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1.
This paper describes the pharmacokinetic profile of procaine penicillin G after intraperitoneal (IP) administration in eight lactating dairy cows. Procaine pencillin G (PPG, 21 000 IU/kg) was deposited into the abdominal cavity of each cow following an incision in the right paralumbar fossa. Blood and milk samples were taken over the following 10 days, at which point the cows were euthanized. Plasma, milk, muscle, liver, and kidney penicillin concentrations were determined by HPLC, with a limit of quantification of 5 ng/mL for plasma and milk and 40 ng/g for tissue samples. A noncompartmental method was used to analyze plasma kinetics. The mean pharmacokinetic parameters (±SD) were: C max, 5.5 ± 2.6 μg/mL; T max, 0.75 ± 0.27 h; AUC 0-∞, 10.8 ± 4.9 μg·h/mL; MRT , 2.2 ± 0.9 h. All milk from treated cows contained detectable penicillin residues for a minimum of three milkings (31 h) and maximum of five milkings (52 h) after administration. Concentrations of penicillin in all muscle, liver, and kidney samples taken 10 days postadministration were below the limit of quantification. Necropsy examinations revealed foci of hemorrhage on the rumenal omentum of most cows but peritonitis was not observed. Systemic inflammation as determined by change in leukogram or plasma fibrinogen was noted in one cow. The results of this study demonstrate that IP PPG is absorbed and eliminated rapidly in lactating dairy cows.  相似文献   

2.
The pharmacokinetics and mammary excretion of eprinomectin were determined in cattle following topical administration at a dose rate of 0.5 mg kg(-1). The kinetics of plasma and milk concentrations were analysed using a one-compartment model. The maximum plasma concentration of 43.76 ng ml(-1)occurred 2.02 days post administration, and the mean residence time was 4.16 days. Eprinomection was detected in the milk at the first sampling time and thereafter for at least 15 days. Comparison of the milk and plasma data demonstrated the parallel disposition of the drug in the milk and plasma with a milk / plasma concentration ratio of 0. 102+/-0.048. The amount of drug recovered in the milk during this period was 0.109% +/- 0.038 of the total administered dose. This very low extent of mammary excretion resulted in low concentrations of eprinomectin in milk. This supports the permitted use in lactating cattle, as the maximum level of residue in milk did not exceed the maximum acceptable limit of 30 ng ml(-1).  相似文献   

3.
The plasma and milk kinetics of ivermectin (IVM) and moxidectin (MXD) was evaluated in lactating camels treated subcutaneously (0.2 mg kg(-1)) with commercially available formulations for cattle. Blood and milk samples were taken concurrently at predetermined times from 12 h up to 60 days post-administration. No differences were observed between plasma and milk kinetics of IVM, while substantial differences were noted between plasma and milk profiles of MXD in that both the maximal concentration (Cmax) and the area under concentrations curves (AUC) were three to four-fold higher for milk than for plasma. The time (Tmax) to reach Cmax was significantly faster for MXD (1.0 day) than that for IVM (12.33 days). The Cmax and the AUC were significantly higher for MXD (Cmax = 8.33 ng ml(-1); AUC = 70.63 ng day ml(-1)) than for IVM (Cmax = 1.79 ng ml(-1); AUC = 30.12 ng day ml(-1)) respectively. Drug appearance in milk was also more rapid for MXD (Tmax = 3.66 days) compared to IVM (Tmax = 17.33 days). The extent of drug exchange from blood to milk, expressed by the AUCmilk/AUCplasma ratio, was more than three-fold greater for MXD (4.10) compared to that of IVM (1.26), which is consistent with the more lipophilic characteristic of MXD. However, the mean residence time (MRT) was similar in both plasma and milk for each drug.  相似文献   

