D.I. Givens

TRANS FATTY ACIDS AND BIOACTIVE LIPIDS IN RUMINANT MILK

There is increasing evidence that nutrition plays an important role in the development of chronic diseases in the human population, including cancer, cardiovascular disease, insulin resistance, and obesity. Developing foods that enhance human health is central to dietary approaches for preventing and reducing the economic and social impacts of chronic disease. Numerous studies in human subjects have implicated a high consumption of saturated fatty acids (SFA) and trans fats as risk factors for cardiovascular disease risk, with evidence that high-SFA intakes may also be related to lowered insulin sensitivity, which is a key factor in the development of themetabolic syndrome.While it is generally accepted that SFA raise plasma total and low-density lipoprotein cholesterol concentrations, atherogenic effects are confined to 12:0, 14:0, and 16:0. Consistent with the effects of individual SFA, there is some evidence to suggest that physiological responses to trans fatty acids (TFA) may also be isomer-dependent. National nutritional guidelines with the target of reducing the incidence of cardiovascular disease have advocated a population-wide reduction in the intake of total fat, SFA, and TFA. Milk and dairy products are the major source of 12:0 and 14:0 in the human diet and also make a significant contribution to 16:0 and TFA intake. However, developing public health policies promoting a decrease in milk, cheese, and butter consumption ignores the value of these foods as a versatile source of nutrients. Furthermore, consumption of milk and dairy products may confer beneficial effects with respect to the prevention of osteoporosis, cancer, atherosclerosis, and other degenerative disorders (Heaney, 2000; Ness et al., 2001; Kalkwarf et al., 2003; Valeille et al., 2006). A number of minerals, proteins, peptides, and lipids in milk and fermented dairy products exhibit bioactive properties with the potential to

The role of meat as a source of n - 3 polyunsaturated fatty acids in the human diet

It is considered that consumption of very long chain (VLC, carbon chain length ⩾20) n-3 PUFAs in most Western populations is sub-optimal and benefits in relation to chronic disease would be gained from increased consumption. This review examines the current contribution that meat makes to dietary intake of VLC n-3 PUFA and given its current low contribution, how ruminant meat may be enriched. Enrichment both directly with VLC n-3 fatty acids and indirectly by increasing intake by the animals of α-linolenic acid (ALNA; C18:3 n-3) are considered. Since it now appears that dietary ALNA is a very limited source of VLC n-3 PUFA in humans, the indirect route is controversial but since some forages are rich sources of ALNA this route has many sustainability and environmental attractions. Consideration is also given to the increased concentrations of trans and conjugated fatty acids that will arise from enriching ruminant meat with PUFA.

The role of animal nutrition in improving the nutritive value of animal-derived foods in relation to chronic disease

Foods derived from animals are an important source of nutrients in the diet; for example, milk and meat together provide about 60 and 55% of the dietary intake of Ca and protein respectively in the UK. However, certain aspects of some animal-derived foods, particularly their fat and saturated fatty acid (SFA) contents, have led to concerns that these foods substantially contribute to the risk of CVD, the metabolic syndrome and other chronic diseases. In most parts of Europe dairy products are the greatest single dietary source of SFA. The fatty acid composition of various animal-derived foods is, however, not constant and can, in many cases, be enhanced by animal nutrition. In particular, milk fat with reduced concentrations of the C12-16 SFA and an increased concentration of 18:1 MUFA is achievable, although enrichment with very-long-chain n-3 PUFA is much less efficient. However, there is now evidence that some animal-derived foods (notably milk products) contain compounds that may actively promote long-term health, and research is urgently required to fully characterise the benefits associated with the consumption of these compounds and to understand how the levels in natural foods can be enhanced. It is also vital that the beneficial effects are not inadvertently destroyed in the process of reducing the concentrations of SFA. In the future the role of animal nutrition in creating foods closer to the optimum composition for long-term human health is likely to become increasingly important, but production of such foods on a scale that will substantially affect national diets will require political and financial incentives and great changes in the animal production industry.

