动物性食品中环境激素对人体的影响及其防治

文中分别介绍了环境激素的定义、激素与环境激素间的关系,以及动物性食品中所包含的环境激素种类,通过分析动物性食品中环境激素的污染途径及其对人体的影响,提出了控制措施以增强人们对其危害的重视,并减少环境激素对人体损害,有利于控制环境激素在动物性食品中的含量。     

蜂王浆对雌性大鼠生长发育的影响

目的：探讨高剂量蜂王浆对雌性大鼠生长发育的影响。方法：实验组大鼠按3 g/（200 g·d）（以体质量计,下同）灌胃新鲜的蜂王浆溶液,对照组按3 mL/（200 g·d）灌胃生理盐水,4 周后,停止灌胃,继续饲养2 周。每两周解剖一批大鼠,称质量计算心、肝、脾、肺、肾、肾上腺、子宫、卵巢脏器系数,用放射免疫技术检测血清雌二醇（estradiol,E2）、促卵泡素（follicle stimulating hormone,FSH）、促黄体素（luteinizing hormone,LH）、孕激素（progestrone,P）含量,实时定量聚合酶链式反应（real-timepolymerase chain reaction,real-time PCR）检测卵巢和子宫中雌激素受体α（estrogen receptor α,ERα）、雌激素受体β（estrogen receptor β,ERβ）、促卵泡素受体（follicle stimulating hormone receptor,FSHR）、促黄体素受体（luteinizing hormone recepter,LHR）、孕激素受体（progestrone receptor,PR）mRNA表达量。结果：灌胃2 周,实验组大鼠体质量、主要脏器系数、血清主要性激素含量及其卵巢和子宫中受体表达量与对照组相比均无显著差异;灌胃4 周,实验组大鼠体质量显著低于对照组,实验组血清E2显著高于对照组,实验组卵巢PR mRNA表达量显著高于对照组,实验组子宫中ERα、ERβ、PR mRNA表达量显著高于对照组。实验组与对照组脏器系数无显著差异;停止灌胃2 周后,实验组大鼠体质量、主要脏器系数、血清主要性激素含量与对照组相比均无显著差异,实验组卵巢中FSHR、ERβ、PR mRNA表达量显著高于对照组,实验组子宫中ERα、ERβ、FSHR和PR mRNA表达量显著高于对照组。结论：高剂量的蜂王浆在一定程度上影响雌性大鼠的生长发育。     

半胱胺对鲤鱼生长及血液生化指标的影响

在鲤鱼基础饵料中分别添加0、200、400、600和800 mg/kg的半胱胺,经过42 d的饲养试验,研究不同水平的半胱胺对鲤鱼生长、相关激素水平、血清生化指标的影响.结果表明:①与对照组相比,鲤鱼饵料中添加200、400、600 mg/kg半胱胺均不同程度提高了鲤鱼的生长性能,400 mg/kg半胱胺显著提高了鲤鱼的相对增重率(P＜0.05),并降低了鲤鱼的饵料系数(P＞0.05).②与对照组相比,400 mg/kg半胱胺显著提高了鲤鱼血液中GH水平(P＜0.05),T3水平也高于其他各组(P＞0.05).③400 mg/kg半胱胺组的碱性磷酸酶活性、血糖和总蛋白质水平均高于其他各组,其中总蛋白质水平显著高于对照组(P＜0.05).分析认为,本试验鲤鱼饵料中半胱胺适宜的添加量为400 mg/kg.     

Effect of elevating luteinizing hormone action using low doses of human chorionic gonadotropin on double ovulation,follicle dynamics,and circulating follicle-stimulating hormone in lactating dairy cows

