Nutritional and hormonal control of muscle and peripheral tissue metabolism in farm species

Comparative analysis of signalling pathways in tissue protein metabolism in efficient and non-efficient beef cattle: acute response to an identical single meal size

Protein turnover has been associated to residual feed intake (RFI) in beef cattle. However, this relationship may be confounded by feeding level and affected by the composition of the diet being fed. Our aim was to assess postmortem the protein metabolism signalling pathways in skeletal muscle and liver of 32 Charolais young bulls with extreme RFI phenotypes. Bulls were fed two contrasting diets during the whole fattening period but were subjected to a similar and single nutritional stimulus, induced by their respective concentrate, just prior to slaughter. The key targets were protein degradation (autophagy and ubiquitin) and synthesis signalling pathways through western-blot analysis, as well as hepatic transaminase activity. To ensure a precise assessment of all animals at the same postprandial time, they were provided with a test meal (2.5 kg of either a high-starch and high-protein concentrate or high-fibre and low-protein concentrate) 3 hours prior to slaughter, irrespective of their RFI grouping. Blood and tissues were sampled at the slaughterhouse (3 h and 3 h30 postprandially, respectively). In response to an identical single meal size, efficient RFI animals showed higher (P < 0.05) postprandial plasma β-hydroxybutyrate concentrations and insulinemia (only with the high-starch concentrate) than non-efficient animals. Moreover, efficient RFI bulls had lower muscle (P = 0.04) and liver (P = 0.08) ubiquitin protein abundance (degradation pathway) and tended to have lower alanine transaminase activity in the liver (P = 0.06) compared to non-efficient bulls, regardless of diet. A positive correlation between protein degradation potential and amino acid catabolism was identified in this study (r = 0.52, P = 0.004), which was interpreted as being biologically linked to the RFI phenotype. Efficient RFI bulls also had a faster potential for protein synthesis in the muscle, as indicated by their greater ratio of phosphorylated to total form of ribosomal protein S6 kinase (P = 0.05), regardless of diet. Results on protein synthesis pathway in muscle and plasma metabolite concentrations suggested that efficient RFI cattle may have a faster nutrient absorption and insulin responsiveness after feeding than inefficient cattle. We did not find significant differences in hepatic protein synthesis pathways between the two RFI groups (P > 0.05). Our findings suggest that, in response to an identical single meal size, efficient RFI animals exhibited lower activation of tissue protein degradation pathways and faster muscle protein synthesis activation compared to their inefficient counterparts. This pattern was observed regardless of the composition of the tested meals.

Review of Feeding Systems Affecting Production, Carcass Attributes, and Meat Quality of Ovine and Caprine Species

Growth rate, carcass attributes, and meat quality traits of small ruminants (i.e., sheep and goats) depend on various factors, among which the feeding system is one of the most important factors. However, how feeding systems affect these parameters differ between sheep and goats. Therefore, this review aimed to evaluate the differences in how different feeding systems affect the growth performance, carcass characteristics, and meat quality of sheep and goats. It also explored the effects of a new finishing strategy-time-limited grazing with supplements on these traits. Compared with stalled feeding, finishing lambs/kids on pasture-only feed reduced the average daily gain (ADG) and carcass yield, while supplemented-grazing lambs/kids had near-equivalent or higher ADG and carcass attributes. Pasture-grazing increased the meat flavor intensity and healthy fatty acid content (HFAC) of lamb/kid meat. Supplemental grazing lambs had comparable or superior meat sensory attributes and increased meat protein and HFAC compared to stall-fed ones. In contrast, supplemental grazing only improved the meat color of kids but had little effect on other meat qualities. Moreover, time-limited grazing with supplemental concentrates increased the carcass yield and meat quality in lamb meat. Overall, the effects of different feeding systems on growth performance and carcass traits were comparable between sheep and goats but differed in terms of the meat quality.

Stall feeding of sheep and goats: An alternative system to traditional grazing on community lands

Sheep and goats in the country are mostly raised on grazing resources. But these resources are gradually shrinking over the periods both in term of areas under them and also in yield and quality. On the contrary, populations of sheep and goat are increasing rapidly to meet the demand of meat. This is resulting in overstocking and overcrowding on available grazing lands and sharp deterioration of grazing resources. The intensive system (stall feeding) as an alternative to traditional grazing and semi-intensive system, may be useful to maintain pace with growing meat demand in the changing scenario of grazing resources in the country. Studies have shown that lambs and kids on stall feeding with adequate nutrition and management attain faster growth, attain slaughter weights at an early age and produce heavier carcass weights, more dressing yield and desirable lean, fat and bone contents. Although initially intensive system seems costly due to more feed cost and more capital investment, but this is justified by higher economic returns to farmers. Therefore, it can be concluded that intensive feeding system for sheep and goats is better than extensive system and at par or better than semi-intensive system for lamb and kid fattening purpose from 3–6 months of age. This review article also discusses the possibility of economic viability of sheep and goats rearing under stall feeding.

