Both Dietary Fatty Acids and Those Present in the Cecotrophs Contribute to the Distinctive Chemical Characteristics of New Zealand Rabbit Milk Fat

The relationship between the fatty acid (FA) profile of cecotrophs and that of the milk fat was evaluated in nine multiparous New Zealand does during the first 12 days of lactation. Milk samples were obtained manually on days 6, 8, 10, and 12 postpartum and cecotrophs and feces were collected on days 7, 9, and 11 postpartum. The FA profiles of feed, milk, cecotrophs, and feces were determined using gas chromatography. The principal FA found in rabbits' milk were 8:0, 10:0, 16:0, 18:1 cis-9, and 18:2 n-6. Bacteria-derived FA found in the milk fat included branched FA from 14 to 16 carbons, and 18:1 trans. Two isomers of conjugated linoleic acid (CLA) were also present, namely cis-9,trans-11 (0.09 ± 0.006 mol%) and trans-10,cis-12 (0.06 ± 0.01 mol%). The content of total FA in the cecotrophs was the 1.10 ± 0.08 mg/100 mg freeze-dried sample, with 2.50 ± 0.83 mol% 18:1 trans-11. Significant correlations between cecotroph and milk FA profiles were found for numerous FA, and those with correlation coefficients greater than 0.90 were 12:0, 14:0, 15:0, 16:0, 18:0, 18:1 trans-6/8, 18:1 trans-9, 18:1 cis-9, 18:2 n-6, 18:3 n-3, 20:1 cis-9, 20:2 n-6, and 22:0. Cecum biohydrogenation processes were evident based on the greater content of saturated FA (p = 0.008) found (54.46 ± 4.37 mol%) in the cecotrophs relative to that in feces (43.08 ± 4.37 mol%). Under conditions of the present study, the milk FA profile was influenced by the FA profile of diet and the cecotrophs consumed by lactating does.

Time-dependent effect of trans-10,cis-12 conjugated linoleic acid on gene expression of lipogenic enzymes and regulators in mammary tissue of dairy cows

Trans-10,cis-12 conjugated linoleic acid (CLA) has been identified as an intermediate of rumen fatty acid biohydrogenation that caused milk fat depression (MFD) in the dairy cow. Previous studies in cows experiencing CLA- and diet-induced MFD have identified reduced mammary expression of the master lipogenic regulator sterol response element transcription factor 1 (SREBF1) and many of its dependent genes. To distinguish between primary mechanisms regulating milk fat synthesis and secondary adaptations to the reduction in milk fat, we conducted a time-course experiment. Eleven dairy cows received by abomasal infusion an initial priming dose of 6.25 g of CLA followed by 12.5 g/d delivered in multiple pulses per day for 5 d. Cows were milked 3×/d and mammary biopsies were obtained under basal condition (prebolus control) and 12, 30, and 120 h relative to initiation of CLA infusion. Milk fat concentration and yield decreased progressively reaching a nadir at 69 h (1.82% and 38.2 g/h) and averaged 2.03 ± 0.19% and 42.1 ± 4.10 g/h on the last day of treatment (±standard deviation). Expression of fatty acid synthase (FASN) and lipoprotein lipase (LPL) were decreased at 30 and 120 h compared with control. Expression of SREBF1 and THRSP were also decreased at 30 and 120 h compared with control. Additionally, we failed to observe changes in other factors, including peroxisome proliferator-activated receptor γ and liver × receptor β and milk fat globular membrane proteins, during CLA treatment. However, expression of milk fat globular membrane proteins were decreased after 14 d of diet-induced MFD in samples from a previous experiment, indicating a possible long-term response. The rapid decrease in lipogenic enzymes, SREBF1, and THRSP provide strong support for their transcriptional regulation as a primary mechanism of milk fat depression.

Quantitative Risk Assessment of Antimicrobial-Resistant Foodborne Infections in Humans Due to Recombinant Bovine Somatotropin Usage in Dairy Cows

Recombinant bovine somatotropin (rbST) is a production-enhancing technology that allows the dairy industry to produce milk more efficiently. Concern has been raised that cows supplemented with rbST are at an increased risk of developing clinical mastitis, which would potentially increase the use of antimicrobial agents and increase human illnesses associated with antimicrobial-resistant bacterial pathogens delivered through the dairy beef supply. The purpose of this study was to conduct a quantitative risk assessment to estimate the potential increased risk of human infection with antimicrobial-resistant bacteria and subsequent adverse health outcomes as a result of rbST usage in dairy cattle. The quantitative risk assessment included the following steps: (i) release of antimicrobial-resistant organisms from the farm, (ii) exposure of humans via consumption of contaminated beef products, and (iii) consequence of the antimicrobial-resistant infection. The model focused on ceftiofur (parenteral and intramammary) and oxytetracycline (parenteral) treatment of clinical mastitis in dairy cattle and tracked the bacteria Campylobacter spp., Salmonella enterica subsp. enterica, and Escherichia coli in the gastrointestinal tract of the cow. Parameter estimates were developed to be maximum risk to overestimate the risk to humans. The excess number of cows in the U.S. dairy herd that were predicted to carry resistant bacteria at slaughter due to rbST administration was negligible. The total number of excess human illnesses caused by resistant bacteria due to rbST administration was also predicted to be negligible with all risks considerably less than one event per 1 billion people at risk per year for all bacteria. The results indicate a high probability that the use of rbST according to label instructions presents a negligible risk for increasing the number of human illnesses and subsequent adverse outcomes associated with antimicrobial-resistant Campylobacter, Salmonella, or E. coli .

The Potential Impact of Animal Science Research on Global Maternal and Child Nutrition and Health: A Landscape Review

High among the challenges facing mankind as the world population rapidly expands toward 9 billion people by 2050 is the technological development and implementation of sustainable agriculture and food systems to supply abundant and wholesome nutrition. In many low-income societies, women and children are the most vulnerable to food insecurity, and it is unequivocal that quality nutrition during the first 1000 d of life postconception can be transformative in establishing a robust, lifelong developmental trajectory. With the desire to catalyze disruptive advancements in global maternal and child health, this landscape review was commissioned by the Bill & Melinda Gates Foundation to examine the nutritional and managerial practices used within the food-animal agricultural system that may have relevance to the challenges faced by global human health. The landscape was categorized into a framework spanning 1) preconception, 2) gestation and pregnancy, 3) lactation and suckling, and 4) postweaning and toddler phases. Twelve key findings are outlined, wherein research within the discipline of animal sciences stands to inform the global health community and in some cases identifies gaps in knowledge in which further research is merited. Notable among the findings were 1) the quantitative importance of essential fatty acid and amino acid nutrition in reproductive health, 2) the suggested application of the ideal protein concept for improving the amino acid nutrition of mothers and children, 3) the prospect of using dietary phytase to improve the bioavailability of trace minerals in plant and vegetable-based diets, and 4) nutritional interventions to mitigate environmental enteropathy. The desired outcome of this review was to identify potential interventions that may be worthy of consideration. Better appreciation of the close linkage between human health, medicine, and agriculture will identify opportunities that will enable faster and more efficient innovations in global maternal and child health.

