Evaluation of the trace mineral status of ruminants in northeast Mexico

P K Gartenberg*, L R McDowell*, D Rodriguez**, N Wilkinson*, J H Conrad* and F G Martin*

*University of Florida, Gainesville, FL 32611-0691
**Universidad Autónoma Agraria Antonio Narro, Saltillo, México

Florida Agricultural Experiment Station Journal Series No. 9601. Research supported, in part, by the US Department of Agriculture under CSRC Special Grant No. 86-CRSR-2-2843 managed by the Caribbean Basin Advisory Group (CBAG)

A study was conducted to determine micromineral status of grazing livestock in three semiarid regions in northeast Mexico. Soil, forage, blood, hair, and liver samples were collected from a total of 13 different farms. Percentages of microminerals below low critical levels (in parentheses) and suggestive of a deficiency for livestock in regions 1, 2 and 3, respectively, were as follows: soil (ppm) - Fe (2.5) 100, 100, 100; Zn (1.0) 100, 100, 100; Cu (0.3) 100, 100, 100; Mn (5.0) 100, 100, 100; forage (ppm) - Fe (50) 5, 0, 0; Zn (30) 38, 88, 63; Cu (10) 86, 100, 75; Mn (40) 33, 63, 0; Co (0.1) 33, 13, 13; blood plasma (ppm) - Zn (0.6) 30, 6, 31; Cu (0.65) 26, 30, 67; Se (0.03) 0, 0, 0. Percentages of microminerals above high critical levels (in parentheses) and suggestive of a toxicity for livestock in regions 1, 2 and 3, respectively, were as follows: forage (ppm) - Se (2.0) 0, 33, 0; Mo (6.0) 38, 13, 50; hair (ppm) - Se (5.0) 0, 34, 0. The microminerals most likely to be deficient in the Nuevo Leon area were Cu and Zn, with Mn and Co being mildly deficient. Selenium was not present in toxic levels, whereas Mo was present in forages in sufficiently high concentrations to be potentially toxic. In Zacatecas, the microminerals most likely to be deficient were Cu, Zn, and Mn. Selenium concentrations in forage samples from Zacatecas were high enough to be considered toxic, whereas Mo concentrations were only mildly elevated. Microminerals most likely to be deficient in the Coahuila region were Cu and Zn. Cobalt, Mn, Fe and Se concentrations were normal. However, Mo levels in forages were the highest of all three regions and should be considered toxic.

Key words: México, minerals, deficiency, toxicity, selenium, copper, molybdenum.

Mineral deficiencies, imbalances and toxicities are severely inhibiting livestock production in Latin America (McDowell 1985). Grazing livestock in the tropics most often do not receive mineral supplementation, except for common salt, and must depend almost exclusively upon forages for their requirements (McDowell et al 1984). "Latin American Tables of Feed Composition" (McDowell et al 1977) indicated the percentage of forage samples deficient in the following microminerals: iron (Fe), 24%; cobalt (Co), 43%; copper (Cu), 47%; manganese (Mn), 21%; and zinc (Zn), 75%. One study in three regions of Coahuila, Mexico, found the most likely microminerals to be deficient were Cu and Zn, with Mn being deficient in one region (Haro 1986).

The present study was initiated to evaluate the micromineral status of livestock on farms of three regions of northeast Mexico, where many nutritional problems have been observed. A companion paper reports the macromineral and protein status (Gartenberg et al 1989).

Soil, forage, and animal tissues were collected from 13 different farms within three regions. Health observations or reports for the region were summarized. Six farms were sampled in Navidad, Nuevo Leon (Region 1); four farms in San Tiburcio, Zacatecas (Region 2); and three farms in Paila, Coahuila (Region 3). All regions were within 100 km of Saltillo, Mexico, in the northeastern part of the country. Each area had different altitudes, average yearly rainfall, and average temperatures. Mean annual temperatures for the three regions varied from 21.9 to 30.4 degrees centigrade, while rainfall ranged from only 298 to 499 mm. The nature of the soil in all regions was a sandy surface, which below a depth of 2 to 5 cm became a loamy clay which was difficult to penetrate. Samples were collected in May, which is the end of the rainy season in northern Mexico.

