Vagal and splanchnic afferent nerves are not essential for anorexia associated with abomasal parasitism in sheep

Review: Pro-inflammatory cytokines and hypothalamic inflammation: implications for insufficient feed intake of transition dairy cows

Improvements in feed intake of dairy cows entering the early lactation period potentially decrease the risk of metabolic disorders, but before developing approaches targeting the intake level, mechanisms controlling and dysregulating energy balance and feed intake need to be understood. This review focuses on different inflammatory pathways interfering with the neuroendocrine system regulating feed intake of periparturient dairy cows. Subacute inflammation in various peripheral organs often occurs shortly before or after calving and is associated with increased pro-inflammatory cytokine levels. These cytokines are released into the circulation and sensed by neurons located in the hypothalamus, the key brain region regulating energy balance, to signal reduction in feed intake. Besides these peripheral humoral signals, glia cells in the brain may produce pro-inflammatory cytokines independent of peripheral inflammation. Preliminary results show intensive microglia activation in early lactation, suggesting their involvement in hypothalamic inflammation and the control of feed intake of dairy cows. On the other hand, pro-inflammatory cytokine-induced activation of the vagus nerve transmits signalling to the brain, but this pathway seems not exclusively necessary to signal feed intake reduction. Yet, less studied in dairy cows so far, the endocannabinoid system links inflammation and the hypothalamic control of feed intake. Distinct endocannabinoids exert anti-inflammatory action but also stimulate the posttranslational cleavage of neuronal proopiomelanocortin towards β-endorphin, an orexigen promoting feed intake. Plasma endocannabinoid concentrations and hypothalamic β-endorphin levels increase from late pregnancy to early lactation, but less is known about the regulation of the hypothalamic endocannabinoid system during the periparturient period of dairy cows. Dietary fatty acids may modulate the formation of endocannabinoids, which opens new avenues to improve metabolic health and immune status of dairy cows.

Leptin concentrations and the immune-mediated reduction of feed intake in sheep infected with the nematode Trichostrongylus colubriformis

The hypothesis that increases in the concentration of the anorectic peptide leptin may be responsible for the immune-mediated reduction in feed intake (FI) during gastrointestinal parasitism in sheep was investigated. In a 2 x 2 x 2 factorial design, the first factor was age at the start of infection (5 months old v. 17 months old). The second factor was parasite infection (no infection v. administration of eighty L3 infective Trichostrongylus colubriformis larvae/kg live weight (LW) per d three times per week for 77 d). The third factor was immunosuppressive therapy with a corticosteroid (no therapy or weekly intramuscular injection of 40 mg methylprednisolone acetate/30 kg LW). Relative to their uninfected counterparts, a 20 % reduction in FI per unit LW (FI/LW; g DM/kg LW) was observed in infected non-suppressed 5-month-old lambs from 21 to 63 d post-infection (P < 0.001) but not in comparable17-month-old ewes or in corticosteroid-treated lambs or ewes (P>0.05 for all), allowing the suggestion that the anorexia was a consequence of the developing immune response. The reduction in FI/LW in 5-month-old lambs was not associated with an increase in plasma leptin concentration. Furthermore, plasma leptin concentrations were greater in corticosteroid-treated animals (P < 0.001) and in 17-month-old animals (P < 0.001), none of which displayed an infection-induced reduction in FI/LW. Plasma leptin was positively correlated with carcass fat percentage in both 5-month-old (P = 0.016) and 17-month-old (P < 0.001) animals and did not appear to provide a direct feedback mechanism that restricted energy intake. The results do not support the hypothesis that an increase in circulating leptin is directly responsible for the immune-mediated anorexia in lambs during T. colubriformis infection.

Teladorsagia circumcincta: survival of adults in vitro is enhanced by the presence of a mammalian cell line

Adult Teladorsagia circumcincta survival and motility in vitro was examined in a range of different cell culture media, supplements and gas mixes. Under optimum conditions, worms survived for 14 days, exhibiting high motility for 9 days and egg production for 72 h. Optimum conditions involved co-culture of worms with a HeLa cell line in a supplemented cell medium (CEM) and an atmosphere containing 10% CO(2), 5% O(2) 85% N(2), 65% humidity at 37 degrees C. The incubation medium consisted of Minimum Essential Medium with 10% fetal calf serum, 1% non-essential amino acids, 1% glutamax and 1% penicillin-neomycin-streptomycin cocktail mix. Compared with optimum conditions, incubation in CEM alone, cell conditioned CEM, RPMI alone, Medium 199 alone, reduced CO(2) or O(2), or when cells were replaced with Escherichia coli, both survival and motility were reduced. Optimum conditions for adult T. circumcincta maintenance for culture, anthelmintic testing or generation of excretory/secretory products are described.

