Milk Odd- And Branched-chain Fatty Acids Research Articles

Odd- and branched-chain fatty acids in milk fat from Holstein dairy cows are influenced by physiological factors

Dairy products are the major source of odd- and branched-chain fatty acids (OBCFAs), a group of nutrients with emerging health benefits. The animal diet is known to influence milk fat OBCFAs of dairy cows; however, little is known about the effects of physiological factors. The objective of this study was to investigate the effects of parity and lactation stage on OBCFAs in milk fat of dairy cows. Holstein dairy cows (n = 157) were selected according to parity (first, second, third, or greater) and days in milk (DIM) (≤21 DIM, 21 < DIM ≤ 100, 100 < DIM ≤ 200, >200 DIM). All cows were fed the same total mixed ration for three weeks. Milk samples were collected during the last three days of each lactation stage for fatty acid (FA) analyses via gas chromatography. Results showed that first- and second-parity cows displayed significantly higher proportions and yields of iso-14:0, iso-15:0, iso-16:0, total iso-FA, and total branched-chain FA (P < 0.05) compared with other parities. The proportions of C17:0 and C17:1 cis-9 were also greater in first-parity cows (P < 0.05), while the yields of C17:0 and C17:1 cis-9 were similar among different parities (P > 0.05). The proportions of total OBCFAs were greater in first- and second-parity cows (P < 0.05), whereas the highest yield was observed in second-parity cows. Lactation dairy cows in ≤ 21 DIM group displayed lower proportions of iso-13:0, anteiso-13:0, C13:0, iso-14:0, C15:0, iso-16:0, total iso-FA, and total OBCFAs compared with that of the other groups (P < 0.05), and also lower yields of iso-14:0 and iso-16:0 (P < 0.05). In contrast, C17:0 and C17:1 cis-9 proportions and yields were higher in dairy cows with ≤ 21 DIM (P < 0.05). Iso-17:0 and anteiso-17:0 were not affected by lactation stage (P > 0.05). Taken together, our data showed that both parity and lactation stage have considerable effects on milk fat OBCFAs of dairy cows. In summary, first- and second-parity cows had higher milk OBCFAs compared with later parity cows, and OBCFAs with medium chain lengths were lower in dairy cows with ≤ 21 DIM, while C17:0 and C17:1 cis-9 were higher. These findings show that milk OBCFA contents are differentially modulated by physiological state. They will be useful in future studies that seek to alter OBCFA composition of Holstein dairy cow milk fats.

Milk Odd and Branched Chain Fatty Acids in Dairy Cows: A Review on Dietary Factors and Its Consequences on Human Health.

Simple SummaryThe objective of this review is to highlight the importance of odd and branched chain fatty acids and dietary factors that may affect their content in milk acids in dairy cows. The primary source of odd and branched chain fatty acids is ruminal bacteria. In contrast to saturated fatty acids, odd and branched chain fatty acids have health protective effects against certain diseases as cardiovascular diseases, type II diabetes, cancers, Alzheimer’s disease and metabolic syndrome. Ruminant products are the main source of these fatty acids in the human diet. Odd and branched chain fatty acids profile in cow milk is mainly affected by dietary fatty acids and fatty acids metabolism in the rumen. Additionally, lipid mobilization in the body and fatty acids metabolism in mammary glands affect the milk odd and branched chain fatty acids profile. Understanding the origin of odd and branched chain fatty acids in milk and manipulating the diet of dairy cows to produce odd and branched chain fatty acids-enriched milk can be of scientific and industrial significance.This review highlights the importance of odd and branched chain fatty acids (OBCFAs) and dietary factors that may affect the content of milk OBCFAs in dairy cows. Historically, OBCFAs in cow milk had little significance due to their low concentrations compared to other milk fatty acids (FAs). The primary source of OBCFAs is ruminal bacteria. In general, FAs and OBCFAs profile in milk is mainly affected by dietary FAs and FAs metabolism in the rumen. Additionally, lipid mobilization in the body and FAs metabolism in mammary glands affect the milk OBCFAs profile. In cows, supplementation with fat rich in linoleic acid and α-linolenic acid decrease milk OBCFAs content, whereas supplementation with marine algae or fish oil increase milk OBCFAs content. Feeding more forage rather than concentrate increases the yield of some OBCFAs in milk. A high grass silage rate in the diet may increase milk total OBCFAs. In contrast to saturated FAs, OBCFAs have beneficial effects on cardiovascular diseases and type II diabetes. Furthermore, OBCFAs may have anti-cancer properties and prevent Alzheimer’s disease and metabolic syndrome.

