The protein-sparing effect of carbohydrate. 2. The role of insulin

Brain Transcriptome Analysis Reveals Potential Transcription Factors and Biological Pathways Associated with Feed Efficiency in Commercial DLY Pigs

Feed efficiency (FE) is one of the most important economic traits in the porcine industry. In this study, high-throughput RNA sequencing (RNA-seq) was first utilized for brain tissue transcriptome analysis in pigs to indicate the potential genes and biological pathways related to FE in pigs. A total of 8 pigs with either extremely high-FE group (HE-group) or low-FE group (LE-group) were selected from 225 Duroc × (Landrace × Yorkshire) (DLY) pigs for transcriptomic analysis. RNA-seq analysis was performed to determine differentially expressed genes (DEGs) between the HE- and LE-group, and 430 DEGs were identified in brain tissues of pigs (|log₂(FoldChange)| > 1; adjusted p-values <0.05). Gene Ontology and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis showed that the DEGs were mainly enriched in synaptic signaling or transmission, and hormone secretion pathways, in which insulin secretion, and oxytocin signaling pathways were closely associated with FE by regulating feeding behavior and energy metabolism (adjusted p-values <0.05). Further, the transcription factors (TFs) analysis and gene co-expression network analysis indicated three hub differentially expressed TFs (NR2F2, TFAP2D, and HNF1B) that affected FE by mainly regulating feeding behavior, insulin sensitivity, or energy metabolism. Our findings suggest several potential TFs and biological pathways for further investigations of FE in pigs.

Effects of dietary energy and crude protein levels on growth performance, blood profiles, and carcass traits in growing-finishing pigs

This experiment was conducted to evaluate the effect of dietary energy and crude protein (CP) levels on growth performance, blood profiles, and carcass traits in growing-finishing pigs. A total of 180 crossbred pigs ([Yorkshire × Landrace] × Duroc) with an average body weight of 30.96 ± 3.068 kg were used for a 12-week feeding trial. Experimental pigs were allotted to a 2 × 3 factorial arrangement using a randomized complete block (RCB) design. The first factor was two levels of dietary metabolizable energy (ME) density (13.40 MJ/kg or 13.82 MJ/kg), and the second factor was three dietary CP levels based on subdivision of growing-finishing phases (high: 18%/16.3%/16.3%/13.2% middle: 17%/15.3%/15.3%/12.2% and low: 16%/14.3%/14.3%/11.2%). Average daily gain (ADG) and gain-feed ratio (G:F ratio) decreased as dietary CP level was decreased linearly (linear, p < 0.05; p < 0.05, respectively) in the early growing period, and G:F ration also decreased as dietary CP level was decreased linearly (linearly, p < 0.05) over the whole growing phase. Over the entire experimental period, G:F ratio decreased as dietary ME level decreased (p = 0.01). Blood urea nitrogen (BUN) concentration was increased as dietary energy level decreased in growing period (p < 0.01). During finishing period, total protein concentration was decreased by lower dietary energy level (p < 0.05). In this study, there were no significant differences in proximate factors, physiochemical properties, muscle TBARS assay results, pH changes, or color of pork by dietary treatments. However, saturated fatty acid (SFA) increased (p < 0.01) and polyunsaturated fatty acid (PUFA) decreased (p < 0.05) when ME was decreased by 0.42 MJ/kg in growing-finishing pig diets. In addition, monounsaturated fatty acid (MUFA) tended to increase when CP level was decreased in growing-finishing pig diets (p = 0.06). A growing-finishing diet of 13.82 MJ/kg diet of ME with the high CP level can improve growth performance and show better fatty acids composition of pork.

Effects of dietary energy and protein levels on reproductive performance in gestating sows and growth of their progeny

This experiment was conducted to evaluate the effect of dietary energy and crude protein (CP) levels on reproductive performance, litter performance, milk quality, and blood profiles in gestating sows. A total of 59 multiparous sows (Yorkshire × Landrace) with similar body weights (BW), backfat thickness (BF), and parity were assigned to one of six treatments with 9 or 10 sows per treatment using a 2 × 3 factorial arrangement and completely randomized design. The first factor was two levels of dietary metabolizable energy (ME) density (13.40 or 13.82 MJ/kg) and the second factor was three dietary protein levels based from 35 day in gestating phases (10.5%, 12%, and 13.5%). Backfat thickness change in lactating sows decreased linearly as CP level increased (p = 0.03). Increased energy level in the gestating sow diet tended to increase the total number of piglets born (p = 0.07), but piglet weight decreased (p = 0.02). Dietary CP level had a negative effect on colostrum quality. Casein, protein, total solid, and solids-not-fat concentrations decreased linearly and lactose level increased linearly as CP level in the gestating sow diet increased (casein%: p = 0.03; protein%: p = 0.04; lactose%: p = 0.06; total solids: p = 0.03; solid-not-fat: p = 0.03, respectively). However, improving ME by 0.42 MJ/kg had no significant effect on the chemical composition of sow colostrum. There were no significant differences in blood glucose concentration in gestating sows when sows were fed different levels of energy during gestation, but blood glucose increased at 21 day of lactation when energy increased by 0.42 MJ/kg (p = 0.04). Blood urea nitrogen concentration increased linearly when dietary CP levels increased at 110 day in gestation, 24-hours postpartum, and 21 days of lactation (linear, p < 0.05, p < 0.05, and p < 0.05, respectively), and it also increased when dietary energy increased at 110 days of gestation and 24-hours postpartum (p < 0.01, and p < 0.01, respectively). A gestating sow diet containing 13.82 MJ/kg ME and 10.5% CP can improve reproductive performance, litter performance, and colostrum quality.

Effects of dietary energy and crude protein levels on growth performance, blood profiles, and nutrient digestibility in weaning pigs

Objective

This experiment was conducted to investigate the effect of reducing dietary metabolic energy (ME) and crude protein (CP) levels on growth performance, blood profiles, and nutrient digestibility in weaning pigs.

Methods

A total of 240 crossbred pigs (Duroc×[Landrace×Yorkshire]) with an average body weight of 8.67±1.13 kg were used for a 6-week feeding trial. Experimental pigs were allotted to a 2×3 factorial arrangement using a randomized complete block design. The first factor was two levels of dietary ME density (low ME level, 13.40 MJ/kg or high ME level, 13.82 MJ/kg) and the second factor was three dietary CP levels based on subdivision of early and late weaning phases (low CP level, 19.7%/16.9%; middle CP level, 21.7%/18.9%; or high CP level, 23.7%/20.9%).

Results

Over the entire experimental period, there were no significant difference in body weight among groups, but a decrease in diet energy level was associated with an increase in average daily feed intake (p = 0.02) and decrease in gain-feed ratio (G:F) ratio (p<0.01). Decreased CP levels in the diet were associated with a linear increase in average daily gain (p< 0.05) and quadratic increase in G:F ratio (p<0.05). In the early weaning period, blood urea nitrogen concentration tended to increase when ME in the diet decreased and decrease when CP level in the diet decreased (p = 0.09, p<0.01, respectively). Total protein concentration tended to increase when CP level was reduced (p = 0.08). In the late weaning period, blood urea nitrogen concentration decreased linearly as CP level decreased (p<0.01). The CP and crude fat digestibility decreased when ME was decreased by 0.42 MJ/kg (p = 0.05, p = 0.01, respectively). The CP digestibility increased linearly as CP level decreased (p = 0.01).

