Document Type Doctoral Thesis Author Luseba, Dibungi URN etd-03232005-140434 Document Title The effect of Selenium and Chromium on stress level, growth performance, selected carcass characteristics and mineral status of feedlot cattle Degree PhD Department Production Animal Studies Supervisor
Advisor Name Title Prof PA Boyazoglu Supervisor Keywords
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Date 2001-07-06 Availability unrestricted AbstractFeedlot cattle are subjected to numerous stresses that impede on their growth performance and carcass quality. Stress also depletes the animal body with its nutrients subsequently leading to deficiencies. The aim of this study was to investigate the effect of selenium (Se) and chromium (Cr) on stress and subsequently on growth performance, carcass characteristics including meat colour and liver tissue minerals. It is thought that Se, as anti-oxidant and Cr effectiveness in glucose metabolism might be effective on these production parameters. Four experiments were conducted for that purpose.
The first experiment consisted in the assessment of the response of animals to dietary supplement of 0.3 mg.kg –1 DM Se and 0.3 mg.kg –1 DM Cr in a 3x4 factorial design. Seventy-two steers were allocated to 12 pens of six animals each. The results showed no statistical difference in blood cortisol levels on day 0 (d 0). On d 04, cortisol concentrations were lower than on d 0 (P≤0.05) except for treatment “Se X Cr combination” (SEL/CHR). On d 42, the values were high again except for SEL/CHR that had very low cortisol values (P≤0.05). The plots of blood glucose concentrations were almost similar to those of blood cortisol. There was no carry-over effect of alleviation of stress on performance. It was suggested that the animal type used was not appropriate for feedlot. The carcass characteristics were not statistically different. Meat pH measurements were similar but the differences between pH taken on slaughter day (pH 1) and 24 hours later were different (P≤0.05) for CHR and SEL/CR. This suggests that Cr because of its effect on glycogen storage is more effective in maintaining an appropriate meat pH fall and subsequently a longer meat shelf life. The liver tissue mineral status of the animals was normal. However, supplemental Se increased significantly (P≤0.05) the liver tissue Ca, Mg, Co and Mn while Cr decreased the concentrations of Ca, Mg and Co. Selenium was positively correlated to Cu and P while Cr was negatively correlated to Co. There was no relationship between liver tissue mineral and production parameters.
The second trial dealt with the meat colour. Twenty-four prime rib samples were randomly collected from the animals described in Experiment-1 in a 2x3x4 factorial design (two samples per pen). Samples were treated as described by Buys et al. (2000). The readings of metmyoglobin as an indication of meat discoloration were not different between treatments. However, the ratio of metmyoglobin over the rest of meat components showed that supplemental chromium (CHR) had a lower value (P≤0.05). Chromium might have permitted a better glucose utilisation and glycogen storage in muscle of live animal. This might have maintained an adequate drop in meat pH subsequently lowering the lipid peroxidation and preventing the accumulation of metmyoglobin.
The third trial was aimed to verify the findings of Experiment-1 and to compare the effect of Cr sulphate to that of high-Cr yeast and their interactions with Se. Seventy-two weaner calves were allocated to six pens of 12 animals each. Cortisol and glucose concentrations were similar on d 0. On d 04 treatments SEL and Cr sulphate (ICH) had low values (P≤0.05) while on d 42, combined Se and organic Cr (SOC) tended to have low values. These results and those from Experiment-1 showed that Se is efficient in the alleviation of stress in the adaptation days on feed while combined Se and Cr treatments are more efficient in the production phase. The organic Cr is not more effective than Cr sulphate in alleviation of stress. The combination “Se and inorganic Cr” (SIC) had higher ADG and better P-FCR (P≤0.05) and it tended to have better carcass characteristics. Mineral concentrations were normal and similar. As seen in Experiment-1, treatment SEL highly (P≤0.01) increased liver Ca concentration. Chromium and most other mineral concentrations were not affected by supplemental Cr. Overall, organic Cr was not superior to Cr sulphate.
Previous experiments indicated that combining Se to Cr might give better results. The fourth trial aimed to find the best combination. Thirty-six weaner steers were allocated to six pens of six animals each. There was no difference in cortisol levels but a tendency (P=0.1) was noted on d 47 with combined “sodium selenite x Cr sulphate” (ISIC) and “high-Se yeast x Cr sulphate” (OSIC) having low values. Blood glucose values were not different. Blood cortisol concentrations were positively correlated to glucose on d 47. Selenium and Cr did not significantly affect the overall growth efficiency of the steers but during the adaptation period, the controls and OSIC treatments had better ADG and PFCR. Treatments ISIC and “sodium selenite x organic Cr” (ISOC) had similar live weight whilst treatment OSIC had higher live weight than “organic Se x organic Cr” OSOC. The combined organic forms were better than the inorganic ones. The carcass parameters were not affected. However, ISIC tend to have higher carcass mass than ISOC; similarly, OSIC tended to perform better than OSOC. Higher liver tissue Se and Cr were due to supplemental Se and Cr (P≤0.05). Treatment ISIC had the highest liver Se levels (P≤0.05) in this experiment and in Experiment-3. Selenium did not interact with other elements. In contrast, Cr was negatively correlated to Fe and Mn and positively to Mg. Chromium tends to be negatively correlated to other minerals. Precautions might be recommended when feeding excessive Cr because Cr does not augment the liver concentration of other minerals (Chang et al., 1992; Anderson et al., 1997).
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