Nutrient uptake by the hindlimb of growing pigs treated with porcine somatotropin and insulin.

The shift in nutrient partitioning induced by porcine somatotropin (pST) is accompanied by a decrease in insulin sensitivity for whole-body glucose uptake. The relative contribution of metabolic changes in the hindlimb was investigated in eight pigs (55 kg) that had received recombinant pST (120 micrograms/kg) or excipient (control) for 7 d. Uptake of metabolites by the hindlimb was measured under basal conditions and during hyperinsulinemic-euglycemic clamps at low [14 ng/(kg.min)] and high [360 ng/(kg.min)] insulin infusion rates. Dextrose infusion rate required to maintain euglycemia was used as an index of whole-body glucose uptake in response to exogenous insulin. Effects of pST on hindlimb and whole-body glucose uptake were evident only at physiological levels of insulin (basal and low insulin infusion rate). During the low rate of insulin infusion, dextrose infusion rate was 79% lower for pST-treated pigs and glucose uptake by the hindlimb was 59% lower compared with control pigs. The decrease in glucose uptake by the hindlimb was entirely accounted for by the estimated reduction in glucose utilization by adipose tissue of the hindlimb. Glucose:oxygen quotients were reduced during basal (57%) and low insulin infusion (63%) with pST treatment, indicating a change in the pattern of substrate utilization. This is consistent with the concept that pST directs nutrients away from adipose and towards muscle growth by altering the response of tissues to homeostatic signals such as insulin.

Porcine somatotropin affects the dietary lysine requirement and net lysine utilization for growing pigs.

This study was conducted to determine the effects of exogenous porcine somatotropin (pST) on the dietary lysine requirement and efficiency of absorbed lysine utilization for pigs during the 20- to 60-kg phase of growth. Seventy-two crossbred pigs (20 +/- 0.7 kg body wt) received daily intramuscular injections of either excipient (0 dose) or pST (150 micrograms/kg body wt) and were fed diets in which protein and lysine concentrations ranged from 6.4 to 23.5 g/100 g diet and from 0.40 to 1.48 g/100 g diet, respectively. Nutrient density was altered to compensate for reduced feed intake with pST, but diets were approximately isocaloric. Rate and efficiency of gain and whole-body protein accretion rate exhibited a dose-response improvement (P < 0.01) to increases in dietary protein for both excipient and pST-treated pigs. Pigs receiving pST grew more rapidly and more efficiently than control counterparts (P < 0.01). Treatment with pST improved the rate of protein accretion (P < 0.01) at all but the lowest level of dietary protein. The net lysine utilization for lysine accretion and maintenance was 0.46 for control pigs and 0.57 for pigs receiving pST, a 24% improvement in the efficiency. Thus, treatment with pST increased the maximum rate of protein accretion as well as the partial efficiency with which dietary lysine is used for protein accretion. Consequently, only a 9% increase in dietary lysine was required to maximize protein deposition in pST-treated pigs, because the metabolic efficiency of lysine utilization was improved.

Dose-dependent effects of exogenous porcine somatotropin on the yield, distribution, and proximate composition of carcass tissues in growing pigs.

Dose-dependent effects of porcine somatotropin (pST) on mass, distribution, and proximate composition of carcass tissues were investigated in 46 growing pigs. Barrows, weighing 30 +/- 1 kg, were assigned to five treatment groups to receive 0, 50, 100, 150, or 200 micrograms of recombinant pST/kg BW per day until pigs individually reached the 90-kg slaughter weight. Left carcass sides were fabricated into whole-sale cuts that were separated into muscle, adipose tissue, bone, and skin. Despite the reduction in dressing percentage, total muscle mass of the side was significantly increased by 3.9 to 5.7 kg (28 to 36%) by the lowest and highest doses of pST, respectively, whereas adipose tissue mass was decreased by 4.4 to 8.6 kg (38 to 74%). Bone mass was increased by 8 to 27% (P < .05), and skin mass was increased by 16 to 38% (P < .01) across the dose range. Distribution of carcass weight among the wholesale cuts was altered by pST toward lower proportions in the belly, jowl, and fat trimmings and greater proportions in the four lean cuts. Porcine somatotropin substantially reduced lipid concentration in all muscle groups in a dose-dependent manner, resulting in increased protein and moisture concentrations (P < .05). Adipose tissue lipid concentrations were reduced to an even greater extent at each dose. The progressive increase in muscle mass observed with pST doses > 50 micrograms/kg BW was less than the associated decrease in adipose tissue mass, indicating that a dose range of 50 to 100 micrograms/kg BW per day may be optimum for improving carcass value.

Influence of genotype and sex on the response of growing pigs to recombinant porcine somatotropin.

The dose-dependent effects of porcine somatotropin (pST) on growth performance and composition of carcass gain were investigated in 150 growing pigs. The experiment involved two genotypes (barrows from the Pig Improvement Company [PIC] and a University of Nebraska [NEB] gene pool line) and two sexes (PIC barrows and boars). At 30 kg, pigs were randomly assigned within each genotype and sex subclass to receive daily i.m. injections of 50, 100, 150, or 200 micrograms of pST/kg BW or an equivalent volume of an excipient. A diet (3.5 Mcal of DE/kg) supplemented with crystalline amino acids and containing 22.5% CP was available on an ad libitum basis until pigs were slaughtered at approximately 90 kg live weight. Excipient-treated PIC barrows exhibited faster and more efficient growth (P less than .001) and a higher capacity for carcass protein accretion (P less than .001) but similar rates of lipid deposition compared to excipient-treated NEB barrows. Within the PIC genotype, control boars grew at a rate similar to that of barrows, but they were more efficient (P less than .05) and deposited more carcass protein (P less than .05) and less lipid (P less than .001). Carcass protein accretion rate increased (P less than .001) up to approximately 150 micrograms of pST.kg BW-1.d-1, whereas lipid deposition decreased (P less than .001) with each incremental dose of pST. Although differences between PIC boars and barrows for all criteria were negated with increasing pST dose, they were maintained between the two genotypes. Polynomial regressions suggested that a slightly higher pST dose was required to optimize the feed:gain ratio compared with rate of gain and that the dose (micrograms per kilogram BW per day) was a function of the genotype and sex (feed:gain: 185, 170, and 155; rate of gain: 155, 155, and 125 for NEB barrows, PIC barrows, and PIC boars, respectively).