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Long-term divergent selection from a common founder population for a single trait—antibody response to sheep erythrocytes 5 days post-injection—has resulted in two distinct lines of White Leghorn chickens with a well-documented difference in antibody titers: high (HAS)- and low (LAS)-antibody selected lines. Subpopulations—high (HAR)- and low (LAR)-antibody relaxed—were developed from generation 24 of the selected lines to relax selection. The objective of the current experiment was to determine if this long-term selection and relaxation of selection impacted the growth of two organs important to chicken immunity: the spleen and the bursa of Fabricius. Spleens and bursae were obtained from ten chickens per line at nine timepoints (E18, D0, D6, D13, D20, D35, D49, D63, and D91) throughout their rapid growth phase and presented as a percent of body weight. Significance was set at p ≤ 0.05. For the spleen, all lines consistently increased in size relative to body weight to D49, followed by a consistent decline. All lines had a similar growth pattern, but HAS spleens grew faster than LAS spleens. For the bursa, LAS was smaller than the other three lines as an embryo and also smaller than HAS through D63. In the selected lines, bursa weight peaked at D35, whereas the relaxed lines peaked at D49. By D91, there was no difference between lines. Artificial and natural selection, represented by the long-term selected and relaxed antibody lines, resulted in differences in the growth patterns and relative weights of the spleen and bursa of Fabricius.

Histomonas meleagridis, a protozoan parasite, induces blackhead disease (histomoniasis) in poultry. During hatching, chicks from lines divergently selected for high (HAS) and low (LAS) antibody responses to sheep red blood cells were divided into two groups, each of HAS and LAS, and placed in pens with wood shavings as litter. Feed and water were allowed ad libitum. Half of the chicks from each line had Limosilactobacillus reuteri (L. reuteri) inoculated to their drinking water. On day 18, all chicks were given a transcloacal inoculation of 100,000 H. meleagridis cells. Then, 10 days later, they were euthanized, followed by collection of tissues from the brain, cecal tonsil, ceca, liver, thymus, and spleen for qPCR analyses of cytokines involved in immunological development. Changes in cytokine expressions were most numerous in the cecal tonsil, ceca, and liver. In the absence of a functional medication for control of histomoniasis, L. reuteri and/or its secretory product, reuterin, might serve, in some genetic populations, as a means to reduce the impact of histomoniasis in chickens. The data demonstrate that L. reuteri treatment had tissue specificity between the two genetic lines, in which the effects were targeted primarily toward the cecal tonsil, ceca, and liver, which are the primary tissue targets of the parasite (H. meleagridis), as well as the thymus and spleen. However, interactions among main effects reflect that responses to inflammatory markers observed in tissues for one genetic line may not be observed in another.

ABSTRACT: Since the 1970s, 2 lines of White Leghorn chickens, HAS and LAS, have been continuously divergently selected for 5-day postinjection antibody titer to injection with sheep red blood cells (SRBC). Antibody response is a complex genetic trait and characterizing differences in gene expression could facilitate better understanding of physiological changes due to selection and antigen exposure. At 41 d of age, randomly selected HAS and LAS chickens, which had been coraised from hatch, were either injected with SRBC (HASI and LASI) or kept as the noninjected cohort (HASN and LASN). Five days later, all were euthanized, and samples collected from the jejunum for RNA isolation and sequencing. Resulting gene expression data were analyzed combining traditional statistics with machine learning to obtain signature gene lists for functional analysis. Differences in ATP production and cellular processes were observed in the jejunum between lines and following SRBC injection. HASN vs. LASN exhibited upregulation of ATP production, immune cell motility, and inflammation. LASI exhibits upregulation of ATP production and protein synthesis vs. LASN, reflective of what was observed in HASN vs. LASN. In contrast, no corresponding upregulation of ATP production was observed in HASI vs. HASN, and most other cellular processes appear inhibited. Without exposure to SRBC, gene expression in the jejunum indicates HAS generates more ATP than LAS, suggesting HAS maintains a “primed” system; and gene expression of HASI vs. HASN further suggests this basal ATP production is sufficient for robust antibody responses. Conversely, LASI vs. LASN jejunal gene expression implies a physiological need for increased ATP production with only minimal correlating antibody production. The results of this experiment provide insight into energetic resource needs and allocations in the jejunum in response to genetic selection and antigen exposure in HAS and LAS which may help explain phenotypic differences observed in antibody response.

The experiment investigated the effects of limestone particle size and dietary potassium (K) on live performance, blood physiology, and muscle myopathies in broilers raised to 35 days of age. A total of 384 Ross male broilers were placed in 24 floor pens and fed four diets during the starter (0–16 days of age) and grower (17–33 days of age) periods containing two limestone particle sizes (fine: 0.2 mm and coarse: 0.9 mm), and amended with either 0% basal K (K–) or 0.2% added dietary K (K+) as potassium carbonate to complete the 2 × 2 factorial arrangement. Live performance was measured from 1–33 days of age. Blood physiology, woody breast (WB), and white striping (WS) scores were measured at 35 days of age. The K+ dietary treatment reduced (P < 0.05) feed intake and BWG when compared to K– during the starter and grower period. The K+ dietary treatment decreased blood Na (mmol/L), blood glucose (mg/dl), ionized blood Ca (mg/dl), TCO2 (mmol/L), blood HCO3 (mmol/L), and base excess in extracellular fluid (mmol/L) when compared to K– birds of similar body weight at 35 days of age (P ≤ 0.05). Fine limestone diets tended to reduce WB scores (3.0 vs. 2.59) when compared to coarse limestone diets at 35 days of age (P = 0.08). This study demonstrated that using 0.2% of K as potassium carbonate did not negatively affect FCR even though FI and BWG were reduced. Furthermore, fine limestone has the potential to reduce WB in breast muscle tissues; however, further research is needed to confirm these outcomes.