Colostrum is essential for newborn lambs because:

Colostrum is vital for newborn lambs largely because it plays a crucial role in building their immune defenses. The first milk produced by the ewe after giving birth is rich in antibodies, known as immunoglobulins, which are essential for the lamb's health. These antibodies provide passive immunity, protecting the lamb against diseases that it has not yet had the chance to encounter. The immune system of newborn lambs is immature at birth, making them highly susceptible to infectious agents; therefore, the presence of these antibodies significantly reduces the risk of illness and disease during their early life.

Additionally, colostrum contains essential nutrients and growth factors that aid in the development of the lamb's digestive system and overall growth, but the primary importance in this context is its ability to reduce disease incidence. While the other options touch on various aspects of lamb nutrition and health, such as immediate energy supply and growth promotion, the protective effects of colostrum in enhancing immune function are paramount during the critical early days of a lamb's life.