240. Effects of Waterline Delivery of Lactobacillus and Bifidobacterium Combination on Growth Performance, Diarrhea Frequency, and Hematology Responses in Weaned Pigs.

Abstract The post-weaning period is a critical phase in pig production, during which weaning-induced stress disrupts feed intake, intestinal integrity, and immune function, leading to compromised growth performance. Probiotics represent a practical nutritional strategy to modulate gut microbiota, support intestinal health, and enhance immune responses in weaned pigs. This study was conducted to evaluate the effects of a waterline application of a Lactobacillus and Bifidobacterium blend on growth performance, diarrhea frequency, and hematological parameters in weaned pigs. A total of 192 weaned pigs [(Landrace × Yorkshire) × Duroc; 6.28 ± 0.85 kg average of initial body weight (BW); approximately 28 days of age] were allotted to 3 dietary treatments (4 pigs/pen; 18 replicates/treatment) in a randomized complete block design (block = initial BW and sex). All pigs were fed a corn–soybean meal–based weaner diet in a 2-phase feeding program (days 1-14 and 14-42) throughout the study. The probiotic blend was administered via the waterline at daily doses of 0, 5.0 × 10⁸, or 5.0 × 1010 CFU per piglet from weaning through the end of the nursery period. Pigs were weighed individually (days 1, 14, 42), feed intake was recorded per pen at the end of each phase, and average daily gain (ADG), average daily feed intake (ADFI) and feed conversion ratio (FCR) were calculated. Fecal consistency was visually assessed from days 1 to 14 using a 5-point scoring system. Blood samples were collected on days 1, 7, 14 and 28 to assess hematological profiles and indicators of immune function, stress, and antioxidant status. Performance data were analyzed using the Fit Model platform in JMP 16.1, with pen as the experimental unit. Supplementation with the probiotic blend significantly increased final body weight (P = 0.001) and overall average daily gain (P = 0.001) in weaned piglets compared with unsupplemented pigs. Average daily feed intake did not differ among treatments, while overall feed efficiency showed a numerical improvement of 2–4% (P = 0.452). A higher proportion of heavy pigs was observed in probiotic blend–supplemented groups. No dose-dependent effects were detected for growth performance parameters. Average diarrhea scores over the 14-day post-weaning period were similar across treatments; however, the frequency of severe diarrhea was significantly reduced in piglets receiving the probiotic blend (P = 0.002). Hematological parameters remained within normal physiological ranges, with no significant effects of probiotic supplementation. Numerically lower concentrations of TNF-α, interleukins, haptoglobin, and cortisol were observed in probiotic blend–supplemented piglets, suggesting reduced immune and stress responses. In conclusion, waterline supplementation with the probiotic blend improved growth performance and reduced the incidence of severe diarrhea in weaned piglets by modulating immune and stress responses, without affecting feed intake or hematological health.