4.
OBJECTIVE: To determine clinical examination findings, clinicopathologic abnormalities, and outcome of treatment in dairy cattle with abomasal impaction. DESIGN: Retrospective study. ANIMALS: 80 lactating Holstein-Friesian cows > or = 2 years old. PROCEDURE: Medical records of cattle with abomasal impaction admitted between 1980 and 2003 were retrieved, and data were extracted. RESULTS: All cows were reported to have decreased food intake; concurrent diseases were identified in 54 (68%). Seventeen cows did not have detectable ruminal motility, but physical examination findings were nonspecific and variable. In general, cattle had mild hypocalcemia, hyperbilirubinemia, and hyperglycemia, but serum potassium and chloride concentrations were typically within reference limits. Fifty-five (69%) cattle had impaction of the pyloric antrum alone, and 25 (31%) had impaction of the abomasal body and pyloric antrum. Right flank laparotomy and abomasal massage were performed in 73 cattle. After surgery, 54 (74%) cattle received 3 to 4 L of mineral oil, PO, daily for 1 to 5 days. Short-term (ie, discharged from the hospital) survival rate was significantly higher for cows with impaction of the pyloric antrum alone (42/45 [93%]) than for cows with impaction of the body and antrum (12/24 [50%]). CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that physical examination findings and results of serum biochemical analyses do not facilitate the diagnosis of abomasal impaction in lactating Holstein cows and that exploratory right flank laparotomy is necessary to make the diagnosis. Abomasal impaction should be considered as a differential diagnosis for inappetence and poor milk production in lactating dairy cows.  相似文献   

5.
Objectives were to evaluate effects of feeding a calcium salt rich in linoleic and trans -octadecenoic acids (LTFA) on synthesis of prostaglandin F2α based on its metabolite (PGFM), uterine involution and pregnancy rates in lactating dairy cows. Five hundred and eleven Holstein cows were blocked according to parity, body condition score and milk yield in the previous lactation. Primiparous and multiparous cows were randomly assigned to one of the two treatments consisting of calcium salt (2% diet dry matter) of either palm oil (PO) or LTFA from 25 days prepartum to 80 days of lactation. Cows were time-inseminated at 70 ± 3 days postpartum. Feeding LTFA tended (p = 0.08) to decrease the incidence of puerperal metritis (15.1% vs 8.8%). Primiparous cows supplemented with LTFA showed larger increase in plasma PGFM concentration at day 1 postpartum (17018 vs 6897 p m ). Pregnancy rate after first insemination tended (p = 0.07) to be greater at 27 days after insemination (37.9% vs 28.6%), and was greater (p = 0.05) at 41 days after insemination (35.5% vs 25.8%) for cows fed LTFA compared with PO. These results indicate that unsaturated fatty acids fed in a rumen inert form have the potential to modulate reproductive events and improve pregnancy rates in lactating dairy cows.  相似文献   

6.
The pharmacokinetics and mammary excretion of moxidectin and eprinomectin were determined in water buffaloes (Bubalus bubalis) following topical administration of 0.5mgkg(-1). Following administration of moxidectin, plasma and milk concentrations of moxidectin increased to reach maximal concentrations (C(max)) of 5.46+/-3.50 and 23.76+/-16.63ngml(-1) at T(max) of 1.20+/-0.33 and 1.87+/-0.77 days in plasma and milk, respectively. The mean residence time (MRT) were similar for plasma and milk (5.27+/-0.45 and 5.87+/-0.80 days, respectively). The AUC value was 5-fold higher in milk (109.68+/-65.01ngdayml(-1)) than in plasma (23.66+/-12.26ngdayml(-1)). The ratio of AUC milk/plasma for moxidectin was 5.04+/-2.13. The moxidectin systemic availability (expressed as plasma AUC values) obtained in buffaloes was in the same range than those reported in cattle. The faster absorption and elimination processes of moxidectin were probably due to a lower storage in fat associated with the fact that animals were in lactation. Nevertheless, due to its high excretion in milk and its high detected maximum concentration in milk which is equivalent or higher to the Maximal Residue Level value (MRL) (40ngml(-1)), its use should be prohibited in lactating buffaloes. Concerning eprinomectin, the C(max) were of 2.74+/-0.89 and 3.40+/-1.68ngml(-1) at T(max) of 1.44+/-0.20 and 1.33+/-0.0.41 days in plasma and milk, respectively. The MRT and the AUC were similar for plasma (3.17+/-0.41 days and 11.43+/-4.01ngdayml(-1)) and milk (2.70+/-0.44 days and 8.49+/-3.33ngdayml(-1)). The ratio of AUC milk/plasma for eprinomectin was 0.76+/-0.16. The AUC value is 20 times lower than that reported in dairy cattle. The very low extent of mammary excretion and the milk levels reported lower than the MRL (20ngml(-1)) supports the permitted use of eprinomectin in lactating water buffaloes.  相似文献   

