Comparative study of the inclusion of sunflower hulls in the diet on growth performance and digestive tract traits of broilers and pullets from 0 to 21 days of age

Two experiments (Exp.) were conducted to evaluate the effects of inclusion of 3% sunflower hulls (SFH) in the diet of broilers and pullets, in substitution of the whole diet, on growth performance, total tract apparent retention (TTAR), gastrointestinal tract (GIT) traits, and cecal short chain fatty acid (SCFA) concentration from 0 to 21 d of age. The main objectives of the experiments were to ascertain if broilers and pullets responded in similar way to the inclusion of additional fiber in the diet. Experiment 1 had four treatments organized as a 2 × 2 factorial with 2 chicken lines (female broilers vs. Brown pullets laying hens) and 2 levels of SFH inclusion (0 vs. 3%). In this experiment, both chicken lines received a commercial broiler diet that contained 2,980 kcal AMEn/kg, 22.2% crude protein, 1.25% digestible Lys, and 8.7% NDF. Birds were housed in groups of 10 in 28 batteries according to chicken line, and placed in an environmentally controlled room. Feed in mash form and water were offered for ad libitum consumption throughout the experiment. The variable studied were growth performance, TTAR, and GIT traits at 9 and 21 d of age, and SCFA production in the cecum and ileal morphology at 21 d of age. Growth performance was greater (P<0.001) and TTAR of nutrients and AMEn of the diet were better (P=0.097 to P<0.001) in broilers than in pullets. Excreta moisture was higher (P<0.01) in pullets than in broilers at 9 d of age but an opposite effect (P<0.05) was observed at 21 d of age. In absolute terms, all the organs of the GIT were heavier (P<0.001) and the small intestine (SI) and cecum were longer (P<0.001) in broilers than in pullets. At 21 d of age, the relative weight (% BW) of all organs of the GIT (P<0.001) and relative length (cm/kg BW) of SI and cecum (P<0.01) were greater in pullets. Gizzard pH (P<0.001), total SCFA concentration in the cecum (P=0.098), and villus height (P<0.001), crypt depth (P<0.001), and villus height to crypt depth ratio (P<0.001) of the ileal mucosa were greater in broilers. Dietary SFH increased gizzard weight and reduced gizzard pH (P<0.001) at both ages. An interactions between chicken line and SFH inclusion on absolute weight of the empty gizzard and on the fresh digesta content of the gizzard were detected; at both ages inclusion of SFH increased (P<0.05) both weights in broilers but not in pullets. Inclusion (wt:wt) of 3% SFH did not affect bird performance, excreta moisture, or the concentration and profile of SCFA in the cecum and in fact, increased the AMEn content of the diet (P<0.05). In conclusion, broilers showed better growth performance, nutrient retention, and ileal absorptive capacity tan pullets. The inclusion of 3% SFH increased gizzard weight, reduced gizzard pH, and improved the energy content of the diet. In Exp. 2, the variables studied, the design, and the experimental controls, were similar to those indicated for Exp. 1 with the main difference being the type of control diet used. In this experiment, both chicken lines received a commercial pullet diet that contained 2,850 kcal AMEn/kg, 19.1% crude protein, 0.98% digestible Lys, and 10.1% NDF. Growth performance was greater (P<0.001) in broilers than in pullets at all ages. Excreta moisture was higher (P<0.001) in broilers at 21 d but an opposite effect was observed at 9 d of age. An interaction between chicken line and SFH inclusion on excreta moisture was detected at 21 d of age; the inclusion of SFH reduced (P<0.05) excreta moisture in broilers but not in pullets. Nutrient retention (P<0.001) and AMEn of the diet (P<0.01) were higher in broilers than in pullets at 9 d of age but at 21 d of age the only difference detected was for N retention (P<0.001). In absolute terms (g or cm) broilers had heavier (P<0.001) digestive organs and longer SI and cecum than pullets. In relative terms, however, the GIT (P=0.062), proventriculus (P<0.001), gizzard (P<0.001), and pancreas (P<0.01) were heavier at 21 d, and the SI and cecum were longer (P<0.001) at both ages in pullets. The inclusion of SFH did not affect growth performance, excreta moisture, or organ weight at any age but increased the AMEn of the diet at 21 d of age (P<0.05). Also, SFH inclusion increased the absolute length of the SI at 21 d of age and that of cecum at both ages (P<0.05). The pH of the different organs of the GIT and the concentration of SCFA in the cecum were not affected by chicken line or SFH inclusion. Villus height and crypt depth were higher (P<0.001) in broilers than in pullets but were not affected by SFH inclusion. In summary, broilers showed greater growth performance and nutrient retention at 9 d of age and ileal absorptive capacity at 21 d than pullets. The dilution of the diet with 3% SFH did not affect chick performance, but improved the AMEn of the diet in both chicken lines at 21 d of age. In conclusion: 1. Broilers growth faster and were more efficient than pullets. Feeding a broiler diet, increased BW gain and improve growth performance in pullets. 2. Nutrient density, main cereal (corn vs. wheat and barley), and fiber content of the diet can affect the physiological response of chicken lines to inclusion of a moderate amount of insoluble fiber in the diet. 3. Nutrients retention and AMEn of the diets were higher for broilers than for pullets. Higher digestibility of N was noticeable in broilers than in pullets at all ages. 4. In absolute terms, all GIT organs were heavier and SI and ceca were longer in broilers than in pullets. However, often adverse results were observed in relative terms. The gizzard was more developed and heavier in broilers than in pullets. The pH of the gizzard, affected by fiber content of the diet. 5. Short chain fatty acid concentration in the cecum was 11% higher in broilers than in pullets. Diet composition can modify the fatty acid proportion in the cecum. 6. Ileal VH and CD of the ileum were greater in broilers than in pullets. However, the inclusion of SFH did not affect VH, CD, or VH:CD ratio of birds. 7. The inclusion of SFH (wt:wt basis), improved the AMEn of the diet without any negative effects on growth performance of the birds. These effects were more pronounced when SFH was included in the broiler diet than when included in the pullet diet. 8. Lack of interactions in many of traits studied in main traits studied such as performance and organ size indicated that existing data available for broilers would be generalized to a certain degree to pullets.