The effect of subclinical experimental Cowdria ruminantium infection in ewes on the growth and milk consumption of pre-weaning lambs

An alternative control option for heartwater (Cowdria ruminantium infection ) is the establishment and maintenance of endemic stability which would les sen the existing dependence on acaricides. In an endemically stable state, animals become infected by vaccination or natural challenge at an early age , following which the immunity so created is boosted by continuing tick cha llenge. In this study, growth rates, health and hematological parameters we re monitored at regular intervals for lambs born to two matched groups of e wes until weaning at 4 mo of age. One group of ewes was infected multiple t imes with Cowdria ruminantium; the other group remained uninfected. The ove rall mean leucocyte count of lambs born to infected ewes was significantly lower than that of lambs born to uninfected ewes (P=0.04), However, there w ere few other significant differences in the other hematological data betwe en the two groups. The mean birth weight of single lambs born to uninfected ewes (4.6 kg) was significantly higher than the mean birth weight of singl e lambs born to infected ewes (4.4 kg) (P=0.02). Trends in milli consumptio n and growth rates were similar for the two groups, with few significant di fferences detected, Likewise, there were no significant differences in the incidences of health problems or pre-weaning mortalities between the two gr oups of lambs. The results of this study indicate that there is no detectab le effect on productivity of pre-weaning lambs when their dams are carriers of C, ruminantium - a situation likely to occur in an endemically stable s tate. Hence, maintenance of endemic stability would be a suitable control o ption for heartwater. (C) 1999 Elsevier Science B.V. All rights reserved.