Trans-9, Cis-11 Conjugated Linoleic Acid Reduces Milk Fat Synthesis in Lactating Dairy Cows

Dietary supplementation of Aloe vera extract modulates rumen microbes and improves the functional food value of milk by altering phenolic content, antioxidant capacity, and fatty acid profile in lactating goats

Twenty-four cross-breed (Alpine × Beetal) lactating goats (average body weight: 37.5 ± 2.7 kg and milk yield: 1.78 ± 0.31 kg/day) were chosen for the ninety days duration of the experiment and divided into three groups following a completely randomized design. Group I acted as control (T0) and received only a basal diet as per requirement, whereas group II (T1) and group III (T2) received basal diet added with Aloe vera extract at 2% and 4% of dry matter intake (DMI), respectively. Total phenolic compounds (TPC) and milk antioxidant status were higher (p < 0.05) in T1 and T2 than T0. Relative abundance of methanogen, protozoa, Butyrivibrio proteoclasticus, and Ruminococcus flavefaciens in the rumen were lower, while Butyrivibrio fibrisolvens population was higher (p < 0.05) in T2 and T1 compared to T0. Saturated fatty acids levels in milk were lower, whereas different polyunsaturated fatty acids levels were higher (p < 0.05) in T1 and T2 than T0. Nutritional indices of milk increased in both supplemented groups. Overall, it may be concluded that dietary supplementation of Aloe vera extract at 2% and 4% of DMI may enhance the functional characteristics of milk by boosting TPC and antioxidant status, as well as the FA profile and nutritional quality indices of milk fat.

Review: genetic background of milk fatty acid synthesis in bovines

Milk fat composition is an important trait for the dairy industry as it directly influences the nutritional and technological properties of milk and other dairy products. The synthesis of milk fat is a complex process regulated by a network of genes. Thus, understanding the genetic variation and molecular mechanisms regulating milk fat synthesis will help to improve the nutritional quality of dairy products. In this review, we provide an overview of milk fat synthesis in bovines along with the candidate genes involved in the pathway. We also discuss de novo synthesis of fatty acids (ACSS, ACACA, FASN), uptake of FAs (FATP, FAT, LPL), intracellular activation and channelling of FAs (ACSL, FABP), elongation (EVOLV6), desaturation (SCD, FADS), formation of triglycerides (GPAM, AGPAT, LIPIN, DGAT), and milk lipid secretion (BTN1A1, XDH, PLIN2). The genetic variability of individual fatty acids will help to develop selection strategies for obtaining a healthier milk fat profile in bovines. Thus, this review will offer a potential understanding of the molecular mechanisms that regulate milk fat synthesis in bovines.

Animal board invited review: The contribution of adipose stores to milk fat: implications on optimal nutritional strategies to increase milk fat synthesis in dairy cows

A wide range of nutritional and non-nutritional factors influence milk fat synthesis and explain the large variation observed in dairy herds. The capacity of the animal to synthesize milk fat will largely depend on the availability of substrates for lipid synthesis, some of which originate directly from the diet, ruminal fermentation or from adipose tissue stores. The mobilization of non-esterified fatty acids from adipose tissues is important to support the energy demands of milk synthesis and will therefore have an impact on the composition of milk lipids, especially during the early lactation period. Such mobilization is tightly controlled by insulin and catecholamines, and in turn, can be affected indirectly by factors that influence these signals, namely diet composition, lactation stage, genetics, endotoxemia, and inflammation. Environmental factors, such as heat stress, also impact adipose tissue mobilization and milk fat synthesis, mainly through endotoxemia and an immune response-related increase in concentrations of plasma insulin. Indeed, as proposed in the present review, the central role of insulin in the control of lipolysis is key to improving our understanding of how nutritional and non-nutritional factors impact milk fat synthesis. This is particularly the case during early lactation, as well as in situations where mammary lipid synthesis is more dependent on adipose-derived fatty acids.

Variety of rumen microbial populations involved in biohydrogenation related to individual milk fat percentage of dairy cows

Our objective was to investigate the contribution of the rumen microbiome on the individual milk fat percentage (MFP) of Holstein dairy cows under the same nutritional and management conditions. From 92 early lactation dairy cows, the top 10 with the highest MFP (HF; n = 10) and the last 10 with the lowest MFP (LF; n = 10) were selected for the study. As a result, the milk trans-10, cis-12 C18:2 content was significant lower in the HF group than that in the LF group (P < 0.001). The rumen acetate to propionate ratio was significant higher in the HF group than that in the LF group (P = 0.035). According to the results of 16S rRNA gene sequencing, a minor but significant difference existed between the groups (P = 0.040). Three genera of the family Lachnospiraceae and four genera of the order Bacteroidales were identified to be the biomarkers for the LF group and HF group in the LEfSe analysis, respectively. Three microbial modules enriched by the family Lachnospiraceae were positively related to the milk trans-10, cis-12 C18:2 content (r _s > 0.60, P < 0.05). According to the results of shotgun metagenome sequencing, three kinds of linoleic acid (LA) isomerase genes were present in the gene pools of the rumen microbiome. Among them, the relative abundance of Bifidobacterium LA isomerase (BBI) was higher in the HF group than that in the LF group (P = 0.007). Three metagenome-assembled genomes (MAGs) with LA isomerase genes were positively correlated to the milk trans-10, cis-12 C18:2 content (r _s > 0.40, P < 0.05). Furthermore, all of these three MAGs were found to be able to produce lactate. Taken together, these results indicate that the increased relative abundance of microbial population with the trans-10 biohydrogenation pathway within the rumen microbiome contributes to the decrease of MFP via the increase of rumen trans-10, cis-12 C18:2 production. This study provides a new perspective for the development of measures for improving the milking performance of dairy cows.

The Effects of Feeding Milled Rapeseed Seeds with Different Forage:Concentrate Ratios in Jersey Dairy Cows on Milk Production, Milk Fatty Acid Composition, and Milk Antioxidant Capacity

We aimed to evaluate the effects of milled rapeseed (MR) supplementation of low- or high-concentrate diets on milk production and composition, fatty acids (FAs) profile, and antioxidant capacity. Sixteen Jersey dairy cows were used in a 4 × 4 Latin square design, for four periods of 4 weeks, and assigned to four treatments as a 2 × 2 factorial design. Dietary treatments consisted of iso-nitrogenated total mixed rations with high (65:35; LC-low concentrate) or low (50:50; HC-high concentrate) forage:concentrate (FC) ratios, supplemented with MR to provide 30 g oil/kg dry matter (DM) (LR and HR), or without MR supplement (L and H). Increasing the proportion of concentrates led to an increase in DM intake (DMI), net energy (NE_L) intake, and milk production, but milk fat and protein content decreased. Supplementing diets with MR led to an increase in NE_L intake and milk production, but did not affect DMI and milk composition. Diets supplemented with MR caused a decrease in the concentration of FAs with atherogenic effect and the increase in the level of FAs beneficial for human health (C18:1 cis-9, C18:1 trans-11, and C18:3 n-3), while the decrease in the FC ratio had a negative effect on omega-3 FAs. An improvement in the antioxidant capacity of milk was observed with diets with the high FC ratio but also by supplementing the feed with MR. These results could contribute to the development of effective strategies to improve the nutritional quality of milk without affecting the productive performance of cows.

