Macro-mineral utilization in West African dwarf goats fed combinations of fertilized and unfertilized Guinea grass (Panicum maximum, cv. ntchisi), Verano stylo (Stylosanthes hamata cv Verano) and a concentrate mix

M A Bamikole* and O J Babayemi

Department of Animal Science, University of Ibadan, Ibadan, Nigeria
*(Correspondent author’s new address) Department of Animal Science, University of Benin, Benin City, Edo State, Nigeria
bankymao@uniben.edu  ;  bankymao@yahoo.co.uk

Abstract

The utilization of macro-minerals (Ca, Mg, Na, K, Cl and S) in energy concentrate supplemented forages of nitrogen fertilized Guinea grass (SNFG), Guinea grass-Verano stylo mixture (SGVSM)  and unfertilized Guinea grass (SUFG) was monitored in 15 female West African dwarf goats (mean body weight = 7.61 ± 0.21 kg) using a completely randomized design. Faeces and urine were collected for seven days after seven days of animal adaptation to cages using experimental animals that have been on a previous study for 120 days. 

The range of macro-mineral concentration in the forages were 0.02 – 0.05 % Na, 0.40 – 0.55 % Mg, 0.50 – 1.20 % Ca, 0.81 – 2.20 % K, 0.07 – 0.12 % Cl and 0.03 – 0.15 % S. In the energy concentrate content of Na, Mg, Ca, K, Cl, and S was 0.26, 0.30, 0.16, 1.10, 0.08 and 0.10 % respectively. Significant effect of diets was noticed in the utilization of Ca, Mg, Na, Cl and S. Calcium balance and retention values (0.41 g/d and 20.91 %) were significantly best in SGVSM diet and poor in both the SNFG (-0.13 g/d and -14.31 %) and SUFG (-0.52 and -112.4 %) diets.  Magnesium balance values were similar (P > 0.05) in all the diets (mean = 0.35 g/d), while its retention value was significantly highest (P < 0.05) in SUFG diet (42.03 %) and similar (P > 0.05) in both the diets of SNFG (33.53 %) and SGVSM (33.35%).  Sodium balance (g/d) and retention (%) were significantly enhanced (P < 0.05) in SGVSM (0.41 and 86.04), followed by SNFG (0.37 and 72.06) and least in SUFG (0.25 and 56.25).  Effect of diet was not noticed in the value of K balance (range = 1.88 – 2.23 g/d) and retention (range = 42.50 – 50.45 %).  Chlorine balance (0.07 g/d) and retention (22.70 %) values in SNFG were not significantly different from that of SGVSM (0.07 g/d and 17.52 %) but were significantly lowest in SUFG (0.022 g/d and 9.74 %).  Sulphur balance and retention were not monitored, however, digestibility was significantly enhanced in SNFG (61.48 %) above those of SGVSM (42.91%) and SUFG (35.41 %). 

The results have shown that while both SNFG and SGVSM diet could favour utilization of Cl, the utilization of Ca and Na are better in SGVSM diet and S is better in SNFG diet.  All the three diets could also support good utilization of Mg and K.  Based on existing information on mineral utilization from these forages when fed solely, feeding them with concentrate supplementation as demonstrated in this study will improve the utilization of Na, Mg, k, S and Cl.

Keywords: digestibility fertilizer, grass, legume, major- elements, ruminant, supplement

