R. Dean Boyd

Mechanisms of Action for Somatotropin in Growth

Physiological processes such as growth are carefully orchestrated and controlled by complex interactions among a multiplicity of hormones (Bell et al., 1987). Somatotropin (ST) is a key somatotropic hormone and homeorhetic control. It exhibits regulatory effects on metabolism and consequently affords control over how absorbed nutrients are partitioned for growth and lactation. ST plays a pivotal role in metabolism not only during nutrient adequacy, but also during periods where nutrients are severely deficient or poorly utilized (e.g., starvation, diabetes). The metabolic and endocrine “axis” for determining how ST effects are manifested, in the two extremes cited, is the subject of an excellent review by Phillips (1986). This chapter assumes relative nutrient adequacy, commensurate with the needs for normal growth in farm animals.

The effect of sodium bicarbonate or potassium bicarbonate on acid-base status and protein and energy digestibility in swine

Abstract Three experiments were conducted to evaluate the effects of Na or K on acid-base status and nutrient utilization in young growing pigs. These studies were carried out to develop a better understanding of the growth response to alkaline salts of these minerals that have been observed in lysine-deficient swine. In experiment 1, a 2×2 factorial arrangement of 2.2 g/kg vs. 7.4 g/kg Na and ad libitum vs. meal feeding regimens was used to evaluated the effects of Na on blood acid-base variables. Na was supplemented as the alkaline salt, NaHCO 3 . For each treatment regimen, blood samples were collected via indwelling vena cava catheters every 2 hr for 28 hr. Sodium supplementation increased (P 3 − and base excess and tended (P 3 (1.3% or 2.6%) or KHCO 3 (3.0%) on apparent nutrient digestibility and nitrogen balance was investigated utilizing pigs fitted with simple T cannulas in the ileum near the ileocecal junction. A 4×4 Latin square design was used. KHCO 3 or 2.6% NaHCO 3 increased (P 3 had no effect (P 3 decreased (P 3 on gastrointestinal pH was studied. No effects (P>0.05) were observed in the stomach, duodenum, jejunum, ileum, cecum or colon. NaHCO 3 or KHCO 3 alter the acid-base balance of the pig. However, their growth-promoting effects in lysine-deficient pigs are not due to enhanced lysine or protein digestibility

Feeder unit environmental factors associated with partial carcass condemnations in market swine

Tuovinen, V.K., Gr~Shn, Y.T., Straw, B.E. and Boyd, R.D., 1992. Feeder unit environmental factors associated with partial carcass condemnations in market swine. Prev Vet. Med., 12:175-195. The impact of feeder pig finishing unit environment on partial carcass condemnations was evaluated in two studies. In a case-control study, momtonng data from 40 farms were used in the analysis. The average partial carcass condemnation percentage of 23 case farms in 1987 was 6.7%, and that of 17 control farms was 1.3%. The following factors differed (P< 0.10 ) between case and control farms in umvariate analysis: herd size, population density, ammonia concentration, amount of bedding, joint trough between pens, water delivery system, light intensity and education of the manager. Large differences between different geographical areas were also found but, owing to a relatively small sample size, could not be used in the analysis without problems. The final multiple logistic regression model (R = 0.63 ) included herd size, ammonia concentration and number of pigs per pen. In a follow-up study, a multiple regression model was developed to explain the impact of environmental factors on partial carcass condemnations in swine. Farms were selected by simple random samphng. The analysis included environmental data from 103 farms. Nine variables were significant (P<0.10) m unlvanate screemng. The final multiple linear regression model (R2=0.51) included the following variables: geographic area, amount of bedding, maximum airflow in pens, water delivery from topple, feeder, and feeding type.

Relationship between hepatic fatty acid oxidation and gluconeogenesis in the fasting neonatal pig

Hepatocytes were isolated from sixteen fasting neonatal pigs and used in two experiments: (1) to determine the effect of various factors on the ability for hepatic oxidation of fatty acids and (2) to clarify the relationship between fatty acid oxidation and glucose synthesis. In Expt 1, newborn pigs were either fasted from birth for 24 h or allowed to suck ad lib. for 3 d followed by a 24 h fast. In the presence of pyruvate, oxidation of octanoate (2 mM) was about 30-fold greater than oleate (1 mM) regardless of age, but glucose synthesis was not enhanced beyond that observed for pyruvate alone. Inclusion of carnitine (1 mM), glucagon (100 nM) or dibutyryl cAMP (50 microM) in the incubation media did not stimulate either fatty acid oxidation (octanoate or oleate) or glucose synthesis. Extending the period of fasting to 48 h (Expt 2) failed to enhance the fatty acid oxidative capacity or glucose synthesis rate. Likewise, the redox potential of the gluconeogenic substrate (lactate v. pyruvate) did not influence glucose synthesis regardless of the oxidative capacity exhibited for fatty acids. These data indicate that fatty acid oxidative capacity is not the first limiting factor to full expression of gluconeogenesis in hepatocytes isolated from fasted newborn pigs.

Decreased Glucose Response to Insulin is Maximal Within 24 Hours of Somatotropin Injection in Growing Pigs

Porcine somatotropin (pST) administration reduces the sensitivity of pigs to insulin, and after several days of treatment, it alters baseline circulating concentrations of pST, insulin, glucose, and other metabolites. The length of time required to develop this reduction in whole-body insulin sensitivity has not been established. To investigate this, eight castrate pigs received daily injections of either recombinant pST (120 micrograms/kg BW) or exicipient. Intravenous insulin tolerance tests (1.0 microgram/kg BW) were done before the first pST injection (Day 0) and on Day 1, 3, 5, and 8 of pST treatment. Control animals had insulin tolerance tests on Day 0 and again on Day 8 of treatment. By Day 8, the glucose response to the insulin tolerance tests in pST-treated pigs was 45% of the response of the control group (P < 0.01). Glucose response areas between Day 1, 3, 5, and 8 of pST treatment were not different (P > 0.10). The maximum effect of pST on glucose response to insulin was achieved by Day 1. Therefore, factors responsible for the development of reduced whole-body insulin sensitivity in pST-treated pigs are fully expressed within 21 hr of the initial pST treatment.