Effect of dietary supplementation or cessation of magnesium-based alkalizers on milk fat output in dairy cows under milk fat depression conditions

We aimed to evaluate the effects of dietary supplementation with magnesium oxide and calcium-magnesium dolomite on milk fat synthesis and milk fatty acid profile or persistency in milk fat synthesis after their cessation in dairy cows under milk fat depression conditions. Twenty-four multiparous dairy cows in early lactation (mean ± standard deviation; 112 ± 14 d in milk) were used in a randomized complete block design. Milk fat depression was induced in all cows for 10 d by feeding a diet containing 35.2% starch, 28.7% neutral detergent fiber, and 4.8% total fatty acid (dry matter). The experiment was conducted in 2 periods. During the Mg-supplementation period (d 1-20), cows were randomly assigned to (1) the milk fat depression diet used during the induction phase (control; n = 8), (2) the control diet plus 0.4% magnesium oxide (MG; n = 8), or (3) the control diet plus 0.8% calcium-magnesium dolomite (CMC; n = 8). Compared with the control group, feeding the magnesium-supplemented diets increased milk fat concentration and yield by 12% within 4 d. During the 20-d Mg-supplementation period, both the MG and CMC diets increased milk fat concentration and yield, as well as 3.5% fat-corrected milk and energy-corrected milk yield, without affecting dry matter intake, milk yield, and milk protein and lactose concentrations. In the Mg-cessation period (d 21-30), all cows received the control diet, which resulted in a greater milk fat concentration and yield in the cows that had already received the MG and CMC diets in the Mg-supplementation period. Whereas, milk fat concentration and yield remained high after discontinuation of the magnesium-containing alkalizer until d 27. The difference in milk fat synthesis was associated with lower trans-10 C18:1 (-22%) and higher trans-11 C18:1 (+12.5%) concentrations in milk during the Mg-supplementation period. Furthermore, it was evident that within 2 d of supplementation, the trans-10:trans-11 ratio was lower in MG and CMC cows compared with cows receiving the control. This suggested that the effect of magnesium-based alkalizers on milk fat synthesis was mediated via a shift in ruminal biohydrogenation of cis-9,cis-12 C18:2 in the rumen. In conclusion, abrupt addition of magnesium oxide and calcium-magnesium dolomite increased milk fat synthesis, which persisted for 7 d after cessation of magnesium-based alkalizers. A similar ability to recover milk fat synthesis and normal fatty acid biohydrogenation pathways was observed for magnesium oxide and calcium-magnesium dolomite.

Annatto seeds as Antioxidants Source with Linseed Oil for Dairy Cows

Simple Summary

Currently, functional foods are gaining widespread attention. Polyunsaturated fatty acids (PUFA) and antioxidant compounds have beneficial effects on health. It is possible to increase the concentration of these compounds in the milk obtained from dairy cows by manipulating their diets, thereby improving milk quality and consequently the health of animals and humans who consume this milk. Annatto seed (Bixa orellana L.) is a source of antioxidants, whereas linseed oil is rich in omega 3 fatty acid. We evaluated the inclusion of annatto seeds and linseed oil in the diets of dairy cows and their effects on dry matter intake (DMI), nutrient digestibility, milk yield, milk composition and antioxidant capacity in milk and blood. There was no effect of treatment on nutrient digestibility and antioxidant capacity, but the addition of annatto seeds decreased DMI and milk production and linseed oil supplementation reduced milk fat content.

Abstract

This study aimed to evaluate the effects of annatto seeds, linseed oil and their combination on DMI, apparent total tract digestibility, antioxidant capacity and milk composition of dairy cows. Four lactating Holstein cows (120 ± 43 days in milk; 15.98 ± 2.02 kg of milk/day, mean ± SD) were allocated in a 4 × 4 Latin square with a 2 × 2 factorial arrangement (with or without annatto seeds at 15 g/kg of dry matter (DM); with or without linseed oil at 30 g/kg of DM) and provided four different diets: control (no annatto seeds or linseed oil); annatto seeds (15 g/kg of DM); linseed oil (30 g/kg of DM); and a combination of both annatto seeds and linseed oil. Annatto seeds reduced DM intake, and milk yield, protein and lactose, but increased content of fat, total solids and short chain fatty acid, with no effect on total antioxidant capacity of milk. Linseed oil supplementation decreased medium chain fatty acid proportion and n-6/n-3 ratio, conversely it increased long chain fatty acids and n-3 fatty acid content of milk, ether extract intake and total-tract digestibility. Thus, linseed oil supplementation in dairy cow diets improved the milk FA profile but decreased milk fat concentration, whereas annatto seeds did not influence antioxidant capacity and depressed feed intake and milk yield.

Influences of Maternal Conjugated Linoleic Acid and Essential Fatty Acid Supply During Late Pregnancy and Early Lactation on T and B Cell Subsets in Mesenteric Lymph Nodes and the Small Intestine of Neonatal Calves

Conjugated linoleic acid (CLA) isomers are known for their health-promoting effects in mammals and metabolic functions in dairy cows and are synthesized in the forestomach depending on essential fatty acid (EFA) intake. The current preliminary study investigated effects of a maternal fatty acid supplementation (MFAS) during late pregnancy and early lactation with coconut oil (CON, control), CLA (Lutalin®), or CLA + EFA (Lutalin® linseed oil; safflower oil) on plasma fatty acid composition and T and B cell subsets in mesenteric lymph nodes (MLN) and the small intestine of 5-day-old calves. MFAS of CLA + EFA increased α-linolenic, eicosapentaenoic, docosapentaenoic, and n-3 fatty acid proportions in calf plasma fat on days 1 and 5 after birth (P < 0.05). On day 5, CLA and CLA + EFA calves showed higher plasma fat trans-10, cis-12 CLA proportions, and CLA calves had higher plasma cis-9, trans-11 CLA proportions compared with CON calves (P < 0.1). MFAS of CLA tended to increase CD4⁺ T cell subsets in MLN and increased CD21⁺ B cell subsets in ileal lamina propria compared with CON but decreased CD2⁺ T cell subsets in jejunal lamina propria (P < 0.05). CLA + EFA decreased CD4⁺ T cell subsets in MLN compared with CLA (P < 0.05). MFAS of CLA seemed to affect the intestinal adaptive immune system of calves, but additional EFA supplementations reversed CLA effects. Possible direct CLA and EFA effects or whether changes in milk composition affected this immune modulation must be clarified in further studies.

