14C-Cobalamin Absorption from Endogenously Labeled Chicken Eggs Assessed in Humans Using Accelerator Mass Spectrometry

Traditionally, the bioavailability of vitamin B-12 (B12) from in vivo labeled foods was determined by labeling the vitamin with radiocobalt (⁵⁷Co, ⁵⁸Co or ⁶⁰Co). This required use of penetrating radioactivity and sometimes used higher doses of B12 than the physiological limit of B12 absorption. The aim of this study was to determine the bioavailability and absorbed B12 from chicken eggs endogenously labeled with ¹⁴C-B12 using accelerator mass spectrometry (AMS). ¹⁴C-B12 was injected intramuscularly into hens to produce eggs enriched in vivo with the ¹⁴C labeled vitamin. The eggs, which provided 1.4 to 2.6 μg of B12 (~1.1 kBq) per serving, were scrambled, cooked and fed to 10 human volunteers. Baseline and post-ingestion blood, urine and stool samples were collected over a one-week period and assessed for ¹⁴C-B12 content using AMS. Bioavailability ranged from 13.2 to 57.7% (mean 30.2 ± 16.4%). Difference among subjects was explained by dose of B12, with percent bioavailability from 2.6 μg only half that from 1.4 μg. The total amount of B12 absorbed was limited to 0.5–0.8 μg (mean 0.55 ± 0.19 μg B12) and was relatively unaffected by the amount consumed. The use of ¹⁴C-B12 offers the only currently available method for quantifying B12 absorption in humans, including food cobalamin absorption. An egg is confirmed as a good source of B12, supplying approximately 20% of the average adult daily requirement (RDA for adults = 2.4 μg/day).

Use of metabolomics and lipidomics to evaluate the hypocholestreolemic effect of Proanthocyanidins from grape seed in a pig model

SCOPE

This work aims to evaluate changes in the fecal metabolomic profile due to grape seed extract (GSE) intake by untargeted and targeted analysis using high resolution mass spectrometry in conjunction with multivariate statistics.

METHODS AND RESULTS

An intervention study with six crossbred female pigs was performed. The pigs followed a standard diet for 3 days, then they were fed with a supplemented diet containing 1% (w/w) of MegaNatural® Gold grape seed extract for 6 days. Fresh pig fecal samples were collected daily. A combination of untargeted high resolution mass spectrometry, multivariate analysis (PLS-DA), data-dependent MS/MS scan, and accurate mass database matching was used to measure the effect of the treatment on fecal composition. The resultant PLS-DA models showed a good discrimination among classes with great robustness and predictability. A total of 14 metabolites related to the GSE consumption were identified including biliary acid, dicarboxylic fatty acid, cholesterol metabolites, purine metabolites, and eicosanoid metabolites among others. Moreover, targeted metabolomics using GC-MS showed that cholesterol and its metabolites fecal excretion was increased due to the proanthocyanidins from grape seed extract.

CONCLUSION

The results show that oligomeric procyanidins from GSE modifies bile acid and steroid excretion, which could exert a hypocholesterolemic effect.

Phenolic metabolites and substantial microbiome changes in pig feces by ingesting grape seed proanthocyanidins

Proanthocyanidin (PAC) consumption has been linked to better colonic health, but PACs are poorly absorbed, making them a target for colonic metabolism. The resulting metabolites are low molecular weight and could potentially be absorbed. To understand the effects of dietary PACs it would be important to resolve the metabolic issue and link these changes to microbial population changes in a suitable model for human digestion. Here, six crossbred female pigs were fed a diet containing 1% (w/w) of MegaNatural® Gold grape seed extract (GSE) daily for 6 days. Fecal samples were analyzed by normal phase LC coupled to fluorescence detection and LC-MS/ToF. DNA was extracted from pig fecal samples and the V3/V4 region of the 16S rRNA gene was sequenced using an Illumina MiSeq. Intact parent PACs (dimer-pentamer) were observed in the feces on days 3 and 6 at similar high levels (∼400 mg kg(-1) total) during ingestion of GSE but were absent 48 h post-feeding. The major phenolic metabolites were 4-hydroxyphenylvaleric acid and 3-hydroxybenzoic acid which increased by ∼30 and 3 mg kg(-1) respectively. The GSE diet also caused an ecological shift in the microbiome, dramatically increasing Lachnospiraceae, Clostridales, Lactobacillus and Ruminococcacceae. The relationship between dietary PACs and colon health may be attributable to the altered bacterial populations or phenolic compounds in the colon.

Body composition and amino acid concentrations of select birds and mammals consumed by cats in northern and central California

The diet of the feral domestic cat consists of primarily birds and small mammals, but the nutritional composition is relatively unknown. Because of the increasing popularity of natural diets for cats and other wild captive carnivores, the purpose of this study was to describe the body composition and AA concentrations of select birds and small mammals in northern and central California: wild-caught mice (n = 7), Norway rats (n = 2), roof rats (n = 2), voles (n = 4), moles (n = 2), gophers (n = 3), and birds (n = 4). Body water, crude fat (CFa), CP, ash, and AA composition for each specimen were determined. Results are reported as mean ± SD. All results are reported on a DM basis except body water (as-is basis) and AA (g/16 g N). Combined, carcasses had this mean composition: 67.35 ± 3.19% water, 11.72 ± 6.17% CFa, 62.19 ± 7.28% CP, and 14.83 ± 2.66% ash. Concentrations of Arg, Tau, Cys, and Met were 5.63 ± 0.46, 0.92 ± 0.33, 1.91 ± 0.89, and 1.82 ± 0.19 g/16 g N, respectively. Using NRC physiologic fuel values for CP, CFa, and carbohydrate by difference, the combined average energy content of the carcasses was 3,929 kcal/kg DM, but the fiber content was not determined. With the exception of mice and rats, little historical data exist regarding the body and AA composition of many of the species analyzed in this study. Wild-caught mice and rats were composed of less fat but more ash compared with previously reported data in their purpose-bred counterparts. The CP content of mice in this study was similar to previous reports in purpose-bred mice. The CP content of rats was similar or slightly greater compared with historical findings in purpose-bred rats. The N content of rats and AA concentrations on a per-N basis for both rats and mice were similar to previously published data on purpose-bred rodents. The discrepancies in nutrient composition, especially fat concentration, indicate that using purpose-bred animals to represent the diet of the feral domestic cat may not be valid in many instances. When consumed to meet energy needs, the nutrient content of the species reported in the present study exceed the NRC (2006) recommended allowances (RA) for total fat, CP, and essential AA for felines at all life stages.

Circulating estradiol suppresses luteinizing hormone pulse frequency during dietary restriction

The influence of dietary restriction on the negative feedback potency of 17-beta-estradiol (E2) was evaluated in both castrated male (wethers) and female sheep (OVX ewes) during the breeding season. In study 1, OVX ewes received maintenance or restricted dietary energy for 7 weeks or maintenance energy for 6 weeks prior to a 5 day fast (n=12ewes/feeding group). Estradiol (0.31microg E2/50kg/h) or vehicle (10% EtOH-saline) was continuously infused into half the animals in each dietary treatment for the final 54h of the study. The dynamic pattern of LH secretion was assessed during the final 6h of infusion. Estradiol inhibited luteinizing hormone (LH) pulse amplitude independent of nutrition (P=0.02); fasting increased mean LH, LH peak height, and LH nadir in the absence of E2 (P=0.004, P=0.02, and P=0.02, respectively); while E2 inhibited pulse frequency (P=0.02) and increased peak width (P=0.04) in restricted ewes. Interestingly, despite uniform E2 delivery, serum concentrations of E2 differed with feeding status. Therefore, 12 wethers were infused with 0.31microg E2/50kg/h (6 fed, 6 fasted) and six wethers received 0.19microg E2/50kg/h (fasted) to establish similar serum concentrations of E2 in fed (0.31microg/50kg/h) and fasted (0.19microg/50kg/h) wethers. When fed and fasted wethers had uniform serum concentrations of E2 LH pulse frequency was suppressed (P<0.05) in fasted relative to fed animals, supporting the postulate that energy restriction enhances the E2 negative feedback potency. Collectively, these studies demonstrate that nutrition affects E2 feedback potency and clearance.

