Growth heterogeneity in rearing sea bass ( Dicentrarchus labrax): test of hypothesis with an iterative energetic model.

This study aimed at modeling the relative importance of food intake on growth heterogeneity among cultured sea bass (Dicentrarchus labrax). First, we designed an individual growth model comprising five compartments (Energy intake, Losses, Net Energy, Recovered Energy and Maintenance). This model was calibrated with a first experiment carried out in eight tanks; A total of 130 juveniles (11 g) per tank were fed by a self-feeder (84 days, 20°C, 16L : 8D, 30 g NaCl/l). A second experiment was performed to better understand the relation between individual food intake, individual growth and growth heterogeneity, using the model as a tool for a hypothetico-deductive approach on growth heterogeneity (135 passive integrated transponder-tagged fish, same rearing conditions as above and individual food intake measured by X-ray every 14 days). The tested hypotheses were that food intake was (a) homogeneous, (b) proportional to the fish weight (i.e. to W1.00) X-ray (c) proportional to W0.66 and (d) reflected by the X-ray measurements of food intake. For each hypothesis, a simple linear regression between experimental and simulated results was produced. The Fitness indicators of these analyses, together with their confidence intervals (calculated by bootstrapping), allowed testing the relevance of these hypotheses. The analysis indicated that growth heterogeneity was largely accounted for by individual variations of food intake, as revealed by the X-ray analysis, and that food intake was proportional to W1.00, which suggests a dominance hierarchy where small fish are incapable of feeding maximally.

Effect of low continuous 99Tc intake on its absorption and metabolism in young rats.

A continuous daily oral dose of (99)TcO(4)(-) (5 Bq g(-1) day(-1)) was given to young rats for 56 days. In one group the intake was continued for 98 days, while in the other the intake was stopped to facilitate the determination of biological half lives in different organs and tissues. The absorbed fraction of (99)Tc increased from 0.7 to 0.9 during the experimental period (m=0.85 sigma=0.02). The whole body retained fraction (m=0.15 sigma=0.05) indicated a storage in the tissues. The liver and kidneys showed increasing concentrations of (99)Tc until a plateau was reached after 6 and 9 weeks, then a rapid decline after the intake was stopped (half life of 6 and 5 days respectively). In hair and thyroid tissue, the accumulation of (99)Tc increased linearly then declined very slowly after the intake was stopped and did not reach a plateau during the experiment. No significant amounts of (99)Tc were detected in the muscular tissues or in the walls of the digestive tract. After the contamination period, urinary and fecal excretions fell off very quickly (1 week), but significant, though low, quantities of urinary and fecal excretions were still observed 6 weeks after stopping intake.

Elevated rate of collagen solubilization and postmortem degradation in muscles of lambs with high growth rates: possible relationship with activity of matrix metalloproteinases.

The extracellular matrix, composed mainly of collagen, is considered responsible for the residual toughness of meat. Matrix metalloproteinases (MMP) responsible for the degradation of connective tissue are found in most tissues, but their participation in meat aging has not been tested. We recently showed that skeletal muscle has multiple MMP activities, as well as regulators and tissue inhibitors of metalloproteinases. Here we present the first observations of physiologic and postmortem variation of MMP activities in muscle. Growing lambs were offered two levels of intake: hay + concentrate for lambs with high growth rate (average daily gain > 250 g) and hay only for those with low growth rate (average daily gain < 25 g). At slaughter and at 21 d of postmortem aging of longissimus and semimembranosus muscles, we studied collagen content, collagen solubility, free hydroxyproline (OH-pro), and levels of latent and active forms of a matrix metalloproteinase (MMP-2) by gelatin zymography. Our results demonstrate the presence of an active isoform of MMP-2 in lamb muscle. Its level was higher (+90%, P < 0.01) in lambs that expressed a high growth rate. Activity of MMP-2 was also present at 21 d postmortem, at levels similar to those detected at slaughter. At slaughter and at 21 d, all muscles contained latent MMP-2 and the quantity of proenzyme was greater than that present in the activated form. The levels of free OH-pro in muscles of lambs with high growth rate increased significantly (P < 0.001) over 21 d from 3.75 to 5.08% of total collagen, and this was significantly related to the level of active MMP-2 at slaughter. By contrast, the amount of free OH-pro in muscles of lambs with low growth rate was not different at 21 d (1.63% of total OH-pro) than it had been at slaughter (1.84% of total OH-pro). These results suggest that collagen degradation all the way to free amino acids occurs postmortem in muscle and that there are active MMP simultaneously present that may account for this catabolism. The growth rate of animals at slaughter influences collagen turnover in vivo, as well as postmortem collagen degradation.

