Stable Carbon Isotope Composition of c9,t11-Conjugated Linoleic Acid in Cow’s Milk as Related to Dietary Fatty Acids

This study explores the potential use of stable carbon isotope ratios (δ¹³C) of single fatty acids (FA) as tracers for the transformation of FA from diet to milk, with focus on the metabolic origin of c9,t11-18:2. For this purpose, dairy cows were fed diets based exclusively on C₃ and C₄ plants. The FA in milk and feed were fractionated by silver-ion thin-layer chromatography and analyzed for their δ¹³C values. Mean δ¹³C values of FA from C₃ milk were lower compared to those from C₄ milk (−30.1‰ vs. −24.9‰, respectively). In both groups the most negative δ¹³C values of all FA analyzed were measured for c9,t11-18:2 (C₃ milk = −37.0 ± 2.7‰; C₄ milk −31.4 ± 1.4‰). Compared to the dietary precursors 18:2n-6 and 18:3n-3, no significant ¹³C-depletion was measured in t11-18:1. This suggests that the δ¹³C-change in c9,t11-18:2 did not originate from the microbial biohydrogenation in the rumen, but most probably from endogenous desaturation of t11-18:1. It appears that the natural δ¹³C differences in some dietary FA are at least partly preserved in milk FA. Therefore, carbon isotope analyses of individual FA could be useful for studying metabolic transformation processes in ruminants.     

Fatigue crack propagation and in-situ observations in three tool steel alloys manufactured using a rapid solidification technique

By utilizing special manufacturing conditions, e.g., using only pure elements and applying a rapid cooling rate, tool materials with high quasi-static fracture toughness can be produced. However, tool materials are often subjected to cyclic loading and, hence, their lifetime is dominated by fatigue failure. This study is focused on fracture mechanics and in-situ experiments to characterize the fatigue crack propagation behavior of three newly developed tool steels at a stress ratio R of 0.05. Microstructural examinations revealed that the materials consist of the phases α′-martensite, retained austenite, and complex carbides in different amounts. Results of preliminary tests are presented, in which it was attempted to grow the crack in a plane parallel to the plane of the starter notch. The determined ?K threshold values ranged between 4 and 5 MPa√m with Paris–Erdogan exponents of 3.3–4.6. In-situ observations were performed to understand the inherent damage mechanisms and microstructural effects during fatigue loading. These observations showed that fatigue crack growth is mainly dominated by the ductility of the martensitic–austenitic matrix. Only in cases in which the primary carbides are oriented favorably (with respect to the direction of crack propagation) does the crack follow the coherent carbide network to a certain extent. Furthermore, for the first time, a phase transformation from retained austenite to α′-martensite was detected at the crack tip during fatigue crack propagation for the material group of tool steels.     

Protein composition, plasmin activity and cheesemaking properties of cows' milk produced at two altitudes from hay of lowland and high-alpine origins

The influence of high altitude, alpine origin of the forage and roughage-only diets on milk protein content and composition, plasmin activity and cheesemaking properties was investigated. There were four treatment groups, each consisting of six dairy cows in early to mid-lactation. Two groups were fed only with hay ad libitum either at 2000 m or at 400 m a.s.l. One group, kept in the lowlands, was pair-fed to the alpine-site group and another group received a mixed diet of silages, hay and concentrates. Two hay types, harvested either at the alpine site or in the lowlands, were offered to all cows fed with hay alone, following a change-over design in three periods each of 3 weeks. In the respective third week, milk was sampled at every milking. Hay of alpine origin significantly reduced milk protein, in particular whey proteins, which is why the casein number increased. kappa-Casein proportion in total casein was reduced and its glycosylation was increased by the alpine hay. The apparent plasminogen-derived activity was reduced when alpine hay was given, but apparent plasmin activity and rennet coagulation properties of the milk were not affected by hay type. Independent of hay type, the high altitude group showed a significantly reduced milk protein content, lower glycosylation of kappa-casein and impaired rennet coagulation properties. For several of the traits, the trend was the same in the pair-fed group. There was no effect of altitude on apparent plasmin activity. Hay-alone v. the mixed diet resulted initially in marked declines in milk protein content but did not impair cheesemaking properties. Thus the extensive diet without concentrates, typical of high-alpine conditions, contributed less to the overall effect of extensive alpine v. intensive lowland feeding systems than hay quality and altitude did. In conclusion, certain positive influences of the alpine sojourn of cows on cheese processing quality are overruled by the major adverse impact of lower milk protein content.     