Effects of age on body condition and production parameters of multiparous beef cows

Pregnancy rate, calving interval, birth weight, weaning weight, and quarterly BCS were collected for 5 consecutive years on 454 fall-calving multiparous British crossbred cattle (3 to 10 yr of age) to evaluate associations of age with BCS and production parameters. Body weight and BCS were collected pre-calving, prebreeding, at weaning, and midway through the second trimester of pregnancy (August). Body condition score was correlated with age during all seasons (P < 0.01). At calving, breeding, and in August, 3-yr-old cows had the lowest BW and BCS, whereas 8-yr-old cows had the greatest. At weaning, these values were maximal in 10-yr-old cows. Pregnancy rate was near 80% up to 9 yr of age but decreased to 57% in 10-yr-old cows. The relationship of pregnancy rate with age appears to be correlated with the BCS decrease at breeding in the older cows, supported by the fact that inclusion of BCS at breeding in the statistical model eliminated the effect of age on pregnancy rate (P = 0.42). Calving interval was longer in 3-yr-old cows compared with 4- to 9-yr-old cows (P = 0.02); however, among older cows, there was little change in the calving interval. Birth weight reached a maximum at 8 yr of age (35 +/- 0.9 kg) and a minimum in 3-yr-old cows (32 +/- 0.7 kg). Birth weights of calves born to both 3- and 4-yr-old cows were lower than for those born to 5-, 6-, 7-, or 8-yr-old cows (P < 0.05). Ten-year-old cows weaned lighter calves (205-d adjusted weaning weight) than younger dams. Furthermore, 3-yr-old cows weaned calves 9 +/- 2.1 and 14 +/- 2.4 kg lighter than 4- and 5-yr-old cows, respectively (P < 0.001). Interpretation of the age analyses of calving interval, birth weight, and weaning weight was independent of the inclusion of BCS in the model. This study documents the effects of age on calving interval, birth weight, and weaning weight that are independent of BCS.

Dietary lutein and fat interact to modify macrophage properties in chicks hatched from carotenoid deplete or replete eggs

Two experiments were conducted to study the interaction between dietary lutein and fat levels in broiler chicks hatched from lutein depleted (Experiment I) and repleted (Experiment II) eggs. In both experiments, a 2 x 3 factorial arrangement of treatments resulted in six dietary treatments (fat at 3% and 6% and lutein at 0, 25 and 50 mg/kg feed) that were fed for 23 days to 18 birds per treatment (in three replications). In Experiment I, the anti-dinitrophenyl-keyhole-lympet-hemocyanin (anti-DNP-KLM) serum antibody response at day 22 and macrophage phagocytotic index at day 17 did not differ among treatment groups (p > 0.05). The concavalin A and phytohaemagglutinin-P lymphocyte proliferation index at day 19 was greater in birds fed 50 mg of lutein and 3% fat than in birds fed all other diets (p < 0.05). Independent of the level of dietary fat, dietary lutein increased macrophage (day 23) nitrite production measured 46 h after in vitro stimulation with LPS (p < 0.05). Among the birds fed lutein at 25 or 50 mg/kg feed, birds fed 3% fat had higher LPS-induced nitrite production compared to the birds fed 6% fat after 46 (p = 0.014) or 70 h (p < 0.001). In Experiment II, macrophage nitrite production was measured at 54 h after LPS stimulation on days 11, 15, 19 and 23. An interaction between dietary lutein and fat levels on nitrite production was observed on day 19 (p = 0.012), where macrophages from birds fed 0 mg lutein and 3% fat had the highest nitrite production (p = 0.012). Macrophages from birds fed lutein at 25 and 50 mg/kg diet and 3% fat had higher (p = 0.012) nitrite production than birds fed 6% fat. Thus, in birds hatched from lutein deplete and replete eggs, modulation of macrophage nitrite production by lutein is dependent on the level of dietary fat.

Evidence of increased substrate availability to in vitro-derived bovine foetuses and association with accelerated conceptus growth

Changes in placental development have been associated with foetal abnormalities afterin vitroembryo manipulations. This study was designed to investigate bovine conceptus development and substrate levels in plasma and fluids inin vivo- andin vitro-produced (IVP) concepti and neonates.In vivo-produced and IVP embryos were derived by established embryo production procedures. Pregnant animals from both groups were slaughtered on days 90 or 180 of gestation, or allowed to go to term. Conceptus and neonatal physical traits were recorded; foetal, maternal and neonatal blood, and foetal fluids were collected for the determination of blood and fluid chemistry, and glucose, fructose and lactate concentrations. Placental transcripts for specific glucose transporters were determined by quantitative RT-PCR. No significant differences in uterine and conceptus traits were observed between groups on day 90. On day 180, larger uterine, placental and foetal weights, and an increase in placental gross surface area (SA) in IVP pregnancies were associated with increased glucose and fructose accumulation in foetal plasma and associated fluids, with no differences in the expression of components of the glucose transporter system. Therefore, the enlarged placental SA in IVP pregnancies suggests an increase in substrate uptake and transport capacity. Newborn IVP calves displayed higher birth weights and plasma fructose concentrations soon after birth, findings which appeared to be associated with clinical and metabolic distress. Our results indicated larger concepti and increased placental fructogenic capacity in mid- to late IVP pregnancies, features which appeared to be associated with an enhanced substrate supply, potentially glucose, to the conceptus.

Weight gain in gonadectomized normal and lipoprotein lipase-deficient male domestic cats results from increased food intake and not decreased energy expenditure

Gonadectomy predisposes domestic cats to undesired body weight gain and obesity. The disturbance responsible for this disregulation of energy balance has not been clearly identified. Energy intake and expenditure, body composition and plasma concentrations of leptin, insulin, glucose and triacylglycerol were determined during a 36-wk period in adult male (2-5 y) gonadectomized (n = 8) and intact (n = 8) normal cats and gonadectomized (n = 8) and intact (n = 8) lipoprotein lipase (LPL)-deficient cats. Cats were housed individually in temperature- and light-controlled rooms and continuously provided a commercial dry-type diet. In normal and LPL-deficient cats, body weight increased (P < 0.05) after gonadectomy by 27 to 29%, mostly as a result of fat accretion. There was a rapid increase (P < 0.05) in food intake of approximately 12% after gonadectomy of normal and LPL-deficient cats. The metabolic rate (kJ.kg(-1).d(-1)), determined in normal intact (319 +/- 20, n = 5) and gonadectomized (332 +/- 36, n = 5) cats, did not differ after gonadectomy. After gonadectomy, plasma concentrations of glucose and triacylglycerol did not change, whereas plasma insulin and leptin concentrations increased (P < 0.05), but not coincidentally with body weight gain. A stair-step increase in energy intake, and not decreased energy expenditure, appears to drive the weight gain associated with gonadectomy. Body fat mass appears to increase until the energy intake supports no further expansion. Adiposity signaling through insulin or leptin does not appear to mediate the energy intake effect. LPL deficiency did not preclude development of the overweight body condition. Therefore, gonadectomy-induced weight gain in cats is not a result of changed adipose LPL activity, as previously suggested.