Partially replacing sorghum silage with cactus (Opuntia stricta) cladodes in a soybean oil-supplemented diet markedly increases trans-11 18:1, cis-9, trans-11 CLA and 18:2 n-6 contents in cow milk

Based on low 18:0 contents observed in milk fat of cows fed cactus cladodes (CC), we hypothesized that including Opuntia stricta cladodes in a soybean oil (SO)-supplemented diet would promote incomplete rumen biohydrogenation of supplemental PUFA, leading to increased trans-11 18:1 and cis-9, trans-11 CLA contents in milk. Twelve Holstein cows were used in a two-period study: (a) Baseline: all cows received a total mixed ration (TMR) composed of sorghum silage (SS) and a concentrate containing no SO for 14 days; (b) Treatment: cows received one of the following SO-supplemented diets for 21 days: (1) SS-TMR: a TMR composed of SS and a SO-enriched concentrate, (2) CC-TMR: a TMR containing CC as a partial substitute for SS plus the SO-enriched concentrate, and (3) CC-PMR: same diet as in treatment 2, but CC were mixed with the SO-enriched concentrate and fed as a partial mixed ration (PMR). Both CC diets increased relative abundances of trans-11 18:1, cis-9, trans-11 CLA, and 18:2 n-6 in milk fat, whereas opposite effects were observed on 18:0 and cis-9 18:1. Proportion of 18:2 n-6 increased, and cis-9, trans-11 CLA tended to increase with CC-PMR as compared to CC-TMR, whereas 18:3 n-3 was higher with CC-PMR than with SS-TMR. Proportions of several odd- and branched-chain fatty acids, certain 18:1 isomers, and trans-9, cis-11 CLA changed with CC diets, notably with CC-PMR. Milk yield and intake of most nutrients (except fibre) increased or tended to increase with the CC diets, whereas gross milk composition was unaltered. Stearoyl-CoA desaturase-1 index for C18 (SCD₁₈ ) was higher with CC-PMR than with SS-TMR, and milk n-6:n-3 FA ratio and apparent transfer of 18:2 n-6 to milk increased with CC diets. These results indicate that Opuntia stricta cladodes can be a valuable feed ingredient for improving the nutraceutical value of milk fat.

The Effect of Low-Temperature Crystallization of Fish Oil on the Chemical Composition, Fatty Acid Profile, and Functional Properties of Cow's Milk

The study aimed to investigate the effect of supplementation of fish oil after the process of low-temperature crystallization (LTC-FO) enriched with long-chain polyunsaturated fatty acids (LC-PUFAs) on cow milk parameters. The experiment was carried out on 24 Polish Holstein Friesian cows. For 4 weeks, experimental (EXP) group animals (n = 12) were fed LTC-FO (1% of dry matter). Milk was collected two times: on days 14 and 30. LTC-FO supplementation decreased milk fat yield and concentration (p < 0.01). Higher levels of polyunsaturated fatty acids (PUFAs), including these with beneficial biological properties, i.e., eicosapentaenoic (EPA), docosahexaenoic (DHA), docosapentaenoic (DPA), CLA, alpha-linolenic acid (ALA), and TVA (p < 0.01), and lower levels of SFAs, especially short- (p < 0.01) and medium-chain ones (p < 0.05, p < 0.01), were found in the EXP group. The addition of LTC-FO reduced the value of atherogenic and thrombogenic indices as well as SFA/UFA and n-6/n-3 ratios and increased the content of n-3 PUFA and functional fatty acids (p < 0.01). The addition of LTC-FO also increased the delta-9 desaturase index for CLA/TVA and decreased it for pairs C14:1/C14:0 and C16:1/C16:0 (p < 0.05, p < 0.01).

In vitro effects of conjugated linoleic acid (CLA) on inflammatory functions of bovine monocytes

The conjugated linoleic acid (CLA) isomers, a group of naturally occurring isomers of the essential fatty acid (FA) linoleic acid, have received special attention in animal and human nutrition. Although they have long been used as dietary integrators in dairy cows, the effects of CLA isomers on bovine immune cells remain mostly undisclosed. The present study aimed to cover this gap and investigate the in vitro effects of CLA on inflammatory functions, including chemotaxis, phagocytosis, killing capability, and extracellular respiratory burst of purified bovine monocytes (CD14⁺). The apoptosis rate of monocytes was addressed as well. Once assessed, the effects of different concentrations (10, 50, 100, and 500 μM) of the 2 main CLA isomers, namely cis-9,trans-11 and trans-10,cis-12, the experiments were carried out using a concentration of 50 μM of the CLA isomers, both individually and in a mixture (50:50). The immunomodulatory activities of linoleic acid, an essential FA, and stearic acid, a saturated FA, were also investigated. Only the 50:50 CLA mixture was able to reduce monocyte apoptosis and to increase the extracellular respiratory burst during experimental proinflammatory conditions, as assessed by measuring production of reactive oxygen species. Linoleic acid and CLA had no effects on chemotaxis, phagocytosis, or killing capability. Remarkably, treatment of monocytes with stearic acid significantly reduced their chemotactic capability. The present results demonstrated that CLA isomers do have immunomodulatory effects on some functions of bovine monocytes, and that the mixture of the 2 CLA isomers is more effective than the CLA isomers individually.

Invited review: Role of rumen biohydrogenation intermediates and rumen microbes in diet-induced milk fat depression: An update

To meet the energy requirements of high-yielding dairy cows, grains and fats have increasingly been incorporated in ruminant diets. Moreover, lipid supplements have been included in ruminant diets under experimental or practical conditions to increase the concentrations of bioactive n-3 fatty acids and conjugated linoleic acids in milk and meat. Nevertheless, those feeding practices have dramatically increased the incidence of milk fat depression in dairy cattle. Although induction of milk fat depression may be a management tool, most often, diet-induced milk fat depression is unintended and associated with a direct economic loss. In this review, we give an update on the role of fatty acids, particularly originating from rumen biohydrogenation, as well as of rumen microbes in diet-induced milk fat depression. Although this syndrome seems to be multi-etiological, the best-known causal factor remains the shift in rumen biohydrogenation pathway from the formation of mainly trans-11 intermediates toward greater accumulation of trans-10 intermediates, referred to as the trans-11 to trans-10 shift. The microbial etiology of this trans-11 to trans-10 shift is not well understood yet and it seems that unraveling the microbial mechanisms of diet-induced milk fat depression is challenging. Potential strategies to avoid diet-induced milk fat depression are supplementation with rumen stabilizers, selection toward more tolerant animals, tailored management of cows at risk, selection toward more efficient fiber-digesting cows, or feeding less concentrates and grains.

The Effect of CLA-Rich Isomerized Poppy Seed Oil on the Fat Level and Fatty Acid Profile of Cow and Sheep Milk

The aim of the study was to examine the effect of dietary supplementation of isomerized poppy seed oil (IPO) enriched with conjugated dienes of linoleic acid (CLA) on cow and sheep milk parameters (fat content, fatty acid profile, Δ9-desaturase index, and atherogenic index). The process of poppy seed oil alkaline isomerization caused the formation of CLA isomers with cis-9,trans-11, trans-10,cis-12, and cis-11,trans-13 configurations in the amounts of 31.2%, 27.6%, and 4.1% of total fatty acids (FAs), respectively. Animal experiments were conducted on 16 Polish Holstein Friesian cows (control (CTRL) and experimental (EXP), n = 8/group) and 20 East Friesian Sheep (CTRL and EXP, n = 10/group). For four weeks, animals from EXP groups received the addition of IPO in the amount of 1% of dry matter. Milk was collected three times: on days 7, 14, and 30. Diet supplementation with IPO decrease milk fat content (p < 0.01). Milk fat from EXP groups had higher levels of polyunsaturated fatty acids, including FAs with beneficial biological properties, that is, CLA and TVA (p < 0.01), and lower levels of saturated fatty acids, particularly short- (p < 0.01) and medium-chain FAs (p < 0.05). The addition of IPO led to a decrease in the atherogenic index.

