Niels Oksbjerg

Feeding and meat quality - a future approach.

The continuous demand for high standards of quality assurance in the meat production of today and tomorrow calls for development of new tools capable of meeting such demands. The present paper aims to re-think the traditional way of using feeding as a quality control tool in the production of meat and to introduce the potential of a nutrigenomic approach as a first step in the development of pro-active quality control systems which fulfil future demands from industry and consumers. A few chosen examples present how specific feeding strategies can manipulate (i) muscle protein turnover and thereby meat tenderness as well as the cost and sustainability of the production and (ii) muscle energy levels at slaughter and thereby the pH decline, water-holding capacity and the sensory characteristics of meats. The examples are discussed in relation to exploiting essential and basic understanding of physiological and physical processes, which can subsequently be included in a systems biology line of thought of importance for development of unique decision support systems in future meat production.

Histo- and biochemical characteristics of the Longissimus dorsi muscle in pigs and their relationships to performance and meat quality

Histo- and biochemical characteristics of the longissimus dorsi muscle at 65-70 kg body weight and their relationships to performance and meat quality at 100 kg were examined in Danish Landrace and Danish Large White female and castrated male pigs. Breed differences were observed for feed conversion rate, and a number of histochemical and biochemical traits. The organoleptic traits, flavour (13%), tenderness (15%) and overall acceptability (13%) were rated higher in Large White pigs. Significant correlations between histological and biochemical traits of the live muscle on the one side and performance, meat quality and organoleptic traits on the other side, could be demonstrated. However, these correlations were generally low (r < 0.35), and can thus only explain a small part of the variation in the measured quality traits. Consequently live muscle traits measured at 65-70 kg are poor predictors of meat quality characteristics after slaughter at 100 kg.

Long-term changes in performance and meat quality of Danish Landrace pigs: a study on a current compared with an unimproved genotype.

An experiment was conducted in 1995 in order to examine muscle growth, muscle histochemical properties, muscle metabolism and meat quality of two types of Danish Landrace pigs representing the growth potential of years 1976 and 1995, respectively. Danish Landrace pigs representing 1976 (slow-growing, SG) originated from a breeding station where the population was maintained without being selected for production traits such as daily gain, food conversion ratio and meat content. Pigs representing Danish Landrace of 1995 (fast-growing, FG) were bought from certified Danish pig breeders. The pigs were simultaneously tested for performance from 40 to 95 kg live weight. The daily gain, food conversion ratio and meat content of the carcass were improved proportionately by 0·43, 0·24 and 0·03 in FG pigs compared with SG pigs. In m. longissimus dorsi (LD), the cross-sectional area of muscle fibres was smaller in FG pigs compared with SG pigs indicating increased muscle fibre number. Data further suggest increased satellite cell proliferation in muscles of FG pigs. Serum from FG pigs stimulated the proliferation of C2C12 muscle cells to a greater extent than serum from SG pigs, although the serum level of insulin-like growth factor 1 did not differ between pig types. The effect of serum on protein turn-over of C2C12 myotubes did not depend on pig type. The glycogen concentration in the LD did not differ significantly between pig types, while the activity of citrate synthase, 3-OH-acyl-CoA-dehydrogenase, and lactate dehydrogenase were higher in the LD of SG pigs compared with FG pigs. Pork chop colour of FG pigs was proportionately 0·09 lighter (L ⋆ ) and 0·13 less red (a ⋆ ) than pork chops of SG pigs. The total muscle pigment concentration in the LD, m. biceps femoris and m. vastus intermedius was proportionately reduced by 0·17, 0·19 and 0·11, respectively, in FG pigs compared with SG pigs. In the LD, the concentration of myoglobin was proportionately reduced by 0·17 in FG pigs. The chemical composition of the LD differed between pig types such that the water content was higher and protein content lower in LD from FG pigs compared with SG pigs. The pH of the LD measured 45 min and 24 h post mortem, drip loss and thawing loss were similar for both pig types. Meat tenderness of conditioned pork chops of FG pigs was slightly reduced in accordance with a decreased intensity of the 31 kDa peptide band and increased cooking loss. The present study suggests that increased muscle fibre number and rate of muscle DNA deposition (satellite cell proliferation) have contributed to the increased muscle growth as a result of selection for performance in pigs under Danish conditions. However, the increase in growth performance was accompanied by deterioration in muscle colour and slightly reduced tenderness.

Metabolic conditions in Porcine longissimus muscle immediately pre-slaughter and its influence on peri- and post mortem energy metabolism.

