Biomedical subjects

D L Palmquist

Publications and source records attributed to D L Palmquist.

At least 19 recordsLinked to original sources

PubMed2000

Trans-vaccenic acid is desaturated to conjugated linoleic acid in mice.

Mice were fed pure trans11 octadecenoic acid (trans-vaccenic acid; TVA) to determine whether it is desaturated to cis9, trans11 octadecadienoic acid, a predominant isomer of conjugated linoleic acid (CLA). In a preliminary trial, 12% of the TVA consumed during a 2-wk feeding period was recovered in the carcass as CLA. As a proportion of TVA in the tissues available for bioconversion, 48.8% was desaturated. We tested whether desaturation could be modified by supplementing no modifier, 0.5% clofibric acid to stimulate desaturation, or increasing the polyunsaturated fatty acids (PUFA) (10% corn oil vs. 4% corn oil) to inhibit desaturation in diets with or without 1% TVA. These diets were fed to six groups of mice in a 3x2 factorial arrangement of treatments. Feeding 1% TVA with 10% corn oil decreased feed intake (2.70 vs. 3.73 g/d, SEM 0.23; P<0.05). Bioconversion of dietary TVA was 12.0, 7.5 and 5.1% for mice fed no modifier of desaturation, clofibrate and increased PUFA, respectively. Conversion based on TVA available for desaturation was 52.6, 55.5 and 37.0%, respectively. Thus, clofibrate did not increase bioconversion, but increasing PUFA decreased conversion by 30%. To test whether TVA decreases food intake directly or after conversion to CLA, four groups of mice were fed diets containing 1% stearic, TVA, elaidic or conjugated linoleic acid. Dietary CLA decreased food intake and body fat, but did not change body protein. CLA was found in the carcass only when TVA or CLA was fed. CLA was found in both triacylglycerol and phospholipids when CLA was fed, but only in triacylglycerol when TVA was fed, suggesting that bioconversion occurred in the adipose tissue. In three trials, conversion of dietary TVA to CLA was 11.4+/-1.25%; conversion of stored TVA was 50.8+/-1.91%. Similar bioconversion of TVA in humans would increase current estimates of CLA available for the general population by 6- to 10-fold.

Administration, Oral↗

PubMed2000

Short communication: influence of dietary tallow and fish oil on milk fat composition.

Four midlactation Holstein cows in a 4 x 4 Latin square design were fed one of four diets that contained 3% added fat (dry matter basis) as 100:0, 67:33, 50:50, or 33:67 tallow:fish oil. Feed intake and yield and composition of milk were not affected by treatment. The proportion of fatty acids 18:0 and cis-18:1 decreased and trans-18:1, conjugated linoleic acid, 18:3, 20:4, and 20:5 increased in milk fat with increasing fish oil. The efficiency of transferring dietary 20:5 and 22:6 to milk fat was < 7%.

Animal Feed↗

PubMed2000

Effects of fat source and copper on unsaturation of blood and milk triacylglycerol fatty acids in Holstein and Jersey cows.

Fatty acid composition of plasma triacylglycerides and milk fat was analyzed from Holstein and Jersey cows with control or depleted copper status and fed roasted whole soybeans or tallow. Conjugated linoleic acid in plasma was higher in Jersey cows. Dietary fat source influenced the proportions of all fatty acids in plasma and in milk, except for conjugated linoleic acid in milk. Feeding soybeans increased plasma C14:1, C18:0, C18:2, and conjugated linoleic acid, and decreased C14:0, C16:0, C16:1, and cis- and trans-C18:1 compared with feeding tallow. Low copper diets decreased C18:0 and increased cis- and trans-C18:1, and conjugated linoleic acid in plasma. A fat source x copper status interaction occurred for cis-C18:1 in plasma. Proportions of C4:0 to C14:0 were higher, and cis16:1, cis- and trans-C18:1, and conjugated linoleic acid were lower in milk fat of Jersey compared with Holstein cows. Generally, the effects of copper depletion were less apparent in milk than in plasma. Copper depletion increased C4:0, trans-C18:1, and conjugated linoleic acid, and decreased C16:1 in milk. Feeding whole soybeans increased C4:0 to C14:0, C18:0, C18:2, and C18:3, and decreased C14:1, C16:0, C16:1, and cis- and trans-C18:1 in milk. Breed x fat interactions occurred for C4:0, C14:1, C16:1, and conjugated linoleic acid in milk. Copper status x fat source interaction occurred for trans-C18:1. The breed x copper status interaction was apparent in milk fat for C16:1 and C18:0 and conjugated linoleic acid in milk. Both C18:0 and trans-C18:1 were desaturated by mammary tissue; however, whereas desaturation of C18:0 was linear, desaturation of trans-C18:1 reached a plateau that could have been caused by presence of the trans-10 isomer, which is not desaturated and was not separated from trans-11 C18:1 in our analysis. Comparison of the plasma triacylglycerol fatty acid profile with the milk fat profile was useful to interpret separate events of biohydrogenation in the rumen and desaturation by the mammary gland.

