Phase 1 nursery diet
The phase 1 diet is typically fed to pigs from weaning at approximately 12 lb until approximately 15 lb of body weight. During this phase, it is important to provide high-quality feed ingredients to stimulate feed intake and match the digestive capabilities of weanling pigs.
Newly weaned pigs are able to easily digest lactose and specialty proteins but have limited ability to digest plant proteins and utilize fat. Pigs also have a hypersensitivity reaction to soybean meal induced by allergenic proteins and indigestible carbohydrates of soybeans. Pigs experience a transitory period of poor nutrient absorption and low growth performance following the first exposure to a diet with high amounts of soybean meal (Li et al., 1990). The effects are transitory and pigs develop tolerance after 7 to 10 days (Engle, 1994). The best approach to alleviate this problem is to expose weanling pigs to increasing levels of soybean meal in nursery diets to allow pigs to gradually overcome the hypersensitivity reaction. The early exposure to soybean meal reduces the potential for delayed-type hypersensitivity reaction and allows for greater inclusion levels in subsequent nursery diets without an impact on growth performance.
Soybean meal is commonly included at up to 16 to 18% in the phase 1 diet. Other specialty protein sources often used in combination are fermented soybean meal, enzyme-treated soybean meal, soy protein concentrate, spray-dried plasma, or fish meal, among others. Typically, the sources are used in combination to achieve the adequate amino acid profile in the diet and because most specialty protein sources cannot be the sole protein source in the diet without affecting palatability or performance.
Lactose is the carbohydrate component derived from milk and provides an easily digestible source of energy for pigs. The phase 1 diet typically contains around 18% lactose to improve growth rate of weanling pigs (Tokach et al., 1995; Mahan et al., 2004). Common sources of lactose are crystalline lactose, whey permeate, and dried whey, with whey products also providing a highly digestible source of amino acids. However, the addition of lactose products in the diet influences feed processing. The use of high levels of lactose in pelleted diets can increase friction during the pelleting process; and in meal diets can increase bridging and reduce flowability in bins and feeders.
Fat is not easily utilized by weanling pigs for growth performance. In the early post-weaning period, weanling pigs seem to require a more digestible fat source rich in unsaturated and short-chain fatty acids for an efficient energy utilization (Gu and Li, 2003). Vegetable oils like soybean oil and coconut oil are high quality sources of energy for weanling pigs (Weng, 2016), but cost often limits the use in nursery diets. Animal fat sources of good quality like choice white grease or beef tallow are usually more cost-effective to use in nursery diets. The addition of 3 to 4% fat is mainly used to improve the pelleting process of phase 1 diets with high levels of lactose.