Relationship between overfeeding and overconditioning in the dry period and the problems of high producing dairy cows during the postparturient period

Summary

In dairy cows, overfeeding during the dry period leads to overcondition at calving and to depression of appetite after calving. As a consequence, at calving overconditioned high‐producing dairy cows inevitably go into a more severe negative energy balance (NEB) postpartum than cows that have a normal appetite. During the period of NEB, the energy requirements of the cow are satisfied by lipolysis and proteolysis. Lipolysis results in an increased concentration of non esterified fatty acids (NEFA) in the blood. In the liver, these NEFA are predominantly esterified to triacylglycerols (TAG) that are secreted in very low density lipoproteins (VLDL). In early lactation in cows with a severe NEB, the capacity of the liver to maintain the export of the TAG in the form of VLDL in balance with the hepatic TAG production is not always adequate. As a result, the excess amount of TAG accumulates in the liver, leading to fatty infiltration of the liver (hepatic lipidosis or fatty liver). The NEB and/or fatty liver postpartum are frequently associated with postparturient problems. In general, a severe NEB induces changes in biochemical, endocrinological, and metabolic pathways that are responsible for production, maintenance of health, and reproduction of the postparturient dairy cow. These changes include a decrease in blood glucose and insulin concentrations, and an increase in blood NEFA concentrations. High NEFA concentrations caused by intensive lipolysis are accompanied by impairment of the immune system, making the cows more vulnerable to infections. Metabolic diseases such as ketosis, milk fever, and displaced abomasum are related to overcondition at calving. The changes in biochemical, endocrinological, and metabolic pathways are associated with delay of the first visible signs of oestrus, an increase in the interval from calving to first ovulation, a decrease in conception rate, and a prolonged calving interval. It is possible that the increased blood NEFA concentration directly impairs ovarian function.     

Relationship between overfeeding and overconditioning in the dry period and the problems of high producing dairy cows during the postparturient period.

In dairy cows, overfeeding during the dry period leads to overcondition at calving and to depression of appetite after calving. As a consequence, at calving overconditioned high-producing dairy cows inevitably go into a more severe negative energy balance (NEB) postpartum than cows that have a normal appetite. During the period of NEB, the energy requirements of the cow are satisfied by lipolysis and proteolysis. Lipolysis results in an increased concentration of non esterified fatty acids (NEFA) in the blood. In the liver, these NEFA are predominantly esterified to triacylglycerols (TAG) that are secreted in very low density lipoproteins (VLDL). In early lactation in cows with a severe NEB, the capacity of the liver to maintain the export of the TAG in the form of VLDL in balance with the hepatic TAG production is not always adequate. As a result, the excess amount of TAG accumulates in the liver, leading to fatty infiltration of the liver (hepatic lipidosis or fatty liver). The NEB and/or fatty liver postpartum are frequently associated with postparturient problems. In general, a severe NEB induces changes in biochemical, endocrinological, and metabolic pathways that are responsible for production, maintenance of health, and reproduction of the postparturient dairy cow. These changes include a decrease in blood glucose and insulin concentrations, and an increase in blood NEFA concentrations. High NEFA concentrations caused by intensive lipolysis are accompanied by impairment of the immune system, making the cows more vulnerable to infections. Metabolic diseases such as ketosis, milk fever, and displaced abomasum are related to overcondition at calving. The changes in biochemical, endocrinological, and metabolic pathways are associated with delay of the first visible signs of oestrus, an increase in the interval from calving to first ovulation, a decrease in conception rate, and a prolonged calving interval. It is possible that the increased blood NEFA concentration directly impairs ovarian function.     

Ruminant adaptation to negative energy balance. Influences on the etiology of ketosis and fatty liver.

Ketosis and fatty liver occur when physiologic mechanisms for the adaptation to negative energy balance fail. Failure of hepatic gluconeogenesis to supply adequate glucose for lactation and body needs may be one cause of ketosis; however, poor feedback control of nonesterified fatty acid release from adipose tissue is another likely cause of ketosis and fatty liver. The types of ketosis resulting from these two metabolic lesions may require different therapeutic and prophylactic approaches.     

