Table 1.

Parameters proposed to be related to the drug intestinal concentrations, and the parameter distributions used to model variability in possible concentrations of CTC in the small and large intestines of beef cattle during the 5-day per os treatment

Parameter	Definition	Distribution	Data used to derive distribution
	Rate of CTC abiotic degradation in GI tract and other body parts per hour	Beta (0·54, 37·4)	[5, 23, 26, 28–29]
	Fraction of CTC excreted in bile	Uniform (0·39, 0·64)	±25% estimate [26]
	Fraction of CTC adsorbed to the digesta in the lower 2/3 of small intestine	Uniform (0·69, 0·89)	[33–34]
	Fraction of CTC adsorbed to the digesta in large intestine	Uniform (0·69, 0·89)	[33–34]
	Fraction of CTC adsorbed by the microbiome in the lower 2/3 of small intestinea	–	Not separately included in model simulations
	Fraction of CTC adsorbed by the microbiome in large intestinea	–	Not separately included in model simulations
	Fractional digesta flowb through stomachs to small intestine per hour	Ac: 0·0715 B: 0·0588	[35–36]
	Fractional digesta flow through the upper 1/3 of small intestine per hour	A: 0·3333 B: 0·3077	[35, 37]
	Fractional digesta flow through the lower 2/3 of small intestine per hour	A: 0·1330 B: 0·1330	[35, 37]
	Fractional digesta flow through large intestine per hour (to defecation)	A: 0·1330 B: 0·2222	[35]
Vrest_si	Volume of digesta in the lower 2/3 of small intestine, litre	Uniform (4, 23)	[38]
Vli	Volume of digesta in large intestine, litre	Uniform (6, 22)	[38]

The animals ingested CTC in equal portions during each 12 h of day time per day of the 5-day therapy. The animals consumed feed and water at similar intervals to the drug.

The values of the parameters relevant for the drug concentrations in the central circulation were kept constant in all simulations, and were as in (Cazer et al. [6]).

^aA single variable – fraction of CTC adsorbed to the digesta or microbiome – was included in the simulations.

^bIntestinal transit time of CTC was set as the average of the liquid and solid digesta phases.

^cForage scenarios were diets: A – grain based, and B – long-form hay based.