Effect of conjugated linoleic acid and acetate on milk fat synthesis and adipose lipogenesis in lactating dairy cows

During biohydrogenation-induced milk fat depression (MFD), nutrients are spared from milk fat synthesis and are available for other metabolic uses. Acetate is the major carbon source spared and it may increase lipid synthesis in adipose tissue during MFD. The objective of this study was to compare the effect of trans-10,cis-12 conjugated linoleic acid (CLA) and the amount of acetate spared during CLA-induced MFD on adipose tissue lipogenesis. Nine multiparous, lactating, ruminally cannulated Holstein cows (244 ± 107 d in milk; 25 ± 8.4 kg of milk/d; mean ± standard deviation) were randomly assigned to treatments in a 3 × 3 Latin square design. Experimental periods were 4 d followed by a 10-d washout. Treatments were control (CON), ruminal infusion of acetate (AC; continuous infusion of 7 mol/d adjusted to pH 6.1 with sodium hydroxide), or abomasal infusion of CLA (10 g/d of both trans-10,cis-12 CLA and cis-9,trans-11 CLA). Dry matter intake, milk yield, and milk protein yield and percentage were not affected by treatments. Compared with CON, milk fat yield decreased 23% and fat percent decreased 28% in CLA, and milk fat yield increased 20% in AC. Concentration and yield of milk de novo synthesized fatty acids (<C16) were reduced and concentration of preformed fatty acids (>C16) was increased by CLA, compared with CON. Yield of de novo synthesized fatty acids and palmitic acid was increased by AC, compared with CON. Lipogenesis capacity of adipose tissue explants was decreased 72% by CLA, but was not affected by AC. Acetate oxidation by adipose explants was not affected by treatments. Treatments had no effect on expression of key lipogenic factors, lipogenic enzymes, and leptin; however, expression of fatty acid binding protein 4 was reduced in CLA compared with CON. Additionally, hormone-sensitive lipase and perilipin 1 were decreased by CLA and acetate. Plasma glucose and glucagon concentrations were not affected by treatments; however, CLA increased nonesterified fatty acids 17.7%, β-hydroxybutyrate 16.1%, and insulin 27.8% compared with CON, and AC increased plasma β-hydroxybutyrate 18%. In conclusion, during CLA-induced MFD in low-producing cow adipose tissue was sensitive to the anti-lipogenic effects of CLA, while spared acetate did not stimulate adipose lipogenesis. However, acetate may play an important role in stimulating lipogenesis and improving energy status in the mammary gland under normal conditions.

Acetate Dose-Dependently Stimulates Milk Fat Synthesis in Lactating Dairy Cows

Background: Acetate is a short-chain fatty acid (FA) that is especially important to cows because it is the major substrate for de novo FA synthesis. However, the effect of acetate supply on mammary lipid synthesis is not clear.Objective: The objective of this experiment was to determine the effect of increasing acetate supply on milk fat synthesis in lactating dairy cows.Methods: Six multiparous lactating Holstein cows were randomly assigned to treatments in a replicated design to investigate the effect of acetate supply on milk fat synthesis. Treatments were 0 (control), 5, 10, and 15 mol acetate/d continuously infused into the rumen for 4 d. Rumen short-chain FAs, plasma hormones and metabolites, milk fat concentration, and milk FA profile were analyzed on day 4 of each treatment. Polynomial contrasts were used to test the linear and quadratic effects of increasing acetate supply.Results: Acetate increased milk fat yield quadratically (P < 0.01) by 7%, 16%, and 14% and increased milk fat concentration linearly (P < 0.001) by 6%, 9%, and 11% for 5, 10, and 15 mol acetate/d, respectively, compared with the control treatment. Increased milk fat yield predominantly was due to a linear increase in 16-carbon FAs (P < 0.001) and a quadratic increase in de novo synthesized FAs (<16-carbon FAs; P < 0.01), indicating that there was stimulation of de novo synthesis pathways. Apparent transfer of acetate to milk fat was 33.4%, 36.2%, and 20.6% for 5, 10, and 15 mol/d, respectively. Acetate infusion linearly increased the relative concentration of rumen acetate (P < 0.001) before feeding, but not after feeding. Acetate linearly increased plasma ß-hydroxybutyric acid by 29%, 50%, and 78%, respectively, after feeding compared with the control treatment (P < 0.01).Conclusions: Increasing acetate supply to lactating cows increases milk fat synthesis, suggesting that nutritional strategies that increase ruminal acetate absorption would be expected to increase milk fat by increasing de novo FA synthesis.

Deficiency of stearoyl-CoA desaturase-1 aggravates colitogenic potential of adoptively transferred effector T cells

Stearoyl-CoA desaturase-1 (SCD1) is a lipogenic enzyme involved in the de novo biosynthesis of oleate (C18:1, n9), a major fatty acid in the phospholipids of lipid bilayers of cell membranes. Accordingly, Scd1KO mice display substantially reduced oleate in cell membranes. An altered SCD1 level was observed during intestinal inflammation; however, its role in modulating inflammatory bowel disease remains elusive. Herein, we investigated the colitogenic capacity of Scd1KO effector T cells by employing the adoptive T-cell transfer colitis model. Splenic effector T cells (CD4⁺CD25^-) from age- and sex-matched wild-type (WT) and Scd1KO mice were isolated by FACS and intraperitoneally administered to Rag1KO mice, which were monitored for the development of colitis. At day 60 postcell transfer, Rag1KO mice that received Scd1KO CD4⁺CD25^- T cells displayed accelerated and exacerbated colitis than mice receiving WT CD4⁺CD25^- T cells. Intriguingly, Scd1KO CD4⁺CD25^- T cells display augmented inflammatory cytokine profile and cellular membrane fluidity with a concomitant increase in proinflammatory saturated fatty acids, which we postulate to potentially underlie their augmented colitogenic potential.

