This trial was carried out in the rainy (May-October) and the low rainfall (November-April) seasons with 30 suckling lambs by assay. The lambs, from 20 days of born until 125 days of age (weaning) were maintained next to their mothers in continuous grazing at the "La Curva" Unit of the "Antonio Maceo" Company, located at the Bayamo Municipality, Granma Province, Cuba. The grass was
Dichanthium caricosum
and the animals oscillated between 12 and 15 sheep per ha, according to the availability of the grass. The lambs were weighed when born and every 15 days the parasitic load was determined by coprological exam and the results expressed in quantity of eggs per gram of feces, daily weight gain (g), and mortality (%). During the assay the genus
Haemonchus
was the most prevalent and numerically important. In both seasons of the year, it was observed a significant positive lineal relationship between the fecal egg count and the mortality with the age, while this relationship was negative with the mean daily gain of weight. The lambs after the first month of grazing remained infested with
Haemonchus spp,
Oesophagostomum
spp.,
Bunostomum
spp. and
Trichostrongylus
spp.