Introduction

The importance of goats in achieving food and economic securities in developing countries is increasingly being realized.  Goats are animals of multiple utilities producing milk, meat, skin and fibre and their husbandry practices fit-in well into the subsistence livestock production system of small holders in developing countries.  The realization of the immense potential of goats has attracted more interest into the business of keeping these animals.  A fifteen-year study to observe the evolutions of livestock numbers revealed that the number of goats has increased by about 50% at the world level, while that of sheep has diminished by 3% (Morand-Fehr and Boyazoglu 1999).  Coupled with this upsurge in the population of goats is the change in their husbandry systems from the traditional free ranging to confinement system. This is due to the increased pressure on land occasioned by an increase in the arable cropping by farmers.  This development calls for means of achieving supply of forages to the confined goats in the right quantity and quality.  Grass improvement options of application of inorganic nitrogen fertilizer to grass as well as planting of legumes in mixture with stands of grasses have been well researched (Ezenwa and Aken’Ova 1998, Bamikole and Ezenwa 1999, Galdamez-Cabrera et al 2004).  Bamikole et al (2001) reported that better protein utilization as well as weight gain of goats is guaranteed from Guinea grass-Verano stylo legume mixture than nitrogen fertilized grass.  Besides protein and energy content of forages, many mineral elements are also required at optimal levels as their deficiencies could lead to reduced ruminant performance (Galdamez-Cabrera et al 2004).  The study of bioavailability of macro-mineral in these grasses however revealed that more macro-minerals are better utilized in nitrogen fertilized grass than the grass-legume mixture (Bamikole 2003).

A common practice by goat farmers is the feeding of concentrate supplements which are inexpensive and locally available.  Cassava peels and maize offal are popular examples.  Concentrate feeding to ruminants is often associated with changes in the rumen fermentation pattern due to the effect on the pH and proportion of microbial population in the rumen (Carro et al 2000).  Such alteration in the rumen environment may affect mineral availability in the rumen due to possible interactions between microbial cells and soluble minerals to form insoluble compounds (Spears 1994).  More so, low pH, which is a result of high fermentation when energy concentrates are fed, could have an effect on the solubility of minerals like magnesium and its transport across the rumen epithelium (Schonewille et al 1997, Schonewille et al 2002).  Huntington et al (1981) observed an increase in Mg absorption when the amount of concentrate made available to wethers was changed from 65 to 85%.

Based on the likely effect of feeding energy concentrate on mineral utilization in ruminants and the common practices by farmers to feed energy rich peels and offals to goats, it becomes necessary to look at the utilization of macro-minerals in goats when energy concentrate is fed with grasses produced with already embraced grass improvement options of nitrogen fertilization and incorporation of legumes.

Materials and methods 

Location

The study was carried out at the goat’s unit of University of Ibadan Teaching and Research Farm, Ibadan, Nigeria (7⁰   20¹N, 3⁰ 50¹E; altitude about 200 m above sea level).  Average temperature, rainfall and relative humidity during the period of the study were 28 – 34⁰C, 1150 – 2284 mm and 77.90% respectively.

Experimental animals

Fifteen West African dwarf goats were used for the study.  The average weight of the animal at the time of purchase was 5.43 ± 0.39 kg and the age ranged between 7 – 8 months old.  The goats were sourced from goat keepers around the University campus.  They were given prophylactic treatments of long acting (LA) antibiotics and vitamin B-complex through intramuscular route at the dosage rate of 1ml /10kg body weight.  They were also dipped with solution of sumithion against ectoparasites and dewormed with 0.5ml/10kg live weight of levamisol injected subcutaneously.  The goats were kept in well bedded (about 7cm thickness of wood shavings) individual pens measuring 1.5 x 2m, for about 120 days during which the animals were used for an initial study on feed intake, weight gain and nitrogen balance of goats fed unsupplemented forage diets.  At the commencement of this study the animals weighed 7.61 ± 0.21 kg on the average and they were physically examined for signs of disease infection and ectoparasite infestation.  Based on this, the dipping operation was repeated to control the few ectoparasites noticed on them.

Experimental diets and feeding

The forage diets used for the study were nitrogen-fertilized Guinea grass (NFG), Guinea grass-Verano stylo mixture (GVSM) and unfertilized Guinea grass (UFG).  The forages were cultivated on a plot of 40 x 50 m each at the Rockefeller unit of the University farm.  The nitrogen fertilizer used was Calcium Ammonium Nitrate (CAN) and was applied at the rate of 200 kg N/ha in four equal split doses per year.  The details of the pasture management, and the cutting strategy developed for daily availability of six-week old forages have been reported by Bamikole et al (1998) and Bamikole et al (2001) respectively.  The cutting strategy developed evolved a 42-day phase by phase harvesting of forage and the forage used were those of the fourth phase.  The energy concentrate used (Table 1) was simply formulated, using commonly available ingredients like cassava peels and maize offals. 

