Milk Fat Precursors Research Articles

Influence of feeding level on the formation of milk productivity of dry cows

The materials of the publication demonstrate the results of scientific research conducted on Simmental cattle in the farm “Pchany-Denkovych” Stryy district of the Lviv region. The research is based on optimizing the normalized feeding of cows during the start-up period. The diets of experimental animals include low, medium, and high levels of energy nutrition according to detailed standards. The study was conducted on three groups of Simmental cows with eight heads each. The analysis of the obtained results showed that the different levels of energy nutrition of experimental animals did not significantly affect the hematological parameters; their level was within physiological norms for healthy animals. Estimating the intensity of metabolic processes in the body of dry cows was carried out based on the contents of the scar. There was a probable increase in the number of amylo- and cellulolytic bacteria, the number of which prevailed (the second and third groups) in comparison with the control by 1.42–2.32 and 2.32–2.53 million/ml. A similar pattern was observed for the number of proteolytic bacteria. The increase in these populations of microorganisms contributed to their enzymatic activity, which led to a probable increase in the number of LVH, which are precursors of milk fat. According to the indicators of live weight gain during the dry season, animals of the second and third groups had an advantage. Physicochemical parameters of milk were also better in these groups of cows; the higher the level of nutrition, the higher the fat, protein content in milk. A similar analogy is observed for the dynamics of the live weight of calves, which is directly proportional to the level of feeding cows during the dry season. For four months, the calves of the experimental groups had higher growth energy (6.7–10.5 % compared to the control). The control over the level of milk productivity of cows after calving was carried out according to control milk yields, which showed that the hopes for lactation in the experimental groups were 7.2–8.0 % higher than in the control group. This is because the animals of the experimental groups, due to the higher level of feeding according to detailed standards in the dry season, deposited more nutrients in the body and thus provided a higher level of milk productivity. Therefore, the conducted research gives grounds to recommend the farm to use high and medium levels of energy nutrition for cows during the dry season.

High Rumen-Degradable Starch Diet Promotes Hepatic Lipolysis and Disrupts Enterohepatic Circulation of Bile Acids in Dairy Goats

High rumen-degradable starch (RDS) diets decrease milk fat. The increase of LPS in plasma associated with increased RDS impairs liver function, immune response and lipid metabolism, which depress the precursors for milk fat. This study investigated the mechanism of depression of milk fat precursors in the liver and small intestine of dairy goats fed different RDS diets. Eighteen Guanzhong lactating goats (second lactation, 45.8±1.54kg) and 6 ruminally cannulated dairy goats (aged 2-3 y, 54.0±2.40kg) were fed 3 different diets with low dietary RDS concentrations of 20.52% (LRDS), medium RDS of 22.15% (MRDS), and high RDS of 24.88% (HRDS) for 36 and 21 d, respectively, in experiments 1 and 2. The liver metabolites and jejunal microbiota in experiment 1 and LPS concentrations in rumen fluid and plasma in experiment 2 were measured. One-way ANOVA was used to analyze the biochemical parameters and mRNA or protein expression. The MIXED procedure was used to analyze LPS concentrations. In experiment 1, the HRDS diet showed increased activity of alkaline phosphatase (27.4 to 41.4U/L) in plasma (P<0.05) compared with LRDS treatment. The HRDS diet significantly increased the hepatic concentrations of l-carnitine (129%), l-palmitoylcarnitine (306%), taurochenodeoxycholate (856%), and taurodeoxycholic acid (588%) in liver (variable importance in the projection>1, P<0.10) compared with the LRDS treatment. Goats fed the HRDS diet had 33.6% greater liver protein expression of carnitine palmitoyltransferase-1 (P<0.05), and greater relative abundance of Firmicutes and Ruminococcus 2 in the jejunal content (linear discriminant analysis>2.0, P<0.05) than did goats fed LRDS diet. In experiment 2, goats fed the HRDS diet had greater LPS concentrations in rumen fluid (7.57 to 13.6 kEU/mL) and plasma (0.037 to 0.179 EU/mL) (P<0.05) than did goats fed LRDS diet. Feeding the HRDS diet promoted hepatic lipid β-oxidation and disrupted phospholipid and bile acids metabolisms in liver, thereby reducing the supply of lipogenic precursors to the mammary gland in dairy goats.