Energy and nitrogen balance of dairy cattle as affected by provision of different essential amino acid profiles at the same metabolizable protein supply

Amino acid composition of metabolizable protein (MP) is important in dairy cattle diets, but effects of AA imbalances on energy and N utilization are unclear. This study determined the effect of different AA profiles within a constant supplemental MP level on whole-body energy and N partitioning in dairy cattle. Five rumen-fistulated Holstein-Friesian dairy cows (2.8 ± 0.4 lactations; 81 ± 11 d in milk; mean ± standard deviation) were randomly assigned to a 5 × 5 Latin square design in which each experimental period consisted of 5 d of continuous abomasal infusion followed by 2 d of rest. A total mixed ration consisting of 58% corn silage, 16% alfalfa hay, and 26% concentrate (dry matter basis) was formulated to meet 100 and 83% of net energy and MP requirements, respectively, and was fed at 90% of ad libitum intake by individual cow. Abomasal infusion treatments were saline (SAL) or 562 g/d of essential AA delivered in 4 profiles where individual AA content corresponded to their relative content in casein. The profiles were (1) a complete essential amino acid mixture (EAAC), (2) Ile, Leu, and Val (ILV), (3) His, Ile, Leu, Met, Phe, Trp, Val (GR1+ILV), and (4) Arg, His, Lys, Met, Phe, Thr, Trp (GR1+ALT). The experiment was conducted in climate respiration chambers to determine energy and N balance in conjunction with milk production and composition, digestibility, and plasma constituents. Compared with SAL, infusion of EAAC increased milk, protein, and lactose yield, increased energy retained as body protein, and did not affect milk N efficiency. Total N intake and urine N output was higher with all AA infusions relative to SAL. Compared with EAAC, infusions of GR1+ILV and GR1+ALT produced the same milk yield and the same yield and content of milk fat, protein, and lactose, and had similar energy and N retention. Milk N efficiency was not different between EAAC and GR1+ILV, but was lower with GR1+ALT compared with EAAC, and tended to be lower with GR1+ALT compared with GR1+ILV. Infusion of ILV tended to decrease dry matter intake compared with the other AA infusions. Milk production and composition was not different between ILV and SAL. Compared with EAAC, infusion of ILV decreased or tended to decrease milk, protein, and lactose yields and milk protein content, and increased milk fat and lactose content. Milk N efficiency decreased with ILV compared with SAL, EAAC, and GR1+ILV. Milk urea concentration was not affected by essential amino acid (EAA) infusions. Plasma urea concentration did not differ between EAAC and SAL, tended to increase with ILV and GR1+ILV over SAL, and increased with GR1+ALT compared with EAAC and SAL. In conclusion, removing Arg, Lys, and Thr or removing Ile, Leu, and Val from a complete EAA profile when the total amount of EAA infused remained constant did not impair milk production, but milk N efficiency decreased when Ile, Leu, and Val were absent. Infusion of only Ile, Leu, and Val decreased milk protein yield and content and reduced milk N efficiency compared with a complete EAA profile.

Mammary gland metabolite utilization in response to exogenous glucose or long-chain fatty acids at low and high metabolizable protein levels

We investigated mammary gland metabolism in lactating dairy cattle in response to energy from glucogenic (glucose; GG) or lipogenic (palm olein; LG) substrates at low (LMP) and high (HMP) metabolizable protein levels. According to a 6 × 6 Latin square design, 6 rumen-fistulated second-lactation Holstein-Friesian dairy cows (97 ± 13 d in milk) were abomasally infused with saline (LMP-C); isoenergetic infusions (digestible energy basis) of 1,319 g/d glucose (LMP-GG), 676 g/d palm olein (LMP-LG), or 844 g/d essential AA (EAA; HMP-C); or isoenergetic infusions of 1,319 g/d glucose + 844 g/d EAA (HMP-GG) or 676 g/d palm olein + 844 g/d EAA (HMP-LG). Each experimental period consisted of 5 d of continuous infusion followed by 2 d of rest. A total mixed ration (42% corn silage, 31% grass silage, and 27% concentrate on a dry matter basis) formulated to meet 100 and 83% of net energy and metabolizable protein requirements, respectively, was fed at 90% of ad libitum intake by individual cow. Arterial and venous blood samples were collected on d 5 of each period. Infusing GG or LG at the HMP level did not affect milk yield or composition differently than at the LMP level. Neither GG nor LG infusion stimulated milk protein or lactose yield, but fat yield tended to decrease with GG and tended to increase with LG. Infusion of GG increased arterial plasma concentrations of glucose and insulin and decreased concentrations of β-hydroxybutyrate (BHB), nonesterified fatty acids, long-chain fatty acids (LCFA), total AA, EAA, and group 2 AA. Infusion of LG increased arterial triacylglycerides (TAG) and LCFA but did not affect EAA concentrations. Compared with the LMP level, the HMP level increased arterial concentrations of BHB, urea, and all EAA groups and decreased the concentration of total non-EAA. Mammary plasma flow increased with GG and was not affected by LG or protein level. Uptake and clearance of total EAA and group 2 AA were affected or tended to be affected by GG × AA interactions, with their uptakes being lower and their clearances higher with GG, but only at the LMP level. Infusion of LG did not affect uptake or clearance of any AA group. The HMP level increased uptake and decreased clearance of all EAA groups and decreased non-EAA uptake. Infusion of GG tended to increase mammary glucose uptake, and tended to decrease BHB uptake only at the LMP level. Infusion of LG increased mammary uptake of TAG and LCFA and increased or tended to increase clearance of TAG and LCFA. We suspect GG increased mammary plasma flow to maintain intramammary energy and AA balance and stimulated lipogenesis in adipose, accounting for depressed arterial BHB and group 2 AA concentrations. Mammary glucose uptake did not cover estimated requirements for lactose and fat synthesis at the HMP level, except during HMP-GG infusion. Results of this study illustrate flexibility in mammary metabolite utilization when absorptive supply of glucogenic, lipogenic, and aminogenic substrate is increased.