Animal Nutritional Physiological Phenomena↗

PubMed2000

Milk fat composition of Holstein and Jersey cows with control or depleted copper status and fed whole soybeans or tallow.

We studied effects of breed, dietary fat source, and dietary copper intake as factors known to influence unsaturation of milk fat and its potential for development of spontaneous oxidized flavor in milk. Twelve Holstein and 12 Jersey cows were allotted to three blocks with four cows of each breed. Cows within breed were allotted randomly within blocks and fed control or copper-depleting diets for 2 mo to achieve stable or depleted liver copper stores. Cows then were fed tallow or roasted whole soybeans in a two-period switchback (5 wk per period); during the last week of each period additional vitamin E (2000 IU/d) was added. Copper depletion for 2 mo decreased concentrations of copper in liver. Feed intake and milk yield were influenced only by breed. The proportions of C4:0 to C14:0 and C18:0 in milk fat were higher, whereas C16:1 and cis-C18:1 were lower in Jersey cows. Feeding soybeans increased C4:0 to C14:0, C18:0, C18:2, and C18:3 in milk, and decreased C14:1, C16:0, C16:1, trans-C18:1, and cis-C18:1. Depleted copper status increased conjugated linoleic acid in milk. Several breed x fat source interactions for individual milk fatty acids occurred. Feeding soybeans decreased plasma concentrations of copper and zinc, and increased concentrations of alpha-tocopherol in plasma and milk. The concentration of zinc was higher in milk of Jersey cows. Depleted copper status tended to increase copper concentration in plasma and decreased copper in milk. Fat source did not influence plasma copper concentration when status was adequate, but plasma copper concentration was higher when tallow was fed to cows with depleted copper status. Supplementing vitamin E increased concentration of alpha-tocopherol in plasma and milk and decreased concentration of zinc in milk. Factors influencing the potential for oxidized flavor development in milk can be manipulated by changing the diet of the cow.

Animal Nutritional Physiological Phenomena↗

PubMed1998

Trans-octadecenoic acids and milk fat depression in lactating dairy cows.

We examined the role of trans-octadecenoic acids in milk fat depression when low fiber diets were fed. The study consisted of four experimental periods with a 2 x 2 factorial arrangement of treatments to test the effects of dietary fat (saturated vs. unsaturated) and rumen fermentation (high fiber diets vs. low fiber diets) on milk fat depression. Dietary fiber concentration and type of fat had significant effects on milk fat. Effects were most pronounced when unsaturated fat was added to the low fiber diet. When the low fiber diet plus unsaturated fat was fed, milk fat percentage and yield were decreased by 30 and 35%, respectively, compared with the percentage and yield when the high fiber diet plus saturated fat was fed. Alterations in rumen fermentation caused by differences in dietary fiber concentrations had little effect on the amount of trans-octadecenoic acids in milk fat, and the total amount did not correlate with changes in milk fat percentage. Further examination of the isomeric profile of trans-octadecenoic acid revealed substantial differences among the dietary treatments. Although the addition of unsaturated fat resulted in marked increases in the milk fat content of trans-11-octadecenoic acid, regardless of dietary fiber concentration, the low fiber diet plus unsaturated fat increased the content of trans-10-octadecenoic acid. This combination was also associated with a significant decrease in milk fat content and yield. When the low fiber diets were fed, circulating insulin concentrations were elevated, regardless of the type of fat supplement. However, marked milk fat depression occurred only when the low fiber diet was supplemented with unsaturated fat.

Animals↗

PubMed1997

Tracing gluconeogenesis with deuterated water: measurement of low deuterium enrichments on carbons 6 and 2 of glucose.

