Chronic inflammation decreases arcuate kisspeptin expression in male sheep.

Lipopolysaccharide (LPS) from Gram-negative bacteria induces an immune response and impairs reproduction through suppression of gonadotropin releasing hormone (GnRH), subsequently luteinizing hormone (LH) secretion. While there is evidence that acute inflammation inhibits kisspeptin, little is known about the impact of chronic inflammation on this key reproductive neuropeptide in livestock species. Thus, we sought to examine a central mechanism whereby LPS suppresses LH secretion in sheep. Twenty wethers were randomly assigned to one of five treatment groups: control (CON; n=4), single acute IV LPS dose (SAD; n=4), daily acute IV LPS dose (DAD; n=4), daily increasing IV LPS dose (DID; n=4), and chronic subcutaneous LPS dose (CSD; n=4). On Days 1 and 7, blood samples were collected every 12 minutes for 360 minutes using jugular venipuncture. Following blood collection on Day 7, all animals were euthanized, brain tissue was perfused with 4% paraformaldehyde, and hypothalamic blocks were removed and processed for immunohistochemistry. On Day 1, LH pulse frequency was significantly lower (p=0.02) in SAD (0.25 ± 0.1 pulses/hour), DAD (0.25 ± 0.1 pulses/hour), DID (0.35 ± 0.1 pulses/hour), and CSD (0.40 ± 0.1 pulses/hour) compared to CON (0.70 ±0.1 pulses/hour). On Day 7, only DID animals (0.35 ± 0.1 pulses/hour) had significantly lower (p=0.049) LH pulse frequency compared to controls (0.85 ± 0.1 pulse/hour). Furthermore, only DID animals (33.3 ± 10.9 cells/section/animal) had significantly fewer (p=0.001) kisspeptin-immunopositive cells compared to controls (82.6 ± 13.6 cells/section/animal). Taken together, we suggest that daily increasing doses of LPS is a powerful inhibitor of kisspeptin neurons in young male sheep and a physiologically relevant model to examine the impact of chronic inflammation on the reproductive axis in livestock.

Acute-phase protein α-1-acid glycoprotein is negatively associated with feed intake in postpartum dairy cows.

α-1-Acid glycoprotein (AGP) is an acute-phase protein that may suppress dry matter intake (DMI), potentially by acting on the leptin receptor in the hypothalamus. Our objectives were to characterize plasma AGP concentration and associations with DMI during the transition period, and to determine the utility of AGP to identify or predict cows with low DMI. Plasma samples (n = 2,086) from 434 Holstein cows in 6 studies were analyzed on d -21, -13 ± 2, -3, 1, 3, 7 ± 1, 14 ± 1, and 21 ± 1 relative to parturition. A commercially available ELISA kit specific for bovine AGP was validated, and 2 internal controls were analyzed on each plate with interplate variation of 15.0 and 17.3%, respectively. Bivariate analysis was used to assess the relationship between AGP and DMI. For significant associations, treatment(study) was added to the model, and quadratic associations were included in the model if significant. Plasma AGP concentration (±SEM) increased from 213 ± 37.3 µg/mL on d -3 to 445 ± 60.0 µg/mL on d 14. On d 3, AGP was associated negatively with DMI in a quadratic manner for wk 1 and wk 2 and linearly for wk 3. Day 7 AGP was associated negatively with DMI in a quadratic manner for wk 2 and linearly for wk 3. Similarly, d 14 AGP was negatively associated with DMI for wk 3 and wk 4. As d 3 AGP concentration increased over the interquartile range, a calculated 1.4 (8.5%), 0.5 (2.7%), and 0.4 (1.9%) kg/d reduction in predicted DMI was detected during wk 1, 2, and 3, respectively. Using bivariate analysis, d 3 AGP explained 10% of the variation in DMI during wk 1. We explored the clinical utility of d 3 AGP to diagnose low DMI, defined as wk 1 DMI >1 standard deviation below the mean. Receiver operating characteristic analysis identified a threshold of 480.9 µg/mL, providing 76% specificity and 48% sensitivity (area under the curve = 0.60). Limited associations occurred between AGP and blood biomarkers; however, AGP was associated with plasma haptoglobin concentration postpartum and incidence of displaced abomasum, retained placenta, and metritis. These results demonstrate a negative association between plasma AGP concentration and DMI in early-postpartum dairy cows, although its diagnostic performance was marginal. Further investigation into whether AGP directly suppresses DMI in dairy cattle is warranted.