Dietary betaine increases intraepithelial lymphocytes in the duodenum of coccidia-infected chicks and increases functional properties of phagocytes

Betaine is used by cells to defend against changes in osmolarity. We examined relationships among betaine, osmolarity and coccidiosis. In the first experiment, chicks were fed corn-soy diets containing 0.0, 0.5 or 1.0 g/kg betaine; half were challenged with Eimeria acervulina (Cocci). Cocci decreased weight gain and feed efficiency and increased the osmolarity of the duodenal and jejunal mucosa (P < 0.01). Betaine decreased osmolarity of the duodenum (P < 0.01), especially in Cocci-challenged birds. Cocci increased the thickness (P = 0.04) of and number (P < 0.01) of leukocytes in the duodenal lamina propria especially at high betaine levels (interaction P = 0.05). Villi height was decreased by Cocci (P = 0.05) and this was ameliorated by 1.0 g/kg betaine (interaction P = 0.04). Intraepithelial leukocyte numbers were increased by Cocci (P < 0.01) especially at 0.5 and 1 g/kg betaine. Peritoneal macrophages or peripheral blood heterophils were incubated in media with an osmolarity of 200, 310, 600 or 900 mOsmol and 0.0, 0.1, 0.5 or 1.5 mmol/L betaine (4 x 4 factorial) for 6 h and then E. acervulina were added. In general, phagocytosis and NO release were decreased and interleukin (IL)-1 and IL-6 release were increased in hyperosmotic media compared with isosmotic media. Betaine (0.1 mmol/L) increased NO release by heterophils (P = 0.04) and tended to increase (P < 0.1) NO release from macrophages. The chemotaxis of monocytes toward chemotactic factors released by heterophils was increased by betaine. Increased chemotaxis of monocytes and NO release by macrophages may explain the decreased intestinal pathology but increased leukocyte numbers that were observed when betaine was fed during a Cocci infection.

Contributions of tissues to expression of a major gene for growth in chimeric mice

The objective of this research was to determine the effect of genotype of particular tissues and organs on the growth of a chimera produced by aggregating an embryo homozygous for the high-growth (hg) allele with an embryo from a control line of wild-type mice lacking the deletion responsible for the high-growth phenotype. A total of 107 chimeric mice were produced, 81 males and 26 females. The preponderance of male chimeras closely fit the expected 3:1 ratio of males to females in balanced chimeric populations, suggesting that neither of the two genetic lines appeared to have a selective advantage for contributions to chimeric tissues. No single correlation between individual tissue chimerism and mouse growth was remarkable relative to correlations of chimerism of other tissues to growth. Other statistical models, including multiple regression techniques, did nothing to identify particular organs, tissues or various combinations that improved the explanation of expression of the high-growth phenotype by percentage of high-growth cells in that organ. These observations suggest that the chromosomal deletion thought to cause the high-growth phenotype has a systemic effect, without dominant effects of or on individual organs or tissues; the precise mechanism has yet to be determined.

Impact of separating amino acids between plasma, extracellular and intracellular compartments on estimating protein synthesis in rodents

Three models representing different separations of amino acid sources were used to simulate experimental specific radioactivity data and to predict protein fractional synthesis rate (FSR). Data were from a pulse dose of 14C-U Leu given to a non-growing 20-g mouse and a flooding dose of 3H Phe given to a non-growing 200 g rat. Protein synthesis rates estimated using the combined extracellular and intracellular (Ec + Ic) source pool and extracellular and plasma (Ec + Pls) source pool mouse models were 78 and 120% d(-1) in liver, 14 and 16% d(-1) in brain and 15 and 14% d(-1) in muscle. Predicted protein synthesis rates using the Ec + Ic, Ec + Ic + Tr (combined extracellular, intracellular and aminoacyl tRNA source pool) and Ec + Pls rat models were 57, 3.4 and 57% d(-1) in gastrocnemius, 58, 71 and 62% d(-1) in gut, 8.3, 8.4 and 7.9% d(-1) in heart, 32, 23 and 25% d(-1) in kidney, 160, 90 and 80% d(-1) in liver, 57, 5.5 and 57% d(-1) in soleus and 56, 3.4 and 57% d(-1) in tibialis. The Ec + Ic + Tr model underestimated protein synthesis rates in mouse tissues (5.0, 27 and 2.5% d(-1) for brain, liver and muscle) and rat muscles (3.4, 5.5 and 3.4% d(-1) for gastrocnemius, soleus and tibialis). The Ec + Pls model predicted the mouse pulse dose data best and the Ec + Ic model predicted the rat flooding dose data best. Model predictions of FSR imply that identification and separation of the source specific radioactivity is critical to accurately estimate FSR.

A rodent model of protein turnover used to design an experiment for measuring the rates of channeling, recycling and protein synthesis

We described previously a mechanistic model of whole-body protein turnover in rodents. Channeling was defined as the flow of amino acids from the extracellular compartment to aminoacyl tRNA and protein synthesis. Recycling was defined as the flow of amino acids from protein degradation to aminoacyl tRNA (protein synthesis) without mixing with the intracellular pool of amino acids. In this paper, the model is applied to tissues and whole body and is used to develop an experimental protocol for estimating protein fractional synthesis rate, recycling and channeling. Channeling, recycling and protein synthesis must be estimated simultaneously because changes in specific radioactivities over time are highly dependent on the rate of protein synthesis. Injection-specific radioactivities, body weights and experimental variation were used with the model to generate data at different rates of recycling and channeling. The data generated were then used to determine the best time points and experimental method to estimate percentages of recycling, channeling and protein synthesis rate by the iterative Method of Maximum Likelihood. Specific radioactivity at each time point was based on simulated data from three rodents at each of six time points. Predicted protein synthesis rates were within 5%/d of observed rates for all methods. Predicted rates of recycling and channeling were generally within 15% of observed rates except recycling in muscle at high channeling and high recycling. Standard deviations of the predictions of percentages of channeling and recycling were between 0.148 and 44.5% for the pulse dose method, 0.0655 and 197% for the continuous infusion method and 0.351 and 962% for the flooding dose method. The experimental design that yields the best estimates of channeling, recycling and protein synthesis is the pulse dose. Changes in amino acid specific radioactivities in the extracellular, aminoacyl tRNA and protein pools were greatest and should be measured at 2, 6, 10, 40, 70 and 100 min in the pulse method.

Increasing the calcium content of mealworms (Tenebrio molitor) to improve their nutritional value for bone mineralization of growing chicks

The purpose of these studies was to determine the husbandry variables that optimize the Ca content of mealworms (Tenebrio molitor) and to determine the bioavailability of this Ca for bone mineralization in chicks that consume the mealworms. To determine the optimal level of Ca in the substrates used in short-term (< 14 days) holding of mealworms and to determine the length of time that mealworms should be exposed to high-Ca substrates, mealworms were placed in either a wheat bran or a chicken starter substrate supplemented with 0, 4, 8, or 12% Ca from CaCO3. The mealworms were harvested after 0.5, 1, 2, 3, 4, 7, or 14 days. The Ca content of the mealworms was greatest with the use of chicken starter and increased linearly with the Ca content of the substrate. In general, the Ca content of the mealworms increased during the first 24 hr and decreased after > or = 1 wk, especially at the higher levels of Ca supplementation. The chicken starter also resulted in higher levels of vitamin D in mealworms. Mealworms held in wheat bran with 8% Ca were fed to growing chicks. Ca bioavailability was calculated from the chicks' bone ash. The Ca in these mealworms was 76% as bioavailable as the Ca in oyster shell.

