Mineral supplementation and reproductive rate of beef cows grazing tropical natural pastures in Malawi (part II)

Mineral supplementation and reproductive rate of beef cows grazing tropical natural pastures in Malawi (part II)

Table 2: Mineral concentrations in serum, liver, and bone by year and treatment,*

Item	Critical level***	1	2	3	4

Serum (mg/100 ml)		1985

Ca	<9	14.2	14.1	14.7	15.0
P	<4.5	5.5	5.4	4.9	5.0
Mg	<1	2.5	3.0	2.9	3.1

		1986

Ca	<9	14.1	14.4	14.3	14.2
P	<4.5	3.8****d	3.4d,e	2.8e,f	2.7f
Mg	<1	3.2	3.3	3.2	3.0

		1987

Ca	<9	13.2	13.3	12.7	12.9
P	<4.5	4.4	4.5	4.4	4.7
Mg	<1	3.4	3.5	3.1	3.3

Liver (ppm, dry basis)		1985

Cu	<75	149	192	148	101
Zn	<84	71	63	73	146
Fe	<180	332	307	360	377

		1986

Cu	<75	108	94	95	81
Zn	<84	64	54	74	97
Fe	<180	307e	312d	315d	306e

		1987

Cu	<75	136	144	80	125
Zn	<84	136	117	109	127
Fe	<180	317	336	295	331

Bone (dry fat-free %)		1985

Ash	<66.2	64.9	62.7	64.2	64.9
Ca	<24.5	19.7	27.0	18.1	31.4
P	<11.5	7.2	6.6	8.8	7.7
Mg		3.1	5.3	1.6	6.9

		1986

Ash	<66.2	64.9	62.0	62.7	64.2
Ca	<24.5	20.5	19.5	24.9	23.8
P	<11.5	5.4	6.2	7.1	8.6
Mg		3.8	1.5	4.4	4.7

		1987

Ash	<66.2	62.0	62.2	63.1	63.0
Ca	<24.5	19.4	20.8	21.1	21.1
P	<11.5	8.2	8.1	9.4	9.0

* Treatment groups were as follows: (1) salt + phosphorus; (2) salt + phosphorus + copper; (3) salt only; and (4) salt + copper. No mineral supplementation administered in 1985, all groups supplemented with salt, and phosphorus given to groups 1 & 2 in 1986 & 1987; copper given to groups 2 & 4 in 1987.
** Serum means based on not less than 120 samples for each group and not less than 8 samples for liver and bone.
*** Mtimuni, 1982; McDowell, 1985.
**** d,e,f Means within a row with different superscripts differ (P < 0.05).

Bone biopsy phosphorus was slightly lower at the end (May) than at the beginning (December) of the rainy season (Table 3). However, with supplementation, which began in January 1986, bone phosphorus increased slightly in May but did not follow a particular pattern (Table 3).

Liver is the tissue of the greatest value in assessing copper status of animals. Liver copper was above the critical level in 1985 but was just above critical level in 1986 (Table 2). Copper decreased from May to December 1985 and 1986. Liver zinc was mostly below suggested low levels (< 84 ppm) but rose above this concentration in 1987. The significant increase in liver zinc cannot readily be explained (Table 3). Calcium and magnesium were not deficient in the serum. However, the bone biopsy samples indicated that calcium was deficient in all groups (Table 2) and throughout the seasons in all three years (Table 3). Minerals in animal tissues did not show any consistent significant seasonal pattern. Serum calcium values are much higher than values usually reported in literature (Committee on Animal Nutrition 1973; Mtimuni 1982; McDowell et al 1983). However, such figures have been reported elsewhere (Van Schalkwyk and Lambard 1969; Carmago et al 1978). The abnormal high values could be due to impurities in the gas acetylene, used in some developing countries.

Table 3: Mineral concentrations in serum, liver and bone by month and year,*

	Critical	1984	1985
Item	level***	Dec	Feb	May	July	Oct	Dec

Serum (mg/100 ml)**
Ca	<9		****15.6d	14.4e,f	13.8g	14.9e	13.8g
P	<4.5		5.0	4.6	5.7	5.7	4.9
Mg	<1		3.3	2.3	3.0	3.0	2.5

Liver (ppm,dry basis)
Cu	<75	145		150			92
Zn	<84	118		59			91
Fe	<180	340		348			310

Bone (dry fat-free %)
Ash	<66.8	62.2		64.2			64.9
Ca	<24.5	25.1		22.9			24.4
P	<11.5	9.4		5.7			6.5
Mg		5.7		2.7			4.5


