Biochemical differences in Merino sheep selected for resistance against gastro-intestinal nematodes and genetic and nutritional effects on faecal worm egg output

Effects of dietary inclusion of yerba mate (Ilex paraguariensis) extract on lamb muscle metabolomics and physicochemical properties in meat

This study aimed to evaluate the effect of dietary yerba mate (Ilex paraguariensis) extract (YME) on muscle metabolomics and physicochemical properties of lamb meat. Thirty-six uncastrated male lambs (90 d old) were fed experimental diets, which treatments consisted of 0%, 1%, 2%, and 4% inclusion of YME. Animals were fed for 50 d before slaughter. Muscle and meat samples were collected for metabolomics and meat quality analysis, respectively. The experiment was carried out in a randomized block design and analyzed using orthogonal contrasts. There was a quadratic effect of YME inclusion in tenderness (P < 0.05) and a positive linear effect on meat lightness (P < 0.05). No qualitative changes (P > 0.05) on individual metabolites were observed; however, changes in the quantitative metabolic profile were observed, showing that animals fed 1% and 2% of YME have a greater concentration of desirable endogenous muscle antioxidants, with direct impact on metabolic pathways related to beta-alanine metabolism and glutathione metabolism. Therefore, YME dietary supplementation up to 2% of the diet to lambs had little to no effects on the majority of meat quality traits evaluated; moreover, 4% of YME inclusion negatively affected feed intake and meat quality traits.

A desired gains approach for the prediction of genetic gain in resistance to gastrointestinal nematodes in a multi-trait breeding objective in Uruguayan Merino sheep

Gastrointestinal nematodes (GIN) constitute a problem in many sheep production systems, including those in Uruguay, causing reduced productivity and increased expenses. The main strategy to control GIN has consisted of the use of anthelmintics. However, GINs have developed resistance to anthelmintics, reducing their effectiveness. Genetic resistance to GINs has been found in flocks of different breeds. To date, there have been no reports about GINs breaking down genetic resistance in sheep. Heritability estimates of resistance to GIN within breeds are generally moderate, so that achieving genetic gain within a flock is possible. In this study, we predicted genetic gain in worm egg count (WEC), an indirect (and generally preferred) criterion of resistance to GIN, following different strategies. A multi-trait breeding objective including wool and meat traits was assumed and genetic gain over 10 years of selection in a Merino flock was estimated. We used a desired gains approach, examining situations in which the economic contribution of genetic gain in resistance to GIN in percentage terms was 0, 25, 50, 75 or 100. Except when the level of infestation with GIN was low, a considerable amount of emphasis had to be placed on selection for low WEC in order to reach the threshold below which the administration of anthelmintics is not required. High emphasis on reducing WEC lead to a reduction in genetic gain in wool and meat traits, or to their deterioration in the extreme case of 100 per cent emphasis on WEC. Given this finding, coupled with the difficulties encountered in accurately recording and selecting for WEC, we concluded that in addition to embarking upon a programme of within flock selection, sheep breeders interested in improving genetic resistance to GIN should also consider using breeding stock identified as superior for both resistance and production traits in across flock genetic evaluations.

Amino Acids in the Nutrition and Production of Sheep and Goats

In sheep and goats, amino acid nutrition is essential for the maintenance of health and productivity. In this review, we analysed literature, mostly from the past two decades, focusing on assessment of amino acid requirements, especially on the balance of amino acid profiles between ruminal microbial protein and animal production protein (foetal growth, body weight gain, milk and wool). Our aim was to identify amino acids that might limit genetic potential for production. We propose that much attention should be paid to amino acid nutrition of individuals with greater abilities to produce meat, milk or wool, or to nourish large litters. Moreover, research is warranted to identify interactions among amino acids, particularly these amino acids that can send positive and negative signals at the same time.

Expression of worm resistance in sheep selected for low worm-egg counts fed at maintenance or above-maintenance level

