عنوان مقاله [English]
Introduction: Sheep has played an important role in meat production and income generation in Iranian farming systems. Their profitability, however, is highly depended on nutrient supply. Drinking water is major nutrient that is responsible for different utilization of nutrients and thereby productivity and gain of animals in most parts of the world. Inadequate water and its quality such as salinity, acidity, and toxic elements depress the biological, physiological process and performance of sheep. Iran has a different type of Agro-ecological climate but most part of this country is under arid or semi arid condition and thus face to shortage of water. Bluchi sheep is the most important breed which is well adapted in harsh marginal arid in the east region of Iran, however, little information is available regarding of the mechanism of adaptation in this breed for biological process to allowing them to cope during water restriction in this zone. Therefore this experiment was conducted to investigate some electrolytes and blood metabolites and hormones under the influence of different levels of water availability and the ability to tolerate water restriction in Baluchi lambs.
Materials and Methods: This study was conducted during May-June 2013 at the Baluchi sheep research center (Abbas Abad) in Northeast of Iran. Twenty-one single lambs, (90 ± 4 days old and 26.7 ± 2.2 kg BW) were used in this study. Lambs were randomly subjected to three levels of water restriction (seven lambs per group). Lambs in control group, allowed to drinking water freely. For the second treatment, the water supply to the lambs were restricted to 72% of their average daily intake and for the third treatment, water intake was restricted to 44% of their average daily intake. The whole experiment period was 49 days and was divided in 3 periods with 14 days adaptation.. The three time periods were including, 7 days for the stepwise water reduction period, and 14 days fixed limit to the amount of 72% and 44% of their average intake for treatment 2 and 3 and during last period (14 days) all groups had free access to water. The sheep were allocated to individual feeding pens and feed were provided ad libitum. Weight gain, blood metabolites and electrolytes (glucose, triglycerides, creatinine, blood urea, cholesterol, total proteins, cortisol, hematocrit, blood hemoglobin, Na+,Ca2+, K+ were determined on 1, 7, 21 and 35 days of experiment. The data from experiments were analyzed using Minitab and GLM procedure and for comparison of means Duncan test was applied.
Results and Discussion: The obtained results indicated that feed intake, daily weight gain and the ratio of water consumption to feed intake in treatments 2 and 3 in compare with control group was statistically different. The results showed that there was a direct relationship between the reduction in water consumption and feed intake. It seems that this weight loss in treatments 2 and 3 can be due to a combination of reduced feed intake and loss of body water. Additional dehydration led to increase blood concentration creatinine, blood urea in compare with the control group. High blood urea and creatinine may be due to an imbalance in the production and disposal of these substances by the kidneys and fecal .Water restriction led to increased concentration of plasma sodium than the control group, however this increase was not significant. Treatment 3, on day 21, compared with other treatments,was an exception and one of the possible reasons for this can be due the influence of the hormone aldosterone and ADH on the kidneys. Hematocrit and hemoglobin in the blood tend to rise by water restriction but this will not led to significant differences between treatments. Except the hemoglobin on day 21 between treatments 3 with other treatments, significant differences were found which can be due to reduced blood plasma volume because of dehydration lambs. Significant differences in blood cholesterol levels were observed between treatments 3 and others on day 21 which probably this increase may be related to mobilization of fat tissue in lambs that are encountered with reducing water consumption.
Conclusion: The overall results showed that water restrictions could lead to a significant reduction in dry matter intake and daily weight gain in Baluchi lambs. In addition, results showed that Baluchi lamb has potential to withstand under water restriction up to 44% of their average daily water intake without significant changes in blood electrolytes. This breed can survive and adopt under arid conditions which is common in some desert area in Iran.