Dietary Supplementation with Yucca Schidigera Extract Alleviates Heat Stress-Induced Growth Restriction in Chickens

Global warming threatens to adversely impact livestock and poultry productivity. Animals raised in hot climates exhibit elevated concentrations of glucocorticoids, which reduce their growth. Few nutritional means are available to effectively mitigate production problems brought about by heat stress. We used growing chickens to test the hypothesis that Yucca schidigera extract (Yucca; containing steroidal saponins which are natural structural analogues of corticosterone and cortisol) may ameliorate negative effects of heat stress on animal growth. Beginning at 35 d of age, male broilers had free access to a basal diet supplemented with 0, 120 or 180 ppm Yucca. Chickens were assigned randomly to their treatment groups (24/group; 6/pen). The maximum ambient temperature of the chicken housing facility was naturally elevated gradually during 1 wk, which was 27, 29, 32, 35, 36, 37, and 37^oC, respectively, on d 1, 2, 3, 4, 5, 6 and 7 of the trial; the corresponding average ambient temperatures were 18, 21, 23, 27, 29, 31, and 31^oC, respectively. Composition of the basal diet (as-fed basis) was: corn grain, 64.79%; soybean meal, 25.91%; glycine, 0.50%; DL-methionine (98%), 0.21%; L-lysine-HCl, 0.08%; blended fat, 4.98%; limestone, 1.57%; BIOFOS-16, 1.28%; salt, 0.38%; trace mineral premix, 0.05%; and vitamin premix, 0.25%. Body weights of individual chickens and the amounts of feed/pen at the beginning and end of the study were measured. Data were analyzed using one-way ANOVA and the Student-Newman-Keuls test. Results are expressed as means±SEM. During the 1-wk experimental period, birds in the control group exhibited a weight gain of 264±14 g/wk per animal (n=24), an average feed intake of 912±20 g/wk per animal (n=4), and a gain:feed ratio of 0.284±0.013 (n=4). Yucca supplementation did not affect (P>0.05) feed intake by birds, but enhanced (P<0.05) their weight gain by 38-43% and feed efficiency by 46-52%, compared to controls. In a separate experiment, Yucca supplementation matched the previously described treatments, but the chickens were housed at an average ambient temperature of 24^oC (maximum=27^oC); birds in the control group exhibited a weight gain of 756±28 g/wk per animal (n=24), an average feed intake of 1124±27 g/wk per animal (n=4), and a gain:feed ratio of 0.675±0.022 (n=4); Yucca supplementation had no effect on their feed intake or growth under the experimental conditions without heat stress. We suggest that by antagonizing glucocorticoids, Yucca ameliorates the adverse effects of heat stress on chicken growth and feed efficiency. (Supported by AGROIN Baja Agro International, Mexico.)