Yeast such as inactivated Candida utilis produced from lignocellulosic biomass from underutilized wood co-products as a second-generation sugar source is a potentially sustainable protein feed ingredient in diets for piglets. This study aimed to evaluate the effects of C. utilis added to diets for weaned piglets on growth performance and digestive function when replacing main protein sources. Forty-eight piglets weaned at 30 days of age, with a mean starting weight of 11.06 ± 0.84 kg were fed one of four dietary treatments for 28 days: a conventional control diet with soybean meal, fishmeal, rapeseed meal, and potato protein or one of three experimental diets containing 10, 20 or 40% crude protein (CP) from yeast (CU10, CU20, and CU40, respectively). Adding yeast to diets did not affect growth performance compared with the control. The diet with 40% CP from C. utilis had higher apparent total tract digestibility (ATTD) of CP compared with the control (P = 0.034) and higher ATTD of ash (P < 0.001) compared with the control. The ATTD of neutral detergent fiber decreased in the CU40 diet compared with the control (P = 0.006). The apparent ileal digestibility (AID) of ash increased (P = 0.001) in the CU40 diet compared with the control, while the AID of CP and amino acids was unaffected. Villi-height increased in jejunum (P = 0.007) and ileum (P = 0.047), and villus-height: crypt-depth ratio increased (P = 0.001) in jejunum of piglets fed the CU40 diet compared with the control. Fecal dry matter increased linearly with increasing levels of C. utilis in the diets at day 7 after weaning (P = 0.001) and was higher for the CU40 group compared with the control group at day 21 after weaning (P = 0.027). Trypsin activity and messenger RNA expression of nine genes encoding for nutrient transporters in the jejunum did not differ among diets. Collectively, the results indicated that C. utilis can replace 40% of CP from the main protein sources traditionally used in diets for weaned piglets while maintaining growth and improving digestive function.

Europe is heavily dependent on imported feed protein sources such as soybean meal ( SBM ); thus, investigating local sustainable alternatives is crucial to increase self-sufficiency. This study evaluated the effects of the inactivated yeast Cyberlindnera jadinii grown on local lignocellulosic sugars on the growth performance and digestive function of Ross 308 broiler chickens. A total of 1,000 male chicks were allocated to 20 pens. There were 5 replicate pens with 50 birds each, from 1 to 30 D after hatch. The birds were offered one conventional wheat–oat–SBM–based control diet and 3 diets with increasing levels of C. jadinii replacing 10, 20, and 30% of dietary crude protein ( CP ), whereas SBM levels were gradually decreased. The feed intake and weight gain of the birds decreased linearly, and feed conversion ratio increased linearly ( P < 0.01) with increasing dietary levels of C. jadinii . Nevertheless, growth performance and feed intake were similar between the birds fed with control diets and diets containing 10% CP from C. jadinii in the starter and grower periods. The apparent ileal digestibility ( AID ) of dry matter, crude fat, organic matter, and carbohydrates was higher in control diets than in diets with 30% C. jadinii CP ( P < 0.05) and decreased ( P < 0.01) with incremental levels of dietary C. jadinii. Regardless, the AID of CP, starch, ash, and phosphorus was unaffected. Ileal villus height on day 10 was maintained in birds fed with diets containing 30% C. jadinii CP compared with the birds fed with control diets but was lower for birds fed with diets containing 10 and 20% C. jadinii protein ( P < 0.05). To conclude, up to 10% C. jadinii CP can replace SBM CP in broiler chicken diets, maintaining growth performance and digestive function, whereas higher levels of C. jadinii may decrease bird performance. Altogether, this suggests the potential of C. jadinii as a local-based protein source in broiler chicken diets, contributing to a more sustainable feed.

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