Conclusion

A weaning pig diet containing high ME level (13.82 MJ/kg) and low CP level (19.7%/16.9%) can improve pig growth performance and nutrient digestibility.

Effects of Sucrose-based High-lysine Diet on Blood Chemistry, Growth Performance, and Gastrointestinal Morphology of Broiler Chickens During the Growing Stage

This study aimed to investigate the effect of replacing fat in broiler grower diet with sucrose combined with supplementation of the synthetic amino acid lysine on growth performance, gastrointestinal morphology, and blood biochemical parameters in broiler chickens. Broilers were raised for 21 days and then divided into two treatment groups (n=24 in each group). Two dietary treatments were used: corn-soy-based diet with oil (control) and corn-soy-based diet formulated with sucrose (3.30%) and lysine hydrochloride (3.36%). The experimental period was 21 days (from 21 to 42 days of age). At the end of week 6, all the birds in each treatment were slaughtered via neck slit, defeathered, and eviscerated for carcass and intestinal morphological characterization. Blood samples were collected to measure blood lipoprotein, triglyceride, and cholesterol levels. The results showed that supplementation of sucrose and lysine hydrochloride to broiler ration significantly (P<0.05) decreased feed intake by half and reduced average daily gain during the study period compared to those observed in broilers fed control diet. Further, this supplementation significantly altered gastrointestinal morphology and blood lipoprotein (HDL and LDL) and total cholesterol levels. In conclusion, corn-soy-based diet fortified with sucrose (3.30%) and lysine hydrochloride (3.36%) within current nutrient specifications has a negative effect on broiler growth performance.

Hydrolyzed casein and whey protein meals comparably stimulate net whole-body protein synthesis in COPD patients with nutritional depletion without an additional effect of leucine co-ingestion

BACKGROUND & AIMS

Muscle wasting commonly occurs in COPD, negatively affecting outcome. The aim was to examine the net whole-body protein synthesis response to two milk protein meals with comparable absorption rates (hydrolyzed casein (hCAS) vs. hydrolyzed whey (hWHEY)) and the effects of co-ingesting leucine.

METHODS

Twelve COPD patients (GOLD stage II-IV) with nutritional depletion, were studied following intake of a 15 g hCAS or hWHEY protein meal with or without leucine-co-ingestion, according to a double-blind randomized cross-over design. The isotopic tracers L-[ring-(2)H5]-Phenylalanine, L-[ring-(2)H2]-Tyrosine, L-[(2)H3]-3-Methylhistidine (given via continuous intravenous infusion), and L-[(15)N]-Phenylalanine (added to the protein meals) were used to measure endogenous whole-body protein breakdown (WbPB), whole-body protein synthesis (WbPS), net protein synthesis (NetPS), splanchnic extraction and myofibrillar protein breakdown (MPB). Analyses were done in arterialized-venous plasma by LC/MS/MS.

RESULTS

WbPS was greater after intake of the hCAS protein meal (P < 0.05) whereas the hWHEY protein meal reduced WbPB more (P < 0.01). NetPS was stimulated comparably, with a protein conversion rate greater than 70%. Addition of leucine did not modify the insulin, WbPB, WbPS or MPB response.

CONCLUSIONS

Hydrolyzed casein and whey protein meals comparably and efficiently stimulate whole-body protein anabolism in COPD patients with nutritional depletion without an additional effect of leucine co-ingestion. This trial was registered at clinicaltrials.gov as NCT01154400.

Insulin secretion, body composition and pig performance are altered by feeding pattern

Three studies investigated the effect of feeding strategy on production performance and endocrine status of growing pigs. For Experiment 1, 20 entire male pigs (70.0 ± 4.6 kg) were allocated randomly to individual pens in one of four climate-controlled rooms. Pigs were fed for 23 days either ad libitum or entrained to feed bi-phasically for two 90-min periods. For Experiment 2, 20 entire male pigs (41.2 ± 3.5 kg) were housed as per Experiment 1. Pigs were fed for 49 days either ad libitum or fed bi-phasically for two 60-min periods. For Experiment 3, 100 female pigs (66.1 ± 3.5 kg) were randomly allocated to individual pens within a commercial piggery and fed for 42 days either ad libitum or bi-phasically for two 60-min periods. Ear vein catheters were inserted into 10 pigs from each group and hourly blood samples were collected for 24 h in Experiments 1 and 2 and for 11 h in Experiment 3. Plasma insulin, non-esterified fatty acid and glucose concentrations were determined in Experiments 1 and 2, and glucose and insulin concentrations in Experiment 3. Feed intake and performance were recorded in all experiments and carcass composition was assessed by computed tomography for Experiment 2. There were no differences in final liveweight between the two treatment groups for all experiments. Pigs fed for two 90-min periods (Experiment 1) showed no difference in feed intake when compared with feeding ad libitum. Pigs in Experiment 2 fed for two 60-min intervals consumed 2.49 kg/pig.day compared with those fed ad libitum that consumed 2.68 kg/day (P = 0.057). In Experiment 3, pigs fed twice daily consumed 2.82 kg/pig.day compared with 2.91 kg/pig.day in ad libitum-fed pigs (P = 0.051). Bi-phasic fed pigs in Experiment 2 had improved (P < 0.05) feed conversion efficiency compared with pigs fed ad libitum. For all experiments, there was no difference in plasma glucose concentrations between the two treatments. In all three experiments, the circulating insulin concentrations for pigs fed ad libitum remained at a constant level throughout the sampling period. However, plasma insulin concentrations for the bi-phasic fed pigs significantly increased ~1 h after both feeding periods during all three experiments. Insulin secretion of pigs fed for two 90-min periods differed from that of pigs fed for two 60-min periods. Plasma insulin concentration increased five-fold following feeding for 60 min, compared with that in pigs fed for 90 min, which increased two-fold. Bi-phasic-fed pigs from Experiment 2 had reduced (P < 0.05) total carcass fat and significantly increased muscle when compared with pigs fed ad libitum. The data showed that feeding pigs at two succinct periods aligned insulin secretion to the time of feeding. Pigs fed for 60 min, unlike those fed for 90-min intervals, had reduced feed intake in comparison to those fed ad libitum. This may suggest that the duration of the feeding bout is important for this response and this may in turn influence both energy balance and the way energy is partitioned.

