pH ácido em 46,43%. Na sedimentoscopia predominaram hemácias, leucócitos, células de descamação do epitélio uretral e cristais de urato amorfo. Os achados necroscópicos renais mais frequentes foram pielonefrite (61,54% dos casos) e hidronefrose (50%). Nos ureteres foram visualizados ureterite e hidroureter. Na bexiga foi mais evidente a cistite hemorrágica difusa (50%) e a presença de urólitos (57,69%). Na uretra observaram-se urólitos (61,54%) e uretrite hemorrágica difusa (57,69%). Quanto à composição dos urólitos predominaram os compostos por oxalato de cálcio hidratado. Conclui-se que no Agreste de Pernambuco a urolitiase é uma doença importante de ovinos, com alta letalidade, estando associada à alimentação rica em concentrados e sal mineral.

Use of dietary cation anion difference for control of urolithiasis risk factors in goats

OBJECTIVE

To determine correlations between dietary cation anion difference (DCAD) and urine pH, urine specific gravity, and blood pH in goats.

ANIMALS

24 crossbred goat wethers.

PROCEDURES

Goats were randomly assigned to 1 of 4 DCAD groups (-150, -75, 0, or +75 mEq/kg of feed) and fed pelleted feed and ground hay for 7 days. The diet was then supplemented with ammonium chloride to achieve the assigned DCAD of each group for 7 days. Urine was obtained for pH and specific gravity measurements at hours -3 to -1, 1 to 3, 5 to 7, 9 to 11, and 13 to 15 relative to the morning feeding. Blood pH was determined on alternate days of the study period.

RESULTS

Goats in the -150 and -75 mEq/kg groups had a urine pH of 6.0 to 6.5 two days after initiation of administration of ammonium chloride, and urine pH decreased to < 6.0 by day 7. Goats in the 0 mEq/kg group had a urine pH from 6.0 to 6.5 on day 5, whereas urine pH in goats in the +75 mEq/kg group remained > 6.5 throughout the trial. Urine specific gravity differed only between the -150 mEq/kg and the -75 mEq/kg groups. Blood pH in the -150 mEq/kg group was significantly lower than that in the other groups.

CONCLUSIONS AND CLINICAL RELEVANCE

Goats in the 0 mEq/kg DCAD group had a urine pH of 6.0 to 6.5 five days after intitiation of feeding the diet, and that pH was maintained through day 7, without significant reduction in blood pH. This may serve as a target for diet formulation for the prevention of urolithiasis.

Influência da diferença cátion-aniônica da dieta sobre o balanço de cálcio, fósforo e magnésio em ovinos

O efeito do balanço cátion-aniônico da dieta (BCAD) no balanço macromineral (cálcio, fósforo e magnésio), no pH urinário e fecal, na concentração sérica de cálcio, fósforo e magnésio foi estudado utilizando-se 16 carneiros machos, da raça Santa Inês, por um período de 26 dias, sendo sete de adaptação. O delineamento experimental foi em blocos ao acaso, com quatro tratamentos. Para a manipulação do BCAD foram adicionados cloreto de cálcio e bicarbonato de sódio, obtendo-se os seguintes tratamentos: -12; +30; +76 e +133mEq/kg MS da ração. Não foram encontradas diferenças (P>0,10) no pH fecal, pH urinário, balanço de fósforo e magnésio. Com o aumento do BCAD houve decréscimo da absorção e retenção de cálcio, e aumento da excreção fecal. A manipulação do BCAD interferiu no metabolismo de macrominerais, principalmente no de cálcio.

Influência da dieta aniônica no balanço macromineral em novilhos holandeses

O efeito do balanço cátion-aniônico da dieta (BCAD) no balanço macromineral (Ca e P), no pH urinário e fecal, na concentração sérica de cálcio ionizado e total e na ingestão de matéria seca foi estudado utilizando-se quatro novilhos holandeses machos. Inicialmente os animais foram alimentados com dieta basal com BCAD de +74,12mEq/kg de MS e, posteriormente, com dieta suplementada com sulfato de amônio, de maneira a diminuir o BCAD para -154,84mEq/kg de MS. Não foram encontradas diferenças (P>0,05) no pH fecal, no balanço de fósforo e na concentração de cálcio ionizado em função do tempo. A urina acidificou-se com a diminuição do BCAD (P<0,01). Para o balanço de cálcio não foram encontradas diferenças entre tratamentos (P>0,05), entretanto, o cálcio excretado na urina foi maior (P<0,05), com a dieta aniônica. A concentração de cálcio total no soro aumentou significativamente (P<0,05) a partir do 19º dia. Dieta aniônica com uso de sulfato de amônio, em veículo palatável, oferecida na forma de ração total, não interferiu na ingestão de matéria seca. O pH urinário é excelente indicativo da eficiência da dieta aniônica e foram necessários 19 dias de consumo de uma dieta aniônica de -154,84 mEq/kg de MS para aumentar os níveis séricos de cálcio total em bovinos em crescimento.