The contribution of gluconeogenesis to glucose production in vivo can be measured by enriching body water with 0.5% 2H2O and measuring the glucose labeling ratio C6/C2 (Landau et al., J. Clin. Invest. 95, 172-178, 1995). We present further refinements of the measurements of the 2H enrichments on C6 and C2 of glucose. The transfer of 2H from C6 of glucose to hexamethylenetetramine (HMT) and extraction in preparation for gas chromatography-mass spectrometry can be done in a single test tube, without distillation of the intermediate formaldehyde. In addition, extraction of small amounts of HMT is greatly improved by making a HMT-iodine adduct. For C2, glucose is reduced to sorbitol, and 2H on C2 is transferred enzymatically to [U-13C3]pyruvate, forming [U-13C3,2-2H]lactate. The latter is assayed by negative chemical ionization gas chromatography-mass spectrometry of the pentafluorobenzyl derivative. The natural enrichment of the [U-13C3]lactyl ion is only 0.4%, allowing measurements of 2H enrichment down to 0.1%. These techniques were used in dogs infused with 2H2O and in isolated rat livers perfused with buffer containing 1 to 5% 2H2O. Our data reveal a difference in the rate of labeling of C6 and C2 of glucose in vivo. Lastly, in cows infused with [6,6-2H2]glucose, we show that the turnover of glucose can be economically measured by assaying low tracer enrichment (down to 0.1%) via hexamethylenetetramine.

Animals↗

PubMed1997

Sodium mercaptoacetate is not a useful probe to study the role of fat in regulation of feed intake in dairy cattle.

Inhibition of fatty acid oxidation by mercaptoacetate stimulates food intake of rats fed dietary fat. To study regulation of feed intake of ruminants fed fat, dry matter intake and plasma concentrations of insulin and metabolites were determined in eight nonpregnant Holstein heifers in a cross-over design with two 14-d feeding periods by using a 2 x 2 factorial arrangement of treatments. Treatments were combinations of diet (27 or 103 g fatty acids/kg food dry matter) and injection (mercaptoacetate or saline). Half the heifers were fed each diet in Period 1, and diets were reversed in Period 2. On d 10 of each period, two animals per treatment were injected intravenously with either mercaptoacetate (300 mumol/kg body weight 0.75) or saline at 2 h postfeeding. Injections were reversed on d 12. Dry matter intake was suppressed by the high fat diet. Intravenous injection of mercaptoacetate decreased dry matter intake to 25% that of the control during 4 h postinjection. Both the high fat diet and mercaptoacetate injection increased plasma non-esterified fatty acid concentration, whereas plasma beta-hydroxybutyrate concentration was lowered by the high fat diet and by mercaptoacetate injection. Plasma triglyceride concentration was increased by the high fat diet, but was decreased by mercaptoacetate injection. Mercaptoacetate elevated plasma glucose concentrations at 2 and 3 h postinjection, possibly because plasma insulin concentration was lower. Effects of mercaptoacetate on plasma insulin and metabolite concentrations may have been confounded by the effects of decreased feed intake. Therefore, direct effects of mercaptoacetate injection were not separated from effects of feed intake on plasma insulin and metabolite concentration. Because mercaptoacetate injection decreased dry matter intake it was not a useful probe to study mechanisms of feed intake regulation in dairy cattle fed fat.

Animals↗

PubMed1997

Role of insulin in the regulation of milk fat synthesis in dairy cows.

Five lactating Holstein cows were fitted with rumen fistulas and subjected to a hyperinsulinemic-euglycemic clamp and abomasal casein infusion to examine the effects on milk fat synthesis and the composition of milk fatty acids. The experiment consisted of two periods of abomasal infusions (water or 0.5 kg/d of casein); each period was divided into three 4-d intervals. The initial interval allowed for acclimation, and baseline measurements were established during the second interval. During the third 4-d interval, a hyperinsulinemic-euglycemic clamp was maintained, and insulin was infused continuously at the rate of 1 microgram/kg of body weight per h. Circulating concentrations of insulin were increased more than fourfold, and euglycemia was maintained by infusion of glucose at variable rates. Insulin had no effect on milk fat yield but casein infusion increased milk yield and tended to increase fat yield. A trend toward higher milk yield during the clamp, combined with a slight numerical decrease in milk fat yield, resulted in decreased fat percentage. Calculated net energy balance was positive throughout the study, although feed intake decreased during the insulin clamp, particularly for the water infusion period. Minor changes occurred in the composition of milk fatty acids during the clamp when the balance between de novo and preformed fatty acids shifted slightly toward de novo. Overall, results demonstrated that a relatively constant rate of milk fat synthesis was maintained during chronic hyperinsulinemia. Effects on milk fat yield and composition of fatty acids offered no support for the role of insulin on milk fat depression.