Energy and micronutrient composition of dietary and medicinal wild plants consumed during drought. Study of rural Fulani, northeastern Nigeria

Two rural settled Fulani villages, northeastern Nigeria, were surveyed for dietary practices and use of edible wild plants (n = 100 households). Commonly consumed species of edible wild barks, fruits, leaves, nuts, seeds, and tubers were analyzed for protein, fat, and carbohydrate and for minerals. Kuka bark (Adansonia digitata) given to infants to increase weight gain was high in fat, calcium, copper, iron, and zinc. Cediya (Ficus thonningii), dorowa (Parkia biglobosa) and zogale (Moringa oleifera) were good sources of protein and fat and excellent sources of calcium and iron or copper and zinc. Fruits, leaves, and nuts of aduwa (Balanites aegyptiaca) were widely used during the dry season and during drought. Edible wild species available during the wet season generally were inferior in energy and micronutrient mineral content compared to dry season plants. Fruits commonly eaten by children were poor sources of protein and minerals but rich in carbohydrate and fiber. Tsamiya seeds (Tamarindus indica) were good sources of zinc and used to make dawwa (porridge) commonly consumed during pregnancy. Kirya seeds (Prosopos africana) contained the highest zinc concentrations. Shiwaka leaves (Veronia colorate) consumed by pregnant women to increase breastmilk production and to expel intestinal worms, were high in fiber, phosphorus, magnesium, manganese, and were adequate sources of calcium.

Variability among sources and laboratories in nutrient analyses of corn and soybean meal. NCR-42 Committee on Swine Nutrition. North Central Regional-42

A cooperative research study involving members of a regional committee (North Central Regional Committee on Swine Nutrition [NCR-42]) was conducted to assess the variability in nutrient composition (DM, CP, Ca, P, Se, and amino acids) of corn and soybean meal from 16 sources (15 states, mostly in the Midwest) and to assess the analytical variability in nutrient assays among 22 laboratories (labs; 16 experiment station labs and six commercial labs). Corn samples were obtained from each participating station's feed mill during a 3-yr period (1989, 1990, and 1992), as were soybean meal samples during a 2-yr period (1989 and 1990). Both regular soybean meal (with hulls) and dehulled soybean meal were represented in the study. Samples were analyzed for DM and CP by all 22 labs, for Ca and P by 15 labs, for amino acids by 10 labs, and for Se by 6 labs. Each lab used its own analytical procedures. Samples of corn and soybean meal varied in their nutrient composition depending on the area of origin. The greatest variation among sources was in Se concentration, ranging from .02 to .29 mg/kg in corn and .08 to .95 mg/kg in soybean meal. Crude protein and lysine in corn were positively correlated, but the regression coefficient was low (r2 = .49). The relationship between CP and lysine for the two soybean meals combined was considerably stronger (r2 = .81). Lysine in corn increased by .018 percentage point and lysine in soybean meal (regular and dehulled combined) increased by .063 percentage point for each 1 percentage point increase in CP. Except for CP and Se, the analytical variability among labs was as great as, and in some cases greater than, the variability in nutrient composition among sources of corn and soybean meal. Within-lab analytical variability tended to be less than among-lab variability. Some labs performed certain analyses with considerably less variability and more accuracy than others.

Recycling, channeling and heterogeneous protein turnover estimation using a model of whole-body protein turnover based on leucine kinetics in rodents

In the companion paper, a whole-body, mechanistic model of protein turnover in a rodent was described and evaluated with independent data sets that used the flooding dose method. On the basis of fitted fluxes, the model was able to predict specific radioactivity changes in the protein and free leucine pools and whole-body protein fractional synthesis rate (FSR). In this paper, results of model simulations of specific radioactivity changes in the flooding dose, pulse dose and continuous infusion methods were compared and the influence of recycling, channeling and multiple protein pools on model behavior were analyzed. For all methods, the percentage of channeling must be estimated to determine whether the extracellular or intracellular pool specific radioactivities better approximate the aminoacyl tRNA pool specific radioactivity. Recycling also affects the specific radioactivity of the aminoacyl-tRNA pool and therefore must be estimated. An analysis of fits of the flooding dose data indicated that 100% channeling was occurring, but the percentage of recycling could not be determined. Multiple protein pools turning over at different rates overestimated FSR by 2-3% at early time points (5 min) and underestimated FSR by 3-6% at 60 min in the flooding dose method. For the pulse dose method, FSR was underestimated by 40-50% at 5 min and underestimated by 9-10% at 60 min. An increase in time to measure FSR caused a decrease in the estimate of FSR (18% over 3 h) for the flooding dose method and an increase in the estimate of FSR (144% over 3 h) for the pulse dose method.

A model of whole-body protein turnover based on leucine kinetics in rodents

The measurement of fractional synthesis rate is based on the following assumptions: amino acids for protein synthesis are supplied by an intracellular pool; amino acids from protein degradation are not recycled preferentially to protein synthesis; and proteins turn over at a homogeneous rate. To test these assumptions, a mechanistic, theoretical model of protein turnover for a nongrowing 26-g mouse was developed on the basis of data from the literature. The model consisted of three protein pools turning over at fast (102 micromol Leu, t1/2= 11.5 h), medium (212 micromol Leu, t1/2 = 16.6 h) or slow (536 micromol Leu, t1/2 = 71.5 h) rates and extracellular (1.69 micromol Leu), leucyl-tRNA (0.0226 micromol Leu) and intracellular (5.72 micromol Leu) amino acid pools that exchanged amino acids. The flow of amino acids from the protein pools to the leucyl-tRNA pool determined the amount of recycling. The flow of amino acids from the extracellular pool to aminoacyl tRNA determined the amount of channeling. Two flooding dose data sets were used to evaluate specific radioactivity changes predicted by the model. Predictions of specific radioactivities using flooding dose, pulse dose or continuous infusion methods indicated that the model can be a useful tool in estimating the rates of channeling and recycling. However, it was found that use of data from flooding dose experiments might cause inaccurate predictions of certain fluxes.

Methionine deficiency decreases protein accretion and synthesis but not tRNA acylation in muscles of chicks

The effect of supplementing a methionine-deficient, isolated soy protein diet (0.5% total sulfur amino acids) with 0.2% D,L-methionine (DL-MET) or a molar equivalent of D,L-2-hydroxy-4-(methylthio) butanoic acid (DL-HMB) was assessed in chicks over an 8-d feeding study. Chicks consumed DL-HMB diet ad libitum (HIGH) or were restricted to the level consumed ad libitum by chicks fed the basal diet. The DL-MET diet was fed at the same two levels as the DL-HMB diet. Supplementing with either methionine source resulted in significantly greater growth rate, efficiency of feed conversion, and accretion and synthesis of protein in the gastrocnemius and pectoralis muscles. These increases were greater for chicks consuming feed ad libitum as compared with feed-restricted chicks and were not affected by methionine source. Rate of muscle protein degradation appeared to increase with supplementation of either methionine source, but only when feed intake was permitted to increase. The relative in vivo conversion of DL-HMB vs. D-MET to L-MET was similar in all groups as indicated by pool sizes of methionine, tRNA(met), and tRNA(cys), and rates of protein accretion and synthesis. These data demonstrate that dietary DL-HMB and DL-MET are used with similar efficacy to support skeletal muscle protein accretion and rates of protein synthesis when feed intake is equalized.

Identification of porcine sperm plasma membrane proteins that may play a role in sperm-egg fusion

Sperm plasma membrane (PM) proteins that demonstrate affinity for egg PM preparations have the potential to be biologically important during sperm-egg binding and/or fusion. In this study four such proteins have been identified. To provide quantitative evidence for possible biological function, the large natural variation among different porcine sperm populations with regard to their ability to interact with the egg was compared with the relative binding of egg PM material to individual proteins. An aliquot from each of 24 porcine ejaculates was evaluated by the zona-free hamster ova bioassay and the remainder processed to yield sperm PM vesicles. Aliquots of sperm PM were solubilised, separated by SDS-PAGE, western blotted and probed with partially purified, biotinylated egg PM protein. Bound egg PM proteins were visualised on western blots by an avidin/biotin/horseradish peroxidase system and analysed by scanning laser densitometry. Four sperm PM proteins (62, 39, 27 and 7 kDa estimated molecular mass) were the predominant binders of egg PM. The amount of egg PM bound to the 62 kDa protein was significantly correlated with the ability of sperm from the 24 ejaculates to penetrate zona-free hamster ova (percentage of ova penetrated, p = 0.01, R = 0.65; number of penetrated sperm per ovum, p = 0.02, R = 0.63).