Synchronising the availability of amino acids and glucose increases protein retention in pigs

Effects of synchronising the availability of amino acids and glucose within a day on protein and energy metabolism were studied in growing pigs. Ten pigs of on average 54 (s.e. 1.0) kg live weight were assigned to each of two dietary treatments (synchronous v. asynchronous nutrient supply) in a change-over design. On the synchronous treatment (SYN), pigs received two balanced meals: one at 0800 h and one at 1600 h. On the asynchronous treatment (ASYN), pigs received virtually all protein at 0800 h and all carbohydrates at 1600 h. The dietary supply of ingredients and nutrients to pigs was similar for both treatments. Pigs were housed individually in respiration chambers. Faecal apparent nutrient digestibility was determined and nitrogen and energy balances were measured. Faecal apparent digestibility of energy, organic matter and non-starch polysaccharides was higher ( P < 0.05) for SYN than for ASYN. The efficiency of utilisation of digestible protein with protein gain was higher ( P = 0.001) for SYN (56.7%) than for ASYN (47.1%). The substantial decrease ( P < 0.05) in respiratory quotient and 13C enrichment of the expired CO2 after the morning meal indicated higher amino acid oxidation for ASYN than for SYN. Heat production and energy retention as fat were not affected by nutrient synchrony. In conclusion, an asynchronous availability of glucose and amino acids within a day increases amino acid oxidation, resulting in a substantial reduction in protein utilisation but with virtually no effect on fat retention.

Triennial Growth Symposium: effects of polymeric carbohydrates on growth and development in pigs

Polymeric carbohydrates, starch and nonstarch polysaccharides (NSP), quantitatively represent the largest portion of the diets for pigs and are, therefore, the largest energy contributor. The 2 types of polysaccharides, however, have different fates and functions in the gastrointestinal tract and lead to different metabolites upon digestion. Pancreatic and mucosal enzymes in the small intestine break down the majority of starch, whereas NSP primarily are degraded by the microflora in the large intestine. Starch degradation leads to the release of glucose, which is absorbed by an active absorption process that triggers the release of insulin from the pancreas, whereas the fermentation of NSP to short-chain fatty acids (SCFA; i.e., acetate, propionate, and butyrate) occurs at a slower and more constant rate and with SCFA being absorbed by passive diffusion. Type and amounts of polymeric carbohydrates influence growth and development through different mechanisms. First, the proportion of starch to NSP plays an important role for the content of available energy (i.e., DE, ME, and NE); available energy relative to protein is crucial for performance and carcass quality. Second, the proportion of starch to NSP will influence rate and type of metabolites (i.e., glucose vs. SCFA) deriving from carbohydrate assimilation. Third and finally, the type of starch (i.e., types A, B, and C) and soluble NSP will influence the release of insulin, the hormone that facilitates nutrient uptake by tissues, organs, and cells, and thus plays a critically essential role in protein synthesis and muscle growth, as well as lipid synthesis and adipose tissue growth. In conclusion, polymeric carbohydrates influence growth and development through events in the gut and direct and indirect effects of different metabolites deriving from carbohydrate assimilation.

Metabolic control and future opportunities for growth regulation

The last 10 years have seen a significant expansion in the scope of attempts to manipulate the growth of animals (Buttery, Lindsay and Haynes, 1986). The expansion of interest has been driven by a number of factors, both economic and theoretical. At the economic level the need to develop energetically and economically efficient strategies of animal production has been coupled with a renewed awareness of the implications for human health of excessive intakes of saturated fats. Emphasis then has switched from the maximization of weight gain as an end in itself towards a need to promote protein deposition at any given intake and, at the same time, to reduce the fat content of meat and meat products. These twin objectives might be achieved by one of three strategies: the promotion of protein deposition alone, because at any given rate of weight gain this will tend to minimize the rate of fat deposition (the so-called repartitioning effect); the reduction of fat gain (an approach that has received particularly close attention by those concerned primarily with human obesity); or ideally the simultaneous promotion of protein accretion and depression of that of fat.

Sucrose as an energy source for growing pigs: a comparison of the effects of sucrose, starch and glucose on energy and protein retention

The effects of dietary sucrose, glucose and starch were compared to determine whether sucrose as an energy source affected energy or protein metabolism of growing pigs given food either frequently or once daily. Three experiments were conducted using three diets (0·8 g lysine per MJ digestible energy (DE)) containing sucrose, starch or glucose, respectively. In the first experiment, the DE contents of the diets were determined. In the second, the diets were given either once daily (08.00 h) or frequently (3-h intervals) to growing pigs (20 to 45 kg live weight) and growth responses, blood characteristics and energy, protein and fat retention measured. In the third experiment, the three diets were given to seven pigs (50 kg live weight), either once daily or frequently to monitor further the effects on plasma triglycerides, glucose, urea and insulin levels.

Growth rate, on a carcass basis, was slightly lower in pigs given glucose relative to starch (P < 0·05) but there was no effect of carbohydrate source on the retention of energy, protein or fat. Plasma triglyceride levels were lower in pigs given starch (P < 0·05) whilst plasma glucose and insulin concentrations were higher immediately after feeding in pigs given food once daily (7 < 0·05, P < 0·01). All three carbohydrate sources were used less efficiently by the pigs for energy, protein and fat deposition with once daily compared with frequent feeding (V < 0·01). Overall, these results indicate that sucrose as an energy source does not effect energy or protein metabolism by the growing pig. It appears that the metabolism of fructose within sucrose had no effect on metabolism.

Relationship between the milk yield response to short-term bovine somatotropin treatment and the lipolytic response to adrenaline in dairy cows

The aim of this experiment was to determine if the milk yield response of dairy cows to short-term treatment with bovine somatotropin (bST) was correlated with the non-esterified fatty-acid (NEFA) response to an adrenaline challenge. Twenty-six multiparous Holstein cows (58+/-5.4 days postpartum) received daily sub-cutaneous injections of saline for 7 days followed by sub-cutaneous injections of 20mg/day of bST for 14 days. On day 7 of the saline treatment and day 14 of the bST treatment the cows were given an intravenous injection of adrenaline (1.4 microg/kg body weight). Blood samples were taken before and after the adrenaline challenge. The difference in milk yield between the saline and the second week of bST treatment (MYR) varied considerably between animals (from -0.4 to +8.0 kg/day). MYR was positively correlated with the change in the basal concentration of NEFA between the saline and second week of bST treatment, as well as with the change in the area under the profile of NEFA above basal values following the adrenaline challenge. It remains to be established whether the greater lipolytic responses to adrenaline of the cows with the greater MYR reflects the deeper negative energy that these animals also experienced or a fundamental difference in the physiology of their adipose tissue.

