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 det ermine effects of breed (Targhee vs Suffolk), energy intake (Ix vs 3x NEm r equirements, and physiological status (nonpregnant, nonlactating vs lactati ng) on serum GH, insulin, NEFA, glucose, and blood urea nitrogen (BUN) conc entrations. 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 curv e (AUC) than nonlactating ewes. The AUC was greater (P < .01) in ewes fed I x NE, than in ewes fed 3x NE,. Energy intake had no effect on serum GH befo re feeding (P > .23) when evaluated within physiological statuses. After fe eding, GH concentrations were greater (P < .10) for ewes fed Ix NE, than fo r those fed 3x NEm. Insulin and glucose did not differ (P > .23) between en ergy intake levels. Insulin and glucose were greater (P < .001) in nonlacta ting than in lactating ewes when evaluated within breed. Lactating and Targ hee ewes fed Ix NEm had greater (P < .001) NEFA concentration than nonlacta ting and Targhee ewes fed 3x NEm, respectively. Ewes fed 3x NEm and Targhee ewes had greater (P < .005) BUN concentrations than ewes fed Ix NEm and Su ffolk ewes, respectively. Physiological status seems to play a more importa nt role in the regulation of GH than does energy intake. Higher BUN concent rations in Targhee than in Suffolk ewes demonstrates one metabolic event th at distinguishes a breed's adaptation to the environment in which it origin ated.