Double ovulation and twin pregnancy are undesirable traits in dairy cattle. Based on previous physiological observations, we tested the hypothesis that increased LH action [low-dose human chorionic gonadotropin (hCG)] before the expected time of diameter deviation would change circulating FSH concentrations, maximum size of the second largest (F2) and third largest (F3) follicles, and frequency of multiple ovulations in lactating dairy cows with minimal progesterone (P4) concentrations. In replicate 1, multiparous, nonbred lactating Holstein dairy cows (n = 18) had ovulation synchronized. On d 5 after ovulation, all cows had their corpus luteum regressed and were submitted to follicle (≥3 mm) aspiration 24 h later to induce emergence of a new follicular wave. Cows were then randomized to NoP4 (untreated) and NoP4+hCG (100 IU of hCG every 24 h for 4 d after follicle aspiration). Ultrasound evaluations and blood sample collections were performed every 12 h for 7 d after follicle aspiration. All cows were then treated with 200 μg of GnRH to induce ovulation. In replicate 2, cows (n = 16) were resubmitted to similar procedures (i.e., corpus luteum regression, follicle aspiration, randomization, ultrasound evaluations every 12 h, GnRH 7 d after aspiration). However, cows in replicate 2 received an intravaginal P4 device that had been previously used (～18 d). Only cows with single (n = 15) and double (n = 16) ovulations were used in the analysis. No significant differences were detected for frequency of double ovulation, follicle sizes, and FSH concentrations across replicates (NoP4 vs. LowP4 and NoP4+hCG vs. LowP4+hCG), so data were combined. Double ovulation was 40% for control cows with no hCG (CONT) and 62.5% with hCG (hCG). Double ovulation increased as the maximum size of F2 increased: <9.5 mm and 9.5–11.5 mm (7.7%) and ≥11.5 mm (94.1%). The hCG group had more cows with F2 > 11.5 (69%) than with 9.5 ≥ F2 ≤ 11.5 (25%) and F2 < 9.5 (6%). In agreement, F2 and F3 maximum size were larger in the hCG group, but FSH concentrations were lower after F1 > 8.5 mm compared with CONT. In contrast, FSH concentrations were greater before deviation (F1 closest value to 8.5 mm) in cows with double ovulations than in those with single ovulations, regardless of hCG treatment. In addition, time from aspiration to deviation was shorter in cows with double rather than single ovulation and in cows treated with hCG as a result of faster F1, F2, and F3 growth rates before diameter deviation. In conclusion, greater FSH and follicle growth before deviation seems to be a primary driver of greater frequency of double ovulation in lactating cows with low circulating P4. Moreover, the increase in follicle growth before deviation and in the maximum size of F2 during hCG treatment suggests that increased LH may also have a role in stimulating double ovulation.     

Hormonal and lactational responses to growth hormone-releasing hormone treatment in lactating Japanese Black cows

Ten multiparous lactating Japanese Black cows (beef breed) were used to evaluate the effects of bovine growth hormone-releasing hormone (GHRH) analog on milk yield and profiles of plasma hormones and metabolites. The cows received 2 consecutive 21-d treatments (a daily s.c. injection of 3-mg GHRH analog or saline) in a 2 (group) x 2 (period) Latin square crossover design. The 5 cows in group A received GHRH analog during period 1 (from d 22 to 42 postpartum) and saline during period 2 (from d 57 to 77 postpartum), and those in group B received saline and GHRH analog during periods 1 and 2, respectively. Mean milk yield decreased in saline treated compared with that during the 1-wk period before treatment 7.4 and 19.1% during periods 1 (group B) and 2 (group A), respectively. Treatment with GHRH analog increased milk yield 17.4% (period 1, group A) and 6.3% (period 2, group B). Treatment with GHRH analog induced higher basal plasma concentrations of growth hormone (GH), insulin-like growth factor-1 (IGF-1), insulin, and glucose compared with saline-treated cows. In glucose challenge, the GHRH analog-treated beef cows had greater insulin secretion than the saline-treated beef cows. In insulin challenge, however, there were no significant differences in the areas surrounded by hypothetical lines of basal glucose concentrations and glucose response curves between GHRH analog- and saline-treated cows. These results demonstrate that GHRH analog treatment facilitates endogenous GH secretion in lactating Japanese Black cows, leading to increases in milk yield and plasma concentrations of IGF-1, insulin, and glucose.     

