代谢激素及营养对牛卵泡发育的影响

营养与牛繁殖的关系十分复杂，它影响到繁殖过程的诸多方面。该文仅局限于讨论其对卵泡发育的影响，即代谢激素(GH，IGF—1，INS)及短期增加日粮摄入对青年母牛卵泡发育的影响。并讨论营养与代谢激素，卵泡发育的相互关系及生产中的一些实际问题，如高产奶牛繁殖率下降，超排反应不稳定等问题。     

牛血浆中Leptin营养调控的进展

Leptin对哺乳动物整个生命过程中的能量代谢调节起着关键作用.据认为,在奶牛生长阶段对生殖系统和乳腺发育起着一定营养调节作用.然而,通过营养调控增加血浆Leptin的发育阶段没有确定.还不清楚奶牛血浆中Leptin浓度是否影响初情期的开始.设计两个试验研究这些问题.试验中分别饲喂新生犊牛不同水平的代乳品,使犊牛的平均日增重分别达到平均570 g/d或1210 g/d.每周都采取血样直到犊牛体重达到105kg屠宰时为止.低日增重组的Leptin和肥胖素含量一直保持不变,而高日增重组的Leptin和肥胖素含量在试验的第3周开始增加.在第2个试验当中3～5月龄的后备牛饲喂加入棕榈酸钙盐或共轭亚油酸(CLA)的TMR,保证后备牛的平均日增重水平达到1 kg/d.一直采取血样直到第3个初情期黄体出现为止.脂肪来源对与生长有关的参数、体组成、初情期、血浆Leptin含量没有影响.因此,从试验开始直到屠宰,按日龄因素对血浆Leptin含量重新分析.在奶牛1岁前,血浆Leptin浓度一直几乎保持在2.3 ng/ml这一水平,此后血浆Leptin含量明显增加.在奶牛1岁左右血浆Leptin含量几乎保持不变的阶段或者以后血浆Lep-tin含量急剧增加阶段,初情期开始的频率几乎与之相等.可以得出这样的结论,血浆Leptin含量在犊牛出生后的早期阶段受营养因素的调控,Leptin含量的急剧增加并不是奶牛初情期开始所必需的.     

Effects of leptin on hypoxia-induced apoptosis in cultured alveolar typeⅡ cells of fetal rat and its mechanism

AIM: To investigate the effects of leptin (LEP) on the alveolar type Ⅱ cells(AECⅡ) apoptosis induced by Na₂S₂O₄ and explore the molecular mechanisms. METHODS: Primary AECⅡ culture was prepared according to a specific immunosorption procedure with slight modification and the cells were identified by transmission electron microscope and immunocytochemistry. AECⅡ damage was induced by 5 mmol/L Na₂S₂O₄. LEP group cells were treated with LEP at concentrations from 100 μg/L to 1 600 μg/L. The cell survival rate was evaluated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays. Cell cycle and apoptosis were analyzed by flow cytometry and the level of caspase-3 was measured by Western blotting. RESULTS: Highly purified AECⅡ, obtained by the method of modified immunosorption, were identified with the positive expression of SP-A and intracellular lamellarbodies were found under electron micrography. The cells, exposed to 5 mmol/L Na₂S₂O₄, showed characteristic changes of apoptosis and activation of caspase 3. These damages were relieved by the treatment of LEP (100-1 600 μg/L), with survival increasing, apoptosis peak decreasing, cell morphology restoring and caspase 3 activation inhibiting.CONCLUSION: Leptin prevents AECⅡ from apoptosis induced by Na₂S₂O₄ or hypoxia. The potential mechanism of its action may be related to promoting cell cycle from G₁ phase to S phase and inhibiting the activating of caspase 3.     

Growth performance and metabolic responses in barrows fed low-protein diets supplemented with essential amino acids

This study was conducted to determine the effect of supplementation with Lys, Met, Thr to low-protein diets on growth performance and metabolic responses in growing barrows. Seventy crossbred barrows (Duroc × Yorkshine), with an average initial body weight of 16 kg, were fed diets containing five crude protein (CP) levels (18.2, 16.5, 15.5, 14.5, and 13.6%) and 0.83% true ileal digestible lysine. On d 17 of the trial, all pigs were fitted with an indwelling jugular catheter for blood collection. On d 18 and 53, blood samples were obtained at 4 h post feeding. Reducing dietary CP concentration linearly decreased (P < 0.05) ADG, ADFI, feed efficiency, longissimus muscle area (LMA), and plasma concentrations of urea N and protein, while increasing backfat thickness linearly (P < 0.05). Pigs fed the 13.6% CP diet exhibited the poorest growth performance. On d 53, dietary CP affected plasma IGF-I (quadratic, P < 0.01) and leptin (linear, P < 0.01) concentrations. Plasma leptin levels were correlated positively with backfat thickness (r = 0.76, P < 0.05) and negatively with LMA (r = − 0.64, P < 0.01). There was a positive correlation between ADG and plasma IGF-I concentrations (r = 0.91, P < 0.05). Our results suggest that adequate provision of nonessential AA and all EAA is required for achieving maximum growth performance and reducing fat accretion in growing pigs fed low-CP diets.     