Effect of dietary lipids and other nutrients on milk odd- and branched-chain fatty acid composition in dairy ewes

Milk odd- and branched-chain fatty acids (OBCFA) are largely derived from bacteria leaving the rumen, which has encouraged research on their use as biomarkers of rumen function. Targeted research has examined relationships between these fatty acids (FA) and dietary components, but interactions between the effects of lipids and other nutrients on milk OBCFA are not well characterized yet. Furthermore, factors controlling milk OBCFA in sheep are largely unknown. Thus, the present meta-analysis examined relationships between diet composition and milk OBCFA using a database compiled with lot observations from 14 trials in dairy ewes fed lipid supplements. A total of 47 lots received lipid supplements, whereas their respective controls (27 lots) were fed the same basal diets without lipid supplementation. Relationships between milk OBCFA and dietary components were first assessed through a principal component analysis (PCA) and a correlation analysis. Then, responses of milk OBCFA to variations in specific dietary components (selected on the basis of the PCA) were examined in more detail by regression analysis. According to the loading plot, dietary unsaturated C18 FA loaded opposite to major milk OBCFA (e.g., 15:0, 15:0 anteiso, and 17:0) and were strongly correlated with principal component 1, which described 46% of variability. Overall, regression equations supported this negative, and generally linear, relationship between unsaturated C18 FA levels and milk OBCFA. However, the influence of C20-22 n-3 polyunsaturated FA and saturated FA was more limited. The PCA also suggested that dietary crude protein is not a determinant of milk OBCFA profile in dairy ewes, but significant relationships were observed between some OBCFA and dietary fiber or starch, consistent with a potential role of these FA as biomarkers of rumen cellulolytic and amylolytic bacteria. In this regard, regression equations indicated that iso FA would show opposite responses to increasing levels of acid detergent fiber (positive linear coefficients) and starch (negative linear coefficients). Lipid supplementation would not largely affect these associations, supporting the potential of OBCFA as noninvasive markers of rumen function under different feeding conditions (i.e., with or without lipid supplementation). Because consumption of these FA may have nutritional benefits for humans, the use of high-fiber/low-starch rations might be recommended to maintain the highest possible content of milk OBCFA in dairy sheep.

Relationship of Milk Odd- and Branched-Chain Fatty Acids with Urine Parameters and Ruminal Microbial Protein Synthesis in Dairy Cows Fed Different Proportions of Maize Silage and Red Clover Silage.