7.
Milk is considered a perfect natural food for humans and animals. However, aflatoxin B1 (AFB1) contaminating the feeds fed to lactating dairy cows can introduce aflatoxin M1 (AFM1), the main toxic metabolite of aflatoxins into the milk, consequently posing a risk to human health. As a result of AFM1 monitoring in raw milk worldwide, it is evident that high AFM1 concentrations exist in raw milk in many countries. Thus, the incidence of AFM1 in milk from dairy cows should not be underestimated. To further optimize the intervention strategies, it is necessary to better understand the metabolism of AFB1 and its biotransformation into AFM1 and the specific secretion pathways in lactating dairy cows. The metabolism of AFB1 and its biotransformation into AFM1 in lactating dairy cows are drawn in this review. Furthermore, recent data provide evidence that in the mammary tissue of lactating dairy cows, aflatoxins significantly increase the activity of a protein, ATP-binding cassette super-family G member 2 (ABCG2), an efflux transporter known to facilitate the excretion of various xenobiotics and veterinary drugs into milk. Further research should focus on identifying and understanding the factors that affect the expression of ABCG2 in the mammary gland of cows.  相似文献   

8.
The purpose of this study was to elucidate the effects of medium-chain fatty acids (MCFAs) on plasma ghrelin concentration in lactating dairy cows. Five early-lactating Holstein cows were randomly assigned to 2 dietary treatments in a crossover design with 2-wk periods. Treatments consisted of diets supplemented or not (control) with calcium salts of MCFAs (MCFA-Ca; 1.5% dry matter). Plasma hormone and metabolite concentrations in blood samples taken from the jugular vein were measured on the morning of feeding on day 14 of each period. Dry matter intake, milk protein, and lactose content of cows fed the MCFA-Ca diet were decreased compared with controls, but with no change in milk yield. Plasma ghrelin concentrations were higher in cows fed the MCFA-Ca diet; however, no significant effect was found on glucagon-like peptide-1 concentrations in plasma. Plasma insulin concentrations decreased, but plasma glucagon concentrations remained unchanged in cows fed the MCFA-Ca diet. The concentrations of nonesterified FAs, total cholesterol, and β-hydroxybutyrate in plasma increased in these cows. In conclusion, dietary MCFAs increase the plasma ghrelin concentrations in lactating dairy cows.  相似文献   

9.
Three experiments were performed to examine the effects of high ambient temperature and feed restrictions on urinary 3‐methylhistidine (3MH) excretion and plasma 3MH concentrations as a marker of myofibrillar proteolysis in lactating Holstein cows. In a crossover design, four cows were maintained during two 14‐day treatment periods with ad libitum feed intake under constant moderate (18°C) or high (28°C) ambient temperature (Experiment 1), with ad libitum or 70% ad libitum feed intake under constant moderate temperature (Experiment 2), and with 70% ad libitum feed intake under constant moderate or high ambient temperature (Experiment 3). The total digestible nutrients intake was decreased (P < 0.01) under high ambient temperature (Experiment 1) or feed restriction (Experiment 2). Across experiments, urinary 3MH excretion during days 10–14 of each treatment period was not different among treatments. However, the plasma 3MH concentrations at day 14 of treatment were increased significantly under high ambient temperature with subsequent reduced feeding (P < 0.01) or moderate temperature with feed restriction (P < 0.05), and were increased slightly (P = 0.11) under high ambient temperature alone. These results show that the plasma marker of myofibrillar proteolysis in lactating dairy cows was increased at day 14 of treatments of high ambient temperature with subsequent reduced feeding, moderate temperature with feed restriction, or high ambient temperature alone.  相似文献   