Sodium butyrate promotes milk fat synthesis in bovine mammary epithelial cells via GPR41 and its downstream signalling pathways

ObjectiveShort-chain fatty acids were reported to be the precursors of milk fat and can stimulate the de novo synthesis of fatty acids in bovine mammary epithelial cells (bMECs). However, the mechanism has not been elucidated. The purpose of this study was to investigate the effects of sodium butyrate (NaB) on milk fat synthesis in bMECs and explore its potential mechanism. MethodsBovine mammary epithelial cells (bMECs) were isolated for subsequent experimental uses. BODIPY staining and triglyceride kit were used to detect the milk fat synthesis in bMECs. Western blotting and RT-PCR assays were performed to detect the expression of related genes in bMECs. Immunoprecipitation was used to detect the acetylation of SREBP1 in bMECs. ResultsThe results showed that NaB significantly promoted milk fat synthesis, promoted the activity of mechanistic target of rapamycin (mTOR) and S6 kinase (S6K), inhibited the activity of AMP-activated protein kinase (AMPK), and promoted the gene expression of G protein-coupled receptor 41 (GPR41). Knockdown of GPR41 and sterol regulatory element binding protein 1 (SREBP1) and overexpression of sirtuin1 (SIRT1), mTOR inhibitor (rapamycin), and AMPK activator (AICIR) eliminated these effects. These results indicated that NaB increased the nuclear translocation of SREBP1 via the GPR41/AMPK/mTOR/S6K signalling pathway, promoted the acetylation of mature SREBP1a via GPR41/AMPK/SIRT1, and then promoted milk fat synthesis. ConclusionTaken together, these results demonstrated that NaB increased nuclear translocation and acetylation of SREBP1 to promote milk fat synthesis by activating GPR41 and its downstream signalling pathways.

The effectiveness of use of forage animal fat in feeding of lactating cows

The purpose of the work is to scientifically substantiate the complete nutrition of highly productive cows in the beginning period of lactation on the basis of feed resources of local production. Rations of feeding of highly productive cows in the beginning period of lactation on the basis of voluminous forages and forage animal fat have been developed. It was found that the enrichment of the rations of lactating cows fat additive enhances the processes of rumen fermentation, increases the accumulation of precursors of milk fat. Feeding by forage animal fat reduces the energy consumption of the feed at unproductive costs, such as the release of energy from the feces, urine. Animals more effectively use the metabolic energy for the formation of milk and deposits in the body, and heat production is reduced. At the end of the physiological experiment for 2 days in a row the study of gas exchange in experimental animals has been carried out. In animals of the control and 1st experimental groups breathing was more frequent and superficial, pulmonary ventilation was 3,22–9,93 % more than in analogues of the 2nd experimental group. The respiratory coefficient reflecting the nature of feeding and the intensity of deposition in the body of animal fat and protein was higher in control animals, this indicates a high content of concentrated feed in the ration. The state of mineral metabolism in cows has been traced to the two most important elements: calcium and inorganic phosphorus. In the blood serum of animals of the control group the level of calcium during the experiment has increased by 1,33 mg%, in the 1st experimental group by 2,02 (P &lt; 0,05) and in the 2nd experimental group by 3,15 mg%. These data indicate a positive balance of calcium in the body. The content of inorganic phosphorus in animals of all groups was within the physiological norm. Its level has been increased during the main period of the experiment except for cows of the 2nd experimental group, in control it has decreased by 0,06 mg% (P &lt; 0,01). The use of forage animal fat in the rations of lactating cows at the beginning of lactation had a positive effect on the biochemical parameters of blood of cows.

Milk yield and metabolic processes in cows during the usage of the biosprint drug in the diet structure

