Effect of a Diet Supplemented with Nettle (Urtica dioica L.) or Fenugreek (Trigonella Foenum-Graecum L.) on the Content of Selected Heavy Metals in Liver and Rabbit Meat

Simple Summary Herbs can be a good supplement in an animal diet. With the current increase in the use of herbs and herbal preparations as an animal feed additive, it is very important to monitor the contaminants present in plants, i.e., heavy metals, and to study their content in animal tissues. The toxicity of heavy metals, whether essential or not, depends on several factors including the dose in feed (food), a route of exposure, and sex. Hence, it seems advisable to determine the effect of nettle (Urtica dioica L.) leaves and fenugreek (Trigonella foenum-graecum L.) seeds in the feed on the content of selected heavy metals in the liver and meat of the rabbit, and determine differences in sex in metal accumulation. The experiment was conducted at University of Agriculture in Krakow (Poland) in the Experimental Station of the Department of Genetics, Animal Breeding, and Ethology. The research material consisted of Termond White rabbits. Until weaning (on the 35th day of life), young rabbits with does were housed in wooden cages. From weaning until the 84th day of life, rabbits were kept in wire metal cages. Three experimental groups were created: the control group (n = 20; 10 male and 10 female) was fed ad libitum with a complete feed. The animals from group N (n = 20; 10 male and 10 female) were fed a complete mixture with added 1% nettle leaves. The rabbits from the group F (n = 20; 10 male and 10 female) were fed with a complete mixture with added 1% fenugreek seeds. The experiment lasted 7 weeks (from 35th to 84th day of the rabbits' life). All rabbits were slaughtered on the 84th day of age, with an average body weight of 2546 +/- 47 g. Samples of liver were taken during the slaughter. Then, the carcasses were cooled for 24 h at 4 degrees C, and after that time, a sample was taken from the right loin (m. longissimus lumborum) of each carcass. The concentration of heavy metals (Zn, Cu, Ni, Mn, Fe, Pb, Cd) was determined by the atomic absorption spectrometry (AAS). The additives to the feed significantly affected the content of elements in both the liver and the meat of the rabbits (p < 0.05). The highest level of the heavy metals, regardless of the used diet, was recorded in the liver. The meat and the liver of rabbits fed with herbal fodder contained less tested metals than in animals fed with fodder without additives. Moreover, more essential metals were found in the liver of rabbits fed with fenugreek than rabbits fed with nettle (p < 0.05). In the meat and liver of rabbits, the permissible content of cadmium and lead was not exceeded. Additionally, male livers had a significantly higher content of copper and manganese compared to female livers (p < 0.05). This experiment helps to explain the interaction between the heavy metal content of nettle and fenugreek and their content in rabbit meat and liver. The meat (m. longissimus lumborum) and liver of rabbits fed with herbal feed contained fewer tested metals than in animals fed with the feed without additives. Concentrations of toxic metals, i.e., Pb and Cd in liver and meat, were so low that meat consumption does not pose a threat to human health. However, more research is needed to determine how the mechanisms and pathways of heavy metal toxicity act on tissue in which these metals are accumulated. The literature on herbal additives for rabbit feed offers little information on the use of nettle and fenugreek. Both of these herbs are valuable sources of vitamins and minerals. These herbs affect the growth, health, and meat quality of rabbits. They regulate the digestive system, stimulate the appetite, have a positive effect on the functioning of the immune system, and exhibit antibacterial activity. The purpose of the present study was to determine the effect of nettle (Urtica dioica L.) leaves or fenugreek (Trigonella foenum-graecum L.) seeds in the feed on the content of selected heavy metals in the liver and meat of the rabbit. The rabbits were divided into three groups: group C (n = 20; 10 male and 10 female) was fed ad libitum with a complete feed, N group (n = 20; 10 male and 10 female) was fed a complete mixture with 1% added nettle, and group F (n = 20; 10 male and 10 female) was fed with a complete mixture with 1% added fenugreek. The experiment lasted 7 weeks (from the 35th to the 84th day of the rabbits' lives). All the rabbits were slaughtered on the 84th day of age, with a body weight of about 2.6 kg. The concentration of heavy metals (Zn, Cu, Ni, Mn, Fe, Pb, Cd) was determined by the atomic absorption spectrometry (AAS). The additives to the feed significantly affected the content of elements in both the liver and the meat of rabbits (p < 0.05). The highest level of the heavy metals, regardless of the used diet, was recorded in the liver (p < 0.05). The meat (m. longissimus lumborum) and the liver of rabbits fed with herbal fodder contained less tested metals than in animals fed with fodder without additives (p < 0.05). Moreover, more essential metals were found in the liver of rabbits fed with fenugreek than rabbits fed with nettle. In the meat and liver of rabbits, the permissible content of cadmium and lead was not exceeded. Additionally, male livers had a significantly higher content of copper and manganese compared to female livers (p < 0.05). It is important to study the content of heavy metals in the used animal herbal feed additives and their interaction with each other, as they affect the distribution of elements in tissues and organs.