The effect of different levels of zinc on nutrients digestibility, ruminal parameters, nitrogen retention and ruminal protozoa in Mehraban male lambs

Zinc (Zn) is an essential mineral that involved in many vital functions such as growth, DNA synthesis and hormones and enzymes’ structure. So the presence of Zn is necessary in diet of animals. Deficiency of Zn in diet reduces appetite and impairs ruminal fermentation. This study was performed to investigate the effect of different levels of Zn on digestibility and ruminal parameters in Mehraban male lambs.

18 Mehraban male lambs 3-4 months old with an initial body weight of 33.62 ± 2.67 kg were used in a completely randomized design. The basal diet (containing 26.10 mg Zn/kg DM without supplementary Zn) was offered in a total mixed ration twice daily at morning (08:00) and evening (16:00) for 60 days. Experimental treatments included 1) basal diet without adding Zn supplementary (control), 2) basal diet plus 40 mg Zn/kg DM in the form of zinc sulfate and 3) basal diet plus 80 mg Zn/kg DM in the form of zinc sulfate. During the experimental period, feed intake and body weight gain were measured daily and every 15 days, respectively. The rumen fluid was collected from the lambs using the esophagus tube, on the end of the experiment at 3 hours after feeding morning. After determination of pH, rumen fluid was filtered through four layers of cheese cloth, acidificated and then stored at -20 ° C. These samples were used for measurement of total volatile fatty acid and ammonia concentration. Another part of the ruminal fluids (without filtration) was mixed with 18.5% formaldehyde in a ratio of 1: 1 and kept at room temperature away from light for determination of rumen protozoa population. At the end of day 60, 4 lambs from each treatment were randomly transferred to the metabolic cages for 10 days (5 days for adaptation and 5 days for sampling period) for digestibility and nitrogen retention trial. During the sampling period, feed intake, ort, urine and feces excreted for 24 hours were recorded and sampled daily.

The results showed that using different levels of zinc had no significant effect on dry matter, organic matter and crude protein intakes. The digestibility of dry matter and diet ingredients were not affected by zinc supplementation. Nutritive value of the diets (digestible crude protein and total digestible nutrients) did not show significant differences between the treatments. Also, the supplementation of zinc to the basal diet had no significant effect on ruminal parameters (pH, total volatile fatty acids and ammonia concentration), total numbers and observed genus of ruminal protozoa. The highest and lowest numbers of observed protozoa were related to Entodinium and Dasytricha genus, respectively. Supplementation of zinc to the basal diet had no significant effect on retained nitrogen. The amount of nitrogen retention in control and treatments 2 and 3 were 8.95, 8.55 and 8.61 g/day, respectively, which was not affected by zinc supplementation.

Generally, the results of this study showed that the adding 40 and 80 mg Zn/kg DM to the diet of fattening lambs (containing 26.10 mg Zn/kg DM) had no significant effect on measured traits such as feed intake, nutrients digestibility, ruminal parameters and retained nitrogen. It seems that the amount of zinc in the basal diet has provided the animal's needs in this regard and there is no need to adding zinc.