A total of 32 soil, 37 forage, 155 blood serum, 8 liver and 155 hair samples was collected. Animals sampled were 59 Holstein dairy cows, 66 native crossbred goats and 50 Suffolk/Rambouillet crossbred sheep. All animals ranged in age from 6 months to 10 years.

A total of 19, 6 and 7 soil samples were taken from regions 1, 2 and 3, respectively. Each sample was approximately 200 g and was collected according to soil collection procedures described by Bahia (1978). Soil samples were analyzed according to procedures used by IFAS Extension Soil Testing Laboratory in Gainesville, Florida (Mitchell and Rhue 1979). Minerals were extracted from soil samples with the double extractant method (0.025 N H₂SO₄ + 0.05 N HCl). Soil samples were analyzed for Fe, Cu, Mn, Zn, Se and pH.

A total of 21, 8 and 8 forage samples were collected in regions 1, 2 and 3, respectively. Approximately 200 g was collected for each sample. Forages were analyzed for Fe, Zn, Cu, Mo, Co, Mn, and Se.

Blood serum and hair were collected from animals on each farm within each region. A total of 69, 47 and 39 samples of each type were collected from regions 1, 2 and 3, respectively. Blood serum was deproteinated and analyzed for Cu and Zn. A separate one ml aliquot of serum was analyzed for Se. Each hair sample was analyzed for Se.

A total of nine liver samples were collected, with six being analyzed for Co, Cu, Fe, Mn, Mo and Zn and three being analyzed for Se. Seven samples were obtained by percutaneous aspiration biopsy. The remaining liver sample was collected at necropsy. All liver samples were collected in Region 1 from dairy cows. Forage, blood and liver samples were all collected and prepared for analyses according to techniques described by Fick et al (1979), except those samples used for Se analysis. Selenium analysis was the fluorometric technique described by Whetter and Ullrey (1978). Iron, Cu, Mn and Zn were determined using atomic absorption with a Perkin-Elmer model 306 (Perkin-Elmer 1982). Forage and liver Co and Mo were determined on a Perkin-Elmer model 503 with an HGA 2100 graphite furnace (Perkin-Elmer 1984).

The data from each region were analyzed separately, and analysis of variance was applied to data for a nested design with unequal subclass replications (Snedecor and Cochran 1973). Data were analyzed by the General Linear Model of the Statistical Analysis System (Barr et al 1976).

Productivity in this part of Mexico is very low. Many animals suffer from poor health, with observed or reported clinical signs listed in Table 1.

Least square means as related to soil microminerals, pH and critical levels are presented in Table 2. Soil pH was alkaline in all regions, with a mean pH of 8.4. Several essential elements tend to become less available due to a reduction in availability as pH increases. Iron, Mn and Zn are examples of microminerals, which are less available when the pH is raised from 5.0 to 8.0. Molybdenum and Se, on the other hand, are affected in the opposite way, being more available at the higher pH level (Brady 1974).

Table 2: Least square regional means and standard deviations (SD) of soil microminerals (ppm), pH, and critical levels (CL)*

		---- Region 1** ----		---- Region 2** ----		- Region 3**-
Element	CL	Mean	SD	Mean	SD	Mean	SD

Fe	< 2.5***	0.4	0.09	0.4	0.19	0.4	0
Cu 1	< 0.3****	0.151	0.03	0.147	0.08	0.100	.03
Zn 2	< 1.0****	0.012	0.01	0.011	0.01	0.020	.01
Mn 2	< 5.0****	0.576	0.26	0.284	0.071	0.520	.13
Se		0.611	0.42	0.572	0.17	0.137	.11
pH 1		8.37	0.18	8.28	0.425	8.48	.22

* Significant variations between farms within regions 1 = (P < 0.1), 2 = (P < 0.05)
** Numbers of observations for regions 1, 2 and 3 is N1 = 19, N2 = 6, and N3 = 7; except for Se where N1 = 11, N2 = 5 and N3 = 7
*** Viets and Lindsay (1973)
**** Rhue and Kidder (1983) Critical levels (CL) were established for Fe by Viets and Lindsay (1973) and for Cu, Zn and Mn by Rhue and Kidder (1983). All samples for Fe, Cu, Zn and Mn were below critical levels

Soil analyses of microminerals show all samples in all regions to be deficient in Zn, Fe, Cu and Mn. Zinc was the micromineral most severely below the critical level. Samples averaged 0.01 ppm in all regions, with 1 ppm being considered the low critical level (Rhue and Kidder 1983).

