Biomedical subjects
Publications and source records attributed to R S Emery.
Milk composition depends on inheritance, stage of lactation, age, infection, and diet. Fat is the most variable component of milk, and its concentration depends on the supply of acetate, butyrate, and performed fatty acids to the mammary gland. This supply depends on diet and competition among organs. Adequate, effective fiber is the critical dietary consideration.
Contributions of the intestine and liver to triacylglycerol (TG) formation from endogenous fatty acids were investigated in sheep. Cannulation and sampling of the intestinal lymph ducts and portal veins of two mature, nonpregnant ewes followed by an i.v. dose of 100 microCi of [14C]palmitate into a mesenteric cannula suggested intestinal contribution to endogenous TG production to be of no consequence. Turnover rates of TG within the plasma, hepatic microsomal and hepatic fat droplet compartments of four wethers averaged 20 +/- 8, 7.8 +/- 1.5 and 2.3 +/- .8 mg.h-1.kg body weight-1, respectively. A large, relatively inert pool of fat droplets with a slow turnover contained between 80 and 90% of the total hepatic TG. Hepatic TG concentration and turnover rates within the hepatic microsomal and fat droplet pools were inversely (r = -.86) and positively (r = .99) correlated, respectively, indicating that hepatic secretion of TG as lipoprotein was decreased as hepatic TG concentration increased. The model developed from these figures suggest that 40% of the plasma TG turnover is of endogenous origin and that this percentage value decreases when hepatic TG content is increased.
Our objective was to determine the relationship between energy balance and secretion of progesterone in lactating dairy cows. Eight primiparous and 24 multiparous lactating Holstein cows were studied from parturition to 100 d postpartum or conception. Cows calved normally and remained healthy throughout the study. All cows were fed ad libitum a total mixed diet formulated to satisfy requirements for maintenance and lactation. Intake of feed and production of milk per cow were measured twice daily. Body weight was determined weekly. Daily energy balance was determined by subtracting energy required for maintenance and lactation from intake of energy. Concentrations of progesterone were determined in milk sampled every 3rd d. For at least 4 successive d postpartum, 81% of cows were in negative energy balance. Variation in energy balance was explained largely by intake of energy. Duration of luteal phases was not associated with energy balance. Energy balance within 9 d postpartum was correlated positively with concentration of progesterone within second and third postpartum luteal phase. Postpartum interval to nadir and magnitude of nadir of energy balance interacted to reduce progesterone within second and third postpartum estrous cycles. Thus, in lactating cows, secretion of progesterone is reduced by spontaneous caloric deficit and is modulated by timing and magnitude of maximal caloric deficit. Spontaneous caloric deficit is a potential source of infertility in lactating dairy cows.
In a field study of 80 cows in 9 dairy herds, serial liver biopsies were performed over the peripartum period to determine degree of hepatic lipidosis. Cattle were separated into categories of mild, moderate, and severe hepatic lipidosis on the basis of maximal amounts of hepatic triglyceride that accumulated during this period. Number of cattle with mild, moderate, and severe hepatic lipidosis were 52, 16, and 12, respectively. Cattle with severe hepatic lipidosis had greater concentrations of hepatic triglyceride before calving and after parturition, and greater serum nonesterified fatty acid concentrations and body condition loss after parturition than cattle with mild hepatic lipidosis. Rate of disease and culling and death rate because of disease were greater in cattle with severe hepatic lipidosis. Cattle with severe hepatic lipidosis had reproductive performance equal to clinically normal cattle; however, cattle with moderate hepatic lipidosis had increased days to conception, possibly related to greater milk production.
Percutaneous liver biopsies and blood samples were obtained from 80 multiparous dairy cows in nine Michigan herds. Biopsies and samples were obtained serially over the peripartum period. Thirty-nine cows received 17 g of supplemental myoinositol in the diet to test its use as a possible lipotropic substance and 41 received a placebo. Liver biopsies were assayed for triglyceride (TG) and total myoinositol content. Serum was assayed for dextran precipitable cholesterol and non-esterified fatty acids (NEFA). Inositol supplementation had no effect on any of the lipid variables. There was a significant herd effect on liver inositol, serum dextran precipitable cholesterol and NEFA concentrations. Serum NEFA and liver TG concentrations increased in the immediate postpartum period, while dextran precipitable cholesterol decreased. A significant herd X period interaction existed for liver TG and serum dextran precipitable cholesterol concentrations. Liver TG and serum NEFA concentrations were positively correlated. Excessive infiltration of bovine liver with lipid at calving appears to be an exaggerated manifestation of normal metabolic changes.
