Effect of high magnesium intake on apparent magnesium absorption in lactating cows

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1 Animal Feed Science and Technology 113 (2004) Effect of high magnesium intake on apparent magnesium absorption in lactating cows Surasak Jittakhot, J. Thomas Schonewille, Hugo Wouterse, Erick J. Focker, Chalermpon Yuangklang, Anton C. Beynen Department of Nutrition, Faculty of Veterinary Medicine, Utrecht University, P.O. Box , 3508 TD Utrecht, The Netherlands Received 28 May 2003; received in revised form 24 September 2003; accepted 11 November 2003 Abstract We investigated whether the percentage of apparent magnesium (Mg) absorption in dry cows with a low level of dry matter intake is comparable to that in lactating cows with high feed intake, but fed the same diet in terms of composition. Lactating cows were fed rations with an ingredient and nutrient composition which was identical to the rations that were used in a previous study in dry cows. The trial had a day cross-over design and was preceded by a 10-day run-in period. The six non-pregnant, lactating, multiparous cows (Friesian Holstein Holstein Friesian cross) were fed rations with low and high Mg content, the levels being 3.7 and 6.3 g Mg/kg dry matter at a constant dietary potassium (K) concentration of 30.7 g K/kg dry matter. Increasing the level of Mg intake from 68.1 to g Mg per day resulted in absolute Mg absorptions of 9.0 and 18.5 g Mg per day (P = 0.005). Mg absorption, expressed as a fraction of intake, for the low and high-mg rations was and (P = 0.183) these values being similar to those observed earlier in dry cows. Milk production was not significantly influenced by the level of Mg intake (P = 0.075). The combined results of this experiment and that of an earlier one with dry cows indicate that absolute apparent Mg absorption (g per day) depends on dietary Mg intake rather than on dry matter intake and physiological status. Thus, lactating and dry cows are equally efficient in Mg absorption, justifying the use of dry cows as a model for lactating cows Elsevier B.V. All rights reserved. Keywords: Magnesium; Absorption; Lactating cows Abbreviations: S.E., standard error This study was supported by the Product Board Animal Feed (Productschap Diervoeder), The Hague, The Netherlands. Corresponding author. Tel.: ; fax: address: j.schonewille@vet.uu.nl (J.T. Schonewille) /$ see front matter 2003 Elsevier B.V. All rights reserved. doi: /j.anifeedsci

2 54 S. Jittakhot et al. / Animal Feed Science and Technology 113 (2004) Introduction Grass and grass silage are generally rich in potassium (K) in areas with intensive livestock production (Fisher et al., 1994; Schonewille et al., 1997). High K intake inhibits magnesium (Mg) absorption in cows (Schonewille et al., 1999), which enhances the risk of hypomagnesaemia (Kemp, 1960). To prevent hypomagnesaemic tetany in dairy cows, it is common practice to supplement commercial concentrates with MgO. Dietary Mg concentrations up to 3.5 g/kg dry matter are considered normal for lactating dairy cows in The Netherlands (Schonewille, 1999). The dietary Mg requirements can be calculated when both Mg requirements and the coefficient of absorption are known. It is has been shown under controlled feeding conditions, that both Mg and K intake (Schonewille et al., 1999; Schonewille and Beynen, 2002) influence the coefficient of absorption in dry, non-pregnant cows. However, it is not known whether observations in dry cows with a low level of dry matter intake extend to lactating cows with high feed intakes. Therefore, lactating cows were fed rations with an ingredient and nutrient composition which was identical to the rations that were used by Jittakhot et al. (2003) in their study with dry cows. If the lactating cows would show efficiencies of Mg absorption similar to those seen in dry cows, then dry cows may be considered a suitable model for lactating cows in studies on Mg absorption. The use of non-pregnant, dry cows provides a model in steady state which has various practical advantages, including the continuous availability of cows and the possibility of subjecting the cows to trails with a complex Latin-square design. 2. Material and methods 2.1. Cows and experimental design Six non-pregnant, lactating, multiparous cows (age 4.4 year, S.E. 0.3) with a mean body weight of 599 kg (S.E. 4.2) were used. The cows were 140 (S.E. 11.1) days in milk and were of a Friesian Holstein Holstein Friesian cross. During the experiment the cows were housed in a stanchion barn. The trial had a day cross-over design and was preceded by a 10-day run-in period. The animals were randomly assigned to the order of the two treatments; i.e. a ration with 3.7 g Mg/kg dry matter (low Mg) and a ration with 6.3 g Mg/kg dry matter (high Mg) Rations During the run-in period, the cows were gradually changed from their current ration to the experimental rations so as to allow the cows to become adapted to the experimental rations. During the experimental period the cows were offered a restricted amount of artificially dried grass, hay and pelleted concentrates (diameter 5 mm). The experimental concentrates were formulated by the addition of appropriate amounts of MgO and KHCO 3 to the basal concentrate (Table 1). The ingredient and analyzed composition of the whole rations is