The correlation of chemical and physical corn kernel traits with growth performance and carcass characteristics in pigs

Corn kernel composition may affect its nutritive value and, thus, pig growth performance and carcass characteristics. The objective of this study was to determine the influence of the chemical and physical traits of corn kernels from different hybrids on the growth performance and carcass characteristics of pigs. A total of 288 crossbred pigs were grown in a 3-phase program from 21 kg of BW until slaughter at 113 kg of BW with 12 pens (4 pigs/pen) per dietary treatment. Target BW for each phase were 20 to 40 kg (grower 1), 40 to 80 kg (grower 2), and 80 to 120 kg (finisher). In each phase, diets were formulated to be marginally deficient in Lys, TSAA, Ca, Na, and nonphytate P to improve the likelihood of detecting differences in performance due to corn hybrid. Each of 6 corn hybrids represented a wide range of kernel chemical and physical traits and was substituted for corn in a common diet formulation on an equal weight basis to make the 6 dietary treatments. Physical and chemical composition of the kernels were analyzed and correlated with performance measures by multivariate ANOVA. Kernel density was correlated with i.m. fat (IMF) content in LM (r = -.35, P < 0.05). Stenvert grinding time was correlated (P < 0.05) with ADG during the grower 1 phase (r = 0.26), ADFI during the grower 2 phase (r = 0.27), final BW (r = 0.27), and IMF (r = -0.36). The amylose content of the cornstarch was correlated (P < 0.05) with ADG during the grower 2 phase (r = -0.28) and with BW at the end of the grower 2 phase (r = -0.27). The NDF content of the kernels was correlated (P < 0.05) with ADG during the finisher phase (r = -0.30), final BW (r = -0.33), and number of days to market (r = 0.31). The ADF content of the kernels was correlated (P < 0.05) with ADG during the grower 1 phase (r = -0.26), final BW (r = -0.26), and IMF (r = 0.31). The correlations of performance measure variation with individual kernel hybrid physical and chemical traits were statistically significant yet not large enough to base corn hybrid selection for feeding pigs on any single kernel chemical or physical trait.

Interactions among the branched-chain amino acids and their effects on methionine utilization in growing pigs: effects on plasma amino– and keto–acid concentrations and branched-chain keto-acid dehydrogenase activity

The present experiment was designed to elucidate the mechanism of the methionine-sparing effect of excess branched-chain amino acids (BCAA) reported in the previous paper (Langer & Fuller, 2000). Twelve growing gilts (30–35 kg) were prepared with arterial catheters. After recovery, they received for 7 d a semipurified diet with a balanced amino acid pattern. On the 7th day blood samples were taken before (16 h postabsorptive) and after the morning meal (4 h postprandial). The animals were then divided into three groups and received for a further 7 d a methionine-limiting diet (80 % of requirement) (1) without any amino acid excess; (2) with excess leucine (50 % over requirement); or (3) with excesses of all three BCAA (leucine, isoleucine, valine, each 50 % over the requirement). On the 7th day blood samples were taken as in the first period, after which the animals were killed and liver and muscle samples taken. Plasma amino acid and branched-chain keto acid (BCKA) concentrations in the blood and branched-chain keto-acid dehydrogenase (BCKDH; EC 1.2.4.4) activity in liver and muscle homogenates were determined. Compared with those on the balanced diet, pigs fed on methionine-limiting diets had significantly lower (P < 0·05) plasma methionine concentrations in the postprandial but not in the postabsorptive state. There was no effect of either leucine or a mixture of all three BCAA fed in excess on plasma methionine concentrations. Excess dietary leucine reduced (P < 0·05) the plasma concentrations of isoleucine and valine in both the postprandial and postabsorptive states. Plasma concentrations of the BCKA reflected the changes in the corresponding amino acids. Basal BCKDH activity in the liver and total BCKDH activity in the biceps femoris muscle were significantly (P < 0·05) increased by excesses of leucine or all BCAA.

Correlation of blood and milk components with the milk yield response to bovine somatotropin in dairy cows

Our aim was to correlate the individual variation in the milk yield response (MYR) of Holstein dairy cows to bovine somatotropin (bST), with changes in milk plasmin and plasminogen activities as well as with plasma hormone and metabolite levels. Thirty-two housed multiparous Holstein cows (90 +/- 3.8 days post partum) received daily subcutaneous injections of saline for 1 week followed by subcutaneous injections of 20 mg/day of bST for 2 weeks. Blood samples were taken at approximately 4h intervals over 24 h at the end of the saline and bST treatment periods. Milk samples were also taken at the end of the saline and bST treatment periods. The difference in milk yield between the saline and the second week of bST treatment (MYR) varied considerably between animals (from -0.2 to +8.6 kg/day, relative to the saline treatment week). Low milk yield before bST treatment was associated with a high MYR. The plasma growth hormone response to treatment was negatively correlated with MYR. Plasma insulin-like growth factor-1 response to treatment was positively correlated with MYR. Furthermore, a high MYR to bST was associated with a lower milk plasminogen level before treatment and a greater reduction in the level of plasminogen in milk following treatment.

Individual variation in the milk yield response to bovine somatotropin in dairy cows

The objective was to relate the short-term milk yield response (MYR) following use of exogenous bovine somatotropin (bST) to changes in plasma concentrations of metabolites and hormones. Twenty-four Holstein cows (52 +/- 4.1 d postpartum) received daily subcutaneous injections of saline for 1 wk followed by subcutaneous injections of 33 mg/d of bST for 2 wk (Trial 1). The difference in milk yield between wk 1 and 3 for each cow was used to determine the 5 cows with the highest (HR) and 5 with the lowest responses (LR) to bST. These 10 cows were then used in 3 further trials of the same design (Trials 2, 3, and 4, conducted at 122, 181, and 237 +/- 7.6 d postpartum, respectively). Blood samples were taken 2 h after the administration of bST on d 1, 3, 5, 15, 17, and 19 of each trial. The HR group had consistently greater MYR to bST than the LR group throughout their lactation. The LR group had a higher milk yield and lower plasma insulin like growth factor-I (IGF-I) concentrations during the saline treatment in all trials. The increase in plasma somatotropin concentrations following injections of bST was greater for the LR group, whereas the difference in plasma IGF-I level between wk 1 and 3 was greater for the HR group. The HR group had lower levels of 3-hydroxy-butyrate and nonesterified fatty acids before bST treatment. Low short-term response to bST was associated with plasma concentrations of hormones and metabolites that indicate negative energy balance, although other factors may be involved.

Effect of nonwaxy and waxy sorghum on growth, carcass traits, and glucose and insulin kinetics of growing-finishing barrows and gilts12

Two experiments were conducted to determine the effect of nonwaxy (amylose and amylopectin starch) or waxy (amylopectin starch) sorghum on growth, carcass traits, and glucose and insulin kinetics of pigs. In Exp. 1 (95-d), 60 crossbred barrows or gilts (initial and final BW of 24 and 104 kg) were allotted to three treatments with five replications of four pigs per replicate pen in a randomized complete block design. The dietary treatments for Exp. 1 were 1) corn-soybean meal (C-SBM) diet, 2) sorghum-SBM (red pericarp, non-waxy), and 3) sorghum-SBM (red pericarp, waxy). In Exp. 2, 28 crossbred barrows (initial and final BW of 24 and 64 kg) were allotted to two treatments with three replications of four or five pigs per replicate pen in a randomized complete block design. Growth data were collected for 49 d, and then 20 barrows were fitted with jugular catheters, and then a glucose tolerance test (500 mg glucose/kg BW), an insulin challenge test (0.1 IU of porcine insulin/kg BW), and a feeding challenge were conducted. The dietary treatments for Exp. 2 were 1) sorghum-SBM (white pericarp, nonwaxy) and 2) sorghum-SBM (white pericarp, waxy). In Exp. 1, ADG (P = 0.10) and ADFI (as-fed basis; P = 0.02) were increased (P = 0.10) and gain:feed was decreased (P = 0.04) in pigs fed the sorghum-SBM diets relative to those fed the C-SBM diet. These responses may have resulted from the lower energy content of sorghum relative to corn. Plasma NEFA concentration (collected after a 16-h fast on d 77) was decreased (P = 0.08) in pigs fed the waxy sorghum-SBM diet relative to those fed the nonwaxy sorghum-SBM diet. Kilograms of carcass fat was decreased (P = 0.07) in pigs fed the waxy sorghum-SBM diet relative to those fed the nonwaxy sorghum-SBM diet. In Exp. 2, there was no effect (P = 0.57 to 0.93) of sorghum starch type on growth performance by pigs. During the glucose tolerance and insulin challenge tests, there were no effects (P = 0.16 to 0.98) of diet on glucose or insulin kinetics. During the feeding challenge, glucose (P = 0.02) and plasma urea N (P = 0.06) area under the response curves from 0 to 90 min were decreased in pigs fed the waxy sorghum-SBM diet. Feeding waxy sorghum had minimal effects on growth and carcass traits relative to pigs fed corn or nonwaxy sorghum. Waxy sorghum vs. nonwaxy sorghum had no effect on glucose or insulin kinetics in pigs.