To clarify the physiological prerequisites for the course of energy metabolism post mortem, 80 pigs consisting of four females from each of 20 litters of crossbreeds (Duroc as sireline and Danish Landrace×Danish Large White as dam line) were within litter allocated to four different treatments (A, B, C and D) to provide a large variation in the concentration of the key metabolites glycogen, ATP and creatine phosphate at the time of stunning. (A) no stress before stunning, (B) physical stress consisting of treadmill running (3.8 km/h for 10 min) immediately before stunning, (C) intermediate reduction of glycogen at stunning achieved by application of adrenaline (0.2 mg/kg live weight 15-18 h before stunning), and (D) maximal reduction of glycogen achieved by application of adrenaline (0.3 mg/kg live weight 15-18 h before stunning) and treadmill running (3.8 km/h for 5 min). Compared with resting values (measured in samples taken in the pen the day before slaughter by needle biopsy), longissimus muscle glycogen (16, 13, 57 and 66% for A, B, C and D, respectively), creatine phosphate (17, 22, 12 and 9% for A, B, C and D, respectively) and ATP levels (10, 15, 38 and 31% for A, B, C and D, respectively) measured immediately before stunning were all reduced by the treatments. Stunning caused a rather uniform reduction in creatine phosphate level in all the models. Glycogen concentrations were also further reduced in treatments A, C and D, but not in B, and although ATP levels increased in all the models during stunning, this was only significant for the B model. Consequently, the effect of CO(2) stunning on glycogen and ATP levels depends on pre-slaughter handling. It was also shown that an inverse relationship between ultimate pH and glycogen concentration at the time of stunning existed only when glycogen levels at stunning were below 53 mmol/kg (r=0.88, P<0.001). The validity of this threshold value is discussed. Furthermore, the possibility to standardise the physiological prerequisites of the post mortem pH decreases represents a potent tool to investigate metabolic causes of variations in meat quality characteristics.

Compensatory growth response in pigs, muscle protein turn-over and meat texture: effects of restriction/realimentation period

The present experiment was designed to evaluate the effect of different time spans of ad libitum feeding of pigs prior to slaughter after a period of restricted feeding on performance and texture characteristics of the meat. Te n litters of five pigs (Duroc ✕ Landrace ✕ Large White crosses) were allocated to five feeding treatments (AA, R28A42, R43A27, R52A18 and R60A10) at the age of 70 days. AA-pigs were given ad libitum a concentrate diet from day 70 to slaughter at day 140 (approx. 100 kg live weight). R28A42, R43A27, R52A18 and R60A10 pigs were given food at a restricted level (0·6 of ad libitum) for 28, 43, 52 and 60 days, respectively, followed by ad libitum feeding for 42, 27, 18 and 10 days, respectively, until slaughter at day 140. All pigs that had been given food at a restricted level for a period (R28A42, R43A27, R52A18 and R60A10) showed a compensatory growth response in the subsequent ad libitum period. However, only pigs on ad libitum for a minimum of 27 days prior to slaughter (R28A42 and R43A27) had carcass weights and muscle mass similar to that of the control pigs (AA) at slaughter. The restricted feeding increased meat proportion, whereas the feeding strategies had no effect on technological meat quality traits (pH24, drip loss and CIE-colour traits: L*, a* and b*). During compensatory growth, protein turn-over was increased and positively related to the length of the ad libitum period as indicated by the concentration of elongation factor-2 (eEF-2) (P

Control of post mortem pH decrease in pig muscles: experimental design and testing of animal models

From a series of experiments aimed at manipulating and relating the resting levels of glycogen and creatine phosphate (CP) in the live muscle four models were selected to induce different rates and extents of pH decrease post mortem in pig muscle. Model A served as the control, animals being slaughtered under minimal stress, in model B animals were subjected to 10 min treadmill exercise at 3.8 km/h immediately prior to stunning, in model C, animals were given 0.2 mg adrenaline/kg live weight 16 h prior to slaughter, and in model D they were given 0.3 mg adrenaline/kg live weight 16 h before slaughter and subjected to 5 min of treadmill exercise immediately before stunning. After slaughter, the decline in pH and temperature post mortem was recorded in M. longissimus dorsi (LD), M. biceps femoris (BF), M. semimembranosus (SM) and M. psoas major (PM) from 1 min to 24 h after bleeding. Significant differences in ultimate pH and the time course of pH decrease were observed, both as an effect of model as well as type of muscle. No differences in ultimate pH between model A and model B were observed in any of the muscles. Ultimate pH in the C and the D models were significantly higher than in A and B. In the B model lower pH values were observed from 1 min to 6 h post bleeding compared to the other three models. No differences in rate of pH decrease were observed between the A and the B models in any of the muscles. Within the A model no differences in ultimate pH between muscles were seen, indicating that the frequently observed differences in ultimate pH are caused by environmental factors rather than by differences in physiological and morphological characteristics. The exercise bouts caused elevated temperatures during the first hour after bleeding (model B and D). The BF muscle in all the models displayed the fastest rate of pH decrease and SM the slowest; a slower rate of temperature decline occurred in the BF than in the SM.

