Reduced Dietary Protein and Essential Amino Acids Impair Growth Performance and Increase Lysine Sensitivity in Broiler Chickens

Nutrition plays a fundamental role in poultry production. Developing high-quality diets that ensure positive feed perception by birds is a key strategy for enhancing production performance within the industry. This study evaluated the effect of crude protein (CP) and four essential amino acid (AA) reductions on broiler chickens' growth performance and taste sensitivity for Lysine, Methionine, Threonine, and Tryptophan. Sixty-four one-day-old male broiler chickens (Ross 308) were exposed to four dietary treatments consisting of a balanced (control) diet with a total inclusion of CP and Lysine, Methionine, Threonine, and Tryptophan (T1); diets with a 30 g/kg reduction in CP maintaining 100% exogenous incorporation of the four aforementioned AAs (T2); diets with a 30 g/kg reduction in CP and 50% exogenous incorporation of the same four AAs (T3); and diets with a 30 g/kg reduction in CP with no exogenous incorporation of the four previously mentioned AAs (T4). After 7 days of acclimatization to the diets, the birds were offered Lysine, Methionine, Threonine, and Tryptophan at eight concentrations (0.1, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, and 3.5%) each for 4 h/day in a double-choice test for 32 days to determine the preferences and sensory-motivated intake (SMI) of the birds. During the 39-day trial, the birds in the T4 group showed a lower (<i>p</i> < 0.050) average daily feed intake (ADFI), average daily gain (ADG), feed conversion ratio (FCR), and body weight (BW) than the birds of the rest of the treatments. No significant effects of the different dietary treatments, CP content, or AA levels were observed on the preferences or SMI of the birds (<i>p</i> > 0.050). However, differences were found in the preferences and SMI between birds from the different treatments when evaluating the treatment × AA × concentration interaction (<i>p</i> < 0.050), reflecting that dietary treatments generate changes in the consumption behavior of birds in response to the delivery of AAs at different concentrations. The preference and SMI thresholds for Lysine decreased in the birds in the T4 group, while the thresholds for Methionine and Tryptophan increased compared to the birds in the control group (<i>p</i> < 0.050). We concluded that the reduction in CP and AAs in the diet of broiler chickens affects their productive parameters and increases their taste sensitivity, which was reflected in lower weight gain and feed conversion efficiency, along with increased preferences and higher SMI values in the birds exposed to diets with more significant nutritional deficits.