The goats were allocated to the three experimental diets and metabolism cages in a completely randomized design. The experimental diets, which consisted of  the three forages of NFG, GVSM and UFG plus 120g each of the energy concentrate supplement, were designated as SNFG, SGVSM and SUFG. The forages were fed to ensure that each experimental goat received 50 g DM/kg live weight/day.  Animals fed grass-legume mixture received the forages of Guinea grass in the grass – Verano stylo mixture (GGVSM) and Verano Stylo (VS) in separate feeding troughs and the legume was 40% of the fresh mixture. All diets were fed twice daily with 50% of the daily quantity introduced at 0800 and 1600 hours respectively.

Collection of faeces and urine

The metabolism cages were constructed to facilitate easy collection of faeces and urine separately.  Feed intake and excreta data were collected for 7 days and began after one-week adaptation period to cage feeding.  Total quantities of faeces and urine voided per day were determined and 10 % aliquots were taken.  The faecal samples were dried at 60⁰ C to constant weight to determine the dry matter content and the dry samples were kept for further laboratory analysis.  Urine samples were acidified with 10% tetraoxo-sulphate (IV) acid to prevent loss of nitrogen through volatilization and kept in the freezer until they were chemically analysed.

Chemical and statistical analyses

The seven-day faecal samples as well as urine samples were pooled together, mixed thoroughly and final sub-samples taken for chemical analysis.  The feed and faeces were analysed for their respective components of CP (N × 6.25) and OM according to the procedure of AOAC (1990) while NDF component was determined by the detergent method (Van Soest et al 1991).  Analysis of the macro-mineral contents of the feed, faeces and urine was by the wet digestion method involving a 4:1 mixture of nitric and perchloric acid.  The concentration of each mineral element was read using atomic absorption spectrophotometer (Bulk Scientific Model 200a, East Norwalk, USA).  The values obtained were used to quantify the mineral balance for each experimental diet.  The data emanated from the study were subjected to analysis of variance (ANOVA) using the PROC GLM of SAS (2000) in a completely randomized design with five replications and experimental diets as the factor. Significant differences were declared at 5% probability level and means were separated using Duncan multiple range test.

Results 

Chemical composition of the grasses

Grass treatment of the Nitrogen fertilization improved the crude protein (CP) content of NFG over the UFG (Table 1). Such improvement in CP was not noticed in (GGVSM) but high CP value of the VS is noteworthy and could improve the CP of the mixed grass-legume diet.  The concentrates had a CP value that was comparable to that of NFG, but higher than those of GGVSM and UFG and lower than that of VS.  The content of neutral detergent fibre (NDF) was similar in all the grasses and the concentrate but was about 33% lower in VS.  The organic matter (OM) values were similar in VS and concentrate and were about four units lower in the grass forage treatments. The macro mineral profile of the feeds showed higher value of sodium (Na) in the concentrate than the grass and legume forages, while potassium (K) and magnesium (Mg) contents were higher in the grass forages than the concentrate feed.  Calcium (Ca) value was highest in VS and similar in the grass treatments, indicating no effect of the grass treatment options on the Ca level of the grasses.  Verano stylo has the highest value of chlorine but least value of sulphur (S).  The S content of GGVSM was the highest and was 100% above the values obtained in both UFG and NFG.

Calcium and magnesium utilization

Calcium and Magnesium utilization pattern of goats fed SNFG, SGVSM, and SUFG are presented in Table 2.   