Effect of ruminal administration of soy sauce oil on rumen fermentation, milk production and blood parameters in dairy cows

Objective

To evaluate soy sauce oil (a by-product of making whole soybean soy sauce) as a new dietary lipid source, a large amount of soy sauce oil was administered into the rumen of dairy cows.

Methods

Four Holstein dairy cows fitted with rumen cannulae were used in a 56-day experiment. Ruminal administration of soy sauce oil (1 kg/d) was carried out for 42 days from day 8 to day 49 to monitor nutritional, physiological and production responses.

Results

Dry matter intake and milk yield were not affected by soy sauce oil administration, whereas 4% fat-corrected milk yield and the percentage of milk fat decreased. Although ruminal concentration of total volatile fatty acids (VFA) and the proportion of individual VFA were partially affected by administration of soy sauce oil, values were within normal ranges, showing no apparent inhibition in rumen fermentation. Administration of soy sauce oil decreased the proportions of milk fatty acids with a carbon chain length of less than 18, and increased the proportions of stearic, oleic, vaccenic and conjugated linoleic acids. Conjugated linoleic acid content in milk became 5.9 to 8.8 times higher with soy sauce oil administration. Blood serum concentrations of non-esterified fatty acid, 3-hydroxybutyric acid, total cholesterol, free cholesterol, esterified cholesterol, triglyceride and phospholipid increased with administration of soy sauce oil, suggesting a higher energy status of the experimental cows.

Conclusion

The results suggest that soy sauce oil could be a useful supplement to potentially improve milk functionality without adverse effects on ruminal fermentation and animal health. More detailed analysis is necessary to optimize the supplementation level of this new lipid source in feeding trials.

A high dose of conjugated linoleic acid increases fatty liver and insulin resistance in lactating mice

This study aimed to evaluate the effects of a high dose of conjugated linoleic acid (CLA) on lactating mice. In one experiment, Kunming mice were separated into four groups (n = 6 per group); the control (CON) group received 3.0% linoleic acid (LA) oil, the L-CLA group received a mixture of 2.0% LA and 1.0% CLA, the M-CLA group received a mixture of 1.0% LA and a 2.0% CLA, and the H-CLA group received 3.0% CLA. Feeding proceeded from day 4 to day 10 of lactation. In a second experiment, a CON group received 3.0% LA, and an H-CLA group received 3.0% CLA. Plasma parameters were analyzed for all groups, and insulin tolerance tests (ITTs) were conducted. CLA treatment did not affect dam weight but significantly decreased the food intake of dams during lactation. Furthermore, CLA decreased the weight of pups on day 10 of lactation; this effect was attributed to lower milk fat of dams in the CLA group than in those of the other groups. Relative to mice in the CON group, the mice in the H-CLA group displayed increased liver weight and liver triglyceride (TG) content as well as higher TG content and γ-glutamyl transferase (γ-GT) activity in the plasma. Moreover, high-dose CLA resulted in insulin resistance, possibly affecting the red blood cell (RBC) and hemoglobin (HCB) levels in the plasma. In conclusion, lactating mice receiving a high dose of CLA exhibited fatty liver, insulin resistance, and impaired lactation performance.

Dose response of rumen-protected conjugated linoleic acid supplementation to fattening bulls and heifers on growth, and carcass and meat quality

We investigated the influence of rumen-protected conjugated linoleic acid (rpCLA) on growth performances, and carcass and meat quality traits in beef. Twenty-four young bulls and 30 heifers obtained from double-muscled beef sires and dairy cows were fed a low-protein ration (110 g/kg DM of crude protein) supplemented with 0, 8 or 80 g/d of a commercial rpCLA product. The animals were monthly weighed and scored for body muscularity and fatness. Blood samples were collected after 140 days on feed. Animals were slaughtered when they reached average in vivo fatness scores of around 2.5 (heifers) and 2.0 (bulls) points respectively. At slaughter, carcasses, various organs and parts of the gastrointestinal tract were weighed; the 5th rib was dissected and its tissue and muscle chemical composition was determined. The rpCLA had little influence on growth performance but decreased the blood urea content by 28% (p < 0.01). The rpCLA × sex interactions for daily gain (p < 0.05), conformation scores (p < 0.01), and blood creatinine content (p < 0.05) suggest that males were more responsive to rpCLA than females when fed a low-protein ration, probably because of the metabolic protein-sparing effect of CLA. Only slight differences were observed in carcass weight and quality at slaughter. The results indicate that the response of beef cattle to rpCLA is dependent on sex or on their propensity for lean and fat accretion. It is also possible that counteracting feedback mechanisms compensate for the influence of rpCLA administration over the course of growth.

Decreased All- trans Retinoic Acid-Induced Expression of Sodium-Iodide Transporter in Mammary Epithelial Cells Caused by Conjugated Linoleic Acid Isomers

Expression of sodium-iodide symporter (NIS) is stimulated by sterol-regulatory-element-binding transcription factors (SREBFs) in mammary epithelial MCF-7 cells. Because conjugated linoleic acid (CLA) isomers have been shown to inhibit transcriptional activity of SREBFs in the mammary gland, the hypothesis was tested that CLA isomers inhibit NIS expression induced by all- trans retinoic acid (ATRA) in MCF-7 cells through inhibiting SREBF activity. c9t11-CLA and t10c12-CLA decreased ATRA-induced NIS-mRNA expression from 1.00 (ATRA alone) to 0.80 ± 0.12 (200 μM c9t11-CLA, P < 0.05) and 0.62 ± 0.10 (200 μM t10c12-CLA, P < 0.05), NIS-protein expression from 1.00 (ATRA alone) to 0.77 ± 0.08 (200 μM c9t11-CLA, P < 0.05) and 0.63 ± 0.05 (200 μM t10c12-CLA, P < 0.05), and NIS-promoter activity from 1.00 (ATRA alone) to 0.74 ± 0.13 (200 μM c9t11-CLA, P < 0.05) and 0.76 ± 0.13 (200 μM t10c12-CLA, P < 0.05); however, c9t11-CLA and t10c12-CLA increased the mRNA levels of SREBF isoforms and their target genes. In contrast, the mRNA expression of peroxisome-proliferator-activated receptor γ (PPARG) was strongly induced by ATRA alone but decreased by CLA isomers from 1.00 (ATRA alone) to 0.80 ± 0.06 (200 μM c9t11-CLA, P < 0.05) and 0.86 ± 0.06 (200 μM t10c12-CLA, P < 0.05). Overexpression of PPARγ in MCF-7 cells increased basal NIS-promoter activity, and treatment with the PPARγ ligand troglitazone stimulated ATRA-induced NIS-promoter activity. In conclusion, the results suggest that CLA isomers exert their effect on the expression of NIS by decreasing PPARG expression in MCF-7 cells.