Simple SummaryThe purpose of this study is to assess the relationship of milk odd- and branched-chain fatty acids (OBCFA) with urinary purine derivates (PD) and estimated ruminal microbial crude protein (MCP). The correlations and regressions demonstrate that yields and concentrations of individual or total OBCFA are weakly related to urinary PD and are low to moderate markers of MCP synthesis. Nevertheless, milk OBCFA can still be seen as a promising method for predicting rumen function and microbial protein supply to the duodenum in dairy cows because MCP flow was not directly measured in this study but instead indirectly estimated probably comprising considerable deviations of the assumed values from the true ones.The aim of this study was to evaluate the relationship of milk odd- and branched-chain fatty acids (OBCFA) with urinary purine derivates and estimated ruminal microbial crude protein (MCP) synthesis. Forty-four lactating Holstein cows were used in a 4 × 4 Latin square design with 21-day periods comprised of a 13-day adaptation phase to diet followed by an 8-day sampling phase. Differences in estimated MCP yield and milk OBCFA composition were found by feeding total mixed rations containing forage (maize silage, MS; red clover silage, RCS) and concentrates (0.75:0.25) with targeted proportions of RCS to MS of 0.15:0.60, 0.30:0.45, 0.45:0.30, and 0.60:0.15 on a dry matter basis. The MCP was estimated from the total urinary purine derivate (PD) excretion (MCPPD) and intakes of metabolizable energy (MCPME) or digestible organic matter (MCPdOM). The Pearson correlations of individual OBCFA with urinary parameters (uric acid, allantoin, PD and nitrogen) were generally weak (r = −0.37 to 0.55). Yields of individual OBCFA correlated positively with MCPME and MCPdOM (r = 0.21 to 0.55). The prediction of urinary PD concentration was moderate (R2 = 0.64) when including the proportion of iso-C17:0. The prediction of total PD excretion was low (R2 = 0.21) with yields of iso-C15:0, anteiso-C17:0, and iso-C16:0. The prediction of MCPPD was high (R2 = 0.99) when including the iso-C16:0 and cis-9 C17:1 concentrations, while those of MCPME and MCPdOM were low (R2 = 0.37 and 0.36, respectively) when including yields of iso-C15:0, cis-9 C17:1, and iso-C18:0. The correlations and regression analyses demonstrate that the estimated MCP synthesis and urinary PD excretion can be only moderately predicted by yields and concentrations of individual or total OBCFA in cow’s milk. However, milk OBCFA can still be seen as a promising, non-invasive method for predicting rumen function and microbial protein supply in dairy cows because MCP flow was not directly measured in this study but instead indirectly estimated probably comprising considerable deviations of the assumed values from the true ones.

Relations of Ruminal Fermentation Parameters and Microbial Matters to Odd- and Branched-Chain Fatty Acids in Rumen Fluid of Dairy Cows at Different Milk Stages.

Simple SummaryThe objective of this study was to determine the relationships between milk odd- and branched-chain fatty acids (OBCFAs) and ruminal fermentation parameters, microbial populations, and base contents. Significant relationships existed between the concentrations of C11:0, iso-C15:0, anteiso-C15:0, C15:0, and anteiso-C17:0 in rumen and milk. The total OBCFA content in milk was positively related to the acetate molar proportion but negatively correlated with isoacid levels. The adenine/N ratio was negatively related to milk OBCFA content but positively associated with the iso-C15:0/iso-C17:0 ratio.The purpose of this research was to evaluate whether relationships exist between odd- and branched-chain fatty acids (OBCFAs) originating from milk fat and the corresponding data of ruminal fermentation parameters, microbial populations, and base contents that were used to mark microbial protein in rumen. Nine lactating Holstein dairy cows with similar body weights and parity were selected in this study, and the samples of rumen and milk were collected at the early, middle, and late stages, respectively. The rumen and milk samples were collected over three consecutive days from each cow, and the ruminal and milk OBCFA profiles, ruminal fermentation parameters, bacterial populations, and base contents were measured. The results showed that the concentrations of OBCFAs, with the exception of C11:0 and C15:0, were significantly different between milk and rumen (p < 0.05). The concentrations of anteiso-fatty acids in milk were higher than those in rumen, and the contents of linear odd-chain fatty acids were higher than those of branched-chain fatty acids in both milk and rumen. Significant relationships that existed between the concentrations of C11:0, iso-C15:0, anteiso-C15:0, C15:0, and anteiso-C17:0 in rumen and milk (p < 0.05). The total OBCFA content in milk was positively related to the acetate molar proportion but negatively correlated with isoacid contents (p < 0.05). The populations of Ruminococcus albus, R. flavefacients, and Eubacterium ruminantium were significantly related to milk C13:0 contents (p < 0.05). The adenine/N ratio was negatively related to milk OBCFA content (p < 0.05) but positively associated with the iso-C15:0/iso-C17:0 ratio (p < 0.05). Milk OBCFAs were significantly correlated with ruminal fermentation parameters, ruminal bacterial populations, and base contents. Milk OBCFAs had the potential to predict microbial nitrogen flow, and the prediction equations for ruminal microbial nitrogen flow were established for OBCFAs in dairy milk.