Free and total ion concentrations in pig digesta

Mineral bioavailability is related to the activity of the free ion or small-ligand metal ion complexes present in gastrointestinal (GI) tract digesta. Therefore, it is necessary to distinguish between total ion and free-ion/small-ligand complexes (referred to simply as "free") concentrations. Free and total cation concentration in pig digesta from various GI locations were determined. Free ions were operationally defined as those that passed through a 1,000 molecular weight cutoff filter. To test the effect of dietary supplementation on free ion concentrations, pigs were fed either basal diets of corn bran, corn grits, and soybean meal (10, 67, and 20 weight percent, respectively) or basal diets containing added Ca, Zn, Fe, and Cu. In addition, the Ca and K content of corn bran fragments retrieved from digesta was determined by energy dispersive x-ray analysis to examine whether this dietary fiber preferentially absorbed minerals, thus reducing mineral bioavailability. Free cation concentrations, expressed as a percentage of the total, averaged over all locations for both diets were: Na, 86%; K, 96%; Ca, 11%; Mg, 40%; Zn, 5%; Fe, 4%; and Cu, 11%. For Ca, Mg, Zn, and Cu, the free:total cation concentration ratios differed (P < .05) between upper and lower GI tract. Mineral supplementation did not alter free:total ratios of any ion in the GI tract. For supplemented diets, mineral concentrations generally were higher throughout the GI tract, as were concentrations of free Ca. Free concentrations of Zn and Cu in the jejunum and ileum were higher (P < .01) with supplemented diets.(ABSTRACT TRUNCATED AT 250 WORDS)

Regulation of insulin-like growth factor-I and binding protein-3 expression in oMtla-oGH transgenic mice

Growth hormone (GH)-transgenic mice provide a model for studying hormonal regulation of gene products responsible for efficient lean growth. Insulin-like growth factor-I (IGF-I) and IGF binding protein-3 (BP-3) are two products involved in mediating the growth promoting actions of GH. Mice carrying the ovine metallothionein la-ovine growth hormone (oMtla-oGH) transgene were used to study GH regulation of IGF-I and BP-3 expression because these mice do not exhibit elevated basal oGH levels without transgene stimulation by exogenous zinc. C57B1/6XCBA mice with (transgenic = TG) and without control = C) the oMtla-oGH transgene were activated (+ Zn) or inactivated (-Zn) by the addition or removal of 25 mM zinc sulfate in the drinking water. Plasma IGF-I and BP-3 levels were determined by radioimmunoassay and western ligand blotting, respectively. Hepatic IGF-I and BP-3 mRNA levels were determined by slot-blot analysis. TG+Zn mice had higher plasma IGF-I (p < 0.05) and hepatic IGF-I mRNA (p < 0.05) levels as compared to TG-Zn, C+Zn and C-Zn mice. Plasma IGF-I and hepatic IGF-I mRNA levels in TG-Zn mice were not different from C+Zn and C-Zn mice. Removal of Zn decreased hepatic IGF-I mRNA levels to C levels in TG mice. Plasma BP-3 and hepatic BP-3 mRNA levels in TG+Zn mice were increased (p < 0.05) as compared to TG-Zn, C-Zn and C+Zn. Plasma BP-3 and hepatic BP-3 mRNA levels did not differ between TG-Zn, C-Zn and C+Zn mice. Expression of the transgene also increased the level of plasma BP-3 during pregnancy as compared to that observed for pregnant C mice. We conclude that oGH regulates IGF-I and BP-3 expression in the oMtla-oGH transgenic mouse model system.

Dietary energy source and density modulate the expression of immunologic stress in chicks

To determine how dietary energy level and source influence feed intake, growth and energy partitioning drug immunologic stress, growing chicks were fed diets based on cornstarch and casein with varying energy densities and injected every other day for 6 d with either saline (control), Salmonella typhimurium lipopolysaccharide or heat-killed Staphylococcus aureus. Salmonella typhimurium lipopolysaccharide decreased growth and feed consumption at low energy densities. When the dietary energy density was increased above 13.4 kJ/g using cornstarch, but not corn oil, the growth depressing effect of immunogens was eliminated. Immunologically stressed chicks had a greater proportion of gain in visceral organs and less in the carcass, regardless of the nutrient density of the diet. Immunologic stress decreased intake of metabolizable energy of chicks fed a diet with low nutrient density and increased it for those fed a diet with high nutrient density. Chicks injected with S. typhimurium lipopolysaccharide lost more energy as heat than controls when differences in metabolizable energy intakes were accounted for and modified their preference between two diets differing in metabolizable energy density and fat content as a result of the challenge. Control chicks selected between the 11.7 and 14.2 kJ/g diets to obtain an energy density of 13.2 kJ/g compared with 12.5 kJ/g in the S. typhimurium lipopolysaccharide-challenged chicks. The S. typhimurium lipopolysaccharide-challenged chicks consumed similar amounts of the low energy diet but decreased intake of the high energy diet.

Source of amino acids for tRNA acylation. Implications for measurement of protein synthesis

Estimates of protein-synthesis rates using radioisotopes require accurate measurement of the specific radioactivity of the label in protein and in the precursor pool over time. Although the extracellular and intracellular pools of amino acids are easiest to sample, the tRNA pool is the direct precursor and is the appropriate pool for sampling. To test if the intracellular or extracellular pools reflect the tRNA specific radioactivity, a chicken macrophage cell line was incubated in medium containing either 0.23 mM-leucine and 14.5 microCi of [3H]leucine (tracer dose) or 2.3 microM-leucine plus 145.0 microCi of [3H]leucine (flooding dose). At both leucine levels, the tRNA specific radioactivity reached a plateau quickly, but did not equilibrate with either the extracellular or intracellular specific radioactivity within 30 min, and remained closer to that of protein. In a second experiment, proteins in chicken macrophages were labelled with [3H]leucine for 2 days. Labelling medium was removed, and the cells were washed free of residual free [3H]leucine and incubated with medium containing either 0.23 mM- or 2.3 mM-leucine (unlabelled). The specific radioactivity of leucyl-tRNA leucine reached a plateau within 2 min and remained considerably closer to that in the protein than that in intracellular or extracellular pools for at least 60 min. These results suggest that amino acids from protein degradation are a primary source for charging tRNA. When protein-synthesis rates are estimated by label incorporation, use of extracellular or intracellular specific-radioactivity values result in a marked underestimation.

Effects of somatotropin and substrates on patterns of liver metabolism in lactating dairy cattle

Objectives of this study were to quantitate metabolite fluxes in ruminant liver and to delineate effects of recombinant bST on patterns of nutrient metabolism by liver. Nineteen multiparous cows ranging in previous lactational performance from 6400 to 13,500 kg per 305-d lactation were treated with either placebo or bST (40 mg/d) from wk 11 to 18 of lactation. Liver tissue was collected at slaughter. Tissue slices were incubated with various 14C-labeled substrates, and rates of conversion of label to CO2 and metabolites were measured. In vivo recombinant bST treatment increased in vitro conversion of [1-14C]propionate and [2-14C]acetate to glucose more than twofold. At 2.5 mM propionate, bST-treated cows converted propionate to glucose at 90% efficiency. Recombinant bST increased [14C]bicarbonate incorporation into glucose five-fold. Overall, bST treatment resulted in greater C flow from propionate and acetate through the TCA cycle. Acetate had only small effects on propionate metabolism and no effects on lactate plus pyruvate metabolism. Unexpectedly, propionate decreased acetate conversion to ketone bodies. Suggested mechanisms for this observation include depletion of coenzyme A and allosteric regulation of carnitine palmitoyltransferase I by methylmalonyl-coenzyme A formed from propionate. In summary, bST treatment resulted in increased rates of gluconeogenesis and oxidation in liver in support of lactation.

