Natural or replacer sources of milk in lambs during feeding adaptation: influences on performance, metabolism of protein and lipid and oxidative/antioxidant status

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The exploitation of milking sheep is seen as a sustainable alternative with low initial investment, especially for extensive farming. However, in order to this production system to be viable, it is necessary to pay attention to some factors, such as animal breed, nutrition, sanitation of mammary gland and so on (Selaive‐Vilarroel and Osório, 2014). Suitable milk production requires an adequate nutritional plan. In this sense, the nutrients that compose the milk must be produced in enough quantity and quality for the development of lambs in their first days of life. Considering that milk has commercial purpose, often the lambs are separated from the ewes at an early stage, usually after ingesting colostrum. Therefore, normally lambs are raised on liquid diet until they reach approximately 12 kg of body weight, which occurs after 45–60 days of life (Peruzzi et al., 2015). It requires that the lambs have to be well adapted to the consumption of solid food, in order to ensure the continuity of their growth (Bôas et al., 2003).
The milk production peak in ewes occurs approximately 30‐day post‐partum, and as there is the need of withdrawing lamb shortly after ingestion of colostrum. Because of this management, often ewe's milk is used as liquid compound complement or for artificial feeding. This procedure aims to keep normal rates of development of the lambs until they are ready to be weaned. One of the advantages of artificial feeding is the control of feeds. According to the literature, feeding three times daily is recommended during the first 2 days, followed by twice daily for the next 7 days. After that, the management of feeding can be done only once a day (Selaive‐Vilarroel and Osório, 2014).
Artificial feeding may be made with cow's milk; however, this milk must be increased with corn starch or casein. Even with larger amount, cow's milk can lead to losses in the development of lambs when compared to those fed with sheep's milk (Selaive‐Vilarroel and Osório, 2014). The use of milk replacer (powdered food diluted in water for delivery as liquid diets) is a way of feeding the lambs underwent to early ewe's separation. The formula should be suitable for providing nutrients that is similar to breast milk, thus avoiding economic and production loss, once observed that occurs when artificial feeding lambs, performance decreases. Milk replacer, even being of excellent quality, generates losses on animal development, when compared to natural ewe's milk; however, its use is a strategy that minimizes production costs (Castro et al., 1996; Cordeiro, 2008). There are few commercial milk replacers available for feeding lambs, considering the need for provision of solid food. From the eighth day of life, lambs already begin consuming solid food usually provided at feeders. It is not known how this liquid food exchange influences the lambs development, as well as in their antioxidant levels, lipid and protein metabolism. In the normal milk composition, there are essential nutrients to a newborn, such as lactose providing glucose and galactose, casein (80% of total proteins), albumin, alpha and beta‐globulins and milk fat, which provides free fatty acids, triglycerides and phospholipids (Relling and Mattioli, 2002).
The biochemical composition of the blood reveals the metabolic status of tissues, allowing to evaluate tissue damage, disorders in the function of organ, nutritional status or physiological adaptation to challenges and specific metabolic imbalance (González and Scheffer, 2003). There are few parameters that allow to evaluate physiological changes, for example, the balance between oxidants and antioxidants, blood biochemical levels and lipid peroxidation.
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