Effect of exogenous long-chain fatty acids on lipid biosynthesis in dispersed ruminant mammary gland epithelial cells: esterification of long-chain exogenous fatty acids

Potential Role of Lauric Acid in Milk Fat Synthesis in Chinese Holstein Cows Based on Integrated Analysis of Ruminal Microbiome and Metabolome

The composition and metabolic profile of the ruminal microbiome have an impact on milk composition. To unravel the ruminal microbiome and metabolome affecting milk fat synthesis in dairy cows, 16S rRNA and internal transcribed spacer (ITS) gene sequencing, as well as ultra-high performance liquid chromatography-mass spectrometry (UHPLC-MS/MS) methods were used to investigate the significant differences in ruminal bacterial and fungal communities as well as metabolome among Chinese Holstein cows with contrasting milk fat contents under the same diet (H-MF 5.82 ± 0.41% vs. L-MF 3.60 ± 0.12%). Another objective was to culture bovine mammary epithelial cells (BMECs) to assess the effect of metabolites on lipid metabolism. Results showed that the acetate-to-propionate ratio and xylanase activity in ruminal fluid were both higher in H-MF. Microbiome sequencing identified 10 types of bacteria and four types of fungi differently abundant at the genus level. Metabolomics analysis indicated 11 different ruminal metabolites between the two groups, the majority of which were lipids and organic acids. Among these, lauric acid (LA) was enriched in fatty acid biosynthesis with its concentration in milk fat of H-MF cows being greater (217 vs. 156 mg per 100 g milk), thus, it was selected for an in vitro study with BMECs. Exogenous LA led to a marked increase in intracellular triglyceride (TG) content and lipid droplet formation, and it upregulated the mRNA abundance of fatty acid uptake and activation (CD36 and ACSL1), TG synthesis (DGAT1, DGAT2 and GPAM), and transcriptional regulation (SREBP1) genes. Taken together, the greater relative abundance of xylan-fermenting bacteria and fungi, and lower abundance of bacteria suppressing short-chain fatty acid-producing bacteria or participating in fatty acid hydrogenation altered lipids and organic acids in the rumen of dairy cows. In BMECs, LA altered the expression of genes involved in lipid metabolism in mammary cells, ultimately promoting milk fat synthesis. Thus, it appears that this fatty acid plays a key role in milk fat synthesis.

Stearic acid does not overcome conjugated linoleic acid trans-10, cis-12-induced milk fat depression in lactating ewes

The objective of this study was to test the hypothesis that stearic acid (SA) supplementation increases milk fat content and overcomes the antilipogenic effects of trans-10, cis-12 conjugated linoleic acid (CLA) in lactating ewes. Twenty-eight Lacaune ewes (36 (sd 2) days in lactation; 70·5 (sd) 9·6 kg of body weight), producing 1·8 (sd 0·4) kg of milk/d, were used in a completely randomised design (seven ewes/treatment) for 21 d. The treatments were: (1) Control; (2) CLA (6·4 g/d of trans-10, cis-12 CLA); (3) SA (28 g/d of SA) and (4) SA in association with trans-10, cis-12 CLA (CLASA; 6·4 g/d of trans-10, cis-12 CLA plus 28 g/d of SA). All data were analysed using a mixed model that included the fixed effect of treatment and the random effect of ewe. SA did not alter milk fat content and yield relative to Control (91·9 v. 91·2 (sd 4·1) g/d). CLASA was not able to overcome the reduction in fat content and fat yield induced by CLA (75 v. 82 (sd 0·14) g/d). SA increased the relative abundance of CD36, fatty acid-binding protein 4 (FABP4) and PPAR-γ mRNA by 140, 112 and 68 % compared with CLASA. SA also reduced the relative abundance of acetyl-CoA carboxylase α promoter II and stearoyl-CoA desaturase (SCD) when compared with Control (45 and 39 %). Compared with CLA, CLASA treatment had no effect on the mRNA abundance of fatty acid synthase, lipoprotein lipase, CD36, SCD, FABP4, acylglycerolphosphate acyltransferase 6, sterol regulatory element-binding protein 1 and PPAR-γ. In conclusion, SA supplementation did not increase milk fat synthesis and did not overcome the CLA-induced milk fat depression when associated with trans-10, cis-12 CLA.

Compositional and functional properties of milk and dairy products derived from cows fed pasture or concentrate-based diets

Worldwide milk production is predominantly founded on indoor, high-concentrate feeding systems, whereas pasture-based feeding systems are most common in New Zealand and Ireland but have received greater attention recently in countries utilizing conventional systems. Consumer interest in 'pasture-fed' dairy products has also increased, arising from environmental, ethical, and nutritional concerns. A substantial body of research exists describing the effect of different feeding strategies on the composition of milk, with several recent studies focusing on the comparison of pasture- and concentrate-based feeding regimes. Significant variation is typically observed in the gross composition of milk produced from different supplemental feeds, but various changes in the discrete composition of macromolecular components in milk have also been associated with dietary influence, particularly in relation to the fatty acid profile. Changes in milk composition have also been shown to have implications for milk and dairy product processability, functionality and sensory properties. Methods to determine the traceability of dairy products or verify marketing claims such as 'pasture-fed' have also been established, based on compositional variation due to diet. This review explores the effects of feed types on milk composition and quality, along with the ultimate effect of diet-induced changes on milk and dairy product functionality, with particular emphasis placed on pasture- and concentrate-based feeding systems.