Prediction of the Organic Matter Digestibility of Grass Silage

The results of a study into the use of a variety of laboratory methods for the prediction of organic matter digestibility of grass silages measured in vivo are reported. The silages used in the study had been examined in vivo at the Agricultural Development and Advisory Service (100 silages) and Rowett Research Institute (43 silages) Feed Evaluation Units and at the School of Agriculture, Aberdeen (27 silages). Predictions based upon fibre measurements (modified acid detergent fibre and acetyl bromide lignin) produced regression lines for the populations of silages measured in vivo at different centres, which differed significantly (P < 0.001) in intercept but not in slope (R2 = 0.34, 0.52; RSD = 0.051, 0.044, respectively overall). The use of a pepsin-cellulase technique produced regression lines which differed significantly (P < 0.001) between the populations in both intercept and slope (R2 = 0.55, RSD = 0.042 rmoverall). Techniques involving the use of rumen microbes to digest the silages (nylon bag 48-h and in vitro incubations) described the organic matter digestibility of all of the silage populations by single regression lines (R2 = 0.68, 0.74; RSD = 0.036, 0.032, respectively). Near infrared diffuse reflectance spectroscopy (NIR) also gave a single regression line provided that more than five terms were used in the multiple regression equation (R2 = 0.85, SEC = 0.025 for an eight-term equation). However, regression lines for the different populations differed significantly (P < 0.01) when the regressions contained from one to five terms. The best prediction of the organic matter digestibility of a blind test population of silages (n = 48) was obtained by NIR using a multiple linear regression involving eight terms (R2 = 0.76, SEP = 0.026). It is concluded that prediction of in vivo organic matter digestibility using NIR is the most accurate and precise approach available.

The effect of supplementing grass silage with barley on digestibility, in sacco degradability, rumen fermentation and methane production in sheep at two levels of intake

Two experiments are reported which examined the digestibility, in sacco degradability, rumen fermentation and methane production of grass silage unsupplemented or supplemented with rolled barley at three ratios and two planes of nutrition. Grass silage was given with rolled barley to four mature wether sheep using forage:concentrate (F:C) ratios of 1.00, 0.75, 0.50, and 0.25 (dry matter (DM) basis) at near to maintenance (experiment 1) and 1.5 × maintenance (experiment 2) in two consecutive latin square designs. All diets within plane of nutrition were designed to be isoenergetic and all animals received a mineral/vitamin supplement. The diets were fed for 28 d, with rumen fluid sampling on day 12. Apparent digestibility and rumen degradability (in sacco) of diet organic matter (OM) were measured and methane produced was measured in open-circuit respiration chambers for four consecutive 24 h periods. Apparent digestibility of organic matter (OMD) increased linearly (P < 0.001) in both experiments with decreasing F:C ratio (0.74, 0.79, 0.83, 0.88 and 0.72, 0.75, 0.78, 0.82 for experiments 1 and 2 respectively). Decreasing F:C ratio depressed the effective degradability of silage OM from polyester fibre bags in both experiments (quadratic effect P < 0.05) and also for barley in experiment 1 (quadratic effect P < 0.05). Rumen pH was significantly decreased with decreasing F:C ratio in both experiments as was the total mean VFA concentration. The molar proportions of acetate and propionate tended to decrease and that of butyrate increased with decreasing F:C ratio. Over the range of barley inclusion in this study there were no associative effects on methane production (1 d−1) in experiment 1 (37.2, 41.5, 41.9, 44.0 1 d−1 for F:C ratio 1.00, 0.76, 0.51 and 0.26 respectively), but the opposite was true at the higher level of intake (methane 1 d−1, 54.1, 60.1, 58.0, 50.1 for F:C ratios 1.00, 0.78, 0.54, 0.28 respectively). Rumen stoichiometry could not be used to explain the change in methane production. Increased level of intake reduced methane production (1 kg−1 organic matter apparently digested) regardless of F:C ratio. Expressing methane relative to the efficiency of digestion, or the efficiency of animal production, enables the potential for reduction of methane generation by starch supplementation and/or level of intake to be realised.