3 S. Jittakhot et al. / Animal Feed Science and Technology 113 (2004) Table 1 Compositions of the experimental concentrates in grams Treatments Low Mg High Mg Constant components a KHCO MgO Total a The constant components consisted of: 300 g of sugarbeet pulp, 230 g of soybean meal, 150 g of rapeseed meal, 85.8 g of cassava meal, 80 g of maizegluten feed, 50 g of corn meal, 45 g of sugarbeet molasses, 5 g of soya oil, 2 g of NaCl, 5 g of limestone, 2 g of mono-calcium phosphate and 2 g of premix. The premix consisted of (per g): 67.5 mg of ZnSO 4 H 2 O, 57.5 mg of MnSO 4 H 2 O, 15.0 mg of CuSO 4 5H 2 O, 0.6 mg of KIO 3, 0.4 mg of CoSO 4 7H 2 O, 0.3 mg of Na 2 SeO 3 5H 2 O, 1.0 mg of vitamin A preparation (500 IU), 5.0 mg of vitamin D preparation (505 IU), 25.0 mg of vitamin E preparation (12.5 IU) and mg of CaCO 3. shown in Table 2. The ration provided energy (Van Es, 1978) sufficient for maintenance and a milk production of approximately 24 kg fat-corrected milk per day (CVB, 2002). The rations were given daily in two equal portions at 0800 and 1700 h. Orts, if any, were recorded. Table 2 Ingredient and analyzed composition of the experimental rations fed to the lactating cows Treatments Low Mg High Mg Ingredient composition (kg dry matter) Artificially dried grass a Hay b Concentrate c Total dry matter Analyzed composition of the whole ration (g/kg dry matter) Crude protein Crude fat Crude fiber Mg K Ca P Na a The analyzed composition of artificially dried grass; 937 g of dry matter/kg; Mg, 1.66; K, 25.76; Ca, 3.42; P, 2.98 and Na, 0.40 g/kg of dry matter. b The analyzed composition of hay; 944 g of dry matter/kg; Mg, 1.28; K, 19.10; Ca, 3.24; P, 1.92 and Na, 1.71 g/kg of dry matter. c The analyzed compositions of each concentrate as follow, low Mg: 910 g of dry matter/kg; Mg, 5.17; K, 34.79; Ca, 9.73; P, 5.94 and Na, 2.16 g/kg of dry matter. High Mg: 906 g of dry matter/kg; Mg, 9.67; K, 35.00; Ca, 10.06; P, 5.91 and Na, 2.20 g/kg of dry matter.

4 56 S. Jittakhot et al. / Animal Feed Science and Technology 113 (2004) Collection of samples and chemical analysis During the last 6 days of each experimental period, experimental feedstuffs were sampled daily. Thereafter, samples were pooled, ground and stored in sealed jars at room temperature (18 C). Blood samples were taken on the last day of each experimental period. Between 1100 and 1200 h, blood was sampled from the jugular vein into evacuated heparinized tubes. The blood samples were centrifuged for 15 min at 2700 g and the plasma was collected and stored at 18 C in plastic tubes. From days 10 to 16 of each experimental period feces was collected from each cow. Because feces collection had to be done manually, it was decided to focus on the quantitative and separate collection of feces. Consequently, urine could not be collected. The total feces production of each cow was mixed thoroughly, and 3% of the wet weight was stored in a plastic bucket at 18 C. At the end of each collection period, the feces fractions of each cow were combined, mixed thoroughly and sampled. The feces samples were dried at 60 C for 5 days, ground, and stored in sealed jars at room temperature (18 C) until analysis. From days 10 to 16 of each experimental period milk yield was recorded and 10 ml samples were taken after of each milking and stored in plastic tubes at 18 C. Milk samples were pooled for each cow prior to analysis. Chemical analyses were described previously by Schonewille et al. (1999) Statistical analyses Data were evaluated with Student s paired t-test. The level of statistical significance was pre-set at P< Results 3.1. Feed intake and milk production The cows consumed almost all of the feed offered, but negligible amounts of orts were observed; a fraction less than of total dry matter supplied. Milk production was not significantly influenced by the level of Mg intake (P = 0.075); mean milk productions were 21.7 kg (S.E. 0.99) and 22.5 kg (S.E. 1.10) for the low and high-mg ration, respectively (n = 6). Consequently, Mg excretion with milk was not affected by the level of Mg intake. For the two treatments combined, mean Mg excretion with milk was 2.4 g per day (S.E. 0.01, n = 2) Mg absorption and plasma Mg The 1.7-fold increase in Mg intake was associated with a similar increase in the fecal excretion of Mg (Table 3). Apparent Mg absorption was increased two-fold when the high Mg ration was fed (Table 3). Plasma concentrations of Mg were not significantly (P = 0.137) influenced by the level of Mg intake. For the two treatments combined, mean plasma Mg concentration was 0.94 mmol/l (S.E , n = 2).