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.

Meta-analysis of the effects of sometribove zinc suspension on the production and health of lactating dairy cows

OBJECTIVE

To provide an updated evaluation of the efficacy and safety of sometribove zinc suspension (rbST-Zn), a form of recombinant bovine somatotropin, in lactating dairy cows.

DESIGN

Meta-analysis.

SAMPLE

26 studies published in peer-reviewed journals or reviewed by a regulatory agency.

PROCEDURES

To be included, a study had to involve the use of the rbST-Zn formulation available to US producers in accordance with the label instructions for treatment initiation (57 to 70 days postpartum), dose (500 mg, q 14 d), and route (SC).

RESULTS

For cows treated with rbST-Zn, mean milk, 3.5% fat-corrected milk, fat, and protein yields were increased by 4.00, 4.04, 0.144, and 0.137 kg/d (8.8, 8.89, 0.32, and 0.30 lb/d), respectively; however, the concentration of milk components did not change. Pregnancy proportion for the first 2 breeding cycles was increased by 5.4%, and pregnancy proportion for the duration of the trial was reduced by 5.5% for rbST-Zn-treated cows, compared with proportions for untreated cows. Mean body condition score (1 to 5 scale) was reduced by 0.06 points during the period of rbST-Zn use for treated cows. Administration of rbST-Zn had no effect on milk somatic cell count, the number of days to pregnancy, or inseminations per pregnancy; rates of fetal loss, twins, cystic ovaries, clinical lameness, lameness lesions, or traumatic lesions of the integumentary system; and odds of clinical mastitis or culling.

CONCLUSIONS AND CLINICAL RELEVANCE

Results indicated that rbST-Zn administration to dairy cows effectively increases milk production with no adverse effects on cow health and well-being.

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.

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.

Conjugated linoleic acid-induced milk fat depression in lactating ewes is accompanied by reduced expression of mammary genes involved in lipid synthesis

Conjugated linoleic acids (CLA) are produced during rumen biohydrogenation and exert a range of biological effects. The trans-10,cis-12 CLA isomer is a potent inhibitor of milk fat synthesis in lactating dairy cows and some aspects of the mechanism have been established. Conjugated linoleic acid-induced milk fat depression has also been observed in small ruminants and our objective was to examine the molecular mechanism in lactating ewes. Multiparous lactating ewes were fed a basal ration (0.55:0.45 concentrate-to-forage ratio; dry matter basis) and randomly allocated to 2 dietary CLA levels (n=8 ewes/treatment). Treatments were zero CLA (control) or 15 g/d of lipid-encapsulated CLA supplement containing cis-9,trans-11 and trans-10,cis-12 CLA isomers in equal proportions. Treatments were fed for 10 wk and the CLA supplement provided 1.5 g of trans-10,cis-12/d. No treatment effects were observed on milk yield or milk composition for protein or lactose at wk 10 of the study. In contrast, CLA treatment significantly decreased both milk fat percentage and milk fat yield (g/d) by about 23%. The de novo synthesized fatty acids (FA; <C16) were significantly decreased in proportion (15%) and daily yield (27%), and the proportion of preformed FA (>C16) was increased (10%) for the CLA treatment. In agreement with the reduced de novo FA synthesis, mRNA abundance of acetyl-coenzyme A carboxylase α, FA synthase, stearoyl-CoA desaturase 1, and glycerol-3-phosphate acyltransferase 6 decreased by 25 to 40% in the CLA-treated group. Conjugated linoleic acid treatment did not significantly reduce the mRNA abundance of enzymes involved in NADPH production, but the mRNA abundance for sterol regulatory element-binding factor 1 and insulin-induced gene 1, genes involved in regulation of transcription of lipogenic enzymes, was decreased by almost 30 and 55%, respectively, with CLA treatment. Furthermore, mRNA abundance of lipoprotein lipase decreased by almost 40% due to CLA treatment. In conclusion, the mechanism for CLA-induced milk fat depression in lactating ewes involved the sterol regulatory element-binding protein transcription factor family and a coordinated downregulation in transcript abundance for lipogenic enzymes involved in mammary lipid synthesis.

The role of productivity in improving the environmental sustainability of ruminant production systems

The global livestock industry is charged with providing sufficient animal source foods to supply the global population while improving the environmental sustainability of animal production. Improved productivity within dairy and beef systems has demonstrably reduced resource use and greenhouse gas emissions per unit of food over the past century through the dilution of maintenance effect. Further environmental mitigation effects have been gained through the current use of technologies and practices that enhance milk yield or growth in ruminants; however, the social acceptability of continued intensification and use of productivity-enhancing technologies is subject to debate. As the environmental impact of food production continues to be a significant issue for all stakeholders within the field, further research is needed to ensure that comparisons among foods are made based on both environmental impact and nutritive value to truly assess the sustainability of ruminant products.

Sterculic Oil, a Natural SCD1 Inhibitor, Improves Glucose Tolerance in Obese ob/ob Mice

Obesity and its metabolic complications are associated with increased expression/activity of stearoyl-CoA desaturase-1 (SCD1), a major regulator of lipid metabolism. Reduction or ablation of this enzyme is associated with an improved metabolic profile and has gained attention as a target for pharmaceutical development. Sterculic oil (SO) is a known inhibitor of SCD1 and may provide a natural approach for treating obesity and/or insulin resistance. The purpose of this study was to evaluate the effects of SO consumption in leptin-deficient ob/ob mice, a model of obesity and insulin resistance. Five-week-old male mice received either an AIN-93G (control) or an AIN-93G diet containing 0.5% SO. After 9 weeks, SO supplementation did not alter food intake or body weight; however, the desaturase indices, a proxy of SCD1 activity, were reduced in liver and adipose tissue of SO-supplemented animals. This reduction was associated with improved glucose and insulin tolerance and attenuated hepatic inflammation in obese ob/ob mice, while no appreciable changes were observed in lean control mice receiving SO. Future studies are needed to better understand the mechanism(s) by which SO is functioning to improve glucose metabolism and to further explore the nutraceutical potential and health implications of SO supplementation.