Short communication: Effects of diets containing supplemental fats on ruminal fermentation and milk odd- and branched-chain fatty acids in dairy cows

There is a growing interest in odd- and branched-chain fatty acids (OBCFA) in milk following reports that several branched-chain fatty acids (FA) have health promoting effects, and certain milk OBCFA could serve as a biomarker to assess ruminal function. Twenty-four Holstein cows were fed 3 low-forage diets containing 30 g/kg of dry matter of prilled palm fat (PPF), sunflower oil (SO), or an equal mixture of both fats (experiment 1) or 3 diets containing 30 g/kg of dry matter of SO with a forage-to-concentrate ratio of 39:61, 44:56, or 48:52 (Experiment 2); diets were fed to investigate milk OBCFA composition and to explore the relationships between ruminal VFA and milk OBCFA using principal component analysis. Including SO in diets decreased yields of milk 13:0 anteiso, 15:0 anteiso, 15:0, 17:0, cis-9 15:1, and cis-9 17:1 compared with PPF. The molar proportion of ruminal propionate was the lowest and the yields of milk 14:0 iso and 16:0 iso were the greatest with the diet containing both fat supplements. Replacing concentrate with forages linearly increased ruminal acetate and yields of milk 13:0 iso, 14:0 iso, 15:0 iso, 16:0 iso, 17:0 iso, 13:0 anteiso, 15:0 anteiso, 15:0, 17:0, cis-9 15:1, and cis-9 17:1. The principal component analysis revealed that ruminal molar proportion of acetate related to concentrations of milk iso FA containing <17-carbon, whereas ruminal propionate related to milk 15:0, 17:0, cis-9 15:1, and cis-9 17:1, with the stronger correlations between milk OBCFA and ruminal acetate than propionate. No associations were found between ruminal molar proportion of butyrate and milk OBCFA concentrations. The results suggest that complete replacement of PPF with SO at 30 g/kg of dry matter in low-forage diets is not an effective strategy to enhance bioactive branched-chain FA in milk, rather this feeding practice lowers anteiso FA in milk; however, increasing forage proportion in diets containing SO enhances several iso and anteiso FA in milk. The milk OBCFA concentrations have stronger correlations with ruminal acetate molar proportion than with propionate or butyrate in cows fed diets containing supplemental fats.

Optimization of milk odd and branched-chain fatty acids analysis by gas chromatography using an extremely polar stationary phase

Odd and branched-chain fatty acids (OBCFA) are of interest, since they have bioactive properties and could be regarded biomarkers of ruminant fat intake. An accurate analysis of the individual OBCFA in milk by gas chromatography (GC) is not easy due to milk fat complexity. The availability of ionic liquid stationary phases as SLB-IL111 can be a useful tool to discriminate OBCFA from other milk FA eluting in the same chromatographic regions. The elution behavior of OBCFA on SLB-IL111 was evaluated based on different GC oven temperature programs. All programs assayed discriminated 11:0, iso 13:0, anteiso 13:0, iso 15:0, anteiso 15:0, 15:0 and iso 17:0. Using an initial temperature of 150°C for 1h, 13:0 and iso 16:0 were separated from trans-12:1 and 13-14:1, respectively, whereas iso 18:0 was discriminated from cis-16:1 isomers. 17:0 and 21:0 were well resolved only when an initial GC temperature of 160°C was applied.

Odd- and branched-chain fatty acids in goat milk as indicators of the diet composition