5 S. Jittakhot et al. / Animal Feed Science and Technology 113 (2004) Table 3 Intake, fecal excretion and absorption of Mg in lactating cows fed the experimental rations Treatment P-value Low Mg High Mg Mean S.E. Mean S.E. Intake, g per day 68.1 ND ND ND Feces, g per day <0.001 Apparent absorption g per day Coefficient ND: not determined because the cows fed a restricted amount of feed. Table 4 Comparison between dry- and lactating cows for selected variables Dry cows a Lactating cows Low Mg High Mg Low Mg High Mg Dietary Mg content (g/kg dry matter) Dry matter intake (kg per day) Mg intake (g per day) Absorption coefficient (fraction of intake) a Data for the dry cows are derived from Jittakhot et al. (2003). Despite the two-fold increase in absolute Mg absorption, Mg absorption expressed as a fraction of intake was not significantly increased (P = 0.183) when the high-mg ration was fed to the lactating cows (Table 4). 4. Discussion In Table 4, the present data for the lactating cows are compared with those observed in dry cows fed the same rations, but at a lower dry matter intake (Jittakhot et al., 2003). It is clear that for the two rations the coefficient of Mg absorption is similar for dry and lactating cows. This outcome corroborates our preliminary observation (Schonewille and Beynen, 2002) that the efficiency of Mg absorption is independent of the plane of nutrition. Thus, it seems that the absolute amount of Mg absorbed is determined by Mg intake rather than DM intake and or milk yield. Indeed, when a linear regression was performed with Mg absorption (g per day) as dependent variable and Mg intake (g per day) as an independent variable, it appeared that Mg intake and absorption were highly correlated, irrespective of the amount of dry matter ingested (Fig. 1). This result indicates that dry cows can serve as a suitable model for lactating cows when studying Mg absorption. Mg is absorbed essentially in the rumen (Rogers and Van t Klooster, 1969, Tomas and Potter, 1976b; Pfeffer and Rahman, 1974; Greene et al., 1983; Khorasani et al., 1997). The process of Mg uptake by rumen epithelium cells consists of a K-sensitive, electrogenic,

6 58 S. Jittakhot et al. / Animal Feed Science and Technology 113 (2004) Apparent Mg absorption (g/day) Mg intake (g/day) Fig. 1. Apparent Mg absorption in individual cows fed different amounts of Mg. The linear correlation coefficient and regression formula are; r = 0.99, y = x (n = 4, P = 0.008). Symbols: ( ), dry cows; ( ), lactating cows. and a K-insensitive, carrier-mediated transport component (Leonhard et al., 1989). In vitro studies with isolated sheep rumen epithelium (Leonhard-Marek and Martens, 1996) have indicated that the inhibitory action of K on Mg absorption can be explained by the depolarizing action of K on the apical membrane potential of rumen epithelial cells. In this study, the dietary K concentration was similar for all cows and would not have interfered with Mg absorption. The K-insensitive, carrier-mediated transport component at the apical membrane is based on exchanging a Mg ion for two hydrogen ions (Scharrer and Lutz, 1990; Martens et al., 1991, Leonhard-Marek, 1999) while Mg transport across the basolateral membrane might be based on a carrier-mediated process (Schonewille, 1999) exchanging a Mg ion for two Na ions (Schweigel et al., 2000). Thus, at constant K intakes, the amount of Mg absorbed across the rumen epithelium is determined by the ruminal Mg concentration, at least until the carrier-mediated process becomes saturated (Martens, 1983). Both the dry and lactating cows showed a two-fold increase in absolute Mg absorption when the dietary Mg concentration was increased from 3.8 to 6.4 g/kg dry matter. Probably, ruminal Mg concentrations were increased to the same extent in dry and lactating cows. Linear regression of Mg intake on Mg absorption (Fig. 1) produced a non-significant intercept (P = 0.404) of 1.13 g apparently absorbed Mg per day. Thus, this value would represent fecal Mg excretion at zero Mg intake. This value is somewhat lower than that estimated by the ARC (1980) who indicated an endogenous fecal Mg loss of 1.8 g for a 600 kg cow. However, the present estimate of the endogenous fecal Mg loss is not reliable because the lowest Mg intakes in the data set used were 27.1 g per day which is too high for accurate estimation of the intercept. Indeed, it was stated by the ARC (1980) that estimates