Ruminant-produced trans-fatty acids raise plasma HDL particle concentrations in intact and ovariectomized female Hartley guinea pigs

Cardiovascular disease (CVD) is the leading cause of death among women worldwide, and risk for developing CVD increases postmenopause. Consumption of trans-fatty acids (tFA) has been positively associated with CVD incidence and mortality. The current study was designed to assess the effects of diets high in industrially produced (IP)-tFA, from partially hydrogenated vegetable oils (PHVO), and ruminant-produced (RP)-tFA, from butter oil (BO), on risk factors for CVD. Thirty-two female Hartley guinea pigs, one-half of which were ovariectomized (OVX) to mimic the postmenopausal condition, were fed hypercholesterolemic diets containing 9% by weight PHVO or BO (n = 8/diet and ovariectomy) for 8 wk. The plasma and hepatic lipids did not differ between IP- and RP-tFA groups or between intact and OVX guinea pigs. The BO diet resulted in higher concentrations of plasma total and small HDL particle subclass concentrations than the PHVO diet regardless of ovariectomy status. The intact BO group had higher concentrations of large HDL particles than the intact PHVO group. HDL mean particle size tended to be larger (P = 0.07) in the PHVO groups compared with the BO groups regardless of ovariectomy status. There was a trend toward an interaction between diet and ovariectomy status for LDL mean particle size, which tended to be larger in OVX guinea pigs fed PHVO (P = 0.07). In summary, consumption of IP- and RP-tFA resulted in differential effects on HDL particle subclass profiles in female guinea pigs. The effect of tFA consumption and hormonal status on HDL particle subclass metabolism and the subsequent impact on CVD in females warrants further investigation.

Porcine somatotropin alters insulin response in growing pigs by reducing insulin sensitivity rather than changing responsiveness

Exogenous porcine somatotropin (pST) treatment consistently improves growth performance and reduces fat deposition in pigs, and it is hypothesized that one component of the mechanism is through altering the sensitivity and/or responsiveness to insulin. Therefore, a study was conducted to investigate the effect of pST treatment on whole-body glucose metabolism in response to varying doses of insulin. Eight barrows were surgically prepared with indwelling catheters and randomly assigned to one of two treatment groups (0 or 120 μg pST/kg BW · d) for 13 d. Whole-body glucose kinetics were measured during infusion of [6-(3)H]-glucose under basal conditions and during hyperinsulinemic-euglycemic clamps at various insulin infusion rates (7, 28, and 140, and 14, 70, and 280 ng insulin/kg BW · min) and alterations in the dose-response parameters were calculated with nonlinear regression. Treatment with pST increased basal plasma concentrations of glucose (36%; P = 0.005), insulin (276%; P = 0.001), and NEFAs (177%; P = 0.01) and decreased the rate of glucose disappearance (-59%; P = 0.001). The responsiveness (maximum response) for steady state glucose infusion rate to maintain glycemia was not altered by pST (112 vs 106 μmol/min · kg; P = 0.78), whereas the sensitivity (effective dose at 50% of maximum response) was increased almost 7-fold (1.3 vs 8.7 ng/mL; P = 0.027). Similar responses were observed for rate of glucose disappearance and insulin-dependent glucose utilization. Therefore, pST-induced insulin resistance with regard to whole-body glucose uptake is due to a reduced sensitivity to insulin, rather than a change in responsiveness.

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.

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.

Survey of the fatty acid composition of retail milk in the United States including regional and seasonal variations

Consumers are increasingly aware that food components have the potential to influence human health maintenance and disease prevention, and dietary fatty acids (FA) have been of special interest. It has been 25 years since the last survey of US milk FA composition, and during this interval substantial changes in dairy rations have occurred, including increased use of total mixed rations and byproduct feeds as well as the routine use of lipid and FA supplements. Furthermore, analytical procedures have improved allowing greater detail in the routine analysis of FA, especially trans FA. Our objective was to survey US milk fat and determine its FA composition. We obtained samples of fluid milk from 56 milk processing plants across the US every 3 mo for one year to capture seasonal and geographical variations. Processing plants were selected based on the criteria that they represented 50% or more of the fluid milk produced in that area. An overall summary of the milk fat analysis indicated that saturated fatty acids comprised 63.7% of total milk FA with palmitic and stearic acids representing the majority (44.1 and 18.3% of total saturated fatty acids, respectively). Unsaturated fatty acids were 33.2% of total milk FA with oleic acid predominating (71.0% of total unsaturated fatty acids). These values are comparable to those of the previous survey in 1984, considering differences in analytical techniques. Trans FA represented 3.2% of total FA, with vaccenic acid being the major trans isomer (46.5% of total trans FA). Cis-9, trans-11 18:2 conjugated linoleic acid represented 0.55% total milk FA, and the major n-3 FA (linolenic acid, 18:3) composed 0.38%. Analyses for seasonal and regional effects indicated statistical differences for some FA, but these were minor from an overall human nutrition perspective as the FA profile for all samples were numerically similar. Overall, the present study provides a valuable database for current FA composition of US fluid milk, and results demonstrate that the milk fatty acid profile is remarkably consistent across geographic regions and seasons from the perspective of human dietary intake of milk fat.

Ruminant-produced trans-fatty acids raise plasma total and small HDL particle concentrations in male Hartley guinea pigs

Although trans-fatty acid (tFA) intake has been positively associated with coronary heart disease (CHD), the relative effect of consuming industrially produced (IP)- compared with ruminant-produced (RP)-tFA on CHD risk factors is unclear. This study was designed to examine the effects of feeding partially hydrogenated vegetable oil (PHVO), IP-tFA source, and butter oil (BO), RP-tFA source, on the development of atherosclerosis and risk factors associated with CHD. Forty-eight male Hartley guinea pigs were fed a hypercholesterolemic diet containing (9% by weight) PHVO, BO, coconut oil (CO; positive control), or soybean oil (SO; negative control) for 8 or 12 wk (n = 6/group). Morphological analysis revealed that none of the groups developed atherosclerosis. Plasma and hepatic lipids did not differ between the tFA groups, but total and small HDL particles were significantly higher in the BO group than in the PHVO group and mean HDL particle size was significantly smaller in the BO group than in the PHVO group. Compared with the other treatment groups, the SO treatment resulted in significantly lower total cholesterol (TC) and LDL cholesterol in plasma, whereas hepatic TC was significantly higher in the SO group than in the other treatment groups. Plasma and hepatic cholesterol concentrations did not differ between the tFA and CO treatments. These results demonstrate that when fed at a high dose, IP- and RP-tFA had the same effect on established CHD risk factors in male Hartley guinea pigs. The effects of RP-tFA on HDL particle sizes and concentrations warrant further investigation.

