Effects of Organic and Inorganic Zinc Supplements on Performance, Digestibility, Rumen and Blood Parameters in Fattening Lambs

Introduction: To optimize livestock production and health, sufficient amounts of minerals are necessary in the diet. Zinc (Zn) is a trace element and an essential mineral in animal nutrition, and is found in many enzyme systems. The presence of Zn is necessary to ensure the physiological activities of several hormones. In addition, zinc plays an essential role in the metabolism of carbohydrates, proteins, lipids, and nucleic acids, and its deficiency can disrupt several vital cellular reactions. Organic sources of Zn are more biologically active than inorganic sources, and their high accessibility has led to the use of more organic Zn compounds for feeding animals. However, results comparing the bioavailability of organic and inorganic sources of zinc in ruminant nutrition differ. According to the National Research Council (2007), the recommended requirement for Zn in growing lambs is approximately 33 mg Zn/kg DM. The amount of zinc in surface soils of Iran is usually less than 0.8 mg/kg and the plants grown in these soils and used as animal feed are deficient in this element. However, a few studies have been conducted to identify the best source of zinc for growing local lambs; therefore, the present study aimed to compare the effects of supplementing 30 mg Zn/kg DM from common organic sources of zinc (zinc methionine and zinc glycine) with inorganic sources of zinc (zinc sulfate and zinc oxide) on performance, digestibility, blood and rumen parameters in crossbred Zel fattening male lambs.  Materials and Methods: This study was conducted at the research station of the Department of Animal Sciences, Sari University of Agricultural Sciences and Natural Resources, Iran. Twenty-five male lambs aged 3-4 months and with average body weight (25.5 ± 1.4 kg) were assigned to five treatments with five repetitions, as a completely randomized design for 70 days, including 2 weeks of adaptation to basal diet and 8 weeks of data collection. The experimental treatments were as follows: 1) basal diet without zinc supplement (containing 19.39 mg Zn/kg DM) as the control group, 2) basal diet + 30 mg Zn/kg DM as zinc methionine, 3) basal diet + 30 mg Zn/kg DM as zinc glycine, 4) basal diet + 30 mg Zn/kg DM as zinc oxide, and 5) basal diet + 30 mg Zn/kg DM as zinc sulfate. Dry matter intake, daily weight gain, and feed conversion ratio were determined. The acid-insoluble ash (AIA) internal indicator method was used to determine the apparent digestibility of feed nutrients. Blood samples were collected on the 70th day prior to the morning meal. To determine rumen parameters, rumen fluid was collected 3h after morning feed consumption. The chemical compositions of the experimental samples, including (dry matter, organic matter, crude protein, ether extract, NDF, and ADF) were measured according to standard methods.Results and Discussion: The results showed that total weight gain, daily weight gain, and feed conversion ratio were significantly improved in lambs received organic zinc supplements (zinc methionine and zinc glycine) compared to the control group (P<0.05). The apparent digestibility of organic matter in the diets supplemented with zinc methionine and zinc glycine was significantly higher than that of the other treatments (P<0.05). The digestibility of NDF and ADF in lambs receiving zinc methionine, zinc glycine and zinc oxide was improved compared to the treatment containing zinc sulfate and the control group (P<0.05). Serum glucose and zinc concentrations were significantly higher in all lambs receiving zinc supplements than the control group (P<0.05), but there was no significant difference in serum albumin, cholesterol, urea nitrogen, copper and iron concentrations between experimental treatments. Feeding zinc supplements had no effect on pH, ammonia nitrogen and the concentration of volatile fatty acids in the rumen fluid.Conclusion: The results of this study show that the addition of 30 mg Zn/kg DM from organic zinc supplements (zinc glycine and zinc methionine) and inorganic zinc supplements (zinc sulfate and zinc oxide) meets the needs of growing lambs fed a basal diet containing 19.39 mg Zn/kg DM. The use of zinc supplements in the diet of fattening lambs improved growth performance, serum zinc and glucose concentrations, and crude fiber digestibility. There were no differences among the treatments supplemented with organic sources of zinc.