Compensatory Growth and its Effect on Muscularity and Technological Meat Quality in Growing Pigs

This study investigated the effect of various feeding levels from weaning (day 28) to day 170 of age on growth, muscularity and technological meat quality in female pigs. From day 28 to day 90 of age (growing period) and from day 90 to day 170 of age (finishing period), the pigs were fed either ad libitum (A) or restrictively (R) in a 2 2 2 factorial design with treatments named AA, AR, RA and RR. In the growing period, the growth rate of A pigs was 35% higher than that of R pigs. In the finishing period, the growth rate was dependent on the feed intake in the growing period, i.e. pigs fed restrictively in the growing period had 6-8% higher growth rate in the finishing period (RA and RR) than pigs fed ad libitum in the growing period (AA and AR). Furthermore, despite RA pigs being 11 kg lighter at day 90 of age they produced as much muscle tissue at slaughter as did AA pigs, but less subcutaneous fat, which resulted in a 5% higher meat content of the carcass. The increased muscle growth of RA pigs in the finishing period (compensatory growth) was probably accomplished by increased satellite cell proliferation (muscle DNA accumulation) and increased capacity for protein synthesis, as indicated by a higher RNA concentration. Feeding level did not affect the lightness of meat, the ultimate pH or the drip loss. However, a change in feeding level at day 90 of age (RA and AR) led to a reduction in meat redness. The present data suggest that feed restriction in the growing period results in compensatory growth of muscle tissue in the finishing period if ad libitum feeding was applied during this period, accomplished by increased satellite cell proliferation and increased capacity for protein synthesis, without significantly affecting the technological meat quality.

Metabolomics Reveals Relationship between Plasma Inositols and Birth Weight: Possible Markers for Fetal Programming of Type 2 Diabetes

Epidemiological studies in man and with experimental animal models have shown that intrauterine growth restriction (IUGR) resulting in low birth weight is associated with higher risk of programming welfare diseases in later life. In the pig, severe IUGR occurs naturally and contribute substantially to a large intralitter variation in birth weight and may therefore be a good model for man. In the present paper the natural form of IUGR in pigs was studied close to term by nuclear magnetic resonance (NMR-)based metabolomics. The NMR-based investigations revealed different metabolic profiles of plasma samples from low-birth weight (LW) and high-birth weight (HW) piglets, respectively, and differences were assigned to levels of glucose and myo-inositol. Further studies by GC-MS revealed that LW piglets had a significant higher concentration of myoinositol and D-chiro-inositol in plasma compared to larger littermates. Myo-inositol and D-chiro-inositol have been coupled with glucose intolerance and insulin resistance in adults, and the present paper therefore suggests that IUGR is related to impaired glucose metabolism during fetal development, which may cause type 2 diabetes in adulthood.

Changes in proteolytic enzyme mRNAs relevant for meat quality during myogenesis of primary porcine satellite cells.

The objective was to study the regulation of proteolytic enzyme mRNAs in porcine satellite cells during proliferation and differentiation. Beyond 80% confluence, cells were grown in absence or presence of 1μM insulin. The temporal changes in transcription of micro molar-, milli molar- and muscle specific calpains (p94), calpastatin and caspase 3 in response to insulin was evaluated and myogenin transcription and creatine kinase activity was determined to indicate differentiation. The housekeeping genes (GAPDH and β-actin) were slightly affected by developmental stage and transiently by the insulin treatment but this did not affect the conclusions. The mRNA abundance of micro molar calpain, p94 and calpastatin increased from proliferation to differentiation. Milli molar calpain- and caspase 3-transcriptions were up-regulated in two steps, suggesting these two enzymes are involved in two distinct processes. Insulin stimulated differentiation as indicated by elevated creatine kinase activity but did not affect myogenin transcription. Insulin down-regulated milli molar calpain and calpastatin transcription and tended to down-regulate caspase 3 transcription but did not affect p94 or micro molar calpain. In conclusion, proteolytic enzymes relevant for post-mortem tenderisation are regulated at the gene level during myogenesis, indicating they are involved in muscle cell and muscle fibre development. Thus, a porcine satellite cell culture may be a model system to study regulation and relative contribution to proteolysis by the calpains.

Caffeic acid, naringenin and quercetin enhance glucose‐stimulated insulin secretion and glucose sensitivity in INS‐1E cells

Caffeic acid, naringenin and quercetin are naturally occurring phenolic compounds (PCs) present in many plants as secondary metabolites. The aim of this study was to investigate their effect on glucose‐stimulated insulin secretion (GSIS) in INS‐1E cells and to explore their effect on expression of genes involved in β‐cell survival and function under normoglycaemic and glucotoxic conditions.