XBP1 Regulates the Biosynthetic Capacity of the Mammary Gland During Lactation by Controlling Epithelial Expansion and Endoplasmic Reticulum Formation

Cells composing the mammary secretory compartment have evolved a high capacity to secrete not only proteins but also triglycerides and carbohydrates. This feature is illustrated by the mouse, which can secrete nearly twice its own weight in milk proteins, triglycerides and lactose over a short 20-day lactation. The coordination of synthesis and export of products in other secretory cells is orchestrated in part by the transcription factor X-box binding protein 1 (XBP1). To assess the role of XBP1 in mammary epithelial cells (MEC), we studied floxed XBP1 female mice lacking (wild type; WT) or expressing the Cre recombinase under the control of the ovine β-lactoglobulin promoter (ΔXBP1(MEC)). Pregnant ΔXBP1(MEC) females had morphologically normal mammary development and gave birth to the same number of pups as WT mice. Their litters, however, suffered a weight gain deficit by lactation day 3 (L3)3 that grew to 80% by L14. ΔXBP1(MEC) dams had only modest changes in milk composition (-21% protein, +24% triglyceride) and in the expression of associated genes in isolated MEC. By L5, WT glands were fully occupied by dilated alveoli, whereas ΔXBP1(MEC) glands contained fewer, mostly unfilled alveoli and retained a prominent adipocyte population. The smaller epithelial compartment in ΔXBP1(MEC) glands was explained by lower MEC proliferation and increased apoptosis. Finally, endoplasmic reticulum ribbons were less abundant in ΔXBP1(MEC) at pregnancy day 18 and failed to increase in abundance by L5. Collectively, these results show that XBP1 is required for MEC population expansion during lactation and its ability to develop an elaborate endoplasmic reticulum compartment.

Microbiota-Dependent Hepatic Lipogenesis Mediated by Stearoyl CoA Desaturase 1 (SCD1) Promotes Metabolic Syndrome in TLR5-Deficient Mice

The gut microbiota plays a key role in host metabolism. Toll-like receptor 5 (TLR5), a flagellin receptor, is required for gut microbiota homeostasis. Accordingly, TLR5-deficient (T5KO) mice are prone to develop microbiota-dependent metabolic syndrome. Here we observed that T5KO mice display elevated neutral lipids with a compositional increase of oleate [C18:1 (n9)] relative to wild-type littermates. Increased oleate contribution to hepatic lipids and liver SCD1 expression were both microbiota dependent. Analysis of short-chain fatty acids (SCFAs) and (13)C-acetate label incorporation revealed elevated SCFA in ceca and hepatic portal blood and increased liver de novo lipogenesis in T5KO mice. Dietary SCFAs further aggravated metabolic syndrome in T5KO mice. Deletion of hepatic SCD1 not only prevented hepatic neutral lipid oleate enrichment but also ameliorated metabolic syndrome in T5KO mice. Collectively, these results underscore the key role of the gut microbiota-liver axis in the pathogenesis of metabolic diseases.

The effects of feeding rations that differ in neutral detergent fiber and starch concentration within a day on rumen digesta nutrient concentration, pH, and fermentation products in dairy cows

There is a daily pattern of feed intake in the dairy cow, and feeding a single total mixed ration results in variation in the amount of fermentable substrate entering the rumen over the day. The object of this study was to determine if feeding multiple rations over the day that complement the pattern of feed intake would stabilize rumen pool sizes and fermentation. Nine ruminally cannulated cows were used in a 3×3 Latin square design with 23-d periods. Diets were a control diet [33.3% neutral detergent fiber (NDF)], a low-fiber diet (LF; 29.6% NDF), and a high-fiber diet (HF; 34.8% NDF). The LF and HF diets were balanced to provide the same nutrient composition as the control diet when cows were fed 3 parts of LF and 7 parts of HF. Cows on the control treatment (CON) were fed at 0900h, cows on the high/low treatment (H/L) were fed HF at 70% of daily offering at 0900h and LF at 30% of daily offering at 2200h, and cows on the low/high (L/H) treatment were fed LF at 30% of daily offering at 0900h and HF at 70% of daily offering at 1300h. All treatments were fed at 110% of daily intake. Preplanned contrasts compared CON with H/L and H/L with L/H. Feeding the LF diet in the evening resulted in a large increase in the amount of feed consumed immediately after feed delivery at that feeding. Rumen digesta starch concentration increased and NDF concentration decreased following feeding of the LF diet in both the L/H and H/L treatments. Starch pool size also increased following feeding of the LF diet in the evening and tended to increase after feeding the LF diet in the morning. Rumen ammonia concentration was increased following feeding of the HF diet in the morning and the LF diet in the evening in the H/L treatment. Additionally, cis-9 C18:1 and cis-9,cis-12 18:2 are higher in concentrate feeds and were increased after feeding the LF diet in both treatments. Trans fatty acid isomers of the normal and alternate biohydrogenation pathways followed a daily pattern, and the H/L treatment increased isomers of the alternate pathway during the overnight period following the evening feeding of the LF diet. Additionally, C17:0 decreased during the overnight period in the H/L treatment. Feeding multiple rations over the day changed feeding behavior, and the combined effect of diet composition and feeding pattern resulted in a change in rumen nutrient pool sizes and fermentation products. Feeding the low-fiber diet in the evening resulted in a large increase in feed intake after feed delivery and did not increase starch intake during the overnight period. The H/L treatment failed to stabilize rumen fermentation because of the shift in the feeding pattern. Feeding strategies that feed multiple diets over the day must integrate diet composition and feeding behavior to achieve the desired effect on rumen nutrient pools and fermentation.

