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Laying hens have an extra demand on calcium (Ca) homeostasis due to egg-laying. The calcium-sensing receptor (CaSR) plays a central role in Ca homeostasis. The thesis aimed to develop effective methods for maintaining desired Ca homeostasis in laying hens. The first study demonstrated that chicken CaSR (cCaSR) and chicken vitamin D receptor (cVDR) are widely distributed in the kidney, gastrointestinal tract, shell gland, and tibia in laying hens at different laying stages. The second study characterized cCaSR ligands in cCaSR-stably expressing HEK293 cells and investigated the binding modes between cCaSR and its ligands. Results showed that L-tryptophan (L-Trp) and inorganic PO43- are cCaSR modulators, acting as positive and negative allosteric modulators, respectively. The third study isolated chicken mesenchymal stem cells (MSCs) from broilers and layers and demonstrated that cCaSR and cVDR were expressed in broiler and layer MSCs. The osteogenic differentiation process in layer MSCs was faster than that in the broiler MSCs. L-Trp and 1,25-dihydroxycholecalciferol (1,25OHD3) were found to regulate proliferation and osteogenic differentiation in broiler and layer MSCs, depending on the modulator’s doses and treatment time. The fourth study was to investigate the interactive effects of Ca and L-Trp, and of Ca and 25-hydroxycholecalciferol (25HyD) substitution for vitamin D3 on egg production, eggshell quality, bone health, and calcium homeostasis in Dekalb layers from 26 to 29 weeks of age. Results showed that increased dietary Trp levels increased serum Ca level, eggshell quality, and tibia traits. An interactive effect was found that Ca continued to increase the relative eggshell weight and eggshell thickness as Trp level increased. However, 25HyD did not improve egg production, eggshell quality, and bone health. Taken together, the cCaSR and cVDR are widely expressed in laying hens. Ca2+ and L-Trp promoted osteogenic differentiation in chicken MSCs and they impro

Canola meal (CM) which is commonly used in poultry and swine diets as an economically viable alternative to soybean meal is mainly produced by the process called the pre-press solvent extraction. The pre-press solvent extraction does not only involve many steps, each step also involves a wide range of vital conditions including temperature, moisture and time. Variations in these processing conditions among and within processing plants may contribute to inconsistency in the chemical and nutritive compositions of the resulting meals. In addition, the desolventization/toasting step of the pre-press solvent extraction process has been implicated for reducing both the content and availability of amino acids (AA), especially lysine, for both broiler chickens and pigs. Canola meal end-users desire increased meal consistency for a more accurate and cost-effective feed formulation and more information on the nutritive value and heat damage of AA. The first objective of this thesis was to determine the effect of processing plant and year on the chemical composition and indicators of protein damage in CM. To achieve this, a chemical composition survey of CM from 11 processing plants that use the pre-press solvent extraction process was conducted over a 4-year period. Differences among processing plants and years were observed for protein, lysine, dietary fiber and its components, fat, and carbohydrates components. Over the 4 years, the highest variation was observed in the contents of simple sugars having a coefficient of variation (CV) of 41.7%), neutral detergent insoluble crude protein (NDICP; CV = 16.8%) and glucosinolates (CV = 35.3%), the components known to be sensitive to heat treatment. Among all AA, only lysine showed differences (P < 0.05) among processing plants. Lysine content averaged 18.5, 22.1, 22.9 and 20.7 g/kg in years 2011, 2012, 2013 and 2014, respectively, and was lowest in meals showing the highest NDICP and total dietary fiber values. Linear regression

The enrichment of egg with folate is a viable option for supplying the general population of a food product rich in natural folates. However, attempts to increase the concentration of folate in egg beyond the achieved level of enrichment had been unsuccessful because egg folate reached a maximum plateau when folic acid (FA) was increased in the diet. Thus, experiments were conducted to determine the factors regulating the deposition of dietary FA into the eggs. In the first study, the effect of feeding equimolar intake of FA and 5-methyltetrahydrofolate (5-methylTHF), the biologically active form of folate; on egg folate concentrations, indices of folate status, and activities of folate-dependent enzymes was evaluated. Folic acid and 5-methylTHF demonstrated equivalent effects in enhancing the egg folate concentrations and improving the indices of folate status in the laying hen. The activities of folate-dependent enzymes were similar between the two forms of folate except for hepatic dihydrofolate reductase (DHFR) activity which increased in FA-fed birds compared to 5-methylTHF-fed birds. However, this demonstrated the ability of the laying hen to metabolically convert FA into its biologically active forms. Therefore, the influence of intestinal FA absorption in the regulation of FA deposition in the egg was subsequently evaluated. Using the in vitro everted intestinal sac technique, FA was absorbed in all regions of the intestine. Absorption was maximum at acidic pH 6.0, and increased in the duodenum and jejunum compared to the ileum and cecum. The rate of FA absorption in the jejunum diminished at higher FA concentrations. Therefore, further study was conducted to determine the regulation of FA absorption when levels of FA in the laying hen diet are increased. Supplementation of increased FA levels resulted to a down-regulation of FA absorption in the duodenum, but not in the jejunum of the laying hen. This down-regulation was not associated to a decreased mRNA g