The sheep as a model for osteoporosis in humans

There is great interest in large animal models for studying different aspects of osteoporosis. Several laboratories around the world have used ovariectomized sheep as a model because of their ease of housing and handling, low expense compared to other large animals, availability and acceptance in society as a research animal. They have been used to study the response to new therapies for post-menopausal osteoporosis, low-magnitude mechanical stimulation, orthopedic implants in osteoporotic bone and bioactive ceramics to strengthen vertebral bodies. To produce severely osteopenic bone comparable to that seen in humans, a combination of estrogen deficiency following ovariectomy plus a calcium-wasting diet is currently being investigated.

Milk fever control principles: a review

Three main preventive principles against milk fever were evaluated in this literature review, and the efficacy of each principle was estimated from the results of controlled investigations. Oral calcium drenching around calving apparently has a mean efficacy of 50%-60% in terms of milk fever prevention as well as prevention of milk fever relapse after intravenous treatment with calcium solutions. However, some drenches have been shown to cause lesions in the forestomacs. When using the DCAD (dietary cation-anion difference) principle, feeding rations with a negative DCAD (measured as (Na + K)-(Cl + S)) significantly reduce the milk fever incidence. Calculating the relative risk (RR) of developing milk fever from controlled experiments results in a mean RR between 0.19 and 0.35 when rations with a negative versus positive DCAD are compared. The main drawback from the DCAD principle is a palatability problem. The principle of feeding rations low in calcium is highly efficient in milk fever prevention provided the calcium intake in the dry period is kept below 20 g per day. Calculating the relative risk (RR) of developing milk fever from controlled experiments results in a very low mean RR (between 0 and 0.20) (daily calcium intake below versus above 20 g/d). The main problem in implementing the low-Ca principle is difficulties in formulating rations sufficiently low in calcium when using commonly available feeds. The use of large doses of vitamin D metabolites and analogues for milk fever prevention is controversial. Due to toxicity problems and an almost total lack of recent studies on the subject this principle is not described in detail. A few management related issues were discussed briefly, and the following conclusions were made: It is important to supply the periparturient cow with sufficient magnesium to fulfil its needs, and to prevent the dry cows from being too fat. Available information on the influence of carbohydrate intake, and on the effect of the length of the dry period and prepartum milking, is at present insufficient to include these factors in control programmes.

Hypocalcemia induced by intravenous administration of disodium ethylenediaminotetraacetate and its effects on excretion of calcium in urine of cows fed a high chloride diet

Evidence supports the theory that a diet that is rich in nonmetabolizable anions fed to dairy cows during the dry period reduces the risk of hypocalcemic paresis puerperalis. When cows are fed a diet that is rich in anions instead of cations, more Ca is absorbed in the intestine and excreted in urine. We hypothesized that, in cows fed a diet that was rich in anions, the increased flow of Ca through the body could be drained to support the maintenance of plasma Ca concentration around parturition. The hypothesis was tested by binding plasma Ca through intravenous administration of Na2-EDTA and measuring excretion of Ca in urine. In a 2-period x 14-d crossover study, six, nonpregnant, nonlactating, multiparous cows were fed either a diet that was rich in cations (dietary cation-anion difference = +332 meq/kg of dry matter) or rich in anions (dietary cation-anion difference = -230 meq/kg of dry matter). On the last day of each feeding period, Na2-EDTA was infused intravenously until the amount of plasma Ca that was not bound to EDTA reached approximately 1 mmol/L. The amount of EDTA that could be infused was significantly greater when the cows were fed the diet that was rich in anions. During the infusion of Na2-EDTA the rate of Ca excretion in urine dropped to almost 0 when the diet that was rich in anions was fed. After feeding the diet that was rich in cations, excretion of Ca in urine was negligible and was not reduced further by Na2-EDTA infusion. Thus, in cows fed a diet that was rich in anions, the Ca intended for excretion with urine can be used when plasma Ca is under stress as would occur at the onset of lactation. However, the amount of Ca derived from plasma, interstitial fluid, and the skeleton during Na2-EDTA infusion was quantitatively much more important to the supply of Ca than was the reduction in excretion of Ca in urine. Most likely, this relationship would also be true when the production of colostrum begins.