Acute and subacute effects of a synthetic kisspeptin analog, C6, on serum concentrations of luteinizing hormone, follicle stimulating hormone, and testosterone in prepubertal bull calves.

Kisspeptin (KP) is a neuropeptide integral in regulating puberty and gonadotropin releasing hormone. Compound 6 (C6), a KP analog, is more potent in vitro, has a longer half-life, and may have greater therapeutic applications than KP. To determine the acute and subacute effects of KP and C6 on serum concentrations of luteinizing hormone (LH), follicle stimulating hormones (FSH), and testosterone (T), prepubertal bull calves [12.1 ±â€¯1.1 (SD) weeks of age; 91.2 ±â€¯10.8 kg BW] were assigned to one of three treatment groups [Saline (n = 4), KP (n = 4; 20 nmoles), or C6 (n = 4; 20 nmoles). Treatments were administered intramuscularly once daily for four consecutive days. Blood samples were collected every 15 min for 6 h immediately following treatment administration on Day 1 (acute) and Day 4 (subacute). Serum concentrations of LH, FSH, and T were determined by radioimmunoassay. For each day, effects of treatment, time, and interactions on LH and FSH concentrations and pulse parameters were analyzed using procedures for repeated measures with JMP Software (SAS Inst. Inc., Cary, NC). There was a treatment × time interaction during Day 1 (P < 0.0001) and Day 4 (P = 0.02) such that LH concentrations were greatest following administration of C6 (albeit diminished during Day 4). Number of LH pulses were least (P = 0.02) and LH nadirs were highest (P = 0.04) following administration of C6 (P = 0.02). There was no effect of treatment (P = 0.95) or treatment × time interaction (P = 0.10) on serum FSH concentrations during Day 1. During Day 4 FSH concentrations (P = 0.02) and number of FSH pulses (P = 0.02) were least following administration of C6. There was no effect of treatment (P = 0.33), time (P = 0.19) or treatment × time interaction (P = 0.44) on T concentrations. In conclusion, acute and subacute C6 increased LH concentrations and subacute C6 decreased FSH concentrations and pulse parameters. Despite suppression of FSH with subacute daily administration of C6, altered frequency and timing of treatment with KP analogs may have application to affect the onset of puberty in livestock.

Effect of maternal exercise on calf dry matter intake, weight gain, behavior, and cortisol concentrations at disbudding and weaning.

The objective of this study was to determine the effect of maternal physical activity during late gestation on calf dry matter intake, weight gain, behavior, and cortisol concentration during disbudding and weaning. Fifty-five Holstein and 5 Jersey × Holstein crossbred calves were enrolled into the study during gestation. Calves were born from pregnant, nonlactating Holstein (n = 58) and Jersey × Holstein crossbred (n = 2) dairy cows. Cows were assigned to either confinement (n = 20 cows; 13 female calves, 7 male calves), exercise (n = 20 cows; 8 female calves, 12 male calves), or pasture (n = 20 cows; 11 female calves, 9 male calves) treatments at dry-off from January to November 2015. Enrollment in treatment was balanced by parity (1.8 ± 0.9), projected mature-equivalent fat-corrected milk (13,831 ± 2,028 kg/lactation), dam breed, and projected calving date. Cows assigned to confinement remained in the pen throughout the dry period. Cows assigned to exercise were walked 5 times/wk at a targeted 1.5 h at 3.25 km/h. Cows assigned to pasture were turned out 5 times/wk for a targeted 1.5 h/d. Treatments were terminated on the expected due date or at signs of calving. Calves were removed from cows immediately once observed by farm staff and subsequently weighed and moved into a straw deep-bedded hutch. Data loggers were attached to the rear fetlock of each calf -3 d to +6 d relative to disbudding and weaning to monitor changes in lying behavior. Calves were weighed on d -7, -5, -3, -1, 0, 1, 3, 5, and 7, and grain was weighed the 7 d preceding and following disbudding and weaning. Blood was collected 24 h before and 0, 1, and 4 h after disbudding and d -1, 0, 1, and 2 relative to weaning to determine cortisol concentrations. Data were analyzed using mixed linear model in SAS (SAS Institute Inc., Cary, NC). Calf weight gain decreased the day after disbudding and calves tended to have elevated cortisol concentrations 1 h after disbudding, regardless of maternal treatment. Calf weight gain decreased the day of and after weaning; calves had elevated cortisol concentrations the day after weaning, regardless of treatment. Behavior did not differ by treatment at disbudding, but calves from pasture cows lay down for less time compared with confinement and exercise maternal treatments and less frequently than exercise maternal treatments at weaning. More research investigating the significance of lying time and restlessness around stressful events is needed to further understand the implications of such behavioral responses.

