Comparison of different methods to determine the gastrointestinal passage rate in poultry

Gastrointestinal (GI) passage rate of feed influences nutrient digestibility and absorption, as it dictates the amount of time the digesta are exposed to digestive enzymes, the intestinal villi and microbial fermentation (Vergara et al. 1989; Svihus 2010). The titanium dioxide (TO₂) marker technique is currently widely practiced for evaluation of GI passage rate. However, this method requires euthanising the bird to obtain digesta samples, which has negative implications from an animal welfare perspective, is labor intensive and eliminates the possibility of follow up studies with the same individual. The aim of this study was to evaluate alternative methods for evaluating GI passage rate, by comparing the TiO₂ marker method to radiographic evaluation of Barium Impregnated Polyethylene Spheres (BIPS) and barium sulphate suspension (BaSO₄).

Mature laying hens (80 weeks of age) were assigned to three treatment groups; group 1 (n = 5) and group 2 (n = 5) were orally administered with 30 BIPS of 1.5 mm-diameter and 5 ml BaSO₄ (125%) mixed with 5g mash feed, respectively. Whole body radiographs of each individual hen were taken at the following time points: 0, 0.5, 1, 1.5, 2, 3, 4, 8, 12, 24, 36 and 48 hours (h) post-inoculation. Hens in group 3 (n = 36) were orally inoculated with 0.15g TiO₂ mixed with 5g mash feed. Three hens per time point were sacrificed using CO₂ asphyxiation and whole GI organ segments were collected and analysed for TiO₂ content, based on the method of Short et al. (1996). The level of BIPS and TiO₂ in each of the GI segments was quantified, and the presence or absence of BaSO₄ in the GI segment was evaluated. Mean percentage level of BIPS and TiO₂ in each GI segment at each time point was assessed using a one-way ANOVA on SPSS statistics v.24.

There was a significantly higher percentage of BIPS present in the crop at 0, 0.5 and 2 h (P = 0.004, 0.001, 0.038 respectively) post-inoculation and in the gizzard at 48 h (P = 0.004) post-inoculation compared to the amount of TiO₂ observed, indicating a comparatively slower transit time of the BIPS. Furthermore, a higher percentage of TiO₂ was present in the proventriculus (P = 0.003) and small intestine (P = 0.031) at 36 h post-inoculation, indicating a longer retention time of TiO₂ compared to BIPS. The percentage of TiO2 measured at 1.5, 3, 12 and 24h post-inoculation was significantly higher in small intestine (P = 0.006, 0.002, 0.000, 0.002, respectively) and large intestine (P = 0.004, 0.026, 0.011, 0.000, respectively) compared to the BIPS observed. BaSO₄ was found to be present in all the organs in 80% of the hens at 3 h post inoculation and, by 36 h it had passed through the small intestine of all hens, with 20% of the hens displaying its presence in the large intestine until 48 h postinoculation.

In conclusion, the evaluation of the GI transit time is feasible using BIPS, TiO₂ , and BaSO₄. BIPS particles were retained longer in the GI tract mimicking solid feed particles, while BaSO₄ and TiO₂ showed a faster passage rate mimicking the GI transit time of liquids. In order to investigate physiologic digesta transit time, solid and liquid transit time need to be evaluated using different methods.