| Livestock Research for Rural Development 25 (10) 2013 | Guide for preparation of papers | LRRD Newsletter | Citation of this paper |
A study was conducted in Merille location of Marsabit South District, Kenya to estimate the mineral intake of young sheep and goats. The most preferred forages consumed by animals were identified by direct observation of 120 sheep and goats. Each sheep/goat was observed for 10 minutes and complete bites of forages and parts consumed were recorded. Composite samples of ten most preferred forages were formulated based on bite counts and analyzed to determine concentrations of Ca, P, Mg, K, Na, Fe, Zn, and Mn. Mineral intake was then computed based on dry matter intake of animals and macro and micro- mineral content of forage composites.
In both seasons, the most preferred forages provided adequate intake of Ca, Mg and Fe to small ruminants. Sheep and goats also had sufficient intake of K (16.2 vs. 17.1 g kg-1 DM) and Mn (31.8 vs. 27.3 mg kg-1 DM) in the wet season and Zn (72.5 vs.63.5 mg kg-1 DM) in the dry season, respectively. However, sheep and goats showed inadequate intake of Na (0.39 vs. 0.49 g kg-1 DM) in wet season, marginal K (4.58 vs. 4.1 g kg-1 DM) and P (0.56 vs. 0.52 g kg-1 DM) in dry season, respectively. Zinc (15.0 mg kg-1 DM) intake in sheep and Mn (18.1 mg kg-1 DM) in goats during the wet and dry seasons, respectively was below their body requirements. In conclusion, young sheep and goats would need to be supplemented with P, K in the dry season and Na in wet season and sheep would also need Zn in the wet season and goats Mn in the dry season.
Key words: forages, intake,nutrient requirements
Sheep and goats substantially contribute to the animal protein consumed in Kenya. Annual meat production is estimated at 84,000 tonnes of mutton and chevon worth KES 14 billion (GoK 2010). It is estimated that 60% of sheep and goats slaughtered in Kenya originate from the arid and semi-arid areas of the country (EPZ 2005). Albeit the large contribution of small ruminants to the consumption protein pool, the primary problem affecting livestock in Kenya was ranked as inadequate forage (Owen et al 2005).The productivity of these pastures is subjected to high variability between and within years, related to rainfall and seasons (Sanon et al 2007). In the arid areas, options of increasing livestock feed supply is limited (Coppock 1994) and increased knowledge on the quantity and quality of available feeds is prerequisite to correct the nutrient deficits.
Minerals are an important component of animal diets and are required by organisms to utilize other nutrients in the diet (Szefer and Nriagu 2007). In free grazing animals, minerals derived from natural feedstuffs are often inadequate and require supplementation to satisfy animal requirements (Sowande et al 2008). The amounts of nutrients, including minerals, in the forages greatly vary depending on soil, plant species and management factors (Haenlein 1991). Of the nutritional inadequacies, mineral deficiencies have adverse effect on both animal production and health (Schillhorn van Veen and Loeffler 1990). However, in the arid and semi-arid lands of Kenya, where the bulk of small ruminants are found, there is limited information on the mineral intake by grazing sheep and goats.
In free grazing systems, analysis of forages for mineral composition should be coupled with estimating their contribution to the mineral intake of animals. In free-grazing animals, obtaining herbage samples representative of that selected by goats or sheep is normally intricate (Aregheore et al 2006). The objectives of this study were therefore to determine the mineral profile of the composite representing the forages consumed by animals, estimate mineral intake and assess whether the forages provide adequate minerals to young sheep and goats in northern Kenya.
The study was conducted in Merille location of Marsabit South District in northern Kenya. It is characterized by an arid climate, with annual precipitation mean of 275 mm and air temperatures between 28-42oC. The area, has acidic soils with pH of 6.0 and low P of 4.5 ppm. The vegetation types found in the area include riverine woodland, bushed dwarf shrub and bushed grassland. The woodland vegetation comprise of mainly Acacia tortilis, Cordia sinensis, Salvadora persica. Acacia and Commiphora communities, Indigofera spinosa, Sericocomopsis hildebrandtii and Barleria acanthoides are the dominant species of the bush dwarf shrub land.