Feeding laying hens stearidonic acid-enriched soybean oil, as compared to flaxseed oil, more efficiently enriches eggs with very long-chain n-3 polyunsaturated fatty acids

The desaturation of α-linolenic acid (ALA) to stearidonic acid (SDA) is considered to be rate-limiting for the hepatic conversion of ALA to eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) in humans, rodents, and chickens. Thus, we hypothesized that feeding laying hens SDA, as a component of the oil derived from the genetic modification of the soybean, would bypass this inefficient metabolic step and result in the enrichment of eggs with EPA and DHA at amounts comparable to that achieved by direct supplementation of hens' diet with these very long-chain (VLC) n-3 polyunsaturated fatty acids (PUFAs). In a 28-d study, laying hens incorporated 0.132 mg, 0.041 mg, or 0.075 mg of VLC n-3 PUFAs into egg yolk for each milligram of ingested dietary ALA derived primarily from conventional soybean oil (CON), dietary ALA derived primarily from flaxseed oil (FLAX), or dietary SDA derived from SDA-enriched soybean oil, respectively. Moreover, the amounts of total yolk VLC n-3 PUFAs in eggs from hens fed the CON (51 mg), FLAX (91 mg), or SDA (125 mg) oils were markedly less than the 305 mg found in eggs from fish oil-fed hens. Unexpectedly, SDA appeared to be more readily incorporated into adipose tissue than into egg yolk. Since egg yolk FAs typically reflect the hens' dietary pattern, these tissue-specific differences suggest the existence of an alternate pathway for the hepatic secretion and transport of SDA in the laying hen.

Trans-10, cis-12 CLA dose-dependently inhibits milk fat synthesis without disruption of lactation in C57BL/6J mice

BACKGROUND

Trans-10, cis-12 conjugated linoleic acid (10,12 CLA) is a potent inhibitor of milk fat synthesis in mammals. In the cow, 10 g/d of 10,12 CLA specifically and reversibly inhibits mammary lipogenesis, whereas substantially higher doses are not specific and cause a generalized inhibition of milk synthesis.

OBJECTIVE

The objective of this study was to validate a lactating mouse model by establishing the dose response, specificity, and reversibility of the inhibition of milk fat synthesis by 10,12 CLA.

METHODS

Lactating mice (C57BL/6J) received daily doses of 0 (control), 7, 20, or 60 mg of 10,12 CLA for 5 d during established lactation. A second group of lactating mice was treated with 20 mg/d of 10,12 CLA for 4 d and followed post-treatment to evaluate reversibility.

RESULTS

CLA decreased pup growth with a 49% decrease occurring with 60 mg/d of CLA. Milk fat percentage was decreased 11% and 20% with the 7 and 20 mg/d dose, respectively, and all CLA treatments had a decreased concentration of de novo synthesized fatty acids (FAs) in milk fat. In agreement, 20 mg/d of 10,12 CLA decreased the lipogenic capacity of mammary tissue by 30% and mammary expression of FA synthase (Fasn), sterol response element binding protein 1 (Srebf1), and thyroid hormone responsive spot 14 (Thrsp) by 30-60%, whereas milk protein percentage and mammary expression of α-lactalbumin (Lalba) were unaltered. This dose of CLA reduced pup growth by nearly 20% and milk de novo synthesized FAs by >35%, and these effects were completely reversed 5 d after 10,12 CLA treatment was terminated.

CONCLUSION

Inhibition of mammary lipogenesis by 10,12 CLA is dose-dependent in the mouse, with a specific and reversible reduction in milk fat synthesis at the 20 mg/d dose and additional nonspecific effects on milk synthesis at higher CLA doses.

The effects of feeding time on milk production, total-tract digestibility, and daily rhythms of feeding behavior and plasma metabolites and hormones in dairy cows

The timing of feed intake entrains circadian rhythms regulated by internal clocks in many mammals. The objective of this study was to determine if the timing of feeding entrains daily rhythms in dairy cows. Nine Holstein cows were used in a replicated 3 × 3 Latin square design with 14-d periods. An automated system recorded the timing of feed intake over the last 7 d of each period. Treatments were feeding 1×/d at 0830 h (AM) or 2030 h (PM) and feeding 2×/d in equal amounts at 0830 and 2030 h. All treatments were fed at 110% of daily intake. Cows were milked 2×/d at 0500 and 1700 h. Milk yield and composition were not changed by treatment. Daily intake did not differ, but twice-daily feeding tended to decrease total-tract digestibility of organic matter and neutral detergent fiber (NDF). A treatment by time of day interaction was observed for feeding behavior. The amount of feed consumed in the first 2h after feeding was 70% greater for PM compared with AM feeding. A low rate of intake overnight (2400 to 0500 h; 2.2 ± 0.74% daily intake/h, mean ± SD) and a moderate rate of intake in the afternoon (1200 to 1700 h; 4.8 ± 1.1% daily intake/h) was noted for all treatments, although PM slightly reduced the rate during the afternoon period compared with AM. A treatment by time of day interaction was seen for fecal NDF and indigestible NDF (iNDF) concentration, blood urea nitrogen, plasma glucose and insulin concentrations, body temperature, and lying behavior. Specifically, insulin increased and glucose decreased more after evening feeding than after morning feeding. A cosine function within a 24-h period was used to characterize daily rhythms using a random regression. Rate of feed intake during spontaneous feeding, fecal NDF and iNDF concentration, plasma glucose, insulin, NEFA, body temperature, and lying behavior fit a cosine function within a 24-h period that was modified by treatment. In conclusion, feeding time can reset the daily rhythms of feeding and lying behavior, core body temperature, fecal NDF and iNDF concentration, and plasma blood urea nitrogen, glucose, and insulin concentration of dairy cows, but has no effect on daily DMI and milk production.