Rumen-protected arginine alters blood flow parameters and luteinizing hormone concentration in cyclic beef cows consuming toxic endophyte-infected tall fescue seed.

The objective of this study was to determine the effect of rumen-protected arginine on median caudal artery blood flow and LH dynamics in cows fed toxic endophyte-infected tall fescue seed. Four ruminally cannulated nonlactating beef cows (539 ± 30 kg) were used in a 2 × 2 factorial arrangement of treatments utilizing a 4 × 4 Latin square design with 4 periods of 31 d each. Each cow was assigned to individual pens and fed orchardgrass hay (10.3% CP and 85% NDF; OM basis) during a 10-d adaptation period, followed by a 21-d collection period in which each cow was assigned 1 of 4 treatments: 1) rumen-protected Arg (180 mg/kg of BW) and 1.0 kg/d of toxic endophyte-infected fescue seed (AE+), 2) rumen-protected Arg (180 mg/kg of BW) and 1.0 kg/d of endophyte-free fescue seed (AE-), 3) 1.0 kg/d of toxic endophyte-infected fescue seed (E+) alone, or 4) 1.0 kg/d of endophyte-free fescue seed (E-) alone. In each period, Doppler ultrasound measurements for blood flow parameters were quantified on d 1, 5, 10, 15, and 20. On d 20 of each period, blood samples were collected every 10 min for 6 h and then once every hour for 12 h for LH response following exogenous GnRH. There was an Arg × fescue seed type interaction ( = 0.05) for median caudal artery blood flow due to an increase in blood flow in cows fed rumen-protected Arg with endophyte-free fescue seed. In addition, mean blood flow velocity in the artery was greater ( = 0.01) with the inclusion of rumen-protected Arg in the diet. Median caudal artery area ( = 0.03) and diameter ( = 0.01) were decreased in cows consuming E+ compared to those consuming E- with no effect ( ≥ 0.38) by Arg inclusion. Circulating nitric oxide (NO) concentrations tended to be influenced ( = 0.09) by the interaction of Arg × fescue seed type with E+ alone decreasing NO concentrations. Circulating NO concentrations were unaffected by rumen-protected Arg ( = 0.48). Mean serum LH concentration exhibited ( = 0.02) an Arg × fescue seed type interaction. Cows consuming E+ had decreased ( < 0.05) LH concentrations compared to all other treatments. However, cows consuming AE+ had ( ≥ 0.67) LH concentrations similar to those of cows consuming AE- and E-. Thus, supplementing rumen-protected Arg to cows consuming toxic endophyte-infected fescue seed has the potential to increase reproductive performance and peripheral blood flow.

Leukemia inhibitory factor as a mediator of lipopolysaccharide effects on appetite and selected hormones and metabolites.

Leukemia inhibitory factor (LIF) has been suggested to function as a potent inhibitor of feed intake in rodents. In sheep, intravenous injection of lipopolysaccharide (LPS) resulted in an increase in gene expression for LIF in the arcuate nucleus ( < 0.01). In the same experiment, agouti related protein (AgRP) expression was elevated ( < 0.05) but there were no effects on proopiomelanocortin expression. Another group of sheep were provided intracerebroventricular (ICV) injections of LIF at 250, 500, 1,000, and 2,500 ng per sheep. Cumulative feed intake was inhibited by the 1,000- and 2,500-ng doses at 8 and 10 h after ICV injection ( < 0.03). All doses of LIF elevated temperature above 40°C, indicating a fever. When AgRP was intracerebroventricularly injected before LIF, there was no effect of LIF to reduce feed intake, suggesting the LIF inhibition of feed intake is consistent with the concept that the effect is mediated by the melanocortin-4 receptor. In an experiment to determine whether endocrine and metabolic effects of LIF were similar to reported effects of LPS, sheep were intracerebroventricularly injected with 2,500 ng LIF, and blood samples were collected at 10-min intervals for 6 h for assay of LH, samples from the first 3 h were assayed for GH, and samples at 30-min intervals were assayed for glucose and free fatty acids. The effect of treatment and treatment × time interaction was significant, indicating elevated plasma free fatty acids ( < 0.03 and < 0.001, respectively) and glucose ( < 0.01 and < 0.0001, respectively). There was also a treatment × time interaction on circulating concentrations of LH such that LIF caused LH to decrease ( < 0.0001). Additionally, there was a tendency for LIF treatment to increase circulating concentrations of GH (P = 0.0874). The effects of LIF on feed intake and other parameters was similar to the effects of LPS and leads to a hypothesis that LIF expression in response to LPS may be a component of the mechanism for feed intake inhibition and perhaps for changes in selected hormone and metabolites in disease models.

