Partial feed restriction decreases growth hormone receptor 1A mRNA expression in postpartum dairy cows

Uncoupling of the growth hormone (GH) axis in early postpartum dairy cows is correlated with a decrease in liver GH receptor (GHR) 1A mRNA and a decrease in liver GH receptor protein. Postpartum recoupling of the GH axis is also correlated with GHR 1A mRNA and GHR protein. We hypothesized that dry matter intake (DMI) partially controls the increase in GHR 1A mRNA postpartum. Prepartum Holstein dairy cows (n = 11) were offered feed ad libitum. After calving, 6 cows were fed 70% of their expected DMI (feed restriction) for 14 d and 5 cows were fed ad libitum (control). Both groups were fed ad libitum after d 14. Liver was biopsied prepartum and on d 1, 7, 14, and 21 postpartum; blood was sampled throughout the experimental period. Rate of increase in postpartum milk production was less for feed-restricted cows. The GHR 1A mRNA decreased from prepartum to d 1 postpartum and subsequently increased. Rate of postpartum increase in GHR 1A mRNA was less in feed-restricted cows. Diminished GHR 1A persisted for at least 7 d after feed-restricted cows returned to ad libitum feeding. Liver insulin-like growth factor-I mRNA concentrations decreased from prepartum to d 1 as well, but were similar for feed restricted and control thereafter. We concluded that DMI partially controls GHR 1A mRNA expression in early postpartum dairy cows and that the decrease in GHR 1A in response to feed restriction persisted for at least 1 wk after ad libitum feeding was restored.     

Relationships between the concentration of insulin-like growth factor-1 in serum in dairy cows in early lactation and reproductive performance and milk yield

The objective of this study was to evaluate the relationships of different insulin-like growth factor-1 (IGF1) measures [5 distinct IGF1 concentrations on particular days, area under the curve (AUC), and linear regression coefficient] in the postpartum period in lactating dairy cows and reproductive performance. A total of 417 healthy multiparous Holstein-Friesian cows were enrolled in the study. Serum samples for the determination of the concentration of IGF1 were collected on d 0, 4, 10, 20, and 40 postpartum (pp). The concentration of total IGF1 in serum was determined by immunometric chemiluminescence immunoassay. All cows were examined for vaginal discharge as a sign of clinical endometritis at 20 d pp by external inspection and rectal palpation. The mean concentration of IGF1 ranged from 57 ± 18.9 ng/mL within the first 12 h pp to 74 ± 19.9 ng/mL at 40 d pp. On d 10 pp, first and all artificial insemination conception rates were greater in cows with IGF1 concentrations above the median compared with cows with IGF1 concentrations below the median. Cows with greater AUC (second to fourth quartile) conceived earlier (11.4, 16.0, and 18.8 d) than cows in the first IGF1 quartile (117.0 ± 43.6). Proportion of cows pregnant within 200 d pp increased significantly from the first to the third IGF1 quartile of AUC (58.7, 66.7, and 74.0%). The proportion of cows culled decreased from the first to the fourth IGF1 quartile. Correlations between IGF1 measures and days to pregnancy were significant (except for the linear regression coefficients) but low (R² = 0.0009 to 0.025). Differences between single or composite measurements of IGF1 were not significant. We could also demonstrate a statistically significant correlation between the concentration of IGF1 in serum and the average 10-d milk production (31.6 to 44.0 kg). In conclusion, our study indicates that single or multiple measurements of IGF1 concentration in the postpartum period have very limited value to predict individual fertility in dairy cows.     