Can calcium chloride injection facilitate the ageing-derived improvement in the quality of meat from culled dairy cows?

This study investigated whether the positive effects of ageing on tenderness of meat from culled dairy cows can be facilitated by CaCl₂. Injections of 250 mM CaCl₂ solution (10% wt/wt) were performed on Longissimus dorsi samples from 32 7-yrs old cows. Samples were vacuum packaged and aged for 0, 1, 3, 5 and 7 days. Ageing alone produced lighter and less red meat with lower shear force, higher myofibrillar fragmentation and tenderness scores but also elevated lipid oxidation. For most traits investigated, CaCl₂-injected meat exhibited similar ageing effects, but drip loss increased with age. The CaCl₂-injected meat had a lower shear force and myofibrillar fragmentation increased more rapidly, but drip loss, off-flavour scores, colour stability and oxidative stability were inferior to untreated meat. Overall, it was found possible to accelerate tenderisation of such meat with CaCl₂, but only at the cost of adverse effects in some other quality traits.     

Modification of milk fatty acid composition by feeding forages and agro-industrial byproducts from dry areas to Awassi sheep

The study tested the hypothesis that certain underused forages and agro-industrial byproducts available in dry areas may positively influence fatty acid (FA) composition and antioxidative properties of milk by their contents of residual oil or phenolic compounds or both. Sixty multiparous fat-tailed Awassi ewes were allocated to 6 groups in a completely randomized block design. During 50 d, the ewes were group-fed 2.5 kg of dry matter/d per ewe 1 of 6 isonitrogenous and isoenergetic diets (forage:concentrate, 0.3:0.7). The test feeds, comprising 30% of the diets, replaced either barley straw [lentil straw, olive leaves, and Atriplex (saltbush) leaves, rich in phenolic compounds or electrolytes] or conventional concentrate ingredients (olive cake and tomato pomace; ∼10% lipids) from the control diet. The diets containing olive cake and tomato pomace were rich in oleic acid (18:1 cis-9; 27% of total dietary FA) and linoleic acid (18:2 cis-9,cis-12; 37%), respectively. Profiles of FA were determined in individual milk samples drawn on d 0 and in wk 1, 3, 5 and 7. Data was analyzed by repeated measurement analysis. No consistent treatment effects on yield and gross nutrient composition of the milk were observed, although some differences occurred. Milk resulting from the Atriplex leaf diet expressed the highest antiradical activity, which was low with control and olive leaves. Feeding the tomato pomace and olive cake diets decreased the proportions of short- and medium-chain FA, whereas oleic acid clearly increased in proportion to total FA. Olive leaves most effectively increased rumenic acid (18:2 cis-9,trans-11) and α-linolenic acid (18:3 cis-9,cis-12,cis-15) in milk fat. This also resulted in the highest α-linolenic acid transfer rate from feed to milk and suggests that olive leaves affect ruminal biohydrogenation at several steps. Several alternative feeds exist with an added value, as they enhance FA with potential health benefits and the stability of the milk with higher antioxidative activity, even though responses to test feeds differed largely. It remains to be investigated whether combinations of these feeds would be complementary in these beneficial effects.     

