ChileanJAR

This study was done during two seasons, in 1971/72 and 1972/73. Twentyfive Hereford and 25 Holstein, six months oid calves, were used in each season. Animals were ailotted, in a randomized block design, to eight treatments, with 2 x 2 x 2 factorial structure and 5 replications. Two grazing periods were measured: winter, with grass silage and concentrate supplementation, and spring-summer, to test residual effects. Five Hereford and five Hoistein calves were-assigned to a high and a iow plane of nutrition, with and without anthelmintic treatment; they were allocated to one of four 2 ha paddocks, subdivided in 6 plots of 0.333 ha. In two other 1 ha paddocks, 10 extra calves (half of each breed) were maintainéd, but only one group was given antheimintic drenchs. These animals were used to adjust the stocking rateto the dry matter availability of the treatments. The four groups under treatment were kept separate during the winter season and were grazed in one group, during the spring-summer season. The two nutritional planes were adjusted with supplementation (silage + concentrate), according to the grass D.M. availability in each paddock, during the first year, and based on daily gains of the groups with anthelmintic treatment, during the second season. The statistical analysis reveals significant differences for nutritional plane, anthelmintic treatment, breed and ason (P < 0.01), it was concluded that there isa clear difference in resistance to parasitic infestation, since Hereford calves have a much higher death risk, if not treated with anthelmintics; also, daiiy gains are only 43% of those obtained with Holstein calves. The high plane of nutrition may replace the anthelmintic treatment, only in the Holstein breed.