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THE ABILITY OF RAM INTRODUCTION TO INDUCE AN LH SURGE IN FALL BORN EWE LAMBS DURING ANESTROUS AND MODIFICATION OF THE LH SURGE BY PROGESTERONE AND ESTROGEN.
Knights, Marlon1, Baptiste, Quinn1, Lewis, Paul1, 1
ABSTRACT- The ability of ram introduction (RI), estrogen (E2) and progesterone (P4) pre-treatment to induce an LH surge and modification of the surge by E2 and P4 was investigated in fall born ewe lambs of mixed breeding during seasonal anestrus. Fall born ewe lambs were untreated (C, n =7), exposed to rams (R, n = 7), treated with E2 (E, n = 5; 25 mg i.m.), administered P4 with a CIDR device for 5 d only (P, n = 5), treated with a CIDR device and introduced to rams at CIDR withdrawal (PR, n =11), treated as the PR group with E2 24 h after CIDR withdrawal (PER, n = 11), or treated with CIDR and E2 alone (PE). Blood samples for determination of LH concentrations were collected every 4h from CIDR withdrawal/ram introduction for a period of 60h. The onset (first sample in which LH concentration exceeded the baseline by 2 standard deviations), duration (time when LH concentration exceeded the baseline by 2 standard deviations for at least 2 consecutive samples), amplitude (peak LH concentration) and area under the curve (AUC) of the LH surge profiles were determined. Age and weight of ewe lambs were 250.7 ± 1.3 d and 41.8 ± 0.6 kg, respectively. To determine the ability of RI, E2 and P4 to induce an LH surge, comparisons were made among ewes in C, R, E and P treatment groups. More ewes (P < 0.05) showed an LH surge in R (7/7) and E (4/5) than in the C or P groups (0/7 and 0/5, respectively). P4 pre-treatment delayed the initiation of the ram-induced LH surge (P = 0.08; 43.5 ± 3.8 and 32.6 ± 4.6 h, for PR and R groups, respectively), but did not affect the duration, amplitude or AUC. P4 pre-treatment also reduced the duration of the E2-induced LH surge (P < 0.05; 12 ± 1.7 and 8.8 ± 0.5 for E and PE treatment groups respectively). In ewes pre-treated with P4 and introduced to rams, E2 hastened the onset (P < 0.01; 33 ± 1.2 and 43.5 ± 3.8 h) and increased the amplitude of the LH surge (P = 0.05; 151.6 ± 2.4 and 89.6 ± 3.6 for ewes in PER and PR treatment groups, respectively). In summary, during seasonal anestrus, fall born ewe lambs do not show an LH surge in response to P4 pre-treatment alone, however RI or E2 alone or following P4-pre-treatment is capable of eliciting an LH surge.
KEY WORDS: lambs, anestrous, ram-effect, LH
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