Milk and meat in our diet: good or bad for health?

Foods derived from animals are an important source of nutrients in the diet but there is considerable uncertainty about whether or not these foods contribute to increased risk of various chronic diseases. For milk in particular there appears to be an enormous mismatch between both the advice given on milk/dairy foods items by various authorities and public perceptions of harm from the consumption of milk and dairy products, and the evidence from long-term prospective cohort studies. Such studies provide convincing evidence that increased consumption of milk can lead to reductions in the risk of vascular disease and possibly some cancers and of an overall survival advantage from the consumption of milk, although the relative effect of milk products is unclear. Accordingly, simply reducing milk consumption in order to reduce saturated fatty acid (SFA) intake is not likely to produce benefits overall though the production of dairy products with reduced SFA contents is likely to be helpful. For red meat there is no evidence of increased risk of vascular diseases though processed meat appears to increase the risk substantially. There is still conflicting and inconsistent evidence on the relationship between consumption of red meat and the development of colorectal cancer, but this topic should not be ignored. Likewise, the role of poultry meat and its products as sources of dietary fat and fatty acids is not fully clear. There is concern about the likely increase in the prevalence of dementia but there are few data on the possible benefits or risks from milk and meat consumption. The future role of animal nutrition in creating foods closer to the optimum composition for long-term human health will be increasingly important. Overall, the case for increased milk consumption seems convincing, although the case for high-fat dairy products and red meat is not. Processed meat products do seem to have negative effects on long-term health and although more research is required, these effects do need to be put into the context of other risk factors to long-term health such as obesity, smoking and alcohol consumption.

Quantification of ruminal Clostridium proteoclasticum by real-time PCR using a molecular beacon approach

Aims:  All members of the ruminal Butyrivibrio group convert linoleic acid (cis‐9,cis‐12‐18 : 2) via conjugated 18 : 2 metabolites (mainly cis‐9,trans‐11‐18 : 2, conjugated linoleic acid) to vaccenic acid (trans‐11‐18 : 1), but only members of a small branch, which includes Clostridium proteoclasticum, of this heterogeneous group further reduce vaccenic acid to stearic acid (18 : 0, SA). The aims of this study were to develop a real‐time polymerase chain reaction (PCR) assay that would detect and quantify these key SA producers and to use this method to detect diet‐associated changes in their populations in ruminal digesta of lactating cows.

The Digestibility and Metabolisable Energy Content of Grass Silage and their Prediction from Laboratory Measurements

Abstract The results of a study into the prediction of digestible organic matter content (DOMD) and energy values involving a total of 124 grass silages are reported. The silages were examined in vivo using 4 wether sheep per sample fed at maintenance. The most powerful single predictor of DOMD was the rumen fluid in vitro method. The rumen fluid method accounted for 74.1% of the variability in DOMD compared to 55.8% when using modified acid detergent fibre. The rumen fluid and cellulase methods were, in some cases, additive to one another in prediction power, suggesting that they did not measure identical feed characteristics. In addition, the inclusion of total ash and certain other feed fractions such as hemicellulose in multivariate relationships with the major predictors allowed further variability in DOMD to be explained. Equations were derived for prediction of the proportional gross energy (GE) losses in faeces and urine. The prediction of faecal energy losses was always poorer than for DOMD content and urinary losses were more closely related to silage digestibility than crude protein content. In all cases, the relationships between metabolisable energy (ME) and laboratory measurements primarily related to digestibility were much poorer than for DOMD. For example, the rumen fluid in vitro method accounted for only 24% of the variability in ME, although this was increased to 77.4% by the inclusion of GE in a bivariate relationship. The inclusion of GE as a prediction term always substantially improved the prediction of ME and whilst ether extract content appeared to influence GE content the most, GE was not closely related to the organic components measured. It is concluded that the inclusion of GE or terms related to GE is essential if silage ME content is to be predicted with an acceptable error. The implications of this in extension work are discussed.

