A 100-Year Review: Fat feeding of dairy cows.

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

Kinetics of fatty acid biohydrogenation in vitro.

Biohydrogenation (BH) of fatty acids (FA) from fresh alfalfa and alfalfa hay with varying levels of supplemental sucrose and media pH was evaluated in vitro. A multicompartmental model was then developed to estimate pool size and flux of vaccenic acid (VA) during BH of FA in fresh alfalfa. To vary incubation pH, alfalfa samples were inoculated with rumen fluid in 2 media differing in molarity of the bicarbonate buffer. Samples were incubated for 0, 1, 2, 3, 4, 6, 9, and 12 h; pH was measured and tubes were put in ice and stored until analysis. The BH rates of linoleic acid (18:2) and linolenic acid (18:3) were estimated by PROC NLIN of SAS (single pool, first-order kinetic model) and SAAM II (multiple pools, first-order kinetic model). Both methods gave similar estimates for the BH rates of 18:2 and 18:3 as well as the temporal pool size of VA. The BH rates (%/h) in the strong (SB) and weak buffers (WB) were 27.4 (+/-0.7) and 23.5 (+/-0.9) for 18:2, and 43.8 (+/-0.2) and 30.3 (+/-0.6) for 18:3, respectively. The WB decreased the BH rates of 18:2 and 18:3 for both forage sources. However, BH rates of 18:3 were higher from fresh alfalfa than alfalfa hay. There was no effect of sucrose addition on the BH rates of 18:2 and 18:3. Moreover, there was no effect of buffer on the BH of VA estimated by the multiple pools model between the SB and WB (12.5 +/- 2.1 and 14.1 +/- 3.7%/h, respectively). The BH rates of the conjugated linoleic acid isomers were not different between the SB and WB treatments (36.7 +/- 19.8 and 25.9 +/- 27.2, respectively). Because we could estimate fluxes as well as mass of the VA pools, more information was generated from the data when a multiple pools model was used compared with a single pool, first-order kinetic model.

Contribution of intermuscular fat to lipogenesis from dietary glucose carbon in mice.

We assessed the contribution of various tissues to the synthesis of fat from glucose carbon in mice during rapid lipogenic activation induced by a glucose test meal. Nibbling and gorging mice were maintained on a 58% glucose, fat-free diet. The mice were fasted 22 h and refed 5-10 muCi [U-14C]glucose (120 mg/20 g body weight) either by gastric intubation or as a test meal (58% glucose diet). The muscular carcass in both nibblers an gorgers contained more than 75% of the total radioactivity in the fatty acids derived from glucose; liver and epididymal fat pad accounted for only a small percentage. Mort than half the carcass activity was in the "muscular" tissue as neutral lipid acids. We could isolate a discrete fat body in the popliteal region of the leg muscle ("muscle fat", "intermuscular fat"). The popliteal fat converted glucose carbon to fatty acids an order of magnitude faster, per unit weight, than the epididymal fat pad or skeletal muscle. The fatty acid moiety of the triacylglycerols had the major portion of the label in the popliteal fat 2 and 6 h after ingestion of the glucose test meals. The diacylglycerol pool was active at 2 h and its activity faded at 6 h implicating its intermediary role in lipid metabolism similar to published findings in epididymal fat pad. These results indicate that fat cells associated with the muscular carcass may play a major role in the de novo synthesis of fat from dietary carbohydrate in mice.

Selenium status of a rural (predominantly Amish) community living in a low-selenium area.