Uterine and hepatic gene expression in relation to days postpartum, estrus, and pregnancy in postpartum dairy cows

The somatotropic axis consisting of growth hormone, the growth hormone receptor (GHR) insulin-like growth factor (IGF)-I, and IGF binding proteins changes with the stage of lactation and nutrition of the cow and may be 1 mechanism through which lactation and nutrition affect the establishment of pregnancy. The objective of this study was to quantify GHR, IGF-I, and IGF binding protein-2 (IGFBP-2) mRNA in liver and uterine endometrial tissue at 4 stages of lactation (40, 80, 120, and 160 days in milk) and around the time of artificial insemination. Estrus was synchronized with GnRH and PGF_2α, and cows were inseminated 12 h after estrus. Uterine biopsies were collected immediately before the second injection of PGF_2α (before estrus), at the initiation of standing estrus, and 4 d after estrus. Liver biopsies were collected once on 4 d after estrus. The abundance of GHR, IGF-I, and IGFBP-2 mRNA in liver and uterus was determined by real-time quantitative PCR. The amount of liver IGF-I mRNA was positively correlated with plasma IGF-I concentrations. Cows that became pregnant after AI had more GHR and IGFBP-2 mRNA in their liver than cows that did not become pregnant. There was no effect of DIM or pregnancy status on abundance of uterine mRNA; however, uterine GHR and IGF-I mRNA was most abundant at estrus. In summary, cows at different stages of lactation or with different pregnancy statuses had similar quantities of uterine mRNA. In contrast, liver quantities of mRNA differed relative to pregnancy status. These data provide evidence that liver indices of metabolic state may be indicative of pregnancy success.     

Fibroblast growth factor-21 (FGF21) administration to early-lactating dairy cows. II. Pharmacokinetics,whole-animal performance,and lipid metabolism

Dairy cows cope with severe energy insufficiency in early lactation by engaging in intense and sustained mobilization of fatty acids from adipose tissue. An unwanted side effect of this adaptation is excessive lipid accumulation in the liver, which in turn impairs hepatic functions. Mice experiencing increased hepatic fatty acid flux are protected from this condition through coordinated actions of the newly described hormone fibroblast growth factor-21 (FGF21) on liver and adipose tissue. The possibility of an analogous role for FGF21 in dairy cows is suggested by its rapid increase in plasma levels around parturition followed by chronically elevated levels in the first few weeks of lactation. To test this hypothesis, dairy cows were randomly assigned on d 12.6 ± 2.2 (± standard error) of lactation to receive either an excipient (control; n = 6) or recombinant human FGF21 (n = 7), first as an FGF21 bolus of 3 mg/kg of body weight (BW) followed 2 d later by a constant i.v. infusion of FGF21 at a rate of 6.3 mg/kg of metabolic BW for 9 consecutive days. After bolus administration, human FGF21 circulated with a half-life of 194 min, and its constant infusion increased total plasma concentration 117-fold over levels in excipient-infused cows. The FGF21 treatment had no effect on voluntary feed intake, milk yield, milk energy output, or net energy balance measured over the 9-d infusion or on final BW. Plasma fatty acids circulated at lower concentrations in the FGF21 group than in the control group for the 8-h period following bolus administration, but this reduction was not significant during the period of constant i.v. infusion. Treatment with FGF21 caused a 50% reduction in triglyceride content in liver biopsies taken at the end of the constant i.v. infusion without altering the mRNA abundance of key genes involved in the transport, acyl coenzyme A activation, or oxidation of fatty acids. In contrast, FGF21 treatment ablated the recovery of plasma insulin-like growth factor-1 seen in control cows during the 9-d i.v. infusion period despite a tendency for higher plasma growth hormone. This effect was associated with increased hepatic mRNA abundance of the intracellular inhibitor of growth hormone receptor trafficking, LEPROT. Overall, these data confirm the ability of FGF21 to reduce lipid accumulation in bovine liver and suggest the possibility that FGF21 does so by attenuating the hepatic influx of adipose tissue-derived fatty acids.     

