A Comparison of the Immune Performance of Commercial Growth Selected Broiler Genotypes

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Title: A Comparison of the Immune Performance of Commercial Growth Selected Broiler Genotypes
Author: Cheema, Manzoor Ahmed
Advisors: DR. MUQUARRAB A. QURESHI, Committee Member
Abstract: Two studies were conducted to analyze the interaction of genetics and nutrition on immune responsiveness of broilers. The first study involved four modern day broiler strains: Ross 3F8 (3F8, vent sexable), Ross x Cobb (RC, vent sexable), Ross 308 (308, feather sexable), and Cobb x Cobb (CC, vent sexable) raised on marginal (D1) and high protein (D2) diets. The second study compared male and female broiler chickens from a 2001 hatched Ross 308 broiler strain (ROSS) with male and female of 1957 Athens-Canadian Randombred Control (ACRBC) strain, when raised on diets 'typical' of those used in 1957 (D1) and 2001 (D2). The immunological measurements were the lymphoid organ weights relative to body weights, humoral response to sheep red blood cells (SRBC), T-lymphocyte proliferation response to in vivo Phytohemagglutinin-P (PHA-P), and innate macrophage response as measured by elicitation of abdominal exudate cells to Sephadex G-50 , phagocytosis of SRBC and nitrite production. Three additional measurements were included in the first study, namely chemotaxis of peripheral blood lymphocytes to formyl-met-leu-phe, T lymphoblastogenesis in response to Concanavalin-A (Con-A), and non-specific tumoricidal activity by splenic natural killer (NK) cells against 51Cr labeled RP-9 cells. In the first study, the CC strain had persistent antibody titers against SRBC (P = 0.0182) as well as greater innate immune response as measured by macrophage phagocytic ability for SRBC (P = 0.011). Cell-mediated immune response as measured by T-lymphocyte proliferation response to Con-A and PHA-P (P = 0.0018 and P 0.04, respectively) was higher in Ross 308 strain. The high protein diet contributed to a greater T-lymphocyte proliferation whereas the diet effects were variable for monocyte-macrophage functions and humoral response. Interaction between strain and diet was seen in humoral response, and the Ross 308 performed better on D1 while CC performed better on D2. In the second study, the ACRBC strain, despite being a low weight gain strain, showed significantly higher primary and secondary lymphoid organ weights, relative to body weight (P 0.04). Furthermore, the ACRBC strain showed significantly higher antibody titers against SRBC than the ROSS 308 broilers. However, the ROSS 308 strain had significantly greater PHA-P-induced lymphoblastogenic response in vivo (P = 0.012). For macrophage functions, the ROSS 308 strain exhibited a higher number of inflammatory exudate cells in response to Sephadex (P = 0.0261) as well as phagocytic potential against SRBC (P < 0.05). In addition, the ROSS 308 birds had a greater increase in nitrite production after LPS stimulation compared to the ACRBC strain birds. Diet and sex effects were inconsistent in the second study. Overall, these studies indicated that genetic differences for immunocompetence exist in commercial broiler strains. These genetic differences tend to indicate that modern broiler strains are less capable of launching a successful humoral response against SRBC whereas cell mediated and innate immune responses seem to have benefited from artificial selection for increased body weight.
Date: 2003-04-05
Degree: MS
Discipline: Immunology
URI: http://www.lib.ncsu.edu/resolver/1840.16/379

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