Selenium intake and blood selenium and selenium-dependent glutathione peroxidase concentrations were assessed in a rural, 71% Amish, sample of residents in a region with low availability of soil selenium and in urban (Columbus, OH) residents. Subjects were interviewed (24-h dietary recalls) on three separate occasions over an 18-month period, and blood and food samples were taken for analysis (maximum subject observations = 452). Mean selenium intake of the entire population was 82.8 +/- 4.4 micrograms/day. Rural and urban residents at 82.0 +/- 4.9 and 83.6 +/- 4.4 micrograms/day, respectively, did not differ significantly in intake. A breakdown by gender within location demonstrated that rural males consumed the most selenium (104.7 +/- 6.1 micrograms/day) and rural females the least (59.3 +/- 6.3 micrograms/day). Rural subject groups had significantly lower mean whole blood, plasma, and erythrocyte selenium levels (12.5 to 14.5%) as well as blood selenium-dependent glutathione peroxidase concentrations (5.6 to 10.8%) than urban groups. Subjects in both cohorts were in adequate selenium status as judged by blood parameters, even though about one-fourth of the dietary observations were below the safe and adequate range of selenium intake established by the Food and Nutrition Board. The rural diet was 18.3% lower in selenium density than the urban diet. High selenium grain products (greater than 0.2 micrograms/g) were the most important dietary selenium source in both groups, providing 29.3 to 41.6% of total intake.

Polyunsaturated meat and dairy products in fat-modified food patterns for hyperlipidemia.

Polyunsaturated meat and dairy products were compared with their saturated counterparts to determine their usefulness in a fat-modified diet for hyperlipidemic persons and their spouses. These polyunsaturated animal products were produced by feeding cattle a supplement of oil droplets coated with denatured protein. As a result, the polyunsaturated fatty acid content was 27 to 28 per cent of the meat fat and butterfat; saturated fatty acids (C12:0 to tc16:0) were 18 to 19 per cent. Of the eleven free-living subjects three were normocholesteremic, three had type IIa hyperlipidemia and five had type VI (IIb). In the fourteen-week study, an adjustment period of three weeks was followed by two consecutive experimental periods of four weeks each, then by a three-week follow-up period. During the adjustment period, participants continued to follow their usual eating patterns. During both experimental periods all followed the same prescribed fat modified food pattern using polyunsaturated margarine and oil. Five participants ate polyunsaturated beef and dairy products during the first experimental period and their saturated counterparts in the second; six participants ate saturated products first, then polyunsaturated. During the follow-up period, all participants selected all their own food. Serum cholesterol levels in five participants who had not previously followed a fat-modified diet were reduced by 18 per cent with polyunsaturated animal products and 11 per cent with saturated products. Serum cholesterol in six participants, previously on a fat-modified diet, was not significantly changed with polyunsaturated products. In ten of eleven participants, serum cholesterol levels were an average of 6 per cent lower with polyunsaturated products than with saturated products. It is concluded that polyunsaturated animal products are suitable for use in fat-modified food patterns for reducing hyperlipidemia, with some restrictions in the amount of polyunsaturated animal fat and with the inclusion of polyunsaturated oil and margarine.

Selenium content of foods purchased or produced in Ohio.

Approximately 450 samples of about 100 types of foods consumed by rural and urban Ohioans were analyzed for selenium. Meat, dairy products, eggs, and grain products produced in Ohio have considerably lower selenium content than corresponding products produced in high selenium areas, such as South Dakota. Retail Ohio foods with interregional distribution tended to be higher in selenium content than corresponding foods produced in Ohio. Best sources of selenium in Ohio foods commonly consumed were meat and pasta products. Poor sources of selenium were fruits, most vegetables, candies, sweeteners, and alcoholic and nonalcoholic beverages. Establishment of an accurate data base for selenium depends on knowledge of the interregional distribution of foods, the selenium content of foods at their production site, and the selenium content of foods with wide local distribution.

Dietary fat composition influences fatty acid composition of milk fat globule membrane in lactating cows.

Milk fat globule membranes are derived directly from the apical plasma membrane of mammary epithelial cells. To evaluate the effect of dietary fat on mammary membranes, we determined the fatty acid composition of the milk fat globule membrane in lactating dairy cows fed diets supplemented with fats of different fatty acid composition, or infused intravenously with soy oil emulsion. A preliminary survey, using an abbreviated preparation procedure (membranes isolated at 48,000 x g-max for 15 min), yielded about 45% of the total membrane fatty acids that could be recovered by centrifuging at the same speed for 120 min, and showed that changes in fatty acid composition of membranes reflected dietary fatty acids to some extent. Dietary palmitic acid increased the content of 16:0 in the membranes. A high corn diet increased ruminal formation of t18:1, and its level increased to 12% of membrane fatty acids. Infusion of soy oil emulsion increased 18:2 membrane content, and decreased the levels of 18:1 and 20:4. All treatments decreased the ratio of unsaturated/saturated fatty acids as compared to controls, whereas the ratio of polyunsaturated/saturated fatty acids was increased by feeding a high corn diet or by infusing soy oil. The ratio of 18:2/c18:1 increased from 0.31 to 1.0 after infusing soy oil for 4 days. The fatty acids of membranes isolated upon 120-min centrifugation were slightly more saturated. The differences were not sufficiently large, however, to affect overall results significantly.

