Stimulation of delayed puberty in heifers by using a PRID regime

摘要

The objective of the present study was to stimulate delayed puberty in heifers by using a PRID (a progesterone releasing intravaginal device, impregnated with 1.55 g of progesterone and 10 mg of oestradiol benzoate) regime. Prior to the study, individual ages (20 to 30 months) and body condition scores, BCS (2.25 to 3.5 units; 1-5 scale with 0.25 intervals) were recorded. For each of 33 heifers (29 Brown Swiss, 4 Holstein) with delayed oestrus (smaller ovaries with no cyclic structures), a PRID apparatus was then inserted for 12 days. Following the withdrawals, fixed-time intracervical inseminations (AI) were performed at 48 and 72h. Blood samples were collected by jugular venipuncture on the 21st day of AI for determining plasma progesterone (P_4 concentrations by EIA. Rectal palpations were also performed on the 60th day to confirm pregnancies. Results showed that the vast majority of heifers (93.9 per cent, 31/33) showed cyclicity (P_4 greater than 1.0 ng per ml) and a total of 54.6 per cent (18/33) pregnancy rate was obtained by PRID stimulation. A close relationship (R~2=0.718, P lower than 0.001) was found between the P_4 (varying from 0.63 to 5.86 ng per ml) and pregnancies. However, neither the age nor BCS in situ did significantly affectthe cyclicity or pregnancy rates. Findings suggest that PRID can be used effectively to stimulate puberty (cyclicity) and that the early P_4 determination (on the 21st day post-insemination) is highly indicative of the induced cyclicity (P_4 greater than1.0 ng/ml), allowing for the establishment of subsequent pregnancy in heifers with delayed puberty.