B. R. Sinclair

Selenium-Enriched Foods Are More Effective at Increasing Glutathione Peroxidase (GPx) Activity Compared with Selenomethionine: A Meta-Analysis

Selenium may play a beneficial role in multi-factorial illnesses with genetic and environmental linkages via epigenetic regulation in part via glutathione peroxidase (GPx) activity. A meta-analysis was undertaken to quantify the effects of dietary selenium supplementation on the activity of overall GPx activity in different tissues and animal species and to compare the effectiveness of different forms of dietary selenium. GPx activity response was affected by both the dose and form of selenium (p < 0.001). There were differences between tissues on the effects of selenium supplementation on GPx activity (p < 0.001); however, there was no evidence in the data of differences between animal species (p = 0.95). The interactions between dose and tissue, animal species and form were significant (p < 0.001). Tissues particularly sensitive to changes in selenium supply include red blood cells, kidney and muscle. The meta-analysis identified that for animal species selenium-enriched foods were more effective than selenomethionine at increasing GPx activity.

Effect of food intake on energy and protein metabolism in the skin of Romney sheep

Sheep fed on either a low (500 g lucern (Medicago sativa) chaff/d; L) or high (1100 g lucerne chaff/d; H) intake had measurements made, using arterio-venous techniques, of blood flow and energy metabolite and cysteine utilization in the skin. Sheep on the H intake had significantly increased skin blood flow (P = 0.014) and oxygen uptake (P = 0.05). Although the H sheep had higher skin blood flow they showed no difference in skin uptake of either glucose or acetate compared with the L sheep, but the H sheep had a significantly lower output of lactate (P = 0.014). Animals in each group had either [14C]glucose or [14C]acetate infused into the skin which showed that acetate was the predominant precursor of skin sterol and fatty acid synthesis in the H sheep while L sheep skin used both glucose and acetate. The H sheep showed an increase in the net uptake of cysteine by the skin (P = 0.053), and in the uptake of cysteine for protein synthesis (P = 0.078), relative to the L sheep and this increase was of a comparable magnitude to the increase in blood flow to the skin. Although blood flow, protein synthesis and energy supply increased in the skin of the H sheep by 200-300%, wool production would only have increased by 10-20%, suggesting that nutrient flux changes are not the sole level of regulation of wool production.

Grass–endophyte interactions: a note on the role of monosaccharide transport in the Neotyphodium lolii–Lolium perenne symbiosis

Symbiotic mutualistic associations of plants with ectoand endomycorrhizal and endophytic fungi are very common in natural and agricultural ecosystems; these fungi improve nutrient acquisition and ⁄ or tolerance to biotic and abiotic stresses of their hosts (Smith & Gianinazzi-Pearson, 1988; Nehls et al., 2007; Schardl et al., 2007). A major feature of associations between the heterotrophic fungi and autotrophic plants is an exchange of fungus-derived benefits (e.g. phosphorous in ectoand endomycorrhizal associations, or antiherbivorous alkaloids in endophytic Neotyphodium–grass associations) for plant-derived carbohydrates as carbon (C) and energy source for fungal growth and maintenance (Bago et al., 2000; Nehls et al., 2007). Neotyphodium ⁄ Epichloë spp. endophytic fungi occur in 20– 30% of cool-season grass species and are of widespread interest to ecological and agricultural research (Schardl, 2001). These obligate symbiotic fungi are an additional C sink and affect host C metabolism and mobilization (Pan & Clay, 2004; Hunt et al., 2005; Rasmussen et al., 2008, 2009). Under stressful conditions, in particular, such as drought and high temperatures, endophyte symbionts have been shown to enhance host photosynthesis and potentially increase total C reserves (Richardson et al., 1993; Marks & Clay, 1996). It has also been shown that endophyte concentrations are reduced in Lolium perenne cultivars accumulating high amounts of water-soluble carbohydrates compared with control cultivars (Rasmussen et al., 2007; Liu et al., 2011). These studies indicate that endophytic fungi are important regulators of host carbohydrate metabolism; and that carbohydrate supply by hosts and C utilization by endophytes interact with each other. Carbon transfer from host plants to fungal symbionts is catalysed by transporter proteins, and several sugar transporters from mutualistic ectoand endomycorrhizal fungi have been functionally characterized (Schübler et al., 2006; Nehls et al., 2007; Helber et al., 2011). In general, it has been assumed that simple soluble sugars such as glucose and fructose are the major source of C for symbiotic fungi (Bago et al., 2000); however, some of the isolated sugar transporters have been shown to be able to catalyse the uptake of cell wall sugars such as mannose and xylose as well (Schübler et al., 2006; Fajardo López et al., 2008; Helber et al., 2011; Doidy et al., 2012). To provide more information about sugar uptake by endophytic Neotyphodium ⁄ Epichloë fungi from their hosts, we report here the isolation and functional characterization of a monosaccharide transporter from Neotyphodium lolii (MSTN). Initial studies indicated that MSTN preferentially catalyses the uptake of mannose, a monosaccharide mainly found in polymeric cell wall carbohydrates. We therefore hypothesized that N. lolii might be able to hydrolyse cell wall carbohydrates. We tested this hypothesis by quantifying the expression of cell wall carbohydrate hydrolysing fungal mannosidase, cellulase and glucanase, as well as sucrose hydrolysing fungal and plant invertases in cultured N. lolii mycelia and in ryegrass cultivars and tissues differing in their endogenous sugar content.