10.
Endectocide compounds are extensively used for broad-spectrum parasite control and their topical administration to cattle is widespread in clinical practice. Pour-on formulations of moxidectin, ivermectin, eprinomectin and doramectin (DRM) are marketed internationally for use in cattle. However, variability in antiparasitic efficacy and pharmacokinetic profiles has been observed. Although the tissue distribution pattern for different endectocide molecules given subcutaneously to cattle has been described, only limited information on drug concentration profiles in tissues of parasite location after topical treatment is available. Understanding the plasma and target tissue kinetics for topically-administered endectocide compounds is relevant to optimise their therapeutic potential. The current work was designed to measure the plasma and gastrointestinal (GI) concentration profiles of DRM following its pour-on administration to calves. The influence of natural licking behaviour of cattle on DRM concentration in mucosal tissue and luminal content of different GI sections was evaluated. The trial was conducted in two experimental phases. In Phase I, the DRM plasma kinetics was comparatively characterised in free-licking and in 2-day licking-restricted (non-licking) calves. The pattern of distribution of topical DRM to mucosal and luminal contents from abomasum, duodenum, ileum, caecum and spiral colon was assessed in free-licking and non-licking calves restricted over 10 days post-administration (Phase II). The prevention of licking caused marked changes on the plasma and GI kinetics of DRM administered pour-on. In 2-day licking restricted calves, DRM systemic availability was significantly lower (29%) than in free licking animals during the first 9 days post-treatment. Following a 10-day long licking restriction period, DRM concentrations profiles in both mucosal tissue and luminal contents of the GI tract were markedly higher in animals allowed to lick freely. This enhancement in drug concentrations in free-licking compared to non-licking calves, was particularly pronounced in the abomasal (38-fold higher) and duodenal (six-fold higher) luminal content. As shown earlier for ivermectin, licking behaviour may facilitate the oral ingestion of topically-administered DRM in cattle. This would be consistent with the marked lower drug concentration profiles measured in the bloodstream and GI tract of the animals prevented from licking. The work reported here provides relevant information on the pattern of DRM distribution to the GI tract after pour-on treatment, and contributes to understand the variability observed in the antiparasitic persistence of topically-administered endectocides in cattle. The implications of natural licking in topical treatments are required to be seriously assessed to achieve optimal parasite control and to design parasitological and pharmacological studies within the drug approval process.  相似文献   

11.
Serum total bile acid concentrations were determined for various types and ages of cattle. There was extreme variability among all the cattle, but the variance was twice as large (0.50 vs 0.22 in logarithmic scale) for beef cattle than for dairy cattle. There was no significant difference in serum total bile acid concentrations between beef cattle and dairy cattle in midlactation. Values for calves < 6 weeks old and for 6-month-old heifers were significantly (P = < 0.05) lower than values for lactating dairy cows. The 5th to 95th percentile range of values (mumol/L) for beef cattle was 9 to 126; for lactating dairy cattle, 15 to 88; and for 6-month-old dairy heifers, 11 to 64.  相似文献   

12.
苹果发酵物对奶牛产奶性能和疾病的影响   总被引：4，自引：0，他引：4  
将有益微生物接种到以苹果渣为主的培养基中进行有氧和无氧培养,制成颗粒状苹果培养物。对高产奶牛进行饲喂试验表明,用苹果发酵物代替等量的甜菜或苹果发酵物和甜菜粕同时使用,奶牛分别增产鲜奶1.89和1.90千克/头·日,同时乳脂、乳蛋白质、乳固体物都有上升趋势,奶牛发病率明显下降。苹果发酵物是一种新型反刍动物饲料。  相似文献   

13.
Closantel (CLS) is currently used in programs for the strategic control of gastrointestinal nematodes. CLS is extralabel used in different dairy goat production systems. From available data in dairy cows, it can be concluded that residues of CLS persist in milk. The current work evaluated the concentration profiles of CLS in plasma and milk from lactating orally treated dairy goats to assess the residues pattern in dairy products such as cheese and ricotta. Six (6) female Saanen dairy goats were treated orally with CLS administered at 10 mg/kg. Blood and milk samples were collected between 0 and 36 days post‐treatment. The whole milk production was collected at 1, 4, 7, and 10 days post‐treatment to produce soft cheese and ricotta. CLS concentrations in plasma, milk, cheese, whey, and ricotta were determined by HPLC. The concentrations of CLS measured in plasma were higher than those measured in milk at all sampling times. However, the calculated withdrawal time for CLS in milk was between 39 and 43 days postadministration to dairy goats. CLS residual concentrations in cheese (between 0.93 and 1.8 μg/g) were higher than those measured in the milk used for its production. CLS concentrations in ricotta were sixfold higher than those in the milk and 20‐fold higher than those in the whey used for its production. The persistent and high residual concentrations of CLS in the milk and in the cheese and ricotta should be seriously considered before issuing any recommendation on the extralabel use of CLS in dairy goat farms.  相似文献   