In recent years, a significant part of milk has been produced in farms of various organizational forms, mainly using feeds of their own production. At the same time, there are a number of problems, the solution of which affects the yield, quality and value of products, as well as future prospects in this industry. Scientific research has shown that the intensification of such an industry as dairy farming first of all depends on a strong forage base of the farm. In addition, lactating cows do not need generic feed, but a diet balanced in compliance with detailed rules. Their use makes it possible to increase milk yield by 20 and more percent. Therefore, when organizing a comprehensive feeding, it is necessary to take into account the features of protein, carbohydrate, lipid, mineral and vitamin nutrition. However, even a fully balanced ration does not guarantee the desired effectiveness. In this regard, a variety of feed additives of a natural substance, which also include supplements with probiotic action, deserve a special attention in the system of nutrition. One of these is the Biosprint microbial additive, which contains living yeast cultures (Saccharomyces cerevisiae, MUCL strain, 39885) and belongs to the group of biotic additives. This research is based on the need for the optimization of the limited feeding of milk cows through the use of the Biosprint feed additive in addition to a semi-concentrated type of feeding. Based on the conducted test use (90 days), it is necessary to determine the additive’s effect on the rumen digestion processes, milk yield and qualitative indicators of milk and to determine its optimal content in the diet. It was established that feeding the Biosprint additive as part of the diet contributed to the improvement of the intensity of metabolic processes in cows, in particular, in the rumen. The assumed growth of the number of amylo- and cellulolytic and proteolytic bacteria was detected, which contributed to their enzyme activity and, in turn, led to an intensive hydrolysis of carbohydrate feeds, as a result of which an assumed growth of VFAs as milk fat precursors occurred. Positive results were obtained in terms of the value of milk yield of cows in study groups in comparison with the control group across average daily milk yield by 1.2–2 kg, which constitutes a growth of 5.5–9.2%.There was a stable tendency towards an increase of fat content in milk by 0.05–0.1% and protein by 0.02–0.03%, which indicates an improvement in milk quality. Summing up, conducted study focused on the evaluation of the productive effect of the Biosprint drug on the milk yield of cows and the qualitative indicators of milk make a case for the expediency of the use of the above in the diet structure when feeding milk cows.

Effects of infusing milk precursors into the artery on rumen fermentation in lactating cows.

This experiment was conducted to investigate the effects of infusing milk precursors into the external pudic artery on rumen fermentation in lactating dairy cows. Eight multiparous Holstein cows were randomly assigned to Group A (experimental group) and Group B (control group) with 4 cows each. A 2 × 4 complex factor crossover design was used. Cows in Group A were fed corn straw as the only roughage, and cows in Group B were fed mixed roughage. The experiment was divided into two periods. In the first period, cows in Group A, received treatments: 1) a basal infusate as a control (CSC); 2) a milk fat precursor infusion including C16:0, C18:0, C18:1c9, C18:2c6, C18:3n3, acetic acid (CSF); 3) a milk protein precursor infusion including 16 amino acids (CSA); 4) the mixed infusion of milk fat and protein precursors (CSFA). And meanwhile, cows in Group B were infused the basal infusate as a control group. In the second period, the cows in both Groups A and B were crossed over, which cows in Group A were named as Group B and the cows originally in Group B were in Group A. The experimental results showed that cows in experimental group had higher ruminal pH compared with the control, and ruminal pH in CSC, CSF, CSA were significantly higher than those in their respective control group (P < 0.05). The concentration of ammonia nitrogen (NH3–N) was significantly higher in CSA and CSFA compared with Group B (P < 0.05). We also observed that the infusion of mixed amino acids significantly increased the bacterial protein (BCP) content in rumen (P < 0.05) and influenced the rumen acetic acid concentration as well as the acetic to propionic ratio (P < 0.05). Milk fat precursors infusion significantly affected butyric acid concentration (P < 0.05). In addition, the content of lipopolysaccharide (LPS) in CSA was significantly higher than that in the control group (P < 0.05). It is concluded that the milk precursors infused into external pudic artery caused feedback effects on ruminal fermentation under the corn straw roughage conditions. The milk protein precursor increased the ruminal pH, the contents of BCP and acetic acid, which adjust rumen fermentation and improve milk performance.