Effect of feeding a palmitic acid-enriched supplement on production responses and nitrogen metabolism of mid-lactating Holstein and Jersey cows

This study evaluated the effect of feeding a palmitic acid-enriched supplement on production responses and nitrogen metabolism of mid-lactating Holstein and Jersey cows. Eighty mid-lactating dairy cows, 40 Holstein and 40 Jersey, were used in a randomized complete block design with a split-plot arrangement; the main plot was breed and the subplot was fatty acid treatment. Cows within each breed were assigned to 1 of 2 treatments: (1) control diet with no fat supplement or (2) control diet plus a palmitic acid-enriched supplement dosed at 1.5% of diet dry matter (PA treatment). The treatment period was 6 wk with the final 3 wk used for data and sample collection. There were no treatment × breed interactions for the variables analyzed. Compared with control, PA treatment increased milk fat yield (1.36 vs. 1.26 kg/d) and tended to increase 3.5% fat-corrected milk (35.6 vs. 34.0 kg/d) and energy-corrected milk (35.7 vs. 34.1 kg/d). There was no effect of PA treatment on dry matter intake, milk yield, milk protein yield, milk lactose yield, body condition score, body weight (BW) change, nitrogen intake, and variables related to nitrogen metabolism and excretion. Compared with Holstein cows, Jersey cows had greater dry matter intake as a percent of BW (4.90 vs. 3.37% of BW) and lower milk production (29.6 vs. 32.7 kg/d) and milk lactose yield (1.58 vs. 1.42 kg/d), but tended to have greater milk fat yield (1.36 vs. 1.26 kg/d). There was a breed effect on BW change; Holstein cows gained 0.385 kg/d during the experiment, and Jersey cows gained 0.145 kg/d. Jersey cows had lower nitrogen intake (636 vs. 694 g/d), blood urea nitrogen (12.6 vs. 13.8 mg/dL), urine total nitrogen (125 vs. 145 g/d), and urine total nitrogen as a percent of nitrogen intake (19.5 vs. 21.1%). Overall, feeding a palmitic acid-enriched supplement increased milk fat yield as well as dry matter and fiber digestibility in both Holstein and Jersey cows. The PA treatment did not have any major effects on nitrogen metabolism in both Holstein and Jersey cows. In addition, our results indicated that Jersey cows had lower urinary nitrogen excretion (g/d) than Holstein cows.

Impact of post-ruminally infused macronutrients on bovine mammary gland expression of genes involved in fatty acid synthesis, energy metabolism, and protein synthesis measured in RNA isolated from milk fat

Background

Characterising the regulation of milk component synthesis in response to macronutrient supply is critical for understanding the implications of nutritional interventions on milk production. Gene expression in mammary gland secretory cells was measured using RNA isolated from milk fat globules from 6 Holstein-Friesian cows receiving 5-d abomasal infusions of saline, essential amino acids (AA), or glucose (GG) or palm olein (LG) without (LAA) or with (HAA) essential AA, according to a 6 × 6 Latin square design. RNA was isolated from milk fat samples collected on d 5 of infusion and subjected to real-time quantitative PCR. We hypothesised that mRNA expression of genes involved in de novo milk fatty acid (FA) synthesis would be differently affected by GG and LG, and that expression of genes regulating transfer of tricarboxylic acid cycle intermediates would increase at the HAA level. We also hypothesised that the HAA level would affect genes regulating endoplasmic reticulum (ER) homeostasis but would not affect genes related to the mechanistic target of rapamycin complex 1 (mTORC1) or the integrated stress response (ISR) network.

Results

Infusion of GG did not affect de novo milk FA yield but decreased expression of FA synthase (FASN). Infusion of LG decreased de novo FA yield and tended to decrease expression of acetyl-CoA carboxylase 1 (ACC1). The HAA level increased both de novo FA yield and expression of ACC1, and tended to decrease expression of mitochondrial phosphoenolpyruvate carboxykinase (PCK2). mRNA expression of mTORC1 signaling participants was not affected by GG, LG, or AA level. Expression of the ε subunit of the ISR constituent eukaryotic translation initiation factor 2B (EIF2B5) tended to increase at the HAA level, but only in the presence of LG. X-box binding protein 1 (XBP1) mRNA was activated in response to LG and the HAA level.

Conclusions

Results show that expression of genes involved in de novo FA synthesis responded to glucogenic, lipogenic, and aminogenic substrates, whereas genes regulating intermediate flux through the tricarboxylic acid cycle were not majorly affected. Results also suggest that after 5 d of AA supplementation, milk protein synthesis is supported by enhanced ER biogenesis instead of signaling through the mTORC1 or ISR networks.

A 100-Year Review: Fat feeding of dairy cows

Over 100 years, the Journal of Dairy Science has recorded incredible changes in the utilization of fat for dairy cattle. Fat has progressed from nothing more than a contaminant in some protein supplements to a valuable high-energy substitute for cereal grains, a valuable energy source in its own right, and a modifier of cellular metabolism that is under active investigation in the 21st century. Milestones in the use of fats for dairy cattle from 1917 to 2017 result from the combined efforts of noted scientists and industry personnel worldwide, with much of the research published in Journal of Dairy Science. We are humbled to have been asked to contribute to this historical collection of significant developments in fat research over the past 100 years. Our goal is not to detail all the work published as each development moved forward; rather, it is to point out when publication marked a significant change in thinking regarding use of fat supplements. This approach forced omission of critically important names and publications in many journals as ideas moved forward. However, we hope that a description of the major changes in fat feeding during the past 100 years will stimulate reflection on progress in fat research and encourage further perusal of details of significant events.