Percutaneous liver biopsies and blood samples were obtained from 80 dairy cows in nine Michigan herds over the peripartum period. Thirty-nine cows were fed 17 g of supplemental inositol and 41 were fed a placebo. Liver biopsies were assayed for total myoinositol and triglyceride (TG) concentrations. Blood samples were assayed for serum dextran precipitable cholesterol, nonesterified fatty acids (NEFA), insulin, thyroxine (T4), free (FT4), triiodothyronine (T3) and free T3 (FT3) concentrations. Serum concentrations of insulin and the thyroid hormones decreased near parturition, with lowest concentrations occurring in the immediate postpartum period. Concentrations of T3 correlated well with T4, and the concentrations of free thyroid hormones reflected concentrations of total thyroid hormones. The percentage of hormone in the free fraction remained constant over time. Serum insulin, T3 and T4 were negatively correlated with serum NEFA and liver TG concentrations. Thyroid hormone concentrations were positively correlated with serum dextran precipitable cholesterol concentrations. Inositol supplementation was associated with reduced circulating T3 and FT3 concentrations, but not T4 and FT4 concentrations. Changes in hormone concentrations at parturition and their relationship to liver TG and serum NEFA concentrations were consistent with a metabolic adaptation by the dairy cow to the negative energy balance of early lactation.
Concentration of serum growth hormone was increased and feed intake was reduced in lactating dairy cows fed an 84% concentrate diet supplemented with either 100.8 g MgO or 121.2 g of Mg(OH)2. Analysis of serum growth hormone, feed intake, and serum Mg showed an interaction of serum Mg and feed intake, which suggests low concentrations of serum Mg lessen the increase of concentration of serum growth hormone caused by reduced feed intake. Also, compared with control, treatments with Mg supplementation and reduced feed intake increased growth hormone concentration 12 d into the subsequent treatment.
Fatty acid oxidation by bovine liver slices and mitochondria was examined to determine potential regulatory sites of fatty acid oxidation. Conversion of 1-[14C]palmitate to 14CO2 and total [14C]acid-soluble metabolites was used to measure fatty acid oxidation. Oxidation of palmitate (1 mM) was linear in both liver slice weight and incubation time. Carnitine stimulated palmitate oxidation; 2 mM dl-carnitine produced maximal stimulation of palmitate oxidation to both CO2 and acid-soluble metabolites. Propionate (10 mM) inhibited palmitate oxidation by bovine liver slices. Clofenapate, an inhibitor of fatty acid esterification, alone increased palmitate oxidation and was able to prevent the propionate-induced inhibition of palmitate oxidation by liver slices. Propionate (.5 to 10 mM) had no effect on palmitate oxidation by mitochondria, but malonyl Coenzyme A, the first committed intermediate of fatty acid synthesis, inhibited mitochondrial palmitate oxidation (inhibition constant = .3 microM). Liver mitochondrial carnitine palmitoyltransferase (EC 2.3.1.21) exhibited Michaelis constants for palmitoyl Coenzyme A and l-carnitine of 11.5 microM and .59 mM, respectively. Long-chain fatty acid oxidation in bovine liver is regulated by mechanisms similar to those in rats but adapted to the unique digestive physiology of the bovine.
Factors involved in regulation of bovine hepatic fatty acid oxidation were examined using liver slices. Fatty acid oxidation was measured as the conversion of 1-[14C] palmitate to 14CO2 and total [14C] acid-soluble metabolites. Extended (5 to 7 d) fasting of Holstein cows had relatively little effect on palmitate oxidation to acid-soluble metabolites by liver slices, although oxidation to CO2 was decreased. Feeding a restricted roughage, high concentrate ration to lactating cows resulted in inhibition of palmitate oxidation. Insulin, glucose, and acetate inhibited palmitate oxidation by bovine liver slices. We suggest the regulation of bovine hepatic fatty acid oxidation may be less dependent on hormonally induced alterations in enzyme activity as observed in rat liver and more dependent upon action of rumen fermentation products or their metabolites on enzyme systems involved in fatty acid oxidation.