Cryotolerance of Bovine Blastocysts is Affected by Oocyte Maturation in Media Containing Palmitic or Stearic Acid

In this study, non-esterified fatty acids (NEFAs) were added during in vitro maturation at concentrations measured previously in follicular fluid (FF) of high-producing dairy cows in a negative energy status to evaluate their subsequent effect on the embryos cryotolerance. Oocytes were matured for 24 h in serum-free media with or without (negative control) the addition of NEFAs dissolved in ethanol or ethanol alone (positive control). Matured oocytes were fertilized and cultured for 7 days in synthetic oviduct fluid medium supplemented with 5% FCS. Embryos that had at least reached the blastocyst stage were vitrified by open pulled straw (OPS) vitrification. Addition of palmitic (C16 : 0) or stearic acid (C18 : 0) during oocyte maturation had significant negative effects on embryo cryotolerance, whereas ethanol or oleic acid (C18 : 1) had no effect. These in vitro results suggest that high NEFA concentrations in FF during a period of negative energy balance in high-yielding dairy cows can have carry-over effects on embryo quality.     

Decrease in stearic acid proportions in adipose tissues and liver lipids in fatty liver of dairy cows

Samples of liver and perirenal, mesenteric and subcutaneous fat were collected from 16 sick necropsied dairy cows to evaluate the fatty acid profiles in the hepatic and adipose tissues associated with advanced fatty liver or hepatic lipidosis. Hepatic triglyceride and eight fatty acids were measured in the hepatic and adipose tissues. Six cows had more than 3% triglyceride on fresh weight in their livers and were classified as having fatty liver. Stearic and linoleic acid proportions in the liver decreased markedly with increased hepatic triglyceride levels, while the proportion of palmitic and oleic acids increased. The most striking fluctuations in hepatic lipidosis were manifested as decreased stearic acid in the adipose tissues including subcutaneous fat with the trend of decreasing stearic acid. Palmitic acid was elevated in hepatic and perirenal fat in fatty liver cows. In instances of advanced hepatic lipidosis, palmitoleic acid increased in only subcutaneous fat and not in perirenal or mesenteric fat. In addition to the proportions of hepatic fatty acids in fatty liver, this study also clarified the fluctuations observed in the profiles of fatty acids of the adipose tissues in cows with advanced hepatic lipidosis, particularly the decline in the proportions of stearic acid.     

奶牛脂肪肝的发病机理及防制措施

高产奶牛在分娩期易患脂肪肝。脂肪肝的发病机理尚不完全清楚 ,采食量下降并导致体脂动员是脂肪肝发生的直接原因 ,更深入的机制涉及奶牛肝脂代谢的特殊性。防制脂肪肝的思路包括降低体脂的动员、减少肝脂合成量和提高肝脂的输出量。本文对脂肪肝的发病特点、可能机制和预防措施作了讨论     

Disturbed bovine mitochondrial lipid metabolism: a review

In mammals, excess energy is stored primarily as triglycerides, which are mobilized when energy demands arise and cannot be covered by feed intake. This review mainly focuses on the role of long chain fatty acids in disturbed energy metabolism of the bovine species. Long chain fatty acids regulate energy metabolism as ligands of peroxisome proliferator-activated receptors. Carnitine acts as a carrier of fatty acyl groups as long-chain acyl-CoA derivatives do not penetrate the mitochondrial inner membrane. There are two different types of disorders in lipid metabolism which can occur in cattle, namely the hypoglycaemic-hypoinsulinaemic and the hyperglycaemic-hyperinsulinaemic type with the latter not always associated with ketosis. There is general agreement that fatty acid β-oxidation capability is limited in the liver of (ketotic) cows. In accord, supplemental L-carnitine decreased liver lipid accumulation in periparturient Holstein cows. Of note, around parturition concurrent oxidation of fatty acids in skeletal muscle is highly activated. Also peroxisomal β-oxidation in liver of dairy cows may be part of the hepatic adaptations to a negative energy balance (NEB) to break down fatty acids. An elevated blood concentration of nonesterified fatty acids is one of the indicators of NEB in cattle among others like increased β-hydroxy butyrate concentration, and decreased concentrations of glucose, insulin, and insulin-like growth factor-I. Assuming that liver carnitine concentrations might limit hepatic fatty acid oxidation capacity in dairy cows, further study of the role of acyl-CoA dehydrogenases and/or riboflavin in bovine ketosis is warranted.     