Bulls grazing Kentucky 31 tall fescue exhibit impaired growth, semen quality, and decreased semen freezing potential.

Serum prolactin (PRL) and testosterone concentrations, body weight, body composition, semen quality, and semen freezing potential for bulls grazing the toxic tall fescue (Lolium arundinaceum [Schreb.] Darbysh. = Schedonorous arundinaceum [Schreb.] Dumort.) cultivar Kentucky 31 (E+) compared with a novel endophyte cultivar lacking ergot alkaloids (E-) were evaluated. Angus bulls were allotted to treatment (Day 0) and grazed E+ or E- for 155 days. Treatment-by-day interaction was significant (P < 0.05) for serum PRL concentrations with E+treated bulls exhibiting reduced PRL values compared with E- control bulls, but no differences were observed for serum testosterone concentrations (P > 0.05). Further, bulls on the E+ treatment exhibited decreased total gain, average daily gain, and body weight by Day 140 (P < 0.05) compared with the E- bulls. Rump muscle depth was lower because the treatment in bulls grazing E+ compared with E- (P < 0.05) and intramuscular fat in the E- bulls compared with the E+ group was higher by Day 155 (P < 0.05). Analysis of ejaculates showed significant treatment × day effects for sperm concentration with lower values observed for bulls on the E+ treatment (P < 0.05). The percent normal morphology was reduced in ejaculates from E+ bulls compared with E- bulls (P < 0.05), and the difference was due to an increase in abnormal sperm present in the E+ ejaculates from Day 84 to 140 (P < 0.05). In addition, spermatozoa motility and progressive motility were decreased on thawing in semen samples from E+ bulls compared with E- bulls (P < 0.05).

Effect of the first GnRH and two doses of PGF2α in a 5-day progesterone-based CO-Synch protocol on heifer pregnancy.

The objectives were (1) to determine the effects of gonadorelin hydrochloride (GnRH) injection at controlled internal drug release (CIDR) insertion on Day 0 and the number of PGF2α doses at CIDR removal on Day 5 in a 5-day CO-Synch + CIDR program on pregnancy rate (PR) to artificial insemination (AI) in heifers; (2) to examine how the effect of systemic concentration of progesterone and size of follicles influenced treatment outcome. Angus cross beef heifers (n = 1018) at eight locations and Holstein dairy heifers (n = 1137) at 15 locations were included in this study. On Day 0, heifers were body condition scored (BCS), and received a CIDR. Within farms, heifers were randomly divided into two groups: at the time of CIDR insertion, the GnRH group received 100 µg of GnRH and No-GnRH group received none. On Day 5, all heifers received 25 mg of PGF2α at the time of CIDR insert removal. The GnRH and No-GnRH groups were further divided into 1PGF and 2PGF groups. The heifers in 2PGF group received a second dose of PGF2α 6 hours after the administration of the first dose. Beef heifers underwent AI at 56 hours and dairy heifers at 72 hours after CIDR removal and received 100 µg of GnRH at the time of AI. Pregnancy was determined approximately at 35 and/or 70 days after AI. Controlling for herd effect (P < 0.06), the treatments had significant effect on AI pregnancy in beef heifers (P = 0.03). The AI-PRs were 50.3%, 50.2%, 59.7%, and 58.3% for No-GnRH + PGF + GnRH, No-GnRH + 2PGF + GnRH, GnRH + PGF + GnRH, and GnRH + 2PGF + GnRH groups, respectively. The AI-PRs were ranged from 50% to 62.4% between herds. Controlling for herd effects (P < 0.01) and for BCS (P < 0.05), the AI pregnancy was not different among the treatment groups in dairy heifers (P > 0.05). The AI-PRs were 51.2%, 51.9%, 53.9%, and 54.5% for No-GnRH + PGF + GnRH, No-GnRH + 2PGF + GnRH, GnRH + PGF + GnRH, and GnRH + 2PGF + GnRH groups, respectively. The AI-PR varied among locations from 48.3% to 75.0%. The AI-PR was 43.5%, 50.4%, and 64.2% for 2.5 or less, 2.75 to 3.5, and greater than 3.5 BCS categories. Numerically higher AI-PRs were observed in beef and dairy heifers that exhibited high progesterone concentrations at the time of CIDR insertion (>1 ng/mL, with a CL). In addition, numerically higher AI-PRs were also observed in heifers receiving CIDR + GnRH with both high and low progesterone concentration (<1 ng/mL) initially compared with heifers receiving a CIDR only with low progesterone. In dairy heifers, there were no differences in the pregnancy loss between 35 and 70 days post-AI among the treatment groups (P > 0.1). In conclusion, GnRH administration at the time of CIDR insertion is advantageous in beef heifers, but not in dairy heifers, to improve AI-PR in the 5-day CIDR + CO-Synch protocol. In addition, in this study, both dairy heifers that received either one or two PGF2α doses at CIDR removal resulted in similar AI-PR in this study regardless of whether they received GnRH at CIDR insertion.

