Fowl typhoid in cocks. Age dependent susceptibility of the birds´ disease

CHACANA, P. A.; TERZOLO, H. R.

ADVANCES IN AGRICULTURAL SCIENCES

Lugar: Szcezin, Polonia; Año: 2006 p. 13 - 18

This work was carried out to assess experimental models for production of fowl typhosis in cocks and hens. In order to standardize the virulence of the challenge strain, Salmonella gallinarum INTA 91, a limited and fixed number of passages through artificial media were made. Chickens were challenged with S. gallinarum by gavage into the crop and kept in observation during 3 weeks. Mortality was daily recorded. Susceptibility of 24 week-old cocks and laying hens of the same age was compared. The disease was produced when cocks where orally challenged with 1010 or more colony-forming units (CFU) per chicken; Reed and Muench´s LD50 of S. gallinarum value was estimated as 3.16 x 1010 CFU per cock.  In contrast, almost all the hens of the same age died when challenged with 105 CFU onwards. The higher susceptibility of these hens can be explained by their egg production stress while the cocks used in these trials were not exposed to any reproductive pressure. Cocks of 58 weeks of age were more susceptible to infection: the LD50 value was estimated as 1.75 x 107 CFU per cock. In all trials, fowl typhosis signs started after 5 to 15 days after challenge. The disease was acute and septicemia was consistently produced. All challenged chickens that became ill showed anorexia, somnolence, and depression. None of the diseased cocks or hens had diarrhea. Animals died 2 or 3 days after the onset of symptoms. Enumeration of S. gallinarum in livers was around 8 log10 CFU per gram, regardless the age or sex of the examined chickens.