Expression of genes related to liver fatty acid metabolism in fat‐tailed and thin‐tailed lambs during negative and positive energy balances

Fat‐tailed sheep breeds can tolerate periods of negative energy balance without suffering from elevated concentration of plasma non‐esterified fatty acid (NEFA). This ability was attributed to unique metabolism of fat‐tailed adipose depot, whereas role of liver as an influential organ in fatty acid metabolism was not evaluated yet. Hence, current study was conducted to evaluate the effects of negative and positive energy balances on liver expression of genes related to fatty acid metabolism in fat‐tailed and thin‐tailed lambs. Lambs experienced negative (21 days) and positive (21 days) energy balances and were slaughtered at the beginning and end of negative energy balance and at the end of positive energy balance. Real‐time quantitative polymerase chain reaction (RT‐Q‐PCR) was conducted to evaluate changes in gene expression. Expression of diglyceride acyltransferase 1 (DGAT1), 3‐hydroxy‐3‐methylglutaryl‐CoA synthase 2 (HMGCS2) and apolipoprotein B (APOB) was not affected by genotype, energy balance and their interaction. Expression of carnitine palmitoyltransferase 1 (CPT1) was significantly higher in liver of fat‐tailed comparing to thin‐tailed lambs regardless of energy balance (p < 0.02). Catalase mRNA abundance was increased in response to negative energy balance (p < 0.02), and severity of this enhancement was higher in fat‐tailed lambs (p < 0.06). Expression of CPT1 was positively correlated with expression of HMGCS2 in both fat‐tailed (p < 0.05) and thin‐tailed lambs (p < 0.002); however, the correlation was weaker in fat‐tailed lambs (0.72 vs. 0.57, respectively, for thin‐tailed and fat‐tailed lambs). There was a positive correlation between DGAT1 and APOB genes expression in fat‐tailed lambs (0.94; p < 0.001), whereas this correlation was not observed in thin‐tailed lambs. Results demonstrate that liver of fat‐tailed lambs has higher capacity for metabolism of mobilized NEFA exposed to liver during negative energy balance.     

Subcutaneous and intramuscular adipose tissue stearoyl-coenzyme A desaturase gene expression and fatty acid composition in calf- and yearling-fed Angus steers

We proposed that stearoyl-CoA desaturase (SCD) activity dictates fatty acid composition of adipose tissue and muscle in beef cattle, regardless of ruminal or hepatic fatty acid hydrogenation or desaturation. Twelve Angus steers were assigned to a calf-fed (CF) group and slaughtered at weaning (8 mo of age; n=4), 12 mo of age (n=4), or 16 mo of age (n=4). Twelve steers were assigned to a yearling-fed (YF) group and slaughtered at 12 mo of age (n=4), 16 mo of age (n=4), and 17.5 mo of age (n=4; 525 kg, market weight). Data were analyzed based on time on the corn-based finishing diet, with terminal age as a covariate, and orthogonal polynomial contrasts were tested on the main effects of treatment group and time on the finishing diet. Fatty acids from duodenal digesta, plasma, liver, LM, and subcutaneous and intramuscular adipose tissue were measured, and SCD gene expression was measured in intramuscular and subcutaneous adipose tissues. In duodenal digesta, palmitic and linoleic acids increased by 100% over the sampling period, α-linolenic acid decreased over the sampling period, and trans-vaccenic acid was greater in YF than in CF steers (all P < 0.01). The proportion of α-linolenic acid decreased over time in all tissues, including liver. The SCD index (ratio of SCD fatty acid products to SCD fatty acid substrates) increased over time in LM and in intramuscular and subcutaneous adipose tissues. The SCD:glyceraldehyde 3-phosphate dehydrogenase mRNA ratio was virtually undetectable at the initial sampling periods in subcutaneous adipose tissue of YF and CF steers, and it increased over time (P < 0.01). The SCD index and SCD:glyceraldehyde 3-phosphate dehydrogenase ratio were greater in intramuscular adipose tissue of CF steers than in that of YF steers. The SCD index did not change over time in liver and decreased over time in duodenal digesta. We conclude that, unlike essential fatty acids, the SFA and MUFA composition of adipose tissue is regulated by adipose tissue fatty acid desaturation, with little contribution from hepatic or duodenal fatty acids.     