Absence of eicosatrienoic acid in plasma of sheep parenterally infused with a high glucose fat-free solution.

Five yearling wether sheep were maintained on total intravenous, fat-free feeding for periods in excess of 4 weeks. Analysis of plasma total lipid, neutral lipid, and phospholipid fatty acid patterns showed a decrease in linoleic acid during the first week, after which levels tended to stabilize. Rate of decrease in linoleic acid content of plasma phospholipids of two sheep was different. Changes in nonessential fatty acids were variable. 5,8,11- and 8,11,14-Eicosatrienoic acids were not detected in any of the sheep.

Glucose and insulin metabolism in ruminating and veal calves fed high and low fat diets.

Holstein male calves were maintained on conventional (milk to 6 wk of age, fed grain and hay after weaning) and veal (milk replacer only) diets to 16 wk of age. Within each of these 2 physiological states (ruminating or non-ruminating), calves were fed low or high fat diets (ruminating: 3 and 10%; veal: 10 and 18%). Glucose tolerance tests were undertaken at 8 and 16 wk of age in each group. Basal concentrations (4 hr postfeeding) and areas under the response curves for plasma glucose and insulin were higher in veal calves (P < .0001). Ruminating calves fed higher fat utilized glucose more readily (smaller areas under the curves for both glucose and insulin, P < .10) than those fed lower fat. Age did not influence basal glucose concentrations (P > .10), but older calves had higher basal insulin (P < .0001) and greater areas under the curves (P < .0005) for both glucose and insulin after a glucose challenge. Rate of clearance (k) was greater in ruminating calves (P < .001). Though rate of clearance in veal calves was slower, larger plasma pool size caused veal calves on average to utilize glucose at a 15% greater rate per kg body weight than ruminating calves. Whereas fat concentration in the diets did not influence glucose metabolism in veal calves, the high lactose content (> 50% of diet dry matter) of veal diets induced severe insulin resistance in these calves.

Cholecystokinin mediates depression of feed intake in dairy cattle fed high fat diets.

Two experiments were conducted to investigate the effects of 1) different concentrations of dietary fat and 2) i.v. administration of a cholecystokinin receptor antagonist (MK-329) on feed intake and plasma concentrations of hormones and metabolites in dairy cattle. In Experiment 1, 4 lactating Holstein cows were used in a 4 x 4 Latin square design. Treatments were diets with 1) no fat added, 2) 30 g fat/kg feed (calcium salts of long-chain fatty acids as fat supplement), 3) 60 g fat/kg, and 4) 90 g fat/kg added. Cows were fed once daily a diet of concentrate, corn silage, alfalfa haylage, and alfalfa pellets. Dry matter intake decreased linearly with increasing concentrations of dietary fat (P < 0.0001). Overall plasma concentrations of nonesterified fatty acids (P < 0.0001), triacylglycerol (P < 0.0006), and cholecystokinin (P < 0.02), increased linearly with each level of dietary fat, but there was a linear decrease in plasma insulin (P < 0.0008). In Experiment 2, 4 nonpregnant and nonlactating Holstein heifers were used in a cross-over design in a 2 x 2 factorial arrangement of treatments. Treatments were diet (fatty acids, 27 g/kg vs 103 g/kg diet dry matter) and i.v. injections (MK-329 vs vehicle). Heifers were fed once daily a total mixed ration of corn silage, cracked corn and soybean meal with or without fat supplement. Diets were switched by period and either MK-329 (70 microg/kg body weight) or its vehicle was injected i.v. at 2 hr postfeeding. Daily dry matter intake was decreased by feeding the high fat diet (P < 0.02) but was not affected by injections. Injection of MK-329, however, increased dry matter intake by 92% in heifers fed the high fat diet during the first 2 hr postinjection compared to vehicle injection. Plasma pancreatic polypeptide concentration was increased by the high fat diet at 2 hr postfeeding (P < 0.02) but was lowered by MK-329 at 1 hr postinjection (P < 0.001). Plasma insulin was lowered by the high fat diet (P < 0.01) but was not affected by injections. The elevated plasma cholecystokinin concentration may have mediated depressed feed intake of dairy cattle fed the high fat diets.