The most preferred forage species selected by sheep and goats in the dry and wet seasons, were identified by direct observation of 120 growing animals (1-2 year old). During each season, sixty sheep and 60 goats were randomly selected from twelve herds grazing different pastures and directly observed for 10 minutes, between 08:30-11:30 hours for six consecutive days. Forage bites, species selected and forage parts consumed were noted and recorded. The number of feeding bites were summed up and ranked to determine the most preferred forages. For each season, ten most preferred forages were sampled from different grazing areas. The forage samples corresponding to parts consumed (leaves, tender twigs, flowers, seeds and pods) were randomly collected along the grazing path, at the peak of the wet season and late in the dry season. For each selected forage species, 10-15 plants were used to source 200 g which were bulked to 600g representative samples. The samples were air dried to constant weight at 70°C, milled to pass 1mm sieve and packed in sealed zip lock nylon bags.
During both wet and dry the seasons, the ten most preferred forages by sheep and goats were used to simulate the animals diet (Tables 1 and 2). The forage samples were mixed based on bite percent. The composite sample expressed on 100 percent basis, and weighing 100g (Tables 1 and 2) were carefully mixed at the time of formulation and prior to digestion.
|
Table 1: Most preferred forages by sheep and amount in forage composite |
||||
|
Forage |
Dry season |
Amount (g) |
Wet season |
Amount (g) |
|
Browses |
Duosperma eremophilum |
7.5 |
Crotalaria fasicularis |
3.40 |
|
|
Commiphora africana |
9.0 |
Indigofera hochstetteri |
4.49 |
|
|
Cordia sinensis |
9.5 |
Indigofera spinosa |
19.8 |
|
|
Indigofera spinosa |
25.3 |
Indigofera cliffordiana |
2.63 |
|
|
Sericocomopsis hildebrandtii |
2.0 |
|
|
|
Grasses/herbs |
Aristida adscensionis |
28.5 |
Commicarpus stellatus |
2.52 |
|
|
Commicarpus stellatus |
2.2 |
Bracharia leersiodes |
14.9 |
|
|
Blepharis linariifolia |
3.3 |
Tetrapogon cenchriformis |
20.4 |
|
|
Bracharia leersiodes |
4.1 |
Aristida adscensionis |
9.30 |
|
|
Tetrapogon cenchriformis |
8.6 |
Cenchrus pennisetiformis |
4.16 |
|
|
|
|
Mariscus macropus |
18.4 |
|
Table 2: Most preferred forages by goats and amount in forage composite |
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|
Forage type |
Dry season |
Amount (g) |
Wet season |
Amount (g) |
|
Browse |
Acacia tortilis |
6.28 |
Bauhimia taitenis |
3.43 |
|
|
Barleria acanthoides |
4.27 |
Commiphora africana |
3.6 |
|
|
Bauhimia taitenis |
7.58 |
Grewia tenax |
6.72 |
|
|
Combretum aculeatum |
4.62 |
Indigofera hochstetteri |
8.70 |
|
|
Commiphora africana |
8.06 |
Indigofera spinosa |
19.9 |
|
|
Cordia sinensis |
10.1 |
Lippia carviodora |
4.88 |
|
|
Indigofera spinosa |
25.7 |
|
|
|
|
Maerua crassifolia |
3.79 |
|
|
|
Grasses/herbs |
Aristida adscensionis |
24.2 |
Bracharia leersiodes |
33.5 |
|
|
Tetrapogon cenchriformis |
5.40 |
Cenchrus pennisetiformis |
2.80 |
|
|
|
|
Mariscus macropus |
5.67 |
|
|
|
|
Tetrapogon cenchriformis |
10.8 |
Triplicate forage composite samples weighing 0.3 g were digested in tubes with sulfuric acid (H2SO4), salicylic acid and selenium as stabilizer. At relatively low temperatures (100°C) the organic matter in the samples were oxidized by Hydrogen peroxide (H2O2). After decomposition using H2O2, the digestion was completed by use of concentrated H2SO4 at elevated temperatures (330°C) under the influence of selenium as catalyst. The concentration of Ca, Mg, Fe, Zn, and Mn were determined by atomic absorption spectrophotometry (Perkin-Elmer AAS Analyst 100, USA) while flame photometer was used for K and Na analysis. Phosphorus concentration was determined colorimetrically (AOAC 1990).
The mineral content of composite diet was used to compute mineral intake as:
Mineral intake = DM Intake (4 % LW, assumed to be on low quality diet) x
macro (g kg-1DM) and micro (mg kg-1DM) mineral content in composite. The body weight of growing sheep (17 kg) and goats (16 kg)
weighed in the field and estimated DM intake in sheep was (0.68 kg) and goats
(0.64 kg).
The macro and micro-mineral forage data was subjected to a one-way analysis of variance and means between different seasons were compared by LSD using GenStat 12th edition (2010).