Metabolic and hormonal alterations in cats with hepatic lipidosis

Hepatic lipidosis in cats is a commonly diagnosed hepatobiliary disease of unknown cause. The purpose of this prospective study was to characterize the blood hormone and lipid status of cats with hepatic lipidosis, and to compare this status to that of cats with other types of liver disease and to control cats. Twenty-three cats with hepatic disease were assigned to 1 of 2 groups on the basis of cytopathologic or histopathologic examination of the liver: group 1, hepatic lipidosis (n = 18); or group 2, cholangiohepatitis (n = 5). Ten healthy young adult cats were used as controls. Food was withheld from control animals for 24 hours before blood collection. Concentrations of plasma glucagon and serum insulin, cortisol, thyroxine, triglycerides, cholesterol, phospholipids, and nonesterified fatty acids (NEFAs) were determined in all cats, in addition to routine hematologic and serum biochemical testing. Cats with hepatic lipidosis had higher serum NEFA concentrations than cats with cholangiohepatitis or control cats (P < .05). Cats with cholangiohepatitis had higher serum cholesterol and phospholipid concentrations than those of cats with lipidosis or control cats (P < .05); their plasma glucagon concentrations were higher than those of control cats (P < .05), but were not different from those of cats with hepatic lipidosis. Serum insulin concentrations were significantly higher in control cats than in diseased cats (P < .05), but neither serum insulin nor the insulin to glucagon ratio was significantly different among the cats with hepatic disease. The high concentration of NEFAs in cats with hepatic lipidosis suggests that at least 1 factor in the pathogenesis of this syndrome may involve the regulation of hormone-sensitive lipase.     

酮病、脂肪肝奶牛胰岛素受体mRNA丰度

选择自然发生的酮病奶牛、脂肪肝奶牛和正常围产期荷斯坦奶牛（对照）各5头，通过手术方法采取其肝脏样品，采用半定量RT—PCR方法检测了这3组奶牛肝胜样品胰岛素受体（InsR）mRNA丰度的变化。结果表明，酮痛奶牛InsRmRNA相对表达量低于正常对照奶牛，而高于脂肪肝奶牛；脂肪肝奶牛InsR mRNA相对表达量低于正常对照奶牛和酮病奶牛（P〈0．05）。可见，酮病奶牛InsR mRNA相对表达量下降，提示此有利于酮病奶牛糖异生和脂肪动员，从而缓解能量负平衡；脂肪肝奶牛InsR mRNA相对表达量降低，提示奶牛胰岛素应答显著减弱，此时奶牛可能发生了胰岛素抵抗。     

Assessment of the metabolic effects of hydrocortisone on llamas before and after feed restriction

OBJECTIVE: To evaluate the effects of administration of hydrocortisone on plasma concentration of insulin and serum concentrations of glucose, triglyceride, and nonesterified fatty acids (NEFAs) in llamas before and after feed restriction. ANIMALS: 9 adult female llamas. PROCEDURE: Feed was withheld from llamas for 8 hours. Blood samples were collected before (0 minutes) and 120, 180, 240, and 300 minutes after IV injection of hydrocortisone sodium succinate (1 mg/kg) for determination of plasma insulin concentration and serum concentrations of glucose, triglyceride, and NEFAs. The llamas were then fed a limited diet (grass hay, 0.25% of body weight daily) for 21 days, after which the experimental procedures were repeated. RESULTS: Compared with llamas that were not feed-restricted, llamas after feed restriction had significantly higher plasma insulin concentration and serum concentrations of triglycerides and NEFAs. Feed-restricted llamas after hydrocortisone injection had a significantly smaller increase in serum glucose concentration, a decrease (rather than an increase) in serum concentration of NEFAs, and no change in blood concentrations of insulin or triglycerides. CONCLUSIONS AND CLINICAL RELEVANCE: Short-acting glucocorticoid hormones did not appear to increase blood lipid concentrations in healthy llamas, regardless of ongoing fat mobilization. Thus, these hormones appear unlikely to be major direct contributors to diseases such as hepatic lipidosis or hyperlipemia. Although administration of hydrocortisone reduced serum concentration of fatty acids in feed-restricted llamas, its use has not been evaluated in sick camelids and cannot be considered therapeutically useful.     