Endocrine Profile Comparisons of Fat Versus Moderately Conditioned Mares Following Parturition

The influence of progesterone, luteinizing hormone (LH), and estrogen on the mare's estrous cycle has been well researched and documented, but other endocrine profiles have not received as much attention. To evaluate endocrine concentrations in fat-conditioned (body condition score [BCS] of 7–8) versus moderately conditioned mares (BCS of 5–6), 24 mares were allotted to and maintained in respective groups from late gestation until pregnancy was confirmed after breeding on the second postpartum estrus. Serum concentrations of thyroxine (T₄), insulin-like growth factor-1 (IGF-1), and leptin were assayed to characterize circulating blood concentrations. Additionally, LH and progesterone serum concentrations were assayed to evaluate the estrous cycle status of the mares. Leptin and progesterone concentrations were not different (P > .05) between the groups. Nevertheless, serum concentrations of T₄ were higher (P < .01) and IGF-1 concentrations lower (P < .01) in moderately conditioned as compared with fat-conditioned mares during times of ovulation and the interovulatory period. Furthermore, serum concentrations of LH were found to be different between the groups only when the estrous cycle approached the second ovulation (P < .0001). Results of this study suggest that mares maintained in a BCS of 5 or greater are similar in terms of reproductive efficiency. Although the circulating serum concentrations of T₄ and IGF-1 are different after parturition, their influence does not affect reproductive capabilities of mares with a BCS of 5 or greater.     

黄淮山羊Leptin cDNA的克隆及鉴定

根据GenBank中公布的山羊Leptin基因部分基因组核苷酸序列，设计合成一对引物，以山羊脂肪组织总RNA为模板，采用RT—PCR法，扩增出Leptin成熟蛋白编码cDNA序列，将此扩增产物克隆入pMD18-T载体，进行PCR、双酶切鉴定及序列测定与分析。结果表明，扩增的山羊Leptin基因编码序列长为441bp，编码146个氨基酸。同源性分析表明，山羊Leptin基因成熟蛋白编码cDNA与小鼠、人、猪、牛及绵羊基因相应序列的同源性分别为82．22％、87．76％、92．97％、96．15％和98．64％，氨基酸同源性为84．25％、86．99％、92．47％、97．95％和100．00％，说明Leptin是一组在进化上高度保守的蛋白质。山羊Leptin成熟蛋白cDNA的成功克隆，为进一步研究黄淮山羊Leptin基因全结构、基因表达与调控奠定了基础。     

不同能量摄入水平对围产期奶牛脂肪组织Leptin mRNA和HSL mRNA表达的影响

选用围产期健康奶牛30头随机均分为3组,其中组为对照组,组和组为试验组。Ⅰ、Ⅱ、Ⅲ组于产前28d开始分别饲喂中国奶牛饲养标准(2000)标准日粮(能量摄入100%组)、标准日粮增加20%日粮(能量摄入120%组)和标准日粮减少20%日粮(能量摄入80%组),产后各组奶牛均饲喂同一标准日粮至56 d。试验各组奶牛分别于产前28、14 d、产后1、14、28、56 d尾根部手术采取脂肪样品,采用荧光RT-PCR法对脂肪组织Leptin mRNA及HSL mRNA表达水平进行定量分析。结果表明,不同能量摄入水平显著影响脂肪组织Leptin mRNA和HSL mR-NA表达。低能饲喂明显提高了脂肪组织中Leptin mRNA表达,降低了HSL mRNA表达;高能饲喂明显降低了脂肪组织中Leptin mRNA表达,提高了HSL mRNA表达。     

Canine adiponectin: cDNA structure, mRNA expression in adipose tissues and reduced plasma levels in obesity

Adiponectin is a protein synthesized and secreted by adipocytes. Decreased adiponectin is responsible for insulin resistance and atherosclerosis associated with human obesity. We obtained a cDNA clone corresponding to canine adiponectin, whose nucleotide and deduced amino acid sequences were highly identical to those of other species. Adiponectin mRNA was detected in adipose tissues, but not in other tissues, of dogs. When 22 adult beagles were given a high-energy diet for 14 weeks, they became obese, showing heavier body weights, higher plasma leptin concentrations, but lower plasma adiponectin concentrations. The adiponectin concentrations of plasma samples collected from 71 dogs visiting veterinary practices were negatively correlated to plasma leptin concentrations, being lower in obese than non-obese dogs. These results are compatible with those reported in other species, and suggest that adiponectin is an index of adiposity and a target molecule for studies on diseases associated with obesity in dogs.     

Effects of chronic obesity and weight loss on plasma ghrelin and leptin concentrations in dogs

The objective of this study was to evaluate, in dogs, the effects of obesity and weight loss on plasma total ghrelin and leptin concentrations. Twenty-four Beagle dogs, 12 control lean and 12 obese dogs of both genders and aged between 1 and 9 years, were used for the experiments. Mean body weight was 12.7+/-0.7 kg for the lean group and 21.9+/-0.8 kg for the obese group. The trial was divided into three phases. During phase 1, all 24 Beagle dogs were fed a maintenance diet. During phase 2, the obese dogs were submitted to a weight loss protocol with a high protein-low energy diet. The weight loss protocol ended once dogs reached optimal body weight. During phase 3, the dogs that were submitted to the weight loss protocol were maintained at their optimal body weight for 6 months. Plasma total ghrelin, leptin, insulin and glucose concentrations were measured to evaluate the effects of obesity and weight loss on these parameters in dogs. Body weight, body condition score, thoracic and pelvic perimeters, and ingested food amounts were also recorded during the study. Obese dogs demonstrated a significant decrease in plasma ghrelin and a significant increase in plasma leptin and insulin concentrations when compared with control dogs. During weight loss, significant increases in plasma total ghrelin and glucose and significant decreases in plasma leptin and insulin were observed. The increase in plasma ghrelin concentrations seemed to be transient. Body weight and the morphometric parameters correlated positively with leptin concentrations and negatively with total ghrelin concentrations. These results suggest that ghrelin and leptin could play a role in dogs in the adaptation to a positive or negative energy balance, as observed in humans.