Effects of propylene glycol drenching on energy balance, plasma glucose, plasma insulin, ovarian function and conception in dairy cows.

We postulated that daily drenching of propylene glycol to cows in early lactation would increase plasma glucose and insulin concentrations and improve fertility in postpartum cows. Thirty-six Holstein cows were assigned to treatment or control groups. Each treatment cow was given 500 ml of propylene glycol by drenching daily from 7 to 42 days of lactation. Blood samples for glucose, insulin, nonesterified fatty acids (NEFA), and plasma urea N were collected at 0, 30, and 90 min postdrenching once weekly during 1-6 weeks. Blood samples were collected for progesterone analysis and cows were palpated three times per week until 11 weeks to assess ovarian status. Propylene glycol did not affect dry matter intake (DMI), milk yield or energy balance in treatment cows. After drenching, propylene glycol increased (P<0.01) plasma glucose and insulin and decreased (P<0.01) NEFA; plasma urea N of the treatment group tended (P=0.07) to be higher than that of the control group through 90 min. Days to first service, days open, and services per conception were not different between groups. Conception rates to first insemination were 33% in the control group and 57% in treated cows, but these were not significantly different. First ovulation of treatment cows occurred earlier than that of control cows (32.3 versus 44.5 days, P=0.06) and the length of the first luteal phase was longer in treated cows (13.1 versus 7.3 days, P<0.05). These data are consistent with the hypothesis that insulin is important for normal ovarian function. During negative energy balance, treatment with propylene glycol, which induced small increases in plasma concentrations of insulin, prevented the short luteal phase characteristic of the first estrous cycle in control cows.

Challenges with fats and fatty acid methods.

The content and chemical nature of lipids in feedstuffs is heterogeneous. It has long been known that ether extraction by the Weende procedure inadequately characterizes the fat content of feedstuffs, yet it remains the official method. Diethyl ether (or hexanes that are often used) extracts significant amounts of nonnutritive, nonsaponifiable lipids from forages, and often incompletely extracts lipids of nutritional value, especially fatty acids present as salts of divalent cations. Preextraction hydrolysis of insoluble fatty acid salts with acid releases these fatty acids, and this step is included in the official procedure for certain feedstuffs in the United Kingdom; however, acid hydrolysis increases analysis time and decreases precision. Acid hydrolysis also causes confusion as to the proper definition of the fat content of feedstuffs. A preferred method of fat analysis determines the total fatty acid concentration in feed samples by converting fatty acid salts, as well as the acyl components in all lipid classes, such as triacylglycerols, phospholipids, and sphingolipids, to methyl esters using a simple, direct one-step esterification procedure. Fatty acid methyl esters are then quantified by GLC, which provides information on both fatty acid quantity and profile in a single analysis. Adjustments in conditions and reagents may be necessary to overcome difficulty in quantitatively preparing esters from certain types of fatty acids and their derivatives in commercial fat supplements. After correction for glycerol content, analysis of oils by this procedure provides information on the content of nonsaponifiable material, such as chlorophyll, waxes, and indigestible polymers formed from heat- or oxidatively damaged fats. The correct description of feedstuffs for energy value of fats is the content of total fatty acids.

Evaluation of n-alkanes as digesta markers in dairy cows.