Effects of dietary cation-anion difference on the acid-base status of dry cows

Responses in dry matter intake (DMI) and acidbase balance to three sources of anionic salts (dietary cation-anion difference = -63 to -40 meq/kg of dry matter), an acidified fermentation by-product, MgSO4.7H2O + NH4Cl, and MgSO4.7H2O + CaCl2.2H2O + CaSO4, were evaluated relative to the responses of cows fed a control diet (dietary cationanion difference = 203 meq/kg of dry matter) that did not contain anionic salts. Diets were fed for 1-wk periods to eight nonlactating Holsteins assigned to two replicated 4 x 4 Latin squares. Daily DMI increased as time of access to the diet increased up to d 5; mean DMI over d 5 to 7 was reduced by dietary anionic salts. Diets containing anionic salts induced a mild metabolic acidosis that was completely compensated by nonrespiratory mechanisms (decreased blood bicarbonate and base excess; pCO2 and pH values were unaffected). Urinary pH values and bicarbonate excretion were reduced, and urinary NH4+ and titratable acidity excretion were increased, for cows fed diets containing anionic salts. Strong ion difference in urine was decreased by dietary anionic salts because of the relatively greater excretions of Cl- and S2- versus Na+ and K+ by cows fed these diets. Dietary anionic salts decreased mean ruminal pH by 0.12 units, possibly because of the reduced strong ion difference of ruminal fluid. Dietary anionic salts increased mean ruminal NH3 concentration by 2.2 mM, probably because of the higher nonprotein N content of these diets. The strong negative relationship (r2 = 0.95) between urinary pH and net acid excretion by cows fed the diets containing anionic salts suggested that urinary pH measurement might be a useful tool to assess the degree of metabolic acidosis that was imposed by dietary anionic salts.

Dietary cation-anion difference, acid-base status, mineral metabolism, renal function, and milk production of lactating cows

Three switchback experiments were conducted with 12 cows in early lactation, 12 cows in midlactation, and 12 cows in late lactation. Each experiment compared two dietary cation-anion differences. Increasing dietary cation-anion difference increased DMI and milk production in early and midlactation. These effects were not observed in late lactation. Production of milk protein and lactose and concentration of lactose were increased by the higher dietary cation-anion difference in early lactation. Higher dietary cation-anion difference reduced milk fat concentration in midlactation because of the higher milk production. In late lactation, none of the milk components were affected by dietary cation-anion difference. In early and midlactation, apparent absorption of water and urine volume were increased by a higher dietary cation-anion difference; these effects were not caused by higher intake of Na or by higher glomerular filtration rate. Intake, balance, and concentration of S in plasma were increased by the lower cation-anion difference at all stages of lactation. Excretion of HCO3- in urine was reduced by a lower dietary cation-anion difference at all stages of lactation, but secretion of protons in milk was reduced in late lactation only. Increasing dietary cation-anion difference does affect acid-base parameters in urine at all stages of lactation, but DMI and milk production of cows were affected in early and midlactation only.

Acid-base status, renal function, water, and macromineral metabolism of dry cows fed diets differing in cation-anion difference

Dietary cation-anion difference was defined as the summation of the milliequivalents of Na and K minus the sum of the milliequivalents of Cl and S per kilogram of DM. Twelve Holstein cows were used in a crossover experiment to compare the effects of changing the cation-anion difference of a diet based on haylage. Two cation-anion differences, 481.8 and 327.2 meq/kg, were compared. Increased dietary cation-anion difference had no significant effects on BW or intake and digestibility of DM, ADF, NDF, and N. The diet with a cation-anion difference of 481 meq/kg of DM increased apparent absorption of water and urine volume. Fecal excretion of Na and absorption and urinary excretion of S were increased by a cation-anion difference of 327 meq/kg of DM. Although blood concentrations were unaffected, lower dietary cation-anion difference reduced concentrations of H+ and HCO3- in urine and total urinary excretion of HCO3-. Plasma volume, packed cell volume, glomerular filtration rate, and effective renal plasma flow were unaffected by diet. Small changes in dietary cation-anion differences, even within the positive range, affected acid-base status and water metabolism of dry pregnant cows without affecting renal function or blood volume.

