The pattern of GH secretion was studied in Coopworth sheep which have been selected for low (Lean) or high (Fat) ultrasonic backfat depth over 15 years. At each of two developmental stages (February and May) Lean and Fat ram lambs were fed ad libitum or fasted for 48 hours (n=6 per treatment). Animals were blood sampled via an indwelling jugular cannula every 10 minutes for six hours, then slaughtered and the pituitary glands removed and weighted. Mean GH was greater for Lean than Fat animals (2.82 versus 1.42 ng/ml, p<0.001), in February than in May (2.47 versus 1.62 ng/ml, p<0.001) and for fasted than fed animals (2.48 versus 1.62 ng/ml, p<0.001). Analysis of GH secretory patterns showed that peak frequency for Lean animals was more than twice that for Fat animals (2.64 versus 1.17 peaks/6 hours, p<0.001). There was no difference in the peak amplitude. In line with their higher GH concentrations, Lean animals had significantly heavier pituitaries than Fat animals (0.74 versus 0.52 g, p<0.001). Selection for leanness in Coopworth sheep has altered the GH secretory pattern of the animals. The pituitary weight may explain some of these changes in GH secretion.

SM, Francis, BA Veenvliet, RP Littlejohn, SK Stuart, and JM Suttie

Proceedings of the New Zealand Society of Animal Production, Volume 55, , 272-274, 1995
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