Recovery of hentriacontane (C31 alkane) in feces as influenced by amount consumed and level of dietary fat was examined in a 2 x 2 factorial study in a 4 x 4 Latin square. Treatments were 1) alfalfa hay:concentrate (70:30; AH); 2) AH + calcium soap (500 g/d); 3) grass hay:concentrate (70:30, GH); and 4) GH + calcium soap. Fat did not influence C31 recovery in feces. Fecal recovery (grams/day) decreased quadratically with increasing C31 intake. Compared with AIA, which was 100% recovered in feces, DM digestibility was estimated more accurately (P less than .05) by AIA than by C31. In a second experiment, site of loss of alkane in the intestinal tract was examined by dosing C32 into the rumen or duodenum. Recovery was lower with ruminal dosing, suggesting ruminal loss of the marker. Alkanes are potentially useful markers of particulate matter in the digestive tract; however, documentation of their behavior in a wider range of diets is needed.

Site of mineral absorption in lactating cows fed high-fat diets.

Five lactating Holstein cows with ruminal and duodenal cannulas were used in a 5 x 5 Latin square to determine the site of mineral absorption and effects of sources and amount of dietary fat on apparent absorption. Cows were fed (DM, 17.4 +/- .8 kg/d) chopped alfalfa hay, alfalfa haylage, corn silage, and concentrate at 1:1:1:2 (DM) at 12-h intervals. Calcium salts of palm fatty acid distillate (CS) or animal-vegetable (AV) fat were 0% (control), 2.5% (low, L), or 5.0% (high, H) of the diet DM. After 2 wk of adaptation, duodenal and fecal grab samples were collected at 7-h intervals for 5 d and composited by animal. Calcium intake increased (P < .05) with high-fat diets (195 vs 170 g/d), whereas Mg intake remained unchanged (54.3 +/- 9.0 g/d). Apparent absorption, estimated by Cr2O3, was regressed on Ca or Mg intake (grams/day) and fatty acid (FA) intake (grams/day). Total absorption of Ca (grams/day) = -37.4 + .264 Ca (P = .07, R2 = .14). Ruminal absorption of Mg was independent of FA intake, and magnesium was secreted posterior to the duodenum. Total tract Mg absorption (grams/day) was described by -7.685 + .464 Mg -.0044 FA (P < .0005, R2 = .46). Fat intake decreased (P < .05) total tract Mg absorption, and Ca absorption was decreased by high fat compared with low fat intake (P < .05).(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of calcium soaps of long-chain fatty acids on feedlot performance, carcass characteristics and ruminal metabolism of steers.

Two trials were conducted to determine the effects of calcium soaps of long-chain fatty acids (calcium soap) on feedlot performance, diet digestibility, carcass characteristics and ruminal metabolism of steers fed diets (85% concentrate:15% corn silage) containing 0, 2, 4 or 6% calcium soap. In Trial 1, increasing calcium soap decreased (P less than .05) DM, CP and gross energy intake but increased total fatty acid intake. Feed to gain ratio tended to improve with increased calcium soap; gross energy conversion was not affected (P greater than .05) by diet. Average daily gain and hot carcass weight decreased (P less than .05) with addition of calcium soap; other carcass characteristics were not affected (P greater than .05). Apparent digestibilities of DM, N, energy and ash were not affected (P greater than .05) by calcium soap. Neutral detergent fiber digestibility increased linearly (P less than .08) with increasing calcium soap, whereas digestibility of total fatty acids was affected quadratically (P less than .05); fatty acid digestibility was similar among 0, 2 and 4% calcium soap diets but decreased for the 6% calcium soap diet. In Trial 2, increased calcium soap did not affect (P greater than .05) ruminal VFA concentrations, pH or in sacco NDF disappearance of orchardgrass following 12, 24 and 48 h of incubation. Calcium soap increased (P less than .07) ruminal concentrations of calcium soap fatty acids at 1, 2, 4 and 8 h postfeeding. Calcium soap did not improve performance of feedlot cattle fed high-concentrate diets. Further, calcium soap did not affect ruminal fermentation and did not dissociate significantly even when ruminal pH was below 6 for extended periods of time.

Influence of source and amount of dietary fat on digestibility in lactating cows.

