A COMPARISON OF PLASMA PROLACTIN, LH AND PROGESTERONE CONCENTRATIONS DURING ESTRUS AND EARLY-PREGNANCY IN EWE LAMBS AND EWES

An investigation was conducted to compare, the LH, prolactin and progesterone profiles of ewe lambs with ewes during oestrus and early pregnancy. Peak LH concentration, was significantly lower (P < 0.05) and duration of release tended to be shorter during oestrus in ewe lambs, Furthermore, this smaller LH peak tended to be associated with a lower ovulation rate. LH pulse rate, amplitude and concentration were similar in both groups during day 13 of pregnancy. However, LH concentration was higher in ewe lambs compared with ewes on day 28 of pregnancy. Peak prolactin concentration was lower during oestrus in ewe lambs (P < 0.05) but there was no difference between the two groups during early pregnancy. Plasma progesterone concentrations were similar in both groups until day 13 of pregnancy. Thereafter, mean progesterone concentration was lower, from day 14 to 30, in the ewe lambs (P < 0.05). These results indicate that in ewe lambs and ewes maintained under identical conditions plasma hormone profiles differ during oestrus and early pregnancy. Moreover, these differences probably contribute towards the lower reproductive performance of ewe lambs.