Abomasum↗

PubMed1996

High fat diets increase plasma cholecystokinin and pancreatic polypeptide, and decrease plasma insulin and feed intake in lactating cows.

High fat diets often decrease feed intake in dairy cows; however, mechanisms underlying fat-induced depression of feed intake are yet to be established. The postulate that high fat diets decrease feed intake by increasing concentrations of lipid metabolites or satiety hormones in blood was tested by using eight multiparous Holstein cows in a simultaneously replicated 4 x 4 Latin-square design. Treatments were control diet with 1) no fat added, 2) 30 g/kg calcium salts of long-chain fatty acids, 3) 60 g/kg calcium salts of long-chain fatty acids, and 4) 90 g/kg calcium salts of long-chain fatty acids. Cows were fed once daily a diet of concentrate, corn silage, alfalfa haylage and alfalfa hay (50:25:14:11 on a dry matter basis). Dry matter and energy intakes were decreased by inclusion of calcium salts of long-chain fatty acids >30 g/kg of total diet dry matter (P = 0.0001). Plasma nonesterified fatty acids and triglyceride concentrations were increased linearly by feeding increasing amounts of fat (P < 0.003 and P = 0.0001, respectively), whereas plasma beta-hydroxybutyrate and glucose concentrations were not influenced by supplemental fat. Fat supplementation increased postfeeding plasma cholecystokinin concentrations and linearly increased plasma pancreatic polypeptide concentrations. Highest concentrations of plasma cholecystokinin (P < 0.001) and pancreatic polypeptide (P < 0.05) were observed in cows fed the 90 g/kg fat supplement. Plasma insulin was lowered linearly by feeding fat (P = 0.0001). Increased concentrations of cholecystokinin and pancreatic polypeptide were associated with decreased intakes of feed and energy, whereas insulin may not be involved in the control of feed intake in cows fed fat.

Animals↗

PubMed1996

Responses of dairy cows supplemented with somatotropin during weeks 5 through 43 of lactation.

Beginning at wk 5 of lactation, 136 cows (34 per treatment) were supplemented daily for 38 wk with 0, 10.3, 20.6, or 41.2 mg of recombinantly derived bST monomer. Cows were obtained from University of Kentucky, University of Minnesota, University of Pennsylvania, and The Ohio State University. Nine cows (4 at 0 mg/d, 1 at 10.3 mg/d, 1 at 20.6 mg/d, and 3 at 41.2 mg/d) did not complete the experiment because of health problems. Data from these cows were included in the reproduction and health databases but not in the production database. Cows supplemented with bST produced more milk, consumed more feed, had lower rates of BW gain, and had improved efficiencies of milk production (conversion of feed and NEL to milk). Additional increases in productivity were modest at 20.6 and 41.2 mg/d versus productivity at 10.3 mg/d of bST. Concentrations of fat, protein, and TS in milk were unaffected. At 10.3 mg/d, bST did not adversely affect reproduction or health.

Animal Nutritional Physiological Phenomena↗

PubMed1995

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

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

Animals↗

PubMed1994

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.

Animals↗

PubMed1994

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)

Absorption↗

PubMed1994

Blood and hydrolyzed feather meals as sources of undegradable protein in high fat diets for cows in early lactation.

Thirty-six cows were in a 2 x 3 factorial study during the first 2 mo of lactation to examine effects on milk yield and composition of added fat (5% of feed DM) and percentage of ruminally undegradable protein (100, 120, or 140% of recommended intake) in the diet. The main source of added undegradable protein was a 1:1 (wt/wt) mixture of blood meal:hydrolyzed feather meal. Diets were low in ADF (ca. 14%) and were highly fermentable in the rumen. The amount of intermediate dietary protein reduced feed intake. Milk yield was high (40 to 44 kg/d), similar among treatment groups, and was sustained for the entire 60-d trail. All cows yielded milk of low fat content (2.1 to 3.2%); supplemental fat decreased proportions of C6 to C14, C18:2, and C18:3 in milk fat and increased C4, C16:0, C18:0, and C18:1. Higher dietary protein had a positive linear effect on milk fat percentage and increased C16:0 and decreased trans-C18:1 and C18:2 contents of milk fat. Added fat did not change total milk N but increased NPN as a percentage of total milk N. Percentage of total N in milk and yield of whey N was reduced when the intermediate protein diet was fed, associated with the lower DMI of this diet. A requirement for ruminally undegradable protein intake higher than recommended by NRC was not demonstrated with the highly fermentable diets fed in this study; however, ruminal acetate: propionate ratio and milk fat percentage were low.