Transcriptional regulation of milk lipid synthesis by exogenous C16:0 and C18 fatty acids in bovine mammary epithelial cells

The objective of this study was to examine the effects of removing one fatty acid from a combination of long-chain fatty acids (LCFA) on milk lipogenesis in bovine mammary epithelial cells. The incubation concentration of LCFA was determined, and 100 μmol L−1 of C16:0, 5 μmol L−1 of C18:0, 100 μmol L−1 of cis-9 C18:1, 25 μmol L−1 of n-6 C18:2, and 1.2 μmol L−1 of n-3 C18:3 were used in the study. Treatments were C16:0, C18:0, C18:1, C18:2, and C18:3 combinations as control; control absent of C16:0 as A-C16:0; control absent of C18:0 as A-C18:0; control absent of C18:1 as A-C18:1; control absent of C18:2 as A-C18:2; control absent of C18:3 as A-C18:3. Results showed that compared with control, fatty acid synthetase expression was reduced by A-C18:0 and A-C18:1. Palmitic acid decreased expression of lipoprotein lipase. Compared with control, the expression of stearoyl-coenzyme A desaturase-1 and cluster of differentiation 36 was reduced by all treatments. Peroxisome proliferator-activated receptor-α expression was down-regulated by A-C16:0, A-C18:0, A-C18:1, and A-C18:2. Sterol regulatory element binding factor-1 was decreased when treated with A-C18:0, A-C18:1, and A-C18:2. Cells lack of 18-carbon fatty acid synthesized lower amount of intracellular triglyceride compared with control.

Combined effects of oleic, linoleic and linolenic acids on lactation performance and the milk fatty acid profile in lactating dairy cows

The potential combined effects of oleic, linoleic and linolenic acids supplementation on lactation performance and the milk fatty acid (FA) profile in dairy cows have not been well investigated. Our objective was to examine the effects of supplementation with a combination of these FA as well as the effects of removing each from the combination on lactation performance and the milk FA profile in dairy cows. Eight Holstein cows (101±11 days in milk) received four intravenously infused treatments in a 4×4 Latin square design, and each period lasted for 12 days which consisted of 5 days of infusion and 7 days of recovery. The control treatment (CTL) contained 58.30, 58.17 and 39.96 g/day of C18 : 1 cis-9; C18 : 2 cis-9, cis-12; and C18 : 3 cis-9, cis-12, cis-15, respectively. The other three treatments were designated --C18 : 1 (20.68, 61.17 and 41.72 g/day of C18 : 1 cis-9; C18 : 2 cis-9, cis-12; and C18 : 3 cis-9, cis-12, cis-15, respectively), -C18 : 2 (61.49, 19.55 and 42.13 g/day of C18 : 1 cis-9; C18 : 2 cis-9, cis-12; and C18 : 3 cis-9, cis-12, cis-15, respectively) and -C18 : 3 (60.89, 60.16 and 1.53 g/day of C18 : 1 cis-9; C18 : 2 cis-9, cis-12; and C18 : 3 cis-9, cis-12, cis-15, respectively). Dry matter intake and lactose content were not affected by the treatments, but the milk protein content was lower in cows treated with -C18 : 2 than that in CTL-treated cows. Milk yield as well as milk fat, protein and lactose yields were higher in cows treated with -C18 : 3 than the yields in CTL-treated cows, and these yields increased linearly as the unsaturation degree of the supplemental FA decreased. Compared with the CTL treatment, the -C18 : 2 treatment decreased milk C18 : 2 cis-9 content (by 2.80%) and yield (by 22.12 g/day), and the -C18 : 3 treatment decreased milk C18 : 3 cis-9, cis-12, cis-15 content (by 2.72%) and yield (by 22.33 g/day). In contrast, removing C18 : 1 cis-9 did not affect the milk content or yield of C18 : 1 cis-9. The -C18 : 2-treated cows had a higher C18 : 1 cis-9 content and tended to have a higher C18 : 1 cis-9 yield than CTL-treated cows. The yields of C8 : 0, C14 : 0 and C16 : 0 as well as <C16 : 0 tended to increase linearly as the unsaturation degree of the supplemental FA decreased (P=0.06, 0.07, 0.07 and 0.09, respectively). These results indicated that supplementation with C18 unsaturated FA might not independently affect the lactation performance and the milk FA profile of dairy cows.

Nutrient digestibility and milk production responses to increasing levels of palmitic acid supplementation vary in cows receiving diets with or without whole cottonseed