Kinetics of amino acid extraction by lactating mammary glands in control and sometribove-treated Holstein cows

Studies of mammary arteriovenous difference were conducted on multiparous lactating Holstein cows (n = 21) on d 35, 70, 105, and 126 of lactation to examine kinetic relationships between arterial concentration and mammary gland extraction of AA. Additionally, these cows were paired by previous lactational performance and assigned to bST-treated or control groups to examine the effect of bST treatment on AA concentration and extraction by lactating mammary glands. Treated cows were injected daily with 40 mg of recombinant bST from d 71 through 126 of lactation. Arterial concentrations of Asp, Ser, Asn, Gly, beta-aminoisobutyrate, and Met were increased. Concentrations of Val, Ile, Leu, Phe, Orn, and Lys were decreased in bST-treated cows compared with controls. Increased extractions of Asp and Met by mammary glands in treated versus control cows were correlated positively with treatment-induced changes in arterial concentrations of these AA. However, increased mammary extractions of Arg, cystathionine, Leu, and Lys by bST-treated compared with control cows were not correlated with bST-induced changes in arterial concentrations of these AA. Extractions of Asn, His, Thr, Arg, Tyr, Met, cystathionine, cystine, Ile, Phe, Orn, Glu, Gly, Tau, Cit, Leu, and Val were correlated linearly with arterial concentrations (r2 greater than .15) of each AA. Extractions of Asp, Glu, Ser, Asn, Gly, Gln, Tau, His, Cit, Thr, Pro, Tyr, Val, cystine, Ile, Leu, Trp, Orn, and Lys also were correlated with arteriovenous differences of Met.

Relationship of early lactation and bovine somatotropin on nutrient uptake by cow mammary glands

Twenty-one multiparous lactating dairy cows with previous 305-d milk production records varying from 5900 to 13,600 kg were used to investigate effects of bST administration and stage of lactation on nutrient plasma arterial concentrations and arterial-venous differences across the mammary glands (uptake). On d 71 and continuing until d 126 of lactation, cows were injected with 40 mg of sometribove (bST group) or bicarbonate buffer (placebo group). Arterial and venous blood plasma samples were collected over a 12-h period on d 35, 70, 105, and 126 of lactation. Plasma concentration of glucose was 7% higher in midlactation compared with early lactation cows. Plasma concentration of acetate decreased from 2.11 to 1.87 mM in placebo versus bST-treated cows. Plasma arterial concentration and uptake of D-beta-hydroxybutyrate were .52 and .18 mM higher, respectively, in early versus midlactation cows. Concentration and uptake of NEFA were elevated in both early lactation and bST-treated cows. Triacylglyceride concentrations were 24 and 19% lower in early lactation and bST-treated cows compared with midlactation cows receiving placebo. Likewise, uptake of triacylglyceride was reduced in early lactation and with bST treatment compared with midlactation. The mediation of nutrient delivery and uptake by the mammary gland appears to be markedly similar between early lactation and bST-treated cows, suggesting a similarity between these physiological states and the homeostatic and homeorhetic mechanisms regulating nutrient partitioning in the lactating dairy cow. In early compared with midlactation cows receiving placebo, uptakes of D-beta-hydroxybutyrate and NEFA were reduced, and triacylglyceride uptake increased.

Patterns of nutrient uptake by the mammary glands of lactating dairy cows

Twenty-one multiparous lactating dairy cows with previous 305-d milk production records varying from 5900 to 13,600 kg were used to examine patterns of nutrient uptake by the mammary glands. On d 71 and continuing until d 126 of lactation, animals were injected daily with 40 mg of sometribove (bST group) or bicarbonate buffer (control group). Arterial and venous blood plasma samples were collected over a 12-h period on d 35, 70, 105, and 126 of lactation. Regression equations developed to evaluate linear effects of plasma arterial concentrations on net arterial-venous difference across the mammary glands demonstrated that, for acetate, NEFA, and D-beta-hydroxybutyrate, plasma arterial concentration accounted for over 50% of variation in uptake by the mammary glands. Additionally, a sigmoidal equation fitted the relationship between D-beta-hydroxybutyrate plasma arterial concentration and mammary gland uptake (r2 = .70). Triacylglyceride concentration was less effective in predicting uptake (r2 = .25). Administration of bST did not alter patterns of nutrient uptake, but a fourfold increase in NEFA uptake was predicted for bST-treated cows from this study, using NEFA concentrations from the literature. These observations indicate that plasma concentrations of acetate, NEFA, D-beta-hydroxybutyrate, and triacylglyceride are major determinants of uptake by the mammary glands. Factors other than plasma concentration, such as mammary gland biosynthetic capacity, availability of other nutrients, and blood flow, determine uptakes of glucose, lactate, and total and free cholesterol (r2 less than or equal to .03).

Whole blood and plasma amino acid uptakes by lactating bovine mammary glands

The objective of the experiment was to determine the contribution of red blood cells to transport of individual amino acids to lactating bovine mammary glands. Blood samples were collected from coccygeal and subcutaneous abdominal veins of 21 lactating Holstein cows on d 35, 70, 105, and 126 of lactation. Samples were collected every 20 min for 12 h. Subsamples of whole blood and plasma were pooled by hour and day. Hourly plasma samples and daily whole blood and plasma samples were analyzed for amino acid concentration. Plasma glutamate concentration was stable throughout the 12-h collection period, indicating that sample collection did not perturb amino acid homeostasis. Therefore, data from pooled daily samples were used for subsequent comparisons. Whole blood arteriovenous differences of phosphoserine, aspartate, glutamate, hydroxyproline, phosphoethanolamine, serine, asparagine, glycine, glutamine, taurine, histidine, citrulline, threonine, alanine, beta-aminoisobutyrate, carnosine, arginine, proline, alpha-aminobutyrate, tyrosine, valine, methionine, cystine, isoleucine, leucine, phenylalanine, tryptophan, ornithine, and lysine differed significantly from plasma arteriovenous differences. Uptakes of individual amino acids from plasma were poorly correlated with uptake from whole blood. These data clearly indicate that uptake data derived from plasma do not adequately represent whole blood amino acid uptake.