Relationship between fat accumulation in the liver and energy intake, milk fat yield and blood metabolites in dairy cows

In the present study, 42 multiparous Holstein cows were used to investigate the relationship between fat accumulation in the liver and dry matter intake, milk yield and blood metabolites. Based on the percentage of fat in the liver cell at 2 weeks post‐parturition, the cows were classified into three groups. These groups were: (i) less than 10% of fat (normal group, n = 29); (ii) 10–20% of fat (mild group, n = 6); and (iii) more than 20% of fat (moderate group, n = 7). The bodyweight of the moderate group was high (771 kg) before calving. The sufficiency rates of total digestible nutrients (TDN) were remarkably decreased (approximately 65%) in early lactation. The milk fat yield and milk fat composition of the moderate group were higher (P < 0.05) than the other groups at 1 and 2 weeks post‐parturition. It was suggested that non‐esterified fatty acids (NEFA) mobilized from adipose tissues was directly used by the mammary gland for synthesis of milk fat. The percentage of bromsulfalein (BSP) retention of the moderate group was high (21.1%) at 30 min, and it showed that the BSP clearance function was significantly decreased. The concentrations of NEFA, β‐hydroxybutyric acid and glucose were appropriate indicators of energy status; however, aspartate aminotransferase, γ‐glutamyl transpeptidase and total bilirubin were not sensitive indicators of a moderate fatty liver. Thus, high‐yielding cows that calve in an overweight condition are more likely to develop excessive fat accumulation in the liver because of great mobilization from adipose tissues post‐parturition. In cows with a moderately fatty liver, a decrease in TDN sufficiency rates, an increase of milk fat yield and a reduction of liver function were observed in early lactation. The increase of serum NEFA and milk fat composition resulting from mobilization of adipose tissues helped to diagnose moderate fatty liver.     

Effects of hyperinsulinaemia under euglycaemic condition on liver fat metabolism in dairy cows in early and mid-lactation

The objective was to examine the effects of insulin under euglycaemic conditions on liver long chain fatty acids (LCFA) metabolism with special focus on the aetiology of hepatic lipidosis in early lactation. A 4-day hyperinsulinaemic-euglycaemic clamp (clamp) was conducted on four dairy cows starting in weeks 4 and 17 postpartum. Insulin was infused continuously (1 microg/kg BW per h) and a 50% glucose solution was infused to maintain euglycaemia. Liver biopsies were taken 6 days before, the last day of, and 5 days after the clamp, and blood samples were taken in the same period. In the liver tissue, the relative triglyceride content decreased (P < 0.01) and the glycogen content increased (P < 0.0001) in response to the clamp. Hepatic in vitro palmitate oxidation capacity was lowest during the clamp period and could be explained by a significant decrease in incomplete oxidation (ketogenesis) (P < 0.04) and a tendency to a decreased complete oxidation of palmitate (P < 0.10). Plasma non-esterified fatty acids concentration was decreased during the clamp in early lactation (P < 0.05) but there was no effect on the mid-lactation clamp. The present study shows that increased insulin under euglycaemic conditions seems to depress hepatic LCFA oxidation capacity. However, in terms of preventing hepatic lipidosis, the anti-lipolytic effect of insulin on adipose tissue, which results in decreased mobilization of and hence hepatic load with LCFA, appears more important.     

Lipid Composition of Hepatic and Adipose Tissues From Normal Cats and From Cats With Idiopathic Hepatic Lipidosis