Our study evaluated the dose-dependent effects of a palmitic acid-enriched supplement in basal diets with or without the inclusion of whole cottonseed on nutrient digestibility and production responses of dairy cows. Sixteen Holstein cows (149 ± 56 days in milk) were used in a split plot Latin square design experiment. Cows were blocked by 3.5% fat-corrected milk (FCM) and allocated to a main plot receiving either a basal diet with soyhulls (SH, = 8) or a basal diet with whole cottonseed (CS, = 8) that was fed throughout the experiment. A palmitic acid-enriched supplement (PA 88.5% C16:0) was fed at 0, 0.75, 1.50, or 2.25% of ration DM in a replicated 4 × 4 Latin Square design within each basal diet group. Periods were 14 d with the final 4 d used for data collection. PA dose increased milk fat content linearly, and cubically affected yields of milk fat and 3.5% FCM. The PA dose did not affect milk protein and lactose contents, BW, and BCS, but tended to increase yields of milk, milk protein, and milk lactose. Also, PA dose reduced DMI and 16-carbon fatty acid digestibility quadratically, and increased 18-carbon fatty acid digestibility quadratically. There were no effects of basal diet on the yield of milk or milk components, but DMI tended to decrease in CS compared with SH, increasing feed efficiency (3.5% FCM/DMI). Compared with SH, CS diets increased yield of preformed milk fatty acids and 16-carbon fatty acid digestibility, and tended to decrease 18-carbon fatty acid digestibility. We observed basal diet × PA dose interactions for yields of milk and milk protein and for 16-carbon and total fatty acid digestibility, as well as tendency for yields of milk fat and 3.5% FCM. Also, there was a tendency for an interaction between basal diet and PA dose for NDF digestibility, which increased more for CS with increasing PA than for SH. PA dose linearly decreased digestibility of total fatty acids in SH diets but did not affect it in CS diets Results demonstrate that responses to PA dose are affected by the dietary basal diet. Additionally, the decrease in fatty acid digestibility only in the SH diets suggests that digestibility is impacted mainly by the profile of 16- and 18-carbon fatty acids reaching the duodenum. Under the dietary conditions evaluated, the yield of 3.5% FCM and milk fat were optimal when PA was fed at 1.5% of ration DM.

Effect of fish-oil supplementation on levels of (n-3) poly-unsaturated fatty acids in the lipoprotein fractions of bovine plasma

Eight mid-lactation Holstein-Friesian dairy cows were used in an experiment to investigate whether poor transfer to milk of (n-3) long chain (≥C20) poly-unsaturated fatty acids (n-3 LCPUFA), from diets containing fish oil, is related to their mode of transport in plasma lipoproteins. The cows were split into two groups of four, each of which was housed with 24 other cows which did not provide blood data in this experiment. All cows received a basal diet ad libitum consisting of (kg/t dry matter) silage (539), grain distillers’ grains (148), rolled barley (248) and soya (65). All cows also received a mid-day meal of 2·76 kg per cow per day of molassed sugar-beet shreds. The control group (C) received no oil supplement but those in the treatment group (F) received 300 g per cow per day of fish oil absorbed onto the sugar-beet shreds. Fish oil inclusion progressively depressed milk fat concentration of the four cows from each group over the 3 weeks of the experiment so that levels were approximately 20 g/kg lower for cows in treatment F than for those in C (P < 0·05). Mean concentrations over all cows of the long-chain (≥C20, n-3) poly-unsaturated fatty acids in milk fat (g/100 g) were 0·12 and 0·54 for treatments C and F respectively, whilst corresponding output in milk (g/day) increased from 116 to 3·91, an average efficiency of transfer of 4·6%. The fatty acid compositions of the lipoproteins were measured in plasma samples from the four cows from each group after 3 weeks on the experimental diets The proportions (g/100 g fatty acids) of C20: 5 (n-3) in cholesteryl (CE) and phospholipid (PL) of high-density lipoprotein (HDL) in the plasma were respectively increased from 0·97 to 4·39 (P < 0·05) and from 1·15 to 4·74 (P < 0·01) by the fish-oil supplementation. For C22: 6 (n-3), the proportions in CE and PL of HDL respectively increased (P < 0·001) from 0·02 to 0·23 and from 0·16 to 2·18 as a result of the supplementation. The mean proportions (g/100 g fatty acids) of C20: 5 (n-3) and C22: 6 (n-3) in the triglyceride fraction of very low-density lipoprotein were 1·05 and 2·3 respectively and were not significantly altered by fish-oil supplementation (P > 0·05). It is suggested that the low transfer efficiency of (n-3) LCPUFA to the milk is partly due to their transport in the plasma largely as components of HDL lipids which are unavailable to the mammary gland.

Effects of Saturated Long-chain Fatty Acid on mRNA Expression of Genes Associated with Milk Fat and Protein Biosynthesis in Bovine Mammary Epithelial Cells

This study was conducted to determine the effects of saturated long-chain fatty acids (LCFA) on cell proliferation and triacylglycerol (TAG) content, as well as mRNA expression of αs1-casein (CSN1S1) and genes associated with lipid and protein synthesis in bovine mammary epithelial cells (BMECs). Primary cells were isolated from the mammary glands of Holstein dairy cows, and were passaged twice. Then cells were cultured with different levels of palmitate or stearate (0, 200, 300, 400, 500, and 600 μM) for 48 h and fetal bovine serum in the culture solution was replaced with fatty acid-free BSA (1 g/L). The results showed that cell proliferation tended to be increased quadratically with increasing addition of stearate. Treatments with palmitate or stearate induced an increase in TAG contents at 0 to 600 μM in a concentration-dependent manner, and the addition of 600 μM was less effective in improving TAG accumulation. The expression of acetyl-coenzyme A carboxylase alpha, fatty acid synthase and fatty acid-binding protein 3 was inhibited when palmitate or stearate were added in culture medium, whereas cluster of differentiation 36 and CSN1S1 mRNA abundance was increased in a concentration-dependent manner. The mRNA expressions of peroxisome proliferator-activated receptor gamma, mammalian target of rapamycin and signal transducer and activator of transcription 5 with palmitate or stearate had no significant differences relative to the control. These results implied that certain concentrations of saturated LCFA could stimulate cell proliferation and the accumulation of TAG, whereas a reduction may occur with the addition of an overdose of saturated LCFA. Saturated LCFA could up-regulate CSN1S1 mRNA abundance, but further studies are necessary to elucidate the mechanism for regulating milk fat and protein synthesis.

