According to Emmans (1991) the three key parameters in the feed are protein, energy, and minerals. The birds are selecting foods with a nutritional purpose. This is strengthened if their food intake over long periods is compared with the amount which is selected against when choice is given. Flavours can initially influence intake and preference but soon lose this ability as the birds learn that there is no nutritional implication in the different flavours (Balog and Millard 1989). Some flavour preferences are very strong, however, and chickens will not drink solutions of saccharin, salt or quinine but take readily sucrose (Jacobs and Scott 1957), glucose (Engku and Forbes 1989) and citric acid (Balog and Millar 1989). In general, visual cues are probably more useful than oral cues in the chicken.
It has been observed that when a new diet formulation is introduced, or a new type of food is presented, animals will often refuse to eat the food for a period of time or intake is reduced (Jones 1986; Launchbaugh et al 1997). Furthermore, it has been noted that this may also occur when a new batch of the same diet formulation is presented to broiler chickens or turkeys. This has been studied by Haskell et al (2001), who found that food consumption was significantly lower for experimental groups compared to control groups on all days from the day of change onward in broiler chickens.
Bennet (2003) reported that if vitamin and mineral premixes are placed in separate feeders, some birds might not eat them because they will not like the taste, while other individuals may over-consume them and suffer toxic side effects. The same author concluded that when mixing whole grain, supplement and limestone together into a traditional laying hen diet that is fed in one feeder, not more than 50% of the diet should be as whole grain. The rest of the grain in the feed should be ground because at higher levels of inclusion of whole grains the hens sometimes have trouble finding the supplement among all the grains.