Digestibility of commercial fat supplements was determined in two experiments with high (59% of diet DM) forage diets. Experiment 1 was a preliminary trial in which six Jersey cows were in two 3 x 3 Latin squares to evaluate two formulations of calcium soap at two intake levels (500 and 1000 g/d). The two formulations were compared with control (0 supplement) within squares; the squares differed in amount of soap supplemented. Mean apparent digestibilities of fat were not influenced by source or amount of fat supplemented and averaged 82.5, 84.3, and 83.4% for control, 500, and 1000 g/d. In Experiment 2, six Jersey cows were in a 6 x 6 Latin square to compare effects of various commercial fats on digestibility of diet components at 2.85 and 5.7% (DM) added fat. Higher fat decreased digestibility of P and fatty acid. Fatty acid intake affected fatty acid digestibility quadratically, and variability among cows increased at higher fatty acid intake. Endogenous fecal fat was 55.9 g/d; apparent digestibility of fat was relatively constant at 80 to 82% between 2 and 5% of diet DM, whereas marginal true digestibility decreased linearly (4.4% units/100 g fatty acid consumed). There were no differences among fat sources in fatty acid digestibility. Rumen VFA were not influenced by dietary fat.

The role of dietary fats in efficiency of ruminants.

Fat increases energetic efficiency in lactating cows by increasing total energy intake, by generating ATP more efficiently (ATP/unit energy expended) than volatile fatty acids or protein, by direct incorporation into product, and by promoting nutrient partition toward milk production. Factors that limit utilization of large amounts of fat by ruminants include inhibitory effects on ruminal fermentation, lower intestinal absorption at high intake, low contribution to total oxidation of nutrients, and sensitivity to nutrient imbalance, causing reduced energy intake. Research has resolved many problems associated with effects on ruminal fermentation; research in the future may improve fat digestibility and reduce limits of oxidation. Effect of high fat on regulation of feed intake has received little attention.

A kinetic concepto of lipid transport in ruminants.

Summarization of the literature shows a strong correlation between dietary fatty acid intake and total lipid concentration in plasma in lactating cows whereas total milk fat secreted is related to neither of these. In the process of plasma triglyceride removal, chylomicra and very low density lipoproteins are converted to low density lipoproteins. Limited kinetic data indicate that the fractional removal rates for chulomicra and very low density lipoproteins are rapid in lactating cows whereas fractional removal of low density lipoproteins is slower, resulting in accumulation of the latter in plasma. Under such conditions, low density lipoprotein concentrations of plasma would not be expected to reflect quantitatively the transfer of plasma triglyceride fatty acids to milk fat. Quantitative analysis or triglyceride fatty acid turnover in density less than 1.006 lipoproteins should delineate the role of plasma lipid transport in milk fat synthesis. High fat diets protected from rumen biohydrogenation have proven to be a useful approach in studying ruminant fat metabolism and may be used more extensively to elucidate the role of cholesterol in plasma lipid transport and the metabolism of essential fatty acids in ruminants.

Vitamin E supplementation of high fat diets for dairy cows.

High fat diets +/- 1 g alpha-tocopheryl acetate per head per day were fed to 28 cows for 4 mo to determine whether dietary fat increases dietary requirement for vitamin E. Tocopherol supplementation did not affect milk production or composition. After 4 mo there was no difference between treatment groups for oxidative stability (thiobarbituric acid test) of milk stored for 5 days with .1 ppm added copper, but milk of supplemented cows was more stable when 1 ppm copper was added. Oxidative stability was normal in the unsupplemented group. Tocopherol concentration of blood plasma increased and selenium concentration decreased with tocopherol supplementation; activity of glutathione peroxidase was lower in plasma, whole blood, and erythrocytes of the supplemented group. Tissue integrity was unchanged by tocopherol supplementation, as estimated by erythrocyte hemolytic resistance and activities of lactic dehydrogenase and glutamic oxalacetic transaminase in blood serum. Clearance of bromosulphthalein from blood plasma was less for cows fed fat and supplemented with tocopherol than for control cows fed neither fat nor vitamin E. No indication of impaired vitamin E status was observed when 4% stabilized fat was added to the diet.