This work aimed to determine if the milk fat contents of odd- and branched-chain fatty acids (OBCFA) could be linked to the diet composition in goats, by canonical discriminant analysis (CDA). The OBCFA contents of 32 milk fat samples from two feeding trials (two treatments per trial) were used. In both experiments, the goats were fed a diet, with the same forage/concentrate ratio and nutritive value, which was supplemented or not with 30 g/d of linseed oil. The starch/non-forage NDF ratio of the diet was 3.1 in the first experiment and was lowered to 0.8 in the second experiment by replacing part of the cereals in the concentrate with soybean hulls. Milk fat composition analyses were grouped into four classes in the CDA. Stepwise backward selection identified C13:0 iso, C14:0 iso, C17:0 anteiso, C18:0 iso and C17:0 + cis-9 C17:1 as valid predictors. The first two discriminant functions (DF) explained 82.2 and 13.9% of total variance. DF1 and DF2 differentiated milk samples by the non-forage NDF content and linseed oil supplementation of the diet, respectively. C14:0 iso and C17:0 anteiso were indicative of the diets with high non-forage NDF and starch contents, respectively. C17:0 + cis-9 C17:1 and both C18:0 iso and C13:0 iso contributed to identify the diets with and without added linseed oil, respectively. In conclusion, CDA allowed to identify which milk OBCFA were the best indicators of the starch/non-forage NDF ratio and the presence of linseed oil in the diets fed to dairy goats.

Relationship between milk odd and branched-chain fatty acids and urinary purine derivatives in dairy cows supplemented with quebracho tannins—A study to test milk fatty acids as predictors of rumen microbial protein synthesis

The purpose of this study was to explore the potential of milk odd and branched-chain fatty acids (OBCFA) as biomarkers for rumen microbial protein synthesis in dairy cows, and to study the effects of diets supplemented with different levels of quebracho tannin extract (QTE) on milk OBCFA.The experiment included 50 lactating German Holstein dairy cows divided into two groups of 25 animals each and lasted for six consecutive periods of 21 days (13 days of adaptation and 8 days of feed, milk, and urine sampling). The basal diet was a total mixed ration with a constant forage to concentrate ratio of 65:35 (Control, without QTE). A commercial QTE product was added to the basal diet at 15g and 30g/kg dry matter to create diets QTE15 and QTE30, respectively. Milk fat samples were analysed for OBCFA contents and urine for purine derivatives (PD), nitrogen (N), and creatinine concentrations.The QTE addition increased the concentrations of creatinine and the ratio between total PD and N in urine, whereas the concentrations of allantoin, total PD, and N in urine decreased with QTE addition. Similarly, addition of QTE decreased the proportions (g/100g fat) and yields (g/d) of milk OBCFA, with the exception of anteiso-C15:0 and anteiso-C17:0.Multivariate models to predict concentrations and ratios of PD, N, and creatinine in urine from milk OBCFA explained between 10% and 40% of the variance in the dataset of each predicted parameter. However, the explanation of that variance attributed to milk OBCFA was only between 2% and 26%. For most parameters, models developed from milk OBCFA proportions explained more variance in the dataset than those developed from OBCFA yields. Our findings suggest that milk OBCFA are poor indicators of rumen microbial protein synthesis in dairy cows.

Postruminal synthesis modifies the odd- and branched-chain fatty acid profile from the duodenum to milk

Milk odd- and branched-chain fatty acids (OBCFA) have been suggested as potential biomarkers for rumen function. The potential of milk OBCFA as a biomarker depends on whether their profile reflects the profile observed in the duodenum. The objective of this study was to evaluate whether the OBCFA profile in duodenum samples is reflected in plasma and milk. For this, 2 dairy cattle experiments were used. In experiment 1, 4 Holstein cows fitted with rumen and proximal duodenum cannulas were used in a 4×4 Latin square design. The treatments consisted of 2 nitrogen levels (143 vs. 110g of crude protein/kg of dry matter for high and low N, respectively) combined with either 1 of the 2 energy sources (i.e., starch from barley, corn, and wheat or fiber from soybean hulls and dehydrated beet pulp). In experiment 2, 4 Holstein cows fitted with rumen and proximal duodenum cannulas were used in a 3×3 Latin square design, with the treatments consisting of 3 diets: (1) RNB−, a diet with a crude protein content of 122g/kg of dry matter, predicted to provide protein digested in the small intestine according to the requirement of the animals, but with a shortage of rumen degradable protein; (2) RNB− to which 6g/d of niacin was added through inclusion in the mineral and vitamin premix, and (3) RNB− to which urea was added to balance rumen degradable N supply resulting in a CP content of 156g/kg of dry matter. In both experiments, samples of duodenal digesta, plasma, and milk were collected and analyzed for fatty acids. Additionally, lipids in plasma samples were separated in lipid classes and analyzed for fatty acids. The OBCFA profile in milk was enriched in 15:0, iso-17:0, anteiso-17:0, and cis-9–17:1 as compared with duodenal samples, and milk secretions even exceeded duodenal flows, which suggests occurrence of postruminal synthesis, such as de novo synthesis, desaturation, and elongation. The postruminal modification of the OBCFA profile might hamper the application of OBCFA as diagnostic tools of rumen function.