7 S. Jittakhot et al. / Animal Feed Science and Technology 113 (2004) of endogenous Mg losses obtained by regression of fecal output of Mg on Mg intake are subject to bias. 5. Conclusions In the lactating cows apparent Mg absorption (g per day) was dependent on dietary Mg intake. When combining the present data with those of another trial with dry cows (Jittakhot et al., 2003), it followed that the absolute amount of Mg absorbed is determined by Mg intake rather than dry matter intake and or milk yield. Thus, the efficiency of Mg absorption is independent of the plane of nutrition and physiological status. This outcome indicates that dry cows can serve as a suitable model for studying Mg metabolism in lactating cows. Acknowledgements The authors are grateful to the Product Board Animal feed (Productschap Diervoeder), The Hague, The Netherlands for financial support. Jan Van Der Kuilen is appreciated for his laboratory assistance. Hans Lutz is thanked for taking care of the cows. References ARC, The Nutrient Requirements of Ruminant Livestock. Agriculture Research council (ARC), 351 pp. Centraal Veevoeder Bureau (CVB), Voedernormen landbouwhisdieren en voederwaarde veevoeders. CVB, Lelystad, Nederland. Fisher, L.J., Dinn, N., Trait, R.M., Shelford, J.A., Effect of level of dietary potassium on the absorption and excretion of calcium and magnesium by lactating cows. Can. J. Anim. Sci. 74, Greene, L.W., Fontenot, J.P., Webb Jr, K.E., Site of magnesium and other macromineral absorption in steers fed high levels of potassium. J. Anim. Sci. 57, Jittakhot, S., Schonewille, J.Th., Wouterse, H., Uijttewaal, A.W.J., Yuangklang, C., Beynen, A.C., Increasing magnesium intakes in relation to magnesium absorption in dry cows. J. Dairy Res., in press. Kemp, A., Hypomageaesemia in milking cows: The response of serum magnesium to alterations in herbage composition resulting from potash and nitrogen dressings on pasture. Neth. J. Agric. Sci. 8, Khorasani, G.R., Janzen, R.A., McGill, W.B., Kennelly, J.J., Site and extent of mineral absorption in lactating cows fed whole-crop cereal grain silage of alfalfa silage. J. Anim. Sci. 75, Leonhard, S., Martens, H., Gabel, G., New aspects of magnesium transport in ruminants. Acta. Vet. Scand. Suppl. 86, Leonhard-Marek, S., Martens, H., Effects of potassium on magnesium transport across rumen epithelium. Am. J. Physiol. 271, G1034 G1038. Martens, H., Saturation kinetics of magnesium efflux across the rumen wall in heifers. Br. J. Nutr. 49, Pfeffer, E., Rahman, K.A., Untersuchungen zur lokalisierung der magnesium absorption beim wiederkauer. J. Anim. Physiol. Anim. Nutr. 33, Rogers, P.A.M., Van t Klooster, A.T., The fate of Na, K, Ca, Mg and P in the digesta, vol. 69. Mededelingen Landbouwhogeschool, Wageningen, pp Scharrer, E., Lutz, T., Effects of short chain fatty acids and K on absorption of Mg and other cations by the colon and caecum. Z. Ernahrungswiss. 29, Schonewille, J.T., Magnesium Absorption in Ruminants. Ph.D. Thesis, Utrecht University, Utrecht.

8 60 S. Jittakhot et al. / Animal Feed Science and Technology 113 (2004) Schonewille, J.T., Beynen, A.C., Iso-energetic replacement of artificially dried grass by concentrate increases magnesium absorption in cows (a short communication). Folia. Vet. 46, Schonewille, J.T., Ram, L., Van t Klooster, A.T., Wouterse, H., Beynen, A.C., Intrinsic potassium in grass silage and magnesium absorption in dry cows. Livest. Prod. Sci. 48, Schonewille, J.T., Van t Klooster, A.T., Wouterse, H., Beynen, A.C., Effects of intrinsic potassium in artificially dried grass and supplemental potassium bicarbonate on apparent magnesium absorption in dry cows. J. Dairy Sci. 82, Schweigel, M., Vormann, J., Martens, H., Mechanisms of Mg(2+) transport in cultured ruminal epithelial cells. Am. J. Physiol. Gastrointest. Liver Physiol. 278, G400 G408. Tomas, F.M., Potter, B.J., 1976b. The site of magnesium absorption from the ruminant stomach. Br. J. Nutr. 36, Van Es, A.J.H., Feed evaluation for ruminants. Part I. The system in use from May 1977 onwards in The Netherlands. Livest. Prod. Sci. 5,