The intake of calcium was significantly influenced by the experimental diets.  While Ca intake was significantly highest in SGVSM, Mg intake was highest in SNFG and both minerals had lowest intake from SUFG.  The excretion of Ca in the faeces was significantly highest in the SGVSM diet while highest output in the urine was recorded in the SNFG diet.  In all the diets, higher proportions of Ca were excreted in the faeces than in the urine.  Calcium digestibility as well as balance and retention were all better in SGVSM. Respective values obtained for SUFG and SNFG were negative except for Ca digestibility in SNFG.

The intake of Mg was similar in SNFG and SGVSM diets and was significantly enhanced by the two grass treatment options of N-fertilization and Verano stylo legume incorporation, over the untreated grass.  Magnesium excretion in both the faeces and urine tends to follow the pattern of Mg intake and partitioning of output was more through the faecal route than the urinary route.  Digestibility of Mg was not significantly different between SNFG and SUFG diets, while the value in SGVSM was significantly lower than that of SUFG but not SNFG.  Magnesium retention was also significantly better in SUFG and similar in both SNFG and SGVSM diets, while Mg balance was not significantly affected by the experimental diet used.

Sodium and potassium utilization

The intake of Na (Table 3) varied significantly being highest in SNFG and similar in both the diets of SGVSM and SUFG. 

Grass treatments options depressed significantly excretion of Na in the faeces compared with the untreated grass.  Nitrogen fertilization encouraged significantly, more excretion of Na in the urine than the grass-Verano stylo legume mixture.  The digestibility of Na was very high and similar in the treated grasses SNFG and SGVSM and was both significantly higher than that of untreated (SUFG).  Sodium balance and retention were significantly best in SGVSM, followed by SNFG and least in SUFG.

Potassium intake was not significantly affected by diet.  Faecal output of K was highest in SGVSM, and the value was only significantly different from that of SUFG but not SNFG.  All the forage diets favoured losses of K in the urine than in the faeces and the losses were significantly highest in the SNFG.  The digestibility values of K were generally good and not significantly different among the diets. More so, the K balance and retention values were significantly influenced by treatments.

Chlorine and sulphur utilization

More Cl was significantly consumed in SNFG diet, than the SUFG diet, while the intake value in SGVSM diet was not significantly different from those of SNFG and SUFG (Table 4). 

The output of Cl in the faeces was not significantly affected by the type of diet.  The output in urine however varied significantly with the diet consumed; more in the SNFG diet than the SGVSM diet.  The excretion of Cl via the urine was about 150% more than in the faeces in all the diet.  Chlorine digestibility was very high in all the diets and was not significantly influenced.  The Cl balance and retention values were similar in SNFG and SGVSM diets and were both significantly higher than the value obtained for SUFG.

The intake of S was significantly influenced by experimental diet.  The intake was highest in SGVSM, followed by SNFG and lowest in SUFG.  More losses of S consumed in the feed were also recorded in the faeces of animals fed SGVSM diet than those on SNFG diet.  The losses from the diet of SUFG were not significantly different from those of SNFG and SGVSM diets.  The S consumed was best digested in SNFG diet.  The values were below average and did not show significant difference in diets of SGVSM and SUFG.  Sulphur balance and retention could not be studied due to the sulphur contamination of the urine from the tetraoxo-sulphate (VI) acid (H₂SO₄) that was added to urine as preservative.

Discussion 

The observed merit of nitrogen fertilization in enhancing the nitrogen content of grasses and the benefit derivable from intercropping grass with legumes like Verano stylo in this study have been reported in our previous works (Bamikole et al 2001).  The two treatments used did not improve the macro-mineral contents of the grasses in this study except for S in GGVSM. No significant effect of Nitrogen fertilization was found in the Ca concentration of Bermuda grass (Edwards et al 1997) as well as content of K (Galdamez-Cabrera et al 2004).  The Mg content of the Bermuda grass however showed significant improvement with N fertilizer treatment (Galdamez-Cabrera et al 2004).    More so, observation made by Whitehead et al (Whitehead et al 1986) about nitrogen fertilization effect in reducing the mineral contents of grasses was not noticed in this study.  However the result of no effect of legume intercropping with grass on the mineral contents of the grasses corroborated the findings of Bouchet and Gueguen (1983) that nitrogen fixation can only satisfy the nitrogen requirement of legume forages but not the demands for P, K, Ca, Mg and other essential element.