Cellular proliferation rate and insulin-like growth factor binding protein (IGFBP)-2 and IGFBP-3 and estradiol receptor alpha expression in the mammary gland of dairy heifers naturally infected with gastrointestinal nematodes during development

Mammary ductal morphogenesis during prepuberty occurs mainly in response to insulin-like growth factor-1 (IGF-1) and estradiol stimulation. Dairy heifers infected with gastrointestinal nematodes have reduced IGF-1 levels, accompanied by reduced growth rate, delayed puberty onset, and lower parenchyma-stroma relationship in their mammary glands. Immunohistochemical studies were undertaken to determine variations in cell division rate, IGF-1 system components, and estradiol receptors (ESR) during peripubertal development in the mammary glands of antiparasitic-treated and untreated Holstein heifers naturally infected with gastrointestinal nematodes. Mammary biopsies were taken at 20, 30, 40, and 70 wk of age. Proliferating cell nuclear antigen immunolabeling, evident in nuclei, tended to be higher in the parenchyma of the glands from treated heifers than in those from untreated. Insulin-like growth factor binding proteins (IGFBP) type 2 and type 3 immunolabeling was cytoplasmic and was evident in stroma and parenchyma. The IGFBP2-labeled area was lower in treated than in untreated heifers. In the treated group, a maximal expression of this protein was seen at 40 wk of age, whereas in the untreated group the labeling remained constant. No differences were observed for IGFBP3 between treatment groups or during development. Immunolabeling for α ESR (ESR1) was evident in parenchymal nuclei and was higher in treated than in untreated heifers. In the treated group, ESR1 peaked at 30 wk of age and then decreased. These results demonstrate that the parasite burden in young heifers negatively influence mammary gland development, affecting cell division rate and parameters related to estradiol and IGF-1 signaling in the gland.     

Pregnancy and bovine somatotropin in nonlactating dairy cows: I. Ovarian, conceptus, and insulin-like growth factor system responses

Nonlactating dairy cows were used to examine effects of bovine somatotropin (bST) on components of the insulin-like growth factor (IGF) system. Estrus was synchronized in cows with a Presynch + Ovsynch protocol and timed AI (TAI; n = 55) or not TAI (cycling, C; n = 23) on d 0 (time of synchronized ovulation). On d 0 and 11, cows received bST (500 mg) or no bST, and were sacrificed on d 17. Pregnancy rates were less in bST cows (27.2%, 9 of 33) than in controls (63.6%; 14 of 22). In contrast, conceptuses were larger in bST-treated cows (39.2 +/- 4.8 cm) than in controls (20 +/- 4.3 cm). Total interferon-tau in uterine luminal flushings (ULF) was greater in bST-treated cows (7.15 > 2.36 microg). Number of class 2 follicles (6 to 9 mm) was less in bST-C cows on d 7 and 16. On d 17, corpus luteum (CL) weight tended to be greater in bST-treated cows. Concentrations of progesterone were greater after d 10 in C than in pregnant (P) cows. In the ULF, IGF-binding protein-3 was greater in bST-P cows than in pregnant cows. A tendency for an increase in IGF-I hormone concentrations in the ULF was detected on d 17 in bST-treated and cyclic cows. Endometrial mRNA for IGF-I, IGF-II, IGFBP-2, and IGFBP-3 increased in bST-C, but not in bST-P cows. Treatment with bST increased plasma concentrations of insulin, IGF-I, and growth hormone (GH). In conclusion, bST may have hyperstimulated plasma IGF-I and insulin to cause asynchrony between conceptus and uterus that was detrimental to pregnancy.     

Effects of parturition and feed restriction on concentrations and distribution of the insulin-like growth factor-binding proteins in plasma and cerebrospinal fluid of dairy cows

