Submitted to: Poultry Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/20/2004
Publication Date: 2/5/2005
Citation: Kubena, L.F., Byrd II, J.A., Moore, R.W., Ricke, S.C., Nisbet, D.J. 2005. Effects of drinking water treatment on susceptibility of laying hens to Salmonella enteritidis during forced molt. Poultry Science. 84:204-211. Interpretive Summary: Salmonella is a food borne bacteria that lives in the gut of chickens and other animals. It is estimated that up to 4 million people in the United States get sick from Salmonella each year, with about 25% of these illnesses caused by one particular group of bacteria called Salmonella enteritidis (SE). The SE can get into the internal organs, including the ovaries, of laying hens and contaminate eggs that are consumed by humans. Chickens and other avian species undergo a natural process called molting, where feathers are lost, the reproductive tract shrinks, and the hens quit laying eggs; basically, the hens have a period of rest. This is followed by the growth of a new set of feathers, an increase in the size of the reproductive tract, and the beginning of a second cycle of egg production. In commercial egg production, the hens do not experience molting until the end of a long laying period and the number of eggs and the quality of the eggs decreases as the hens get older. Since it is often economically advantageous to add a second productive egg-laying cycle, producers often induce a molt. Feed withdrawal and a reduction in the length of time the hens receive light is the primary method used in the layer industry. Unfortunately, the stress associated with feed withdrawal may cause an increase in the number of hens that become infected with SE and thus increase the risk of human illness from SE contaminated eggs. In the present study, treating laying hens experimentally infected with SE with acetic acid or lactic acid in the drinking water did not reduce the number of hens testing positive for SE. Based on the results of this study, additional research is needed using different acid-water treatments together with some alternative molt feeding regimens. These may prove to be more effective tools to reduce food borne illnesses by reducing disease causing bacteria following molting of laying hens.
Technical Abstract: Feed deprivation is used in the layer industry to induce molting and stimulate multiple egg-laying cycles in laying hens. However, stress due to feed deprivation causes increased susceptibility to Salmonella enteritidis (SE), increases the risk of SE positive eggs, and increases incidence of SE in internal organs. Leghorn hens over 50 wk of age were divided into 4 treatment groups of 12 hens each in Experiment 1 and 3 treatment groups of 12 hens in Experiments 2 and 3 and placed in individual laying hen cages. One treatment group was non-molted and received feed ad libitum (NM) and a second treatment group was force molted by feed removal (M) for 9 d. These 2 groups received distilled water ad libitum. A third treatment group was force molted by feed removal for 9 d and received 0.5% lactic acid (LA) in distilled water ad libitum. An additional group (4) in Experiment 1 only was force molted by feed removal for 9 d and received 0.5% acetic acid in distilled water ad libitum. Seven days before feed removal hens were exposed to an 8-h light and 16 h-dark photoperiod which was continued throughout the experiment. Individual hens in all treatments were challenged orally with 105 SE on day 4 of feed removal. When compared with the NM treatments, weight losses were significantly higher in the M treatments, regardless of water treatments. When compared with NM treatments, crop pH was significantly higher in the M treatment receiving distilled water. Crop pH was reduced to that of the NM controls by 0.5% lactic acid or 0.5% acetic acid in the drinking water. No consistent significant changes were observed for volatile fatty acids. The number of crop and ceca culture positive hens and the number of SE per crop and the number of SE per gram of cecal contents were higher in the M treatments, when compared to the NM treatments but there was no effect from the addition of the either of the acids to the drinking water. Additional research utilizing different acid treatment regimens may prove to be a tool for reducing the incidence of SE in eggs and internal organs during and following molting of laying hens.