Effects of birth weight and postnatal nutrition on neonatal sheep: III. Regulation of energy metabolism.

This study investigated effects of birth weight and postnatal nutrition on regulation of energy metabolism in the neonatal lamb. Low (mean +/- SD 2.289 +/- 0.341 kg, n = 28) and high (4.840 +/- 0.446 kg, n = 20) birth weight male Suffolk x (Finnsheep x Dorset) lambs were individually reared on a liquid diet to grow rapidly (ad libitum fed, ADG = 337 g, n = 20) or slowly (ADG = 150 g, n = 20) from birth to live weights (LW) up to approximately 20 kg. At birth, small newborns had higher plasma concentrations of urea nitrogen (mean +/- SEM 8.31 +/- 0.25 vs 6.39 +/- 0.32 mM, P = 0.002) and somatotropin (ST, 49.1 +/- 17.0 vs 10.8 +/- 4.3 ng/mL, P = .045) and lower IGF-I (36.1 +/- 6.8 vs 157.7 +/- 21.8 ng/mL, P < 0.001) than large newborns. Plasma glucose (1.42 +/- 0.23 vs 2.63 +/- 0.95 mM, P = 0.147) and insulin (0.09 +/- 0.02 vs 0.13 +/- 0.06 ng/mL, P = 0.264) concentrations did not differ. Urea nitrogen concentration in plasma peaked and then declined rapidly in all lambs during the first week postpartum, and plasma ST declined on a body-weight-related basis from birth. During rearing to 20 kg LW, plasma insulin was higher in low- vs high-birth-weight lambs. Lambs fed ad libitum had greater plasma concentrations of glucose, urea nitrogen, insulin, and IGF-I compared to those fed a restricted diet (ADG = 150 g). The results suggest that during the early postpartum period, newborn lambs exhibit the fetal characteristic of high rates of amino acid oxidation. The results also support the notion that, at birth, low-birth-weight lambs are less mature than high-birth-weight lambs in aspects of metabolic and endocrine development, which may enhance their capacity to utilize amino acids for energy production and to support gluconeogenesis during the immediate postpartum period. Being small at birth also resulted in elevated plasma insulin concentrations when adequate nutriment to support moderate or rapid growth was provided postpartum, although it remains to be elucidated whether this more chronic effect persists in the longer term.

Temporal change in skeletal muscle IGF-I mRNA abundance and nitrogen metabolism responses to abomasal casein infusion in steers.

Skeletal muscle IGF-I and alpha-actin mRNA responses to increased amino acid availability were investigated in young, rapidly growing steers. Four Holstein steers (208 kg BW) were surgically implanted with an abomasal cannula and jugular catheters and allowed 2 wk to recover. Steers were offered hourly a 43:57 forage:concentrate diet at 95% of ad libitum intake supplemented with continuous abomasal infusion of glucose (to replace 12.5% of metabolizable ad libitum energy intake) for 13 d before the start of abomasal infusion of 67 g of casein N/d. Biopsies of the liver and both semimembranosus muscles were removed and frozen in liquid N, and casein infusion was begun. Muscle biopsies were collected at 8, 16, 24, and 48 h, and on d 7 and 14. Nitrogen balance increased from 23.6 to 71.5 g/d (P < .001) within 24 h and remained elevated (mean = 58.4 g/d) during the 14 d of casein infusion. Plasma urea N increased from 4 to 9.5 mg/dL at 24 h and remained unchanged to d 14. Muscle IGF-I mRNA abundance increased to 215% of basal values at 16 h (P < .01), 244% of basal values at 24 h, and 222% of basal values at 48 h after initiation of casein infusion. Values reached a maximum of 274% of basal values on d 7 and then declined to near preinfusion levels on d 14. The IGF-I mRNA abundance was approximately 100 times higher in liver than in skeletal muscle and was not different on d 0 and 14. Although plasma IGF-I concentrations were numerically higher during the first 24 h of abomasal casein infusion, they were not significantly higher during the chronic phase of treatment. Plasma IGF binding protein (BP)-2 concentrations were higher at 16, 24, and 48 h after casein infusion was begun, but IGFBP-3 concentrations were not altered at these sampling times. Neither acute (first 24 h) nor chronic (daily) plasma insulin concentrations were altered by abomasal casein infusion. Plasma somatotropin concentrations were lower (P = .008) at 24 h of casein infusion and beyond. Results suggest that enhanced amino acid availability may modulate skeletal muscle protein synthesis and accretion through an autocrine or paracrine IGF-I influence.