Effect of dietary energy and somatotropin on components of the somatotropic axis in Holstein heifers

The somatotropic axis, consisting of growth hormone (GH), GH receptor (GHR), insulin-like growth factor (IGF)-I, IGF binding proteins (IGFBP), and IGF receptors, controls growth and mammary development in heifers. Manipulation of the axis with recombinant bovine somatotropin (rbST) improves heifer growth and reduces age at first calving. The effects of rbST are influenced by dietary energy through partially understood mechanisms. The objective was to characterize the somatotropic axis in Holstein heifers fed a diet for either low or high rate of gain and treated with or without rbST. Heifers (120 d of age) were assigned to one of 2 diets to gain either 0.8 kg/d (low, n = 18) or 1.2 kg/d (high, n = 20). Within each diet, half of the heifers (n = 9 for low and n = 10 for high) received daily rbST injections (25 microg/kg of body weight). Treatments and diets continued until slaughter (2 mo after puberty). Blood was collected 2x per week, and a frequent sampling window was performed 1 d before slaughter. Liver was collected at slaughter. Feeding a high diet or treating with rbST increased serum IGF-I and decreased serum IGFBP-2. The observed changes in serum IGF-I and IGFBP-2 were reflected in their respective liver mRNA amounts. Feeding a high diet decreased serum GH concentrations after rbST injection, but the stimulatory effect of rbST on serum IGF-I was nonetheless greater in high-diet heifers. The differential IGF-I response may be explained by greater GHR 1A in the liver of high-diet heifers. We conclude that a high-gain diet modifies the somatotropic axis in rbST-treated heifers by decreasing serum GH but increasing serum IGF-I after rbST treatment. Greater IGF-I (indicative of an increased GH response) may be a consequence of greater GHR 1A expression in the liver.     

人参茎叶总皂苷对幼年雄性大鼠生殖系统的影响及作用机制

目的：研究人参茎叶总皂苷对幼年雄性大鼠生殖系统的影响及作用机制。方法：将40 只SD幼年大鼠分为对照组及人参茎叶总皂苷低、中、高剂量给药组,灌胃两周后处死,用放射免疫法检测大鼠血清中睾酮的含量,用酶联免疫试剂盒测量大鼠血清中双氢睾酮、促黄体激素和促卵泡素的含量,称量大鼠的睾丸质量,计算体质量增加量、睾丸脏器系数和精子密度。用高效液相色谱仪对比分析高剂量组大鼠血清和对照组血清中成分的差异。将高剂量组大鼠血清和人参茎叶总皂苷溶液,按0%（对照组）、5%、10%、15%的体积分数分别加到培养的大鼠睾丸间质细胞中,用台盼蓝染色法和噻唑蓝法检测细胞存活率和活力,用放免法检测睾丸间质细胞培养液中睾酮的含量,用大鼠环磷酸腺苷酶联免疫试剂盒检测睾丸间质细胞内环磷酸腺苷的变化。用SPSS软件分析各组间差异。结果：人参茎叶总皂苷能剂量依赖性地显著降低幼年大鼠的血清睾酮水平（P＜0.01）、双氢睾酮（P＜0.01）水平和精子密度（P＜0.01）。与对照组相比,高剂量组大鼠血清中含有5 种成分是对照组中所没有的,并且人参茎叶总皂苷给药组的睾丸质量（P＜0.05）和体质量增加量（P＜0.01）显著降低,血清促黄体激素（P＜0.01）、促卵泡素（P＜0.01）和睾丸脏器系数显著上升（P＜0.05）。人参茎叶总皂苷及其含药血清能抑制睾丸间质细胞内内环磷酸腺苷水平和睾酮的合成。结论：人参茎叶总皂苷可能通过抑制蛋白激酶A途径降低大鼠血清中睾酮的生成,从而抑制睾丸发育和精子生成,影响雄性幼鼠生殖系统的发育。     

Effect of lipopolysaccharide on indices of peripheral and hepatic metabolism in lactating cows