Effect of carbohydrate source on growth performance, carcass traits, and meat quality of growing-finishing pigs1,2,3

Two experiments were conducted to determine the effect of substituting a more available dietary carbohydrate (CHO) for portions of corn or fat in the diet on growth performance, carcass traits, meat quality, and serum or plasma metabolites in growing-finishing pigs. A three-phase feeding program was used with corn-soybean meal diets formulated to provide 105% of the Lys requirement for barrows or gilts gaining 325 g of lean daily in Exp. 1 or gilts gaining 350 g of lean daily in Exp. 2. Diets were isoenergetic within experiments. All other nutrients met or exceeded suggested requirements. In Exp. 1, pigs were allotted to three dietary treatments (0, 7.5, or 15.0% sucrose), with three replications of barrows and three replications of gilts, and with three or four pigs per replicate pen; average initial and final BW were 25.2 and 106.7 kg. In Exp. 2, gilts were allotted to two dietary treatments (waxy [high amylopectin] or nonwaxy [75% amylopectin and 25% amylose] corn as the grain source), with five replications of four gilts per replicate pen; average initial and final BW were 37.7 and 100.0 kg. In Exp. 1, ADG and gain:feed ratio increased linearly (P < 0.02) as dietary sucrose increased. Minolta color scores, a* and b*, and drip loss (P < 0.06) also increased linearly with added sucrose. In Exp. 2, ADG, carcass weight and length, and the Minolta a* value were greater for pigs fed waxy corn (P < 0.08) than for those fed nonwaxy corn. Feed intake, longissimus muscle area, 10th-rib and average backfat thickness, dressing percentage, fat-free lean, percentage of lean and muscling, lean gain per day, total fat, percentage fat, lean:fat ratio, serum or plasma metabolites (Exp. 1: serum urea N; Exp. 2: serum urea N, and plasma nonesterified fatty acids, triacylglycerols, total and high-density lipoprotein cholesterol, insulin, and total protein), pH of the longissimus muscle, and subjective muscle scores (color, firmness-wetness, and marbling) were not affected by diet in either experiment. In summary, increasing availability of dietary CHO in growing-finishing pig diets improved growth performance, but it did not affect carcass traits.

Effects of quality of energy intake on growth and metabolic response of enterally fed low-birth-weight infants

Carbohydrate and fat may vary in their ability to support protein accretion and growth. If so, variations in the source of nonprotein energy might be used to therapeutic advantage in enterally fed low-birth-weight infants. To test the hypothesis that high-carbohydrate diets are more effective than isocaloric high-fat diets in promoting growth and protein accretion, low-birth-weight infants weighing 750-1600 g at birth were randomized in a double blind study to receive one of five formulas differing only in the quantity and quality of nonprotein energy. Groups 1, 2, and control received 130 kcal x kg(-1) x d(-1) with 35, 65, and 50% of the nonprotein energy as carbohydrate. Groups 3 and 4 received energy intake of 155 kcal x kg(-1) x d(-1) with 35 and 65% of the nonprotein energy as carbohydrate. Protein intake of all groups was 4 g x kg(-1) x d(-1). Growth and metabolic responses were followed weekly, and macronutrient balances including 6-h indirect calorimetry were performed biweekly. Greater rates of weight gain and nitrogen retention were observed at high-carbohydrate intake compared with high-fat intake at both gross energy intakes. Greater rates of energy storage and an increase in skinfold thickness were observed in group 4 (high-energy high-carbohydrate diet) despite higher rates of energy expenditure. These data support the hypothesis that at isocaloric intakes, carbohydrate is more effective than fat in enhancing growth and protein accretion in enterally fed low-birth-weight infants. However, a diet with high-energy and high-carbohydrate content also results in increased fat deposition.

Glucose and [13C]leucine metabolism by the portal-drained viscera of sheep fed on dried grass with acute intravenous and intraduodenal infusions of glucose

The effect of exogenous glucose supply by either intrajugular (IJG) or intraduodenal (IDG) infusion at 2.0 mg glucose/kg body weight per min was investigated in four wether sheep (average weight 44 (SD 4) kg) chronically catheterized in the carotid artery and portal veins. Sheep were fed on a dried grass pellet diet hourly using continuous belt feeders. Whole-body glucose irreversible loss (IL) rate, measured with [6-3H]glucose, was increased by 0.5 and 0.8 of exogenous supply for IJG and IDG infusions respectively. Portal glucose utilization, measured by isotope dilution across the portal-drained viscera, was unaffected by additional glucose regardless of the route of glucose supply (P = 0.76 for control v. glucose infusions) and was a constant proportion of glucose IL (0.28) for all treatments. Portal plasma flow was higher during IDG infusions compared with IJG infusions (1.65 v. 1.44 litres/min, P = 0.055). Circulating total free amino acid concentrations fell during glucose infusions (2146, 1808 and 1683 mumol/l for control, IJG and IDG treatments respectively, P = 0.067 for treatment effect) but net portal absorption was not affected by increased glucose supply. Recovery in the portal vein of [1-13C]leucine infused into the duodenum averaged 0.65 and was not affected by increasing glucose supply to the gut tissues. The results show that glucose utilization by gut tissues is responsive to changes in both vascular and luminal glucose supply. The effects of changing gut tissue use of glucose and increased whole body glucose IL on metabolism of nutrients is discussed.

Effect of growth hormone-releasing factor on the response to insulin of cows during early and late lactation

The euglycemic clamp technique was used to determine the effect of bovine growth hormone-releasing factor on glucose kinetics and on the response to insulin of 4 dairy cows during early lactation (mean, 35 d postpartum) and of 6 dairy cows during late lactation (mean, 194 d postpartum). Beginning 3 d prior to experiments, cows were injected twice daily with either saline or 2.5 micrograms/kg of growth hormone-releasing factor. On the day of the experiment, saline or the releasing factor (0.0119 microgram/kg per min) was infused into each cow for 5 h. After a basal period, insulin was infused at 1 and then at 6 mU/kg per min; plasma glucose concentrations were maintained at basal concentrations by the infusion of normal glucose. Growth hormone-releasing factor reduced the glucose infusion rate that was required to maintain euglycemia during the insulin infusions during late lactation but had no effect during early lactation. During the insulin infusions of the late lactation experiment only, the rates of glucose appearance, disappearance, and metabolic clearance were lower when plasma growth hormone was elevated. The results demonstrated that elevated concentrations of growth hormone decreased the responsiveness of peripheral tissues to high concentrations of insulin during late lactation but apparently had little effect during early lactation.