Feeding a C16:0-enriched fat supplement increased the yield of milk fat and improved conversion of feed to milk

Previous work has indicated that dietary palmitic acid (C16:0) may increase milk fat yield. The effect of a dietary C16:0-enriched fat supplement on feed intake, yield of milk and milk components, and feed efficiency was evaluated in an experiment with a crossover arrangement of treatments with 25-d periods. A fermentable starch challenge on the last 4d of each period was utilized as a split-plot within period. Sixteen mid-lactation Holstein cows (249 ± 33 d in milk) were assigned randomly to treatment sequence. Treatments were either a C16:0-enriched (~85% C16:0) fat supplement (fatty acid treatment, FAT, 2% dry matter) or a control diet (CON) containing no supplemental fat. Diets containing dry ground corn grain were fed from d 1 through 21 of each period. On the last 4d of each period, dry ground corn was replaced by high-moisture corn grain on an equivalent dry matter basis to provide a fermentable starch challenge. Response variables were averaged for d 18 to 21 (immediately before the fermentable starch challenge) and d 22 to 25 (during the fermentable starch challenge). We observed no treatment effects on milk yield or milk protein yield. The FAT treatment increased milk fat concentration from 3.88 to 4.16% and fat yield from 1.23 to 1.32 kg/d compared with CON. The FAT treatment decreased dry matter intake by 1.4 kg/d and increased conversion of feed to milk (3.5% fat-corrected milk yield/dry matter intake) by 8.6% compared with CON. The increase in milk fat yield by FAT was entirely accounted for by a 27% increase in 16-carbon fatty acid output into milk. Yields of de novo and preformed fatty acids were not affected by FAT relative to CON. The fermentable starch challenge did not affect milk fat concentration or yield. Results demonstrate the potential for a dietary C16:0-enriched fat supplement to improve milk fat concentration and yield as well as efficiency of conversion of feed to milk. Further studies are required to verify and extend these results and to determine whether responses are similar across different diets and levels of milk production.

Growth hormone alters lipid composition and increases the abundance of casein and lactalbumin mRNA in the MAC-T cell line

The MAC-T cell line has been used extensively to investigate bovine mammary epithelial cell function. A lactogenic phenotype is generally induced in this cell line by a combination of dexamethasone, insulin and prolactin and has typically been assessed by milk protein production. Few studies have focused on identifying other factors that may affect milk protein synthesis in the MAC-T cell line, and none have considered the lipid class distribution of MAC-T cells as a component of the lactogenic phenotype. Growth hormone (GH) has been shown to increase milk protein synthesis both in vivo and in mammary cell models, and has been shown to alter the lipogenic profile of mammary explant models. We tested the hypothesis that MAC-T cells would respond directly to GH and that the response would include alterations to the lipid class distribution as well as to milk protein gene expression, leading to a more appropriate model for mammary cell function than treatment with dexamethasone, insulin and prolactin alone. Differentiated cells expressed GH receptor mRNA, and addition of GH to the differentiation medium significantly induced production of alpha-s1 casein and alpha-lactalbumin mRNA. GH also significantly affected the proportion of triacylglycerol and sphingomyelin. These results indicate that GH is an important factor in inducing a lactogenic phenotype in the MAC-T cell line, and support the possibility of a direct effect of GH on milk synthesis in vivo.

Fatty acid composition and milk quality related to feeding Ca-saponified palm acid oil to different breeds of dairy cows

The effect of supplementing a normal dairy feed ration (3–4% fatty acid of DM) with saponified palm acid oil (soap) was investigated in two experiments. The first experiment was carried out in eight herds (four Jersey, four heavy breeds), where the diet was supplemented with 1·0 and 0·5 kg soap for cows in the first and last part of lactation, respectively. Taste and acid degree of milk were not affected, and no breed × soap interaction was found. Fatty acid composition in milk was only slightly but significantly affected. The content of short and medium chain fatty acids was reduced (3·5% unit) and was followed by an increase in the content of 16:0 and 18:1. The increase in 16:0 by the soap supplementation was smaller in Jersey cows than in the other breeds. In the second experiment the effect of supplementing diets either with 0·5 or 1·0 kg Ca-soap to cows in the first part of lactation was investigated in two herds of Danish Black and White cows. Acid degree and time for curd formation on renneting (K20) were significantly lowest at the highest soap inclusion. No general effect on the proportion of short and medium chain fatty acids in the milk fat was observed as a function of level of Ca-soap, but the proportion of 16:0 was increased. It is assumed that the very small effect on milk fatty acid composition obtained when the daily allowance of fatty acids was increased from 600 to ~ 1400 g per cow, is more or less a specific effect of dietary fat rich in palmitic acid and given in excess to the basic diet.

