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Dose effect of human growth hormone-releasing factor and thyrotropin-releasing factor on hormone concentrations in lactating dairy cows |
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| Authors: | H Lapierre D Petitclerc G Pelletier L Delorme P Dubreuil J Morisset P Gaudreau Y Couture P Brazeau |
| Institution: | * Agriculture Canada Lennoxville Research Station, Lennoxville, Quebec, J1M 1Z3, Canada ** University of Sherbrooke, Sherbrooke, Quebec, J1K 2R1, Canada *** University of Montreal, Montreal, Quebec, H2L 4M1, Canada |
| Abstract: | Two experiments were conducted to study the effects of growth hormone-releasing factor (GRF) and thyrotropin-releasing factor (TRF) administration on hormone concentrations in dairy cows. In the first trial, 12 cows were used on 5 consecutive days to determine the effect of four sc doses of GRF (0, 1.1, 3.3 and 10 μg?kg?1 BW) and three sc doses of TRF (0, 1.1 and 3.3 μg?kg?1 BW) combined in a factorial arrangement. GRF and TRF acted in synergy (P = .02) on serum growth hormone (GH) concentration even at the lowest dose tested and GH response to the two releasing factors was higher than the maximal response observed with each factor alone. TRF increased (P<.01) prolactin (Prl), thyrotropin (TSH), triiodothyronine (T3) and thyroxine (T4) concentrations similarly at the 1.1 and 3.3 μg?kg?1 doses and GRF did not interact (P>.40) with TRF on the release of these hormones. In the second trial, the effect of GRF (3.3 μg?kg?1 BW, sc) and TRF (1.1 μg?kg?1 BW, sc) was tested at three stages (18, 72 and 210 days) of lactation on serum Prl and TSH concentrations. Eighteen cows (n = 6 per stage of lactation) were used in two replicates of a 3 × 3 latin square. The TRF and GRF-TRF treatments were equipotent (P>.05) in increasing Prl and TSH concentrations. Prl and TSH responses were similar (P>.40) throughout lactation. In summary, GRF at doses ranging from 1.1 to 10.0 μg?kg?1 and TRF at doses ranging from 1.1 to 3.3 μg?kg?1 act in synergy on GH release and do not interact on Prl, TSH, T3 and T4 concentrations in dairy cows. Furthermore, Prl and TSH response to TRF are not affected by stage of lactation. |
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