Higher concentration of Ca was obtained in the grasses produced in this study than the mean values reported for some grasses grazed by cattle in the derived savannah zone of Nigeria (Smith et al 2000).  The reason for this disparity could be linked with the difference in the forage species and management options (Spears 1994). Grasses used in this study were 6-week regrowth from established plots while those of Smith et al (2000) were old and uncultivated species from rangelands.  Verano stylo had more Ca than the grasses and thus confirmed an earlier report (Underwood 1981).  Both the grasses and the Verano stylo have sufficient concentration of Ca to meet the requirement of a growing goat put at 0.21 – 0.52% Ca DM (McDowell 1985). The K values of the grasses were similar with the values reported in Cenchrus ciliaris and Panicum hallii which are native Mexican grasses (Ramirez et al 2004).  Going by the K requirements of 1.8 - 2.5 g/kg for goats (Underwood 1981, NRC 1981), 6.0 g/kg for gestating and 7.0g/kg for lactating cows (NRC 1996), ruminants being grazed or zero grazed on these forages will have adequate access to potassium.

The Na content of all the forages was lower than the 0.7g/kg required in the diet of goat (NRC 1981, Kessler 1991), hence the need for supplementation for these minerals when forages produced through these options are fed to goats.  The concentrate used in this study however satisfied about 111% of the requirement for sodium.  Magnesium   contents of the forages were adequate and could meet the requirement of goats for this mineral going by the recommended value of 0.08 – 0.25 % (Underwood 1981, Kessler 1991).  The Mg requirement of large ruminants can also be satisfied from these forages considering the value of 1-2 and 2-2.5 g/kg required by beef cattle and dairy cattle respectively (NRC 1989, NRC 1996).  Cows in gestation which required 1.2 g/kg Mg (NRC 1996) are also guaranteed adequate Mg insurance when fed with these forages.

Beside Verano stylo, both the grasses and concentrate were low in Cl and could not satisfy the recommended value of 0.10 – 0.20 % for lactating dairy cows (Fettman et al 1984).  The concentrate as well as the grasses except GGVSM were low in S and were lower than the range of 0.16 - 0.32 % required by growing goat (McDowell 1985).  Calcium intake improved significantly in SGVSM diet and this was a reflection of high level of the mineral in the Verano stylo component of the diet.  Legumes have been indicated to have more concentration of Ca than the grasses (Minson 1983).  Calcium utilization pattern as judged from the digestibility, balance and retention values was poorer in this study compared with the previously reported values in grasses that received the same treatment but without concentrate supplementation (Bamikole 2003).  Depressed Ca utilization could be explained from the nature of the concentrate used which composed of cassava peels and maize offals containing high content of cell wall fractions than the grasses.  Calcium is noted to be physically enclosed in an undigested fiber bundle in the form of Ca oxalate crystals (Playne et al 1978, Ward et al 1979).  This is further evident in the high level of excretion of this mineral in the faeces of animals fed the experimental diets.  The negative Ca balance and retention values obtained for animals fed SNFG and SUFG diets were in agreement with those of earlier reports (Madsen et al 1976, Bamikole 2003).  Concentrate supplementation adopted in the current study could not address these problems.  The endogenous secretion of Ca in the lower part of the gastro-intestinal tract (GIT) which could mask the initial upper GIT absorption of the mineral may explain the reason for this observation.

Magnesium utilization was generally better in this study than in the previous studies where concentrate supplementation was not used.  This observation agreed with the finding of Madsen et al (1976) and Schonewille et al (2002).  This improvement in Mg utilization can be traced to the reduction in K intake of the animals occasioned by the concentrate supplement fed which had lower K concentration than the grasses.  The K concentration of diets that consisted of forage and concentrate had been noted to be lower than those in which forages are the sole component (Adedeji and Suttle 1999, Schonewille et al 2002).  High intakes of K have been shown to inhibit Mg absorption in cows (Schonewille et al 1999), while Mg absorption was reported to have increased by 0.52 percent unit when K intake dropped by 1 g/kg dietary dry matter (Underwood and Suttle 1999).

