It has been shown previously that ovine placental lactogen (oPL) has a growth-promoting effect in the growth hormone (GH)-deficient dwarf rat. However, this effect has not been verified in an homologous system using animals with an intact somatotrophic axis. To examine the effects of oPL in the sheep, we injected lambs with recombinant oPL (0.1 mg/kg liveweight/day, n=16) or saline (n=16) for 21 days commencing on day 3 of life and compared their effects on body growth and energy intake with those in lambs treated with the same dose of recombinant bovine growth hormone (bGH, n=16). Circulating concentrations (ng/ml) of hormones in saline- vs bGH- vs oPL- treated lambs at day 20 of treatment were (mean±SE): oPL, <0.5 vs <0.5 vs 12.8±0.5; GH, 10.8±5.0 vs 48.4±5.0 vs 12.6±5.0, P<0.001; insulin-like growth factor-I (IGF-1), 267.6±14.4 vs 302.4±14.2 vs 291.7±14.4. Average daily gain (kg/day) during treatment was significantly (P<0.05) greater in oPL-treated lambs (0.28±0.01) than in saline-treated (0.25±0.01) or bGH-treated (0.24±0.01) lambs. Similarly, there were significant (P<0.05) increases in total energy intake (over the 21 day treatment period) during treatment with oPL (112.5±3.5 MJ ME), compared with bGH (102.0±3.5 MJ ME) or saline (102.0±3.5 MJ ME) treatment. It is concluded that oPL is somatogenic in young lambs. This effect may be mediated by stimulating voluntary feed intake rather than by elevating circulating concentrations of IGF-I.
Proceedings of the New Zealand Society of Animal Production, Volume 54, , 59-62, 1994
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