Sterol regulatory element binding protein and dietary lipid regulation of fatty acid synthesis in the mammary epithelium

The lactating mammary gland synthesizes large amounts of triglyceride from fatty acids derived from the blood and from de novo lipogenesis. The latter is significantly increased at parturition and decreased when additional dietary fatty acids become available. To begin to understand the molecular regulation of de novo lipogenesis, we tested the hypothesis that the transcription factor sterol regulatory element binding factor (SREBF)-1c is a primary regulator of this system. Expression of Srebf1c mRNA and six of its known target genes increased ≥2.5-fold at parturition. However, Srebf1c-null mice showed only minor deficiencies in lipid synthesis during lactation, possibly due to compensation by Srebf1a expression. To abrogate the function of both isoforms of Srebf1, we bred mice to obtain a mammary epithelial cell-specific deletion of SREBF cleavage-activating protein (SCAP), the SREBF escort protein. These dams showed a significant lactation deficiency, and expression of mRNA for fatty acid synthase (Fasn), insulin-induced gene 1 (Insig1), mitochondrial citrate transporter (Slc25a1), and stearoyl-CoA desaturase 2 (Scd2) was reduced threefold or more; however, the mRNA levels of acetyl-CoA carboxylase-1α (Acaca) and ATP citrate lyase (Acly) were unchanged. Furthermore, a 46% fat diet significantly decreased de novo fatty acid synthesis and reduced the protein levels of ACACA, ACLY, and FASN significantly, with no change in their mRNA levels. These data lead us to conclude that two modes of regulation exist to control fatty acid synthesis in the mammary gland of the lactating mouse: the well-known SREBF1 system and a novel mechanism that acts at the posttranscriptional level in the presence of SCAP deletion and high-fat feeding to alter enzyme protein.

A supplement containing trans-10, cis-12 conjugated linoleic acid reduces milk fat yield but does not alter organ weight or body fat deposition in lactating ewes

Conjugated linoleic acids (CLA) have been demonstrated to be a potent inhibitor of milk fat synthesis in ruminants, but effects on carcass composition and organ weight are unknown. Our objectives in this experiment were to determine the dose response of ruminally protected CLA on the performance, organ weight, and fatty acid (FA) composition of early lactation dairy ewes. Twenty-four multiparous dairy ewes were fed a basal diet for 10 wk that was supplemented with a lipid-encapsulated CLA at 1 of 3 levels: no CLA (control, CON), low CLA (L-CLA), or high CLA (H-CLA) to supply 0, 1.5, or 3.8 g/d, respectively, of both trans-10, cis-12 and cis-9, trans-11 CLA. Dry matter intake was not affected (P > 0.05) by dietary treatment. Ewes fed H-CLA had a 13% higher milk yield compared with those receiving either CON or L-CLA. Compared with CON, milk fat yield (g/d) was 14 and 24% lower in ewes fed L-CLA or H-CLA, respectively. Supplementing ewes with CLA did not affect carcass or organ weights, carcass composition, or organ FA content. Compared with ewes receiving the CON diet, CLA supplementation had little effect on the FA composition of the Longissimus dorsi, although cis-9, trans-11 and trans-10, cis-12 CLA were increased in ewes receiving H-CLA. The current findings are consistent with the view that the energy spared by the CLA reduction in milk fat content was mainly partitioned to milk yield and there was no evidence of organ hypertrophy or liver steatosis.

Survey of the fatty acid composition of retail milk differing in label claims based on production management practices

Consumers are becoming increasingly health conscious, and food product choices have expanded. Choices in the dairy case include fluid milk labeled according to production management practices. Such labeling practices may be misunderstood and perceived by consumers to reflect differences in the quality or nutritional content of milk. Our objective was to investigate nutritional differences in specialty labeled milk, specifically to compare the fatty acid (FA) composition of conventional milk with milk labeled as recombinant bST (rbST)-free or organic. The retail milk samples (n=292) obtained from the 48 contiguous states of the United States represented the consumer supply of pasteurized, homogenized milk of 3 milk types: conventionally produced milk with no specialty labeling, milk labeled rbST-free, and milk labeled organic. We found no statistical differences in the FA composition of conventional and rbST-free milk; however, these 2 groups were statistically different from organic milk for several FA. When measuring FA as a percentage of total FA, organic milk was higher in saturated FA (65.9 vs. 62.8%) and lower in monounsaturated FA (26.8 vs. 29.7%) and polyunsaturated FA (4.3 vs. 4.8%) compared with the average of conventional and rbST-free retail milk samples. Likewise, among bioactive FA compared as a percentage of total FA, organic milk was slightly lower in trans 18:1 FA (2.8 vs. 3.1%) and higher in n-3 FA (0.82 vs. 0.50%) and conjugated linoleic acid (0.70 vs. 0.57%). From a public health perspective, the direction for some of these differences would be considered desirable and for others would be considered undesirable; however, without exception, the magnitudes of the differences in milk FA composition among milk label types were minor and of no physiological importance when considering public health or dietary recommendations. Overall, when data from our analysis of FA composition of conventional milk and milk labeled rbST-free or organic were combined with previous analytical comparisons of the quality and composition of these retail milk samples, results established that there were no meaningful differences that would affect public health and that all milks were similar in nutritional quality and wholesomeness.

t10,c12-CLA decreases adiposity in peripubertal mice without dose-related detrimental effects on mammary development, inflammation status, and metabolism

The trans 10, cis 12-conjugated linoleic acid (10,12-CLA) isomer reduces adiposity in several animal models. In the mouse, however, this effect is associated with adipose tissue inflammation, hyperinsulinemia and hepatic lipid accumulation. Moreover, 10,12-CLA was recently shown to promote mammary ductal hyperplasia and ErbB2/Her2-driven mammary cancer in the mouse. Reasons for detrimental effects of 10,12-CLA on the mouse mammary gland could relate to its effect on the mammary fat pad (MFP), which is essential for normal development. Accordingly, we hypothesized that mammary effects of 10,12-CLA were mediated through the MFP in a dose-dependent manner. Female FVB mice were fed 10,12-CLA at doses of 0%, 0.1%, 0.2%, or 0.5% of the diet from day 24 of age, and effects on mammary development and metabolism were measured on day 49. The 0.5% dose reduced ductal elongation and caused premature alveolar budding. These effects were associated with increased expression of inflammatory markers and genes shown to alter epithelial growth (IGF binding protein-5) and alveolar budding (TNF-α and receptor of activated NF-κB ligand). The 0.5% dose also caused hyperinsulinemia and hepatic lipid accumulation. In contrast, the 0.1% 10,12-CLA dose had no adverse effects on mammary development, metabolic events, and inflammatory responses, but remained effective in decreasing adipose weights and lipogenic gene expression. These results show that a low dose of 10,12-CLA reduces adiposity in the mouse without negative effects on mammary development, inflammation, and metabolism, and suggest that previously reported detrimental effects relate to the use of excessive doses.