Milk fatty acids profile and arterial blood milk fat precursors concentration of dairy goats fed increasing doses of soybean oil

The provision of fatty acid sources in ruminant diets allows the manipulation of fatty acid profiles in milk and meat, permitting to increase the fatty acids of interest, such as conjugated linoleic acid. The objectives of this experiment were to evaluate the inclusion of increasing doses of soybean oil (30, 60 or 90g/d) on intake, total tract digestibility of nutrients, milk production and composition, arterial and milk fatty acid profiles, and arterial concentrations of glucose, acetate, and β-hydroxybutyrate in dairy goats. Four multiparous Saanen goats with mean initial DIM 32±6 and mean initial BW 63±7kg were assigned in a 4×4 Latin square. Does were housed in tie stalls and fed a 40% of corn silage and 60% concentrate diet. Experimental treatments consisted of: (1) basal diet without soybean oil infusion (control); (2) basal diet plus an oral infusion of 30mL soybean oil; (3) basal diet plus an oral infusion of 60mL soybean oil; and (4) basal diet plus an oral infusion of 90mL soybean oil. The DM and OM intakes decreased linearly (P<0.05) with increasing soybean oil supply. Dry matter digestibility was negatively influenced by oil (P<0.01); however, the OM digestibility was not affected by soybean oil doses. Milk production tended to decrease (P=0.07) by soybean oil supply, although when this was corrected to 3.5% fat, it decreased linearly (P<0.01) as a result of the decreasing (P<0.05) milk fat content. Vaccenic acid concentration in arterial blood increased (P<0.01) 127% with 90g/d of soybean oil addition. Appearance of C18:2 t10, c12 in milk caused a reduction (P<0.01) in milk fat and reached a 31% reduction when 90g/d of soybean oil was offered compared to the control diet, while the opposite occurred with C18:2 c9, t11, which decreased (P<0.05) with increasing doses of soybean oil. Increasing soybean oil had no effect on arterial blood concentrations of glucose, acetate and β-hydroxybutyrate. Therefore, the decrease in milk fat concentration was due to the inhibition of mammary synthesis of fatty acids, but not by a limitation of its precursors for fatty acid synthesis.

Transfer of Dietary Zinc and Fat to Milk—Evaluation of Milk Fat Quality, Milk Fat Precursors, and Mastitis Indicators

The present study demonstrated that the zinc concentration in bovine milk and blood plasma is significantly affected by the intake of saturated fat supplements. Sixteen Holstein cows were used in a 4×4 Latin square design with 4 periods of 12 d, and 4 dietary treatments were conducted. A total mixed ration based on corn silage, grass-clover silages, and pelleted sugar beet pulp was used on all treatments. A high de novo milk fat diet was formulated by adding rapeseed meal and molasses in the total mixed ration [39mg of Zn/kg of dry matter (DM)], and a low de novo diet by adding saturated fat, fat-rich rapeseed cake, and corn (34mg of Zn/kg of DM). Dietary Zn levels were increased by addition of ZnO to 83 and 80mg of Zn/kg of DM. Treatments did not affect daily DM intake, or yield of energy-corrected milk, milk fat, or milk protein. The high de novo diet significantly increased milk fat percentage and milk content of fatty acids with chain length from C6 to C16, and decreased content of C18 and C18:1. Treatments did not influence milk free fatty acids at 4°C at 0 or 28h after milking. The average diameter of milk fat globules was significantly greater in milk from cows offered low de novo diets. Furthermore, the low de novo diet significantly increased the concentration of nonesterified fatty acids and d-β-hydroxybutyrate in blood plasma, the latter was also increased in milk. Treatments did not affect the enzyme activity of lactate dehydrogenase and N-acetyl-β-d-glucosaminidase in milk or the activity of isocitrate dehydrogenase and malate dehydrogenase in blood plasma. The low de novo diet significantly increased plasma Zn and milk Zn content, whereas dietary Zn level did not in itself influence these parameters. This indicates that the transfer of fat from diet to milk might facilitate transfer of Zn from diet to milk.

Increasing Milking Intervals Decreases the Mammary Blood Flow and Mammary Uptake of Nutrients in Dairy Cows