Partitioning of Rumen-Protected n-3 and n-6 Fatty Acids is Organ-Specific in Growing Angus Heifers

Dietary polyunsaturated fatty acids (PUFA), especially n-3 and n-6 fatty acids (FA), play an important role in the regulation of FA metabolism in all mammals. However, FA metabolism differs between different organs, suggesting a distinct partitioning of highly relevant FA. For the present study in cattle, a novel technology was applied to overcome rumen biohydrogenation of dietary unsaturated FA. Angus heifers were fed a straw-based diet supplemented for 8 weeks with 450 g/day of rumen-protected oil, either from fish (FO) or sunflower (SO). The FA composition in blood and five important organs, namely heart, kidney, liver, lung, and spleen, was examined. In blood, proportions of polyunsaturated FA were increased by supplementing FO compared to SO. The largest increase of eicosapentaenoic acid (EPA) proportion was found with FO instead of SO in the kidney, the lowest in the lung. Docosahexaenoic acid (DHA) was increased more in the liver than in kidney, lung, and spleen. The heart incorporated seven times more EPA than DHA, which is more than all other organs and described here for the first time in ruminants. In addition, the heart had the highest proportions of α-linolenic acid (18:3n-3) and linoleic acid (18:2n-6) of all organs. The proportions of polyunsaturated FA in the lung and spleen were exceptionally low compared to heart, liver, and kidney. In conclusion, it was shown that the response to FO in the distribution of dietary n-3 FA was organ-specific while proportions of n-6 FA were quite inert with respect to the type of oil supplemented.     

Preferential Partitioning of Rumen-Protected n-3 and n-6 Fatty Acids into Functionally Different Adipose Tissues

Lipids are stored at various sites inside the body as adipose tissue (AT). These include subcutaneous, abdominal, and intermuscular locations. The AT substantially differ in their metabolic function. It is, however, unclear whether AT have specific requirements for individual essential n-3 and n-6 fatty acids (FA). If so, control mechanisms would partition FA from the blood. To investigate the hypothesis of a selective FA incorporation, 18 beef heifers were fed diets supplemented with 60 g/kg diet with lipids from either fish oil (FO) or sunflower oil (SO). The lipids had partially been rumen-protected to ruminal biohydrogenation of n-3 and n-6 FA. The AT analyzed for n-3 and n-6 FA by gas chromatography were obtained from pericardial, longissimus thoracis (LT) intermuscular, perirenal, and subcutaneous sites. The greatest proportions of n-3 and n-6 FA were found in the pericardial AT. Despite generally low abundance, n-3 FA proportions increased with FO compared to SO supplementation in all AT, but to a different extent. No such partitioning was found for the n-6 FA when supplementing SO. Concomitantly, the n-6/n-3 FA ratio was reduced with FO in all AT, except in the pericardial AT. The latter has specific metabolic functions and thus appears to be quite resistant to diet-induced changes in FA profile in order to maintain its function. The present findings showed the special role of specific n-3 and n-6 FA in bovine AT.     

Geographic origin of meat—elements of an analytical approach to its authentication

This review article discusses recent analytical developments with respect to the determination of the geographic origin of raw meat. The main emphasis is laid on lamb, beef and poultry. So far, some methods have shown quite promising potential (e.g. stable isotope ratios, trace elements), others have remained unsatisfactory in their discriminating power to authenticate the geographic origin of meat (e.g. microbiological profile, sensory traits, volatile compounds). Other methods (e.g. animal genotype, gross chemical composition) could be auxiliary criteria as they help to determine related indicators such as feeding or housing conditions but not directly the origin. The complexity of this question is large. An integrated approach simultaneously addressing various species and production characteristics such as environment, animal husbandry conditions, breed, feeding and drinking water has to be developed. Strategies have to be different for global and micro-regional scales.     

Farm-gate nutrient balances of grassland-based milk production systems with full- or part-time grazing and fresh herbage indoor feeding at variable concentrate levels

Nutrient Cycling in Agroecosystems - Farm-gate balances for nitrogen (N) and phosphorus (P) were used to determine the potential nutrient surplus and nutrient-use efficiency of three...