Manganese is the micromineral next most likely to be deficient, as all samples were less than the low critical level of 5 ppm (Rhue and Kidder 1983). Iron and Cu were also deficient in all samples collected.

Least square mean forage micromineral concentrations are shown in Table 3. Correlations between soil and forage micromineral concentrations were low and nonsignificant.

Table 3: Least square means and standard deviations (SD) of forage microminerals (ppm) and critical levels (CL)*

		----- Region 1** ------		------ Region 2** ------		------ Region 3** ------
Element	CL***	Mean	SD	Mean	SD	Mean	SD

Fe 1	< 50	283.0	258.1	370.2	272.8	569.7	271.5
Cu 2	< 10	6.05	6.11	5.19	3.09	7.00	14.24
Zn 1	< 30	34.43	160	20.82	8.96	30.05	343
Mn 2	< 40	62.11	42.13	55.63	51.1	87.86	55
Mo 2	> 6.0	7.34	10.40	2.03	2.86	6.85	4.97
Co 1	> 0.1	0.24	1.88	0.26	0.18	0.71	2.71
Se 1	> 2.0	0.20	.20	9.63	26.44	0.69	.89

* Significant variation among farms within a region, 1 = (P < 0.05) and 2 = (P < 0.01).
** Numbers of observations for regions 1, 2 and 3 are 21, 8 and 8, respectively
*** Critical levels based on the following references: NRC (1984) and McDowell et al (1984) Percentages of samples below critical levels (above for Mo and Se) for regions 1, 2 and 3, respectively, are as follows: Fe (5, 0, 0), Cu (86, 100, 75), Zn (38, 88, 63), Mn (33, 63, 0), Mo (43, 13, 63), Co (33, 13, 13) and Se (0, 33, 0)

Copper was found to be the most deficient micromineral in plant tissue samples. All samples collected in Region 2 were below the low critical level (10 ppm). Region 1 had 86% of samples, and Region 3 had 75% of samples deficient in Cu.

Zinc is the micromineral next most likely to be deficient. Region 2 proved to be most deficient, having 88% of samples less than the low critical concentration (30 ppm). Region 3 samples were 63% deficient and Region 1 samples were 38% deficient in Zn.

These findings are consistent with a 1986 study of three regions in the state of Coahuila, Mexico, where Cu and Zn were found to be deficient to marginal in forages in all three regions (Haro 1986).

Manganese was deficient (< 40 ppm) in 63% of forage samples collected in Region 2. Region 1 was only marginally deficient in Mn with 33% of samples being less than the low critical level, with none of the samples from Region 3 deficient in Mn. Cobalt was deficient (< 0.1 ppm) in 33% of samples collected in Region 1, with regions 2 and 3 only slightly deficient. Iron was not deficient (< 50 ppm) in any of the forage samples. Evidence of Mo and Se toxicity was found. Forages in Region 3 showed 63% of samples exceeded the upper critical level for Mo (> 6 ppm). Region 1 had 43% and Region 2 had 13% of Mo samples higher than the upper critical level. Forage Se in regions 1 and 3 was less than the toxic level (> 2 ppm). However, 33% of samples in Region 2 contained more Se than the upper critical level, with several of the samples having many times greater than the toxic level (ie 76 ppm).

Mean serum micromineral concentrations with respect to region and critical levels are shown in Table 4. Zinc was found to be most deficient in Region 3, with 31% of blood samples containing less than the low critical Zn concentration (0.6 ppm). Region 1 blood samples were 30% deficient, and Region 2 samples were 6% Zn deficient.

