Investigations into glucose tolerance test in cattle. I. Relations to stage of lactation and milk yield.

Intravenous glucose tolerance test was used in 104 randomly selected milk c ows to proove the influence of stage of lactation on test results. The test period enclosed the time from 8 weeks ante partum ( begin of dry period) t o 36 weeks post partum. In another trial the glucose tolerance test was app lied in 68 first lactation cows in the time from 2 to 7 days post partum. T he test results were correlated to parameters of milk yield of the followin g lactation. The probands belong to two breeds (Friesian Dairy Cattle, SMR and Holstein-Friesian, HF). The parameters of glucose tolerance test show s ignificant changes in the time from the dry period to the lactation cycle, which can be seen as a mean for supporting milk production. The glucose and insulin related parameters differ in their reaction in dependence on time of lactation. Back fat thickness as an parameter for body fat content shows a similar behaviour as insulin related parameters. In this context their w ere prooved significant correlation coefficients between parameters of milk yield and insulin function in the range from 0,3 to 0,6. But there were se en no relevant relations between glucose related parameters and milk yield datas. No substantial differences were established between the Friesian Dai ry Cattle and Holstein-Friesian cows.