Mycoplasma infections are common in laying hens. In the UK a recent survey showed that 83% of flocks were infected with M. synoviae. M. gallisepticum is less common but usually more serious, as an acute outbreak can cause a drop of 10-20% in egg production and a chronic non-clinical infection can reduce egg production by 5.3% over the laying period. M. synoviae is less damaging but it also can cause a drop in production in the acute phase, which commonly occurs at the main stress periods of point of lay and approaching peak production, so performance is not quite optimal. Coincidental virus infections, which often flare up at this time, such as infectious bronchitis virus, can also compound matters.
Many producers monitor mycoplasma status at point of lay and subsequently, especially if they have a history of the infection or it is a multi-age site. However, positive results by rapid slide agglutination test (rapid plate test) and by ELISA test usually indicate the challenge occurred respectively, 1 or 2 weeks earlier, so often the initial infection and early damage has taken place some time prior to detection.
As a result, the prophylactic use of antimicrobials is commonly employed at stress times, usually at point of lay (approximately 20 weeks of age) and again approaching peak production (approximately 5-6 weeks later) where Denagard has a zero withdrawal for eggs permitted. Denagard at both 0.0125 and 0.025% in the drinking water for 3 days (approximately 12.5-25mg tiamulin/kg bwt) have been used to minimise the impact of a mycoplasma infection at this time and to maintain production. The higher dose rate may have an impact on water intake and may transiently depress egg production; hence the lower level is usually preferred. Denagard can be administered in feed as an alternative at 250-500 ppm and does not appear to affect palatability and performance.
| Denagard prevention programme |
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In some countries, Denagard Premix is regularly used in feed at 20ppm continuously to improve egg production and feed conversion efficiency (FCE). An improvement on average of 5.5% has been consistently achieved (see Egg production). An alternative approach was to use Denagard at 50ppm in feed for 1 week each month. This was shown to improve egg production by over 5% but FCE was improved by 0.9%.
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