Milk odd- and branched-chain fatty acids as biomarkers of rumen function—An update

The main odd- and branched-chain fatty acids (OBCFA) in milk of dairy cows are isomers of tridecanoic acid (iso C13:0), tetradecanoic acid (iso C14:0), pentadecanoic acid (C15:0, iso C15:0 and anteiso C15:0), hexadecanoic acid (iso C16:0) and heptadecanoic acid (C17:0, iso C17:0 and anteiso C17:0). OBCFA are suggested to reflect rumen function (e.g. ruminal fermentation pattern, including methane, duodenal flow of microbial protein and acidosis). This relies on their predominant origin, i.e. bacteria leaving the rumen. The OBCFA are synthesized de novo by ruminal bacteria and incorporated in their cell membrane, suggesting a direct relation with bacterial biomass. Their potential as duodenal markers to quantify bacterial protein is strengthened by their constant relation with bacterial N content over a diversity of bacterial groups. From a limited database, evidence was shown of a useful relation of milk OBCFA yield with microbial protein flow from the rumen, but more research is needed to elucidate some discrepancies under diverse dietary regimes.Further, variation in the OBCFA profile of pure strains of ruminal bacteria were reported and are, in the current review, linked with their production of metabolites. From this, it can be assumed that the rumen fermentation pattern is related to the rumen OBCFA profile, which seems consistent for milk OBCFA. The close stoichiometric relation between ruminal VFA and methane further opens perspective for the use of OBCFA profiles in milk to quantify methane emissions. OBCFA consistently contributing to the predictive models, irrespective of the modeling approach are: iso C14:0 and iso C15:0, which positively relate to acetate and methane and negatively to propionate; and C15:0 and C17:0 which show an inverse relationship. Anteiso C15:0 seemed only relevant in the prediction of butyrate proportions.As changes in the ruminal microbial population (e.g. increased dominance of Streptococcus bovis) sometimes initiate a chain of events that eventually might lead to (sub-acute) ruminal acidosis, OBCFA in milk fat are targeted as candidates for the early detection of ruminal acidosis. Increasing C17:0+C17:1 cis-9 and decreasing iso C14:0 concentration show potential as indicators of sub-acute acidosis or were obvious before clinical symptoms of acute acidosis occurred. Collection of more experimental data is currently on-going for the development of more robust models to classify rumen health in continuous probability classes rather than discrete acidotic vs. non-acidotic cases.

Relationships between odd- and branched-chain fatty acid profiles in milk and calculated enteric methane proportion for lactating dairy cattle

The purpose of this study was to explore the relationships between odd- and branched-chain fatty acids (OBCFA) in milk with calculated enteric CH4 production for lactating dairy cows using multiple linear regression (MLR), partial least squares regression (PLS) and a genetic algorithm approach (GA). A dataset collected from 13 experiments containing 224 paired observations of measured acetate, propionate and butyrate proportions in rumen fluid VFA and 7 measured OBCFA was used. Methane proportion (mmol/mol VFA) was calculated from acetate, propionate and butyrate and expressed relative to the sum of these volatile fatty acids (VFA). Calculated CH4 production was related to milk OBCFA using MLR and PLS, resulting in a linear prediction model. The GA approach resulted in a model which predicted rumen VFA proportions of total VFA from milk OBCFA. Methane proportion was calculated from predicted acetate, propionate and butyrate proportions in total VFA based on rumen stoichiometry and compared with CH4 proportion calculated from measured VFA proportions. The prediction error was low (i.e., root mean square prediction error <5%), and models captured up to 66% of the variance in the data and the concordance correlation coefficient was close to 0.8. The variance of the prediction error was less than 40% of the variance of the calculated CH4 proportion. Seven milk OBCFA were initially considered as predictors, from which the branched-fatty acids iso C14:0, iso C15:0, iso C16:0 were positively related to calculated enteric CH4 production and the odd-fatty acids C15:0 and the sum of C17:0 and C17:1 cis–9 were negatively related to it. Relationships in this large data set identify the most relevant OBCFA in milk as potential predictors of rumen methanogenesis.This paper is part of the special issue entitled: Greenhouse Gases in Animal Agriculture – Finding a Balance between Food and Emissions, Guest Edited by T.A. McAllister, Section Guest Editors; K.A. Beauchemin, X. Hao, S. McGinn and Editor for Animal Feed Science and Technology, P.H. Robinson.