Hormones and metabolites act as satiety signals in the brain and play an important role in the control of feed intake (FI). These signals can reach the hypothalamus and brainstem, 2 major centers of FI regulation, via the blood stream or the cerebrospinal fluid (CSF). During the early lactation period of high-yielding dairy cows, the increase of FI is often insufficient. Recently, it has been demonstrated that insulin-like growth factors (IGF) may control FI. Thus, we asked in the present study if IGF-binding proteins (IGFBP) are regulated during the periparturient period and in response to feed restriction and therefore might affect FI as well. In addition, we specifically addressed conditional distribution of IGFBP in plasma and CSF. In one experiment, 10 multiparous German Holstein dairy cows were fed ad libitum and samples of CSF and plasma were obtained before morning feeding on d −20, −10, +1, +10, +20, and +40 relative to calving. In a second experiment, 7 cows in second mid-lactation were sampled for CSF and plasma after ad libitum feeding and again after feeding 50% of the previous ad libitum intake for 4 d. Intact IGFBP-2, IGFBP-3, and IGFBP-4 were detected in plasma by quantitative Western ligand blot analysis. In CSF, we were able to predominantly identify intact IGFBP-2 and a specific IGFBP-2 fragment containing detectable binding affinities for biotinylated IGF-II. Whereas plasma concentrations of IGFBP-2 and IGFBP-4 increased during the periparturient period, IGFBP-3 was unaffected over time. In CSF, concentrations of IGFBP-2, both intact and fragmented, were not affected during the periparturient period. Plasma IGF-I continuously decreased until calving but remained at a lower concentration in early lactation than in late pregnancy. Food restriction did not affect concentrations of IGF components present in plasma or CSF. We could show that the IGFBP profiles in plasma and CSF are clearly distinct and that changes in IGFBP in plasma do not simply correspond in the brain. We thus assume independent control of IGFBP distribution between plasma and CSF. Due to the known anorexic effect of IGF-I, elevated plasma concentrations of IGFBP-2 and IGFBP-4 during the postpartum period in conjunction with reduced plasma IGF-I concentrations may be interpreted as an endocrine response against negative energy balance in early lactation in dairy cows.     

Reduced insulin-like growth factor-I after acute feed restriction in lactating dairy cows is independent of changes in growth hormone receptor 1A mRNA

Growth hormone receptor (GHR) and insulin-like growth factor-I (IGF-I) mRNA decrease in the liver of dairy cows at parturition. Epinephrine is released and feed intake is decreased at the same time. The objective of this study was to determine whether feed restriction and (or) administration of epinephrine could recapitulate the changes in the hepatic GHR 1A and IGF-I mRNA that occur at parturition. Eight lactating cows were randomly assigned to one of two rations (ad libitum or restricted). The cows assigned to the restricted ration were fed 75, 60, 60, and 25% of feed consumed by the ad libitum cows on successive days to mimic the changes in feed intake around parturition. Liver samples were collected by needle biopsy before and after feed restriction. Cows received either 0.02 mg/kg of epinephrine or saline approximately 24 h before the second liver biopsy so that a 2 x 2 factorial arrangement of treatments was created. Feed restriction increased plasma nonesterified fatty acids and liver triglyceride percentages and decreased plasma IGF-I concentrations. The decrease in plasma IGF-I after feed restriction was associated with a decrease in IGF-I mRNA in feed-restricted cows. The amount of GHR 1A mRNA did not change after feed restriction. Epinephrine treatment did not affect the amount of GHR 1A or IGF-I mRNA. We conclude that the decrease in feed intake at parturition may be partially responsible for the decrease in IGF-I but may not cause the decrease in GHR 1A.     

Effects of feeding fish meal and n-3 fatty acids on milk yield and metabolic responses in early lactating dairy cows

