Biokemistri Nigerian Society for Experimental Biology ISSN: 0795-8080 Vol. 14, Num. 1, 2003, pp. 57-63

Biokemistri, Vol. 14, No.1, Jan, 2003, pp 57-63

Cyanide, Nitrates and Nitrite Contents of Livestock Feeds  in Umuahia, Nigeria.

P.N. Okafor* and C.U. Nwabuko

Department of Chemical Sciences College of Biological and Physical Sciences,MichealOkparaUniversity of Agriculture, Umudike,Umuahia Abia State, Nigeria.
*Correspondence Author. E-mail address: pnokafor@yahoo.com

Code Number: bk03009

The cyanide nitrate and nitrite contents in pig feeds from six different farms in Umuahia, Nigeria were assayed using spectrophotometric and enzymatic methods.  Enzymatic analysis of the feed samples indicated mean total cyanide level of 59.30  +3.72 – 361.90 + 11.2mg^-1 DM. The mean cyanide content of cyanogenic plant materials used in the feed formulation ranged from 85.60 + 13.2 – 888.10 + 23.17mgkg^-1. Observation was made that the cyanide measured in these feed samples were higher than the recommended dietary cyanogens levels for both non-ruminants and ruminants; 100mg HCN equivalent kg^-1 for cassava ration. The mean levels of nitrate and nitrite ranged 25.5 + 2.76mg – 285.5 + 12.70 and 2.20 + 0.3 – 218.80 + 13.42mg kg^-1DM respectively. The toxicological and nutritional significance of the results obtained are discussed.

Keywords: Cyanide, nitrate, nitrite, animal feeds.

INTRODUCTION

The high demand for cereals by increasing human population and their use by millers for compounding livestock feed coupled with the need for livestock products have led to the use of unconventional feeds for animal production (Iyayi and Tewe, 1994). These unconventional feed materials include sorghum spent grains and wheat offals ( by-products of sorghum and wheat malting respectively) as well as cassava peels. One of the factors that limits the use of these products as livestock feeds is their content of cyanogenic glycosides which on hydrolysis by endogenous β-glycosidase enzyme yield hydrogen cyanide (Conn, 1969) which is a potent poison (Coursey, 1973).

The use of cassava formulation for livestock feed dated back to 1903 when Tracy reported the use of this root crop for swine feeding. Despite overwhelming evidence from two decades of satisfactory performance of animals fed on cassava chips in European community countries, arguments still persist in the scientific circles as to the safety of cassava for sustainable livestock production (Tewe, 1994). The work of Osuntokun (1970) on Wistar rats substantiates the claim of the unsuitability of cassava as animal feed. His investigation revealed that when rats were fed “puru - puru” a cassava product for a period of 18 – 24 months, plasma thiocyanate levels were raised and rats developed ataxic and segmented demyelination similar to that which is found in patients suffering from Tropical Ataxic Neuropathy (TAN). Other studies (Charavanaparavana 1944;Ekpechi, 1967,1969; Delange, and Ahiluwalia 1983) sconstitute strong circumstantial evidence which have continued to influence current thinking on the safety of cassava for human and livestock feeding.

Moreover, there is now an increasing evidence that thiocyanate, the main cyanide metabolite can lead to the promotion of N-nitrosamine formation in vivo which enhances carcinogenesis (Maduagwu and Umoh1988; Okoh, 1992,). However, deaths reported in livestock fed forage sorghum products, fresh or processed cassava roots or leaves have been sporadic. In most instances, dietary cyanide exposure from cassava or sorghum has been implicated without the determination of the amount of cyanogens in the materials thus making the evidence circumstantial.

This paper descirbes the cyanide, nitrate and nitrite contents of pig feeds in six farms in Umuahia, Abia State-Nigeria.

MATERIALS AND METHODS 

Feed Samples

Animal feed samples and the raw materials used for their formulation were collected from six different Pig Farms that are involved in semi-intensive animal production in Umuahia, Abia State-Nigeria. These included Michael Okpara University Farm, designated (A), Umunwanwa Farm (B), Ngodo Farm (C), Umuopara Farm (D), Ubakala Farm (E) and Afara Farm (F). 

Feed composition.

Feed sample from farm A contained sorghum spent grains (25%), wheat offals (25%), soybean cake (15%), fish meal (2%), palm kernel mean (25%), bone meal (3%), Oyster shell (2%), salt (0.25%), vitamin min-Premix (2.5%), methionine (0. 1%) and Cysine (0. 1%). Feed sample from Farm B is made up of 80% fermented spent grains and 20% other constituents while feed sample from Fram C contained 75% wheat offals and 25% palm kernel. Feed sample from Farm D contained cassava peels (50%), palm kernel cake (25%) and sorghum spent grains (25%). Feed samples from Farms E and F were cassava peels (50%), palm kernel cake (25%) and soybean meal 25% for E and sorghum spent grains (>90%) for F.

Cyanide determination.

Cyanide content of each feed sample was extracted according to the method of O’Brien et al (1991) and their cyanogens contents determined spectrophotometrically using exogenous β-glucosidase (Ikediobi et al 1980).

Nitrate and nitrite determination.