Increasing the milking intervals reduces milk yield. The aims of this study were to determine whether the reduction in milk yield could be explained by a decrease in mammary uptake of the nutrients or a decrease in the efficiency of the mammary gland in using the milk precursors to synthesize milk components, or both. In a Latin square design with 5 periods, 4 multiparous lactating dairy cows in midlactation were milked at 8-, 12-, 16-, or 24-h intervals over a period of 7 d. The cows were surgically prepared to estimate the net mammary balance of nutrient precursors of milk components (glucose, α-amino nitrogen, acetate, β-hydroxybutyrate, and total glycerol). The efficiency of the mammary gland in synthesizing milk components was estimated by the mammary uptake:milk output ratio. After 7 d of treatment, the decrease in milk yield of 6.1 kg/d between 8- and 24-h milking intervals was associated with a reduction in the uptake of nutrients by the mammary gland, whereas the efficiency of the mammary gland in synthesizing milk components remained relatively unchanged. The mammary uptake decreased by 26% for glucose, 32% for α-amino nitrogen, 18% for acetate, 24% for total glycerol, and 24% for β-hydroxybutyrate, respectively. These reductions in nutrient uptake were due to a decrease in the mammary blood flow (1.23±0.24 L/min). For milk fat precursors (acetate, β-hydroxybutyrate, and total glycerol), the decrease in mammary blood flow explained the entire reduction in the mammary uptake. For glucose and the milk protein precursors, the reduction in the mammary blood flow explained 60% of the decrease in the mammary uptake, with the other 40% being accounted for by a reduction in the mammary extraction of nutrients. The nutrient uptake was altered as milk yield decreased. These decreases began with the 16-h milking interval and were higher at the 24-h milking interval.

Longer Milking Intervals Alter Mammary Epithelial Permeability and the Udder's Ability to Extract Nutrients

Increasing the milking interval decreases milk yield and modifies milk composition. To gain a clearer understanding of the regulation of milk yield and composition, a study was conducted to establish the response curves of nutrient extraction by the mammary gland and mammary epithelial permeability in response to increasing milking intervals. Four multiparous lactating dairy cows were milked at 8-, 12-, 16-, or 24-h intervals over a period of 7 d using a Latin square design. Between the 8- and 24-h milking intervals, milk yield and milk protein levels fell curvilinearly from 38.2 to 29.2kg/d and from 1,086 to 827 g/d, respectively. Milk fat yield decreased linearly from 1,475 to 1,235 g/d. Indicators of the opening of tight junctions increased linearly with increasing milking intervals: milk BSA increased from 148 to 207mg/L and plasma lactose increased from 22.9 to 32.0mg/L. The mammary gland's ability to extract nutrients decreased with increasing milking intervals. Extraction rates of glucose, β-hydroxybutyrate, and total glycerol decreased significantly (from 27.2 to 23.3%, from 42.3 to 34.4%, from 36.6 to 30.8% between 8- and 24-h milking intervals, respectively), and not significantly for α-amino nitrogen (from 23.2 to 20.0%). The extraction rate of acetate remained constant. Moreover, the extraction of milk fat precursors appeared to be less regulated than those of the precursors of milk protein and lactose, which could partly explain why milk yield and milk protein yield decreased more than milk fat yield. The arteriovenous differences of β-hydroxybutyrate and total glycerol remained constant, whereas those of glucose decreased significantly from 0.98 to 0.87±0.05 mmol/L and not significantly from 0.74 to 0.64±0.12 mmol/L for α-amino nitrogen. As a result, the mammary gland's ability to extract nutrients appears to be downregulated explaining partly the decrease in daily milk yield observed in response to increased milking intervals.

Effects of thyroxine and growth hormone treatment of dairy cows on mammary uptake of glucose, oxygen and other milk fat precursors.

Four cows received thyroxine injections (T4; 20 mg/d) and three cows received growth hormone injections (GH, 44 mg/d) for 4 d during successive 16-d experimental periods. Milk fat, lactose output, mammary uptake of glucose, oxygen and milk fat precursors were determined with each treatment. Injection of T4 increased lactose yield by 25% and fat yield 42%. The injection of GH increased fat and lactose yields by 24%. Both GH and T4 increased mammary glucose uptake by 35% and 45%, respectively, while T4 administration was associated with an increase in plasma glucose concentration from 67 to 84%. Thyroxine, but not GH, increased the ratio of mammary glucose uptake to lactose output from 1.24 to 1.58. Blood plasma acetate concentration declined following GH and T4 treatment by 17%. Mammary acetate uptake increased in response to GH injection in two of three cows but did not change with T4 injection. The injection of GH had no effect on plasma propionate concentration or mammary uptake. Thyroxine reduced plasma propionate content and mammary uptake. Neither T4 nor GH changed plasma free fatty acid concentration or mammary uptake. Thyroxine had no effect on plasma triglyceride concentration or mammary uptake, whereas GH increased mammary triglyceride uptake to the end of the experimental period. Mammary oxygen uptake was increased by GH as milk production increased. Increased mammary oxygen uptake following T4 treatment was transient. Change in mammary metabolism with T4 treatment permitted increased milk output without change in mammary oxygen consumption. Such a change may involve increased mammary utilization of pre-formed long-chain fatty acid and increased metabolism of glucose via glycolysis.

