|Peebles, E -|
Submitted to: Journal of Applied Poultry Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 25, 2011
Publication Date: September 15, 2012
Citation: Peebles, E.D., Branton, S.L. 2012. Mycoplasma gallisepticum in the commercial egg-laying hen: an historical perspective considering effects of pathogen strain, age of bird at inoculation, and diet on performance and physiology. Journal of Applied Poultry Research. 212:897-914. Interpretive Summary: Mycoplasma gallisepticum (MG) is a pathogenic bacteria that affects approximately 90% of the nation’s egg-laying chickens. Once the organism infects a chicken, the infection remains for the life of the bird as no antibiotic will completely rid the bird of the organism. The presence of the organism in the chicken results in a loss of about 16 eggs over the typical 45 week laying cycle which equates to a loss of about $140 million annually in the US. Four live MG vaccines are now available to help poultry table-egg producers cope with MG: all have limitations and, as such, dietary supplementation with various poultry feed additives has been investigated. Information derived from various experiments with the various vaccines and supplements is reported and may be useful in improving the productivity and profitability of the commercial egg industry.
Technical Abstract: Mycoplasma gallisepticum (MG), a pathogenic organism, primarily causes respiratory distress, but can also spread systemically to subsequently reduce egg production and egg quality in laying hens. However, the effects of MG on the performance and physiology of the commercial laying hen have been shown to vary in relation to the strain of MG and the age of the bird when challenged. In an effort to protect birds against more virulent field strains of MG, such as the R- and S6-strains of MG, on multi-age commercial farms where eradication is not feasible, milder strains of MG, such as the F-, 6/85-, and ts11-strains of MG, have been introduced as live vaccines to help displace the natural field strains. The benefits and drawbacks of the individual and combined use of these various vaccine strains are discussed in this article along with a comparative analysis of their subsequent effects on various performance and physiological variables and their interrelationships. The effects of the strains of MG examined in this report on layer performance have been found to be associated with changes in various characteristics of the blood and of the liver, ovary, and oviduct. The limited influences of the 6/85- and ts11-strains of MG on the reproductive system of the layer that have been reported are likely a result of their lower relative level of virulence in comparison to the F-strain of MG. Nevertheless, pre-lay inoculations of either the 6/85- or ts11-strains of MG used in conjunction with an overlay of the F-strain of MG during lay has the potential of being an effective vaccination regimen for the continual protection of commercial flocks against field strain MG infections, while preventing the adverse effects on performance associated with an individual inoculation of the F-strain of MG. In an additional effort to positively modify the effects of MG vaccination regimens on layer production, outcomes of the use of various dietary supplements have been explored. The supplemental dietary regimens discussed in this article include 0.75 or 1.50% poultry fat, the combination of phytase and 25-hydroxycholecalciferol, and the combination of 1.50% poultry fat, phytase, and 25-hydroxycholecalciferol. The 1.50% level of poultry fat alone or the combination of phytase and 25-hydroxycholecalciferol alone have shown potential in alleviating depressions in the egg production of layers as a result of being vaccinated with the F-strain of MG. Consideration of the information provided in this article concerning differences in the effects of MG strain, the age at which MG vaccines are given, and the use of dietary supplementation on laying hen performance and physiology may be useful in improving the productivity and profitability of the commercial egg industry.