Intragastric bolus feeding of meals containing elementary, partially hydrolyzed or intact protein causes comparable changes in interorgan substrate flux in the pig

Dietary protein given as pre-digested protein improves the nutritional value of the meal. However, studies measuring absorption kinetics of pre-digested protein or free amino acid mixtures are scarce and suffer from methodological problems. Therefore, the study was designed to study whether differences in absorption kinetics play a role. The kinetics of substrate production or consumption after a rapid gastrically-infused meal was studied across the portal drained viscera, liver and hindquarter in conscious, multicatheterized healthy pigs of 20-22 kg (n = 12). The meal contained carbohydrates and protein (1.44 g/kg body weight) as intact whey protein isolate, moderately-hydrolyzed protein digest or equivalent amino acid mixture (including glutamine and asparagine). For almost all amino acids and glucose, intestinal production, liver and hindquarter uptake were similar. The higher liver urea production (less than 15% of total alpha-amino intake) after the meals with pre-digested protein or free amino acids was related to the marginally higher intestinal glutamine breakdown (not significant) and ammonia production. Our results suggest that in the normal healthy pig, uptake and metabolism of moderately hydrolyzed,free amino acid or intact protein meals with identical composition is not different.

Nutrient interactions with reference to amino acid and protein metabolism in non-ruminants; particular emphasis on protein-energy relations in man

Because the regulation of protein and energy balance is of major research interest in the nutrition and physiology of humans and animals, a selected account of interactions between protein and energy is given here, with particular emphasis on studies in human subjects. The discussion begins with reference to the relations between protein and energy intakes and nitrogen balance; selected aspects of the relations between protein dynamics and energy metabolism among the various mammalian species are then considered. This leads to a brief account of oxidative amino acid catabolism and its relevance to the assessment of amino acid requirements, particularly in adult man. It is concluded that obligatory oxidative losses of amino acids can be used to predict or approximate amino acid requirements in children and adults. The nitrogen-sparing properties of carbohydrate and lipid-derived fuels are then considered. Despite the well-known and profound, yet differential, impacts of dietary protein and energy sources, and their interactions on body protein balance, there remain wide gaps in our understanding of the mechanisms responsible for their effects, such as the quantitative and mechanistic involvement of hormones, including insulin and the counter-regulatory hormones, and the roles played by the major amino acids responsible for the interorgan transport of nitrogen and the regulation of urea production. Additional studies focusing on metabolic nitrogen trafficking would significantly enhance an understanding of how protein and energy interact to achieve the efficient utilization of dietary protein for maintenance and promotion of lean body gain.

Effect of dietary tryptophan on muscle, liver and whole-body protein synthesis in weaned piglets: relationship to plasma insulin

Two experiments were carried out with piglets, 3-5 kg live weight, to evaluate the effects of feeding a tryptophan (TRP)-deficient diet for 2 weeks on protein synthesis rates measured in vivo 2 h after a meal. In the first experiment on twenty piglets fed on 250 g protein/kg diets, TRP deficiency (0.77 g/16 g nitrogen) as compared with adequacy (1.17 g/16 g N) significantly decreased feed intake, growth performance and fractional protein synthesis rates (FSR), without variation of RNA in longissimus dorsi (LD) and with parallel increases in RNA in semitendinosus (ST) muscle and liver. In the second experiment thirty-two piglets were tube-fed deficient and adequate diets at the two feeding levels (LF) previously achieved. Both TRP and LF significantly increased growth performance and FSR, but not RNA, in LD and ST muscle, with a trend to a synergy between the two factors (TRP x LF interaction). In another muscle, trapezius (TR), the same interaction was only apparent in RNA content. Among the three muscles it was in LD that FSR was the most responsive to dietary TRP (significant muscle x TRP interaction). In the liver the TRP x LF interaction on FSR and not RNA was the major significant effect, indicating that higher TRP and higher LF were both required to get the maximum protein synthesis rate. At 30 min after a meal the same significant interaction effect was shown on plasma glucose, whilst the higher LF increased plasma insulin with both diets. After a further 30 min the appearance of a similar significant effect of the TRP x LF interaction on plasma insulin resulted from its abatement when the deficient diet had been fed at high LF. These results suggest that dietary TRP deficiency decreased muscle and liver protein synthesis rates in relation to a decrease in the post-prandial release of insulin following a decreased rate of nutrient absorption.

Muscle protein synthesis in response to testosterone administration in wether lambs

A method has been developed based on stable isotopes and biopsy procedures which allows the large-dose procedure for measurement of protein synthesis to be applied in serial studies to farm species. Measurements of total nitrogen retention and protein synthesis in m. longissimus dorsi and m. vastus lateralis were made in five wether lambs (40-44 kg) infused intravenously, successively, with vehicle (10 d); testosterone (15 d; 9 mg/d); vehicle (15 d). N retention was improved by testosterone infusion (+2.9 g N/d; a 96% improvement total over control periods). Muscle protein synthesis was not significantly altered by exogenous hormone administration, nor were RNA:protein, RNA:DNA or protein:DNA. The implication of the developed procedure for dynamic studies in accessible tissues of large animals is discussed.

Effect of plane of nutrition on insulin sensitivity during lactation in the ewe

The hyperinsulinaemic euglycaemic insulin clamp technique was used to compare insulin sensitivity in lactating ewes at two levels of feeding. Clamps were performed at two (restricted intake) or three (ad libitum intake) stages of lactation and also 30 d after drying off. Dose response curves for insulin were constructed using the glucose metabolic clearance rate (MCR) as the measure of glucose metabolism and these were statistically compared between stages of lactation within the feeding levels, and also between feeding regimes. Animals on a restricted feed intake showed a weight loss throughout lactation, coupled with a lower insulin sensitivity as measured by the ED50 (concentration of insulin required to produce a half maximal increase in MCR), while those on ad libitum feeding showed a weight gain and a decreased insulin sensitivity in the dry period. Endogenous glucose production was less sensitive to inhibition by insulin in the animals subjected to restricted food intake, compared with those on the ad libitum regime, which suggested a major role for the plane of nutrition in adjusting the homeorhetic control of metabolism during lactation.

Effects of guar gum on plasma urea, insulin and glucose in the growing pig

1. Six growing pigs fitted with portal and arterial blood cannulas were given a barley-fishmeal diet, either alone or supplemented with guar gum at 60 g/kg basal diet. Blood samples were taken during 8 h following test meals given at 08.00 hours. 2. Ingestion of the guar-gum-supplemented diet appeared to increase systematically portal and arterial levels of plasma urea. At peak values, 4 and 5 h after the test meal, this effect was statistically significant (P less than 0.05). 3. Irrespective of which diet was given, portal and arterial blood samples, withdrawn at the same time, were found to have about the same concentration of urea. This was found throughout the 8 h studied and implies that no net exchange of urea between the circulation and the gastrointestinal tract, as a whole, took place. 4. In the time-period 30-60 min following the test meal, guar gum significantly reduced the postprandial hyperglycaemia and hyperinsulinaemia in portal blood.