Hot topic: Enhancing omega-3 fatty acids in milk fat of dairy cows by using stearidonic acid-enriched soybean oil from genetically modified soybeans

Very long chain n-3 fatty acids such as eicosapentaenoic acid (EPA; 20:5n-3) are important in human cardiac health and the prevention of chronic diseases, but food sources are limited. Stearidonic acid (SDA; 18:4n-3) is an n-3 fatty acid that humans are able to convert to EPA. In utilizing SDA-enhanced soybean oil (SBO) derived from genetically modified soybeans, our objectives were to examine the potential to increase the n-3 fatty acid content of milk fat and to determine the efficiency of SDA uptake from the digestive tract and transfer to milk fat. Three multiparous, rumen-fistulated Holstein cows were assigned randomly in a 3 x 3 Latin square design to the following treatments: 1) control (no oil infusion); 2) abomasal infusion of SDA-enhanced SBO (SDA-abo); and 3) ruminal infusion of SDA-enhanced SBO (SDA-rum). The SDA-enhanced SBO contained 27.1% SDA, 10.4% alpha-linolenic acid, and 7.2% gamma-linolenic acid. Oil infusions provided 57 g/d of SDA with equal amounts of oil infused into either the rumen or abomasum at 6-h intervals over a 7-d infusion period. Cow numbers were limited and no treatment differences were detected for DMI or milk production (22.9+/-0.5 kg/d and 32.3+/-0.9 kg/d, respectively; least squares means +/- SE), milk protein percentage and yield (3.24+/-0.04% and 1.03+/-0.02 kg/d), or lactose percentage and yield (4.88+/-0.05% and 1.55+/-0.05 kg/d). Treatment also had no effect on milk fat yield (1.36+/-0.03 kg/d), but milk fat percentage was lower for the SDA-rum treatment (4.04+/-0.04% vs. 4.30+/-0.04% for control and 4.41+/-0.05% for SDA-abo). The SDA-abo treatment increased n-3 fatty acids to 3.9% of total milk fatty acids, a value more than 5-fold greater than that for the control. Expressed as a percentage of total milk fatty acids, values (least squares means +/- SE) for the SDA-abo treatment were 1.55+/-0.03% for alpha-linolenic acid (18:3n-3), 1.86+/-0.02 for SDA, 0.23 +/- <0.01 for eicosatetraenoic acid (20:4n-3), and 0.18+/-0.01 for EPA. Transfer efficiency of SDA to milk fat represented 39.3% (range=36.8 to 41.9%) of the abomasally infused SDA and 47.3% (range=45.0 to 49.6%) when the n-3 fatty acids downstream from SDA were included. In contrast, transfer of ruminally infused SDA to milk fat averaged only 1.7% (range=1.3 to 2.1%), indicating extensive rumen biohydrogenation. Overall, results demonstrate the potential to use SDA-enhanced SBO from genetically modified soybeans combined with proper ruminal protection to achieve impressive increases in the milk fat content of SDA and other n-3 fatty acids that are beneficial for human health.

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.

The environmental impact of dairy production: 1944 compared with 2007

A common perception is that pasture-based, low-input dairy systems characteristic of the 1940s were more conducive to environmental stewardship than modern milk production systems. The objective of this study was to compare the environmental impact of modern (2007) US dairy production with historical production practices as exemplified by the US dairy system in 1944. A deterministic model based on the metabolism and nutrient requirements of the dairy herd was used to estimate resource inputs and waste outputs per billion kg of milk. Both the modern and historical production systems were modeled using characteristic management practices, herd population dynamics, and production data from US dairy farms. Modern dairy practices require considerably fewer resources than dairying in 1944 with 21% of animals, 23% of feedstuffs, 35% of the water, and only 10% of the land required to produce the same 1 billion kg of milk. Waste outputs were similarly reduced, with modern dairy systems producing 24% of the manure, 43% of CH(4), and 56% of N(2)O per billion kg of milk compared with equivalent milk from historical dairying. The carbon footprint per billion kilograms of milk produced in 2007 was 37% of equivalent milk production in 1944. To fulfill the increasing requirements of the US population for dairy products, it is essential to adopt management practices and technologies that improve productive efficiency, allowing milk production to be increased while reducing resource use and mitigating environmental impact.

Individual trans octadecenoic acids and partially hydrogenated vegetable oil differentially affect hepatic lipid and lipoprotein metabolism in golden Syrian hamsters

Trans fatty acids (TFA) from industrial sources [i.e. partially hydrogenated vegetable oil (PHVO)] have been associated with several chronic human diseases, especially coronary heart disease (CHD). The possible contribution of individual TFA to overall CHD risk remains largely unknown. The objective of the present study was to investigate the effects of 2 major trans 18:1 isomers, trans-9 18:1 [elaidic acid (EA)] and trans-11 18:1 [vaccenic acid (VA)] on plasma lipid biomarkers of CHD risk. Thirty-two male Golden Syrian hamsters were randomly assigned to 1 of 4 dietary treatments: 1) control "Western" diet; 2) PHVO supplement; 3) EA supplement; and 4) VA supplement. Fat supplements were incorporated into the respective treatment diets at 2.5 g/100 g of diet. Compared with the control diet, the PHVO diet increased the plasma ratios of total:HDL-cholesterol and nonHDL:HDL-cholesterol by 17 and 23%, respectively. In contrast, these values decreased by 27 and 46% after the EA treatment and 8 and 14% after the VA treatment, respectively, indicating an improvement (reduction) in CHD risk. With regard to liver lipids, the EA diet reduced the content of (n-3) and (n-6) PUFA relative to the other treatments, suggesting an inhibition of enzymes common to the 2 biosynthesis pathways. Overall, results demonstrate that the hypercholesterolemic effects of PHVO are not dependent on the presence of EA or VA and that other bioactive components in PHVO must be responsible for its associated adverse health effects.

Short communication: Regulation of milk fat yield and fatty acid composition by insulin

Diet-induced milk fat depression in dairy cows has been known for many years and several theories have been proposed. One that continues to receive support is the glucogenic-insulin theory. Previous studies testing this theory using a hyperinsulinemic-euglycemic clamp have had variable results attributable to variability in the use of body fat reserves as a source of milk fatty acids. Our objective was to test the glucogenic-insulin theory using cows immediately postpartum, a period when the use of body fat for milk fat synthesis is greatest. During wk 2 postpartum, 5 cows were given a 2-d baseline period and then clamped for 4 d. Insulin was increased more than 2-fold during the clamp while the blood glucose concentration was maintained. Milk yield was not altered by administration of the clamp (38.7 vs. 39.0 +/- 1.4 kg/d); however, the milk fat percentage and yield were reduced by 27% and plasma nonesterified fatty acids were reduced by 68%. Analysis of the milk fatty acid composition revealed that the decrease in milk fat yield during use of the clamp was almost exclusively due to reductions in preformed fatty acids; this is the exact opposite of what is observed with diet-induced milk fat depression. Therefore, our results do not support the glucogenic-insulin theory of diet-induced milk fat depression. The results further indicated that reductions in milk fat observed previously with hyperinsulinemic-euglycemic clamps or with glucose or propionate infusions were most likely consequences of the ability of insulin to inhibit lipolysis, thereby limiting the mammary availability of preformed fatty acids mobilized from body reserves.