The study was designed to test the effects of feeding fish meal (FM) and specific n-3 fatty acids on milk yield and composition, dry matter intake, plasma concentrations of metabolic hormones and metabolites, and liver triglyceride accumulation in early lactating cows. From 5 to 50 d in milk (DIM), cows were fed diets that were isonitrogenous, isoenergetic, and isolipidic containing none (control), 1.25, 2.5, or 5% menhaden FM or 2.3% Ca salts of fish oil fatty acids (CaFOFA). Milk yield (48.2, 49.8, 48.6, 53.5, and 52.2 ± 1.0 kg/d, respectively) and dry matter intake (22.7, 22.8, 23.0, 23.8, and 24.7 ± 0.5 kg/d, respectively) differed among diets. Average daily plasma glucose concentration (53.4, 55.3, 51.1, 57.6, and 57.3 ± 1.3 mg/dL, respectively) was also affected by diet, and plasma insulin concentration was increased by 5% FM and 2.3% Ca-FOFA. At 25 and 50 DIM, blood was collected before feeding and hourly for 11 h after feeding. Plasma glucose concentrations in cows during the day were similar among diets at 25 DIM, but differed at 50 DIM (54.6, 54.4, 52.4, 60.5, and 58.3 ± 1.4 mg/dL for 0, 1.25, 2.5, and 5% FM or 2.3% CaFOFA, respectively). Plasma insulin was increased in cows fed 5% FM and 2.3% CaFOFA at 25 DIM and was similar among diets at 50 DIM. Dietary treatments had no significant effect on milk composition, energy balance, or on daily plasma concentrations of nonesterified fatty acids, β-hydroxybutyrate, and urea. Plasma aspartate aminotransferase and hepatic triglyceride concentration in cows did not differ among diets at 21 DIM. Results from this experiment demonstrate that dietary supplementation with FM or n-3 polyunsaturated fatty acids in early lactating dairy cows significantly increased milk yield and DMI with no change in milk composition.     

Impact of single nucleotide polymorphisms in leptin, leptin receptor, growth hormone receptor, and diacylglycerol acyltransferase (DGAT1) gene loci on milk production, feed, and body energy traits of UK dairy cows

The impact of 9 single nucleotide polymorphisms (SNP) in the leptin (LEP), leptin receptor (LEPR), growth hormone receptor (GHR), and diacylglycerol acyltransferase (DGAT1) gene loci on daily milk production, feed intake, and feed conversion, and weekly measures of live weight, BCS, and body energy traits was evaluated using genetic and phenotypic data on 571 Holstein cows raised at the Langhill Dairy Cattle Research Center in Scotland. Six SNP were typed on the LEP gene and 1 on each of the other 3 loci. Of the 6 LEP SNP, 3 were in very high linkage disequilibrium, meaning there is little gain in typing all of them in the future. Seven LEP haplotypes were identified by parsimony-based analyses. Random-regression allele-substitution models were used to assess the impact of each SNP allele or haplotype on the traits of interest. Diacylglycerol acyltransferase had a significant effect on milk yield, whereas GHR significantly affected feed intake, feed conversion, and body energy traits. There was also evidence of dominance in allelic effects on milk yield and BCS. The LEP haplotype CCGTTT (corresponding to leptin SNP C207T, C528T, A1457G, C963T, A252T, and C305T, respectively) significantly affected milk yield and feed and dry matter intake. Animals carrying this haplotype produced 3.13 kg more milk daily and consumed 4.64 kg more feed. Furthermore, they tended to preserve more energy than average. Such results may be used to facilitate genetic selection in animal breeding programs.     

The effects of dairy processes and storage on insulin-like growth factor-I (IGF-I) content in milk and in model IGF-I-fortified dairy products

The effects of several dairy processes on insulin-like growth factor-I (IGF-I) concentrations in milk and the storage stability of IGF-I-fortified dairy products were examined. The IGF-I content in raw milk determined by radioimmunoassay was significantly changed by the strength of heat treatments. In commercial manufacture of whole milk dry powder, IGF-I concentration was not significantly changed. A significant reduction in IGF-I content was found as the result of fermentation with a commercial starter culture. The IGF-I content in fortified milk and dried milk powder exhibited no significant changes over the tested storage periods (12 d for milk, 4 wk for dried milk powder), but the IGF-I content in the yogurt decreased significantly during storage. The use of IGF-I was varied by lactic strains and was apparent in the viable cells. When IGF-I was encapsulated using the surface-reforming process, the remaining IGF-I content after fermentation was significantly higher compared with that of the untreated control. Therefore, enteric coating of IGF-I before fermentation might be an effective method for the prevention of IGF-I degradation during fermentation.     