	1986				1987
***	Apr	May	Oct	Dec	Feb	Apr	May

Serum (mg/100 ml)
Ca	13.0e	15.4d	13.5e	14.9d	13.6e	11.3d	14.2e
P	4.1d	4.1e	2.3e	2.2e	4.0d	4.5e	5.1e
Mg	2.2d	3.6e	3.3e	3.5e	3.9d	3.2e	2.8e

Liver (ppm, dry basis)
Cu		97		81d			161e
Zn		53		87d			158e
Fe		310		360			271

Bone (dry fat-free %)
Ash		65.3		62.5			63.1
Ca		20.4		18.4			22.8
P		7.2		8.3			9.0
Mg		2.7		3.5

* No mineral supplementation administered in 1985; all groups supplemented with salt, and phosphorus given to groups 1 & 2 in 1987; copper given to groups 2 & 4 in 1987.
** Serum means based on not less than 120 samples for each groups and not less than 12 samples for liver and blood.
*** Critical levels (Mtimuni, 1982; McDowell, 1985).
**** d,e,f,g Means within a row, within a year, with different superscripts differ (P < 0.05).

Table 4: Forage mineral concentrations for three years (dry basis)*

	Critical	Forage collected in 1985
Mineral	level**	Feb	May	Oct	Dec

Ca, %	<0.3	0.88d	1.47c	2.03c	1.67c
P, %	<0.25	0.15	0.23	0.14	0.23
Mg, %	<0.20	0.11	0.14	0.12	0.09
Na, %	<0.06	0.01	0.05	0.12	0.28
K, %	<0.8	0.29d	0.38d	0.28d	0.98c
Fe, ppm	<50	216b	306a	342b	435a
Zn, ppm	<40	13	15	19	21
Cu, ppm	<8	3.5	3.8	2.3	3.7

		Forages Collected in 1986
		Apr	May	Oct	Dec

Ca, %	**	1.62d	1.34d	0.08c	0.07c
P, %		0.21	0.23	0.21	0.28
Mg, %		0.15	0.13	0.19	0.21
Na, %		0.09	0.04	0.31	0.01
K, %		1.52	0.41	0.47	1.16
Fe, ppm		261	214	175	130
Zn, ppm		15	16	14	19
Cu, ppm		3.9	3.9	1.9	4.3

		Forages Collected in 1987
		Feb	Apr	May

Ca, %	**	0.06c	0.32d	0.25d
P, %		0.23c	0.14d	0.19e
Mg, %		0.22	0.46	0.45
Na, %		0.06	0.60	0.03
K, %		1.18	1.16	1.14
Fe, ppm		90	102	111
Zn, ppm		19	27	27
Cu, ppm		3.2	1.7	--

* Mean for each month is based on not less than 18 samples.
** Critical levels (Mtimuni, 1982; McDowell, 1985).
*** c,d,e Means within a row for each year with different superscripts differ (P < 0.05).

Forage analysis can be useful in determining mineral deficiencies (Du Toit et al 1940; McDowell 1985). Forage mineral analysis for the three years are presented in Table 4 and forage species concentrations by year in Table 5. Forage phosphorus was just below the critical level (< 0.25) in May and December (Table 4) but was below critical level in October at 62% of the critical level in 1986, probably because of more favourable prolonged rainfall in 1986 than in 1985. A short rainfall in 1987 was probably the reason for low phosphorus levels in forage that were below critical concentrations.

Only a few species analyzed, namely Elyamanrdra grallata, Elyonurus sp, Panicum maximum, Tristachya rehmannii, Tistachya superba (Table 5) exceeded the critical level in three years. However, these forage species were not dominant grasses in all paddocks.

Phosphorus has been found to be deficient in foraqes collected throughout Malawi and that phosphorus content of forages was lower during the dry season than during the rainy season (Mtimuni 1982) in agreement with the others (Theiler et al 1924; Du Toit et al 1940; Van Nierkerk 1978). Forage phosphorus is highly mobile and phosphorus content decreases and is transferred to the roots and possibly to the soil as the plant matures (Blue and Tergas 1969). According to the information presented on forage analysis, the animals could benefit from phosphorus supplementation because forages were deficient in phosphorus. Although it was difficult to estimate the daily forage intake, forages would not contribute much to the daily phosphorus requirement and the daily supplementation of 6.3 g of phosphorus was inadequate because bone phosphorus did not rise above a critical concentration.

Forages supplied less than 50% of the copper requirement of the animals for each of the three years, and the copper levels were lowest in October (Table 4). There was no species that exceeded copper requirement (Table 5), except Echinochloa pyramidalis in 1986. Copper was previously found to be deficient in forages in Malawi (1982).