Comparison of enriched palmitic acid and calcium salts of palm fatty acids distillate fat supplements on milk production and metabolic profiles of high-producing dairy cows

A variable response to fat supplementation has been reported in dairy cows, which may be due to cow production level, environmental conditions, or diet characteristics. In the present experiment, the effect of a high palmitic acid supplement was investigated relative to a conventional Ca salts of palm fatty acids (Ca-FA) supplement in 16 high-producing Holstein cows (46.6±12.4kg of milk/d) arranged in a crossover design with 14-d periods. The experiment was conducted in a non-heat-stress season with 29.5% neutral detergent fiber diets. Treatments were (1) high palmitic acid (PA) supplement fed as free FA [1.9% of dry matter (DM); 84.8% C16:0] and (2) Ca-FA supplement (2.3% of DM; 47.7% C16:0, 35.9% C18:1, and 8.4% C18:2). The PA supplement tended to increase DM intake, and increased the yields of milk and energy-corrected milk. Additionally, PA increased the yields of milk fat, protein, and lactose, whereas milk concentrations of these components were not affected. The yields of milk de novo and 16-C FA were increased by PA compared with Ca-FA (7 and 20%, respectively), whereas the yield of preformed FA was higher in Ca-FA. A reduction in milk fat concentration of de novo and 16-C FA and a marginal elevation in trans-10 C18:1 in Ca-FA is indicative of altered ruminal biohydrogenation and increased risk of milk fat depression. No effect of treatment on plasma insulin was observed. A treatment by time interaction was detected for plasma nonesterified fatty acids (NEFA), which tended to be higher in Ca-FA than in PA before feeding. Overall, the palmitic acid supplement improved production performance in high-producing cows while posing a lower risk for milk fat depression compared with a supplement higher in unsaturated FA.

The daily rhythm of milk synthesis is dependent on the timing of feed intake in dairy cows

Regulation of the daily rhythm of milk synthesis is important to production animals and breastfeeding, but is difficult to observe in nursing animals. The rate of food intake varies over the day and is expected to create a daily rhythm of nutrient absorption. The objective of this study was to determine if the timing of food intake entrains a daily pattern of milk synthesis. Seventeen Holstein cows were used in a crossover design. Treatments were ad libitum feeding of a total mixed ration once daily (1× fed) or fed in four equal meals every 6 h (4× fed). Cows were milked every 6 h the last 7 days of each period. There was a treatment by time of day interaction for milk and milk component yield and concentration. Milk fat and protein concentration and yield exhibited a daily rhythm and the amplitude of the rhythm was reduced in 4× fed. In addition, milk fat percent was higher in 4× fed than 1× fed at three of the four milking intervals (0.22–0.45% higher) and 4× fed increased daily milk fat yield. Treatment by time of day interactions were detected for plasma glucose, insulin, and blood urea nitrogen. These variables also fit a cosine function with a 24 h period and the amplitudes of plasma glucose, insulin, and blood urea nitrogen rhythms were decreased by 4× feeding. In conclusion, there is a circadian pattern of milk synthesis in the dairy cow that is responsive to the timing of food intake.

Regulation of the daily rhythm of milk synthesis is important to production animals and breastfeeding. The objective of this study was to determine if the timing of food intake entrains a daily pattern of milk synthesis. A circadian pattern of milk synthesis was observed that was responsive to the timing of food intake.

Effect of a high-palmitic acid fat supplement on milk production and apparent total-tract digestibility in high- and low-milk yield dairy cows

The effect of a high-palmitic acid fat supplement was tested in 12 high-producing (mean = 42.1 kg/d) and 12 low-producing (mean = 28.9 kg/d) cows arranged in a replicated 3 × 3 Latin square design. Experimental periods were 21 d, with 18d of diet adaptation and 3 d of sample collection. Treatments were (1) control (no supplemental fat), (2) high-palmitic acid (PA) supplement (84% C16:0), and (3) Ca salts of palm fatty acid (FA) supplement (Ca-FA). The PA supplement had no effect on milk production, but decreased dry matter intake by 7 and 9% relative to the control in high- and low-producing cows, respectively, and increased feed efficiency by 8.5% in high-producing cows compared with the control. Milk fat concentration and yield were not affected by PA relative to the control in high- or low-producing cows, although PA increased the yield of milk 16-C FA by more than 85 g/d relative to the control. The Ca-FA decreased milk fat concentration compared with PA in high-, but not in low-producing cows. In agreement, Ca-FA dramatically increased milk fat concentration of trans-10 C18:1 and trans-10, cis-12 conjugated linoleic acid (>300%) compared with PA in high-producing cows, but not in low-producing cows. No effect of treatment on milk protein concentration or yield was detected. The PA supplement also increased 16-C FA apparent digestibility by over 10% and increased total FA digestibility compared with the control in high- and low-producing cows. During short-term feeding, palmitic acid supplementation did not increase milk or milk fat yield; however, it was efficiently absorbed, increased feed efficiency, and increased milk 16-C FA yield, while minimizing alterations in ruminal biohydrogenation commonly observed for other unsaturated fat supplements. Longer-term experiments will be necessary to determine the effects on energy balance and changes in body reserves.

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.

A rumen unprotected conjugated linoleic acid supplement inhibits milk fat synthesis and improves energy balance in lactating goats