Effects of an enhanced vitamin A intake during the dry period on retinoids, lactoferrin, IGF system, mammary gland epithelial cell apoptosis, and subsequent lactation in dairy cows

Studies in vitro show important interactions among vitamin A, lactoferrin, and insulin-like growth factor (IGF) binding proteins (IGFBP) and, thus, the IGF system. As a consequence, mammary gland epithelial cell proliferation and apoptosis during the bovine dry period and potential milk yield may be affected. We have studied effects of feeding vitamin A (550,000 IU/ d) that exceed daily requirements about 8-fold for up to 2 mo to dairy cows during the dry period on concentrations of retinol and its metabolites in plasma and milk, milk lactoferrin, plasma and milk IGF-I and IGFBP-3, lactoferrin and IGF-I mRNA levels in mammary gland tissue, mammary gland apoptosis, and 100-d milk yield in the ensuing lactation. In the group supplemented with vitamin A, the peripartal decrease of plasma retinol was delayed and attenuated, and colostral retinol plus retinylester concentration was enhanced, but colostral beta-carotene concentration decreased. The retinoic acid isomer 9,13-dicis retinoic acid that coeluted with 13-cis retinoic acid, was the predominant circulating retinoic acid and was higher in GrA than the control group. Plasma IGFBP-3 concentrations were positively correlated with plasma retinol concentrations (r = 0.51), but there were no group differences. Numbers of apoptotic epithelial cells in mammary epithelium were higher at drying off and parturition than in the middle of the dry period, coinciding with high concentrations of IGF-I and lactoferrin in mammary secretions. At parturition, numbers of apoptotic cells in mammary gland biopsies in cows supplemented with vitamin A were higher than in control cows. In conclusion, supplementation of dairy cows during the dry period with high amounts of vitamin A did not significantly modify concentrations of lactoferrin, IGFBP-3, and IGF-I in plasma and in mammary secretions, but slightly decreased energy-corrected 100-d milk yield and milk fat yield, possibly because of enhanced apoptic rates of mammary cells.     

pH值对牛初乳中胰岛素样生因子-1(IGF-1)分离纯化的影响

通过搅拌式超滤器对牛初乳中的IGF-1超滤粗提，制备IGF-1的粗提物。对超滤条件的研究发现，在pH值为8．0碱性条件下的IGF-1回收率比在pH值为4．2酸性条件下高,将超滤后的粗提物分别用SDS-PAGE电泳检测，来验证每步骤的提纯效果,再将浓缩后的IGF-1粗提物用葡聚糖G-200柱层析进一步分离纯化，得到IGF-1纯品,每一步骤的IGF-1质量浓度利用放射免疫测定法（RIA）测定。     

Effect of human growth hormone-releasing factor (1-29)NH2 on growth hormone release and milk production in dairy cows

Twelve cows (209 d in lactation, 642 kg BW) were used in an experiment conducted over four 10-d periods (one preinjection, one injection, and two postinjection). Gelatine (n = 6) or 10 mg of growth hormone-releasing factor in gelatine (n = 6) was injected subcutaneously at 1000 h every day on d 11 to 20. Data were averaged for the last 5 d of each period. During the injection period, milk, fat, and protein yields increased by 3 kg.d-1 (14.3%), .14 kg.d-1 (16.7%), and .12 kg.d-1 (15.4%), respectively. Moreover, milk, fat, and protein yields for the treated cows remained higher than for the control cows until the last postinjection period. Growth hormone response was evaluated from blood samples withdrawn from 2 h prior to 8 h postinjection on d 11, 15, and 20 and on d 40. After growth hormone-releasing factor injection, peaks and area under the curve were 24.5, 30.8, and 47.0 ng.ml-1 and 2475, 3979, and 3741 ng.ml-1.min-1 on d 11, 15, and 20, respectively. On d 40, there was no difference in growth hormone concentrations in blood between control and treated cows. These results demonstrate that 10 d of daily injection of a growth hormone-releasing factor increases milk production by 14.3% (3 kg.d-1) and still induces growth hormone release at the end of the injection period without any sign of refractoriness.