Temporal changes in milk fatty acid composition during diet-induced milk fat depression in lactating cows

Diet-induced milk fat depression (MFD) in lactating cows has been attributed to alterations in ruminal lipid metabolism leading to the formation of specific fatty acid (FA) biohydrogenation intermediates that directly inhibit milk fat synthesis. However, the mechanisms responsible for decreased lipid synthesis in the mammary gland over time are not well defined. The aim of this study was to evaluate the effect of diet on milk FA composition and milk fat production over time, especially during MFD, and explore the associations between MFD and FA biohydrogenation intermediates in omasal digesta and milk. Four lactating Finnish Ayrshire cows used in a 4 × 4 Latin square with a 2 × 2 factorial arrangement of treatments and 35-d experimental periods were fed diets formulated to cause differences in ruminal and mammary lipid metabolism. Treatments consisted of an iso-nitrogenous total mixed ration based on grass silage with a forage to concentrate ratio of 65:35 or 35:65 without added oil, or with sunflower oil at 50 g/kg of diet dry matter. The high-concentrate diet with sunflower oil (HSO) induced a 2-stage drop in milk fat synthesis that was accompanied by specific temporal changes in the milk FA composition. The MFD on HSO was associated especially with trans-10 18:1 and also with trans-9,cis-11 conjugated linoleic acid (CLA) in milk and omasal digesta across all diets and was accompanied by the appearance of trans-10,cis-15 18:2. Trans-10,cis-12 CLA was increased in HSO, but milk fat secretion was not associated with omasal or milk trans-10,cis-12 CLA. The temporal changes in milk fat content and yield and milk FA composition reflect the shift from the predominant ruminal biohydrogenation pathway to an alternative pathway. The ambiguous role of trans-10,cis-12 CLA suggests that trans-10 18:1, trans-9,cis-11 CLA and trans-10,cis-15 18:2 or additional mechanisms contributed to the diet-induced MFD in lactating cows.

Feeding high oleic acid soybeans in place of conventional soybeans increases milk fat concentration

It is well established in the literature that feeding free vegetable oils rich in oleic acid results in greater milk fat secretion than does feeding linoleic-rich oils. The objectives of these experiments were to analyze the effects of oleic and linoleic acid when fed in the form of full-fat soybeans and the interaction between soybean particle size and fatty acid (FA) profile. Soybeans were included in diets on an iso-ether extract basis and diets were balanced for crude protein using soybean meal. Experiment 1 used 63 cows (28 primiparous, PP; 35 multiparous, MP) housed in a freestall barn with Insentec roughage intake control gates (Marknesse, the Netherlands). Cows were divided into 4 mixed parity groups within the same pen. Two groups were assigned to each of the 2 diets: whole raw Plenish (WP, high oleic; Dupont-Pioneer, Johnston, IA) soybeans or whole raw conventional (WC, high linoleic) soybeans. The MP cows exhibited significantly increased milk fat yield on the WP diet compared with the WC diet. A significantly greater C18 milk FA yield by the MP cows fed WP was observed compared with those fed WC, but no difference was present in the C16 or short-chain FA yield. No effects were seen in the PP cows. Experiment 2 used 20 cows (10 PP, 10 MP) in 2 balanced 5 × 5 Latin squares within parity. Cows received 5 diets: raw WP and WC diets, raw ground Plenish and conventional soybean diets (GP and GC, respectively), and a low fat control. A significant benefit was found for the GP diet compared with the GC diet for milk fat concentration and yield. In experiment 2, no difference was observed between cows fed the WP compared with the WC diet. In experiment 2, cows consuming the Plenish diets produced less milk than when consuming the conventional soybean diets. The soybean diets resulted in significantly more C18 and less Collapse

Key Words

• bioactive fatty acid
• linoleic acid
• milk fat depression
• milk fatty acid
• oleic acid

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MESH Headings

• Animal Feed/analysis
• Animals
• Cattle/physiology
• Diet/veterinary
• Dietary Fiber
• Female
• Lactation/drug effects
• Linoleic Acids/pharmacology
• Linoleic Acids, Conjugated/pharmacology
• Milk/chemistry
• Milk/metabolism
• Oleic Acid/pharmacology
• Particle Size
• Plant Oils/pharmacology
• Random Allocation
• Glycine max/chemistry

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Affiliation(s)

K A Weld Department of Dairy Science, University of Wisconsin, Madison 53706
L E Armentano Department of Dairy Science, University of Wisconsin, Madison 53706.

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Conjugated linoleic acid: A potent fatty acid linked to animal and human health

Conjugated linoleic acid (CLA) is a mixture of isomers of linoleic acid (C18:2 n-6), which is mostly found in the ruminant meat and dairy products. The CLA is known to have many potential health benefits, and considered a potent powerful fatty acid, which is linked to animal and human health. The present work aims to discuss the source and production, mechanism of action, and effects of CLA on humans, poultry, and ruminants by reviewing the recent studies carried out on CLA. Despite most of the recent studies indicating beneficial effects of CLA on improving body weight control parameters, its effects on reducing risk factors of cardiovascular diseases (CVD), inflammation, blood glucose, and insulin are still controversial, and need to be further studied in different hosts.

Effects of dietary CLA supplementation, parity and different concentrate levels before calving on immunoglobulin G1, G2 and M concentrations in dairy cows

Peripartal dairy cows exhibit a higher susceptibility for infectious diseases, which might be linked to the negative energy balance occurring at the onset of lactation. A dietary supplementation of conjugated linoleic acids (CLA) may reduce milk fat yield and subsequently lower the energy deficit. The utilization of immunoglobulins (Ig) for colostrogenesis might impair humoral immunity in peripartal dairy cows; therefore this study investigated the effects of a CLA supplement, parity and different dietary energy levels on plasma and colostrum IgG1, IgG2 and IgM levels in dairy cows and their calves. Blood samples were collected from 64 cows from 21days before until 56days after parturition and colostrum samples for the first 3days of lactation. Plasma immunoglobulin concentrations of 19 calves were determined before colostrum uptake. Neither plasma IgG1, nor IgG2 levels were affected by CLA or dietary energy level. However, immunoglobulin levels were affected by parity. Heifers possessed the lowest IgG1 concentrations. IgG2 concentrations were highest in cows with 2 lactations prior to parturition and in heifers after parturition. Plasma IgM levels were characterized by a sharp decrease 3days prior to parturition and were scarcely affected by the feeding regimen or parity. Generally, immunoglobulin levels appear to be mostly independent from the peripartal energy balance of the cows and are not influenced by dietary CLA. However, pronounced differences among parities for IgG1 and IgG2 were revealed which should be further evaluated.