Manipulation of dietary cation-anion difference on nutritionally related production diseases, productivity, and metabolic responses of dairy cows

Dietary cation-anion difference has been defined as milliequivalents of (Na+K)-(Cl+S) per kilogram of DM and has a direct impact on blood acid-base metabolism. As this difference decreases, one or more of the following blood parameters change: increased H+, decreased HCO3-, and decreased pH. These changes are accompanied by reduced urinary HCO3- excretion and pH as compensatory mechanisms. Although other minerals have an impact on acid-base metabolism, the four minerals used in dietary cation-anion difference have the greatest effect. Manipulation of acid-base balance can be used to manipulate other biological functions to benefit health and productivity of cows. Low cation-anion difference prepartum can mitigate hypocalcemia peripartum via increased urinary Ca, blood-ionized Ca, and responsiveness to Ca homeostatic hormones. These changes reduced the incidence of paresis and increased productivity by reducing the severity and length of hypocalcemia in all cows (periparturient), regardless of the occurrence of paresis. Reduced cation-anion differences prepartum have been related to a reduced severity of udder edema, likely related to increased renal loss of water and unchanged water intake. However, the effects on acid-base balance cannot be ruled out because of effects on biochemical and transport processes. Elevated cation-anion difference in lactation has been shown to increase DMI and production and to mitigate the effects of heat stress. Because production and heat stress are acidogenic, elevated cation-anion difference improves blood-buffering capacity to cope with H+. In heat stress, elevated water intake with elevated cation-anion difference cannot be ignored. Other diseases related to metabolic acid, such as laminitis and ketoacidosis, may be influenced by elevated cation-anion difference in lactation; however, research in these areas has not been forthcoming.

Effects of various dietary cation-anion balances on response to experimentally induced hypocalcemia in sheep

We examined the effect of dietary cation-anion balance on bone Ca mobilization, measured by challenging wethers with a 5.6% EDTA infusion at a rate of 1.4 ml kg of BW-1. Dietary cation-anion balance was calculated as milliequivalents [(Na + K) - (Cl + S)]. Six crossbred wethers (average BW, 67.8 kg) were fed rations with high Ca (.74% dry basis) or normal Ca (.45%) and three different dietary cation-anion treatments, which differed in their mineral supplementation. Dietary cation-anion balances were 354, 125, and 32 meq kg of DM-1 for control and two treatments. A 6 x 4 incomplete Latin square design (six treatments, four periods) was used with five 15-d periods of 14 d of adaptation followed by 1 d of EDTA infusion. Concentrations of total and EDTA titratable plasma Ca were not affected by the level of dietary Ca or treatments. The decrease in plasma EDTA titratable Ca at conclusion of EDTA infusion (120 min) was least in wethers fed the lowest cation-anion balance within high Ca, and recovery of plasma EDTA titratable Ca during the 240-min postinfusion period was faster for sheep fed this diet than for the control. The amount of Ca mobilized and its rate of mobilization during the EDTA infusion period tended to be higher for diets with reduced cation-anion balances than for the control. Thus, reducing cation-anion balance increased the sheep's ability to mobilize Ca during hypocalcemia.

Effects of reducing dietary cation-anion balance on calcium kinetics in sheep

A Ca kinetic study with a four-compartment model being fitted to radioisotope and balance data using the CONSAM (conversational, simulation, analysis, and modeling) computer program was conducted to examine the effects of dietary cation-anion balance, calculated as milliequivalents [(Na + K] - (Cl + S)]. Twelve crossbred wethers were used as eucalcemic control (period 1); then Ca loss during lactation was simulated by continuous infusion of ethylene glycol tetraacetate (period 2). Dietary cation-anion balance was manipulated by supplementation of various mineral salts and was +339, +35, and -127 meq of kg DM-1 during period 1 and +429, +68, and -147 meq of kg DM-1 during period 2 for control and two treatments, respectively. Animals responded to the simulated lactational Ca loss (period 2) by increasing true intestinal absorption of Ca and bone resorption and by reducing Ca accretion by bone. No difference was observed in concentration of total Ca in plasma, but treatments produced increased concentration of plasma ionized Ca during both periods. Both treatments produced hypercalciuria during both periods, and the lowest cation-anion balance increased true intestinal absorption of Ca and reduced bone accretion during period 2. The size of total exchangeable Ca pool did not differ between treatments or periods, but amount of Ca movement between the pools increased with the intermediate cation-anion balance during period 1 and with both treatments during period 2 compared with control. These results indicated that feeding reduced cation-anion balance diets increased Ca flux through the exchangeable Ca pool with no changes in the size of the pool, particularly when Ca demand was increased.