Value of raw soybeans and soybean oil supplementation in sow gestation and lactation diets: a cooperative study

A cooperative study using 215 sows during two parities (349 litters) was conducted at six stations to determine the effect of raw soybeans in gestation and lactation diets on sow and litter performance. Sows were bred and allotted to fortified corn diets containing either soybean meal (control) or raw soybeans. A corn-soybean meal-soybean oil diet, isocaloric to the raw soybean diet, was included as a third treatment at three stations. All diets contained 14% CP. These diets were fed during both gestation and lactation through two parities. The daily gestation feed intake ranged from 1.8 to 2.3 kg/sow, depending on station. During lactation, the sows were allowed ad libitum access to their respective diets. Gestational weight gain was not influenced by diet, but sows fed raw soybeans consumed less (P less than .01) feed during lactation and had greater (P less than .01) lactational weight loss and their pigs were lighter in weight (P less than .05) both at 21 d and at weaning (varied between 3 and 5 wk of age). Sows fed the diet with supplemental oil had reproductive and lactational performance similar to those fed the control diet. Milk obtained at d 10 to 14 of lactation from sows fed raw soybeans had lower (P less than .05) protein content than milk from sows fed the other two diets, but fat content of the milk tended to be increased by raw soybeans or by added soybean oil. Return to estrus was not affected by diet.(ABSTRACT TRUNCATED AT 250 WORDS)

Reduced male reproductive capacity in mice with high genetic potential for post-weaning growth

Male reproductive capacity was examined in 5 lines of mice which differed markedly in mature body weight (30-73 g) due to selection for growth and/or substitution of the high growth gene (hg). Testes weight ranged from 0.75-0.77% of body weight in control lines to 0.33% in the largest mice which had the hg gene in a growth selected background. Both selection for growth and the hg gene in a control background reduced absolute testes size (0.200 and 0.207 g vs 0.236 and 0.228 g in control lines) as well as relative testes size although body weight was increased by at least 50%. Although the combination of growth background and hg gene reduced sperm production per g testis compared to the outbred control, the primary cause of reduced sperm production per mouse in lines containing either the growth background or the hg gene alone was reduced absolute testes size. At 24, but not at 11, weeks of age, the hg gene reduced sperm motility. In these lines, high genetic potential for post-weaning growth was associated with decreased male reproductive capacity.

Energy-dispersive X-ray analysis of the mineral content of corn bran treated in vitro and by passage through the pig gastrointestinal tract

Energy-dispersive X-ray (EDX) analysis was tested as a method for examining the mineral contents of corn bran loaded in vitro or passed through the GI tract of pigs. Particles of dry-milled corn pericarp treated in vitro or retrieved from the stomach, ileum, and colon of killed pigs were prepared as microtomed bulk specimens directly embedded in resin. Because of heterogeneity caused by differences in substrate cell density and mineral content, X-ray count averages for a number of different specimens had a coefficient of variation greater than or equal to 0.24. Detectable amounts of K, Ca, S, and P, but not Na, Cu, Fe, or Zn were found in specimens of initial bran. Although detectable concentrations of Cu, Fe and Zn could be loaded in vitro, these elements generally were not detected in bran retrieved from the pig GI tract. During GI tract passage, sodium was loaded onto bran mainly in the small intestine and unloaded in the large intestine. Calcium was loaded in the stomach and unloaded mainly in the small intestine. At each GI tract location, content of Na, Ca, K, and P in retrieved bran was greater than in the initial bran. EDX microprobe methods can be applied successfully to plant tissues treated in vitro and in vivo to investigate interactions with minerals in a diet.

On the application of compartmental models to radioactive tracer kinetic studies of in vivo protein turnover in animals

A mathematical framework is presented for unifying and extending the various compartmental models and formulae used to calculate fractional protein synthesis and degradation rates in animals from data obtained by infusing labelled amino acids. It is shown how the various schemes can be derived as special cases of the product-precursor model or some three-pool variant. Three-compartment representations, which circumvent the need to measure the specific radioactivity of the precursor pool, are proposed. The mathematical solutions are generally presented in a form that is amenable to parameter estimation by non-linear least squares. The problems of measuring the true precursor pool for protein synthesis are addressed, and theoretical consideration is given to assaying aminoacyl-tRNA.

Effect of varying dietary zinc intake of weanling mouse pups during recovery from early undernutrition on growth, body composition and composition of gain

Catch-up growth during recovery from undernutrition is characterized by rapid body weight gain often marked by disproportionately high fat gain. In this study dietary zinc intake of mouse pups during recovery from undernutrition affected composition of gain as well as growth. Mouse pups were undernourished during the suckling period and then fed 25% casein recovery diets containing 5, 10, 40 or 110 micrograms Zn/g diet. Pups given dietary zinc levels of 40 micrograms Zn/g ad libitum achieved recovery body weights and had normal body composition. However, previously undernourished pups given marginal levels of dietary zinc (10 micrograms Zn/g diet) had similar food intakes, similar final body weights, lower lean body mass gains and greater fat gains (males only) than controls. Pups fed low zinc diets (5 micrograms Zn/g diet) were unable to attain recovery body weight and had less protein gain than previously undernourished animals fed higher zinc-containing diets or healthy pups fed the same zinc levels. The results were consistently more pronounced in males. Thus dietary zinc deficiency during catch-up growth after undernutrition limited both recovery and protein gain, whereas marginal dietary zinc intake limited protein gain in mice.

Effects of dietary excesses of the branched-chain amino acids on growth, food intake and plasma amino acid concentrations of kittens

The effect of excesses of the branched-chain amino acids (BCAA), particularly leucine, on growth, food intake and plasma amino acid concentrations were investigated in kittens. Effects of excess leucine were tested in kittens fed five basal diets that varied in their nitrogen and amino acid contents. Compared to rats, kittens were much less sensitive to excesses of the BCAA. Addition of 10% leucine to basal diets that provided nitrogen just at or below the minimal requirement of kittens resulted in no change or increased growth and food intake of kittens when the isoleucine and valine concentrations in the basal diet were just at or slightly in excess of the kitten's minimal requirements for those amino acids. An adverse effect of leucine added to low nitrogen basal diets was observed only when isoleucine and valine were provided below the kitten's requirement (80% of requirement). When basal diets containing adequate nitrogen (24% amino acids) were tested, the addition of leucine (10%) resulted in an adverse effect when isoleucine and valine were provided at 80% of the kitten's requirement and in mild growth depressions when isoleucine and valine were provided at 1.1 times the requirement. Leucine-induced growth depression was alleviated by the addition of isoleucine and valine at 0.5%, indicating that excess leucine caused a BCAA antagonism or an amino acid imbalance. With the addition of leucine to the basal diets, there were consistent decreases in concentrations of alanine and tyrosine in plasma but no consistent depressions in the concentrations of isoleucine and valine.

Energetics of protein synthesis in mice with a major gene for growth

The effect of the level of food intake on protein synthesis rate in carcass, liver, gastrointestinal tract (GIT) and heart, kidneys and lungs (HKL) was determined in male mice with a major gene for rapid postweaning gain (line Ch) and normal controls (line CH) at 31 d of age. In both lines of mice, food restriction lowered carcass, HKL and liver absolute protein synthesis rates (ASRs) while GIT protein ASR was not affected by food intake. As a result, whole-body protein ASR increased with increasing food intake. It was estimated that heat production from protein synthesis (HrpsE) was responsible for 8.3 and 10.8% of the maintenance energy requirement of CH and Ch mice, respectively. It was also calculated that HrpsE represents 19.4 and 18.3% of the heat increment of growth of CH and Ch mice, respectively. Energetic efficiencies of protein deposition in CH and Ch mice were 58.6 and 66.7%, respectively.

Delayed excretion of 3-methylhistidine in goats

The purpose of this study was to evaluate the use of 3-methylhistidine (3MH) as an index of muscle protein degradation in dairy goats. The criterion for validation was the rapid and quantitative excretion of radiolabeled 3MH. Three adult dry does and four bucks were confined to metabolism cages and injected with 5 ml of L-3-[14C]methylhistidine dihydrochloride (4 microCi/mL) diluted in normal saline. The does' urine was collected from catheters and the bucks' urine from stainless steel separators protected with fecal collection bags. The daily urine samples were analyzed for labeled amino acid. Urinary recovery of radioactivity from all does was less than 33% after 3 d and was proceeding at less than 5% d. After 9 d, total recovery was less than 50% of total dose for the does. Elimination rates were slightly higher and more variable for the yearling bucks (25-63% after 4 d). On the basis of these data, 3MH does not appear to be a valid index of muscle protein degradation in either male or female dairy goats.