Associations between blood gastrin, ghrelin, leptin, pepsinogen and Ostertagia ostertagi antibody concentrations and voluntary feed intake in calves exposed to a trickle infection with O. ostertagi

Twenty-five, castrated male Holstein-cross calves, between 4 and 5 months of age, weighing 156.5+/-12.2 kg and reared under conditions designed to minimise the risk of parasitic infection, were allocated to one of the five treatment groups on the basis of initial bodyweight. The groups were (1) ad libitum (ad lib) fed controls (ALC); (2) ad lib fed infected (INF) and treated with topical eprinomectin on Day 56; (3) controls pair-fed with the INF group (PFC); (4) ad lib fed controls treated with eprinomectin on Days 0 and 56 (E-ALC) and (5) ad lib fed, infected and treated with eprinomectin on Days 0 and 56 (E-INF). Infection comprised a trickle infection with the equivalent of 10,000 larvae of Ostertagia ostertagi per day from Day 0 to Day 56 and the study concluded on Day 77. Parameters measured throughout the study included: liveweight, feed intake, faecal egg counts; plasma pepsinogen, gastrin, ghrelin and leptin; plasma antibodies to adult O. ostertagi. No significant differences in feed intake or liveweight gain were observed between any of the different groups, a finding thought to result from the high quality of feed offered. Significant differences between the INF and control groups however were observed in faecal egg counts, plasma pepsinogen, gastrin and O. ostertagi antibodies, which were all elevated, and leptin, which was reduced. Values of these parameters for the E-INF group were intermediate between the INF and ALC groups. Plasma ghrelin showed no association with either feed intake or parasitism. Further studies are needed to fully elucidate the roles of various biochemical and neuroendocrine mediators for inappetence in ruminants with parasitic gastroenteritis.

Six costs of immunity to gastrointestinal nematode infections

The strength of the immune response and the outcome of the interaction of a host with a parasite are influenced by genetic and phenotypic characteristics of both parties, and by environmental variables. Allocation of host resources to immune defence reduces resources available for other life-history traits. This review identifies six potential costs to the host from immune activation. The costs are likely to be broadly applicable to other immune responses in vertebrate species. Five phenotypic costs arise from: (i) increased metabolic activity; (ii) reduced nutrient availability due to anorexia; (iii) altered priorities for nutrient utilization; (iv) change in size and turnover of pools of immune cells and proteins; and (v) immunopathology from inappropriate or excessive immune activation. Subsumed by these costs is the cost of altered efficiency of nutrient use. A sixth cost is the genetic cost which arises from a change in the capacity of offspring to express production and life-history traits following selection for parasite resistance. The sensitivity of immune responses to the phenotypic status of the host, and the role the immune system shares with the neuroendocrine system in controlling use of resources underpin the importance of immunocompetence to the life-history of the host.

Effect of genetic resistance to gastrointestinal nematodes on plasma concentrations of insulin-like growth factor-1 and leptin in Merino sheep

Gastrointestinal nematode infection in sheep changes the nutritional economy of the host, but little is known about the effects of infection on the hormonal systems that regulate the metabolism of the animal. This study examined two key hormones, insulin-like growth factor-1 (IGF-1) and leptin, in genetically resistant and random bred control Merino sheep in the presence or absence of nematode infection. Sixty-four 10-month-old Rylington Merino wethers, half from the parasite-resistant line and half from unselected control line, were initially maintained at two body conditions (body condition scores averaged 1.7 and 2.5) in individual pens in an animal house. The animals were kept parasite-free for 9 weeks, then ‘trickle-infected’ with Trichostrongylus colubriformis and Teladorsagia circumcincta larvae, each at a rate of 10 000 per week, for 13 weeks. Each body condition score group was subdivided into two groups at the beginning of the infection procedure and feed supply was controlled at 1× or 1.5× the maintenance metabolisable energy requirement. Plasma IGF-1 concentrations decreased marginally by day 21 of infection, then markedly by day 49, and then remained low until day 84. Plasma leptin concentrations tended to increase during the infection period. Both body condition and feed intake had significant effects on IGF-1 and leptin concentrations, and the higher concentrations were related to the good body condition or high feed intake. The parasite-resistant sheep had consistently higher concentrations of IGF-1 compared with the controls, whereas the concentrations of leptin were similar. The significant changes in IGF-1 but not leptin suggest that infection may have a more significant impact on protein anabolism, and least impact on lipid metabolism. Selection for parasite resistance appears to result in enhanced protein anabolism.