Four multiparous lactating cows (175 to 220 d in milk [DIM]) were used in a 4 x 4 Latin square design to assess the effects of four doses (0.0, 0.5, 1.0, and 1.5 microg/kg of body weight) of lipopolysaccharide (LPS; Escherichia coli 0111:B4) on performance and plasma metabolite and hormone concentrations. In addition, effects of immune activation on in vitro hepatic metabolic capacity were evaluated in 12 multiparous lactating cows (150 to 220 DIM) infused with 0 (n = 6), 1.0 (n = 4) or 2.0 (n = 2) microg of LPS/kg. Milk production and DMI decreased linearly with LPS dose for 24 h after LPS infusion. Overall mean plasma tumor necrosis factor-alpha, insulin, glucagon, and cortisol concentrations increased linearly with LPS dose, and plasma beta-hydroxybutyrate decreased linearly by dose after LPS infusion. Infusion of LPS decreased the insulin:glucagon molar ratio, but did not affect plasma concentrations of growth hormone, insulin-like growth factor-1, leptin, or L-(+)-lactate. Plasma concentrations of glucose tended to increase initially and subsequently decrease, and there was a quadratic tendency for increased plasma nonesterified fatty acid concentrations after LPS administration. In vitro hepatic capacity for conversion of [1-(14)C]L-(+)-lactate and [1-(14)C]palmitate, but not [1-(14)C]propionate or [1-(14)C]L-alanine, to CO2 increased after LPS administration. Hepatic capacity to convert [1-(14)C]propionate to glucose tended to increase, but neither esterification nor the conversion of palmitate to acid soluble products was altered by LPS. The LPS infusion resulted in significant changes of endocrine mediators responsible for regulation of energy metabolism of lactating cows and tended to alter subsequent in vitro hepatic metabolic capacity.     

Intravaginal instillation of gonadotropin-releasing hormone analogues with an absorption enhancer induced a surge of luteinizing hormone in lactating dairy cows

Our objectives were to evaluate circulating LH concentrations after intravaginal (IVG) instillation of GnRH analogs in lactating dairy cows. In 2 experiments, lactating Holstein cows (experiment 1: n = 32; experiment 2: n = 47) received the experimental treatments 48 h after the first of 2 PGF_2α treatments given 12 h apart and 7 d after a modified Ovsynch protocol (GnRH at ?7 d, PGF_2α at ?24 h, PGF_2α at ?56 h, GnRH at 0 h). In experiment 1, cows were stratified by parity and randomly allocated to receive the following treatments: 2 mL of saline IVG (SAL, n = 6), 100 µg of gonadorelin (Gon) i.m. (G100-IM, n = 5), and 100 (G100, n = 7), 500 (G500, n = 8), or 1,000 µg of Gon IVG (G1000, n = 7). In experiment 2, treatments were SAL (n = 8), G100-IM (n = 8), G1000 (n = 7), 1,000 µg of Gon plus 10% citric acid (CA) IVG (G1000CA, n = 8), 80 µg of buserelin IVG (B80, n = 8), and 80 µg of buserelin plus 10% CA IVG (B80CA, n = 8). In both experiments, blood was collected every 15 min from ?15 min to 4 h, and every 30 min from 4 to 6 h after treatment. Data for area under the curve (AUC), mean LH concentrations, and time to maximum LH concentration were analyzed by ANOVA with (mean LH only) or without repeated measures using PROC MIXED of SAS (version 9.4, SAS Institute Inc., Cary, NC). The proportion of cows with a surge of LH was evaluated with Fisher's exact test using PROC FREQ of SAS. In both experiments, LH concentrations were affected by treatment, time, and the treatment by time interaction. In experiment 1, the AUC for LH and maximum LH concentration were greatest for the G100-IM treatment and were greater for the G1000 than for the SAL and G500 treatments. The proportion of cows with an observed surge of LH was 100 and 0% for cows that received Gon i.m. and IVG, respectively. In experiment 2, the AUC and maximum LH concentrations were greater for the G100-IM, G1000CA, and B80CA treatments than for the other IVG treatments. The proportion of cows with a surge of LH differed by treatment (SAL = 0%, G100-IM = 100%, G1000 = 14%, G1000CA = 88%, B80 = 13%, and B80CA = 100%). For the treatments with a surge of LH, time to maximum concentration of LH was the shortest for the G100-IM treatment, intermediate for the G1000CA treatment, and the longest for cows in the B80CA treatment. In conclusion, Gon (up to 1,000 µg) absorption through intact vaginal epithelium after a single IVG instillation was insufficient to elicit a surge of LH of normal magnitude. Conversely, IVG instillation of 1,000 µg of Gon and 80 µg of buserelin with the addition of citric acid as absorption enhancer resulted in a surge of LH of similar characteristics than that induced after i.m. injection of 100 µg of Gon.     

