Influence of gestation on oestrone sulphate concentration in milk of zebu and crossbred cows and Murrah buffaloes.

Single milk samples collected during pregnancy from 128 Sahiwal (zebu), 295 Karan Swiss and 198 Karan Fries cows and 164 Murrah buffaloes were analysed for oestrone sulphate by a sensitive, direct, radioimmunoassay procedure developed in the laboratory. Mean oestrone sulphate levels were below detection limit (< 50 pg/ml) during the first 2 months of pregnancy in all animals. There was an exponential increase in the hormone concentration beginning at the fourth month of pregnancy in cows, although the rate of increase was greatest among Sahiwal cows, followed by Karan Swiss and Karan Fries cows in that order (P < 0.01). An exponential increase in oestrone sulphate levels was also recorded in buffaloes beginning at the fourth month of gestation. However, the mean hormone levels in this species, after initially being lower than Sahiwal and Karan Swiss cows up to 6 months of pregnancy, increased to higher levels thereafter. From this study it was concluded that in addition to genetic factors, environmental adaptation could also influence the oestrone sulphate levels. In addition, the study also provided a basis for pregnancy confirmation by milk oestrone sulphate determination after 110 days in gestation in cattle and buffaloes using a simple, direct, assay procedure.