Post-mortem evolution of non-protein nitrogen and its peptide composition in growing lamb muscles.

Twenty-two 4-month-old lambs were used in two experiments to assess the effects of growth rate, induced by different feeding levels, and ageing (21 days, 4°C) on non-protein nitrogen (NPN) contents and their peptide composition. Muscle (Longissimus dorsi, Semimembranosus) and sex (male, female) effects were also studied. During ageing, NPN contents increased (15-20%). This variation represented 1.6-2.8% of total nitrogen. Peptides extracted from fresh muscles were in the range of molecular weight (MW) up to 12 kDa, the majority being less than 2.4 kDa (45-48%). During ageing, peptide average MW decreased (11.5-27.6%). High growth rate increased NPN contents at slaughter (+6-14%) and during ageing. Peptide average MW and post-mortem proteolysis rate as with to NPN variations were also higher. Differences between sex were observed at the end of the ageing period. Muscle effects were observed on the peptide class from 6.8 to 3.4 kDa.

Release of major ions during rigor mortis development in kid Longissimus dorsi muscle.

Ionic strength plays an important role in post mortem muscle changes. Its increase is due to ion release during the development of rigor mortis. Twelve alpine kids were used to study the effects of chilling and meat pH on ion release. Free ions were measured in Longissimus dorsi muscle by capillary electrophoresis after water extraction. All free ion concentrations increased after death, but there were differences between ions. Temperature was not a factor affecting ion release in contrast to ultimate pH value. Three release mechanisms are believed to coexist: a passive binding to proteins, which stops as pH decreases, an active segregation which stops as ATP disappears and the production of metabolites due to anaerobic glycolysis.

Liberation of peptides during meat storage and their interaction with proteinase activity.

The content of nitrogenous material extracted in perchloric acid from kid longissimus lumborum (LL), semimembranosus (Sm) and triceps brachii (TB) muscles increased 30% during storage for three weeks at 4 °C. The extract of fresh muscle contained a range of molecular sizes up to 13 kDa, the majority less than 4 kDa. The amount of the larger polypeptides (> 4 kDa) extracted from meat decreased to 50% of its initial level in meat stored for five days and to 20% after 25 days. The amount of intermediate sized peptides (1.9 to 4 kDa) remained largely constant throughout storage of meat of normal pH, whilst in meat of high ultimate pH, they showed a transitory increase during the first two weeks storage. Smaller size peptides increased with storage time; increasing more slowly in meat of high ultimate pH. This time-dependent pH effect indicates a sequential autolysis involving neutral followed by acidic proteolytic and peptidic activity. Calpain from beef muscle degraded peptides in the extract and the extract acted as a competitor against a synthetic substrate. This implies that the in-situ autolysis and tenderisation of meat postmortem could be reduced by peptide products.

Changes affecting the Longissimus dorsi, Triceps brachii caput longum and Rectus femoris muscles of young Friesian bulls during meat ageing.

The chemical composition and post-mortem changes during 3-14 days of ageing were studied on three muscles (Longissiums dorsi, Triceps brachii caput longum, Rectus femoris) from 13 young Friesian bulls. Chemical composition varied widely between animals (p < 0.001) and muscles (p < 0.001), and did not change during post-mortem storage. Significant changes affecting the non-protein nitrogen and soluble protein nitrogen contents were similar in all three muscles but differed from animal to animal. The increase in non-protein nitrogen can be considered as an indicator of proteolysis. Proteolysis extended to 14 days post mortem. The myofibril fragmentation index increased significantly (p < 0.001) between 3 and 7 days post mortem along the same pattern, irrespective of the muscle and animal. A ceiling was reached at around 7 days post mortem, by which time maximum breakdown of the structure had probably occurred. No significant relationship was observed between chemical composition, changes in the soluble protein nitrogen, breakdown of structures and carcass characteristics.

Release of free amino-acids during ageing in bovine meat.

The amounts of free amino-acids in Longissimus dorsi (LD), Triceps brachii (TB) and Rectus femoris (RF) from 8 Friesian 20-month old bulls were determinated using gas chromatography. The amounts of free amino-acids released during storage from 3 to 14 days post mortem at 4 °C depended on the muscle. Total free hydroxyproline in LD increased from 3% at 3 days to 11% at 14 days post mortem. Free amino-acids seemed to increase more after 10 days than between 3 and 10 days post mortem. The myofibrillar fragmentation index was highly correlated with leucine, isoleucine, threonine and methionine contents in TB and RF. MFI was correlated with hydroxyproline, leucine and isoleucine in LD.