A study was undertaken to test the effect of 2 commercially available probiotics on the production efficiency of broiler chickens hatched from the same breeder flock at 3 different ages (28, 43, and 57 wk). At each of the 3 breeder flock ages, 1,600 broiler chickens were hatched and randomly allocated to 1 of 4 treatments: 1) no probiotics (control), 2) probiotic 1 administered in the drinking water, 3) probiotic 1 administered as a spray, and 4) probiotic 2 administered in the feed. A coccidiostat was included in the feed, but no other antimicrobial agents were given. Broilers were then reared on straw litter in identical floor pens for a period of 6 wk. There were no significant differences in broiler BW, feed conversion, or mortality between the probiotic treatments and the control group in any of the trials. The 43-wk-old breeder flock had the highest fertility and hatchability and the lowest percentage of chicks culled at hatching. Throughout the broiler production period, the broilers from the 43- and 57-wk-old breeder flocks had higher BW and weight gains than the broilers produced at 28 wk of breeder flock age. Broiler feed conversion over the 6-wk production period decreased as the breeder flock aged. Probiotics had no effect on chick quality or production efficiency in broilers produced by the breeder flock ages examined.

Straight-run broiler chickens were raised either in floor pens or wire-floored cages (trial 1) or in floor pens only (trials 2, 3, and 4). Birds raised in floor pens had lower BW and feed intakes than those raised in cages. The administration of bacitracin in the feed increased feed intake from d 12 to d 35, decreased the feed conversion ratio during the same period in trial 2, and improved the weight gain of broilers from d 0 to 10 in trial 3. The concentrations of conjugated bile salts (taurocholic and taurochenodeoxycholic acids) were higher in the ileal contents of broilers administered the antimicrobials compared with untreated birds. Supplementation of the feed with monensin increased fat digestibility in the ileum of the birds. Although total numbers of bacteria in ileal contents were the same regardless of whether antimicrobials were administered or not, the bacterial community differed qualitatively. Populations of Lactobacillus salivarius were reduced in birds fed antimicrobials relative to untreated broilers. A representative ileal isolate of L. salivarius deconjugated bile salts in pure culture in the laboratory and in the ileal contents of ex-Lactobacillus-free chickens maintained in a protective environment and colonized by the Lactobacillus isolate. These observations provide a link between bile salt deconjugation in the ileum by L. salivarius and decreased weight gain of broilers. Lactobacillus salivarius populations could be targeted in future studies aimed at modification of the ileal bacterial community to achieve growth promotion of broilers without the administration of antimicrobial drugs.

Thirty-eight isolates of Lactobacillus gallinarum cultured from the crops of broiler chickens were screened for the presence of genes encoding S-layer proteins. All of the isolates had two S-protein genes, which were designated Lactobacillus gallinarum S-protein (lgs) genes. One gene in each isolate was either lgsA or lgsB. The Lactobacillus isolates were further characterized by pulsed-field gel electrophoresis of DNA digests, which grouped the isolates into 17 genotypes (strains). The second gene in each of eight representative strains was sequenced and shown to differ among strains (lgsC, lgsD, lgsE, lgsF, lgsG, lgsH, and lgsI). The genome of each strain thus encoded a common S-protein (encoded by either lgsA or lgsB) and a strain-specific S-protein. The extraction of cell surface proteins from cultures of the eight strains showed that each strain produced a single S-protein that was always encoded by the strain-specific lgs gene. Two of the strains were used to inoculate chickens maintained in a protected environment which were Lactobacillus-free prior to inoculation. DNAs and RNAs extracted from the digesta of the chickens were used for PCR and reverse transcription-PCR, respectively, to demonstrate the presence and transcription of lgs genes in vivo. In both cases, only the strain-specific gene was transcribed. Both of the strains adhered to the crop epithelium, consistent with published data predicting that S-proteins of lactobacilli are adhesins. The results of this study provide a basis for the investigation of gene duplication and sequence variation as mechanisms by which bacterial strains of the same species can share the same habitat.

The microflora of the crop was investigated throughout the broiler production period (0 to 42 days) using PCR combined with denaturing gradient gel electrophoresis (PCR-DGGE) and selective bacteriological culture of lactobacilli followed by amplified ribosomal DNA restriction analysis (ARDRA). The birds were raised under conditions similar to those used in commercial broiler production. Lactobacilli predominated and attained populations of 108 to 109 CFU per gram of crop contents. Many of the lactobacilli present in the crop (61.9% of isolates) belonged to species of the Lactobacillus acidophilus group and could not be differentiated by PCR-DGGE. A rapid and simple ARDRA method was developed to distinguish between the members of the L. acidophilus group. HaeIII-ARDRA was used for preliminary identification of isolates in the L. acidophilus group and to identify Lactobacillus reuteri and Lactobacillus salivarius. MseI-ARDRA generated unique patterns for all species of the L. acidophilus group, identifying Lactobacillus crispatus, Lactobacillus johnsonii, and Lactobacillus gallinarum among crop isolates. The results of our study provide comprehensive knowledge of the Lactobacillus microflora in the crops of birds of different ages using nucleic acid-based methods of detection and identification based on current taxonomic criteria.