Fatty liver syndrome or hepatic lipidosis (HL) is a condition thought to contribute to an increased incidence of peripartum disease, reduced response to therapy and decreased fertility in dairy cows. This syndrome is characterized by excess triglyceride (TG) accumulation in the liver and apparent decreased hepatic lipoprotein output. In lactating rats, a similar condition results from feeding an inositol-deficient diet. It is also characterized by excess hepatic TG accumulation and decreased hepatic lipoprotein output. Myo-inositol is a necessary component of the phospholipid phosphatidyl-inositol, which is an important membrane constituent. Myo-inositol occurs in feed mainly as the inositol hexaphosphate phytic acid. Phytic acid is undigestible by the monogastric but rumen phytases are assumed to adequately hydrolyze it. In early lactation dairy cows, lipid mobilization is intense, and the myo-inositol requirement may exceed the dietary supply or availability. Myo-inositol is being tested in a field trial as a potential lipotropic agent for dairy cows. Preliminary results suggest no lipotropic benefit from added myo-inositol.
Feeding for 150 days of 25 g per day of methionine hydroxy analog was tested on 100 cows (52 treated and 48 controls) in the Brigham Young University herd. Effect of days after parturition of initiating methionine hydroxy analog feeding also was observed. Milk yields were not affected by methionine hydroxy analog, but fat percent and fat yields were increased 21 and 17% by the additive. Abnormally low milk fat by control cows (2.84%) magnified the response to methionine hydroxy analog feeding. Feeding methionine hydroxy analog beginning 0 to 12 days postpartum elicited much larger increases of milk fat than started later (17 to 102 days). Blood from the coccygeal vein of 20 cows from each treatment had 10% more triglycerides from cows fed methionine hydroxy analog than from control cows. Increases of arterio-venous differences across the mammary gland of triglycerides and lipoproteins of blood serum suggested that increases of milk fat could have resulted from greater uptake of performed fat by the udder. Feeding methionine hydroxy analog increased methionine, isoleucine, and leucine in serum of coccygeal vein, but methionine was the only amino acid with significantly higher arteriovenous differences across the mammary gland.
To determine the ability of mineral supplements to elevate depressed milk fat percent, we placed 42 Holstein cows in early to midlactation in seven blocks and assigned each to one of six treatments: control (25% corn silage and alfalfa haylage, 75% concentrate, mostly corn, dry matter); control plus magnesium oxide ground to pass a .425-mm sieve; control plus prilled magnesium oxide sieved to between 1.70 and .425 mm; control plus sodium bicarbonate; control plus reactive powdered magnesium oxide to pass a 45 microns sieve; and control plus powdered magnesium hydroxide. Sodium bicarbonate was 1% of diet as fed, magnesium oxide .5%, magnesium hydroxide .7% later reduced to .5%. Cows were fed control ration for 3 wk to induce milk fat depression, then were changed to treatment rations for 5 wk. Five cows (unblocked) were continued on each dietary treatment for a digestibility study after the feeding trial. All mineral supplements produced greater milk fat percent and yield of milk fat per day than control and all magnesium treatments produced greater milk fat percent than sodium bicarbonate. Magnesium oxide passing a .425-mm sieve produced the greatest increase of milk fat percent. Milk production was most for sodium bicarbonate treatment. Supplementation with magnesium increased ruminal magnesium concentration by factors of 1.26 to 3.75. Blood serum, urine, and fecal magnesium concentrations and fecal pH were more for cows fed magnesium than those fed sodium bicarbonate treatments. Kidney filtration ratios of element to creatinine increased for magnesium when diets were supplemented with magnesium and increased for phosphorus and sodium when diets were supplemented with sodium bicarbonate.
The lipid content of bovine liver was found to be highly correlated with its specific gravity. This observation was used as the basis for a clinical test to estimate the liver lipid content in dairy cows. The test consisted of submerging needle biopsy specimens of liver into water and copper sulfate solutions with specific gravities of 1.025 and 1.055. On the basis of buoyancy in these liquids, bovine liver samples were classified accurately as containing greater than 34% lipid, greater than 25% lipid, greater than 13% lipid, or less than 15% lipid.