Selection for residual feed intake affects appetite and body composition rather than energetic efficiency

Residual feed intake (RFI) is the difference between an animal’s actual feed intake and that which would be expected based on production. This experiment was to test the hypothesis that part of the variation in RFI may be due to differences in energetic efficiency through changes in heat production, these being in part due to differences in protein metabolism. Following three generations of divergent selection for RFI, eight High and eight Low-RFI heifers were fed at both 105% and 180% of predicted maintenance feed requirements. Between-RFI line and feeding-level differences were assessed for energy intake, protein metabolism, heat production, body composition, energy and nitrogen balance and digestibility. The RFI lines did not differ in protein metabolism or heat production. The High-RFI heifers deposited 51% and 56% more subcutaneous fat at the P8 rump and 12/13th rib sites, respectively, with no difference in eye muscle area gain or average daily weight gain. The greater fat deposition of High-RFI heifers was due to a larger ad libitum feed consumption compared with the Low-RFI heifers. Energy and nitrogen balance did not differ between the RFI lines. The energy transactions indicated no difference in the efficiency of energy use on 105% maintenance, although when fed 180% of maintenance the differences in feed intake suggest variation in appetite as the mechanism contributing to RFI. All of the extra energy consumed by High-RFI heifers above maintenance and deposition of protein was associated with additional energy retained as fat. This study suggests that selection for RFI may not lead to improved efficiency of energy use.

The Effect of Extensive Feeding Systems on Growth Rate, Carcass Traits, and Meat Quality of Finishing Lambs

This review aims to summarize the relevant published information about the effects of extensive feeding systems on the carcass and meat quality characteristics of lambs. Lambs finished in a feedlot or with supplementation under extensive systems exhibit faster growth rates, achieve target weights quicker, and produce heavier carcass weights when compared to grazing lambs. However, the literature also shows that finishing lambs on high-quality pasture can produce satisfactory growth rates without compromising carcass and meat quality traits. Lately, the consumer demand for products perceived as "healthy" and that are produced where animal welfare is optimal under systems which do not impact negatively on the environment, has heightened the interest in lamb production under extensive systems. Lambs raised on pasture can meet many of these specifications. Also, lambs fed higher quality green pasture can produce meat with greater amounts of health-claimable omega-3 fatty acids such as eicosapentaenoic acid plus docosahexaenoic acid than feeding systems based on feedlot pellets, grain, or dry pasture/straw. It is apparent that in some previous published research, the number of animals allocated for each treatment, and the lack of replicates, makes it difficult to formulate a correct understanding of the effect of forages on lamb carcass and meat quality. Future research should concentrate on the effect of legume, improved pasture, and specialized forage finishing systems on growth rate, carcass traits, and nutritional value of meat using well-designed experiments with an adequate number of lambs and appropriate paddock replicates per treatment.

Effects of incremental changes in forage: concentrate ratio on plasma hormone and metabolite concentrations and products of rumen fermentation in fattening beef steers

As part of an investigation of factors responsible for a previously reported lower efficiency of carcass lean gain in steers offered grass silage diets, 16 Simmental × Friesian steers (515 (s.e. 6·4) kg) were offered perennial ryegrass silage ad libitum (C0) or silage plus rolled barley at 200 (C20), 400 (C40) or 600 (C60) g/kg total diet dry matter (DM). Barley-supplemented diets were intake-restricted to provide equal DM and metabolizable energy (ME) intakes to those offered C0. Eight steers were selected at random to determine the ME contents of the diets by open-circuit respiration calorimetry. The other eight steers were offered the same diets and were blood-sampled at 20- to 60-min intervals, for 10 h, to monitor changes in the concentrations of a number of nutritionally related plasma metabolites and hormones. Estimated ME intakes in these steers were 85·7, 83·1, 84·4 and 86·2 (s.e. 0·91) MJ/day from diets C0, C20, C40 and C60 respectively. Rumen-fistulated Hereford × Friesian steers provided 24-h rumen data for the same diets offered at equal amounts of ME per kg metabolic live weight.

Mean 24-h plasma concentrations of insulin and insulin-like growth factor 1 (IGF-1) were linearly and positively related (P < 0·01 and P < 0·001 respectively) and glucagon quadratically related (P < 0·05) to the proportion of barley in the diet. Plasma insulin increased after feeding on all diets but concentrations on diets C40 and C60 were significantly higher than those on C0 and C20 at all post-feeding sampling times up to 9 h after feeding. Plasma IGF-1 concentrations increased above pre-feeding levels following feeding of the higher barley diets (C40 and C60; P = 0·053) but remained unchanged in steers offered C0 and C20. Mean plasma concentrations of glucose were unaffected by diet but those of β-hydroxybutyrate (BOHB) and urea were positively and negatively related respectively (both P < 0·001) to the proportion of barley in the diet. Plasma BOHB and urea concentrations also changed with time after feeding (P < 0·001). Amongst the rumen parameters measured (pH; ammonia and volatile fatty acid concentrations and proportions) only the mean 24-h concentrations and proportions of butyrate were positively related to the proportion of barley in the diet (P = 0·051 and P < 0·05 respectively). All rumen parameters were affected by time after feeding (acetate, P < 0·01; others, P < 0·001) but there was no interaction between treatment and time for any parameter.