Effect of a major gene for growth on protein synthesis in mice

Rates of protein synthesis of mice with a major gene (hg) for rapid postweaning gain (line Ch) and their normal counterparts (line CH) were determined at 21, 31 and 42 d of age with an intraperitoneal injection of a flooding dose of 14C-leucine. A preliminary experiment demonstrated that the relationship between the specific activities of leucine in acid-soluble supernatants and carcass protein corresponded to the theoretical precursor-product relationship, indicating that the method is valid for estimating protein synthesis rates. Using this method at 21, 31 and 42 d of age, whole-body protein fractional synthesis rates (FSR) were 43.7, 32.7 and 29.1%/d and 41.9, 32.6 and 33.1%/d for lines CH and Ch, respectively. Although differences between lines were not significant, FSR decreased with age. Absolute synthesis rate (ASR), where ASR = (FSR) X (whole body protein), was greater (P less than .001) at 21, 31 and 42 d of age in line Ch as compared with CH, and increased (P less than .001) with age. The relative contributions of liver, gastrointestinal tract, heart-kidney-lung and remaining carcass to whole body protein ASR were not affected by line, but did change (P less than .05) with age. Whole body protein fractional breakdown rate (FBR), calculated as FSR minus whole body protein fractional growth, indicates that differences between lines CH and Ch whole-body FSR and(or) FBR exist only between 24 and 33 d of age, and that the maximum value of this difference probably does not exceed 10%.

Growth characteristics, protein synthesis, and protein degradation in muscles from fast and slow-growing chickens

Developmental changes in muscle growth were studied in Single Comb White Leghorn (SCWL) and broiler-type (B) chickens. The extensor digiti communus (EDC) and ulnaris lateralis (UL) muscles were chosen for study because these muscles can be maintained in vitro, permitting the direct measurement of the fractional rate of protein synthesis (FSR) and the fractional rate of degradation (FDR). These muscles were removed from chicks at 1, 5, 10, and 20 days of age. Muscles for B were heavier, grew at a faster rate, and had greater fractional rates of growth than muscles from SCWL. Muscle protein concentrations were similar for SCWL and B. The deoxyribonucleic acid (DNA) concentrations were greater in EDC muscles from SCWL than B at all time periods. Concentrations of DNA were greater in UL muscles from SCWL than B after Day 1. The FSR and FDR were measured in muscles incubated in vitro. At 9 days of age, FSR in broiler and SCWL chicks was not significantly different in either muscle. The FDR was 12 and 19% lower in broiler EDC and UL muscles, respectively, demonstrating that broiler EDC and UL muscles accrete protein at a greater rate and more efficiently than SCWL muscles because of a slower rate of protein degradation. The FSR and FDR were also compared in B and SCWL chicks of 8 and 11 days, respectively, with equal DNA unit sizes. The FSR in B was 27 and 13% greater in EDC and UL muscles, respectively, demonstrating that protein synthesis per nucleus is greater in B chicks.

Relative contributions of hyperplasia and hypertrophy to growth in cattle

The relationship between postweaning DNA accumulation and body weight was calculated for a reference growing steer. Accumulation of DNA (hyperplasia) was calculated from patterns of protein accretion derived from literature data and protein-to-DNA ratios (Pro/DNA) measured in samples of muscles from chuck, round and plate, hides, intestines, rumens and livers of steers slaughtered at body weights ranging from 150 to 700 kg. Amounts of protein relative to DNA found in muscles from chuck, round and plate were used to estimate Pro/DNA changes in carcass. Corresponding values from intestines, rumen and liver were used to estimate Pro/DNA patterns for viscera. This ratio increased in carcass until animals reached body weights of approximately 300 kg and leveled off thereafter. No cell enlargement was evident in viscera. Thus, postweaning protein accretion in carcass results from both cell enlargement (hypertrophy) and DNA accumulation (hyperplasia) until body weights of 300 kg are attained, subsequent growth appeared to be hyperplastic in nature. In viscera, hyperplasia was the primary determinant of protein accretion.

Energetic efficiency of protein and fat deposition in mice with a major gene for rapid postweaning gain

Previous research demonstrated the existence of a major gene (hg), expressed as a homozygous recessive, that increases postweaning growth 60% in C57B1/6 mice (line Ch) compared to the same genetic stock without the major gene (line CH). Effects of the hg gene on the partial energetic efficiencies of protein and fat deposition in mice between 21 and 42 d of age were examined by using comparative slaughter data and multiple regression techniques. Efficiency estimates for fat deposition were biologically impossible and unstable, probably as a result of high correlations between the independent variables (multicollinearity). Use of biased regression techniques gave rise to biologically possible estimates for efficiencies of fat and protein gain. However, biased regression procedures introduced subjectivity in an otherwise objective analysis. Since these regression techniques produce biologically possible estimates, the physiological implications of the results are discussed in relation to protein and fat turnover. Although the usefulness of these statistical methods for predictive purposes is not questioned, it is concluded that they do little toward advancing our understanding of energy metabolism. Rather, we suggest that mechanistic models be used wherein specific biological processes are presented separately and effects of energy intake on these processes accommodated explicitly.

Gluconeogenesis in isolated lamb hepatocytes

Isolated sheep hepatocytes were used to obtain estimates of kinetic parameters, identify substrate preference and interactions and study regulation of gluconeogenesis. Respective Vmax estimates for propionate, pyruvate and alanine conversion to glucose were 59.5, 12.8 and 21.5 mol glucose formed X (h X g dry weight)-1. Respective KS estimates for propionate and pyruvate were 1 mM and 18 to 40 microM. Rates of lactate utilization varied among cell preparations, possibly because of loss of lactate dehydrogenase during isolation. Dihydroxyacetone and glycerol were utilized for glucose synthesis at similar rates of 8.6 and 8.7 mumol glucose formed X (h X g dry weight)-1, respectively. Respective rates of glucose synthesis from 5 mM fructose and 10 mM galactose were 63.2 and 31.4 mumol X (h X g dry weight)-1. Maximum rates of pyruvate carboxylase and phosphoenolpyruvate carboxykinase were estimated to be 101.6 and 160.4 mumol substrate converted X (h X g dry weight)-1, respectively. Neither butyrate nor acetate accelerated gluconeogenesis from propionate while acetate increased glucose synthesis from pyruvate, presumably through activation of pyruvate carboxylase. Glucagon stimulated gluconeogenesis from propionate. Dibutyrylcyclic AMP mimicked the effect of glucagon, implying that the glucagon effect is translated via the adenyl cyclase system as in rats. The kinetic parameters established in these experiments should be useful in future experiments and in computer modeling analyses of ruminant liver and whole animal metabolism where Michaelis-Menten type equations are widely used.

Relationships among dietary protein, feed intake and tissue protein turnover in lactating rats

Effects of protein and energy intake on tissue protein synthesis and degradation were studied in rats fed 12, 24 and 36% protein diets at 100, 70, 50 and 30% of ad libitum intake begining on d 7 of lactation. Rates of protein synthesis were measured in liver, mammary, abdominal viscera and remaining carcass of rats on d 10 of lactation. Tissue protein loss was estimated as the difference in tissue protein from d 7 to 14. Data were analyzed using stepwise multiple quadratic regression to define response surfaces of protein loss, synthesis and degradation to intake of protein and energy. Protein loss increased with restriction of energy and protein intake in all tissues. However, carcass protein synthesis and degradation did not vary systematically with either energy or protein intake. Energy intake restriction increased visceral protein turnover while protein intake restriction decreased rate of protein turnover. Liver protein loss increased with decreased dietary protein due to increased liver protein degradation. Decreased energy intake also increased liver protein loss without directly affecting rate of synthesis or degradation. Mammary protein synthesis decreased very slightly with energy restriction while decreased protein intake sharply inhibited protein synthesis.