Structural growth, rumen development, and metabolic and immune responses of Holstein male calves fed milk through step-down and conventional methods

Structural growth, feed consumption, rumen development, metabolic response, and immune response were studied in Holstein calves fed milk through either a conventional method or a step-down (STEP) method. In the conventional method, calves (n = 20) were fed colostrum and then milk at a rate of 10% of their BW for the entire period of 44 d. In the STEP method, calves (n = 20) were given colostrum and then milk at a rate of 20% of their BW for 23 d, which was reduced (between d 24 to 28) to 10% of their BW for the remaining 16 d. The calves on both methods were weaned gradually by diluting milk with water between d 45 and 49. After weaning, feed consumption, structural growth, and body weight gain were monitored until calves were 63 d of age. At d 63, twelve calves (6/treatment) were euthanized and rumen papillae length, papillae width, rumen wall thickness, and emptied forestomach weight were recorded. At wk 4, 7, and 9, ruminal contents were collected to enumerate rumen metabolites. The STEP-fed calves consumed a greater amount of milk than conventionally fed calves during the pre-STEP (d 1 to 28), post-STEP (d 29 to 49), and preweaning (d 1 to 49) periods. Consumption of starter and hay was greater during the pre-STEP period and lesser during the post-STEP and postweaning (d 50 to 63) periods in calves on the conventional method than on the STEP method. Body weight gain and structural growth measurements of calves were greater on the STEP method than on the conventional method. A hypophagic condition caused by greater milk consumption depressed solid feed intake of STEP-fed calves during the pre-STEP period, and a hyperphagic response caused by a reduced nutrient supply from milk triggered their consumption of solid feed during the post-STEP and postweaning periods. Ruminal pH and concentrations of ammonia, total volatile fatty acids, acetate, propionate, butyrate, and plasma β-hydroxybutyrate were higher in calves on the STEP method and at weaning and postweaning (d 63) were lower in calves on the conventional method. Emptied weight of the forestomach, rumen wall thickness, papillae length, papillae width, and papillae concentration were higher in calves on the STEP method than in those on the conventional method. Blood glucose was lower, and blood urea nitrogen and β-hydroxybutyrate at weaning and postweaning were higher in STEP-fed calves. Serum IgG, IgA, and triglycerides for 1, 2, and 3 wk of age were higher in calves on the STEP method than in those on the conventional method. In conclusion, greater feed consumption, BW gain, and structural growth, and a more metabolically and physically developed rumen were observed in calves on the STEP method than in those on the conventional method.     

Stress and the skin

'The skin is the mirror which reflects the state of the mind.'The skin is the window of the mind.' These have been proverbs since ancient times. It is the topic of this article. Our life became convenient with the information technology these days but too much information often drives us on. We suffer from mental stress rather than physical stress. Since Selye advocated stress reaction, various reactions in the body have been described. Skin is also a target organ of the stress reaction. What the effects of stress are and how stress affects the skin are summarized in this review. Possible use of fragrance for the regulation of the stress reaction is also introduced.     

Naturally occurring mastitis effects on timing of ovulation, steroid and gonadotrophic hormone concentrations, and follicular and luteal growth in cows