Effects of a dietary mixture of meat and bone meal, feather meal, blood meal, and fish meal on nitrogen utilization in finishing Holstein steers.

Our objective was to determine to what extent rate and efficiency of protein gain in finishing cattle can be enhanced by feeding an amino acid-balanced mixture of undegraded intake proteins. The Cornell Net Carbohydrate and Protein System (CNCPS) model was used to formulate a corn-based diet that would meet the rumen requirements for 410-kg large-framed steers with an estrogen implant and fed an ionophore. The CNCPS model was also used to formulate a highly undegradable intake protein (UIP) mixture from meat and bone meal, blood meal, fish meal, and hydrolyzed feather meal to provide the amino acids needed to supplement those derived from microbial protein to better meet amino acid requirements for growth. Four Holstein steers weighing 407 kg were offered a 90:10 concentrate-forage diet at hourly intervals at 95% of ad libitum intake. The steers were injected with 500 microg of estradiol-17beta at 12-h intervals to mimic the effects of an estrogenic implant. Treatments planned consisted of inclusion of the UIP mixture at 0, 2.5, 5, and 7.5% of the diet DM. Dry matter intake was fixed at 6.4 kg/d, and DM digestibility was not significantly affected by varying the amount of UIP addition. Apparent digestibility of N increased (P = .011) from 63.8 to 65.8, 70.7, and 71.5%, the amount of N absorbed increased (P = .001) from 73 to 84, 100, and 106 g/d, and N balance increased (P = .003) from 20 to 30, 33, and 39 g/d when UIP was fed at 0, 2.6, 5.2, and 7.8% of diet DM, respectively. The efficiency of N use increased 39.7%, and biological value increased 31.6% when the UIP mixture was added to the diet. Circulating concentrations of plasma urea N (PUN) were increased (P = .017) from 4.5 for the control diet to 5.7, 6.2, and 6.1 mg/dL when the UIP mixture was added at 2.6, 5.2, and 7.8%, respectively. Corresponding IGF-I concentrations were also increased from 491 to 558 and 624 ng/mL with 2.6 and 5.2% levels of UIP addition. Plasma glucose, NEFA, and insulin concentrations were not affected by feeding the UIP mix. The rate and efficiency of N use for growth improved with addition of an amino acid-balanced UIP mixture to the diet.

Acute and chronic hormone and metabolite changes in lambs fed the beta-agonist, cimaterol.

The objective of this study was to determine if acute and chronic changes in circulating metabolic hormone and metabolite concentrations are associated with beta-agonist-induced nutrient repartitioning in young growing lambs. Two groups of 12 Dorset and Dorset-Finn cross ram lambs weighing 36 or 33 kg live weight were assigned to 3- or 6-week treatment intervals, respectively, to achieve similar slaughter weights. Six lambs within each treatment interval were fed ad libitum a complete mixed high-concentrate diet containing either 0 or 10 ppm cimaterol. During the first 12 hr of cimaterol administration plasma somatotropin (ST), thyroxine (T4), and triiodothyronine (T3) concentrations were not altered by treatment, but plasma insulin, glucose, non-esterified fatty acids (NEFA) and glycerol concentrations were elevated 2 hr after ingestion. These acute responses suggest direct stimulation of glycogenolysis and lipolysis by cimaterol, which is characteristic of beta-adrenergic alteration of carbohydrate and lipid metabolism. Chronic administration of cimaterol significantly decreased insulin concentrations by 36% and 52% at 3 and 6 weeks, respectively, while glucose concentrations remained unchanged. Serum IGF-I concentrations were not significantly altered by cimaterol. T4 levels were reduced 22.1% after 3 weeks of cimaterol treatment. Although plasma NEFA concentrations were chronically elevated 56% to 65% in lambs fed cimaterol, plasma glycerol concentrations remained at baseline levels. The relative changes in plasma NEFA and glycerol concentrations are consistent with a decreased rate of lipogenesis, rather than an increase in lipolysis.