The macro and micro- mineral contents of composite samples simulating the diet of sheep and goats are presented in Table 3.
The Ca and Mg concentrations in forage composite of sheep and goats were not influenced (P>0.05) by season. The concentrations of Ca and Mg were comparable to those reported by Aganga et al (2008) in Botswana, Kuria (2004) in northern Kenya and Temesgen and Mohammed (2012) in Ethiopia. Green plants are excellent sources of Mg, which is attributed to the presence of magnesium in the chlorophyll moiety (Wilkinson et al 1990). Thus, the shift in diets selected by sheep and goats in dry and wet seasons ensured consumption of diets rich in Mg.
In the composite of both animals, the contents of P and K were higher (P<0.05) in wet than dry season. The concentrations of P and K in forages decline with plant maturity and translocation of minerals to the root system (Reid and Horvath 1980). Kuria et al (2006) in Marsabit reported that about 22-50% of forages in camel diets were marginal in P and K. The acidic soils (pH 6.0) of the area favors uptake of K particularly during the wet season.
The forage composite of sheep had higher level (P = 0.045) of Na in dry (1.97±0.52 g kg-1 DM) than wet season (0.57±0.03 g kg-1 DM), while Na in goat composite was similar (P = 0.094) in both seasons. In the wet season, the low levels of Na underpins the report by Minson (1990) that most tropical pastures contains less than 1.5 g Na kg-1 DM.
|
Table 3: Mineral content (DM basis± SE) of composite forage in dry and wet seasons in sheep and goats |
||||||||
|
|
Sheep |
|
Goat |
|
||||
|
Element |
Dry |
Wet |
SEM |
Prob. |
Dry |
Wet |
SEM |
Prob. |
|
Ca, g kg-1 |
16.7a |
16.9a |
2.7 |
0.974 |
15.3a |
22.8a |
2.5 |
0.099 |
|
P, g kg-1 |
0.87a |
2.57b |
0.033 |
<0.001 |
0.80a |
2.23b |
0.151 |
0.003 |
|
Mg, g kg-1 |
3.2a |
2.23a |
0.281 |
0.072 |
3.33a |
2.77a |
0.323 |
0.283 |
|
K, g kg-1 |
6.73a |
23.8b |
0.467 |
<0.001 |
6.4a |
26.7b |
0.642 |
<0.001 |
|
Na, g kg-1 |
1.97a |
0.57b |
0.369 |
0.045 |
1.37a |
0.77a |
0.194 |
0.094 |
|
Fe, mg kg-1 |
790a |
1001a |
166 |
0.42 |
905a |
712a |
220 |
0.568 |
|
Zn, mg kg-1 |
107a |
22.0b |
8.79 |
0.002 |
99.3a |
18.6b |
4.01 |
<0.001 |
|
Mn, mg kg-1 |
37.1a |
46.8a |
2.49 |
0.06 |
28.2a |
42.7a |
6.86 |
0.21 |
|
abMeans within a row of same animal lacking common letters differ (P<0.05) |
||||||||
The Fe concentrations in forage composite of sheep and goats were similar (P>0.05) in both seasons. The high values of Fe can be attributed to soil contamination of forages (Underwood and Suttle 1999). During the dry season, dusty winds are common feature of the area and in the rainy season floods contaminate pastures in the riverine valley. Also, acidic soil conditions of the area favour availability and plant uptake of Fe (Khan et al 2006). However, the contents of Fe were similar to those reported by Kuria et al (2004) in mineral sources of camels in western Marsabit, Kenya.
The forage composites of sheep and goats, had higher contents of Zn in dry (P<0.05) than wet season. In dry season, the levels of Zn were remarkably higher than the mean of 36 mg Zn kg-1DM reported in most tropical grasses (Minson 1990). Ramírez et al (2006) also reported high levels of Zn (161 mg kg-1DM) in some browse species in north eastern Mexico.The concentration of Zn in herbage is mostly influenced by Soil pH, soil texture, soil mineral concentration and botanical composition (Espen et al 2005).
The Mn contents in forage composite of sheep were not affected by season (37.1±3.46 vs. 46.8±0.64 mg kg-1 DM). In the case of goats, although not significant (P = 0.21) manganese concentration tended to increase in wet season (42.7±5.78 mg kg-1 DM) than dry season (28.2±7.8 mg kg-1 DM). In both seasons, Mn concentrations in sheep and goat composites were lower than those reported by Rubanza et al (2005) in Tanzania, Temesgen and Mohammed (2012) in Ethiopia. However, during the wet season Mn in sheep and goats composite were comparable to the values of 43.47-44.47 ppm (DM) reported by Shamat et al (2009) in browses selected by camels in western Sudan. The Mn concentrations in plants were highest in leaves (Marković et al 2009) and acidic soils (Underwood and Suttle 1999).