[Effects of reduced food intake on digestive flux and use of nitrogenous matter by goats]. / Influence d'une réduction des apports alimentaires sur les flux digestifs et l'utilisation des matières azotées par les Caprins.

Limited feeding effects (75% of ad libitum) were studied in 3 adult dry goats. Their diet was composed of dried beet pulps (1/3 DM), dried alfalfa (1/3 DM) and hay (1/3 DM). The CP content was 11.9% DM. Rumen fermented OM was decreased by 243 g.d-1, but rumen pH and ammonia content remained the same. Rumen bacteria synthesis efficiency was decreased (-4%), but the value (151 g crude bacteria protein.kg-1 DOM) was higher than conventional values used in PDI and NRC systems. Nitrogen rumen balance (duodenal N-N intake) was lower (-1.9 g.d-1) with restricted goats. This could be related to the increase in urinary urea excretion (+0.4 gN.d-1). There was no significant effect of the limiting feeding on total OM and N digestibilities. The disappearance rate of OM in the rumen and the small intestine tended to be higher (+4 and +8%, respectively) in the restricted animals. Nitrogen retention was lower (-5.7 g.d-1) in restricted goats. Only 59 (or 56%) of the duodenal nitrogen was protein. Their digestibility in the small gut was higher (+8 pts) than NPN digestibility. A total of 86% of duodenal RNA disappeared in the small gut but less than 60% of DAPA was digested in this part.

Tissue protein synthesis in lactating and dry goats.

Intravenous infusion of L-[3H]phenylalanine (Phe) was carried out for 8 h in dry, non-pregnant and lactating dairy goats. Nitrogen balance was positive in the dry group and negative in the lactating group. Whole-body Phe flux was 50% greater in lactating goats (P less than 0.01). Fractional synthesis rates (Ks) of tissue proteins were estimated from plasma- (Ksp) and tissue- (Ksh) specific radioactivities of Phe. In lactating goats, Ksp for mammary gland, duodenum and diaphragm was increased (P less than 0.05). Ksp also tended to increase in liver, kidney and rumen (P less than 0.08) of lactating goats, but was not different in uterus, spleen, caecum or heart. Values of Ksh were higher than Ksp; however, these measures agreed qualitatively. When absolute rates of protein synthesis were calculated, an increased contribution of mammary and visceral organs was seen in lactating goats. Ks and absolute rates of protein synthesis of hind-limb skin were less in lactating goats (P less than 0.05). A decreased proportion of skeletal muscle (P less than 0.05). Decreased rates of muscle and skin protein synthesis would appear to participate in alterations of protein metabolism, permitting lactation to occur at the expense of body reserves.

[Effect of dietary restriction on the flow of organic matter and nitrogen in the digestive tract of goats]. / Effet d'une restriction alimentaire sur le flux de matière organique et d'azote dans le tube digestif des caprins.

A restriction in intake (75% of ad libitum) did not modify significantly the disappearance of energy in the rumen, the small and the large intestine. It decreased the N disappearance in the small intestine. Microbial synthesis was between 48 and 62 g N/kg of organic matter apparently degraded in the rumen.

[Comparison of goats and sheep with respect to the ingestion, digestibility and nutritive value of various diets]. / Comparaison des caprins aux ovins quant á l'ingestion, la digestibilité et la valeur alimentaire de diverses rations.

The voluntary food intake, organic matter, crude protein and crude fiber digestibility and nitrogen balance of 23 diets have been measured simultaneously using 5 to 7 wethers and 5 to 7 castrated billy-goats in digestibility trials. The goats ate more than the wethers (58 vs 46 g DM/kg W0.75). The digestibilities obtained for goats were highly correlated with those obtained for wethers, and the mean values were similar in both species: Organic matter: digestion coefficient (CUD)goats = 1.22 CUDwethers -14.5 r = 0.93 Crude protein: digestion coefficient (CUD)goats = 1.07 CUDwethers -4.8 r = 0.94 Crude fiber: digestion coefficient (CUD)goats = 0.56 CUDwethers +29.6 r = 0.78 The mean nitrogen balance for goats (226 mg/kg W0.75) was significantly higher than that of wethers (152 mg/kg W0.75). Based on the regression equations for each species, the calculated efficiency of proteins digestible in the intestine (PDI) was 55 p. 100, the endogenous urinary nitrogen 160 mg/kg W0.75 and the nitrogen maintenance requirement 1.8-1.9 g of PDI/kg W0.75.