Animal Feed Science and Technology 113 (2004) 53–60
Effect of high magnesium intake on apparent magnesium absorption in lactating cows夽 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 80.152, 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 16 × 16-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 116.3 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 0.131 and 0.159 (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. © 2003 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.: +31-30-2531581; fax: +31-30-2531817. E-mail address:
[email protected] (J.T. Schonewille). 夽
0377-8401/$ – see front matter © 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.anifeedsci.2003.11.006
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1. 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 16 × 16-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). 2.2. 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 KHCO3 to the basal concentrate (Table 1). The ingredient and analyzed composition of the whole rations is
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Table 1 Compositions of the experimental concentrates in grams Treatments
Constant componentsa KHCO3 MgO Total
Low Mg
High Mg
956.8 40.0 3.2
956.8 40.0 10.8
1000.0
1007.6
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 ZnSO4 ·H2 O, 57.5 mg of MnSO4 ·H2 O, 15.0 mg of CuSO4 ·5H2 O, 0.6 mg of KIO3 , 0.4 mg of CoSO4 ·7H2 O, 0.3 mg of Na2 SeO3 ·5H2 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 827.7 mg of CaCO3 .
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 Ingredient composition (kg dry matter) Artificially dried grassa Hayb Concentratec Total dry matter
High Mg
7.3 0.7 10.7
7.3 0.7 10.7
18.6
18.6
Analyzed composition of the whole ration (g/kg dry matter) Crude protein 154 Crude fat 28 Crude fiber 186 Mg 3.7 K 30.7 Ca 7.0 P 4.7 Na 1.4
152 27 182 6.3 30.8 7.2 4.6 1.5
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.
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2.3. 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). 2.4. Statistical analyses Data were evaluated with Student’s paired t-test. The level of statistical significance was pre-set at P < 0.05. 3. 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 0.005 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). 3.2. 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. 0.015, n = 2).
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Table 3 Intake, fecal excretion and absorption of Mg in lactating cows fed the experimental rations Treatment
P-value
Low Mg
Intake, g per day Feces, g per day Apparent absorption g per day Coefficient
High Mg
Mean
S.E.
Mean
S.E.
68.1 59.1
ND 0.66
116.3 97.7
ND 1.76
9.0 0.131
0.63 0.0093
18.5 0.159
1.95 0.0165
ND
