تأثیر سطوح مختلف تغذیه میش‎ها در دوره انتقال بر الگوی مواد معدنی خون بره‌های آن‎ها

Abstract
Introduction: The intricate relationship between minerals and the biological functioning of living organisms has long been a subject of scientific inquiry and practical importance. Minerals, present in small yet crucial quantities, play multifarious roles in satisfying the diverse physiological needs of various species. This is particularly evident in tropical regions, where animals reared under extensive systems often face limitations in their feed, leading to a heightened risk of mineral deficiencies. These deficiencies can have far-reaching consequences, disrupting the performance of livestock production, compromising reproductive functions, and ultimately diminishing the overall profitability of farms (Suttle 2010; Parent et al. 2018). The concentration of minerals within living organisms is influenced by numerous factors, including species, sex, genotype, stage of production (such as lactation), geographical region, prevailing climate, tissue characteristics, and the specific animal management practices employed, including rearing and feeding systems (Alturiqi and Albedair 2012; Hernandez-Castellano 2017; Lin et al. 1989; Ozcelik et al. 2017).
Reducing the availability of feed will cause a lack of mineral substances received by livestock (Haenlein and Anke 2011), and affect the composition and amount of colostrum and milk produced (Norgaard et al. 2008) which increases mortality in lambs (Hashemi et al. 2008).
Therefore, it is necessary to know the amount of minerals in the lambs of animals that are faced with reduced access to feed during the transition period. This study aimed to investigate the effect of feed restriction in ewes during the transition period on the plasma concentration of mineral elements in their lambs.
Materials and Methods: Twenty pregnant fat-tailed ewes were allotted to two experimental groups of Control, (n=10) and feed restriction (Restriction; n=10). After adaptation, during the pre-partum period, the control group from five weeks before parturition to parturition (-5 to -1) was fed with 100% of the balanced ratio. Restriction in the same period during the first to fifth weeks of the study were fed with 100, 50, 65, 80, and 100% of the recommended ration, respectively. The same nutritional program was repeated from the first to the fifth week after parturition for both groups (1 to 5). After lambing, blood samples were taken at zero (parturition), 1, 12, 24, 36, 48 and 72 hours. During the feed restriction (wk 1-wk 5), lamb blood samples were taken weekly. Blood samples were collected at various time points, including parturition, and at specific intervals throughout the study. The samples were kept on ice and centrifuged to harvest the plasma, which was then analyzed for the concentrations of key minerals, including phosphorus (P), magnesium (Mg), potassium (K), sodium (Na), and chloride (Cl), using an atomic absorption spectrophotometer (Hitachi - Science & Technology - Z-2300, Japan). The data were statistically analyzed using the Mixed model procedure of SAS to determine the effects of the feed restriction on the mineral status of the lambs.
Results and discussion: The feed restriction had no significant impact on the plasma concentrations of phosphorus, magnesium, potassium, sodium, and chloride, and the concentrations of these elements did not differ between the two treatment groups. However, sampling time showed that the blood mineral except sodium, changed during the experiment. Blood phosphorus concentration gradually increased from birth (hour 0) to the end of the experiment, and from the second week, the phosphorus concentration showed a significant increase compared to the first week and the early hours of parturition (P<0.001). The sampling times indicated a difference in the blood magnesium concentration in the lambs (P<0.001), where the concentration of this element was low in the early hours of parturition and reached the highest concentration in the final weeks of the experiment (weeks 4 and 5) compared to the early stages of birth in both experimental groups. The results showed that the potassium concentration in both treatment groups followed a specific pattern from birth to the end of the experiment, being almost identical from the early hours of birth (0) to 24 hours in the restricted group and 36 hours in the control group, but then began a decreasing trend (P<0.05) and reached the lowest value at 72 hours after birth compared to the previous hours. The concentration of this element was at its lowest in the first and second weeks after parturition compared to the early parturition and other sampling weeks. From the third week, the concentration of this element showed an increasing trend and reached a higher concentration in the fourth and fifth weeks compared to the first week after birth. With the increase in the age of the lambs, the chloride concentration changed (P<0.001), such that 12 hours after birth, the concentration of this element increased in both groups, and this increase continued until 72 hours after parturition. Contrary to the increasing trend until 72 hours after parturition, the concentration of this element showed a significant decrease in both treatment groups at the end of the first week after parturition (P<0.05), and from the second week, it resumed an increasing trend. The concentration of this element increased from the third week after parturition to the initial concentration at birth. Due to the effective role of minerals in growth, development of bones, general health and optimal functioning of biological systems, the optimal amount of these elements in lambs is of great importance. Different studies have shown that, probably due to the use of reserves of mineral elements in the body that compensate for their deficiency, the clinical symptoms of the lack of these elements are not visible except in very acute conditions (Ramirez-Perez et al. 2000). As previous studies have shown, one of the characteristics of long-tailed ewes is their ability to retain nutrients and influence the growth and health of their lambs, such as colostrum, milk and immunogenic factors (Zarrin et al. 2021; Nouri et al. 2023). Therefore, according to the role of minerals in the growth and development of body tissues, as well as their very important role in health and maintaining the body's antioxidant capacity (Ataollahi et al. 2018), it is concluded that lambs are able to, even in conditions of food restriction, Maintain appropriate plasma concentrations of these elements. The changing the concentration of some of these elements with the increasing age of lambs, especially in the second and third weeks after birth, indicates the physiological changes of the body and, accordingly, the difference in the need for minerals and other nutrients, which was emphasized by Hernández-Castellano et al. (2017).
Conclusion: The study explored the impact of maternal dietary restriction on the mineral levels in the plasma of lambs. The findings revealed that maternal dietary restriction during pregnancy and after birth did not significantly affect the mineral concentrations in the lambs. However, the study highlighted that the mineral concentrations varied with the age of the lambs. This suggests that ewes efficiently utilize their energy and mineral reserves during pregnancy to ensure proper mineral levels in their offspring at birth. Furthermore, the ewes continue to provide minerals to their lambs through colostrum and milk until the lambs become independent. Once the lambs are independent, they acquire the necessary minerals from their feed.