Leucine is a major regulator of muscle protein synthesis in neonates

Approximately 10% of infants born in the United States are of low birth weight. Growth failure during the neonatal period is a common occurrence in low birth weight infants due to their inability to tolerate full feeds, concerns about advancing protein supply, and high nutrient requirements for growth. An improved understanding of the nutritional regulation of growth during this critical period of postnatal growth is vital for the development of strategies to improve lean gain. Past studies with animal models have demonstrated that muscle protein synthesis is increased substantially following a meal and that this increase is due to the postprandial rise in amino acids as well as insulin. Both amino acids and insulin act independently to stimulate protein synthesis in a mammalian target of rapamycin-dependent manner. Further studies have elucidated that leucine, in particular, and its metabolites, α-ketoisocaproic acid and β-hydroxy-β-methylbutyrate, have unique anabolic properties. Supplementation with leucine, provided either parenterally or enterally, has been shown to enhance muscle protein synthesis in neonatal pigs, making it an ideal candidate for stimulating growth of low birth weight infants.

Reduced supplementation frequency increased insulin-like growth factor 1 in beef steers fed medium quality hay and supplemented with a soybean hull and corn gluten feed blend

Reducing supplementation frequency in calf growing programs can reduce labor and equipment operation costs. However, little is understood about the metabolic response of ruminants to large fluctuations in nutrient intake. Eighteen Angus or Angus × Simmental cross steers (287 ± 20 kg and 310 ± 3.6 d of age) were individually fed 1 of 3 dietary treatments using Calan gates. Dietary treatments consisted of ad libitum hay and no supplement (NS), ad libitum hay and 1% BW (as-fed basis) of supplement daily (DS), or ad libitum hay and 2% BW (as-fed basis) of supplement every other day (SA). The supplement was 90% DM and contained (as-fed basis) 47% corn gluten feed, 47% soybean hulls, 2% feed grade limestone, and 4% molasses. Hay intake and ADG was measured over a 52-d period. Steers were then moved to individual tie stalls. Steers were fed at 0800 h and blood samples were collected every hour from 0600 to 1400 h and at 1800, 2200, and 0200 h over a 2-d period. Gains were increased (P < 0.01) by supplementation but did not differ (P = 0.68) due to supplementation frequency. Average daily gain was 0.45, 0.90, and 0.87 kg ·hd(-1)·d(-1) (SEM ± 0.05) for steers NS, DS, and SA, respectively. Across the 2-d supplementation cycle area under the concentration time curve (AUC) for plasma glucose was increased (P < 0.01) by supplementation but did not differ (P = 0.41) due to supplementation frequency. The AUC for plasma insulin was increased by supplementation (P < 0.01) but did not differ (P = 0.67) due to supplementation frequency. Plasma IGF-1 was increased (P = 0.01) by supplementation and was greater (P = 0.04) for steers supplemented SA than DS. Gains of steers supplemented with a soybean hull and corn gluten feed blend on alternate days did not differ from those supplemented daily suggesting the steers were able to efficiently utilize large boluses of nutrients fed every other day. The effect of less frequent supplementation on IGF-1 deserves further examination as this hormone has been shown to increase protein synthesis.

Asynchronous supply of indispensable amino acids reduces protein deposition in milk-fed calves

A balanced supply of indispensable amino acids (AA) is required for efficient protein synthesis. Different absorption kinetics (e.g., free vs. protein-bound AA) may, however, create asynchrony in postabsorptive availability of individual AA, thereby reducing the efficiency of protein deposition. We studied the effects of AA asynchrony on protein metabolism in growing, milk-fed calves. In 2 experiments, each with a change-over design including 8 calves, a milk replacer deficient in Lys and Thr was used. In Expt. 1, L-Lys and L-Thr were parenterally supplemented, either in synchrony (SYN), asynchrony (ASYN), or partial asynchrony (PART) with dietary AA. In Expt. 2, l-Lys and l-Thr were orally supplemented, either in SYN or ASYN with dietary AA. In Expt. 1, digested protein was used less efficiently for growth for ASYN (31.0%) than for SYN (37.7%), with PART being intermediate (36.0%). Indicator AA oxidation tended (P = 0.06) to be higher for ASYN. In Expt. 2, the efficiency of protein utilization was lower for ASYN (34.9%) than for SYN (46.6%). Calves spared AA from oxidation when the limiting AA were provided in excess after a short period (<24 h) of deprivation. Restoring AA balance by parenteral supplementation resulted in a 19% lower efficiency of digestible protein utilization than by oral supplementation, likely caused by splanchnic oxidation of imbalanced AA in excess to Thr. In conclusion, asynchronous availability of individual indispensable AA reduces the efficiency by which digested protein is retained in milk-fed calves. Furthermore, an AA imbalance in the splanchnic tissues may result in disproportionate AA oxidation.

Responses to nutrients in farm animals: implications for production and quality

It is well known that any quantitative (energy and protein levels) and qualitative (nature of the diet, nutrient dynamic) changes in the feeding of animals affect metabolism. Energy expenditure and feed efficiency at the whole-body level, nutrient partitioning between and within tissues and organs and, ultimately, tissue and organ characteristics are the major regulated traits with consequences on the quality of the meat and milk produced. Recent progress in biology has brought to light important biological mechanisms which explain these observations: for instance, regulation by the nutrients of gene expression or of key metabolic enzyme activity, interaction and sometimes cross-regulation or competition between nutrients to provide free energy (ATP) to living cells, indirect action of nutrients through a complex hormonal action, and, particularly in herbivores, interactions between trans-fatty acids produced in the rumen and tissue metabolism. One of the main targets of this nutritional regulation is a modification of tissue insulin sensitivity and hence of insulin action. In addition, the nutritional control of mitochondrial activity (and hence of nutrient catabolism) is another major mechanism by which nutrients may affect body composition and tissue characteristics. These regulations are of great importance in the most metabolically active tissues (the digestive tract and the liver) and may have undesirable (i.e. diabetes and obesity in humans) or desirable consequences (such as the production of fatty liver by ducks and geese, and the production of fatty and hence tasty meat or milk with an adapted fatty acid profile).

