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The intestinal tract of chickens is characterized by efficient nutrient digestion. Disturbances of this fragile system results frequently in reduced animal health and welfare and subsequently increased use of antibiotics. Feed additives and various feed processing technologies can be used in order to affect intestinal function of the chicken. The goal of this study was to study the impact of acidification and thermal treatment of feed, the use of various feed particle sizes, and the impact of milling methods on intestinal physiology of poultry.
The aims of this thesis were:
I) to adapt the Ussing chamber method for reliable assessment of transport physiology of the intestinal mucosa of poultry,
II) to evaluate the impact of acidified feed on apparent ileal digestibility of starch, the glucose transporter expression, and intestinal transport function in broiler chickens, III) to investigate the impact of the milling method, thermal treatment and particle size of feed on performance, apparent ileal nutrient digestibility, and pH of digesta in laying hens.
Part I was performed by stripping the tunica mucosa from a total of 104 jejunal samples from 10 hens and using a net device for stabilizing support. In order to investigate the benefit of glutamine, 50 samples were maintained with a conventional buffer (group 1), and 54 samples were maintained with additional 5 mM glutamine (group 2). Mean short circuit current (ΔIsc) of samples exposed to 10 mM glucose in group 1 and group 2 was 17.0 ±2.47 μA/cm2 and 14.6 ±1.54 μA/cm2 (p = 0.836), of samples exposed to 100 μM phloridzin -13.3 ±1.63 μA/cm2, and -11.8 ±1.22 μA/cm2 (p = 0.712) and of samples exposed to 100 μM carbachol 4.7 ±0.70 μA/cm2, and 3.7 ±0.43 μA/cm2 (p = 0.450), respectively. While glutamine had no beneficial effect on tissue response, the method described here allowed for reliable investigation of the intestine.
Part II of this thesis was performed by feeding broilers a standard diet without or with 1.5 % Lupro-Cid® (64 % formic acid, 25 % propionic acid, 11 % water) for 32-35 days. Apparent ileal starch digestibility was determined using 0.2 % titanium dioxide as indigestible marker. Intestinal transporter function was analyzed in Ussing chamber experiments where jejunal samples were sequentially exposed to 10 mM glucose, 100 μM phloridzin, 100 μM histamine, and 100 μM carbachol. Additionally, gene expressions of SGLT-1 and GLUT-2 transporters were analyzed using qPCR analysis. Apparent ileal starch digestibility of the control group (97.5 ±0.35 %) and the acid-treated group (97.0 ±0.59 %) did not differ significantly (p = 0.674). Tissue conductance of intestinal samples obtained from the control group and the acidtreated group was 10.6 ±0.68 mS/cm2, and 9.4 ±0.80 mS/cm2, respectively (p = 0.147). The mean short circuit currents (ΔIsc) of the samples exposed to glucose, phloridzin, histamine, and carbachol did not differ (p = 0.209, p = 0.296, p= 0.498, and p = 0.640, respectively). Additionally, no differences in the expression of SGLT-1 and GLUT-2 could be observed (p = 0.942, p = 0.431).
Part III of this thesis was performed using twelve variants of a complete diet that were produced by four different milling techniques including hammer mill, roller mill, disc mill, and a wedge-shaped disc mill. Coarse feed particles were obtained from all mills, additional fine feed particles were obtained from the hammer mill and the roller mill. Each of this six feed variants was offered as mash or expandate, resulting in twelve treatments in total. Laying hens at 20 weeks of age were kept for three weeks in eight replicates with six hens per feeding group. Performance parameters (feed consumption, laying performance, feed conversion ratio) and apparent ileal digestibility of crude protein, amino acids, ether extract, and starch were determined. The pH of the digesta was determined along the gastrointestinal tract. In week 1 and 2 of the experiment, feed intake was significantly increased in hens fed with mash feed compared to hens fed expanded feed (p = 0.003 and p = 0.023). The apparent ileal digestibility of starch was improved (p < 0.001) by feeding mash and correlated positively to increased particle size (p-linear = 0.001; p-quadratic = 0.006; r = 0.363). The apparent ileal digestibility of ether extract correlated negatively to increased particle sizes (p-linear = 0.003; p-quadratic = 0.225; r = -0.311). The pH of the ileum content (p-linear = 0.044; p-quadratic = 0.146; r = 0.212) and feces (p-linear = 0.010; p-quadratic = 0.016; r = 0.267) correlated with increased particle sizes.
Based on the results of this thesis, organic acids had no impact on ileal starch digestibility and intestinal nutrient uptake. Therefore, the investigation of the mode of action needs further studies. Feeding coarse particle sizes improved ileal starch digestibility. Unconventional, energy saving milling methods enabling coarse particle sizes of feed may be used without negative impact on laying performance and the digestive function of laying hens.