Effects of level of energy intake and energy demand on growth hormone, insulin, and metabolites in targhee and suffolk ewes

Yearling ewes (n = 32) were used in a 2 x 2 x 2 factorial experiment to determine effects of breed (Targhee vs Suffolk), energy intake (1x vs 3x NE(m) requirements, and physiological status (nonpregnant, nonlactating vs lactating) on serum GH, insulin, NEFA, glucose, and blood urea nitrogen (BUN) concentrations. Blood collections were made in two periods that began 21 and 32 d after ewes lambed. Lactating ewes had more GH peaks (P < .10), higher (P < .01) mean GH concentration, and greater (P < .01) area under the GH curve (AUC) than nonlactating ewes. The AUC was greater (P < .01) in ewes fed 1x NE(m) than in ewes fed 3x NE(m). Energy intake had no effect on serum GH before feeding (P > .23) when evaluated within physiological statuses. After feeding, GH concentrations were greater (P < .10) for ewes fed 1x NE(m) than for those fed 3x NE(m). Insulin and glucose did not differ (P > .23) between energy intake levels. Insulin and glucose were greater (P < .001) in nonlactating than in lactating ewes when evaluated within breed. Lactating and Targhee ewes fed 1x NE(m) had greater (P < .001) NEFA concentration than nonlactating and Targhee ewes fed 3x NE(m), respectively. Ewes fed 3x NE(m) and Targhee ewes had greater (P < .005) BUN concentrations than ewes fed 1x NE(m) and Suffolk ewes, respectively. Physiological status seems to play a more important role in the regulation of GH than does energy intake. Higher BUN concentrations in Targhee than in Suffolk ewes demonstrates one metabolic event that distinguishes a breed's adaptation to the environment in which it originated.