A note on the effect of individual housing conditions on LH secretion in ewes after exposure to a ram

Abstract

To determine whether it is feasible to use the stimulus of exposure to a ram to induce sexual activity in individually housed ewes, 33 adult anoestrous ewes were randomly allocated to two treatments: Group 1, n=20, housed in individual pens, with a ram’s pen situated between every two ewes (exposed to rams through the pen’s bars) and Group 2, n=13, housed in a communal pen with five rams (full contact with the rams). The day before the introduction of rams, blood samples were collected from Group 1 ewes, for 6 h at 15 min intervals commencing 10:00 h. Rams were introduced in both groups the following day at 8:00 h. Two hours later, blood samples were collected from Group 1 ewes for 6 h at 15 min intervals. Thereafter, ewes and rams were moved to a communal pen and blood samples collected every 3 h until 10:00 h the next day. In Group 2, blood samples were collected every 3 h for 24 h starting at 10:00 h, 2 h after the rams were introduced. From the samples collected at 15 min intervals, no differences between mean LH concentrations, pulse frequencies and amplitudes before or after the introduction of rams were observed in Group 1. The percentage of ewes presenting a pre-ovulatory surge of LH in the first 24 h after the introduction of rams was similar in both groups (Group 1: 50%, 10 ewes; Group 2: 61.5%, 8 ewes). The pre-ovulatory LH surges began approximately 7 h later ( P=0.05) in Group 1 than in Group 2 (18.5±2.2 h versus 11.8±2.6 h, respectively). Mean plasma LH concentrations were significantly higher in Group 2, during the first 8 h after the introduction of rams, these differences disappeared when all the animals were moved to the communal pen. In conclusion, individual housing together with frequent blood sampling conditions do not induce a significant increase of LH secretion of anoestrous ewes after a ram effect, as compared with that in rams and ewes in communal pens. Further experiments are necessary to separate, on one hand, the effect of housing and on the other hand, the effect of sampling frequency on LH secretion after a ram effect.