Voluntary feed intake and diet selection of Merino sheep divergently selected for genetic difference in resistance to Haemonchus contortus

This research was designed to determine if divergent selection for resistance to Haemonchus contortus had produced correlated changes in voluntary feed intake and diet selection. Voluntary feed intake, diet selection and production were determined in 54 Merino weaner rams from the CSIRO Haemonchus selection flock, increased resistance to Haemonchus (IRH), decreased resistance to Haemonchus (DRH) and random bred control (C) selection lines. Weaner rams were fed ad libitum either a high (9.2 MJ ME/kg DM, 90 g MP/kg DM) or moderate (6.3 MJ ME/kg DM, 30 g MP/kg DM) quality diet and given the choice between the two diets, when uninfected (NIL) or infected with H. contortus (INF). Symmetrical response to divergent selection for worm egg count (WEC) was not matched by a symmetrical change in feed intake and there was no difference in diet selection between selection lines. Feed intake, growth and wool production of DRH animals remained the same as that of IRH, yet DRH animals had five times greater WEC than IRH. This study begins to explain the mechanisms that allow resistant animals to effectively prevent establishment and/or development of H. contortus, by maintaining a greater immune response to infection through higher circulating eosinophils, plasma globulin and IgG(1) antibody titres. Susceptible animals have displayed resilience by improving feed conversion efficiency and increasing protein synthesis.

Fat depth, muscle depth, fat score and wool growth in Merino dams selected for high or low clean fleece weight and bodyweight

Concerns exist that selection for increased clean fleece weight (CFW) is expected to reduce body fatness. Such an effect is likely to impact on reproduction; however, all previous studies have examined non-reproductive yearlings or hoggets. The present study, using adult reproductive dams examined the impact of phenotype [based on high or low phenotypic CFW and bodyweight (BWT) performance], stocking rate (high or low) and litter size on body composition and wool traits. High CFW dams were heavier (P < 0.01) with lower fat depth (P < 0.01) and muscle depth (P < 0.05). The high CFW twin-weaning dams had a lower fat score from lamb marking to pre-joining (P < 0.05), but tended to replete fat reserves faster (P < 0.1) between weaning and pre-joining. At these times of repletion these animals grew longer wool staples (P < 0.05). High BWT ewes had reduced staple length (P < 0.01), and when adjusted for maternal liveweight also reduced fat depth (P < 0.001) and muscle depth (P < 0.05). We conclude that the CFW phenotype impacts on fat reserves but that management of dams in groups according to their CFW performance is not warranted.

Early energy and protein reduction: effects on growth, blood profiles and expression of genes related to protein and fat metabolism in broilers

1. A total of 320-d-old Ross broilers were used in a 6-week study to investigate the effects of feeding lower energy and protein diets from d 8 to 14 on growth performance, blood profiles, and gene expression of leptin and myostatin. 2. Broilers were randomly allotted to 4 treatments, each treatment applied to 4 pens with 20 birds in each. During first week, all the birds were fed on a common starter diet (13.4 MJ ME/kg, 230 g/kg CP and 11.0 g/kg lysine). The birds were then subjected to their respective treatment diets from d 8 to 14. Treatment diets comprised two ME levels, 13.4 and 12.0 MJ/kg, each with two levels of CP, 230 and 184 g/kg. This was followed by feeding common starter and finisher diets for the last 4 weeks. 3. Dietary protein reduction resulted in poor performance and feed efficiency while energy reduction resulted in poor feed efficiency between d 8 and 14. From d 14 to 42 birds previously fed diets lower in energy and protein showed similar body weight gain and feed intake to well-fed birds. Moreover from d 8 to 14, birds fed on energy and protein-reduced diets had lower nutrient metabolisability coefficients. 4. The blood urea nitrogen (BUN) and relative weights of heart and breast muscle were lower in birds fed protein-reduced diets while energy reduction resulted in lower plasma glucose, abdominal fat and intestinal weight at d 14. At d 42, birds fed on the protein-reduced diets had lower BUN, breast muscle weight and small intestine length, while feeding on the energy-reduced diets resulted in lower abdominal fat. 5. Upregulated myostatin mRNA expression in breast muscle and downregulation of leptin mRNA expression in abdominal fat were observed in birds fed on protein and energy-reduced diets, respectively. 6. In conclusion, early nutrient reduction affected growth performance and produced lesser abdominal fat in broilers. Moreover, early energy and/or protein reduction could change muscle and fat metabolism by regulating the expressions of myostatin and leptin.