Acetates↗

PubMed1994

Evaluation of chemical and physical properties of feeds that affect protein metabolism in the rumen.

The goal of the NC-185 Cooperative Regional Research Project is to provide the information needed to improve the nutrition and feeding of dairy cattle, a major factor determining composition of milk and cost of milk yield. Emphasis is placed on understanding how energy and protein nutrition of lactating cows can be manipulated to increase the quantity and improve the profile of AA passing to the small intestine and to improve yield of milk and milk protein. To achieve this goal, one of the major objectives of this project has been to evaluate quantitatively the chemical and physical properties of protein and energy sources that determine AA availability to lactating cows. Reliable measurements of microbial protein synthesis and protein degradation in the rumen are critical in the evaluation process. Therefore, one of the ongoing areas of investigation of this research project has been to determine the most appropriate methods for estimating microbial protein synthesis and dietary protein degradation in the rumen. Other areas have been investigated, using continuous culture fermenters and ruminally and duodenally cannulated cows, including factors that alter microbial metabolism of N in the rumen and subsequently protein supply to the small intestine, such as sources of carbohydrate, protein, and fat and interrelationships of protein and carbohydrate. Findings of the NC-185 Cooperative Regional Research Project Committee and other investigators are summarized in this review.

Animal Feed↗

PubMed1993

Diurnal variation of rumen ammonia, serum urea, and milk urea in dairy cows at high and low yields.

Milk urea content as an indicator of nutritional status may be a useful tool if major sources of variation are considered. Blood and milk samples were collected frequently during 16 to 19 h from four Holstein cows to study diurnal variation of urea content. Corn silage, alfalfa hay, and concentrates were fed. Rumen ammonia, VFA, and pH were measured in three of the cows. A clear serum urea peak, 70 to 85% higher than the lowest concentration, was observed in the higher yielding cows. The serum urea peak occurred 1.5 to 2.0 h after the rumen ammonia peak. Urea in milk equilibrated with serum with a time lag of 1 to 2 h when the rate of change in serum was .5 to 1.0 mM/h. At this rate, the average difference between serum and milk urea content was .8 mM. Urea in total milk tended to be more closely correlated to serum than samples from the gland cistern, but deviations were minor. Our results indicate a relatively rapid equilibration between blood serum and milk urea, also in the gland cistern. Equilibration may be explained by diffusion of urea along the mammary ducts and through the mucosa in the alveoli. If urea is to be used as an indicator of nutritional status, diurnal variations of serum and milk urea should be considered; time of sampling versus time of feeding is crucial. A small milk sample from a healthy quarter may give information on urea that is as good as that of a sample from regular milking.

Ammonia↗

PubMed1993

Ruminal, intestinal, and total digestibilities of nutrients in cows fed diets high in fat and undegradable protein.

To study relationships of high undegradable intake protein and dietary fat on intestinal AA supply, the ruminal, intestinal, and total digestibilities of diets with or without added fat (5% of DM) and animal protein (blood meal: hydrolyzed feather meal, 1:1; 8% of DM) were examined with four cows in a 2 x 2 factorial design in a 4 x 4 Latin square experiment. Ruminal degradabilities were 14.9 and 18.6%, and intestinal digestibilities were 98.9 and 68.3%, respectively, for CP in blood meal and feather meal. Treatment effects on ruminal digestibilities were small. Protein supplementation increased total N intake by 29%, duodenal AA N flow by 39%, and AA N absorbed by 37%; absorption of Leu and Lys increased 60 and 33%, and absorption of Ile and Met increased 11 and 7%, respectively. Measured duodenal AA N flow (Cr2O3 marker) was 33% higher in cows cannulated adjacent to the pylorus compared with cows cannulated 100-cm distal to the pylorus, but only when cows were fed protein-supplemented diets; the estimates from those diets caused calculated microbial protein efficiency to exceed theoretical values. We postulated that blood meal and feather meal segregated near the pylorus, yielding high estimates of duodenal AA N flow. Removal of data for protein-supplemented diets obtained from cows cannulated at the pylorus yielded estimates of microbial protein synthetic efficiency consistent with literature values. Microbial synthesis of AA N was related linearly to ruminal digestion of carbohydrate. Location of intestinal cannulas may influence accuracy of nutrient flow estimates.

Amino Acids↗

PubMed1993

Feed and animal factors influencing milk fat composition.

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

Animal Feed↗