Characterization of the liver X receptor-dependent regulatory mechanism of goat stearoyl-coenzyme A desaturase 1 gene by linoleic acid

Stearoyl-coenzyme A desaturase 1 (SCD1) is a key enzyme in the biosynthesis of palmitoleic and oleic acid. Although the transcriptional regulatory mechanism of SCD1 via polyunsaturated fatty acids (PUFA) has been extensively explored in nonruminants, the existence of such mechanism in ruminant mammary gland remains unknown. In this study, we used goat genomic DNA to clone and sequence a 1,713-bp fragment of the SCD1 5' flanking region. Deletion assays revealed a core region of the promoter located between -415 and -109 bp upstream of the transcription start site, and contained the highly conserved PUFA response region. An intact PUFA response region was required for the basal transcriptional activity of SCD1. Linoleic acid reduced endogenous expression of SCD1 and sterol regulatory element binding factor-1 (SREBF1) in goat mammary epithelial cells. Further analysis indicated that both the sterol response element (SRE) and the nuclear factor Y (NF-Y) binding site in the SCD1 promoter were responsible for the inhibition effect by linoleic acid, whereas the effect was abrogated once NF-Y was deleted. In addition, SRE and NF-Y were partly responsible for the transcriptional activation induced via the liver X receptor agonist T 4506585 (Sigma-Aldrich, St. Louis, MO). When goat mammary epithelial cells were cultured with linoleic acid, addition of T 4506585 markedly increased SCD1 transcription in controls, but had no effect on cells with a deleted SRE promoter. These results demonstrated that linoleic acid can regulate SCD1 expression at the transcriptional level through SRE and NF-Y in a liver X receptor-dependent fashion in the goat mammary gland.

Diet-induced milk fat depression is associated with alterations in ruminal biohydrogenation pathways and formation of novel fatty acid intermediates in lactating cows

The biohydrogenation theory of milk fat depression (MFD) attributes decreases in milk fat in cows to the formation of specific fatty acids (FA) in the rumen. Trans-10, cis-12-CLA is the only biohydrogenation intermediate known to inhibit milk fat synthesis, but it is uncertain if increased ruminal synthesis is the sole explanation of MFD. Four lactating cows were used in a 4×4 Latin square with a 2×2 factorial arrangement of treatments and 35-d experimental periods to evaluate the effect of diets formulated to cause differences in ruminal lipid metabolism and milk fat synthesis on the flow of FA and dimethyl acetal at the omasum. Treatments comprised total mixed rations based on grass silage with a forage:concentrate ratio of 35:65 or 65:35 containing 0 or 50 g/kg sunflower oil (SO). Supplementing the high-concentrate diet with SO lowered milk fat synthesis from -20·2 to -31·9 % relative to other treatments. Decreases in milk fat were accompanied by alterations in ruminal biohydrogenation favouring the trans-10 pathway and an increase in the formation of specific intermediates including trans-4 to trans-10-18 : 1, trans-8, trans-10-CLA, trans-9, cis-11-CLA and trans-10, cis-15-18 : 2. Flow of trans-10, cis-12-CLA at the omasum was greater on high- than low-concentrate diets but unaffected by SO. In conclusion, ruminal trans-10, cis-12-CLA formation was not increased on a diet causing MFD suggesting that other biohydrogenation intermediates or additional mechanisms contribute to the regulation of fat synthesis in the bovine mammary gland.

Effects of common dietary fatty acids on milk yield and concentrations of fat and fatty acids in dairy cattle

The objective of the present article was to summarise the effects of five common dietary fatty acids (C16:0, C18:0, C18:1, C18:2 and C18:3) on the major milk fat groups (<C16, C16 and C18). Forty published papers were reviewed to evaluate the effect of adding free fat or oil supplements rich in C16 and C18 fatty acids on the response of milk fat secretion and composition. From those 40 studies, 21 were used to investigate the effect of total dietary concentration of C16:0, C18:0, C18:1, C18:2 and C18:3 on milk secretion or concentrations of milk <C16, C16 and C18 fatty acid groups. The results indicated that C16 supplementation increased total milk fatty acids, mainly by increasing milk C16 yield, without affecting milk <C16 and C18 yield. Supplements rich in unsaturated fatty acid decreased total milk fatty acid by inhibiting secretion of milk fatty acids shorter than C18, with linoleic acid being the most inhibitory. Mixtures of feed fatty acid (C16:0 + C18:0 and C16:0 + C18:1) did not significantly affect total milk fatty acid yield. According to regression of milk C16 yield on dietary fatty acid, endogenous C16 contributes ~80% of total milk C16, but this proportion varies with the level and type of dietary fatty acid fed. Milk mid-infrared analysis can be used to routinely measure the presence of milk <C16 fatty acid, the concentration of which provides a good indicator of inhibition of milk fatty acid secretion. In contrast, measurement of total milk fat content is less effective as a diagnostic tool due to the masking effect of the exogenous supply of C16 and C18 dietary fatty acids.

Sterol regulatory element-binding proteins are regulators of the sodium/iodide symporter in mammary epithelial cells

The sodium/iodide symporter (NIS), which is essential for iodide concentration in the thyroid, is reported to be transcriptionally regulated by sterol regulatory element-binding proteins (SREBP) in rat FRTL-5 thyrocytes. The SREBP are strongly activated after parturition and throughout lactation in the mammary gland of cattle and are important for mammary epithelial cell synthesis of milk lipids. In this study, we tested the hypothesis that the NIS gene is regulated also by SREBP in mammary epithelial cells, in which NIS is functionally expressed during lactation. Regulation of NIS expression and iodide uptake was investigated by means of inhibition, silencing, and overexpression of SREBP and by reporter gene and DNA-binding assays. As a mammary epithelial cell model, the human MCF-7 cell line, a breast adenocarcinoma cell line, which shows inducible expression of NIS by all-trans retinoic acid (ATRA), and unlike bovine mammary epithelial cells, is widely used to investigate the regulation of mammary gland NIS and NIS-specific iodide uptake, was used. Inhibition of SREBP maturation by treatment with 25-hydroxycholesterol (5 µM) for 48h reduced ATRA (1 µM)-induced mRNA concentration of NIS and iodide uptake in MCF-7 cells by approximately 20%. Knockdown of SREBP-1c and SREBP-2 by RNA interference decreased the mRNA and protein concentration of NIS by 30 to 50% 48h after initiating knockdown, whereas overexpression of nuclear SREBP (nSREBP)-1c and nSREBP-2 increased the expression of NIS in MCF-7 cells by 45 to 60%, respectively, 48h after initiating overexpression. Reporter gene experiments with varying length of NIS promoter reporter constructs revealed that the NIS 5'-flanking region is activated by nSREBP-1c and nSREBP-2 approximately 1.5- and 4.5-fold, respectively, and activation involves a SREBP-binding motif (SRE) at -38 relative to the transcription start site of the NIS gene. Gel shift assays using oligonucleotides spanning either the wild-type or the mutated SRE at -38 of the NIS 5'-flanking region showed that in vitro-translated nSREBP-1c and nSREBP-2 bind only the wild-type but not the mutated SRE at -38 of NIS. Collectively, the present results from cell culture experiments with human mammary epithelial MCF-7 cells and from genetic studies show for the first time that the NIS gene and iodide uptake are regulated by SREBP in cultured human mammary epithelial cells. Future studies are necessary to clarify if the regulation of NIS expression and iodide uptake by SREBP also applies to the lactating bovine mammary epithelium.