Hypothalamic integration of nutrient status and reproduction in the sheep.

Nutrient availability is a determinant of reproductive success. It is well known that inadequate nutrition results in reproductive failure due to a number of factors including delay of puberty or anoestrous in post-pubertal animals. The lack of nutrients is detected primarily by changes in circulating nutrient molecules and hormones and communicated directly or indirectly to the hypothalamus and brain stem for integration. The general effect is that low nutrition leads to increased appetite stimulation and reduced reproductive performance. When nutrition is adequate, the reverse is true. Both aspects will be the focus of this review. One result of the lack of nutrients is a reduction in luteinizing hormone (LH) concentrations and pulse frequency. Nutrient signals, such as glucose availability, hormonal signals, such as insulin and leptin, and neuroendocrine signals, such as neuropeptide Y and corticotropin-releasing hormone, have been clearly demonstrated to interact to produce changes in LH and reproductive success. Other signals, such as fatty acids, ghrelin, agouti-related peptide, melanin-concentrating hormone, orexin, melanocyte-stimulating hormone, kisspeptin, neurokinin, dynorphin and gonadotropin inhibitory hormone may also play a role in integrating nutrition and reproduction. This review will focus on the major features of the reciprocal control of appetite and reproduction in sheep.

Electroejaculation increased vocalization and plasma concentrations of cortisol and progesterone, but not substance P, in beef bulls.

Electroejaculation is a reliable method of obtaining a semen sample for a bull breeding soundness examination, but is sometimes regarded as painful. Substance P is a neuropeptide involved in the integration of pain, stress, and anxiety. We hypothesized that substance P is a measure of pain in bulls following electroejaculation. The specific objective was to compare vocalization and plasma concentrations of cortisol, progesterone, and substance P immunoreactivity in bulls following electroejaculation. Nine Angus bulls (501.9 ± 14.3 kg) were used. Blood samples were collected at -60, -30, 0, 2, 10, 20, 30, 45, 60, 75, 90, 120 min relative to treatment. At Time 0, bulls were subject to electroejaculation, rectal probe insertion without electroejaculation, or no manipulation. Treatments were administered contemporaneously to three bulls. Treatments were repeated weekly until each bull had received each treatment in a 3 × 3 Latin square design. More bulls (P = 0.0147) in the electroejaculation group vocalized (5 of 9 bulls; 55.6%) when compared to controls (0 of 9 bulls; 0%). Mean plasma cortisol and progesterone concentration following electroejaculation in bulls were higher (P < 0.05) than concentrations in probed and control bulls through the 45 min sample. However, mean plasma substance P concentration following electroejaculation in bulls (77.2 ± 17.2 pg/mL) was not different (P = 0.6264) from probed (79.1 ± 17.2 pg/mL) or control bulls (93.4 ± 17.2 pg/mL). A significant increase in vocalization and plasma cortisol and progesterone concentrations in bulls following electroejaculation was likely owing to acute stress. However, the lack of a difference in plasma concentrations of substance P after electroejaculation was interpreted as a lack of pain associated with nociception.

Triennial Growth Symposium: neural regulation of feed intake: modification by hormones, fasting, and disease.