The present study reports on changes in faecal worm-egg counts (WEC), larval composition, and the number of worms at different developmental stages in young sheep sourced from a flock selected for reduced faecal worm-egg counts over 15 years. The sheep were individually penned and fed a maintenance (1.0 M) or a 1.5 times maintenance (1.5 M) diet over two periods, namely, worm-free and infection phases. They were dosed weekly with 10000 Trichostrongylus colubriformis and 10000 Teladorsagia circumcincta L3 infective larvae for 11 weeks. Sheep on the 1.5 M diet had lower WEC and higher bodyweights than did sheep on the 1.0 M diet. A significant decline in the percentage T. colubriformis occurred during the experiment, but no concomitant change in T. circumcincta was noticed. Resistant sheep had significantly (P &lt; 0.001) fewer worms at necropsy, and also shed significantly (P &lt; 0.001) fewer worm eggs during the experiment. Restricted feeding reduced bodyweight significantly (P &lt; 0.001) and had a small but significant (P &lt; 0.04) effect on the faecal worm-egg output and on the number of T. colubriformis worms (P &lt; 0.01) in both the control and resistant sheep. The study showed that sheep selected for low WEC resulted in significantly (P &lt; 0.001) lower WEC than in an unselected control line fed at a maintenance (1.0 M) and at an above-maintenance (1.5 M) level. Restricted feeding reduced bodyweight and had a small negative, and inconsistent, effect on the faecal worm-egg output in both the control and resistant lines.

Heritabilities of IgA and IgE activities against Teladorsagia and Trichostrongylus L3 larval antigens correlated with traits for faecal worm egg count, health and productivity in Merino sheep

Low faecal worm-egg count (FEC) has been used as a phenotypic trait for breeding sheep for resistance to nematode infection. Application of this trait has resulted in a major reduction in worm-egg output in faeces, but in certain environments some of the resistant sheep develop what is believed to be a hypersensitivity-associated diarrhoea, resulting in soiling of the breech area (dags). To avoid breeding sheep with a propensity to scour, it, therefore, seems logical to combine selection for low FEC with selection for a trait based on the immune response to worm infection. We, therefore, investigated the relationships between immunoglobulin A (IgA) and immunoglobulin E (IgE) activities against L3 larval antigens of Teladorsagia circumcincta and Trichostrongylus colubriformis and measured their inheritance and their genetic relationships with FEC, dag traits and measures of production. Total plasma IgE concentrations were also determined and included in the study. We used 762 progeny from 23 Merino sires selected for resistance to helminths (the ‘Rylington Flock’) and to breech flystrike. Total plasma IgE and IgE activities against T. circumcincta were negatively correlated with liveweight, longissimus dorsi muscle depth, and fleece weight, but positively correlated with severity of dags, softer faeces and back-fat depth. The IgA activity against T. circumcincta was negatively correlated with liveweight and clean fleece weight, but positively correlated with back-fat depth and faecal consistency score. The IgA activity against T. colubriformis was not correlated with any measure, except the breeding value for dags around yearling age. The heritability for the IgA activity against T. circumcincta and T. colubriformis was 0.13 and 0.08 respectively. The heritability for both IgE activity against T. circumcincta and total plasma IgE concentration was 0.39. We conclude that it is feasible to combine FEC and dag traits with an immune trait (in this case, helminth-specific IgE activity and total plasma IgE concentration) and, thus, genetically select sheep for resistance to both helminths and diarrhoea. However, under natural worm-challenge conditions, blood sampling protocols need to developed, on the basis of animal age, season and environment, for optimum estimation of the immune trait and its relationships with other traits.

Genetic aspects of sheep parasitic diseases

There is evidence of genetically determined host resistance mechanisms for most of the sheep parasites evaluated. The mechanisms vary; from no or reduced establishment, early expulsion, to suppression of parasites resulting in reduced size and fecundity. There is a need to integrate breeding for parasite resistance with the genetic improvement of production traits in farm animals, aiming for optimum solutions for potentially conflicting responses. Sustainable parasite control must be based on Integrated Parasite Management utilising an interdisciplinary approach.

The gastrointestinal nematode Trichostrongylus colubriformis down-regulates immune gene expression in migratory cells in afferent lymph

Background

Gastrointestinal nematode (GIN) infections are the predominant cause of economic losses in sheep. Infections are controlled almost exclusively by the use of anthelmintics which has lead to the selection of drug resistant nematode strains. An alternative control approach would be the induction of protective immunity to these parasites. This study exploits an ovine microarray biased towards immune genes, an artificially induced immunity model and the use of pseudo-afferent lymphatic cannulation to sample immune cells draining from the intestine, to investigate possible mechanisms involved in the development of immunity.

Results

During the development of immunity to, and a subsequent challenge infection with Trichostrongylus colubriformis, the transcript levels of 2603 genes of cells trafficking in afferent intestinal lymph were significantly modulated (P < 0.05). Of these, 188 genes were modulated more than 1.3-fold and involved in immune function. Overall, there was a clear trend for down-regulation of many genes involved in immune functions including antigen presentation, caveolar-mediated endocytosis and protein ubiquitination. The transcript levels of TNF receptor associated factor 5 (TRAF5), hemopexin (HPX), cysteine dioxygenase (CDO1), the major histocompatability complex Class II protein (HLA-DMA), interleukin-18 binding protein (IL-18BP), ephrin A1 (EFNA1) and selenoprotein S (SELS) were modulated to the greatest degree.