Changes in fermentation and biohydrogenation intermediates in continuous cultures fed low and high levels of fat with increasing rates of starch degradability

Excessive levels of starch in diets for lactating dairy cattle is a known risk factor for milk fat depression, but little is known about how this risk is affected by differences in rates of starch degradability (Kd) in the rumen. The objective of this study was to compare accumulation of biohydrogenation intermediates causing milk fat depression, including conjugated linoleic acid (CLA), when corn with low or high Kd were fed to continuous cultures. Diets contained (dry matter basis) 50% forage (alfalfa pellets and grass hay) and 50% concentrate, with either no added fat (LF) or 3.3% added soybean oil (HF). Within both the LF and HF diets, 3 starch degradability treatments were obtained by varying the ratio of processed (heat and pressure treatments) and unprocessed corn sources, giving a total of 6 dietary treatments. Each diet was fed to dual-flow continuous fermenters 3 times a day at 0800, 1600, and 2400h. Diets were fed for four 10-d periods, with 7d for adaptation and 3d for sample collection. Orthogonal contrasts were used in the GLIMMIX procedure of SAS to test the effects of fat, starch degradability, and their interaction. Acetate and acetate:propionate were lower for HF than for LF but daily production of trans-10 18:1 and trans-10,cis-12 CLA were higher for HF than for LF. Increasing starch Kd from low to high increased culture pH, acetate, and valerate but decreased butyrate and isobutyrate. Changes in biohydrogenation intermediates (expressed as % of total isomers) from low to high starch Kd included reductions in trans-11 18:1 and cis-9,trans-11 CLA but increases in trans-10 18:1 and trans-10,cis-12 CLA. The results show that increasing the starch Kd in continuous cultures while holding starch level constant causes elevation of biohydrogenation intermediates linked to milk fat depression.

Comparison of ruminal lipid metabolism in dairy cows and goats fed diets supplemented with starch, plant oil, or fish oil

Direct comparison of cow and goat performance and milk fatty acid responses to diets known to induce milk fat depression (MFD) in the bovine reveals relevant species-by-diet interactions in ruminal lipid metabolism. Thus, this study was conducted to infer potential mechanisms responsible for differences in the rumen microbial biohydrogenation (BH) due to diet and ruminant species. To meet this objective, 12 cows and 15 goats were fed a basal diet (control), a similar diet supplemented with 2.2% fish oil (FO), or a diet containing 5.3% sunflower oil and additional starch (+38%; SOS) according to a 3 × 3 Latin square design with 25-d experimental periods. On the last day of each period, fatty acid composition (by gas chromatography) and bacterial community (by terminal-RFLP), as well as fermentation characteristics, were measured in rumen fluid samples. Results showed significant differences in the response of cows and goats to dietary treatments, although variations in some fermentation parameters (e.g., decreases in the acetate-to-propionate ratio due to FO or SOS) were similar in both species. Main alterations in ruminal BH pathways potentially responsible for MFD on the SOS diet (i.e., the shift from trans-11 to trans-10 18:1 and related increases in trans-10,cis-12 18:2) tended to be more pronounced in cows, which is consistent with an associated MFD only in this species. However, changes linked to FO-induced MFD (e.g., decreases in 18:0 and increases in total trans-18:1) were stronger in caprine rumen fluid, which may explain their unexpected susceptibility (although less marked than in bovine) to the negative effect of FO on milk fat content. Altogether, these results suggest that distinct ruminal mechanisms lead to each type of diet-induced MFD and confirm a pronounced interaction with species. With regard to microbiota, differences between cows and goats in the composition of the rumen bacterial community might be behind the disparity in the microorganisms affected by the experimental diets (e.g., Ruminococcaceae, Lachnospiraceae, and Succinivibrionaceae in the bovine, and Pseudobutryrivibrio, Clostridium cluster IV, Prevotella, and Veillonellaceae in the caprine), which hindered the assignation of bacterial populations to particular BH steps or pathways. Furthermore, most relevant variations in microbial groups corresponded to as yet uncultured bacteria and suggest that these microorganisms may play a predominant role in the ruminal lipid metabolism in both cows and goats.

Intake, milk production, ruminal, and feed efficiency responses to dietary cation-anion difference by lactating dairy cows

Previous meta-analyses of the effects of dietary cation anion difference (DCAD; mEq/kg; Na + K - Cl - S) in lactating dairy cow diets used studies conducted after the development of the DCAD concept. Dietary buffers, such as NaHCO3 and K2CO3, increase DCAD and have been used in lactating dairy cow diets for several decades. However, most published studies on buffer feeding were conducted before the development of the DCAD concept. Our objective was to determine the intake, milk production, ruminal, and feed efficiency responses to DCAD using previous studies with dietary buffer addition and more recent studies that focused on DCAD as dietary treatments. The database consisted of 43 articles that were published between 1965 and 2011. The studies included 196 dietary treatments and 89 treatment comparisons with a range in DCAD from -68 to 811mEq/kg of diet DM, with the vast majority between 0 and 500mEq/kg of diet DM. For studies that lacked analyses of one or more of the dietary strong ions (Na, K, Cl, or S), ion percentages were estimated from ingredient composition using the 2001 dairy National Research Council software. Two basic models were used to evaluate DCAD responses using the NLMIXED procedure in SAS 9.2 (SAS Institute Inc., Cary, NC): (1) a simple linear model, Y=A + B × (DCAD), where A=intercept and B=the increment (slope) in performance per unit DCAD (mEq/kg of diet DM); and (2) a nonlinear model, Y=A + M[1 - e((K × DCAD))], where M=maximal increment in performance from DCAD and K=the rate constant. In both models, study was designated as the random effect. The DCAD effects best described by the linear model included milk fat percent, fat yield, ruminal pH, NDF digestibility, and feed efficiency [3.5% fat-corrected milk (FCM; kg)/dry matter intake (DMI; kg)] where a 100mEq/kg increase in DCAD resulted in respective increases of 0.10%, 36g/d, 0.032 pH units, 1.5% NDF digestibility, and 0.013 FCM/DMI units. The DMI, milk yield, and 3.5% FCM were best described by the nonlinear model where the maximal responses were 1.92, 1.11, and 4.82kg/d, respectively. The expected increments in DMI, milk production, and 3.5% FCM by increasing DCAD from 0 to 500mEq/kg were 1.7, 1.2, and 3.4kg/cow per day, respectively. The results of this meta-analysis suggest that DCAD has significant effects on intake, milk production and composition, digestion, and feed efficiency in lactating dairy cows.

Does trans-10, cis-12 conjugated linoleic acid affect the intermediary glucose and energy expenditure of dairy cows due to repartitioning of milk component synthesis?

The overall goal of this study was to evaluate if intermediary energy metabolism of cows fed with trans-10, cis-12 conjugated linoleic acid (CLA) was modified such that milk-energy compounds were produced with less intermediary energy expenditure as compared to control cows. Published data on supplemented CLA were assembled. The extent was calculated to which the trans-10, cis-12 CLA isomer has an impact on glucose and energy conversion in the mammary gland by modifying glucose equivalent supply and energy required for fatty acid (FA) and fat synthesis, and if this will eventually lead to an improved glucose and energy status of CLA-supplemented high-yielding dairy cows. A possible relationship between CLA supplementation level and milk energy yield response was also studied. Calculations were conducted separately for orally and abomasally administered CLA and based on energy required for supply of glucose equivalents, i.e. lactose, glycerol and NADPH2. Further, modifications of milk FA profile due to CLA supplementation were considered when energy expenditures for FA and fat synthesis were quantified. Differences in yields between control and CLA groups were transformed into glucose energy equivalents. Only abomasal infusion (r2 = 0·31) but not oral CLA administration (r2 = 0·11) supplementation to dairy cow diets resulted in less glucose equivalent energy. Modifications of milk FA profiles also saved energy but the relationship with CLA supplementation was weaker for abomasal infusion (r2 = 0·06) than oral administration (r2 = 0·38). On average, 10 g/d of abomasally infused trans-10, cis-12 CLA saved 1·1 to 2·3 MJ net energy expressed as glucose equivalents, whereas both positive and negative values were observed when the trans-10, cis-12 CLA was fed to the cows.