Mechanisms through which sulfur amino acids control protein metabolism and oxidative status

Amino acids regulate protein synthesis and breakdown (i.e., protein turnover) and consequently protein deposition, which corresponds to the balance between the two processes. Elucidating the mechanisms involved in such regulation is important from fundamental and applied points of view since it can provide a basis to optimize amino acid requirements and to control protein mass, body composition and so forth. Amino acids, which have long been considered simply as precursors of protein synthesis, are now recognized to exert other significant influences; that is, they are precursors of essential molecules, act as mediators or signal molecules and affect numerous functions. For example, amino acids act as mediators of metabolic pathways in the same manner as certain hormones. Thus, they modulate the activity of intracellular protein kinases involved in the regulation of metabolic pathways such as mRNA translation. We provide here an overview of the roles of amino acids as regulators of protein metabolism, by focusing particularly on sulfur amino acids. The potential importance of methionine as a "nutrient signal" is discussed in the light of recent findings. Emphasis is also placed on mechanisms controlling oxidative status since sulfur amino acids are involved in the synthesis of intracellular antioxidants (glutathione, taurine etc.) and in the methionine sulfoxide reductase antioxidant system.

Lysine metabolism across the hindquarters of sheep; effect of intake on transfers from plasma and red blood cells

Both plasma and red blood cells contain amino acids (AA), but the relative amount of AA transferred from each vascular compartment to the tissues remains unclear. For splanchnic tissues, the relative transfers between the plasma, the red blood cells and the tissues may vary with nutritional state, but whether the same situation pertains for other tissues is not known. The current study focused on the transfer of lysine from plasma and red blood cells across the hindquarters of sheep offered four levels of intakes (0.5, 1.0, 1.5 and 2.5×maintenance energy). This design, coupled with use of [U-13C]lysine as tracer, also allowed the effect of intake on protein kinetics to be examined. At all intakes, the concentration of lysine in the sheep’ red blood cells exceeded that in plasma by 50 % (P<0.001), while the distribution of labelled lysine between the plasma and the red blood cells was 0.71:0.29. Net lysine uptake by the hindquarters increased in a linear manner (P<0.001) with intake, with more than 90 % extracted from the plasma. Free lysine enrichments in plasma from the posterior vena cava were less than that from the artery (P<0.001), but those in red blood cells were not different between the artery and vein. The red blood cells thus play a minor role in the transfers to and from the hindquarter tissues, regardless of intake. Based on plasma transfers and the enrichment of lysine in arterial plasma, hindquarter protein synthesis increased linearly with intake (P<0.001). In contrast, protein breakdown was unaffected by intake. The contribution of hindquarter protein synthesis to whole-body lysine flux remained unchanged with intake (18–20 %).

Determinants of meat quality: tenderness

Meat quality is a term used to describe a range of attributes of meat. Consumer research suggests that tenderness is a very important element of eating quality and that variations in tenderness affect the decision to repurchase. The present paper highlights recent information on the factors that affect tenderness. While the precise aetiology is not fully understood, a number of factors have been shown to affect tenderness. Of these factors, postmortem factors, particularly temperature, sarcomere length and proteolysis, which affect the conversion of muscle to meat, appear most important. However, it is now becoming clear that variation in other factors such as the muscle fibre type composition and the buffering capacity of the muscle together with the breed and nutritional status of the animals may also contribute to the observed variation in meat tenderness.

Effect of genetic resistance to gastrointestinal nematodes on plasma concentrations of insulin-like growth factor-1 and leptin in Merino sheep

Gastrointestinal nematode infection in sheep changes the nutritional economy of the host, but little is known about the effects of infection on the hormonal systems that regulate the metabolism of the animal. This study examined two key hormones, insulin-like growth factor-1 (IGF-1) and leptin, in genetically resistant and random bred control Merino sheep in the presence or absence of nematode infection. Sixty-four 10-month-old Rylington Merino wethers, half from the parasite-resistant line and half from unselected control line, were initially maintained at two body conditions (body condition scores averaged 1.7 and 2.5) in individual pens in an animal house. The animals were kept parasite-free for 9 weeks, then ‘trickle-infected’ with Trichostrongylus colubriformis and Teladorsagia circumcincta larvae, each at a rate of 10 000 per week, for 13 weeks. Each body condition score group was subdivided into two groups at the beginning of the infection procedure and feed supply was controlled at 1× or 1.5× the maintenance metabolisable energy requirement. Plasma IGF-1 concentrations decreased marginally by day 21 of infection, then markedly by day 49, and then remained low until day 84. Plasma leptin concentrations tended to increase during the infection period. Both body condition and feed intake had significant effects on IGF-1 and leptin concentrations, and the higher concentrations were related to the good body condition or high feed intake. The parasite-resistant sheep had consistently higher concentrations of IGF-1 compared with the controls, whereas the concentrations of leptin were similar. The significant changes in IGF-1 but not leptin suggest that infection may have a more significant impact on protein anabolism, and least impact on lipid metabolism. Selection for parasite resistance appears to result in enhanced protein anabolism.