Appetite is a complex process that results from the integration of multiple signals at the hypothalamus. The hypothalamus receives neural signals; hormonal signals such as leptin, cholecystokinin, and ghrelin; and nutrient signals such as glucose, FFA, AA, and VFA. This effect is processed by a specific sequence of neurotransmitters beginning with the arcuate nucleus and orexigenic cells containing neuropeptide Y or agouti-related protein and anorexigenic cells containing proopiomelanocortin (yielding the neurotransmitter α-melanocyte-stimulating hormone) or cells expressing cocaine amphetamine-related transcript. These so-called first-order neurons act on second-order orexigenic neurons (containing either melanin-concentrating hormone or orexin) or act on anorexigenic neurons (e.g., expressing corticotropin-releasing hormone) to alter feed intake. In addition, satiety signals from the liver and gastrointestinal tract signal through the vagus nerve to the nucleus tractus solitarius to cause meal termination, and in combination with the hypothalamus, integrate the various signals to determine the feeding response. The activities of these neuronal pathways are also influenced by numerous factors such as nutrients, fasting, and disease to modify appetite and hence affect growth and reproduction. This review will begin with the central nervous system pathways and then discuss the ways in which hormones and metabolites may alter the process to affect feed intake with emphasis on farm animals.

Interaction of kisspeptin and the somatotropic axis.

Kisspeptin, a regulator of gonadotropin-releasing hormone, has been hypothesized as an integrator of nutrition and hormones critical to metabolism and the regulation of reproduction. Growth hormone (GH) is necessary for optimal reproduction and recent evidence suggests that its secretion may be influenced by kisspeptin. The objectives of this study were to determine whether the effect of kisspeptin to stimulate GH release is due to an interaction with growth hormone-releasing hormone (GHRH) or somatostatin (SS), or an effect at the hypothalamus. Intravenous injection and infusion of kisspeptin [500 pmol/kg BW (650 ng/kg)/h × 5 h] to cows (n = 5) increased serum concentrations of luteinizing hormone (LH) but not GH. Pretreatment with kisspeptin injection and infusion in cows (n = 5) reduced the stimulatory effect of GHRH (0.05 µg/kg BW) on GH secretion. However, the magnitude of the GH response to GHRH (assessed by incremental AUC) was not affected by kisspeptin. In these same cows, administration of kisspeptin prevented the increase in GH induced by SS infusion (0.5 µg/kg BW/ h × 1.5 h) withdrawal. Peripheral administration of kisspeptin [200 and 1,000 pmol/kg BW (260 and 1,300 ng/kg)] increased serum concentrations of LH but not GH in ewes (n = 8). However, concentrations of GH were stimulated by central kisspeptin treatment [100 and 200 pmol/kg BW (130 and 260 ng/kg)] in ewes. In addition to activating the gonadotropic axis, kisspeptin can activate the somatotropic axis in ruminants. Present data support the concept of a central site of action for this effect.

Selected hormonal and neurotransmitter mechanisms regulating feed intake in sheep.

Appetite control is a major issue in normal growth and in suboptimal growth performance settings. A number of hormones, in particular leptin, activate or inhibit orexigenic or anorexigenic neurotransmitters within the arcuate nucleus of the hypothalamus, where feed intake regulation is integrated. Examples of appetite regulatory neurotransmitters are the stimulatory neurotransmitters neuropeptide Y (NPY), agouti-related protein (AgRP), orexin and melanin-concentrating hormone and the inhibitory neurotransmitter, melanocyte-stimulating hormone (MSH). Examination of messenger RNA (using in situ hybridization and real-time PCR) and proteins (using immunohistochemistry) for these neurotransmitters in ruminants has indicated that physiological regulation occurs in response to fasting for several of these critical genes and proteins, especially AgRP and NPY. Moreover, intracerebroventricular injection of each of the four stimulatory neurotransmitters can increase feed intake in sheep and may also regulate either growth hormone, luteinizing hormone, cortisol or other hormones. In contrast, both leptin and MSH are inhibitory to feed intake in ruminants. Interestingly, the natural melanocortin-4 receptor (MC4R) antagonist, AgRP, as well as NPY can prevent the inhibition of feed intake after injection of endotoxin (to model disease suppression of appetite). Thus, knowledge of the mechanisms regulating feed intake in the hypothalamus may lead to mechanisms to increase feed intake in normal growing animals and prevent the wasting effects of severe disease in animals.

Comparative aspects of the endotoxin- and cytokine-induced endocrine cascade influencing neuroendocrine control of growth and reproduction in farm animals.