This study revealed a weak to moderate dose-dependent relationship between the amount of trans-10, cis-12 CLA administered and the amount of energy in glucose equivalents and energy for the synthesis of milk fat conserved from milk ingredient synthesis. Because abomasal infusion of the trans-10, cis-12 CLA more consistently conserved energy in glucose equivalents compared with oral CLA intake, rumen protection of the fed CLA products appears incomplete. Milk fat synthesis showed an energy saving with a weak dose-dependent relationship when CLA was supplemented orally or by abomasal infusion.

Effect of dietary fatty acid supplements, varying in fatty acid composition, on milk fat secretion in dairy cattle fed diets supplemented to less than 3% total fatty acids

Dietary fatty acids can affect both milk fat yield and fatty acid (FA) composition. This relationship is well established when the dietary level of FA exceeds 3% of diet dry matter (DM). We could find no reports directly examining the effects of dietary FA profile on milk fat at levels below 3%. Twenty-four primiparous and 36 multiparous lactating cows were paired by production (1 high with 1 low, within parity) to form 30 experimental units. Pairs were fed 6 diets in five 6×6 balanced Latin squares with 21-d periods, and data were collected during the last 5d of each period. Two control diets were fed: a corn control diet (CC; 29% corn silage, 16% alfalfa silage, 19% corn grain, and 8% distillers grain on a DM basis) containing 1.8% FA; and a low-oil control diet (LOC; 9% corn silage, 35% alfalfa silage, 20% food-grade corn starch, and 8% corn gluten feed on a DM basis) containing 1.2% FA. A portion of the food-grade corn starch in LOC was replaced with 4 different FA supplements to create the 4 treatment diets. Treatments were 1.7% (DM basis) of a 50:50 blend of corn oil and high-linoleic safflower oil (LO), 1.7% high-oleic sunflower oil (OO), 1.7% palm oil (PO), or 1.8% calcium salts of palm fatty acids (PFA). The resultant diets were thus enriched in linoleic (LO), oleic (OO), or palmitic acid (PO and PFA). Dietary treatments did not affect dry matter intake. Addition of any of the fat sources to LOC resulted in increased milk yield, but milk fat yields and milk FA composition were variable for the different treatments. The LO treatment resulted in lower milk fat yield, fat concentration, and C16:0 yield but increased both trans-10 C18:1 and trans-10,cis-12 C18:2 yields compared with the other added FA treatments. Diets PO and PFA resulted in increased milk C16:0 yield and decreased total milk C18 yield compared with OO. Regression analysis revealed a negative coefficient for dietary linoleic acid content over basal (LOC) for both milk short-chain FA yield and C16:0 yield. Dietary linoleic acid content also had a positive coefficient for milk trans-10 C18:1 and trans-10,cis-12 conjugated linoleic acid yield. These results demonstrate that even when total dietary FA are below 3%, free oils rich in linoleic acid can reduce milk fat yield by reducing secretion of milk FA with fewer than 18 carbons. Fatty acid composition of fat supplements is important even at this low level of total dietary fat.

Desempenho produtivo e perfil de ácidos graxos do leite de vacas que receberam níveis crescentes de óleo de girassol em dietas à base de capim-elefante

Este experimento teve como objetivo principal avaliar as alterações no perfil de ácidos graxos do leite decorrentes do fornecimento de diferentes níveis de óleo de girassol (OG) para vacas leiteiras alimentadas com dietas completas à base de capim-elefante. Doze vacas da raça Holandesa receberam quatro níveis de OG na dieta (0; 1,3; 2,5 e 3,7% da MS) em delineamento quadrado latino 4 x 4. Não houve efeito (P>0,05) dos níveis de OG sobre o consumo de MS, a produção de leite ou os teores de sólidos do leite. Por outro lado, o perfil de ácidos graxos (AG) do leite foi amplamante modificado com a inclusão de OG na dieta, e observou-se redução (P<0,0001) dos teores dos AG de cadeia curta e média, elevação dos teores de ácido oleico (P<0,0001), dos isômeros de ácido linoleico conjugado, em especial do ácido rumênico (P<0,0001) e da relação entre os ácidos graxos hipo e hipercolesterolêmicos (P<0,0001). Apesar da maior ingestão diária de ácido linoleico (P<0,01) com o aumento do nível de OG na dieta, sua concentração na gordura do leite não foi alterada. Isso indica extensiva bio-hidrogenação ruminal deste AG no rúmen, o que é compatível com o aumento (P<0,0001) da concentração de ácido esteárico e dos AG C18:1 trans, especialmente do vacênico, na gordura do leite. Em geral, os resultados observados no presente estudo indicam que a inclusão de até 3,7% de OG em dietas completas de vacas leiteiras à base de capim-elefante promove melhoria da qualidade nutricional da gordura do leite, sem comprometimento do desempenho produtivo dos animais.

Liver x receptors stimulate lipogenesis in bovine mammary epithelial cell culture but do not appear to be involved in diet-induced milk fat depression in cows

Abstract Milk fat synthesis of ruminants can be inhibited by intermediates of ruminal fatty acid biohydrogenation including trans-10, cis-12 conjugated linoleic acid (CLA). These biohydrogenation intermediates signal a coordinated downregulation of genes involved in mammary FA synthesis, transport, and esterification. We have previously reported decreased mammary expression of sterol response element-binding protein 1 (SREBP1), SREBP1-activating proteins, and thyroid hormone-responsive spot 14 (S14) in the cow during diet-induced milk fat depression (MFD), and treatment with trans-10, cis-12 CLA. Liver x receptors (LXR) and retinoid x receptors (RXR) regulate lipogenesis and are known to bind polyunsaturated FA and LXR agonist increases lipid synthesis in mammary epithelial cell culture. The current studies investigated if biohydrogenation products of rumen origin inhibit mammary lipogenesis through LXR and/or RXR. Expression of LXRs was not different in lactating compared to nonlactating bovine mammary tissue, and expression of LXRs, RXRα, and selected LXR and RXR target genes was not changed in mammary tissue during diet-induced or CLA-induced MFD in the cow. In bovine mammary epithelial cell culture, LXR agonist stimulated lipogenesis and expression of LXRß, ATP-binding cassette 1 (ABCA1), SREBP1c, and S14, but LXR activation did not overcome CLA inhibition of lipogenesis and downregulation of LXRß, SREBP1c, and S14 expression. Lastly, expression of the LXR-regulated carbohydrate-responsive element-binding protein (ChREBP) was higher in lactating than nonlactating tissue and was decreased during CLA-induced MFD. We conclude that changes in mammary LXR expression in dairy cows are not involved in MFD and that trans-10, cis-12 CLA inhibition of lipogenesis and diet-induced MFD appears independent of direct LXR signaling.