14.
OBJECTIVE: To determine the elimination kinetics of ceftiofur hydrochloride in milk after intramammary administration in lactating dairy cows. DESIGN: Prospective study. ANIMALS: 5 lactating dairy cows. PROCEDURE: After collection of baseline milk samples, 300 mg (6 mL) of ceftiofur was infused into the left front and right rear mammary gland quarters of each cow. Approximately 12 hours later, an additional 300 mg of ceftiofur was administered into the same mammary gland quarters after milking. Milk samples were collected from each mammary gland quarter every 12 hours for 10 days. Concentrations of ceftiofur and its metabolites in each milk sample were determined to assess the rate of ceftiofur elimination. RESULTS: Although there were considerable variations among mammary gland quarters and individual cows, ceftiofur concentrations in milk from all treated mammary gland quarters were less than the tolerance (0.1 microg/mL) set by the FDA by 168 hours (7 days) after the last intramammary administration of ceftiofur. No drug concentrations were detected in milk samples beyond this period. Ceftiofur was not detected in any milk samples from nontreated mammary gland quarters throughout the study. CONCLUSIONS AND CLINICAL RELEVANCE: Ceftiofur administered by the intramammary route as an extra-label treatment for mastitis in dairy cows reaches concentrations in milk greater than the tolerance set by the FDA. Results indicated that milk from treated mammary gland quarters should be discarded for a minimum of 7 days after intramammary administration of ceftiofur. Elimination of ceftiofur may be correlated with milk production, and cows producing smaller volumes of milk may have prolonged withdrawal times.  相似文献   

15.
OBJECTIVE: To determine the effect of continuous IV administration of 50% dextrose solution on phosphorus homeostasis in lactating dairy cows. DESIGN: Clinical trial. ANIMALS: 4 multiparous Jersey cows. PROCEDURES: Cows were administered 50% dextrose solution IV (0.3 g/kg/h [0.14 g/lb/h]) for 5 days. Plasma concentrations of glucose, immune-reactive insulin (IRI), and phosphorus were determined before, during, and for 72 hours after dextrose infusion. Phosphorus intake and losses of phosphorus in urine, feces, and milk were determined. Each cow received a sham treatment that included instrumentation and sampling but not administration of dextrose. RESULTS: Plasma glucose, IRI, and phosphorus concentrations were stable during sham treatment. Plasma phosphorus concentration decreased rapidly after onset of dextrose infusion, reaching a nadir in 24 hours and remaining less than baseline value for 36 hours. Plasma phosphorus concentration increased after dextrose infusion was stopped, peaking in 6 hours. Urinary phosphorus excretion did not change during dextrose infusion, but phosphorus intake decreased because of reduced feed intake, followed by decreased fecal phosphorus loss and milk yield. Rapid changes in plasma phosphorus concentration at the start and end of dextrose infusion were temporally associated with changes in plasma glucose and IRI concentrations and most likely caused by compartmental shifts of phosphorus. CONCLUSIONS AND CLINICAL RELEVANCE: Hypophosphatemia developed in response to hyperglycemia or hyperinsulinemia in dairy cows administered dextrose via continuous IV infusion. Veterinarians should monitor plasma phosphorus concentration when administering dextrose in this manner, particularly in cows with decreased appetite or preexisting hypophosphatemia.  相似文献   

16.
Abstract

Fifteen multiparous dairy cows were used in a five replicated 3×3 Latin square design to study the effects of ratio of rumendegradable-protein (RDP) and rumen-undegradable-protein (RUP) on nitrogen (N) conversion in Chinese Holstein dairy cows. Three diets were formulated isonitrogenously with varying ratio of RDP/RUP. High ratio of RDP/RUP resulted in high urinary N excretion and total N excretion, but no significant dietary effects were observed on milk yield, milk composition, and nitrogen excretion in faeces. Different protein degradability changed the partitioning of the N excretion between urine and faeces. Results indicated that reduction in ratio of RDP/RUP could improve the efficiency of N utilization in lactating dairy cows by reduced N excretion in urine and faeces without impairing milk production.  相似文献   

17.
Concentrations of plasma glucose, immunoreactive insulin (IRI) and free fatty acid (FFA) and activities of enzymes related to energy metabolism and lactate dehydrogenase (LDH) isoenzyme pattern in plasma and leukocytes were investigated in lactating Holstein cows (dairy cattle) and fattening Japanese Black Wagyu x Holstein steers (beef cattle). IRI concentrations and LDH and malate dehydrogenase (MDH) activities in the plasma of beef cattle were significantly higher than those in dairy cattle. The cytosolic ratio of MDH/LDH activity in the leukocytes of beef cattle was significantly higher than that of dairy cattle. These findings might be associated with the different energy metabolism between dairy and beef cattle.  相似文献   