Differences in whole-body protein turnover between Iberian and Landrace pigs fed adequate or lysine-deficient diets1,2

The capacity for protein deposition in Iberian pigs is lower than in modern (e.g., Landrace) pig breeds, and the reasons for this remain unknown. The hypothesis tested in this work is that under similar nutritional and physiological conditions, whole-body protein turnover as well as the protein synthesis to protein deposition ratio differs between Iberian and Landrace breeds, resulting in dissimilar protein deposition rates. As a main objective, these variables were compared at different protein and Lys intakes in growing gilts. The study examined the effect of Lys deficiency because this is the prevalent condition during the fattening period of the Iberian pig in the Mediterranean forest, where the main feed source is oak acorn, which provides approximately one-third of the available Lys present in an ideal protein. Three diets were tested within each breed: 2 diets with an optimal essential AA pattern, containing 12 or 16% CP as-fed, or a Lys-deficient diet (35% of the recommended Lys content). This diet was supplied at 12% CP for the Iberian and 16% CP for the Landrace pigs, respectively. The contrasts made were breed x dietary protein concentration and breed x AA pattern (adequate vs. inadequate Lys content). Cumulative urinary (15)N excretion over 60 h after receiving an oral dose of [(15)N]-glycine was used to calculate N flux. Mean BW for Landrace and Iberian pigs were 25.8 +/- 0.55 kg and 30.8 +/- 0.74 kg, respectively. Protein deposition (g of N/(kg(0.75).d) was lower in the Iberian than in the Landrace gilts (4 to 16%; P = 0.002) and increased with dietary protein content. In contrast, protein synthesis and degradation [g of N/(kg(0.75).d)] were greater for the Landrace breed (16 to 18 and 23%, respectively, for the 2 dietary protein contents studied; P < 0.05), but no breed differences were detected in fractional protein synthesis and degradation rates. The ratio of protein synthesis:protein deposition (S/PD) did not change with dietary protein concentration or breed and achieved a mean value of 5.4. Irrespective of breed, Lys deficiency had a strong negative effect on N balance (P < 0.001) and increased the ratio of S/PD (P = 0.012). The greater rates of protein deposition, synthesis, and degradation in Landrace pigs than in Iberian pigs fed optimal AA-pattern diets were then attributed to differences in body protein mass. Consequently, these results validate the hypothesis of unequal synthesis and degradation, but not of unequal S/PD, between breeds.

Oxidation of essential amino acids by the ovine gastrointestinal tract

It is not known if the ruminant animal gastrointestinal tract (GIT) can oxidise essential amino acids (AA) other than leucine. Therefore, the oxidation of four essential AA (leucine, lysine, methionine and phenylalanine), supplied systemically as labelled 1-13C forms, was monitored across the mesenteric-drained viscera (MDV; small intestine) and portal-drained viscera (PDV; total GIT), as part of a Latin square design, in four wether sheep (35-45 kg) fed at 1.4 x maintenance. Oxidation was assessed primarily by appearance of 13CO2, corrected for sequestration of [13C]bicarbonate. The GIT contributed 25 % (P<0.001) and 10 % (P<0.05) towards whole-body AA oxidation for leucine and methionine respectively. This reduced net appearance across the PDV by 23 and 11 % respectively. The contribution of MDV metabolism to total PDV oxidation was 40 % for leucine and 60 % for methionine. There was no catabolism of systemic lysine or phenylalanine across the GIT. Production and exchange of secondary metabolites (e.g. 4-methyl-2-oxo-pentanoate, homocysteine, 2-aminoadipate) across the GIT was also limited. Less AA appeared across the PDV than MDV (P<0.001), indicative of use by tissues such as the forestomach, large intestine, spleen and pancreas. The PDV: MDV net appearance ratios varied (P<0.001) between AA, e.g. phenylalanine (0.81), lysine (0.71), methionine (0.67), leucine (0.56), histidine (0.71), threonine (0.63) and tryptophan (0.48). These differences probably reflect incomplete re-absorption of endogenous secretions and, together with the varied oxidative losses measured, will alter the pattern of AA net supply to the rest of the animal.

Effect of feed intake on amino acid transfers across the ovine hindquarters

Responses in variables of amino acid (AA) metabolism across peripheral tissues to feed intake were studied in six sheep (mean live weight 32 kg) prepared with arterio-venous catheters across the hindquarters. Four intakes (0.5, 1.0, 1.5 and 2.5 x maintenance energy) were offered over 2-week periods to each sheep in a Latin square design with two animals replicated. Animals were infused intravenously with a mixture of U-13C-labelled AA for 10 h and integrated blood samples withdrawn from the aorta and vena cava hourly between 5 and 9 h of infusion. Biopsy samples were also taken from skin and m. vastus lateralis. Data from both essential (histidine, isoleucine, leucine, lysine, phenylalanine, threonine) and nonessential (glycine, proline, serine, tyrosine) AA were modelled to give rates of inward and outward transport, protein synthesis and degradation, plus the fraction of total vascular inflow that exchanged with the hindquarter tissues. Rates of inward transport varied more than 10-fold between AA. For all essential AA (plus serine), inward transport increased with food intake (P<0.04). There were corresponding increases in AA efflux (P<0.05) from the tissues for threonine and the branched-chain AA. Protein synthesis rates estimated from the kinetics of these AA also increased with intake (P<0.02). Rates of inward transport greatly exceeded the amount of AA necessary to support protein retention, but were more similar to rates of protein synthesis. Nutritional or other strategies to enhance AA transport into peripheral tissues are unlikely to increase anabolic responses.