The purpose of this study was to characterize the lipid classes in hepatic and adipose tissues from cats with idiopathic hepatic lipidosis (IHL). Concentrations of triglyceride, phospholipid phosphorus, and free and total cholesterol were determined in lipid extracts of liver homogenates from 5 cats with IHL and 5 healthy control cats. Total fatty acid composition of liver and adipose tissue was also compared. Triglyceride accounted for 34% of liver by weight in cats with IHL (338 ± 38 mg/g wet liver) versus 1% in control cats {9.9 ±1.0 mg/g wet liver, P < .001). The mass of cholesterol ester was significantly higher in triglyceride-free (TG-free) liver from cats with IHL (741 ± 340 μg/g TG-free wet liver) compared to healthy cats (31 ± 11 μg/g TG-free wet liver, P < .05). Total fatty acid composition of hepatic tissue in the 2 groups differed; pa Imitate was higher (19.5 ± 1.1% of total fatty acids in cats with IHL versus 9.2 ± 2.7% in controls, P < .05), stearate was lower (8.5 ± 0.8% versus 16.8 ± 1.1%, P < .05), oleate was higher (41.2 ± 1.6% versus 31.1 ± 1.8%, P < .05), and arachidonate was lower (1.2 ± 0.2% versus 6.0 ± 0.9%, P < .05). The total fatty acid composition of adipose tissue also differed between the 2 groups; palmitate was higher (25.2 ± 1.2% in cats with IHL versus 21.3 ± 0.6% in controls, P < .05), total monounsaturated fatty acids were higher (48.4 ± 1.0% versus 45.0 ± 0.8%, P < .05), linoleate was lower (13.3 ± 1.6% versus 17.5 ± 0.9%, P < .05), total (n-6) fatty acids were lower (13.8 ± 1.38% versus 18.4 ± 0.83%, P < .05), linolenate was lower (0.2 ± 0.04% versus 0.7 ± 0.06%, P < .05), and total (n-3) fatty acids were lower (0.3 ± 0.02% versus 1.3 ± 0.32%, P < .05). The fatty acid composition of both liver and adipose tissue was similar for stearate, oleate, linoleate, and linolenate in cats with IHL. These results support the hypothesis that the origin of hepatic triglyceride in cats with IHL is the mobilization of fatty acids from adipose tissue.     

丙二醇对围产期奶牛能量平衡及代谢产物的影响

为了研究丙二醇对围产期奶牛能量平衡、血液指标和肝脏甘油三酯与糖原含量的影响。选用24头体质量(683.1±14.9)kg、胎次(2.5±0.2)、上一泌乳期305d产奶量(7 339±18)kg和预产期(24.5±0.2)d的经产奶牛,随机分为4组,从分娩前19d开始分别在基础日粮中添加丙二醇0、150、300和450mL.d-1。结果表明:与对照组相比,添加丙二醇300和450mL.d-1,显著提高了奶牛分娩后7、21和35d体况评分,缓减了奶牛体质量下降程度,改善了奶牛分娩前14d和分娩后7、21和35d奶牛能量平衡(P<0.05)。300和450mL.d-1组奶牛分娩前14d和分娩后7、21和35d血糖和胰岛素浓度显著高于对照组(P<0.05)。300和450mL.d-1组奶牛分娩后7、21和35d血浆游离脂肪酸、β-羟丁酸和甘油三酯浓度显著低于对照组(P<0.05)。300和450mL.d-1组奶牛分娩后7、21和35d肝脏甘油三酯含量显著低于对照组(P<0.05),但分娩后7、21和35d肝脏糖原含量显著高于对照组(P<0.05)。结果提示在日粮中添加丙二醇能够减少肝脏脂肪沉积,加强葡萄糖异生作用,改善奶牛能量平衡,适宜添加量为300mL.d-1。     

Relevance of apolipoproteins in the development of fatty liver and fatty liver-related peripartum diseases in dairy cows

Most metabolic diseases in dairy cows occur during the peripartum period and are suggested to be derived from fatty liver initially developed during the nonlactating stage. Fatty liver is induced by hepatic uptake of nonesterified fatty acids that are released in excess by adipose tissues attributable to negative energy balance. The fatty accumulation leads to impairment of lipoprotein metabolism in the liver, and the impairment in turn influences other metabolic pathways in extrahepatic tissues such as the steroid hormone production by the corpus luteum. Detailed understanding of the impaired lipoprotein metabolism is crucial for elucidation of the mechanistic bases of the development of fatty liver and fatty liver-related peripartum diseases. This review summarizes results on evaluation of lipoprotein lipid and protein concentrations and enzyme activity in cows with fatty liver and those with ketosis, left displacement of the abomasum, milk fever, downer syndrome and retained placenta. Obtained data strongly suggest that decreases in serum concentrations of apolipoprotein B-100, apolipoprotein A-I and apolipoprotein C-III, a reduction in activity of lecithin:cholesterol acyltransferase and induction of haptoglobin and serum amyloid A are intimately related to the development of fatty liver and fatty liver-related diseases. Moreover, determination of the apolipoprotein concentrations and enzyme activity during the peripartum period is useful for early diagnoses of these diseases.     