Do trans fatty acids from industrially produced sources and from natural sources have the same effect on cardiovascular disease risk factors in healthy subjects? Results of the trans Fatty Acids Collaboration (TRANSFACT) study

BACKGROUND

The consumption of monounsaturated trans fatty acids (TFAs) increases the risk of cardiovascular disease (CVD). Putative differences between the effects of TFAs from industrially produced and natural sources on CVD risk markers were not previously investigated in healthy subjects.

OBJECTIVE

We aimed to compare the effects of TFAs from industrially produced and natural sources on HDL and LDL cholesterol, lipoprotein particle size and distribution, apolipoproteins, and other lipids in healthy subjects.

DESIGN

In a randomized, double-blind, controlled, crossover design, 46 healthy subjects (22 men and 24 women) consumed food items containing TFAs (11-12 g/d, representing approximately 5% of daily energy) from the 2 sources.

RESULTS

Forty subjects (19 men and 21 women) completed the study. Compared with TFAs from industrially produced sources, TFAs from natural sources significantly (P = 0.012) increased HDL cholesterol in women but not in men. Significant (P = 0.001) increases in LDL-cholesterol concentrations were observed in women, but not in men, after the consumption of TFAs from natural sources. Apolipoprotein (apo)B and apoA1 concentrations confirmed the changes observed in LDL and HDL cholesterol. Analysis of lipoprotein subclass showed that only large HDL and LDL concentrations were modified by TFAs from natural sources but not by those from industrially produced sources.

CONCLUSIONS

This study shows that TFAs from industrially produced and from natural sources have different effects on CVD risk factors in women. The HDL cholesterol-lowering property of TFAs seems to be specific to industrial sources. However, it is difficult in the present study to draw a conclusion about the effect of TFAs from either source on absolute CVD risk in these normolipidemic subjects. The mechanism underlying the observed sex- and isomer-specific effects warrants further investigation.

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.

Evaluation of the Mechanism of Action of Conjugated Linoleic Acid Isomers on Reproduction in Dairy Cows

The objective of this study was to evaluate the mechanism of action through which conjugated linoleic acid (CLA) beneficially affects reproduction. Lactating Holstein cows (n = 45, 20 +/- 1 DIM) were assigned to 1 of 3 treatments: 70 g/d of Ca salts of tallow (control); 63 g/d of lipid-encapsulated CLA providing 7.1 g/d of cis-9, trans-11 CLA and 2.4 g/d of trans-10, cis-12 CLA (CLA 75:25); or 76 g/d of lipid-encapsulated CLA providing 7.1 g/d each of cis-9, trans-11 and trans-10, cis-12 CLA (CLA 50:50). Supplements were top-dressed for 37 d, milk production and DMI were recorded daily, and blood samples were taken 3 times per week. At 30 +/- 3 DIM, ovulation was synchronized in all cows with a modified Ovsynch protocol, and on d 15 of the cycle cows received an oxytocin injection; blood samples were obtained frequently to measure 13,14 dihydro, 15-keto PGF2alpha. On d 16 of the cycle cows received a PGF2alpha injection and ovarian follicular aspiration was performed 54 h later. Follicular fluid was analyzed for fatty acids, progesterone, and estradiol. Endometrial biopsies were taken before and again near the end of the supplementation period for fatty acid analysis. The CLA resulted in decreased milk fat content of 14.1 and 6.1% at wk 5 of treatment of CLA 50:50 and CLA 75:25, respectively. There were no differences in energy balance or plasma nonesterified fatty acids; however, plasma IGF-I was greater in cows supplemented with CLA 50:50. The CLA isomers were not detectable in endometrial tissue, but cis-9, trans-11 CLA tended to be greater in follicular fluid of supplemented cows. Response to the oxytocin challenge was not different among treatments. Progesterone during the early luteal phase and the estradiol:progesterone ratio in follicular fluid tended to be greater in cows supplemented with CLA 50:50. Overall, these results indicate that short periods of CLA supplementation do not alter uterine secretion of PGF2alpha. The mechanism through which CLA affects reproduction may involve improved ovarian follicular steroidogenesis and increased circulating concentrations of IGF-I.

Effect of Supplementation with Calcium Salts of Fish Oil on n-3 Fatty Acids in Milk Fat

Enrichment of milk fat with n-3 fatty acids, in particular eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), may be advantageous because of their beneficial effects on human health. In addition, these fatty acids play an important role in reproductive processes in dairy cows. Our objective was to evaluate the protection of EPA and DHA against rumen biohydrogenation provided by Ca salts of fish oil. Four Holstein cows were assigned in a Latin square design to the following treatments: 1) ruminal infusion of Ca salts of fish oil and palm fatty acid distillate low dose (CaFO-1), 2) ruminal infusion of Ca salts of fish oil and palm fatty acid distillate high dose (CaFO-2), 3) ruminal infusion of fish oil high dose (RFO), and 4) abomasal infusion of fish oil high dose (AFO). The high dose of fish oil provided approximately 16 and approximately 21 g/d of EPA and DHA, respectively, whereas the low dose (CaFO-1) provided 50% of these amounts. A 10-d pretreatment period was used as a baseline, followed by 9-d treatment periods with interceding intervals of 10 d. Supplements were infused every 6 h, milk samples were taken the last 3 d, and plasma samples were collected the last day of baseline and treatment periods. Milk fat content of EPA and DHA were 5 to 6 times greater with AFO, but did not differ among other treatments. Milk and milk protein yield were unaffected by treatment, but milk fat yield and DM intake were reduced by 20 and 15%, respectively, by RFO. Overall, results indicate rumen biohydrogenation of long chain n-3 fatty acids was extensive, averaging >85% for EPA and >75% for DHA for the Ca salts and unprotected fish oil supplements. Thus, Ca salts of fish oil offered no protection against the biohydrogenation of EPA and DHA beyond that observed with unprotected fish oil; however, the Ca salts did provide rumen inertness by preventing the negative effects on DM intake and milk fat yield observed with unprotected fish oil.