Effect of feed intake on ovine hindlimb protein metabolism based on thirteen amino acids and arterio-venous techniques

It has been suggested that protein synthesis in peripheral tissues: (1) responds in a curvilinear manner to increasing feed intake over a wide range of feeding levels; and (2) has a greater sensitivity to intake than protein breakdown. The aim of the present experiment was to test these hypotheses across the ovine hindlimb. Six growing sheep (6-8 months, 30-35 kg), with catheters in the aorta (two), posterior vena cava and jugular vein, received each of four intakes of dried grass pellets (0.5, 1.0, 1.5 and 2.5 x maintenance energy; M) for a minimum of 7 d. A U-13C-labelled algal hydrolysate was infused intravenously for 10 h and from 3-9 h para-aminohippuric acid was infused to measure plasma flow. Arterial and venous plasma were obtained over the last 4 h and the concentrations and enrichments of thirteen (13)C-labelled amino acids (AA) were determined by GC-MS. As intake increased, a positive linear response was found for plasma flow, arterial concentrations of the aromatic and branched-chain AA, total flow of all AA into the hindquarters and net mass balance across the hindquarters (except glycine and alanine). Based on two separate statistical analyses, the data for protein synthesis showed a significant linear effect with intake (except for phenylalanine, glycine and alanine). No significant curvilinear effect was found, which tends not to support hypothesis 1. Nonetheless, protein synthesis was not significantly different between 0.5, 1.0 and 1.5 x M and thus the 2.5 x M intake level was largely responsible for the linear relationship found. There was no significant response in protein breakdown to intake, which supports hypothesis 2.

Response in hepatic removal of amino acids by the sheep to short-term infusions of varied amounts of an amino acid mixture into the mesenteric vein

Under conditions of chronic supply the liver removes most amino acids (AA) in excess of net anabolic needs. Little information is available, however, on how acute alterations in AA supply (as might occur with once-daily feeding regimens) are controlled by the liver. Are these also extracted completely in a 'first-pass' manner or are there limitations to hepatic uptake? Furthermore, is the rate of removal 'saturable' (by Michaelis-Menten kinetics) over the range of supply experienced under normal feeding conditions? These questions have been addressed in a study that involved acute (4.5 h) increases in AA supply. Four sheep were prepared with trans-hepatic vascular catheters and were offered a basal diet (equivalent to 1.6xenergy maintenance) throughout. On four occasions, at 7 d intervals, they were infused with various amounts of an AA mixture into the mesenteric vein over a 4.5 h period. The mixture contained fourteen AA in the proportions present in rumen microbial protein. The amounts infused were calculated to provide an additional one, two, three and four times that absorbed from the basal diet. Continuous blood collections were removed over 2 h intervals before (basal diet only) and at 0.5-2.5 and 2.5-4.5 h of AA infusion. Transfers of AA, from the digestive tract and to the liver, were calculated for both plasma and total blood. The recovery of the infused AA across the portal-drained viscera (PDV) was quantitative (100%) only for histidine and proline, the remaining AA were recovered at 56-83 %. These losses correlated with the arterial concentrations and were probably due to removal of AA from the systemic circulation by the tissues of the digestive tract. Despite the wide range of net PDV appearances (i.e. absorbed plus infused), the percentage of most AA removed by the liver remained constant, but the percentage varied with AA (from 34 for proline to 78 for tryptophan for blood transfers). Thus, even when supply was increased 5-fold over baseline there was no indication that the transport into the liver declined, indeed the absolute removals continued to increase. In contrast, the branched-chain AA (isoleucine, leucine and valine) did not exhibit constant percentage extractions. Their percentage extractions were always the lowest (16, 10 and 25 respectively) and tended to decline at the highest infusion rates, indicative of saturation in hepatic transport and/or metabolism. The arterial concentrations of all infused AA increased with rate of infusion, again indicative that the liver did not extract all the net AA available across the PDV. Absolute amounts removed were similar between plasma and blood, indicating that most of the hepatic transfers occurred from plasma. The fractional rates of transfer from total inflow to the liver (i.e. with re-circulated AA included) were 3- to 4-fold lower than rates based on the amounts absorbed plus infused. The highest percentage extraction for total blood inflows was for serine (27), but most were between 6 and 16, except for the branched-chain AA, which were all <1. Use of percentage extractions based on total inflows are probably more appropriate for development of mathematical models of liver metabolism, and the current data suggest that constant values may be applied. The needs of the liver for specific mechanisms involving phenylalanine and histidine (plasma protein synthesis), glycine (detoxification of xenobiotics) and alanine (gluconeogenesis) probably also require to be included in such models.

Effects of altering the energy and protein supply to dairy cows during the dry period. 2. Metabolic and hormonal responses

We offered 48 multiparous Holstein-Friesian cows one of three different dry-period diets for 6 wk before predicted calving: A) a grass silage and barley straw mix (60:40 on a dry-matter basis), with a low protein content; B) grass silage only (medium protein); or C) grass silage plus 0.5 kg of high protein corn gluten meal (high protein)/d. A standard grass silage-based diet was offered to all cows following calving. All animals were blood sampled at weekly intervals during the dry period, and at wk 1, 3, 5, 7, 13, 17, and 21 of lactation. Nitrogen balance was measured in a subset of 12 cows (four per treatment) at 3 wk before calving, and at wk 8 and 18 of lactation. Nitrogen balance in the dry period increased significantly as dietary protein supply increased [9, 34, and 50 g of N/d (SED 8.8) for the three diets, respectively]. We measured no residual effects of dry-period treatment on N balance during lactation. Plasma concentrations of growth hormone became significantly higher in the late dry period in cows offered the silage and straw diet, although treatment differences disappeared after calving. Insulin concentrations were significantly affected by treatment throughout the dry period and indicated inadequate nutrient supplies from the low protein diet, leading to losses in body reserves of energy and protein. The results indicate that animals offered the low protein diet accumulated less N per day than is required for fetal development, suggesting that protein must have been repartitioned from maternal tissues.