Effects of Saccharomyces Boulardii-Based Feed Additive on Performance, Hormone Level, Diarrhea Scoring and Fecal Microbial Population in Holstein Calves Experiencing Heat Stress

As the climate changes, heat stress (HS) is becoming an increasing concern for heavily utilized agriculture assets like dairy calves. Dairy calves subjected to HS may benefit from supplementation with probiotics. The objective of this study was to investigate the impact of a Saccharomyces cerevisiae boulardii CNCM I-1079 (SB) based feed additive in Holstein calves fed diets with three concentrations of SB during HS. Sixteen Holstein calves (28 ± 2.1 d-old) grouped according to their body weights (46 ± 3.1 kg BW) were randomly divided into 4 groups: Control (milk replacer and starter diet), a low SB diet (1.4 × 10⁹ cfu/L milk replacer), a middle SB diet (2.5 × 10⁹ cfu/L milk replacer) and a high SB diet (5.0 × 10⁹ cfu/L milk replacer) - and housed in a temperature-humidity controlled chamber (four dairy calves per chamber). Dairy calves were subjected to ambient temperature (21°C) for 21 days, after which chamber temperature was raised to 30°C (HS) for 7 days. Temperature-humidity index (THI) values during ambient condition never exceeded 71, whereas THI values during HS peaked at 83 and were above 80 for 10 h/d. Calves were fed twice (0700 h and 1900 h) per day for 28 days. Compared with the control diet during ambient temperature, SB diets reduced diarrhea score and heart rate (P < 0.05) but had no effect on growth performance. The low and middle SB diets decreased rectal temperature (P < 0.05). The Enterobacteriace population in feces was decreased by the low (P < 0.05) and high (P < 0.05) SB diets. Compared with the control diet during HS, SB diets reduced diarrhea score, rectal temperature and Enterobacteriace population in feces (P < 0.05), but had no effect on growth performance. In addition, both low and middle SB diets decreased heart rate (P < 0.05). the middle SB diet alone suppressed the level of serum cortisol (P < 0.05). In conclusion, the HS elicited the increased in rectal temperature, heart rate and diarrhea, but the supplementation of SB ameliorates the health responses of dairy calves experiencing HS.