Effect of Lactation Stage on the Odd- and Branched-Chain Milk Fatty Acids of Dairy Cattle Under Grazing and Indoor Conditions

The pattern of odd- and branched-chain fatty acids (OBCFA) in milk fat reflects rumen microbial activity and proportions of different rumen microbial groups. Therefore, these milk fatty acids (FA) are used to predict rumen proportions of volatile fatty acids, duodenal flow of microbial protein, and occurrence of rumen acidosis. However, current models do not correct for the potential effects of lactation stage on the level of OBCFA in milk fat. Hence, the objectives of this study were 1) to describe progressive changes related to lactation stage in concentrations of milk FA, with emphasis on the OBCFA, using the incomplete gamma function of Wood, and 2) to analyze whether lactation curves of milk FA on the one hand and milk production or milk fat content on the other hand coincide through evaluation of the correlation between the parameters of the Wood functions fitted to individual animal data. Data were collected from 2 trials in which milk FA during lactation were monitored. The first experiment was a stable trial with 2 groups of 10 cows receiving 2 dietary treatments from wk 1 to 40 of lactation. The second experiment was a grazing trial with 9 cows that were followed during the first 18 wk of lactation. Lactation curves of milk production, milk fat content, and individual milk FA were developed using the incomplete gamma function of Wood for each of the 3 dietary strategies separately. For almost all of the milk FA, lactation curve shapes were similar for all 3 dietary treatments. The OBCFA with chain lengths of 14 and 15 carbon atoms followed the lactation curves of the short- and medium-chain milk FA, which increased in early lactation. The OBCFA with chain length of 17 carbon atoms decreased during the early lactation period, following the pattern of milk long-chain fatty acids. The short- and medium-chain milk FA and OBCFA in the early lactation period seemed to be negatively correlated with the starting milk production and milk fat content, but correlations were modest. Information of milk FA lactation curves should be incorporated in predictive and classification models based on these milk FA, to improve their performance.

Apparent Recovery of Duodenal Odd- and Branched-Chain Fatty Acids in Milk of Dairy Cows

This study compared flows of odd- and branched-chain fatty acids (OBCFA) at the duodenum with corresponding yields in milk. Four mid-lactation Holstein-Friesian dairy cows were offered 4 dietary treatments, based on different ratios of ryegrass silage and concentrates (80:20, 65:35, 50:50, and 35:65 on a dry matter basis), in a 4×4 Latin square design experiment with 4-wk periods. Samples of milk and duodenal digesta were collected during the final week of each period and analyzed for fatty acids. Biohydrogenation of linoleic and α-linolenic acids (C18:2 and C18:3) was extensive for all treatments, with a tendency to be lower for C18:3 with increased concentrate feeding. The proportion of duodenal flows of these fatty acids that appeared in milk declined with increasing concentrate feeding. There was little change in the yield of OBCFA in milk in response to increasing level of concentrate inclusion and no significant relationship with the yield of microbial protein at the duodenum. The efficiency of transfer of iso C15:0 and anteiso C15:0 from the duodenum to milk was similar to that for C18:3, with a reduced proportion transferred into milk at higher flows. Yields of C15:0, C17:0, and iso C17:0 in milk were higher than duodenal flows, confirming synthesis in animal tissues.