Disease in animals is a well-known inhibitor of growth and reproduction. Earlier studies were initiated to determine the effects of endotoxin on pituitary hormone secretion. These studies found that in sheep, growth hormone (GH) concentration was elevated, whereas insulin-like growth factor-I (IGF-I) was inhibited, as was luteinizing hormone (LH). Examination of the site of action of endotoxin in sheep determined that somatotropes expressed the endotoxin receptor (CD14) and that both endotoxin and interleukin-I beta activated GH secretion directly from the pituitary. In the face of elevated GH, there is a reduction of IGF-I in all species examined. As GH cannot activate IGF-I release during disease, there appears to be a downregulation of GH signalling at the liver, perhaps related to altered nitration of Janus kinase (JAK). In contrast to GH downregulation, LH release is inhibited at the level of the hypothalamus. New insights have been gained in determining the mechanisms by which disease perturbs growth and reproduction, particularly with regard to nitration of critical control pathways, with this perhaps serving as a novel mechanism central to lipopolysaccharide suppression of all signalling pathways. This pathway-based analysis is critical to the developing novel strategies to reverse the detrimental effect of disease on animal production.

Heritable bovine fetal abnormalities.

The etiologies for congenital bovine fetal anomalies can be divided into heritable, toxic, nutritional, and infectious categories. Although uncommon in most herds, inherited congenital anomalies are probably present in all breeds of cattle and propagated as a result of specific trait selection that inadvertently results in propagation of the defect. In some herds, the occurrence of inherited anomalies has become frequent, and economically important. Anomalous traits can affect animals in a range of ways, some being lethal or requiring euthanasia on humane grounds, others altering structure, function, or performance of affected animals. Veterinary practitioners should be aware of the potential for inherited defects, and be prepared to investigate and report animals exhibiting abnormal characteristics. This review will discuss the morphologic characteristics, mode of inheritance, breeding lines affected, and the availability of genetic testing for selected heritable bovine fetal abnormalities.

Pregnancy-associated glycoproteins and pregnancy wastage in cattle.

Accurate diagnosis of non-pregnancy and prompt re-enlistment of "non-pregnant" cattle into an appropriate breeding protocol are essential components of successful reproductive programs. Various methods aimed at improving detection of pregnancy and identification of non-pregnant cows earlier and more accurately are the focus of previous review articles and beyond the scope of this manuscript. Recently, the ability to measure pregnancy-associated glycoproteins (PAGs) in cattle has changed how pregnancy and, more importantly, non-pregnancy are detected. This presentation provides an overview of current research on the pregnancy-associated glycoprotein family, and how these glycoproteins might be utilized as indicators of pregnancy wastage in cattle.

Central role of the melanocortin-4 receptors in appetite regulation after endotoxin.

Melanocortin-4 receptors (MC4R) are key factors in the depression of appetite during disease. This study was designed to determine the role of agouti-related protein (AgRP) in the effect of endotoxin (lipopolysaccharide, LPS) on appetite. Sheep received an intracerebroventricular injection of either saline or AgRP (0.5 nmol/kg of BW) 1 h before intravenous injection of either saline or LPS (0.6 microg/kg of BW) at time 0 and again at 4 h. Agouti-related protein prevented the reduction in feed intake due to LPS (P < 0.05). In a second experiment, AgRP gene expression was unaffected at 3 h and increased (P < 0.01) at 6 h after LPS. Immunohistochemical evidence indicated that there was an increase in the percentage of AgRP neurons with c-Fos immunoreactive nuclei 6 h after sheep were injected with LPS (P < 0.04) and a corresponding decrease in a-melanocyte-stimulating hormone neurons coexpressing c-Fos (P < 0.001). In situ hybridization provided evidence for an increase in AgRP gene expression and a decrease in proopiomelanocortin gene expression 6 h after LPS (P < 0.05). In a final experiment, physiological elevation of orexigenic agents by short-term fasting kept feed intake at the same level as controls, in spite of the presence of LPS, similar to the effects of AgRP in Exp. 1. The AgRP inhibition of the MC4R prevents appetite inhibition in response to LPS and well after LPS inhibition of feed intake, both AgRP and a-melanocyte-stimulating hormone may change in a pattern that favors appetite increases. These studies support the notion of the MC4R as a critical component of the mechanism for appetite suppression due to endotoxin.

Long-term feed intake regulation in sheep is mediated by opioid receptors.

