## 3 Results and Discussion
### Volatile Compounds in the Calves' faeces

Table 4: Volatile compound percentage profiles of faeces in the calf group fed with milk replacer only (CON0 and CON14 group) or supplemented with fermented milk permeate (MP0 and MP14 group). \begin{table}
\begin{tabular}{c c c c} \hline \hline  & **Day** & **CON** & **MP** & \(p\) **Day x Treat. Int.** \\ \hline pH & Baseline & 5.66 \(\pm\) 0.18 \({}^{\rm\wedge\wedge}\)* & 5.61 \(\pm\) 0.18 \({}^{\rm\wedge\wedge}\)* & 0.001 \\  & 14 & 6.60 \(\pm\) 0.28 \({}^{\rm\wedge\wedge}\)* & 6.38 \(\pm\) 0.25 \({}^{\rm\wedge\wedge}\)* & 0.001 \\ \hline Dry matter (\%) & Baseline & 32.28 \(\pm\) 4.63 \({}^{\rm\wedge\wedge}\)* & 33.65 \(\pm\) 7.58 \({}^{\rm\wedge\wedge}\)* & 0.001 \\  & 14 & 14.90 \(\pm\) 5.82 \({}^{\rm\wedge\wedge}\)* & 22.74 \(\pm\) 4.80 \({}^{\rm\wedge\wedge}\)* & 0.001 \\ \hline Texture (m) & Baseline & 0.11 \(\pm\) 0.03 \({}^{\rm\wedge\wedge}\)* & 0.11 \(\pm\) 0.03 \({}^{\rm\wedge\wedge}\)* & 0.090 \\  & 14 & 0.07 \(\pm\) 0.05 \({}^{\rm\wedge\wedge}\)* & 0.11 \(\pm\) 0.06 \({}^{\rm\wedge\wedge\wedge}\)* & 0.090 \\ \hline _Colour coordinates_, _NBS:_ & & & & \\ \hline L* & Baseline & 38.97 \(\pm\) 7.30 \({}^{\rm\wedge\wedge}\)* & 38.67 \(\pm\) 9.74 \({}^{\rm\wedge\wedge}\)* & 0.0001 \\  & 14 & 63.19 \(\pm\) 14.56 \({}^{\rm\wedge\wedge}\)* & 61.21 \(\pm\) 11.47 \({}^{\rm\wedge\wedge}\)* & 0.0001 \\ \hline a* & Baseline & 1.38 \(\pm\) 2.30 \({}^{\rm\wedge\wedge}\)* & 0.19 \(\pm\) 2.87 \({}^{\rm\wedge\wedge}\)* & 0.044 \\  & 14 & \(-\)1.14 \(\pm\) 1.88 \({}^{\rm\wedge\wedge}\)* & \(-\)0.57 \(\pm\) 1.01 \({}^{\rm\wedge\wedge}\)* & 0.044 \\ \hline b* & Baseline & 14.31 \(\pm\) 7.72 \({}^{\rm\wedge\wedge}\)* & 11.45 \(\pm\) 5.51 \({}^{\rm\wedge\wedge}\)* & 0.059 \\ \hline \hline \end{tabular}  
* The data are presented as the mean \(\pm\) standard error (\(n\) = 10/group). Baseline measurements were done on day 2 before the start of the feeding experiment. L*, lightness; a*, redness or \(-\)a*, greenness; b*, yellowness or -b*, blueness; NBS, National Bureau of Standards units; Treat. Int., treatment interaction. \({}^{\rm\wedge\wedge\wedge}\)B different capitals indicate significant time-related differences (\(p\) < 0.05). \({}^{\rm\wedge\wedge}\)b different letters indicate differences among treatments (\(p\) < 0.05).  
\end{table} 
Table 3: The pH, dry matter, and colour coordinates of faeces in the calf group fed with milk replacer only (CON group) or supplemented with fermented milk permeate (MP group). The production of faecal VCs (volatile fatty acids (VFA), alcohols, and phenolic and aromatic compounds) results from the colonic fermentation of non-utilised nutrients in the small intestine [48]. \(p\)-Cresol is formed during tyrosine fermentation, while indole is the principal end-product of tryptophan catabolism [49]. VFA maintain gut epithelium functionality and are derived mostly from lactose, non-utilised fibrous nutrients, and starch [50]. [PERSON] and [PERSON] [48] stated that the reduced concentration of VFA in the faeces of newborn calves is related to rapid lactic fermentation in the acidic lumen, while [PERSON] [51] reported increased concentrations of these acids, especially acetic acid, as well as reduction in _E. coli_ in the faeces following administration of probiotic bacteria. Higher concentration of VFA in faeces is related to better adaptation of probiotics in the gut of calves and improved utilisation of prebiotics by beneficial gut bacteria [52]. In our study, the total concentration of VFA in the faeces was lower in the MP14 group (43%) compared with the CON14 group (54%). However, there was a significantly higher concentration of acetic acid in the CON14 group (\(p\) = 0.002).