Effects of Trans-10, Cis-12 Conjugated Linoleic Acid on Ovine Milk Fat Synthesis and Cheese Properties

Trans-10, cis-12 conjugated linoleic acid (CLA) reduces milk fat synthesis in sheep in a manner similar to that seen in dairy cows, but its effects on cheese yield and flavor are unknown. Additionally, when dietary energy supply is restricted, CLA can increase milk and milk protein yield, which may alter cheese yield and eating quality. The objectives of the study were to examine the effects of supplementing ewe diets with a rumen-protected source of CLA at a high and low dietary energy intake on milk fat and protein synthesis and on cheese yield and eating quality. Sixteen multiparous ewes were randomly allocated to 1 of 4 dietary treatments: a high (6.7 Mcal of metabolizable energy/d) or low (5.0 Mcal of metabolizable energy/d) feeding level that was either unsupplemented or supplemented with 25 g/d of a lipid-encapsulated CLA (to provide 2.4 g/d of CLA) in each of 4 periods of 21 d duration in a 4 x 4 Latin square design. There was no effect of treatment on milk yield (g/d), but milk fat percentage and milk fat yield were reduced by 23 and 20%, respectively, in ewes supplemented with CLA. Milk fatty acid concentration (g/100 g) of chain length < C16 was decreased and > C16 was increased in milk and cheese following CLA supplementation, whereas decreasing the feeding level increased fatty acids > or = C16. Milk fat contents of CLA were 0.01 and 0.12 g/100 g of fatty acids for the unsupplemented and CLA-supplemented treatments, respectively, whereas cis-9, trans-11 CLA was unaffected by CLA supplementation. There was no main effect of treatment on cheese yield, which was 0.11 +/- 0.001 kg of cheese/kg of milk, but cheese yield was highest, at 0.12 +/- 0.001 kg/kg, when made from milk of ewes fed the high feeding level + unsupplemented treatment. Cheese made from the milk of ewes supplemented with CLA, compared with the unsupplemented diet, was rated (scale 0 to 10) higher in the creaminess (2.1 vs. 1.4; SEM 0.15) and less oily (0.8 vs. 1.3; SEM 0.17) attributes, and was preferred overall (4.5 vs. 3.9; SEM 0.21). Cheese produced from sheep on the high vs. low feed level was rated less yellow (2.8 vs. 4.2; SEM 0.11), less salty (1.9 vs. 2.3; SEM 0.15), and more sour (1.5 vs. 1.1; SEM 0.13). We concluded that the effect of feeding level on animal performance and cheese characteristics was small, whereas supplementing the diets of ewes with a ruminally protected CLA source reduced milk fat yield, did not affect cheese yield, and beneficially altered the flavor characteristics of the cheese.

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

Under certain dietary situations, rumen biohydrogenation results in the production of unique fatty acids that inhibit milk fat synthesis. The first of these to be identified was trans-10, cis-12 conjugated linoleic acid (CLA), but others are postulated to contribute to diet-induced milk fat depression (MFD). Our objective was to examine the potential role of trans-9, cis-11 CLA in the regulation of milk fat. In a preliminary study, we used gas-liquid and high-performance liquid chromatography techniques to examine milk fat samples from a diet-induced MFD study and found that an increase in trans-9, cis-11 CLA corresponded to the decrease in milk fat yield. We investigated this further using a CLA enrichment of 9, 11 isomers to examine the biological effect of trans-9, cis-11 CLA on milk fat synthesis. Four rumen-fistulated Holstein cows were randomly assigned in a 4 x 4 Latin square experiment involving 5-d treatment periods and abomasal infusion of 1) ethanol (control), 2) a 9, 11 CLA mix (containing 32% trans-9, cis-11, 29% cis-9, trans-11, and 17% trans-9, trans-11), 3) a trans-9, trans-11 CLA supplement, and 4) a trans-10, cis-12 CLA supplement (positive control). The trans-9, trans-11 CLA and trans-10, cis-12 CLA supplements were of high purity (>90%), and all supplements were infused at a rate to provide 5 g/d of the CLA isomer of interest. Milk yield and dry matter intake did not differ among treatments. Compared with the control treatment, milk fat yield was reduced by 15% for the 9, 11 CLA mixture and by 27% for the trans-10, cis-12 CLA treatment. We also found that trans-9, trans-11 CLA had no effect on milk fat yield, and previous research has shown that milk fat yield is unaltered when cows are infused with cis-9, trans-11 CLA. When all treatments were considered, results suggested that trans-9, cis-11 was the CLA isomer in the 9, 11 CLA mix responsible for the reduction in milk fat synthesis, although the magnitude was less than that observed for trans-10, cis-12 CLA. Interestingly, trans-9, trans-11 CLA altered the milk fat desaturase index, further demonstrating that alterations in desaturase can occur independently of effects on milk fat synthesis. Overall, our investigations identified that an increase in milk fat content of trans-9, cis-11 CLA was associated with diet-induced MFD and provided evidence of a role for this isomer in MFD based on the 15% reduction in milk fat yield with abomasal infusion of a CLA enrichment that supplied 5 g/d of trans-9, cis-11 CLA.

Effects of a Supplement Containing Trans-10, Cis-12 Conjugated Linoleic Acid on Bioenergetic and Milk Production Parameters in Grazing Dairy Cows Offered Ad Libitum or Restricted Pasture

Conjugated linoleic acid (CLA) reduces milk fat synthesis in grazing dairy cows and may improve calculated net energy balance (EBAL). Study objectives were to determine whether CLA-induced milk fat depression could be utilized during times of feed restriction to improve bioenergetic and milk production parameters. Twelve multiparous rumen-fistulated Holstein cows (204 +/- 7 d in milk) were offered ad libitum (AL) or restricted (R) pasture and abomasally infused twice daily with 0 (control) or 50 g/d of CLA (CLA; mixed isomers) in a 2-period crossover design. Treatment periods lasted 10 d and were separated by a 10-d washout period. Milk and plasma samples were averaged from d 9 and 10, and EBAL was calculated from d 6 to 10 of the infusion period. Pasture restriction reduced the yield of milk (3.9 kg/d) and milk components. The CLA treatment reduced milk fat yield by 44 and 46% in AL and R, respectively. There was no effect of CLA on milk yield or milk lactose content or yield in either feeding regimen; however, CLA increased the milk protein content and yield by 7 and 6% and by 5 and 8%, in AL and R, respectively. The CLA-induced changes to milk fat and protein doubled the protein:fat ratio in both AL and R. Calculated EBAL improved following the CLA infusion (-0.44 vs. 2.68 and 0.38 vs. 3.29 Mcal/d for AL and R, respectively); however, CLA did not alter plasma bioenergetic markers. Data indicate that during short periods of nutrient limitation, supplemental CLA may be an alternative management tool to enhance protein synthesis and improve the milk protein:fat ratio and calculated EBAL in cows grazing pasture. Further studies are required to determine whether CLA is effective at improving bioenergetic and production parameters during more severe or longer term nutrient restriction.