Zinc was deficient in the forages in all three years, and forages supplied only 67% of the requirement of the animal at its peak (Table 4). There was no single species that supplied more than the zinc requirement (Rudert and O'Donovan 1976) of the animal (Table 5).

Calcium was more than adequate in 1985 (Table 4), but calcium was below the critical level (< 0.30%) in October and December 1986 and February and May in 1987. Mtimuni (1982) found that calcium and magnesium were lower in the rainy season (December to April) than in the dry season (July to December). Most species had calcium levels above the critical level (Table 5), and it seems calcium levels decreased from 1985 to 1987 (Table 4). The paddocks have been burnt almost every year since 1985, and, consequently, less older material is found in these paddocks ever since the burning became more frequent.

Table 5: Mineral composition for three years of indigenous forage species at Kuti Ranch (dry basis)*

	Calcium (%)			Phosphorus (%)			Magnesium (%)
Species	1985	1986	1987	1985	1986	1987	1985	1986	1987

Andropogon gayanus	1.26	0.65	0.16	0.09	0.21	0.14	0.12	0.12	0.46
Digitaria decumbens	1.82	0.66	0.16	0.23	0.16	0.11	0.10	0.17	0.26
Echinochloa pyramidalis	-	0.65	0.15	-	0.15	0.13	-	0.39	0.29
Elyonurus trapnellii	2.39	0.25	0.15	0.28	0.22	0.22	0.16	0.09	0.46
Heteropogon contortus	1.80	-	0.16	0.22	-	0.21	0.13	-	0.32
Hyparrhenia colina	3.18	1.20	0.16	0.14	0.19	-	0.18	0.18	0.66
Hyparrhenia filipendula	2.40	0.72	0.45	0.13	0.15	0.18	0.15	0.18	0.36
Hyparrhenia rufa	1.69	0.67	-	0.02	0.21	-	0.09	0.18	-
Hyparrhenia species	1.43	0.45	0.15	0.20	0.25	0.16	0.16	0.24	0.34
Panicum maximum	1.53	0.72	0.31	0.24	0.38	0.13	0.15	0.20	0.40
Setaria sphacelata	1.15	0.54	0.19	0.20	0.23	0.24	0.12	0.10	0.36
Tristachya rehmannii	1.66	0.76	0.21	0.16	0.28	0.18	0.12	0.29	0.53
Tristachya superba	1.75	2.59	-	0.20	0.19	0.28	0.18	0.29	-


	Iron (ppm)			Zinc (ppm)			Copper (ppm)
	1985	1986	1987	1985	1986	1987	1985	1986	1987

Andropogon gayanus	254	120	58	17.9	20.3	25.6	4.2	3.2	2.6
Digitaria decumbens	556	490	61	19.0	11.8	12.0	3.7	2.5	2.2
Echinochloa pyramidalis	-	178	71	-	60.6	20.1	-	10.0	2.0
Elyonurus trapnellii	150	155	48	10.3	11.9	15.7	5.0	3.8	3.4
Heteropogon contortus	172	-	94	20.6	-	27.9	3.5	-	1.3
Hyparrhenia colina	277	159	-	19.0	10.8	16.2	4.4	4.1	1.9
Hyparrhenia filipendula	174	195	68	17.0	20.5	24.2	2.5	2.3	2.2
Hyparrhenia rufa	199	196	-	12.1	21.6	-	-	3.9	-
Hyparrhenia species	325	175	83	24.9	16.1	41.6	6.2	3.5	2.4
Panicum maximum	359	245	186	14.0	14.6	18.3	4.0	3.8	3.1
Setaria sphacelata	211	159	50	20.9	20.1	28.1	3.8	5.3	2.7
Tristachya rehmannii	322	87	125	16.3	17.3	20.5	3.6	2.6	1.1
Tristachya superba	222	181	289	19.0	11.1	-	4.9	1.3	-

* Critical levels (Mtimuni, 1982; McDowell, 1985) are as follows: Ca (0.30%), P (0.25%), Mg (0.20%), Fe (50 ppm), Zn (40 ppm), and Cu (8 ppm).

Phosphorus concentration in the soil was above the critical level (< 10 ppm) for plant growth in 1985 (Table 6) using double acid method, but soil phosphorus was below 25 ppm (considered medium) in 1985 and below the critical level (< 10 ppm) in 1987. There was no consistent pattern of soil phosphorus throughout the year. Lowole (1981) reported phosphorus deficiencies in a number of paddocks at the Kuti Ranch. Phosphorus was deficient in forage and in the bone biopsy samples from the animals consuming the forage. It was the deficiency of phosphorus in the soil that explained the phosphorus deficiencies in animals in South Africa (Theiler et al 1924). Therefore, soil analysis can be relevant in diagnosis of phosphorus deficiencies in animals. Mtimuni (1982) found mineral deficiencies in soils in many areas of Malawi, and response of crops and pasture plants, especially maize, to phosphorus fertilizer attests to the existence of phosphorus deficiencies in the soils in Malawi.