Feeding trans-10, cis-12 CLA supplements in a rumen-protected form has been shown to cause milk fat depression (MFD) in cows, ewes, and goats. Methyl esters of CLA were shown to be as effective as FFA in inducing MFD when infused postruminally, but their efficacy as a feed supplement has not been addressed in studies with lactating ruminants. In the present study, we investigated the effects of an unprotected trans-10, cis-12 CLA supplement as methyl esters on performance, milk composition, and energy status of dairy goats. Eighteen multiparous Toggenburg goats were randomly assigned to dietary treatments in a crossover experimental design (14 d treatment periods separated by a 7 d washout interval): 30 g/d of calcium salts of fatty acids (Control) or 30 g/d of a rumen unprotected CLA supplement containing 29.9% of trans-10, cis-12 CLA as methyl esters (CLA). Lipid supplements were mixed into a concentrate and fed individually to animals 3 times a day as a total mixed ration component. The DMI, milk yield, milk protein and lactose content and secretion, and somatic cell count were unaffected by CLA treatment. On the other hand, milk fat content and yield were reduced by 19.9 and 17.9% in CLA-fed goats. Reduced milk fat yield in CLA-fed goats was a consequence of a lower secretion of both preformed and de novo synthesized fatty acids. The CLA treatment also changed the milk fatty acid profile, which included a reduction in the concentration of SFA (2.5%), increased MUFA and PUFA (5.6 and 5.4%, respectively), and a pronounced increase (1576%) in milk fat trans-10, cis-12 CLA. Consistent with the high milk fat trans-10, cis-12 CLA content, all desaturase indexes were reduced in milk fat from CLA-fed goats. The MFD induced by CLA reduced the energy required for milk production by 22%, which was accompanied by an improvement in the estimated energy balance (P < 0.001), greater blood glucose concentration (P < 0.05), and a trend for increased BW (P = 0.08). Approximately 7.2% of trans-10, cis-12 CLA was estimated to escape from rumen biohydrogenation and indirect comparisons with data obtained from other studies suggest equivalent MFD between dietary CLA in the methyl ester form and rumen protected sources. Thus, despite the apparent low degree of rumen protection, our results suggest that methyl esters of CLA could be an alternative to rumen protected CLA supplements due to manufacturing and cost advantages.

Supplementation with fish oil as a source of n-3 fatty acids does not downregulate mammary lipogenesis in lactating mice

The very long chain n-3 (ω-3) polyunsaturated fatty acids (VLCn3PUFAs) are potent regulators of hepatic lipid synthesis, but their effect on lipid synthesis in the lactating mammary gland is less well investigated. The objective of the present study was to examine effects of fish oil (FO) supplementation on mammary lipogenesis and the expression of lipogenic genes in mammary and hepatic tissues of lactating mice. Beginning on day 6 of lactation and continuing for 7 d, female C57BL/6J mice (n = 8/diet) were fed 1 of 3 dietary treatments: a 5%-fat diet containing mainly saturated fatty acids (FAs) (low-fat control) or 2 10%-fat diets, 1 enriched with FO as a source of VLCn3PUFAs and the other enriched with a safflower/palm oil mixture (high-fat control) as a source of oleic acid. Mammary lipogenic capacity, measured by (14)C-glucose incorporation into FAs by mammary explants, was similar among treatments, and there were no treatment effects on the proportion of de novo synthesized FAs in milk fat or on litter weight gain, a proxy for milk energy secretion. Also, there were no treatment effects on mammary mRNA abundance for key lipogenic enzymes and proteins involved in the regulation of milk lipid synthesis. In contrast, there was a treatment effect on hepatic lipogenesis, with FO resulting in a decrease of ~50% in hepatic lipid content and a similar downregulation of lipogenic gene expression compared with the 2 control diets. Overall, there were tissue-specific differences in dietary VLCn3PUFA effects on lipid synthesis with no observed effects for mammary lipogenic variables but marked reductions occurring in hepatic lipogenesis.

Characterization of the acute lactational response to trans-10, cis-12 conjugated linoleic acid

Trans-10, cis-12 conjugated linoleic acid (CLA) is a potent inhibitor of milk fat synthesis in the dairy cow. The decrease in milk fat yield during abomasal infusion of CLA reaches a nadir after 3 to 5 d. The acute responses to CLA were evaluated using 4 cows in a crossover design. Cows were milked with the aid of oxytocin every 4h from -28 to 80h and every 6h from 86 to 116h relative to the initiation of abomasal CLA infusion. An initial priming dose of 7.5g of CLA was given at time zero followed by infusion of 2.5g every 4h for 72h. Plasma CLA reached a near-steady-state concentration by 4h, and initial plasma enrichments were greatest in the triglyceride and nonesterified fatty acid fractions. Milk CLA concentration peaked at 6h and reached steady state by 22h. At termination of the infusion, decreases in milk CLA concentration and yield and plasma CLA concentration were best fit by a reciprocal-linear function. Milk fat percentage decreased progressively after 2h and was significant by 14h. Milk fatty acid profile was initially unchanged, but between 18 and 36h after initiation of the CLA dose the proportions of fatty acids progressively shifted, resulting in an increase in fatty acids >C16 and a decrease in fatty acids <C16 by 38 to 46h. In contrast, changes in the desaturase index were immediate, with a significant decrease by 6h and a near-maximal decrease by 10h. Thus, stearoyl desaturase enzyme was more acutely responsive to CLA than other enzymes in milk fat synthesis. The initial decrease in milk fat synthesis involved an equal depression of short- and long-chain fatty acid pathways and was followed thereafter by a more pronounced decrease in the synthesis of de novo fatty acids.

Plasma FGF21 is elevated by the intense lipid mobilization of lactation

In many mammals, lactation success depends on substantial use of lipid reserves and requires integrated metabolic activities between white adipose tissue (WAT) and liver. Mechanisms responsible for this integration in lactation are poorly understood, but data collected in other conditions of elevated lipid use suggest a role for fibroblast growth factor-21 (FGF21). To address this possibility in the context of lactation, we studied high-yielding dairy cows during the transition from late pregnancy (LP) to early lactation (EL). Plasma FGF21 was nearly undetectable in LP, peaked on the day of parturition, and then stabilized at lower, chronically elevated concentrations during the energy deficit of EL. Plasma FGF21 was similarly increased in the absence of parturition when an energy-deficit state was induced by feed restricting late-lactating dairy cows, implicating energy insufficiency as a cause of chronically elevated FGF21 in EL. Gene expression studies showed that liver was a major source of plasma FGF21 in EL with little or no contribution by WAT, skeletal muscle, and mammary gland. Meaningful expression of the FGF21 coreceptor β-Klotho was restricted to liver and WAT in a survey of 15 tissues that included the mammary gland. Expression of β-Klotho and its subset of interacting FGF receptors was modestly affected by the transition from LP to EL in liver but not in WAT. Overall, these data suggest a model whereby liver-derived FGF21 regulates the use of lipid reserves during lactation via focal actions on liver and WAT.