Effects of photoperiod and plane of nutrition on growth, serum concentrations of prolactin (PRL) and growth hormone (GH) and puberty were assessed in Holstein heifers. Sixty pre-pubertal heifers were assigned to one of four treatment groups arranged in a 2 X 2 factorial. The two main effects were photoperiods of 8 h light: 16 h dark (8L:16D) vs 16L:8D, and a low vs high plane of nutrition. Heifers on the low plane of nutrition were fed a diet formulated to achieve a body growth rate of approximately .7 kg/d. Daily feed intake was restricted and similar in both groups of low plane heifers subjected to either 8 or 16 h of light daily. Heifers on the high plane of nutrition were fed ad libitum to achieve a growth rate greater than 1 kg/d. Body weight was recorded every month for 5 mo. The PRL and GH concentrations were measured at d 9, 53 and 132 in serum collected every 30 min for 6 h from five heifers in each treatment group. Progesterone was monitored biweekly in all heifers as an index of puberty (greater than 1 ng/ml). Heifers subjected to 8L:16D-low plane, 16L: 8D-low plane, 8L:16D-high plane or 16L:8D-high plane gained .61, .72, .98 and 1.08 kg/d, respectively. In the same treatment order, averaging across all bleedings, concentrations of PRL were 32, 37, 38 and 46 ng/ml serum, and GH averaged 10.9, 9.3, 9.8 and 9.0 ng/ml serum. Similarly, body weight at puberty averaged 268, 257, 278 and 268 kg, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)
The hepatic and serum lipid concentrations in 49 dairy cows with displaced abomasum, 7 postpartum cows fasted for 6 days, and 14 healthy postpartum cows were studied. The cows with displaced abomasums were retrospectively allotted to 2 groups: those with greater than 15% liver fat (DAHF) and those with less than 15% liver fat (DALF). Liver total lipid concentrations were high in the DAHF group, exceeding these values in the fasted cows by 30% and in the healthy and DALF cows by 63% on the average. In contrast, the liver phospholipid concentrations were low in the DAHF group, intermediate in the fasted and DALF groups and high in the healthy group. On a group basis, an inverse relationship was observed between serum and liver lipid concentrations. The serum concentrations of both total and dextran-sulfate-precipitable (DSP) lipids were high in the fasted cows and were less in the DALF and healthy cows and in the DAHF cows (lowest). The between-group differences in serum total and serum DSP concentrations of triacylglycerol, cholesterol, and phospholipid followed the same quantitative pattern as the total lipids. However, the relative difference between groups was greater for each of the DSP lipid fractions. These results support the hypothesis that severe hepatic lipidosis in cattle occurs due to impaired hepatic lipoprotein synthesis and secretion.
To determine if energy and phosphorus status would affect postpartum health and lactational performance, first-calf heifers were assigned at parturition, 12 per group, to either high (135% of requirement) or low (85% of requirement) energy, high (138% of requirement) or adequate (98% of requirement) phosphorus in a 2 X 2 factorial design. Treatments extended 84 days postpartum after which standard rations were fed. Milk yields were similar until wk 5 of lactation. From wk 5 to 12, cows fed adequate phosphorus (98% of requirement) yielded 1.8 kg/day more milk than high phosphorus groups. Energy did not affect milk yield until wk 9 when persistency of low energy groups declined. High energy groups had almost twice as much disease and higher rectal temperatures than low energy groups in the first 3 mo of lactation. All heifers had temperatures above expected during the 1st mo of lactation. Excess energy should be avoided for the 1st mo of lactation and then gradually increased. Phosphorus should be fed as recommended and no more.
Effect of glucose on palmitate and octanoate metabolism was studied in bovine mammary tissue slices. Glucose stimulated palmitate esterification principally to form partial glycerides while decreasing palmitate oxidation. Glucose stimulated octanoate but not palmitate incorporation into triacylglycerols, suggesting that availability of intracellular medium-chain fatty acids may limit the final acylation reaction in triacylglycerol synthesis.
Milk production and dry matter intake of 21 cows subjected to 16 h of fluorescent light and 8 h dark and of 21 cows subjected to natural light 9 to 12 h daily between October 25 and March 14 were measured beginning in early (37 to 74 days postpartum) and late (94 to 204 days postpartum) lactation. Cows that received 16 h of fluorescent light produced 6.7% (1.4 kg) more milk per day (adjusted for parity and pretreatment production) than cows exposed to natural photoperiods. Increases of milk production with 16 h of fluorescent light were similar for early and late lactation. Photoperiod did not alter percent of fat in milk. Dry matter intake increased 6.1% for cows in 16 h of light, and this increase could account for increased milk yields. Basal prolactin in serum and that released by thyrotropin releasing hormone were 1.5 to 1.8 times greater for cows exposed to 16 h of light than for cows in 9 to 12 h of natural light daily. Photoperiod did not affect release of prolactin by milking. Cold ambient temperatures reduced basal prolactin and prolactin released by thyrotropin releasing hormone but had no effect on concentrations of growth hormone or glucocorticoids. Compared with cows in late lactation, cows in early lactation released 2.4 times more prolactin after milking, but they released similar amounts of prolactin after thyrotropin releasing hormone. Photoperiod did not affect concentrations of growth hormone or glucocorticoids in blood sera.