Copper was just slightly above the critical level (< 0.6 ppm) for plant growth. However, copper availability is affected by many factors, including molybdenum and sulphur (McDowell et al 1983; Allen et al 1984). Zinc was deficient in the soil, and no monthly average exceeded the critical level (< 2 ppm). Manganese was only deficient (< 19 ppm) during 1987 and April 1986. Soil calcium and magnesium were far above critical levels.

The results obtained for three breeding seasons (1985-1987) indicate that salt and phosphorus supplementation for two years did not increase the calving rate of the cows grazing natural pastures. Supplementation of salt, phosphorus and copper (+ Co and Se) did not increase the conception rate of the cows in three breeding seasons nor did it increase the calving rate of the cows. The lack of response in these animals is despite severe phosphorus and copper deficiencies in animal tissues, forage and in the soil.

Table 6: Soil mineral concentrations for three years (dry basis)*

	Critical	Soils Collected in 1985
Item	level**	May	Oct	Dec

pH		***6.2d	5.9c	6.1b
Ca, meq/100 g	<0.35	12.9c	4.4d	3.9d
Mg, meq/100 g	<0.07	4.6	1.3	1.1
Na, meq/100 g		0.06	0.05	0.05
K, meq/100 g	<0.15	0.43	0.69	0.52
P, ppm	<10	15.8d	25.5c,d	34.5c
Fe, ppm	19	50	47	28
Zn, ppm	<2	0.7	1.2	1.0
Cu, ppm	<0.6	0.9	1.0	1.0
Mn, ppm	<19	22	23	43

		Soils Collected in 1986
		Apr	May	Oct	Dec

pH	**	6.1d	6.0d	6.4c	5.9d
Ca, meq/100 g		5.2c	2.7e	4.7d	2.9e
Mg, meq/100 g		3.5c	1.0d	2.0d	1.3d
Na, meq/100 g		0.05c	0.0	0.03	0.03
K, meq/100 g		0.45	0.41	0.34	0.32
P, ppm		21.7c	21.1c	9.4d	7.3d
Fe, ppm		77c	69c	31d	30d
Zn, ppm		1.5c	0.8d	1.2c,d	0.8d
Cu, ppm		1.0	1.1	0.7	0.8
Mn, ppm		14d	28c	24c	12d

		Forages Collected in 1987
		Feb	Apr	May

pH	**	6.1	6.0	6.2
Ca, meq/100 g		4.8	5.1	5.0
Mg, meq/100 g		1.6c	0.7d	1.4c
Na, meq/100 g		0.03	0.05	0.03
K, meq/100 g		0.43	0.50	0.49
P, ppm		7.6	6.1	4.7
Fe, ppm		40	42	47
Zn, ppm		0.9	0.7	1.1
Cu, ppm		0.8	1.1	0.7
Mn, ppm		15	14	16

* Mean for each month is based on not less than 15 samples.
** Critical levels (Mtimuni, 1982; McDowell, 1985).
*** c,d,e Means within a row within year with different superscripts differ (P < 0.05).

Animal tissue analyses indicate that the phosphorus supplementation of 6.3 g was quite low, as it did not increase bone phosphorus above the critical level. Since the cows were nursing calves of different ages some nearing weaning during the breeding season when they were being supplemented with minerals, it is conceivable that the amount of minerals supplemented was too little to make an impact. It seems probable that although certain minerals were deficient it is likely that energy and protein supplies were even more limiting in animal reproduction. Other researchers have shown that mineral supplementation is only beneficial providing the diet is relatively adequate in energy and protein (McDowell 1985). Mineral deficiency will be expressed once energy-protein requirements are provided. The treatment effects in the third breeding season were confounded with the bull effect, for some of the bulls used needed replacement in the herd. The Brahman breed is considered shy breeders and it is strongly suspected as one cause of lack of response to mineral supplementation.

The authors wish to thank the International Development Research Centre of Canada for funding the Project. Appreciation is also extended to Dr Roger Jones of Chance Pilkington, Wales, United Kingdom, for donating the copper boluses.

The authors further wish to thank the Officer-In-Charge of Chitedze Research Station for granting the permission to use its laboratories and for the technical assistance of the Soil Fertility Unit, especially of Mr W A Kadyampakeni.

The authors acknowledge the assistance of Dr E Ayeh of Bunda College with the statistical analyses and of the Chief Veterinary Officer for providing the animals and the facilities at the Kuti Ranch.

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