Nutrigenomics, rumen-derived bioactive fatty acids, and the regulation of milk fat synthesis

Mammary synthesis of milk fat continues to be an active research area, with significant advances in the regulation of lipid synthesis by bioactive fatty acids (FAs). The biohydrogenation theory established that diet-induced milk fat depression (MFD) in the dairy cow is caused by an inhibition of mammary synthesis of milk fat by specific FAs produced during ruminal biohydrogenation. The first such FA shown to affect milk fat synthesis was trans-10, cis-12 conjugated linoleic acid, and its effects have been well characterized, including dose-response relationships. During MFD, lipogenic capacity and transcription of key mammary lipogenic genes are coordinately down-regulated. Results provide strong evidence for sterol response element-binding protein-1 (SREBP1) and Spot 14 as biohydrogenation intermediate responsive lipogenic signaling pathway for ruminants and rodents. The study of MFD and its regulation by specific rumen-derived bioactive FAs represents a successful example of nutrigenomics in present-day animal nutrition research and offers several potential applications in animal agriculture.

The acid-labile subunit is required for full effects of exogenous growth hormone on growth and carbohydrate metabolism

Normal postnatal growth is dependent in part on overlapping actions of GH and IGF-I. These actions reflect GH stimulation of IGF-I production in liver and extrahepatic tissues, representing respectively the endocrine and autocrine/paracrine arms of the IGF system. Recent experiments in genetically modified mice show that each source of IGF-I can compensate for absence of the other but do not resolve their relative role in postnatal growth. In an effort to address this issue, we studied the GH responsiveness of mice harboring a null mutation of the acid-labile subunit (ALS). Null ALS mice have a substantial reduction in endocrine IGF-I but, unlike other models of plasma IGF-I deficiency, have no obvious additional endocrine defects. Wild type and null ALS mice of both sexes received daily sc injections of saline or recombinant bovine GH between d 35 and 63 of postnatal age. The GH-stimulated body weight gain of null ALS mice was reduced by more than 30% relative to wild type mice, irrespective of sex. Reductions in GH responsiveness were also seen for kidney and linear growth. Absence of ALS eliminated the ability of GH to increase plasma IGF-I despite intact GH-dependent stimulation of IGF-I expression in liver, adipose tissue, and skeletal muscle. GH treatment was also less efficient in antagonizing insulin action in null ALS mice. Overall, these results suggest that the GH effects mediated by endocrine IGF-I depends on ALS, and accordingly null ALS mice are less responsive to exogenous GH therapy.

Expression of enzymes and key regulators of lipid synthesis is upregulated in adipose tissue during CLA-induced milk fat depression in dairy cows

Milk fat depression (MFD) is a naturally occurring condition in dairy cows where milk fat synthesis is inhibited by intermediates of ruminal biohydrogenation. One of these bioactive fatty acids (FA), trans-10, cis-12 conjugated linoleic acid (CLA), decreases milk fat synthesis through transcriptional downregulation of genes involved in mammary lipid synthesis. Energy partitioning during MFD is not well characterized because of the complexity of observing energy metabolism in ruminant animals. To investigate energy partitioning during MFD, adipose tissue biopsies were taken from 4 cows arranged in a switchback design. Treatments were control and 4-d abomasal infusion of trans-10, cis-12 CLA (7.5 g/d). CLA decreased milk fat yield by 38% and milk fat content by 34%, but yields of milk and other milk components were unchanged. In contrast to reported changes in mammary tissue, adipose tissue expression of lipid synthesis enzymes, including lipoprotein lipase, FA synthase, stearoyl-CoA desaturase, and FA binding protein 4, was increased. Expression of regulators of lipid synthesis, including sterol-response element binding protein 1, thyroid hormone responsive spot 14, and PPARgamma, also increased in adipose tissue. Thus, a CLA dose resulting in near maximal inhibition of mammary lipid synthesis resulted in increased expression of lipid synthesis-related genes in adipose tissue. A meta-analysis of intake response during CLA infusion was conducted to extend the investigation of energy metabolism during MFD. Voluntary intake decreased (P < 0.001) by 1.5 kg/d during CLA-induced MFD in the 14 studies analyzed, but the reduction in intake only partially accounts for the energy spared from reduced milk fat synthesis. Results are consistent with energy spared from the reduction in milk fat synthesis being partitioned toward adipose tissue fat stores during short-term MFD.

Regulation of fat synthesis by conjugated linoleic acid: lactation and the ruminant model

Conjugated linoleic acid (CLA) isomers effect an impressive range of biological processes including the ability to inhibit milk fatty acid synthesis. Although this has been demonstrated in several mammals, research has been most extensive with dairy cows. The first isomer shown to affect milk fat synthesis during lactation was trans-10, cis-12 CLA, and its effects have been well characterized including dose-response relationships. Recent studies have tentatively identified 2 additional CLA isomers that regulate milk fat synthesis. Regulation by CLA occurs naturally in dairy cows when specific CLA isomers produced as intermediates in rumen biohydrogenation act to inhibit milk fat synthesis; this physiological example of nutritional genomics is referred to as diet-induced milk fat depression. Molecular mechanisms for the reduction in mammary lipid synthesis involve a coordinated down-regulation of mRNA expression for key lipogenic enzymes associated with the complementary pathways of milk fat synthesis. Results provide strong evidence of a role for sterol response element-binding protein 1 and Spot 14 in this translational regulation. Effects of CLA on body fat accretion have also been investigated in nonlactating animals, but CLA effects on mammary fatty acid synthesis occur at an order-of-magnitude lower dose and appear to involve very different mechanisms than those proposed for the antiobesity effects of CLA. Overall, results demonstrate the unique value of cows as a model to investigate the role of CLA in the regulation of milk fat synthesis during lactation.