These experiments were conducted to determine if 1) syndyphalin-33 (SD33), a mu-opioid receptor ligand, affects feed intake; 2) SD33 effects on feed intake are mediated by actions on opioid receptors; and 3) its activity can counteract the reduction in feed intake associated with administration of bacterial endotoxin. In Exp. 1, 5 mixed-breed, castrate male sheep were housed indoors in individual pens. Animals had ad libitum access to water and concentrate feed. Saline (SAL; 0.9% NaCl) or SD33 (0.05 or 0.1 micromol/kg of BW) was injected i.v., and feed intake was determined at 2, 4, 6, 8, 24, and 48 h after the i.v. injections. Both doses of SD33 increased (at least P < 0.01) feed intake at 48 h relative to saline. In Exp. 2, SAL + SAL, SAL + SD33 (0.1 micromol/kg of BW), naloxone (NAL; 1 mg/kg of BW) + SAL, and NAL + SD33 were injected i.v. Food intake was determined as in Exp. 1. The SAL + SD33 treatment increased (P = 0.022) feed intake at 48 h relative to SAL + SAL. The NAL + SAL treatment reduced (at least P < 0.01) feed intake at 4, 6, 8, 24, and 48 h, whereas the combination of NAL and SD33 did not reduce feed intake at 24 (P = 0.969) or 48 h (P = 0.076) relative to the saline-treated sheep. In Exp. 3, sheep received 1 of 4 treatments: SAL + SAL, SAL + 0.1 micromol of SD33/kg of BW, 0.1 microg of lipopolysaccharide (LPS)/kg of BW + SAL, or LPS + SD33, and feed intake was monitored as in Exp. 1. Lipopolysaccharide suppressed cumulative feed intake for 48 h (P < 0.01) relative to saline control, but SD33 failed to reverse the reduction in feed intake during this period. These data indicate that SD33 increases feed intake in sheep after i.v. injection, and its effects are mediated via opioid receptors. However, the LPS-induced suppression in feed intake cannot be overcome by the opioid receptor ligand, SD33.

Interleukin-1beta and tumor necrosis factor-alpha mediation of endotoxin action on growth hormone.

In humans and sheep, endotoxin (LPS) administration results in increased growth hormone (GH) concentrations. To determine the role of cytokines in the effect of LPS on GH, sheep were challenged with IL-1beta or TNF-alpha. GH data were compared with results with LH, where the major effects of LPS are known to act via the hypothalamus. Intracerebroventricular (icv) administration of IL-1beta or TNF-alpha did not alter plasma concentrations of GH. Endotoxin was then administered intravenously (iv) in combination with icv injection of IL-1 receptor antagonist (IL-1RA), TNF antagonist (sTNF-R1), or saline. Administration of LPS increased GH (P < 0.0001), although coadministration of IL-1ra or sTNF-R1 icv did not alter GH response to LPS. In contrast, plasma concentrations of LH were profoundly inhibited by icv administration of either cytokine (P < 0.03), but the LH response to LPS was not altered by cytokine antagonists. Intravenous administration of either IL-1beta or TNF-alpha increased plasma concentrations of GH (P < 0.0001). Administration of IL-1RA and sTNF-R1 iv prevented LPS-induced increases in GH. Although LH was suppressed by high iv doses of IL-1beta (P = 0.0063), the antagonists did not alter the LH response to LPS. To determine whether LPS might directly activate GH release, confocal microscopy revealed colocalization of CD14, the LPS receptor, with GH and, to a lesser extent, LH and some prolactin (PRL)-containing cells, but not ACTH or TSH. These data are consistent with the effects of LPS on GH secretion originating through peripheral cytokine presentation to the pituitary, as well as a potential to act directly on selective populations of pituitary cells via CD14.

Intracerebroventricular melanin-concentrating hormone stimulates food intake in sheep.

Melanin-concentrating hormone (MCH) stimulates feeding when injected intracerebroventricularly (ICV) in rats. At present it is not clear whether the function of MCH is similar in ruminants, which are species with a continuous delivery of nutrients. Therefore the current investigation sought to determine the role of MCH in sheep. In the first experiment, six, castrate male sheep were satiated and received one of four treatments [saline, 0.1, or 1.0 nmol/kg MCH, and NPY (0.1 nmol/kg)] injected ICV over 30s, then infused ICV for 6 h ( approximately 500 microl/h). Food intake was measured for 2 h before and at 2, 4, 6, 8, 12 and 24 h. In this experiment, feed intake was increased (P