Occurrence of peri-parturient rise in trichostrongylid nematode egg output in Dorper ewes in a semi-arid area of Kajiado District of Kenya.

An investigation on the occurrence of peri-parturient rise in trichostrongylid nematode egg output in breeding ewes was carried out on a Ranch in the semi-arid area of Kajiado District in Kenya during the period May 1999-April 2000. During the study, 20 ewes randomly selected from the breeding stock and 20 un-mated female yearlings were monitored for faecal strongyle egg output every 3 weeks. A significant peri-parturient rise in faecal egg output occurred at around the time of lambing and throughout the lactation period in the mated ewes, but not in the un-mated yearlings. The occurrence of peri-parturient rise in breeding ewes towards the end of the dry season and at the onset of the short rains was enhanced by the resumption of development of hypobiotic larvae. Self-cure occurred in the un-mated yearlings in September 1999 during the dry season and in November-December 1999 during the wet season, but was less obvious in the pregnant and lactating ewes. The peri-parturient ewes contributed to higher pasture contamination at a time when highly susceptible lambs were grazing alongside. Therefore, the control of gastrointestinal nematode parasites in ewes in this area should aim at reducing the effects of this phenomenon through treatment of ewes about 2-3 weeks to lambing and during lactation.