Influence of feeding programs on innate and adaptive immunity in broiler breeders
Montiel, Enrique Rodolfo
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The use of feed restriction is standard practice for rearing broiler breeder pullets in order to achieve performance goals in the poultry industry worldwide. Automatic trough or plate feeders are used to apply restriction programs that typically include off-feed days also known as skip-a-day (SAD). In order to study the influence of the various feeding methods, groups of broiler breeder pullets were fed skip-a-day in an experimental pullet facility at The University of Georgia (SAD) or in a commercial pullet farm (SADF); every day using mechanical chain feeders (EDF) or every day broadcasting the feed on the litter (EDL). Innate and adaptive immune responses and production parameters were evaluated as follows: 1) organ weight and organ: body weight ratios and microscopic examination of the spleen and bursa at 2, 3, 4, 5, 7, 12 and 17 weeks of age in the SAD, EDF and SADF groups; microscopic examination of the thymus at 2, 3, 4, 5, 7, 12 and 17 weeks of age; 2) comparison of the colonization ability in spleen and ceca of a nalidixic acid-resistant Salmonella enteritidis (SE) strain with a field SE strain (SEF) as candidates for challenge studies; 3) innate immunity, measured by the time of clearance of Escherichia coli (E coli) after intravenous inoculation and SE colonization in spleen and ceca after oral challenge with a nalidixic acid-resistant SE strain at 14, 22 and 35 weeks of age; 4) adaptive immune responses, measured by antibody titers against Infectious bursal disease following vaccination with an HVT+ IBD vector and inactivated vaccines in hens and progeny expressed as geometric mean titer (GMT) using two different ELISA kits plus response to inactivated SE vaccination measured through decrease in spleen and cecal colonization at 22, 35 and 65 weeks of age; and 5) production parameters including weekly body weights during rearing and egg production between 24 and 60 weeks of age in one study and 24 through 31 weeks of age in a second study. Although bursal weights were higher in the EDF group at 3, 4, 5, 7, 12 and 17 weeks, the difference was not significant among groups (P= 0.12). The differences in spleen weights were not significant (P=0.94) either. Histopathology results revealed no bursal lesions up to 7 weeks of age in any of the groups. At 12 weeks only the SAD-Field group showed score 2-3 out of 5 bursas evaluated and at 17 weeks only the SAD group showed score 2 lesions in 2 out of 5 bursas examined. Thymus histopathology showed no lesions in any of the groups at 2, 3 and 5 weeks of age. At 4, 7, 12 and 17 weeks of age the EDF, SAD and SADF groups had thymus microscopic lesion score averages of 1, 2, 1; 2.2, 1.8, 1.8; 1.2, 2, 1.6 and 1.4, 1.2, 1.8, respectively. The number of spleen germinal centers (GC) ranked from 1.2 to 34.8 GC/ tissue section throughout the sampling period and there were no significant differences (P>0.05) between groups. The colonization ability of the nalidixic acid-resistant SE strain was significantly higher than the SEF strain in ceca at 107 and 108 cfu/ml challenge doses. Pullets fed EDL cleared E coli faster from the blood stream than the birds fed SAD or EDF and the bacterial load measured in colony forming units per ml of blood (cfu/ml) was significantly lower in the EDL group 10 minutes after inoculation (P< 0.05). Bacterial loads at 20 and 60 minutes after inoculation were also lower in the group fed EDL but not statistically significant (P>0.05). SE colonization was numerically lower in the EDL group at 22 weeks of age and significantly less (P<0.05) at 65 weeks of age. Vaccination with an inactivated SE vaccine at 55 weeks of age reduced re-isolation of the challenge SE in SAD vaccinated hens 11 days post challenge with a nalidixic acid-resistant strain by 28% and 30% in the spleen and ceca respectively and by 68% and 56% respectively in the EDF group. In the EDL-vaccinated group, Salmonella colonization increased 17 and 27% in spleen and ceca respectively. Colonization rates were significantly lower in the EDL unvaccinated group (P<0.05) than the unvaccinated SAD and EDF groups. Antibody titers against Infectious bursal disease virus in the hens at 4, 9, 14, 26, 30, 35, 39, 45 and 59 weeks of age and one-day-old chicks from 34, 41 and 55 week-old hens were very similar across feeding groups. The GMT values for kits A and B ranked 167 to 9035 and 21 to 43180 for the EDL group; 159 to 10729 and 9131 to 43283 in the EDF group; 117 to 9025 and 9113 to 39589 for the SAD group respectively, without significant difference (P>0.05) among groups. Pullet weights were significantly higher (P < 0.05) in the EDF and EDL groups at 9, 13 and 17 weeks of age with the same amount of feed provided per bird in all treatment groups. Per hen-weekly egg production in the first study was not significantly different (P>0.05) between 24 and 60 weeks of age and significantly higher (P<0.05) in the EDF group between 24 and 31 weeks of age in the second study. There was no significant difference in egg production between the EDF and EDL groups. Every day feeding using the EDF or EDL approach did not have a negative effect on egg production or antibody response to vaccination against IBDV. The EDL feeding program decreased SE colonization after challenge and improved cell mediated immune response measured by the time of clearance of E coli after intravenous inoculation with a pathogenic E coli strain at 17 weeks of age.