Quantitative measurement of endogenous amino acid absorption in unanaesthetized pigs

The present experiment was carried out with 11 pigs (mean body weight: 53.9 +/- 1.3 kg) fitted with permanent catheters in the portal vein and carotid artery and with an electromagnetic flow probe around the portal vein. They were each subjected to 2 or 3 trials at 3 to 4-day intervals. During each trial the animals received after a previous fasting of 20 h a given amount of a protein-free diet (200 to 1200 g). The blood was collected either continuously for a quantitative determination of amino nitrogen, reducing sugars, urea and ammonia (number of meals 12, mean intake: 727 +/- 60 g) or discontinuously every 30 min between 0 and 8 h after the meal for amino acid analysis (number of meals 8; mean intake 709 +/- 105 g). A rather constant appearance (2 g/h) of amino acids in the portal blood was observed throughout the postprandial period. The intestinal absorption of each amino acid was however variable and represented between 10 and 50% of the daily requirements of the animal during the measuring period (8 h). Glutamine and to a less extent glutamic acid were exceptions as they were taken up by the gut wall from the arterial blood. There was also a marked synthesis of ornithine and citrulline by the latter. Because of the low blood level of urea, there were no apparent exchanges of urea between the blood and the intestine; in contrast, the ammonia absorption represented about 70% of that observed after ingestion of normal protein diets. Most amino acids are largely taken up by the liver and peripheral tissues, but in the case of alanine the syntheses exceed the uptake.

Effect of insulin on hind-limb and whole-body leucine and protein metabolism in fed and fasted lambs

1. A combination of isotope-dilution and arterio-venous difference techniques was used to determine rates of leucine metabolism and protein synthesis and degradation in a hind-limb preparation (predominantly muscle) and the whole body of eight lambs fed on milk to appetite and eight lambs fasted from 24 to 48 h. 2. Compared with fed lambs, fasted lambs showed decreased rates of protein synthesis in both whole body and hind-limb, and in hind-limb muscle, elevated rates of protein degradation. 3. The effects of two rates of insulin infusion on whole-body and hind-limb-muscle leucine metabolism, and in turn on protein metabolism, were determined. Insulin had no significant effect on leucine flux or oxidation (and hence protein synthesis and degradation) in whole-body or hind-limb muscle of fed lambs. In fasted lambs insulin progressively reduced arterial leucine concentration and whole-body leucine flux and oxidation, indicating a reduction in both protein synthesis and degradation. Insulin reduced the rate of leucine efflux from hind-limb muscle, which was followed by a reduction in leucine uptake. Insulin increased hind-limb-muscle glucose uptake in both fed and fasted lambs. 4. On the basis that hind-limb muscle was representative of skeletal muscle in general, we estimated that muscle accounted for the same percentage (about 27) of whole-body protein synthesis in both fed and fasted lambs. This percentage was unaffected by infusion of insulin, although the absolute rates differed in fed and fasted lambs.

Urea synthesis and leucine turnover in growing pigs: changes during 2 d following the addition of carbohydrate or fat to the diet

1. Studies have been made of the time-sequence of protein metabolic and hormonal changes following an abrupt increase in carbohydrate or fat intake. [3H]leucine and [14C]urea were infused for 72 h, via the aorta, into fourteen female pigs (30-38 kg body-weight). At 24 h after the start of the infusion their feed was either changed to one of two isonitrogenous diets containing additional starch (group BS, five animals) or fat (group BF, five animals), or remained unaltered (group BB, four animals). The distribution space of urea was measured by the dilution of a single dose of [14C]urea given both 48 h before and 48 h after the change in diet. The changes in the concentration and specific radioactivity of blood leucine were used to infer changes in protein turnover and those of plasma urea to measure total amino acid catabolism. The concentrations of blood glucose and plasma insulin and cortisol were also measured at approximately two-hourly intervals for the 48 h period following the change in diet. 2. Within 4 h of either change in diet blood leucine concentration was lowered and the leucine specific radioactivity was raised above that in group BB, but after 24 h both the concentration and specific radioactivity of leucine returned to values similar to those in group BB. Eventually the blood leucine specific radioactivity was slightly but not significantly reduced below that of group BB. 3. The addition of starch to the diet significantly reduced the synthesis and concentration of urea within 4 h but, although the addition of fat to the diet eventually lowered the urea concentration and synthesis, both changes were delayed for 18-24 h. 4. In group BS plasma glucose and insulin rose after the addition of starch, but after 24-36 h both returned to values that were the same as those in the animals that received the same diet throughout (group BB). The addition of fat to the diet altered neither blood glucose nor plasma insulin concentrations. The addition of either carbohydrate or fat to the diet eventually reduced plasma cortisol concentrations, but the change did not occur until 24 h after the change in diet. 5. The results suggest that alterations in non-protein energy supply exert their immediate effect on the degradation of whole-body protein. They do not exclude the possibility that these early changes may reflect opposing changes at different sites.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of dietary triolein and sunflower oil on insulin release and lipid metabolism in Zucker rats

Obese and lean male Zucker rats were fed ad libitum on diets containing either 50 (L) or 200 (H) g/kg diet of either triolein (T) or sunflowerseed oil (S). The specific activity of the hepatic microsomal delta 9 desaturase enzyme was depressed in both lean and obese rats fed the HS diet compared with the other three diets. The fatty acid composition of liver and subcutaneous white adipose tissue lipids were consistent with a lower delta 9 desaturation activity in rats fed the H diets, particularly for the HS diet. In both genotypes, microsomal delta 9 desaturase activity and the ratio of 16:1/(16:0 + 16:1) fatty acids in liver lipids were inversely related to the proportion of 18:2 in liver lipid. Plasma insulin concentrations and rates of glucose-stimulated insulin release in vivo were higher in obese rats compared with lean rats, and plasma insulin levels were higher in rats fed S compared with T. There was no relationship between delta 9 desaturase activity and either plasma insulin concentration or rates of insulin release in vitro. These findings suggest that hepatic delta 9 desaturase activity of Zucker rats is responsive to changes in the proportion of 18:2 in liver lipids but is not affected by changes in insulin secretion.

