1a. Objectives (from AD-416):
The overall objective of this project is to determine the effect of lysozyme and antibiotics on growth, feed efficiency, composition of growth, immune response, and pathogen shedding using an indirect disease challenge model. The immune response elicited by bacterial and/or viral challenges are energetically costly and reduce growth performance in pigs. Lysozyme and subtherapeutic levels of antibiotics improve growth and feed efficiency and reduce pathogen shedding in normal, healthy pigs. The specific objectives of the proposal are to: 1) determine if lysozyme and/or antibiotics improves growth performance, including composition of gain, of nursery pigs during an indirect disease challenge, 2) determine if lysozyme and/or antibiotics alters the immune response of nursery pigs during an indirect disease challenge, 3) determine if lysozyme and/or antibiotics decreases the shedding of bacteria potentially harmful to humans, including Campylobacter, Salmonella, and shigatoxinic Escherichia coli (stx genes) during an indirect disease challenge, and 4) determine if lysozyme and/or antibiotics reduces the subsequent days to market following an immune response in the nursery.
1b. Approach (from AD-416):
Two replicates of 720 pigs will be weaned from the sow at 24 days of age. Pigs will be blocked by litter and gender, and then randomly assigned to either a nursery room that has been fully cleaned and disinfected or a nursery room left unclean since the previous group of pigs. Within a room, pigs will be randomly assigned to either control diets (3 phase nursery regime), control diets + antibiotics (cholorotetracycline/Denegard), or control diets + lysozyme (500 mg/kg diet) and allowed to consume diets ad libitum for four weeks. Pig weights and feed disappearance will be measured weekly. On d 0, 14, and 28 of treatment, blood will be collected via jugular venipuncture from the same 14 pigs per diet room combination (n= 28 per treatment for the entire experiment). Serum will be analyzed for IgA, PUN, acute phase proteins (C-reactive protein, haptoglobin, and pig major acute phase protein. An initial group of pigs (24 d of age; n=10 per replicate) will be killed for initial body composition analysis. After four weeks of treatment, 10 pigs of median weight will be killed per diet room combination for body composition analysis. Rectal swabs will be taken from pigs on d 0, 14, and 28 d of treatment. Swabs will be analyzed for campylobacter and salmonella, and DNA from samples will be subjected to PCR to determine the presence of shiga-toxin genes. After four weeks in the nursery, pigs will be moved to finishing facilities and where feed intake and weights will be recorded every two weeks until 120 kg body weight.
3. Progress Report:
Approximately 1200 pigs were weaned at 24 d of age in two replicates. Pigs were randomly assigned to either a nursery room that had been fully cleaned and disinfected or a nursery room left unclean since the previous group of pigs to induce an indirect immune challenge. Within a room, pigs were randomly assigned to either control diets, control diets + antibiotics (cholorotetracycline/Denegard), or control diets + lysozyme and allowed to consume diets ad libitum for four weeks. Pig weights and feed disappearance were measured weekly. As expected, immune-challenged pigs grew at a slower rate than nonchallenged pigs and both antibiotics and lysozyme improved growth performance. Blood was collected from a portion of pigs (n=28 per treatment) on d 0, 14, and 28 of treatment. Rectal swabs were taken on d 0 and 28 of treatment for pathogen analysis. After four weeks of treatment a subsample of the pigs (n=20 per treatment) were harvested to determine their body composition. The remaining pigs were moved to finishing facilities consuming common diets where pig weight and days to market are currently being recorded. Pigs for body composition have been ground and subsamples frozen until further analysis. Proximate analysis is currently underway on those samples. Serum was harvested and frozen for further analysis. Cytokine and acute phase protein analysis is currently underway. Initial pathogen analysis was completed and confirmation via real time RT-PCR is currently underway.