Effects of Feeding Fish Meal and n-3 Fatty Acids on Ovarian and Uterine Responses in Early Lactating Dairy Cows

The study was designed to test the effects of dietary supplementation with fish meal or specific n-3 fatty acids on ovarian activity and uterine responses in early lactating cows. From 5 to 50 d in milk (DIM), cows were fed diets that were isonitrogenous, isoenergetic, and isolipidic containing none (control), 1.25, 2.5, or 5% menhaden fish meal (FM) or 2.3% Ca salts of fish oil fatty acids (CaFOFA). Ovarian follicular dynamics were monitored along with plasma concentrations of estradiol and progesterone. Beginning at 23 DIM, cows were induced into a synchronized ovulatory cycle. On d 15 after ovulation (49 DIM), cows were injected with oxytocin and blood samples were collected to monitor uterine release of PGF(2alpha) (measured as 13, 14-dihydro-15-keto PGF(2alpha); PGFM). Uterine endometrial biopsies were collected for fatty acid analysis and cyclooxygenase-2 (COX-2) protein measurement. Ovarian follicular activities as well as plasma estradiol and progesterone concentrations were similar across diets. Endometrial fatty acid composition of eicosapentaenoic acid (C20:5, n-3) and docosahexaenoic acid (C22:6, n-3) were increased as much as 3-fold by supplementation with fish meal and CaFOFA. Conjugated linoleic acid (C18:2 cis-9, trans-11) in the endometrium was also increased; conversely, arachidonic acid (C20:4, n-6) percentage was decreased by 5% FM. Plasma PGFM response to oxytocin injection was not different among diets and endometrial COX-2 protein abundance did not differ. Results from this experiment demonstrate that dietary supplementation with fish meal or n-3 fatty acids in early lactating dairy cows significantly increased uterine n-3 fatty acid concentrations, but had no apparent effect on endometrial COX-2 or PGF(2alpha) production in response to oxytocin challenge.

Effects of Feeding Fish Meal and n-3 Fatty Acids on Milk Yield and Metabolic Responses in Early Lactating Dairy Cows

The study was designed to test the effects of feeding fish meal (FM) and specific n-3 fatty acids on milk yield and composition, dry matter intake, plasma concentrations of metabolic hormones and metabolites, and liver triglyceride accumulation in early lactating cows. From 5 to 50 d in milk (DIM), cows were fed diets that were isonitrogenous, isoenergetic, and isolipidic containing none (control), 1.25, 2.5, or 5% menhaden FM or 2.3% Ca salts of fish oil fatty acids (CaFOFA). Milk yield (48.2, 49.8, 48.6, 53.5, and 52.2 +/- 1.0 kg/d, respectively) and dry matter intake (22.7, 22.8, 23.0, 23.8, and 24.7 +/- 0.5 kg/d, respectively) differed among diets. Average daily plasma glucose concentration (53.4, 55.3, 51.1, 57.6, and 57.3 +/- 1.3 mg/dL, respectively) was also affected by diet, and plasma insulin concentration was increased by 5% FM and 2.3% Ca-FOFA. At 25 and 50 DIM, blood was collected before feeding and hourly for 11 h after feeding. Plasma glucose concentrations in cows during the day were similar among diets at 25 DIM, but differed at 50 DIM (54.6, 54.4, 52.4, 60.5, and 58.3 +/- 1.4 mg/dL for 0, 1.25, 2.5, and 5% FM or 2.3% CaFOFA, respectively). Plasma insulin was increased in cows fed 5% FM and 2.3% CaFOFA at 25 DIM and was similar among diets at 50 DIM. Dietary treatments had no significant effect on milk composition, energy balance, or on daily plasma concentrations of nonesterified fatty acids, beta-hydroxybutyrate, and urea. Plasma aspartate aminotransferase and hepatic triglyceride concentration in cows did not differ among diets at 21 DIM. Results from this experiment demonstrate that dietary supplementation with FM or n-3 polyunsaturated fatty acids in early lactating dairy cows significantly increased milk yield and DMI with no change in milk composition.

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.

Response to Conjugated Linoleic Acid in Dairy Cows Differing in Energy and Protein Status

The trans-10, cis-12 conjugated linoleic acid (CLA) isomer inhibits milk fat synthesis, whereas milk yield and synthesis of other milk components generally remain unchanged in established lactation. However, in some CLA studies increases in milk yield, milk protein yield, or both have been observed in cows limited in energy, either in early lactation or when grazing pasture. Our objective was to evaluate the performance and monitor peripheral tissue responses to homeostatic signals regulating lipolysis and glucose uptake with CLA supplementation when cows were limited in metabolizable energy in combination with moderate or excess metabolizable protein supply. Holstein cows (n = 48; 112 +/- 5 d in milk; mean +/- SE) were provided ad libitum access to a diet that met energy and protein requirements for a 16-d standardization interval. Based on performance during this interval, the Cornell Net Carbohydrate and Protein System was used to design energy-limiting rations that provided 80% of metabolizable energy requirements, and these were fed throughout the treatment periods. Cows were randomly allocated to 4 treatments, in a 2-period crossover design. Treatments were 1) moderate metabolizable protein (MP) supply, 2) moderate MP supply + CLA, 3) excess MP supply, and 4) excess MP supply + CLA. Moderate and excess MP supply were at 88 and 117%, respectively, of the MP requirement established during the standardization period, as estimated by the Cornell Net Carbohydrate and Protein System. Each experimental period comprised 16 d, with crossover of CLA within each protein level. The lipid-encapsulated CLA supplement provided 12 g/d of trans-10, cis-12 CLA. Conjugated linoleic acid treatment reduced milk fat yield by 21% but increased milk yield and milk protein yield by 2.6 and 2.8%, respectively. Milk yield and content and yield of both milk protein and fat were unaltered by either protein treatment alone or in combination with CLA. Basal concentrations of glucose, insulin, and nonesterified fatty acids were unaffected by CLA supplementation. The fractional rate of glucose clearance in response to an insulin challenge and the nonesterified fatty acid response to an epinephrine challenge were also not altered by either CLA treatment or MP supply. Overall, the results demonstrate that CLA supplementation when cows are energy-limited allows for repartitioning of nutrients, resulting in increased yields of milk and milk protein, and this can occur without changes in whole-body glucose homeostasis and adipose tissue response to lipolytic stimuli.