The effects of naturally occurring subclinical chronic or clinical short-term mastitis on time of ovulation, plasma steroid and gonadotropin concentrations, and follicular and luteal dynamics were examined in 73 lactating Holstein cows. Cows were sorted by milk somatic cell count and bacteriological examination into an uninfected group (n = 22), a clinical mastitis group (n = 9; events occurring 20 ± 7 d before the study), and a subclinical chronic mastitis group (n = 42). In addition, uninfected and mastitic cows were further sorted by their estrus to ovulation (E-O) interval. About 30% of mastitic cows (mainly subclinical) manifested an extended E-O interval of 56 ± 9.2 h compared with 28 ± 0.8 h in uninfected cows and 29 ± 0.5 h in the other 70% of mastitic cows. In mastitic cows with extended E-O interval, the concentration of plasma estradiol at onset of estrus was lower than that of uninfected cows or mastitic cows that exhibited normal E-O intervals (3.1 ± 0.4, 5.8 ± 0.5, and 5.5 ± 0.5 pg/mL, respectively). The disruptive effect of mastitis on follicular estradiol probably does not involve alterations in gonadotropin secretion because any depressive effects of mastitis on pulsatile LH concentrations were not detected. Cortisol concentrations did not differ among groups. The preovulatory LH surge in mastitic cows with delayed ovulation varied among individuals, being lower, delayed, or with no surge noted compared with the normal LH surge exhibited by uninfected cows or mastitic cows with normal E-O interval (6.8 ± 0.7 ng/mL). The diameter of the second-wave dominant follicle was larger and the number of medium follicles was smaller in uninfected and subclinical cows with normal intervals compared with subclinical cows with extended intervals (13.4 ± 0.5 vs. 10.9 ± 0.9 mm, and 3.8 ± 0.2 vs. 6.7 ± 0.14 follicles, respectively). Mid-luteal progesterone concentrations were similar in uninfected and mastitic cows. These results indicate for the first time that around 30% of cows with subclinical chronic mastitis exhibit delayed ovulation that is associated with low plasma concentrations of estradiol and a low or delayed preovulatory LH surge.     

Impact of gonadotropin-releasing hormone administration at the time of artificial insemination on conception risk and its association with estrous expression

Cows with reduced estrous expression have compromised fertility. The aim of this study was to determine whether the administration of GnRH at the time of artificial insemination (AI) would affect ovulation rates and the fertility of animals expressing estrous behavior of lesser intensity. Cows were enrolled at the time of estrus from 3 farms (n = 2,607 estrus events; farm A: 1,507, farm B: 429, farm C: 671) and randomly assigned to receive GnRH at AI or not (control). The intensity of estrous expression, monitored through leg-mounted activity monitors, was determined using the maximum activity during estrus; estrous expression was categorized as greater or lower relative to the farm median. On farm A, cows were assessed at alert, and 24 h, 48 h, and 7 d post-alert for ovulation using ultrasonography. Pregnancy per AI was confirmed at 35 ± 7 d post-estrus for cows that were inseminated. Differences between treatments were tested using the GLIMMIX procedure of SAS. Treatment with GnRH at the time of AI increased pregnancy per AI (41.3 ± 1.6 vs. 35.7 ± 1.7%). An interaction between treatment and estrous expression on pregnancy per AI was found. Control cows with greater estrous expression had greater pregnancy per AI than those with lesser expression, whereas GnRH administration increased pregnancy per AI for cows with lesser estrous expression but not those with greater expression (GnRH, greater intensity: 43.5 ± 2.1; GnRH, lesser intensity: 37.8 ± 2.2; control, greater intensity: 42.6 ± 2.2; control, lesser intensity: 31.0 ± 2.2%). A higher proportion of cows with greater estrous expression that were administered GnRH at AI were found to ovulate by 48 h and 7 d post-estrus; however, ovulation of cows with lesser estrous expression was unaffected by GnRH administration. In conclusion, fertility of cows with reduced estrous expression may be increased using GnRH at the time of AI; however, increased ovulation rates do not seem to be the direct mechanism behind this relationship.     

美食蕉的降血糖活性及其对糖脂代谢指标、激素的影响

美食蕉是我国香蕉新品种，富含抗性淀粉、膳食纤维等，根据国食药监保化[2012]107号文件附件3“辅助降血糖功能评价方法”对美食蕉的降血糖活性进行研究。将24 只正常大鼠随机分为空白对照组（NC）、美食蕉高剂量空白对照组（NH），将造模成功的48 只糖尿病大鼠随机分为糖尿病模型对照组（DM）以及美食蕉低、中、高剂量组（LP、MP、HP），测定大鼠血液生化指标、激素水平等，初步探索美食蕉对糖脂代谢的影响。结果表明，美食蕉对正常大鼠无不良作用且在一定程度上呈现减缓正常大鼠体质量增加的效果；美食蕉干预能够缓解糖尿病大鼠多食、多饮、多尿、消瘦的症状，降低糖尿病大鼠血清葡萄糖浓度，提高其葡萄糖耐受能力。与DM组相比，LP、MP、HP组大鼠血清葡萄糖浓度分别显著降低10.70%、10.19%和13.94%（P＜0.05）。美食蕉干预能够缓解糖脂代谢紊乱，降低血清甘油三酯、总胆固醇、低密度脂蛋白胆固醇和游离脂肪酸浓度，降低血清胰岛素、C肽、胰淀素和胰高血糖素样肽-1的水平。与DM组相比，低、中、高剂量组大鼠胰岛素水平分别降低了28.54%、39.50%和49.14%。结论：美食蕉具有降血糖活性，通过调节激素分泌从而影响糖脂代谢。     