Expression and nutritional regulation of lipogenic genes in the ruminant lactating mammary gland

The effect of nutrition on milk fat yield and composition has largely been investigated in cows and goats, with some differences for fatty acid (FA) composition responses and marked species differences in milk fat yield response. Recently, the characterization of lipogenic genes in ruminant species allowed in vivo studies focused on the effect of nutrition on mammary expression of these genes, in cows (mainly fed milk fat-depressing diets) and goats (fed lipid-supplemented diets). These few studies demonstrated some similarities in the regulation of gene expression between the two species, although the responses were not always in agreement with milk FA secretion responses. A central role for trans-10 C18:1 and trans-10, cis-12 CLA as regulators of milk fat synthesis has been proposed. However, trans-10 C18:1 does not directly control milk fat synthesis in cows, despite the fact that it largely responds to dietary factors, with its concentration being negatively correlated with milk fat yield response in cows and, to a lesser extent, in goats. Milk trans-10, cis-12 CLA is often correlated with milk fat depression in cows but not in goats and, when postruminally infused, acts as an inhibitor of the expression of key lipogenic genes in cows. Recent evidence has also proven the inhibitory effect of the trans-9, cis-11 CLA isomer. The molecular mechanisms by which nutrients regulate lipogenic gene expression have yet to be well identified, but a central role for SREBP-1 has been outlined as mediator of FA effects, whereas the roles of PPARs and STAT5 need to be determined. It is expected that the development of in vitro functional systems for lipid synthesis and secretion will allow future progress toward (1) the identification of the inhibitors and activators of fat synthesis, (2) the knowledge of cellular mechanisms, and (3) the understanding of differences between ruminant species.

Acetyl CoA Carboxylase Shares Control of Fatty Acid Synthesis with Fatty Acid Synthase in Bovine Mammary Homogenate

The objectives of this research were to determine the flux control coefficients for acetyl CoA carboxylase and fatty acid synthase using an in vitro preparation of bovine mammary homogenate. For an enzyme to be considered rate limiting with the use of metabolic control analysis, its control coefficient would be equal to unity. The hypothesis for this experiment was that the control coefficient for acetyl CoA carboxylase was not equal to unity, and that this enzyme was not, therefore, the rate-limiting step. Mammary tissue was isolated from lactating Holstein cows at slaughter and frozen in liquid nitrogen. Tissue was ground, homogenized, and centrifuged to obtain a postmitochondrial supernatant for use in in vitro incubations containing labeled acetate. Specific inhibitors for acetyl CoA carboxylase and fatty acid synthase were used to fractionally inhibit de novo synthesis for the calculation of flux control coefficients. The composition of fatty acids synthesized in the absence of enzyme inhibitors was similar to the composition of fatty acids in the presence of inhibitors. Calculations following avidin inhibition of acetyl CoA carboxylase determined the flux control coefficient was 0.63 +/- 0.15, which means that 63% of the control of fatty acid synthesis is exerted by acetyl CoA carboxylase. The remaining control (37%) was from fatty acid synthase, which indicates a significant degree of control over the flux of acetate in de novo synthesis resides with this enzyme. The rate-limiting status ascribed to acetyl CoA carboxylase was not supported, because the flux control coefficient was less than unity. Metabolic control analysis, through its use of pathway product measurements, allows for potential interactions in the pathway such as feedback inhibition contribution to the flux control coefficients, which would not otherwise be considered in studies measuring enzyme kinetics with purified enzymes.

Effects of duodenal infusions of palmitic, stearic, or oleic acids on milk composition and physical properties of butter

Four dairy cows fitted with a duodenal cannula were used in a 4 x 4 Latin square design to investigate the effects of daily duodenal infusion of 500 g of fatty acids (containing mainly C16:0, C18:0, or cis-C18:1) on fecal concentrations of fatty acids, fatty acid profiles of milk fat, and solid fat content of butter. Fecal concentrations of C16:0 and especially of C18:0 were increased by duodenal infusion. Infusion with C16:0 increased the proportion of C16:0 in milk fat and delayed softening of butter when the temperature rose. Infusion with C18:0 resulted only in a slight increase of C18:0 proportion in milk fat and did not significantly affect solid fat in butter between -10 and 30 degrees C. With the infusion of cis-C18:1, the proportion of cis-C18:1 in milk fat was more than twice that of control, to the detriment of C16:0. Butter contained low proportion of solid fat, even at low temperatures. Increasing C16:0 or cis-C18:1 in milk fatty acid via duodenal infusion can be used to study their specific effects on butter characteristics, but, because of a low transfer from infusion to milk, this method is less efficient with C18:0.

Targets and procedures for altering ruminant meat and milk lipids

Beef and dairy products suffer from a negative health image, related to the nature of their lipid fraction. Rumen lipid metabolism involves the presence of saturated lipids in ruminant tissues. Lipolysis, fatty acid biohydrogenation and formation of microbial fatty acids in the rumen and their effects on rumen outflow of fatty acids are discussed. Special emphasis is given to the formation of trans-fatty acids and the possibilities of decreasing biohydrogenation. Small differences in intestinal digestibilities of fatty acids are mentioned, followed by a discussion on transfer of absorbed fatty acids into milk and adipose tissue lipids. The preferential retention of polyunsaturated fatty acids as well as the balance between synthesis and incorporation of fatty acids in tissues is described. Dietary means for the modification of milk fat are listed, with special emphasis on the possibilities for enrichment in polyunsaturated fatty acids and the presence of conjugated linoleic acids. A description of the nature and development of fat depots in beef cattle is followed by a discussion of breed, conformation and feed effects on adipose tissue distribution and fatty acid composition. Special emphasis is given to the very lean Belgian Blue double-muscled breed. The review ends with a consideration of the limits to the modification of ruminant fats, involving considerations of consumer acceptance as well as animal welfare and environmental effects.