The estimated macro and micro-mineral intake and requirement of young sheep and goats are presented in Table 4.
|
Table 4: Estimated mineral intake in dry and wet season (DM basis) and requirement in young sheep and goats |
||||||
|
|
Mineral intake/day |
|
||||
|
|
Sheep |
|
Goats |
|
Mineral requirements1 |
|
|
Element |
Dry |
Wet |
Dry |
Wet |
Sheep |
Goats |
|
Ca, g kg-1 |
11.4 |
11.5 |
9.8 |
14.6 |
2.0 |
3.5 |
|
P, g kg-1 |
0.56 |
1.75 |
0.52 |
1.43 |
1.6 |
2.45 |
|
Mg, g kg-1 |
2.18 |
1.52 |
2.13 |
1.77 |
1.2 |
0.8-2.5 |
|
K, g kg-1 |
4.58 |
16.2 |
4.1 |
17.1 |
5 |
5 |
|
Na, g kg-1 |
1.34 |
0.39 |
0.88 |
0.49 |
0.9 |
0.8-1 |
|
Fe, mg kg-1 |
537 |
681 |
579 |
456 |
30-50 |
30-100 |
|
Zn, mg kg-1 |
72.5 |
15.0 |
63.5 |
11.9 |
20-33 |
>10-50 |
|
Mn, mg kg-1 |
25.2 |
31.8 |
18.1 |
27.3 |
20-40 |
20-40
|
|
1Requirements for growing sheep and goats (Kessler 1991; Heinlein 1980; NRC 1981; NRC 1985). |
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Irrespective of season, sheep and goats intake of Ca was above the recommended requirement of 2.0 and 3.5 g kg-1 DM respectively (NRC 1981; NRC 1985). Thus sheep and goats consume adequate levels of Ca. In both seasons, goats P intake was below the recommended requirement 2.45 g kg-1 DM (NRC 1981). However, growing sheep in the dry season consumed less than recommended while in wet season they consumed levels above the recommended requirement of 1.6 g kg-1 DM (NRC 1985). Low P intake can affect the concentration of Mn in the liver (Neathery et al 1990). In dry and wet seasons, sheep and goats consumed adequate levels of Mg to satisfy their body requirements.
However, for K, sheep and goats with daily requirement of 5 g kg-1 DM (NRC 1981) consumed high levels during the wet season, but had marginal deficiency in the dry season (Table 4).
In the dry season, sheep and goats with a Na requirement of 0.8 and 0.8-2.5 g kg-1 DM respectively, consumed sufficient levels of Na to certify their body requirement. However, in the wet season Na intake in sheep and goats were below the recommended requirement. Imbalances of Na and K intake in the wet season can inhibit the ATP dependent Na+-K+ pump and energy metabolism in animals (Underwood and Suttle 1999).
In both seasons, sheep and goats consumed levels of iron above the requirements of 50 and 100 mg kg-1 DM in sheep and goats, respectively (NRC 1985; Kessler 1991; Haenlein 1980). High levels of Fe may cause nutritional problems of decreasing phosphate absorption (Zaman et al 2011). However, symptoms of P deficiency were not observed in the young sheep and goats.
In the wet season sheep consumed low levels of Zn, but during the dry season the intake of Zn in growing sheep was above the maximum requirement of 33 mg kg-1 DM (NRC 1985). However, goats in both seasons consumed adequate levels above the requirement of >10 mg kg-1 DM (Kessler 1991; Haenlein 1980). Therefore growing sheep and goats consumed adequate levels of Zn in the dry season, but sheep seems to suffer from Zn deficiency in the wet season.
Both sheep and goats, with a requirement of 20 mg Mn kg-1 DM (NRC 1985; Kessler 1991; Haenlein 1980), consumed adequate levels in the wet season. During the dry season, Mn intake in goats was below the minimum requirement. Manganese is poorly absorbed in ruminants and antagonism with high dietary Ca can reduce Mn bioavailability (Spears 2002). However, Mn requirements are substantially lower for growth than for optimal reproductive performance (McDowell and Arthington 2005).
The authors wish to thank Kenya Arid and Semi-Arid lands (KASAL) project for funding this study, University of Nairobi and KARI-NARL for laboratory analysis.
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Received 13 February 2013; Accepted 13 September 2013; Published 1 October 2013