Implication of Forage Particle Length on Chewing Activities and Milk Production in Dairy Goats

Twenty-four primiparous Alpine does fed a high concentrate ration were utilized to study the effect of forage particle length on chewing activity, ruminal components, and milk composition. Treatments were Bermudagrass hay with mean particle length of 2.38 and 3.87mm. Forage particle length was determined with an oscillating screen particle separator. Feeding forage with 3.87-mm mean particle length to lactating dairy goats resulted in higher total chewing and rumination times, slightly higher milk fat content, and fat-corrected milk production. Results from this experiment support the hypothesis that forage particle length affects chewing activities and production of milk fat precursors in the rumen and alters milk fat content and output of fat-corrected milk. Forage particle length appeared to be an important index for forage quality and a quantitative approach could be feasible to establish a system relating forage particle length to milk production in dairy goats.

Effect of feeding protected lipid on the uptake of precursors of milk fat by the bovine mammary gland.

The feeding of protected lipid to lactating dairy cows resulted in a substantial increase in the proportion of fatty acid 18:2 and a decrease in fatty acids 4:0 to 16:0 in milk fat.

Studies on the mode of uptake of blood triglycerides by the mammary gland of the lactating goat. The uptake and incorporation into milk fat and mammary lymph of labelled glycerol, fatty acids and triglycerides.

1. The mode of uptake of the precursors of milk fat by the mammary gland of the lactating goat has been examined by infusing radioactive fatty acids, glucerol or doubly labelled triglycerides into the mammary artery or jugular vein of animals surgically prepared to permit samples of arterial and venous blood to be withdrawn without disturbance to the animal. 2. Acetate was taken up by the mammary gland and incorporated into milk fat. The decrease in the specific radioactivity of blood acetate across the gland was evidence of acetate production, but there was no significant release of labelled lipid from the mammary gland. 3. When labelled long-chain fatty acids or glycerol were infused into the lactating goat, there was extensive transfer of radioactivity into milk in spite of the absence of net uptake of substrate by the mammary gland. The decrease in the specific radioactivity of each substrate across the mammary gland, however, showed that both fatty acids and glycerol were simultaneously taken up and released by mammary tissue. 4. The infusion of chylomicra and triglyceride emulsions labelled with (3)H and (14)C revealed that both glycerol and fatty acids were released during triglyceride uptake by mammary tissue. Changes in the (3)H/(14)C ratio during the transfer of triglyceride from blood into milk showed that at least 80% of the triglyceride was hydrolysed during uptake, but the potential re-utilization of both products of hydrolysis for triglyceride synthesis in mammary tissue implied that only a minimum value could be obtained from the change in the ratio. 5. The time-course of the transfer of (3)H and (14)C into milk and lymph were closely similar after the infusion of [2-(3)H]glycerol tri[1-(14)C]oleate or of a mixture of [2-(3)H]glycerol and [1-(14)C]oleate. 6. The results were consistent with the hypothesis that plasma triglycerides are extensively or completely hydrolysed during mammary uptake.

Composition of Bovine Milk as Affected by Intravenous Infusion of Sunflower Oil. Fixation of Milk Fat for Electron Microscopy

A stable, nontoxic, 15% sunflower oil emulsion containing 65% linoleic acid was formulated for intravenous infusion into a cow. An infusion of 500ml of this emulsion into a Jersey cow caused a parallel increase in the fat and protein of the milk and a decrease in lactose. The correlations obtained, between the percentages of fat-protein (morning's milk, r = 0.99; evening's milk, r = 0.85), and fat-lactose (r = −0.71) and yields of fat-protein (r = 0.98) and fat-lactose (r = 0.98) indicated the existence of some control mechanism in the cow, relating fat, protein, and lactose synthesis. There was an increase of 5% in linoleic acid at the second post-infusion milking. Consequently, the unsaturation of the milk fat was increased which, in turn, improved its fixation by osmium tetroxide for electron microscopy. The appearance of large extraalveolar fat droplets, 3 to 85 μ in diameter, and the prolonged effect of the infusion on the milk fat composition is indicative that the emulsion was cleared from the blood stream and stored as milk fat precursors until they could be used in the formation of milk fat by the secreting alveolar cells.