Table 4: Mean serum micromineral (ppm), hair selenium concentrations and standard deviations (SD) by region and their critical levels (CL)*

		---- Region 1 ----		---- Region 2 ----		---- Region 3 ----
Element	CL**	Mean	SD	Mean	SD	Mean	SD

Zn	< 0.6	0.77	0.40	1.02	0.39	0.85	0.43
Cu	< 0.65	0.81	0.25	0.91	0.34	0.53	0.20
Se	< 0.03	0.09	0.02	0.30	0.16	0.22	0.14
Hair Se	> 5.0	0.72	0.34	4.47	4.83	0.95	0.35

* Significant variation among farms within a region occurred for cow serum Zn (P < 0.01), Se (P < 0.01), and hair Se (P < 0.01), goat serum Zn (P < 0.01), Se (P < 0.01). and hair Se (P < 0.01)
** Critical levels based on the following references: Underwood (1981) and McDowell et al (1983). Percentages of samples below critical levels (above for Se) for regions 1, 2 and 3, respectively, are as follows: Zn (30, 6, 31), Cu (26, 30, 67), Se (0, 0, 0) and hair Se (0, 34, 0)

Copper was found to be most deficient in Region 3, with 67% of samples having less than the low critical Cu concentration (0.65 ppm). In Region 2, 30% of samples, and in Region 1, 26% of samples were deficient in Cu. It is interesting to note that the most severe Cu deficiency occurs in the area with the highest forage Mo concentrations. This can logically be explained by the antagonistic relationship between Cu and Mo. It is known that Mo will complex with Cu and interfere with Cu metabolism. The exact mechanism of that interference is unknown (NRC 1984). High Mo concentrations may not be the only antagonistic relationship contributing to low serum Cu concentrations. Extremely high levels of Ca, as exist in the soil of all three regions, may also be interfering with Cu metabolism and exacerbating depressed blood Cu levels (Maynard et al 1979).

Selenium was not deficient (< 0.03 ppm) in any of the samples collected. Upper critical levels for serum Se have not been established. As expected, Region 2 had the highest mean serum Se concentration (0.3 ppm). Region 3 samples had a mean of 0.22 ppm, and Region 1 had the lowest mean serum Se with 0.09 ppm.

Least square means for hair Se as related to region, species and critical levels are given in Table 5. Region 2 showed 30% of hair sampled to contain more than the upper critical level (5 ppm) for Se. None of the hair samples from regions 1 or 3 contained more than 5 ppm. Within Region 2, there was tremendous variability between animals. Hair Se concentrations within Region 2 ranged from 0.31 ppm to 17.28 ppm. There was not as much variability within or between Regions 1 and 3.

Table 5: Least square mean and standard deviation (SD) for hair selenium (ppm) by region, species, and critical levels (CL)*

Element	SD	Cows %	Sheep %	Goats %

Region 1 hair Se	.34	0.86	0.55	0.35
Region 2 hair Se	4.83	--	3.68	4.62
Region 3 hair Se	.35	0.91	--	1.04

* The critical level of above 5 ppm (Underwood 1988) was exceeded only in Region 2; 30% of sheep and 59% of goats were greater than the critical level

Mean liver micromineral concentrations and standard deviations (in parentheses) were as follows: Cu 117.8 (86.3), Fe 171.6 (375), Zn 88.9 (22.6), Mn 9.48 (4.34), Co 0.46 (0.16), Mo 1.64 (0.85), Se 1.27 (0.68). None of the liver samples were deficient in Co (< 0.05 ppm). Two samples were low in Cu (< 75 ppm) and one in Mn (< 6 ppm). Three samples were low in Zn (< 84 ppm) and Fe (< 180 ppm). All liver samples contained less than 4 ppm Mo and 2 ppm Se, indicating that neither mineral was in toxic concentrations in these animals.

Because of unequal sampling, it was not possible to detect differences between forages and animal tissues of different regions. A comparison of farms within a region shows significant variation in soil Zn and Mn (P < 0.05); forage Cu, Mn, Mo (P<0.01); and forage Fe, Zn, Cu, Se (P < 0.05). There was also significant variation among farms in hair Se, and serum Zn and Se for both cows and goats (P < 0.01).

The three regions of Mexico studied have severe mineral deficiencies and toxicities. It is important to note that consistently high soil pH, ranging from 8.3 to 8.6, may be exacerbating the conditions experienced by livestock in these regions. The microminerals most severely deficient were Cu, Zn and Mn, while various farms within regions had Mo and Se toxicities.

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