Parity-related changes in bovine follicle and oocyte populations,oocyte quality,and hormones to 90 days postpartum

Ultrasound-guided transvaginal follicular aspiration was used to obtain oocytes from Holstein cows to study follicular development and oocyte morphology during early lactation. A single aspiration was conducted on each of the 120 cows during wk 1 to 12 postpartum. On the day of aspiration, the number of follicles and their sizes were recorded. The collected oocytes were morphologically classified into four grades. Blood and follicular fluid samples were collected for hormone and metabolite assays. Greater serum nonesterified fatty acids concentrations for first- and second-parity cattle on d 7 implied a more negative energy balance status than for third-parity cattle. The numbers of follicles and oocytes retrieved were affected by linear days postpartum x parity interactions, with second-parity cattle having increases compared with decreases for third-parity cattle. Oocyte quality score was affected by the quadratic days postpartum x parity interaction. First- and second-parity cattle had greater oocyte quality scores from d 20 to 70 postpartum compared with third-parity cattle, but third-parity cattle had greater quality oocytes near the end of the 12-wk period. In contrast to cattle subjected to multiple aspirations, first- and second-parity cattle had higher estradiol and insulin-like growth factor I concentrations in follicular fluid associated with greater numbers of oocytes retrieved than third-parity cattle. This study demonstrated that conditions related to early lactation have a negative effect on oocyte quality and endocrine measures of dairy cattle and that animals of various parities may be differentially affected.     

Extending lactation in pasture-based dairy cows. II: Effect of genetic strain and diet on plasma hormone and metabolite concentrations

Fifty-six genetically divergent New Zealand and North American Holstein-Friesian (HF) cows grazed pasture, and were offered 0, 3, or 6 kg of concentrate DM/cow per day for an extended lactation (605 ± 8.3 d in milk; mean ± standard error of the mean). Weekly blood samples collected from individual cows from wk 1 to 10 postpartum (early lactation), and from wk 47 to 63 postpartum (extended lactation) were analyzed for nonesterified fatty acids (NEFA), glucose, insulin, leptin, growth hormone (GH), insulin-like growth factor-I (IGF-I), calcium, and urea. During early lactation, NEFA and GH concentrations were greater and IGF-I concentrations were less, and increased at a slower rate in North American HF. During this 10-wk period, there were no strain effects on plasma glucose, leptin, insulin, or calcium. During the extended lactation period, North American HF had greater NEFA and GH concentrations; there were strain × diet interactions for insulin and leptin, and a tendency for a strain × diet interaction for glucose. These interactions were primarily due to greater plasma insulin, leptin, and glucose concentrations in the New Zealand HF fed 6 kg of concentrate DM/cow per day, a result of excessive body condition in this treatment. In this period, there was no strain effect on plasma IGF-I, calcium, or urea concentration. During early lactation, there was a linear increase in glucose and IGF-I, and a linear decrease in GH and urea with increasing concentrate in the diet. However, plasma calcium, NEFA, insulin, and leptin remained unchanged. During the extended lactation period, there was an effect of feed supplementation on GH and urea, which decreased linearly with increasing concentrate in the diet. There was, however, no supplementation effect on NEFA, calcium, or IGF-I. These data indicate potential strain differences in recoupling of the somatotropic axis, insulin resistance, and energy partitioning, and may help explain the physiology behind the previously reported greater milk production and body condition score loss in North American HF. The results have implications for breeding and diet management during an extended lactation.