18.
The time of parasite exposure to active drug concentrations determines the persistence of the antiparasitic activity of endectocide compounds. This study evaluates the disposition kinetics of moxidectin (MXD) in plasma and in different target tissues following its subcutaneous (s.c.) administration to cattle. Eighteen male, 10-month old Holstein calves weighing 120-140 kg were subcutaneously injected in the shoulder area with a commercially available formulation of MXD (Cydectin 1%, American Cyanamid, Wayne, NJ, USA) at 200 micrograms/kg. Two treated calves were killed at each of the following times post-treatment: 1, 4, 8, 18, 28, 38, 48, 58 and 68 days. Abomasal and small intestine mucosal tissue and fluids, bile, faeces, lung, skin and plasma samples were collected, extracted, derivatized and analysed to determine MXD concentrations by high performance liquid chromatography (HPLC) with fluorescence detection. MXD was extensively distributed to all tissues and fluids analysed, being detected (concentrations > 0.1 ng/g; ng/mL) between 1 and 58 days post-treatment. MXD peak concentrations were attained during the first sampling day. MXD maximum concentration (Cmax) values ranged from 52.9 (intestinal mucosa) up to 149 ng/g (faeces). The mean residence time (MRT) in the different tissues and fluids ranged from 6.8 (abomasal mucosa) up to 11.3 (bile) days. MXD concentrations in abomasal and intestinal mucosal tissue were higher than those detected in plasma; however, there was a high correlation between MXD concentrations observed in plasma and those detected in both gastrointestinal mucosal tissues. MXD concentrations were markedly greater in the mucosa than in its respective digestive fluid (P < 0.01). MXD concentrations in skin were higher than those found in plasma (P < 0.01). Drug concentrations recovered in the dermis were greater than those detected in the hypodermal tissue (P < 0.05). Large concentrations of MXD were excreted in bile and faeces. These findings may contribute to an understanding of the relationship between the kinetic behaviour and the persistence of the antiparasite activity of MXD against different ecto-endoparasites in cattle.  相似文献   

19.
Increased embryonic losses may be associated with inadequate progesterone (P4) concentrations in high‐producing lactating dairy cattle. The objectives of the present studies were to determine if chronic administration of a gonadotropin‐releasing hormone (GnRH) agonist, Deslorelin, would increase circulating P4 concentrations and subsequently increase pregnancy rates in dairy cattle. Administration of Deslorelin for 12 days increased (p < .05) luteal volume and circulating P4 concentrations in primiparous lactating dairy cows, but increased only luteal volumes in multiparous cows. Treatment with Deslorelin increased Day 45 pregnancy rates in cows as compared to untreated controls. Chronic treatment with Deslorelin in dairy cattle; (a) increased luteal volume of the primary CL, (b) induced accessory CL, (c) increased circulating P4 concentration in primiparous cows only, (d) did not lengthen the estrous cycle upon removal of treatment, and (e) increased pregnancy rates. Although luteal volume was increased in multiparous cows and circulating P4 concentrations were not with Deslorelin treatment, there was an apparent effect on pregnancy rates. This hormonal strategy may represent a suitable model to address local effects of P4 and GnRH/luteinizing hormone on uterine environment and subsequent embryonic survival.  相似文献   

20.
Release of growth hormone (GH) is known to be regulated mainly by GH-releasing hormone (GHRH) and somatostatin (SRIF) secreted from the hypothalamus. A novel peripheral release-regulating hormone, ghrelin, was recently identified. In this study, differences of the GH secretory response to ghrelin and GHRH in growing and lactating dairy cattle were investigated and an alteration of plasma ghrelin levels was observed. The same amounts of ghrelin and GHRH (0.3 nmol/kg) were intravenously injected to suckling and weanling calves, early and mid-lactating cows and non-lactating cows. Plasma ghrelin levels were also determined in dairy cattle in various physiological conditions. The peak values of ghrelin-induced GH secretion were increased in early lactating cows compared to those in non-lactating cows. The relative responsiveness of GH secretion to ghrelin was also increased compared with that to GHRH in early lactating cows. GH secretory responses to GHRH were blunted in mature cows with and without lactation. Conversely, GHRH-induced GH secretory response was greater than that to ghrelin in calves, and also greater in calves than in mature cows. Plasma ghrelin concentrations were elevated in early lactating cows compared to those in non-lactating cows. Plasma GH concentrations were higher in suckling calves and early lactating cows compared with those in non-lactating cows. These results suggest that GHRH is an effective inducer of GH release in growing calves, and that the relative importance of ghrelin in contributing to the rise in plasma GH increases in early lactating cows.  相似文献   

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