Trans-10 octadecenoic acid does not reduce milk fat synthesis in dairy cows

Diet-induced milk fat depression (MFD) involves the interrelation between rumen fermentation and mammary synthesis of milk fat, and the reduction in milk fat coincides with a marked increase in the trans-10 18:1 content of milk fat. Our objective was to directly examine the effect of trans-10 18:1 on milk fat synthesis in dairy cows. Three mid-lactation cows were used in a 3 x 3 Latin square design; treatments were abomasal infusion of: 1) ethanol (control); 2) trans-10 18:1 (t10); and 3) trans-10, cis-12 conjugated linoleic acid (CLA; positive control). The t10 and CLA supplements (>90% purity) were infused for 4 d and provided 42.6 and 4.3 g/d of trans-10 18:1 and trans-10, cis-12 CLA, respectively. Milk yield, feed intake, milk protein, and milk lactose were unaffected by treatment. Compared with the control, the t10 treatment had no effect on milk fat synthesis, whereas the CLA treatment resulted in a 27 and 24% reduction in milk fat content and yield, respectively. The transfer efficiency of the abomasally infused trans-10 18:1 and trans-10, cis-12 CLA into milk fat was 15 +/- 1 and 23 +/- 5% (means +/- SD), respectively. Overall, trans-10 18:1 had no effect on milk fat synthesis when abomasally infused at approximately 43 g/d, although it was taken up by the mammary glands and incorporated into milk fat. Therefore, our results offer no support for the concept that changes in rumen production of trans-10 18:1 within the physiological range play a role in the regulation of fatty acid synthesis during diet-induced MFD.

SREBP1 and thyroid hormone responsive spot 14 (S14) are involved in the regulation of bovine mammary lipid synthesis during diet-induced milk fat depression and treatment with CLA

Milk fat synthesis in dairy cows can be inhibited by unique fatty acid intermediates that are produced during rumen biohydrogenation. One of these inhibitory intermediates is trans-10, cis-12 conjugated linoleic acid (CLA), and this milk fat depression (MFD) involves a coordinated decrease in mammary expression of lipogenic enzymes. We investigated the sterol response element binding protein (SREBP) transcription factor system in the mammary tissue of cows during MFD, which was induced by a low forage, high oil (LF/HO) diet and trans-10, cis-12 CLA infusion. The LF/HO diet and CLA treatment decreased milk fat yield by 38 and 24%, respectively. Treatments causing MFD decreased expression of SREBP1 and the insulin responsive gene (INSIG) 1, consistent with decreased abundance of active SREBP1. The LF/HO diet also decreased expression of INSIG2 and SREBP cleavage activating protein. In addition, we identified the involvement of thyroid hormone responsive spot 14 (S14) in the regulation of mammary synthesis of milk fat. A broader role for S14 in the trans-10, cis-12 CLA-mediated decrease in fat synthesis was explored by mining publicly available microarray datasets, and we found that mouse adipose expression of S14 was decreased in response to CLA treatment. Overall, the decreased mammary expression of SREBP1, SREBP activation protein, and the coordinated reduction in SREBP1-responsive lipogenic enzymes provides strong support for a central role of SREBP1 in the regulation of milk fat synthesis. In addition, our results provide evidence for an involvement of S14 in mammary regulation of milk fat synthesis and a possible broader role for S14 in the reported antiobesity effects of CLA.

Effects of Fatty Acid Supplements on Feed Intake, and Feeding and Chewing Behavior of Lactating Dairy Cows

Saturated and unsaturated fatty acid supplements (FS) were evaluated for effects on feed intake, meal patterns, and chewing behavior. Eight ruminally and duodenally cannulated cows were used in a replicated 4 x 4 Latin square design experiment with 21-d periods. Treatments were control and a linear substitution of 2.5% fatty acids from supplemented saturated FS (SAT; prilled, hydrogenated free fatty acids) for partially unsaturated FS (UNS; calcium soaps of long-chain fatty acids). All rations contained identical forage and concentrate components including 37.2% forage and 13.5% cottonseed. Dry matter intake for SAT was not different from control, whereas increasing unsaturated FS linearly decreased dry matter intake by 3.2 kg. Wet weight of ruminal digesta decreased linearly up to 11.3 kg (13%) with increasing unsaturated FS. Adding supplementary fatty acids did not change meal number, meal length, or time between meals compared with control, but increasing unsaturated FS decreased meal size 0.22 kg (9%) within FS. The SAT treatment increased time spent ruminating by 56 (10%) and 42 (7%) min/d compared with control and UNS, respectively. Increasing saturated FS did not affect frequency of rumination bouts or interval between bouts, but increased rumination bout length by 5.6 min. Water intake was not affected by treatment, but increasing saturated FS linearly decreased the number of drinking bouts per day by up to 2.9 bouts (23%). Increased unsaturated fatty acid flow to the duodenum decreased feed intake by decreasing meal size, and increased saturated fatty acid flow to the duodenum increased rumination time per day by increasing rumination bout length.

Fat supplements affect fractional rates of ruminal fatty acid biohydrogenation and passage in dairy cows

Rates of fatty acid biohydrogenation and passage were determined for fat supplements varying in saturation using lactating dairy cows. First-order fractional passage rates were determined by dividing the duodenal flux of fatty acids by their respective ruminal pool sizes. The determination of rates of biohydrogenation required the development of a model to account for the transfer of fatty acids among pools. Ruminally and duodenally cannulated multiparous Holstein cows (n = 8) were used in a replicated 4 x 4 Latin square design with 21-d periods. Treatments were control and a linear substitution of 25 g/kg supplemented fatty acids varying in saturation as follows: saturated (prilled hydrogenated free fatty acids), intermediate mix of saturated and unsaturated (calcium soaps of long-chain fatty acids), and partially unsaturated fatty acids. Passage rates of 16:0, 18:0, and total 18-carbon fatty acids were linearly decreased with increasing unsaturated fatty acids and the trans-18:1 fractional passage rate was quadratically affected with a maximum for the intermediate treatment. Increasing unsaturated fatty acids increased the extent of 18:2 and 18:3 biohydrogenation and decreased the extent of 18:1 and trans-18:1 biohydrogenation. Calcium salts did not protect PUFA from ruminal biohydrogenation despite a mean ruminal pH of 6.0, and unsaturated fatty acids decreased ruminal biohydrogenation of trans-18:1, resulting in increased duodenal flow of these fatty acids. The model allows a mechanistic description of ruminal biohydrogenation and determination of the extent of 18:1 biohydrogenation.