Conclusions

This report describes gene expression profiles of afferent lymph cells in sheep developing immunity to nematode infection. Results presented show a global down-regulation of the expression of immune genes which may be reflective of the natural temporal response to nematode infections in livestock.

Selenium supplementation and increased muscle glutathione concentration do not improve the color stability of lamb meat

In the eyes of the consumer, a red surface color of lamb meat is desirable. This red color is caused by oxymyoglobin; however, under conditions of retail display this pigment slowly oxidizes and turns brown, deterring consumers. The antioxidant activity of both glutathione (GSH) and selenium has been suggested to slow myoglobin oxidation, thus improving color stability. The following experiment was designed to test the hypothesis that high muscle GSH will improve the color stability of lamb meat, and this effect of GSH will be further improved by supplementing animals with selenium. Forty-eight 12-month-old Merino wether lambs were selected from a flock for high (n = 24) or low (n = 24) GSH concentration in whole blood. Each GSH group was then randomly allocated into two selenium treatments (supplemented with or without 2.5 mg of selenium/kg for 8 weeks). The lambs were slaughtered, and samples were taken from m. semimembranosus (SM) and m. longissimus dorsi (LD) to measure muscle GSH, selenium, and vitamin E concentrations. Further samples were taken to measure color stability (as oxy/metmyoglobin ratio, reflectance at 630/580 nm) over 96 h of retail display. There was no effect of muscle GSH concentration or selenium supplementation on oxy/metmyoglobin ratio at 60, 48, or 30 h of retail display, with the only exception being the non-selenium-supplemented SM samples, which actually decreased in ratio as the muscle GSH concentration increased (P < 0.05). There was a poor correlation between blood and muscle GSH, with a correlation coefficient of 0.18 for the SM and 0.026 for the LD. Thus, it is apparent that neither GSH nor selenium improved the color stability of meat from merino lambs.

Nematode challenge induces differential expression of oxidant, antioxidant and mucous genes down the longitudinal axis of the sheep gut

To characterize the role of a range of oxidant, antioxidant and mucous-related genes in the primary response to gastrointestinal nematodes, groups of genetically resistant sheep were challenged with either Haemonchus contortus or Trichostrongylus colubriformis and necropsied for retrieval of tissue at days 0, 3, 7, 14 and 21. To determine if the response was localized to the site of parasite infection, four different gut tissues were sampled: the abomasum, proximal and distal jejunum and ileum. Basal expression patterns of all candidate genes were determined using the day 0 (pre-challenge) samples. A conserved innate response involving elevated expression of dual oxidase, glutathione peroxidase and trefoil factor was initiated within 3 days of challenge and extended out to 21 days. An increase in host gene expression levels at the preferred site of infection (the abomasum for H. contortus and the proximal jejunum for T. colubriformis) was also common to both nematodes. However, these increases were concomitant with reduced expression in other areas of the gut suggesting a compartmentalized response. Other aspects of the response were parasite-specific, with T. colubriformis challenge inducing expression peaks at times corresponding to nematode life-stage transitions.

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.

Associations between blood parasite infection and a microsatellite DNA allele in an Australian scincid lizard (Egernia stokesii)

We used blood samples from 175 individuals of the Australian lizard Egernia stokesii to determine infection status of three apicomplexan blood parasites from the genera Hemolivia, Schellackia, and Plasmodium and to determine genotypes at 12 microsatellite DNA loci. We found one significant association between genotype and infection status. For locus Est4, individuals carrying allele 159 had lower prevalence of infection with Hemolivia (14.3% of 28 lizards) than individuals that did not carry the allele (58.4% of 89 lizards). We interpret this as a linkage to a functional gene associated with parasite resistance. We found no evidence among seven lizard populations that the frequency of allele 159 was related to the population prevalence of Hemolivia infection and discuss several explanations of that pattern.

Glutathione: its implications for animal health, meat quality, and health benefits of consumers

There has been an increasing focus on the role of antioxidants for human health. This review outlines associations of the most predominant antioxidant, glutathione (GSH), in the body and some ageing-related diseases. Strategies to replete GSH, particularly developing animal-source food products, are discussed. Potentials to alter GSH content in the animal’s body and its possible effects on health are also explored.