Duodenal infusions of palmitic, stearic or oleic acids differently affect mammary gland metabolism of fatty acids in lactating dairy cows

The effect of dietary lipids on the fatty acid (FA) profile of cows' milk fat is mainly dependent on digestive processes and mammary gland uptake and metabolism of FA. The objective of this study was to determine the separate effects of high arterial concentrations of 16:0, 18:0 and cis-18:1(n-9) on uptake, synthesis and 18:0 desaturation rate in the mammary gland of lactating dairy cows, via arterio-venous differences and mammary gland balance of FA. In a 4 x 4 Latin square, four lactating Holstein cows with cannula in the proximal duodenum were infused duodenally with a mixture providing daily 0 (C treatment) or 500 g FA with mainly 16:0 (P treatment), 18:0 (S treatment) or cis-18:1(n-9) (O treatment). Significantly higher arterial concentrations of infused FA in arterial plasma nonesterified FA and triglycerides (NETGFA) were observed with P and O treatments, but the effect of the S treatment was much lower. Arterio-venous differences of NETGFA increased with arterial concentrations. The number of synthesized FA in the mammary gland was not significantly affected by duodenal infusion of FA. Mean chain length was significantly reduced by P and O treatments, suggesting an effect of mammary gland uptake of long-chain FA on the termination process of mammary gland synthesis of FA. Across all treatments, 4:0 mammary gland balance increased linearly (r = 0.67, P = 0.004) with mammary gland FA uptake. Mammary gland desaturation of 18:0 to cis-18:1(n-9) averaged 52% and was not significantly affected by treatments, but was reduced by trans-18:1 mammary gland uptake. Uptake, synthesis and desaturation of FA by the mammary gland of dairy cows are affected by arterial concentrations of 16:0, 18:0 and cis-18:1(n-9).

An in vitro approach to ruminant mammary gland biology

This review discusses both fundamental and applied in vitro studies on ruminant mammary gland biology and summarizes progress made over the last decade in development of in vitro techniques to study growth, function and pathology of the mammary gland. The advantages and limitations of different in vitro systems are considered including explant cultures, primary cell cultures and immortalized lines of mammary-derived cells from cow, sheep and goat. The cell growth, differentiation and response to lactogenic hormones and growth factors are discussed as well as the relevance of the cell behavior in different culture conditions.

Regulation of milk lipid secretion and composition

Triacylglycerols make up 98% of the lipid content of milk, ranging in different species from 0 to 50% of the total milk volume. The fatty aid composition of the triacylglycerols depends on the species, the dietary fatty acid composition, and the carbohydrate-to-lipid ratio of the diet. The rate of lipid synthesis in the lactating mammary gland depends on the stage of mammary development and is decreased by fasting and starvation in ruminants and rodents but not in species that fast during lactation, such as seals and hibernating bears. Regulatory agents include insulin, prolactin, and non-esterified fatty acids. Dietary trans fatty acids may depress milk lipid synthesis under certain conditions. Evidence is presented that fatty acids may play a major regulatory role in acute changes in de novo mammary fatty acid synthesis, acting primarily on the activity of acetyl coenzyme A carboxylase.

Differential effects of high fat diets on fatty acid composition in milk of Jersey and Holstein cows

Effects of increasing dietary intake of calcium salts of palm fatty acid distillate (0, .25, .50, and .75 kg/d) on milk yield and milk fat composition were investigated for Jersey and Holstein cows. Increased dietary fat decreased DMI but did not influence milk yield or fat and protein contents. Jersey milk fat contained a higher proportion of short- and medium-chain fatty acids and lower proportions of palmitic and oleic fatty acids than did Holstein milk fat. With few exceptions, increased dietary fat altered the proportions of milk fatty acids in a parallel manner in both breeds. Except for butyrate, for which an effect was inconsistent, and palmitate, which was increased, additional dietary fat inhibited de novo synthesis of the milk fatty acids. The inhibition increased as the chain length of the fatty acids increased. Additional dietary fat increased the ratio of C18:1:C18:0 in Holstein cows, but the ratio was unchanged by dietary fat in Jersey cows. The regulation of fluidity of milk fat may differ between the two breeds.

Duodenal infusion of rapeseed oil in midlactation cows. 6. Interaction with niacin on dairy performance and nutritional balance

Rapeseed oil and niacin, alone or in combination, were infused continuously into the proximal duodenum of ruminally and duodenally fistulated midlactation cows in a 4 x 4 Latin square design. Although niacin in plasma was higher for cows infused with niacin no significant effect occurred on milk production and composition. When cows were infused with oil, milk production and fat content were unchanged, milk protein content was decreased, and lactose content was increased. The magnitude of decrease in the percentage of medium-chain fatty acids in milk of cows infused with oil was similar to the magnitude of the increase in the long-chain fatty acids of milk. Except for the decrease in milk C4:0 and the increase in C14:0 and C14:1 percentages, niacin did not exert a significant influence on the fatty acid profile of milk. Oil-free DMI tended to decrease in the cows that were infused with oil, but nutrient digestibility was unchanged with all infusates. Energy and protein intake and energy balance were similar, but protein balance tended to be higher with oil infusion. However, body condition score was decreased by oil infusion. For midlactation cows that received oil infusion, the limitation in DMI or the direct effect of absorbed fatty acids limited milk protein synthesis and body condition score. Effectiveness of postruminal niacin (alone or with oil) at midlactation is questioned.

