Stimulation of delayed puberty in heifers by using a PRID regime

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 21(st) day of AI for determining plasma progesterone (P-4) concentrations by EIA. Rectal palpations were also performed on the 60(th) day to confirm pregnancies. Results showed that the vast majority of heifers (93) 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 affect the cyclicity or pregnancy rates.