Regional Cattle Hypomagnesaemia in Finland 1979–1996 - Associations with Cropland Mg/Ca Ratio, Acid Rain and Lead Pollution

Hypomagnesaemia (HMg) of ruminats is a metabolic, possible acute and lethal, disease associated with relative or absolute dietary Mg-deficiency. This study assesses associations of HMg morbidity with cropland (Mg/Ca) ratio from 1986-90 [(Mg/Ca).88] and the late observed bias in 1979-83 against the general trend. National total SO 2 emission and lead (Pb) pollution via gasoline are assessed as additional factors, too. Population density [Pop.dens] has been used as a measure for pollution distribution. The cattle and (Mg/Ca) data are the same available as in earlier publication. Data are processed by Whole Country (WhC) and by continental Finland (CONT).Periods are used by their last two numbers, as (79-83) for 1979-1983. Period (79-93) includes data from 8 Decembers, (94-96) from 36 months. Results: (explanation proportion, R square %)(signif.)(sign(s) of coefficients) (proportions of beta coefficients): HMg associated inversely with [(Mg/Ca).88] and positively with [Pop.dens] in both periods. [HMg.(79-93)] was better explained by [Pop. dens] and HMg.(94-96) better by [Mg/Ca).88] Combined regression by [(Mg/Ca).88;Pop. dens] explained HMg.(79-93) by 61.4 % (p = 0.014)(+;-)(45:55), and HMg.(94-96) by 42.2 % (p = 0.085)(+;-)(60:40). In Uusimaa, with the highest [Pop.dens], the decreasing trend of SO2 and Pb pollution complied with simultaneous decrease in HMg. Carbonate soils of Åland did not protect, but was possibly even a risk on HMg as expected by the soil analyses. Conclusion: HMg associated regionally generally negatively with cropland Mg/ Ca ratio. The exception in 1979-83 can be explained by associations with SO 2 and lead pollution. [Pop.dens] associated highly significantly positively with regional HMg.(73-93) in continental Finland. Ratio,


Introduction
Hypomagnesemia (HMg) of ruminats is a metabolic disease, most common in early spring and late autumn, affected e.g. by amounts of utilized potassium (K) and Nitrogen (N) fertilizers [1].
For prophylaxis has been suggested to avoid high K/(Ca+Mg) ratio in fodder and for balancing K excess has been recommended to add NaCl to pasture salt mixtures. "The simpliest and cheapest method against grass tetany is to give to cows such pasture salt mixture, which is rich in magnesium and contains effective amounts of phosphor, NaCl and copper" [2].
Weather conditions (associated with poor sugar content of grass) and poor appetite can cause grass tetany even when pasture magnesium has been in the normal limits, anyhow moderately low [3]. Disturbances in fermentation processes of rumen can (often) be associated with overproduction of NH4+, which reduces Mg absorption [4]. The most prominent signs of hypomagnesemia are excitations and muscle cramps, which are closely correlated with the Mg concentration in the CSF. It is suggested that the clinical signs are caused by spontaneous activation of neurons in the CNS DOI: 10.26717/BJSTR.2020.30.004955 at low Mg concentrations, which leads to tetany [4]. Veterinary surgeon Seppo Haaranen represented that disturbances in rumen function with excess NH4+ production could be the most important factor in the development of hypomagnesaemic tetany and explain the rapid progression of HMg [5]. SO 2 emissions has been the main cause for acid rains [6]. Acid rains increase leaching of main cations, Ca and Mg, which are replaced (usually by carbonates, sulfates or another non-silicates), so diluting soil Si(OH) 4 content, which could additionally influence on Mg uptake by cells [7]. Acid rains can increase uptake of harmful metals like aluminium and influence on micro-organisms and water economy of plants. Lead (Pb) pollution via gasoline consumption in traffic could cause irritability and loss of appetite, which could promote the development of HMg [8].
Cropland Mg/Ca has shown association with timothy Mg/ Ca [9] and bovine provincial HMg/HCa ratio [10]. Cattle HMg associated negatively with cropland Mg/Ca ratio in periods (79-93) and (94-96) [11], but in subperiod (79-83), this association was positive (not reported in [11], because positive explanation by 7.9 % seemed to be below threshold of publication). The aim of this study is to clarify the bias in 1979-1983 by assessing associations of provincial HMg [incidence (1/100,000)] with cropland (Mg/Ca) ratio and changes in SO 2 and Pb pollution.

