Differences in growth hormone and prolactin secretion associated with environmental temperature and energy intake

The combined effects of environmental temperature and level of energy intake on plasma concentrations of growth hormone (GH) and prolactin (PRL) have been investigated in 14 week old pigs acclimated to 35 or 10 degrees C on a high (H) or low (L) energy intake (H = 2L). Measurements were made at 15 min intervals between 08.00 and 18.00 hours, after feeding at 17.00 hours on the previous day. Mean values of GH were greater in pigs on the L than H intake and there was a tendency for values to be higher at 35 than 10 degrees C. However, there was wide individual variation within each treatment group and the differences were not statistically significant. Mean PRL concentrations were greater at 35 than 10 degrees C (P less than 0.05). It is concluded that circulating levels of plasma GH do not have a major role in maintaining the differences in growth and morphology of young pigs kept in widely different environmental conditions. However, these differences could be related at least in part to the GH-like properties of PRL.