Changes in mammary uptake of free fatty acids, triglyceride, cholesterol and phospholipid in relation to milk synthesis during lactation in goats

Uptake of free fatty acids (FFA), triglycerides (TG), cholesterol (CHOL) and phospholipids (PL) was measured in both mammary glands of dairy goats during lactation. Arterial concentrations of TG, CHOL and PL as well as arterio-venous difference (AV) and extraction rate (E) for TG were highest in goats with the highest dietary feed intake. AV were linearly related to arterial concentrations for the four lipid classes, and arterial concentrations of CHOL were linearly related to output of lactose, protein and fat in milk. Arterial supply, and not mammary synthetic activity, is the main determinant of mammary FFA, TG and CHOL uptake.

Feed and animal factors influencing milk fat composition

Genetic selection for increased milk fat percentage leads to increased proportions of short-chain fatty acids in milk fat and decreased proportions of long-chain fatty acids. Milk fat composition is strongly influenced by stage of lactation; proportion of short chains (de novo synthesis) is low initially and increases until at least 8 to 10 wk into lactation. Milk fat composition is changed more by the amount and composition of dietary fat than any other dietary component. Seasonal and regional differences in milk fat composition are measurable, most likely because of local differences in feed supplies. Milk fat composition can be modified readily by changing the feeding regimen. The most significant changes in milk fat quality relate to rheological (melting) properties, which influence numerous aspects of character and quality of manufactured dairy products. Dietary fat fed to change milk fat composition may also influence contents of protein, urea, citrate, and soluble calcium in milk and influence oxidative stability and flavor. It is important for both dairy nutritionists and dairy food chemists to understand the consequences of feeding programs on milk quality.

Effects of feeding diets containing calcium salts of long-chain fatty acids to lactating dairy cows

Four cows were utilized in a 4 x 4 Latin square design to investigate the effects of feeding Ca salts of long-chain fatty acids. Treatments were control diet with 1) no added fat, 2) 3% Ca salts of long-chain fatty acids, 3) 6% Ca salts of long-chain fatty acids, and 4) 9% Ca salts of long-chain fatty acids. Cows were fed chopped alfalfa hay, alfalfa haylage, corn silage, and concentrate (15:22:13:50) on a DM basis. Dry matter intake, energy intake, and ruminal fermentation were not altered greatly until Ca salts of long-chain fatty acids constituted 9% of DMI. Digestibilities of DM, OM, ADF, NDF, and hemicellulose were not affected by treatment. Digestibilities of cellulose, soluble residue, total C18 fatty acids, and total fatty acids followed quadratic patterns. Absorption of N was increased linearly when fat was fed, but digestibility of Ca was decreased linearly. Milk production, CP, and SNF were not altered greatly by inclusion of 3 or 6% Ca salts of long-chain fatty acids in the diet, but inclusion of 9% Ca salts of long-chain fatty acids decreased their production. Calcium salts of long-chain fatty acids increased milk fat percentage and production of fat and FCM when fed as 3 or 6% of the dietary DM but decreased yields of milk fat and FCM when fed as 9%. Calcium salts of fatty acids can be fed to provide up to 6% of the dietary DM without deleterious effects on ruminal fermentation and digestibilities of most nutrients.

Duodenal rapeseed oil infusion in early and midlactation cows. 5. Milk fatty acids and adipose tissue lipogenic activities

Lipogenic activities of perirenal adipose tissue were investigated in early (wk 3) and midlactation (wk 19 to 26) cows that received a duodenal rapeseed oil infusion (1.0 to 1.1 kg/d). In midlactation, oil infusion resulted in a decreased rate of fatty acid synthesis from acetate and a decreased rate of the activities of fatty acid synthetase and glucose-6-phosphate dehydrogenase, whereas lipoprotein lipase activity tended to increase. The rate of glucose incorporation into glyceride-glycerol and the activities of glycerol-3-phosphate dehydrogenase and malic enzyme were not significantly affected. Fatty acid C14:0 content of perirenal adipose tissue was decreased, and fatty acid C18:2 and C18:3 contents were increased in oil-infused cows. In early lactation, rates of acetate incorporation into fatty acids and activities of fatty acid synthetase and lipoprotein lipase were very low. Activities of glucose-6-phosphate dehydrogenase and glycerol-3-phosphate dehydrogenase were lower in the early than in the midlactation trial. Oil infusion did not change the measured parameters. In both trials, percentages and yields of milk fatty acids C18:1, C18:2, and C18:3 were increased, whereas those of C14:0 and C16:0 were decreased by oil. Calculated transfer rates of absorbed fatty acid C18:2 from oil to milk fat were 16 to 26%. Results suggested that oil fatty acids affected adipose and mammary de novo lipogenesis in a direct way without affecting fatty acid esterification in adipose tissue or total fat secretion in mammary tissue.

Effect of exogenous long-chain fatty acids on individual fatty acid synthesis by dispersed ruminant mammary gland cells

We investigated the effect of exogenously added fatty acids on de novo synthesis of individual fatty acids and their incorporation into triacylglycerols by dispersed lactating ruminant mammary gland epithelial cells. Palmitate addition strongly stimulated synthesis and incorporation of butyrate and, to a smaller extent, palmitate synthesis and incorporation. Oleic acid strongly inhibited synthesis of all fatty acids except butyrate, whereas the effect of lauric acid was nearly neutral. Free fatty acid depletion of the mammary gland cells potentiated the effect of palmitate and made oleate less inhibitory.