Materials and Methods
Cropland (Mg/Ca) values from 1986-90, number of dairy cows and morbidity data on HMg (based on monthly reports of veterinary surgeons) are the same as in [11]. Periodical morbidity numbers are re-calculated and slightly revised: Periodical HMg incidence is attained by dividing mean number of periodical cases by mean periodical number of cattle.

Results
The means and medians of HMg had increased slightly between periods (79-83) and (85-93) and after that more, so that mean of whole year values (94-96) was two-fold and median about threefold to December values of (79-93) (   Change in exposition to pollutants was great during the experimental period. SO 2 and Pb expositions were declined ca 60 % until 1983 and until 1993 Pb exposition was stopped and SO 2 exposition was decreased by 80 % (Figure 3). In (94-96) SO 2 exposition was still slightly reduced (Table 1). HMg values (black colums) of Uusimaa is based on data in [11]. Missing data grey colums are estimated by linear interpolation.
First are assessed regional associations between HMg and pollutants. [Pop.dens] is replacing here more delicate measures of co-incident exposure (( Figure 4, 5)) ( Table 4).

Discussion
During the period of heavy and decreasing atmospheric pollution by SO2 (and Pb) HMg complied with these changes in Uusimaa with highest population density (Fig. 3). Mg supplementation of croplands had increased strongly since 1972 [16], but this increase was to be seen in organic soils first since 1985 [17], after the reduction of acid rain. It is possible that SO2 (acid rains) could have participated in cropland Mg loss in Finland, especially in 1968-82, when SO2 exposition was > 400,000 t/a, as in [7].  Fig. 7 &9). This could suggest that low CHD mortality in Åland is obviously not based on high Mg availability [18].
Obviously indoor feeding (in Decembers) could protect against grass tetany (Tabl.3). This shows seasonal dependence, i.e. HMg was obviously still in the 1990's more pasture than indoor disease.
In the 1950's when large scale prophylaxis with Mg-containing fodder salt mixture begun the expositions to SO2 [12] and Pb [14] were low. It is possible that the strong acid rain caused some biases in field trials by fertilizers and liming agents.
Possibly acid rains primarily (have) reduce(d) biological activity of soil [6,19] and reduced availability of plant nutrients, e.g.
[20], reduced biological weathering of silicates, e.g. [21], so reduced Si(OH)4 production and reduced the antacid effect of silicates, CO2 consumption, in croplands [22]. There are obviously anyhow only indirect data for supporting that acid rain as such could decrease cropland Si(OH)4: Acid rain can decrease soil main cations [6,7].
Cropland Cation Exchange Capacity is "the total capacity of a soil to hold exchangeable cations", CEC [23]. Amorphous SiO2 [anhydride of Si(OH)4] can increase cropland water capacity [24], i.e. by decreasing leaching it could resist decrease of soil cations.
On the other side the author has not seen reports that acid rains had decreased or increased cropland Si nor increases in cropland Si after decline in acid rains.
The role of copper (Cu) [2] in HMg seems not to have been discussed in the HMg reviews during the last years. Remarkable is that acid soluble Cu (6.5 mg/l) [25] and groundwater silicon (Si) (4.82 mg/l) [26] have been moderately low in Åland and Si has shown to have synergistic effects with Cu [27], which could partially explain the high HMg in Åland.

Conclusion
HMg associated inversely with cropland Mg/Ca ratio and