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 (p < 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 (p > 0.050). However, differences were found in the preferences and SMI between birds from the different treatments when evaluating the treatment × AA × concentration interaction (p < 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 (p < 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.

Environmental enrichment is key for improving the broiler welfare in intensive production systems. This study lasted for 43 days and evaluated the effects of physical and social enrichment on broiler welfare. A total of 96 one-day-old male broilers were divided into two treatments: control treatment, provided with physical enrichment (n = 48) including perches, platforms, and straw bales; and social treatment (n = 48), involving regular positive interactions with a human. The behavioral repertoire, footpad health, taste preferences for sweet and umami compounds, affective states (through tonic immobility and attention bias tests), and growth performance were evaluated. No effects were found for feeding, drinking, locomotion, lying, or standing behaviors, although differences were observed at specific time points: the Social group had more feeding time on day 21 (p = 0.046), while physical treatment showed reductions on days 28 and 35 (p < 0.001). The Social group showed increased drinking on day 42 (p < 0.001), reduced locomotion (p = 0.022), and increased lying (p = 0.046) on day 42. Foraging was higher in the Social group (p = 0.027), but preening showed no differences. Footpad lesions showed no significant differences. The Control group preferred sucrose 100 mM (p = 0.022), but no preference for MSG 300 mM was observed. With regard to tonic immobility, the Control group showed a tendency towards larger durations (p = 0.078), indicating a potential increase in fearfulness. In the attention bias test, although the freezing behavior increased, the latency to begin feeding was shorter in the Social group (p < 0.001), suggesting an improved affective state. Lastly, no significant differences were observed for any of the growth parameters, including average daily feed intake, average daily gain, feed conversion ratio, or final body weight, indicating that the Social group maintained productivity. This approach provides a practical solution for improving the quality of life for broilers in intensive systems.

Due to substantial differences between studies, the understanding of avian taste perception remains incomplete. Also, studies on chicken taste preferences have mainly focused on measuring consumption differences, neglecting consumption behaviour patterns. This study investigated how age, the compound delivery matrix, and the number of birds per pen affect broiler chicken preferences and consumption behaviour, and established their preference values for four taste compounds. Ninety-six one-day-old male broiler chickens (Ross 308) were divided into two age groups (initial: days 7–23; final: days 26–42), with two compound delivery matrices (water or ground wheat) and two numbers of birds (one or two chickens per pen), following a 2 × 2 × 2 factorial design. Four taste compounds (sucrose, monosodium glutamate (MSG), L-lysine, and calcium carbonate) were tested at different concentrations. Preferences were assessed at 2, 4, and 8 h post-test, along with recording various behavioural parameters. Initial-stage birds showed higher (p < 0.001) preference values, time of approach (TA), number of bouts (NB), duration of bouts (DB), and number of pecks (NP) than final-stage birds. Birds exposed to a water matrix also exhibited higher (p < 0.001) preference and NB, while those exposed to a ground wheat matrix showed a higher (p < 0.001) NP. Pens with a pair of birds had a higher (p < 0.003) 2 h preference, TA, NB, DB, and NP, than pens with a single chicken. Chickens showed significant preference values for 100 mM sucrose at 2 h (p = 0.025), 150 mM MSG at 4 h (p = 0.026) and 8 h (p = 0.013), and 300 mM MSG at 2 h (p = 0.013). We concluded that all the variables evaluated influence broilers’ taste preferences and consumption behaviour during selection tests. Future studies should prioritize including chickens in the initial stage of the production cycle, testing them in pairs or groups, and delivering compounds via a liquid matrix.

Umami taste compounds are perceived in broilers through taste buds that detect peptides and amino acids, which can positively or negatively affect their feeding behavior. In this study, we evaluated the intake behavior for four essential amino acids (Lysine, Methionine, Threonine, and Tryptophan) in chickens. Sixty-four one-day-old male birds (Ross 308) were used. For 16 days during the early stage of the birds, two-choice preference tests were performed, in which 16 combinations composed of four amino acids in four concentrations (0.1 to 1.5%) diluted in water were evaluated, which were supplied in contrast to the delivery of water (a neutral compound) to a pair of birds in a pen for 4 h of administration after a prior 1 h fast. Amino acid solutions such as Threonine and Tryptophan tended to show less preference at the highest exposed concentrations (1.5%) concerning drinking water, which was confirmed in the case of Threonine when performing a sensory-motivated intake analysis (SMI). The opposite occurred with Lysine (1.5%), which numerically showed a higher preference ratified by SMI and acceptability analysis concerning water and other concentrations of the same amino acid, respectively. When palatability was measured with pecking cluster size, no significant differences across amino acid concentrations were observed, which is probably attributed to short recording periods and differences in solution intake behavior between chickens and previous experimental models such as rats. The results reinforce the notion that it is necessary to standardize feeding behavior tests in birds according to their feeding patterns and nutritional needs.

Dietary composition and the intestinal nutrient availability modulate metabolic pathways linked to nutrient sensors, generating molecular adaptations that influence birds’ feeding behavior and performance. The present study investigated the impact of reducing dietary crude protein (CP) and the essential amino acids (AA) lysine (Lys), methionine (Met), threonine (Thr), and tryptophan (Trp) on mRNA expression of the nutrient sensors T1R1 and T1R3, as well as on feeding behavior and productive performance in broiler chickens. A total of 64 one-day-old male Ross 308 broiler chicks were allocated to four dietary treatments: a control diet meeting recommended CP and AA levels (target live weight < 2.0 kg; T1); a diet with 3% reduction in CP and full exogenous AA supplementation (T2); a diet with 3% reduction in CP and 50% AA supplementation (T3); and a diet with 3% reduction in CP without AA supplementation (T4). After a 7-day adaptation, a 32-day single-choice test offered an AA matrix, containing Lys, Met, Thr, and Trp at eight concentrations (0.1–3.5%) for 4 h/day to assess acceptability and palatability. On day 39, six birds per treatment were sampled from the duodenum, jejunum, and ileum for quantitative PCR. Relative to controls, birds fed diets T2, T3, and T4 displayed lower feed consumption, daily gain, feed conversion ratio, and body weight (p < 0.050). These diets downregulated T1R1 and T1R3 mRNA expression (p < 0.001), indicating a molecular adaptation to the nutritional environment, and increased acceptability but reduced palatability (p < 0.050), suggesting altered feeding motivation and sensory perception. Overall, CP and AA reduction impaired performance and modified nutrient-sensor expression and feeding behavior.