泌乳奶牛脂肪肝早期诊断的研究

为了寻找泌乳奶牛脂肪肝早期诊断方法,本研究从某千头奶牛场随机选取了30头乳酮阳性的奶牛,其中临床酮病牛10头,亚临床酮病牛20头,测定其肝脂含量以及血中代谢指标和肝功指标。试验结果表明,脂肪肝的奶牛存在能量负平衡现象,机体呈现高游离脂肪酸血症、高酮血症,肝脂浸润越重,能量代谢障碍越严重;乳酮阳性出现时间的早晚与脂肪肝的严重程度密切相关,乳酮阳性产后出现的越早,乳酮阳性越明显,肝脂浸润越重;随肝脂浸润程度的加重,肝功多个指标会出现异常,重度的脂肪肝会引发肝功能不全。本试验证明,酮粉法可以作为早期诊断奶牛脂肪肝的初选方法,肝功指标异常可作为诊断脂肪肝的辅助方法,两者结合可作为奶牛脂肪肝的实用、有效和准确的早期诊断方法,准确率可达80%。     

家禽脂肪酸代谢及其在禽蛋中的沉积和营养调控

在肝脏中载脂蛋白作用下,内源合成或外源获取的脂肪酸以甘油三酯的形式同胆固醇及其他脂类组装形成极低密度脂蛋白(VLDL)。VLDL经血液循环到达卵巢,穿过卵母细胞外层屏障后,经卵母细胞受体介导的内吞作用进入卵母细胞发生沉积。而机体的营养状况或饲粮中营养成分的改变可通过影响脂肪酸的从头合成或VLDL结构直接或间接影响禽蛋中脂肪酸的最终沉积。本文阐述了家禽体内脂肪酸的来源、转运与沉积过程,并探讨了脂肪酸代谢及其在禽蛋中沉积的营养调控。     

Plasma lipids, lipoproteins and post-heparin lipases in ponies with hyperlipaemia.

The metabolic origins of equine hyperlipaemia were investigated by analysing the concentration and composition of plasma lipoproteins in 18 ponies with the condition. The mean concentrations of cholesterol, triglyceride and very low density lipoproteins (VLDL) were increased by 4-, 52- and 19-fold, respectively, compared with a control group of 18 healthy ponies. These increases were due to the appearance of a buoyant VLDL fraction (VLDL1) not present in healthy ponies. The mean diameter of VLDL1 particles was 44% greater than control VLDL, and the particles were enriched in triglyceride and free cholesterol and depleted of cholesteryl esters, phospholipid and protein. The apolipoprotein (apo) B-100 content of VLDL1 was reduced and the ratio of apoB-100 to apoB-48 particles was 1:1, compared with 2:1 in control VLDL. The VLDL1 was also enriched in apoE, but had normal complements of apoC-II and apoC-III. The conventional VLDL (called VLDL2), LDL and HDL fractions were moderately enriched with triglyceride, and HDL contained increased amounts of apoE, apoC-II and apoC-III. The activities of lipoprotein lipase and hepatic lipase, the enzymes responsible for the catabolism of VLDL and their remnants, were increased by 2- and 3-fold, respectively, in response to the increased concentrations of their substrates. The composition of VLDL1 suggested that the liver was maximising the secretion of triglyceride by producing larger number of VLDL particles that accommodated a greater mass of triglyceride by having apoB-48 rather than apoB-100 as their structural protein. Plasma free fatty acid (FFA) concentrations were elevated in 17 of the 18 ponies, suggesting that increased FFA flux might be the stimulus for hepatic triglyceride synthesis and VLDL secretion. We conclude that overproduction, rather than defective catabolism, of VLDL was the cause of the hyperlipidaemia and that lipid lowering agents which reduce VLDL synthesis, by decreasing adipose lipolysis and FFA flux, are candidates for the management of hyperlipaemia.