Pituitary and serum growth hormone levels in Duroc and Yorkshire swine genetically selected for high and low backfat.

Serum and pituitary growth hormone (GH) concentrations were measured by radioimmunoassay in 69 Duroc and 70 Yorkshire swine genetically selected for at least 14 generations for either high backfat (high line) or low backfat (low line). For both breeds, the high line pigs had lower serum GH at weaning (P<.05) and lower serum and pitui tary GH at slaughter (P<.01) than the unselected control lines, indicating that lower GH levels were associated with selection for high backfat. Serum GH was higher in neonatal swine (within 48 hr of birth, P<.01) than in swine at weaning (8 wk of age) or slaughter (95 kg body weight). There was no significant differences in pituitary or serum GH between barrows and gilts. Pituitary GH was higher in Durocs (P<.01) than in Yorkshires, but serum GH was not different between breeds. (