Nitrite content of the samples was determined spectrophotometrically by the method of Follet and Ratcliff (1963) and nitrate after reduction to nitrite using cadmium column based on the same method.

Statistical analysis: Student’s t-test was used for statistical comparisons. 

RESULTS AND DISCUSSION. 

The mean total cyanide content of the feed samples ranged from 59.30 +3.72 – 361. 90 +15. 9mgkg^-1 DM ( Table 1). The feed sample D (from Umuopara Farm) contained the highest level of mean total cyanide; 361. 90 +15. 9 mgkg^-1 DM while the least of mean cyanide 59.30 +3.72 mgkg^-1 DM was measured in feed sample C from Ngodo Farm   (Table 1). The cyanide levels in these feeds reflect the percentage of cyanogenic plant materials that make up the rations. The levels of mean cyanide content of cassava peels, sorghum spent grains and wheat offals that make up high percentage of the feed samples were 888. 10 + 23. 17, 127. 9 +13. 07, and 85. 6 +1. 32 mgkg^-1 DM respectively (see Table 1). For example, while the feed sample from Umuopara Farm contained 50% cassava peel, 25% palm kernel cake and 25%spent grains (ie, 75% of the feed materials are from cyanogenic plants), the feed samples C 75% wheat offals and 25% palm kernel cake.

The cyanide content of the cassava peels used as component of these feeds contained about 888.1+ 23.17mg kg^-1 DM while sorghum spent grains contained 127.90+ 13.07mg kg ^–1 DM (see Table 2).

There was a statistically significant difference (p<0.01) between the levels of cyanide content of feed sample C and the others. Feeds sample A which is from Michael Okpara University Farm contained 197.50 + 10.3mgkg^-1DM cyanide. This value is higher than the recommended cyanide level for animal rations; less than 100mgkg^-1 (Wood, 1992). Levels of dietary cyanide as low a 40-60mg HCN equivalent kg^-1 in fermentated cassava product called “puru-puru” have been reported to cause neurological abnormalities in humans and rats (Osuntokum, 1970). Elevated serum thiocyanate and reduced thyroxin have also been reported in pigs fed cassava peel-based diets containing 96mg HCN equivalent kg^-1 (Tewe, 1994) while elevated placenta thiocyanate transfer and elevated milk thiocyanate were reported from cassava diets containing 500mg HCN equivalent kg^-1 (Tewe and Maner, 1981).

The most consistent report on the levels of dietary cyanogens tolerated in animal feeds is that from European Community countries where cassava has been used in livestock rations for the past two decades. Wood (1992) stated that a level of 100mgHCN equivalent kg^-1 was the highest, which could be tolerated in cassava chips imported into European Community countries. This report agrees with earlier report of Bolhius (1954) which gave a level below 50mgHCN equivalent kg^-1 as safe. According to Bolhius, 50 – 100mgHCN equivalent kg^-1 was set as moderately toxic and above 100mg HCN equivalent kg^-1 as dangerously toxic. Based on the experience from European Community countries; it has been suggested that a level of cyanogens below 50mg HCN equivalent kg^-1 should be the target for cassava based rations. Thus, the cyanide contents of the feed samples under study could be said to be quite high. It is note worthy that the animals in most of the Farms in this study are rarely given veterinary care. Thus, poisoning from cyanogens even if it occurs are not taken into account.           

Since these animals depend solely on plant protein, it is necessary that such feed diets be enriched with protein supplements. The need to supplement cassava diets with methionine and cysteine has been demonstrated for monogastric species (Maner and Gomez, 1973); the role of these supplements in cyanide detoxification for ruminants has been demonstrated (Tewe 1981).    

The mean levels of nitrate and nitrite measured in these feed samples ranged from 25. 5 + 2. 76 – 285. 5 + 12. 70 and 2. 2 +0. 3 – 218. 8 + 13. 42mg kg^-1 respectively. The lethal dose of sodium nitrite for pigs is 88mg kg^-1 body weight (Jones, 1988) and doses of 48 – 77 mg kg^-1 cause moderate to severe but total methemoglobinemia (Norton and Campbell 1990). Nitrite is known to interact with haemoglobin, for ming methemoglobin by oxidation of ferrous iron to ferric state, preventing or reducing the ability of blood to transport oxygen, a condition known as methemoglobinemia (Philips,1971; Bruning-Farnn and Kaneene, 1993; Jones 1993).

Nitrite is also involved in the formation of nitrosamines, compounds known to be carcinogenic, mutagenic, embryopathic and teratogenic in experimental animals (Gray et al; 1979). The ingestion of 8 – 15g of nitrate can cause severe gastroenteritis with abdominal pain, blood in stool and urine, weakness and collapse. Chronic ingestion of smaller doses can cause dyspepsia, mental depression and headache (Magee, 1983). Though pigs are highly susceptible to nitrite poisoning, the results from this study indicate no possible acute effect on the animals fed on them.

In conclusion, the results from this study indicate that the unconventional feeds mainly cassava peels,  sorghum spent grains and wheat offal being used in some animal farms in Umuahia, Abia State, Nigeria contain high levels of cyanide, nitrate and nitrite. The levels of these compounds in animal feed should be of much concern considering their toxicological implications for both animals and humans who consume these animals.

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