Enhancing Weaned Piglet Health and Performance: The Role of Autolyzed Yeast (<i>Saccharomyces cerevisiae</i>) and β-Glucans as a Blood Plasma Alternative in Diets

The objective of this study was to evaluate the inclusion of the autolyzed yeast (AY) <i>Saccharomyces cerevisiae</i> with or without an immunomodulator (1,3/1,6 β-glucans) as a total/partial substitute for blood plasma (BP) in the diet of post-weaning piglets; zootechnical performance, intestinal health and microbiota, immune responses and energy metabolism were assessed. A total of 240 castrated male and female piglets, with a mean age of 22 days and mean initial weight of 5.24 ± 0.82 kg, were randomly divided into blocks of four treatments with 12 replicates. The dietary inclusions were blood plasma (BP), autolyzed yeast (AY), autolyzed yeast + immunomodulator (AYI) and 50% BP and 50% AY (BPAY). In pre-initial phase II (29–35 days), piglets fed AY showed better feed conversion (FCR = 1.358) than the piglets in the BP (1.484), AYI (1.379) and BPAY (1.442) groups, i.e., 8.49% (0.126), 1.52% (0.021) and 4.50% (0.084), respectively (<i>p</i> = 0.0293). In the total period (21–42 days), better FCR was observed in the AYI (1.458) group, i.e., 4.64% (0.071), 1.15% (0.017) and 4.58% (0.070), than in the BP (1.529), AY (1.475) and BPAY (1.528) groups, respectively (<i>p</i> = 0.0150). In piglets fed AY (n = 3) and BPAY (n = 2), there was a reduction in the number of medications, i.e., 82.35% (−14n) and 88.23% (−15n), respectively (<i>p</i> = 0.0001), compared with that in the BP group (n = 17). In the AY group (73.83 mg/dL), AYI group (69.92 mg/dL), and BPAY group (69.58 mg/dL), piglets exhibited increases in triglyceride levels of 79.32%, 69.83%, and 69.00%, respectively, in comparison to those in the BP group, which had triglyceride levels of 41.17 mg/dL (<i>p</i> = 0.0400). The beta-hydroxybutyrate concentration in the AY group (79.96 ng/μL) was lower by 31.95%, 22.64%, and 5.89% compared to the BP group (117.50 ng/μL), AYI group (103.36 ng/μL), and BPAY group (84.67 ng/μL), respectively (<i>p</i> = 0.0072). In the AYI group, there was modulation of the microbiota, with an increase in the relative abundance of bacteria of the genera <i>Lactobacillus</i>, <i>Collinsella</i> and <i>Bulleidia</i>. AY, associated or not associated with an immunomodulator, is a potential substitute for BP in diets for piglets in the nursery phase, with positive effects on immune, metabolic, and intestinal microbial performance.