Concentrate supplementation apart from making the intake of K low have also been indicated to enhance the intake of starch which could produce increased ruminal fermentation and lower ruminal pH resulting in more solubility of Mg and its transport across the rumen epithelium (Schonewille et al 1997, Schonewille et al 2002).  The digestibility values recorded in this study are in agreement with 51.2 % recorded by Perdomo et al (1976).  A lower wide range of Mg digestibility (16 – 30%) has been reported by Grace et al (1974), while a high value of 75% was obtained by Chicco et al (1972).

Sodium was better utilized in this study than in the work reported previously (Bamikole 2003), where no supplement was supplied.  All the forages were analysed to contain lower amounts of Na than the requirement of growing goats.  The higher level of Na in the concentrate supplement improved the availability of this mineral to the animals leading to improvement in the digestibility, balance and retention values.  Sodium has been generally observed to be almost completely absorbed by both ruminants and non ruminant animals (McDowell 1992).

Potassium intakes were lower for respective diets in the current study than the values reported earlier (Bamikole 2003), due to low K content of the concentrate fed.  The digestibility, balance and retention values for K were as good as those obtained in the unsupplemented grasses of the earlier study.  This implies that while a reduction in K intake occasioned by concentrate supplementation can be used to an advantage of improving Mg utilization, it does not disturb the efficient utilization of K in the animals.  Reduction in K intake is accompanied by a reduction in K loses in the urine as K intake has been shown to have positive effect on urinary K excretion (Bannink et al 1999).  This could however translate to improved utilization of K as demonstrated in this study where urinary K output declined with reduction in K intake and a consequent increase in retention.  The digestibility values were as high as those values reported in sheep fed four tropical forages (Perdomo et al 1976) and differently fertilized Bermuda grass incubated in the rumen of steers (Galdamez-Cabrera et al 2004).  The K balance results also compared with the values reported by Madsen et al (1976).  There is paucity of information about the utilization of Cl and S by ruminants.  Results from this study showed good digestibility values for Cl and compared well with values obtained for unsupplemented forages of the same type and treatment in our previous study (Bamikole 2003).  Calcium balance and retention values were low, but also compared with values obtained from the same study.  Intake of S as well as its digestibility was better than values obtained in the earlier study with unsupplemented forages (Bamikole 2003).

The consistently highest value of urinary excretion of minerals from SNFG diet is noteworthy.  All the minerals studied had their losses in urine being highest from SNFG diet, irrespective of the amount consumed.  Losses of nutrient from animals to the environment are of major concern in livestock production due to the resultant effect of environmental pollution in which contamination effect on fresh water and groundwater is an example.  Nitrogen fertilization of grass has been noted to promote high losses of nitrogen in the urine of ruminants (Zhang et al 1995, Delargarde et al 1997, Bamikole et al 2001).  Such losses can as well be experienced with some macro- minerals as demonstrated in this study, when N-fertilized grass is fed to animals.

Conclusions 

• The forages irrespective of the treatment received can meet the Mg, K and Ca requirement of ruminant animal but not their requirement for S, Na and Cl. 

  
  

• Concentrate supplemented grass-Verano stylo mixture can favour better Ca and Na utilization in goats while concentrate supplemented nitrogen fertilized grass can favour better utilization of S. 

  
  

• Both SGVSM and SNFG can guarantee good utilization of Cl. 

  
  

• All the three diets can support good utilization of Mg and K.

  
  

• Using the initial results of mineral utilization obtained from the same forages as the basis for comparison, introducing concentrate supplement when feeding these forages can improve the utilization of Na, Mg, K, S and Cl.

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Received 22 May 2009; Accepted 2 June 2009; Published 1 September 2009

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