Effect of replacing grass silage with maize silage in the diet on bovine milk fatty acid composition

Even though extensive research has examined the role of nutrition on milk fat composition, there is less information on the impact of forages on milk fatty acid (FA) composition. In the current study, the effect of replacing grass silage (GS) with maize silage (MS) as part of a total mixed ration on animal performance and milk FA composition was examined using eight multiparous mid-lactation cows in a replicated 4 × 4 Latin square with 28-day experimental periods. Four treatments comprised the stepwise replacement of GS with MS (0, 160, 334 and 500 g/kg dry matter (DM)) in diets containing a 54 : 46 forage : concentrate ratio on a DM basis. Replacing GS with MS increased (P < 0.001) the DM intake, milk yield and milk protein content. Incremental replacement of GS with MS in the diet enhanced linearly (P < 0.001) the proportions of 6:0-14:0, decreased (P < 0.01) the 16:0 concentrations, but had no effect on the total milk fat saturated fatty acid content. Inclusion of MS altered the distribution of trans-18:1 isomers and enhanced (P < 0.05) total trans monounsaturated fatty acid and total conjugated linoleic acid content. Milk total n-3 polyunsaturated fatty acid (PUFA) content decreased with higher amounts of MS in the diet and n-6 PUFA concentration increased, leading to an elevated n-6 : n-3 PUFA ratio. Despite some beneficial changes associated with the replacement of GS with MS, the overall effects on milk FA composition would not be expected to substantially improve long-term human health. However, the role of forages on milk fat composition must also be balanced against the increases in total milk and protein yield on diets containing higher proportions of MS.

Comparison of algal and fish sources on the oxidative stability of poultry meat and its enrichment with omega-3 polyunsaturated fatty acids

Human consumption of long-chain n-3 polyunsaturated fatty acids (LC n-3 PUFA) is below recommendations, and enriching chicken meat (by incorporating LC n-3 PUFA into broiler diets) is a viable means of increasing consumption. Fish oil is the most common LC n-3 PUFA supplement used but is unsustainable and reduces the oxidative stability of the mat. The objective of this experiment was to compare fresh fish oil (FFO) with fish oil encapsulated (EFO) in a gelatin matrix (to maintain its oxidative stability) and algal biomass at a low (LAG, 11), medium (MAG, 22), or high (HAG, 33 g/kg of diet) level of inclusion. The C22:6n-3 contents of the FFO, EFO, and MAG diets were equal. A control (CON) diet using blended vegetable oil was also made. As-hatched 1-d-old Ross 308 broilers (144) were reared (21 d) on a common starter diet then allocated to treatment pens (4 pens per treatment, 6 birds per pen) and fed treatment diets for 21 d before being slaughtered. Breast and leg meat was analyzed (per pen) for fatty acids, and cooked samples (2 pens per treatment) were analyzed for volatile aldehydes. Concentrations (mg/100 g of meat) of C20:5n-3, C22:5n-3, and C22:6n-3 were (respectively) CON: 4, 15, 24; FFO: 31, 46, 129; EFO: 18, 27, 122; LAG: 9, 19, 111; MAG: 6, 16, 147; and HAG: 9, 14, 187 (SEM: 2.4, 3.6, 13.1) in breast meat and CON: 4, 12, 9; FFO: 58, 56, 132; EFO: 63, 49, 153; LAG: 13, 14, 101; MAG: 11, 15, 102; HAG: 37, 37, 203 (SEM: 7.8, 6.7, 14.4) in leg meat. Cooked EFO and HAG leg meat was more oxidized (5.2 mg of hexanal/kg of meat) than the other meats (mean 2.2 mg/kg, SEM 0.63). It is concluded that algal biomass is as effective as fish oil at enriching broiler diets with C22:6 LC n-3 PUFA, and at equal C22:6n-3 contents, there is no significant difference between these 2 supplements on the oxidative stability of the meat that is produced.