EFFECT IN THE COW OF INTRARUMINAL INFUSIONS OF VOLATILE FATTY ACIDS AND OF LACTIC ACID ON THE SECRETION OF THE COMPONENT FATTY ACIDS OF THE MILK FAT AND ON THE COMPOSITION OF BLOOD.

1. The effects in the cow of intraruminal infusions of acetic acid, propionic acid or butyric acid on the secretion of the component fatty acids of the milk fat, and of these acids and of lactic acid on the composition of the blood plasma of the jugular vein, have been studied. 2. The infusion of acetic acid or butyric acid increased the yield of the C(4)-C(16) acids of milk fat but decreased the yield of C(18) acids. The infusion of propionic acid decreased the yields of all major component acids except palmitic acid and possibly lauric acid. 3. The changes in the concentrations in blood plasma of glucose and of ketone bodies were consistent with the glucogenic effect of propionic acid and the ketogenic effects of butyric acid and acetic acid. The effects of lactic acid were not consistent from cow to cow. Only with the infusion of acetic acid was a significant increase in the concentration of total volatile fatty acids in blood plasma found. Infusions of butyric acid and of propionic acid tended to depress the concentration of citric acid in the blood plasma and infusion of acetic acid increased it. No consistent effects of the infused acids on the concentration in blood plasma of esterified cholesterol, free cholesterol, triglyceride or phospholipid were observed. 4. The possibility is discussed that the effects of the infused acids on milk-fat secretion are caused through an alteration of the concentrations of precursors of milk fat in mammary arterial blood.

The effect of starvation on the uptake of the precursors of milk fat by the bovine mammary gland.

The relative changes imposed by a 4.day starvation on the arteriovenous difference across the mammary gland, for triglyceride, free fatty acids, glucose, B-hydroxybutyrate, and acetate have been studied in three lactating cows.

The biosynthesis of milk-fat in the intact cow

The behavior of the principal metabolites of the cow as precursors of milk-fat has been studied. This has been carried out by determining the specific activities of the various fat-constituents after the injection of the metabolites labelled with 14C. Significant fixation of carbon dioxide into the glycerol moiety was observed; that into fatty acids was almost neglible. Glucose is important in fat synthesis as a precursor of glycerol, but fatty acid synthesis from glucuse is on a very small scale. Acetate is the most potent precursor of fatty acids, but it is also a source of glycerol. The transfer of acetate carbon to glycerol appears to be by way of the tricarboxylic acid cycle, through both the incorporation of acetyl CoA and by carbon dioxide fixation. Propionate is unimportant in fatty acid synthesis, but the activity of glycerol following the injection of labelled propionate supports the view that propionate is the main carbohydrate precursor in the cow. Butyrate shows intermediate lipogenic and glycogenic functions. Formate is not a source of fatty acids in milk-fat, but does contribute some carbon to glycerol. The peak radio-activity in all of the fat-constituents was observed in the second milk-samples (taken at II hours), whereas for the casein and lactose it was in the first (3 hours after injection of the tracer).

A METHOD OF ASSAY FOR THE FAT METABOLISM HORMONE OF THE ANTERIOR PITUITARY1

FOR THE FURTHER chemical purification of the fat metabolism hormone of the anterior pituitary and study of its physiology, quantitative assay methods become important. In the early studies of this factor, its influence on fat catabolism as measured by ketonemia and ketonuria was described. Later the fatty infiltration of the liver was observed to follow the injection of AP extracts. On the basis of this observation, Campbell (i) has recently suggested an assay technique using the mouse. Recently, Houchin and Turner (2) reported that single injections of an AP extract depressed the blood fat of rabbits about 36% in from 6 to 8 hours. As our interest in this hormone centers about its relation to fat secretion by the mammary gland (that is milk fat precursors in blood) it seemed desirable to develop an assay method dependent upon blood lipid changes. The rabbit would serve very well as an assay animal except for the rather large amount of hormone required to induce a response.