Effects of Fatty Acid Supplements on Milk Yield and Energy Balance of Lactating Dairy Cows

Saturated and unsaturated fatty acid supplements (FS) were evaluated for effects on yield of milk and milk components, concentration of milk components including milk fatty acid profile, and energy balance. Eight ruminally and duodenally cannulated cows and 8 noncannulated cows were used in a replicated 4 x 4 Latin square design experiment with 21-d periods. Treatments were control and a linear substitution of 2.5% fatty acids from saturated FS (SAT; prilled, hydrogenated free fatty acids) for partially unsaturated FS (UNS; calcium soaps of long-chain fatty acids). The SAT treatment did not change milk fat concentration, but UNS linearly decreased milk fat in cannulated cows and tended to decrease milk fat in noncannulated cows compared with control. Milk fat depression with UNS corresponded to increased concentrations of trans-10, cis-12 conjugated linoleic acid and trans C18:1 fatty acids in milk. Milk fat profile was similar for SAT and control, but UNS decreased concentration of short- and medium-chain FA. Digestible energy intake tended to decrease linearly with increasing unsaturated FS in cannulated and noncannulated cows. Increasing unsaturated FS linearly increased empty body weight and net energy gain in cannulated cows, whereas increasing saturated FS linearly increased plasma insulin. Efficiency of conversion of digestible energy to milk tended to decrease linearly with increasing unsaturated FS for cannulated cows only. Addition of SAT provided little benefit to production and energy balance, whereas UNS decreased energy intake and milk energy yield.

Effects of Fatty Acid Supplements on Ruminal and Total Tract Nutrient Digestion in Lactating Dairy Cows

Saturated and unsaturated fatty acid supplements (FS) were evaluated for effects on ruminal digestion kinetics, and ruminal and postruminal nutrient digestion. Eight early lactation ruminally and duodenally cannulated cows (77 +/- 12 days in milk, mean +/- SD) were used in a replicated 4 x 4 Latin square design experiment with 21-d periods. Treatments were control and a linear substitution of 2.5% fatty acids from supplemented saturated FS (SAT; prilled, hydrogenated free fatty acids) for partially unsaturated FS (UNS; calcium soaps of long-chain fatty acids). All rations contained identical forage and concentrate components including 37.2% forage and 13.5% cottonseed. Saturated FS linearly decreased ruminal digestibility of dry matter and organic matter and linearly decreased ruminal neutral detergent fiber (NDF) digestibility. The reduction in ruminal NDF digestibility was because of a linear decrease in digestion rate and a linear increase in passage rate of potentially digestible NDF with increasing saturated FS. Total tract digestibility of NDF was not different between treatments because of compensatory postruminal digestion. Ruminal fatty acid and C18 fatty acid digestibility tended to increase linearly with increasing unsaturated FS, and postruminal C18 fatty acid digestibility decreased with increasing saturated FS. Saturated FS linearly decreased ruminal organic matter digestibility and decreased intestinal long-chain fatty acid digestibility, although differences in fatty acid digestibility may be partially explained by fatty acid intake.

The Effect of Production Level on Feed Intake, Milk Yield, and Endocrine Responses to Two Fatty Acid Supplements in Lactating Cows

Animal responses to dietary treatment may interact with metabolic state, which differs for cows across a wide range of milk yield. Responses to dietary saturated vs. unsaturated fatty acid (FA) supplement was evaluated using 32 multiparous Holstein cows arranged in a crossover design with 14-d periods. Treatments were 2.5% FA from unsaturated FA (calcium salts of palm FA) or saturated FA (prilled, hydrogenated free FA). Unsaturated FA treatments decreased dry matter intake (0.8 kg/d) and time spent ruminating (25 min/d) compared with saturated FA treatment. Treatments did not differ in milk or 3.5% fat-corrected milk yield. Intake and milk yield responses were not related to milk yield across cows. Saturated FA treatment increased milk protein and lactose concentrations, but treatment did not affect yield of milk components. Saturated FA treatment increased insulin over 25% and decreased nonesterified FA nearly 20% with no effect on plasma somatotropin, glucose, or beta-hydroxybutyrate concentrations. Milk protein concentration and yield responses to treatment were positively correlated with pretrial fat-corrected milk yield. Milk protein response was not related to insulin response, supporting the importance of insulin sensitivity in control of milk protein synthesis. Unsaturated FA treatment decreased dry matter intake and rumination time compared with saturated FA treatment, consistent with reports of unsaturated fat increasing satiety and decreasing gut motility. Decreased milk protein synthesis by fat supplementation may be related to FA saturation and milk yield of cows.

THE COW AS A MODEL TO STUDY FOOD INTAKE REGULATION

Animal models have been invaluable for studying aspects of food intake regulation that for various reasons cannot be observed in humans. The dairy cow is a unique animal model because of an unrivaled energy requirement; its great drive to eat results in feeding behavior responses to treatments within the physiological range. Cows' docile nature and large size make them ideal for measuring temporal treatment effects because digestion and absorption kinetics and responses in endocrine systems, gene expression, metabolite pools and fluxes, and feeding behavior can be measured simultaneously. Thus, cows are important models to investigate interactions of short-term signals regulating food intake. Furthermore, different physiological states throughout the lactation cycle provide powerful models to study how short- and long-term signals interact to affect long-term energy status. The use of the cow as a model can lead to breakthroughs in understanding the complex interactions of signals regulating food intake.