Insulin action and glucose metabolism in sheep fed on dried-grass or ground, maize-based diets

The effect of an exogenous supply of glucose, provided by the digestion of maize starch in the small intestine, on endogenous glucose metabolism and insulin action was studied in sheep using the euglycaemic insulin clamp procedure. Insulin was infused intravenously at rates of 0.2, 0.5, 1.0 and 6.0 mU/min per kg live weight for four consecutive periods in each of four sheep fed on dried-grass and maize-based diets. Glucose was also infused intravenously at a variable rate, sufficient to maintain the plasma glucose concentration at basal levels. Whole-body rates of glucose metabolism were determined using a continuous infusion of [6-3H]glucose. From the resulting insulin dose-response curves, it was observed that, when the sheep were fed on the dried-grass diet, the responsiveness of glucose metabolism to insulin was less than that reported for non-ruminants. When fed the maize-based diet, the glucose metabolic clearance rates (MCR) observed during insulin infusions were significantly greater (P less than 0.05) than those observed for the dried-grass diet. However, after correcting for the non-insulin-mediated glucose disposal, differences between diets were not significant. The sensitivity of glucose utilization to insulin was not affected by diet. The plasma insulin concentrations causing half-maximal insulin-mediated glucose MCR were 103 (SE 21) and 85 (SE 11) mU/l for the dried-grass and maize-based diets respectively. The sensitivity of endogenous glucose production to insulin was also unaffected by diet. The plasma insulin concentrations resulting in the suppression of endogenous glucose production to half the basal level were 80 (SE 26) and 89 (SE 29) mU/l for the dried-grass and maize-based diets respectively. It is concluded that the observed increase in glucose utilization on the maize-based diet was due partly to a slight change in responsiveness to insulin and also partly to a change in the rate of non-insulin-mediated glucose disposal.

Glucagon and tolbutamide as insulin secretagogues in the pig (Sus domesticus)

1. Glucagon tolbutamide, either alone or in combination, were injected i.v. into pigs and the effect upon plasma glucose and insulin concentrations measured. 2. Glucagon gave similar insulin responses to those seen in humans, but insulin responses to tolbutamide were less than in humans. 3. Combined doses of glucagon and tolbutamide gave similar, though reduced, responses to those seen in humans. At the highest combined doses applied, glucose concentration remained reduced for up to 6 hr. The insulin responses were approximately equal to the sum of the responses to each substance given alone.

Effects of changes in the intakes of protein and non-protein energy on whole-body protein turnover in growing pigs

1. The relationships between the intakes of protein and of non-protein energy (NPE), nitrogcn retention and body protein synthesis have been studied in female pigs weighing 30 and 35 kg.

2. Four animals were assigned to three regimens and given a conventional (basal) diet supplemented with fat, carbohydrate or protein. After 1 week, measurements of N excretion in urine and faeces (7 d collection) and gaseous exchange (3–4 d) were made. At the end of the balance period a solution of [l-14C]leucine was infused at a constant rate. Body protein synthesis was then calculated as the difference between the apparent irreversible loss of blood leucine and the loss of 14C in expired air.

The animals were then offered the basal diet without supplement for 10 d and the measurements of N retention, energy retention and protein synthesis were repeated.

3. The intakes of metabolizable energy (ME; MJ/kg body-weight (W)0.75per d) were 1.75 for fat, 1.58 for carbohydrate, 1–25for protein and 1.18 for the basal diet; corresponding intakes of apparently digestible N (ADN; g N/kgW0.75 per d) were 2.30,2.31,4.35 and 2–17. Daily N retention, which during the period of basal feeding was 13.6 g was increased by between 3.4 and 7.2 g by the supplements. Daily fat deposition was also increased in the animals that received the diets supplemented with carbohydrate and fat.

4. The rate of leucine catabolism was significantly reduced in the animals receiving the diets that were supplemented with W Eand increased by the addition of protein to the diet.

5. When based on the specfic radioactivity of blood leucine both the synthesis and breakdown of body protein (per unit metabolic body-weight) were increased by 30% in the animals receiving the high-protein diet but the increases in protein synthesis associated with the addition of carbohydrate (+14%) and fat (+12%) were much less marked. Consideration of these results together with previous observations (Reeds et al. 1980) suggested that body protein synthesis(g N/d) increased by 0.88 for each g increase in daily ADN and by 0.93 for each MJ increase in daily ME intake.

6. Comparison of the results obtained with the animals given high-carbohydrate diets and those given high-protein diets suggested an increase in heat production of 14 KJ/g of additional fat deposition. A similar comparison of animals receiving the high-protein and basal diets suggested a heat increment of 23.5KJ/g additional protein deposition. The changes in heat production and protein synthesis in the animals given the protein supplement were compatible with a heat increment of 5.3 KJ/g additional protein synthesized. Because of the large proportion of heat production associated with the deposition of fat this could not be confirmed with either of the other supplements, but it is possible that the energy cost of protein accretion varies with the relative proportions of protein and NPE in the diet.

Insulin and myoelectric activity of the small intestine of the pig

The effect of insulin on the myoelectric activity of the small intestine was determined in conscious pigs. Animals were implanted with electrodes along the small intestine, a strain gage on the stomach and catheters in both saphenous arteries. Feeding modified the migrating myoelectric complex (MMC), a cyclic pattern of action potential activity of the small intestine characteristic of fasting. The first period of regular spiking activity (RSA) on the duodenum after feeding was delayed and was not followed by quiescence. Plasma insulin and glucose concentrations during the first three MMC after feeding were highest just before periods of duodenal RSA. Injection or infusion of insulin into fasted pigs with production of hypoglycemia caused disruption of stomach motility and duodenal electrical activity. The duodenal MMC was not altered when glucose to prevent hypoglycemia was infused together with insulin or when glucose was infused alone. These studies suggest that insulin is not directly responsible for the postprandial modification of MMC activity as insulin infusions only modify the MMC when hypoglycemia occurs.

Protein turnover in growing pigs. Effects of age and food intake

1. Measurements were made of the nitrogen and energy balances of pigs of 30, 60 and 90 kg given a conventional diet at various daily rates. 2. Body protein synthesis was estimated from the irreversible loss of leucine from the blood following the infusion of [1-14C]leucine, and from the oxidation of the labelled amino acid. 3. Protein synthesis (g/d) increased by 2.17 for each 1 g increase in daily protein accretion and by 1.55 for each 1 g increase in daily protein intake. 4. At 30 kg, pigs close to energy equilibrium synthesized 270 g protein daily compared with 406 g and 512 g when their ration supplied twice and three times their maintenance requirement. 5. There was a close correlation between the daily urinary excretion of urea + ammonia and total amino acid catabolism estimated from the catabolism of leucine, but the latter underestimated the observed excretion by 2.5 g N/d. 6. The results imply that protein turnover accounts for only a proportion of the heat production associated with protein deposition.

The protein-sparing effect of carbohydrate. 1. Nitrogen retention of growing pigs in relation to diet

1. Measurements were made of the losses of nitrogen in the faeces and urine of sixty pigs of approximately 33 kg, given dietary regimens comprising twenty-nine combinations of fish flour (0-800 g/d) and maize starch (0-1200 g/d). 2. The results were used to develop a generalized equation describing N retention as a joint function of N intake and starch intake. 3. The protein-sparing effect of starch was exerted in all circumstances. It was greatest when protein intake exceeded 220 g/d but some effect persisted with protein-free diets. With a high protein supply, the increase in N retention per unit increase in dietary starch decreased from 36 mg/g with the first increment to 3 mg/g with the highest attainable starch intake. 4. From the generalized equation the relationships between net protein utilization and protein concentration and food intake could be described as continuous functions. The equations may be of use in comparing the protein values of diets measured under non-standardized conditions.