Mammary transcriptome analysis of lactating dairy cows following administration of bovine growth hormone

The galactopoietic effect of growth hormone (GH) in lactating ruminants is well established; however the mechanisms that mediate these effects are not well understood. The first objective of this study was to determine the effect of GH on the synthesis of the major casein and whey proteins. The second objective was to identify the genes and pathways that may be involved in mediating the effect of GH on milk synthesis. A single subcutaneous injection of a commercially available slow release formulation of GH (Lactatropin®), or physiological saline solution (control) was administered to non-pregnant dairy cows (n=4/group) in mid-late lactation. Milk samples were collected for composition analysis and mammary lobulo-alveolar tissue was collected postmortem 6 days post injection. Gene expression profiles were evaluated using either a 22 000 bovine complementary DNA microarray or quantitative PCR (qPCR), and microarrays were validated by qPCR. The yield of all the major casein and whey proteins was increased 32% to 41% in GH-treated cows, with the exception of α-lactalbumin yield which was elevated by 70% relative to controls. Treatment with GH treatment tended to increase the concentration of α-lactalbumin but had no effect on the concentration of any of the major milk proteins. Messenger RNA (mRNA) abundance of the major whey and casein genes, with the exception of α-s2-casein, was increased in response to GH compared with controls, which is consistent with the positive effect of GH on milk production. Treatment with GH treatment influenced the mRNA abundance of genes involved in cell growth and proliferation, transcriptional and translational regulation, actin cytoskeleton signalling, lipid metabolism and cell death. This study has provided new insights into the cell signalling that may be involved in mediating the effect of GH on milk production in the mammary gland of lactating dairy cows.

Adult Trichostrongylus colubriformis infection did not affect protein synthesis rate in whole-body, intestinal, hepatic and skeletal muscle tissues of lambs fed fresh Lucerne (Medicago sativa)

The effects of an established Trichostrongylus colubriformis infection on the whole-body and fractional protein synthesis rates in the small intestine, liver, lymphoid tissues, skeletal muscle and skin were determined in lambs fed fresh Lucerne (Medicago sativa; 800 g DM d-1) on day 48 post-infection. Lambs were dosed with 6000 L3 T. colubriformis larvae for 6 d (n = 5) or kept as parasite-free controls (n = 6). On day 45, the lambs received a bolus injection of deuterated water to measure the size of the whole-body water pool. On day 48, the lambs were continuously infused with [3, 4-3H]-valine into the jugular vein and [1-13C]-valine in the abomasum for 8 h. During the infusion, mesenteric artery blood and terminal tissue samples were collected for measuring the isotopic activity of plasma water, plasma valine, intra cellular valine and protein-bound valine. Intestinal worm numbers on day 48 were higher (P 0.10) of parasitic infection on ...

Intestinal, hepatic, splanchnic and hindquarter amino acid and metabolite partitioning during an established Trichostrongylus colubriformis infection in the small intestine of lambs fed fresh Sulla (Hedysarum coronarium)

Increased partitioning of amino acids (AA) from skeletal muscle to the intestine and immune system during parasitic infection may be the cause of poor growth in parasitised animals. The effect of an established Trichostrongylus colubriformis infection (6000 L3 T. colubriformis larvae for 6 d (n 5) or kept as parasite-free controls (n 6)) on AA fluxes across the mesenteric-drained viscera, portal-drained viscera (PDV), liver, total splanchnic tissues (TSP) and hindquarters were determined in lambs fed fresh Sulla (Hedysarum coronarium; 800 g DM/d) 48 d post-infection. The lambs were infused with rho-aminohippuric acid (PAH; 723 mg/h) into the mesenteric vein for 8 h to measure TSP plasma flow. Concurrently, indocyanine green (ICG; 14.6 mg/h) was infused into the abdominal aorta to measure plasma flow across the hindquarters. Blood was continuously collected from the mesenteric, portal and hepatic veins, vena cava and the mesenteric artery and plasma harvested. PAH, ICG, AA, metabolite and insulin concentrations were measured. Intestinal worm burdens on day 48 post-infection were higher in the infected lambs (P 0.10). There was a 28 % reduction in the release of AA from the PDV of infected lambs (P < 0.05). The uptakes of most AA were similar in the liver; however, there was increased uptake (P < 0.10) of AA by the TSP of infected lambs. Despite this reduction in AA availability at the liver, there was no effect of parasitic infection on AA uptake across the hindquarters (P < 0.05).

Insulin regulation of amino-acid metabolism in the mammary gland of sheep in early lactation and fed fresh forage

Insulin plays an important role in regulating the partitioning of nutrients to the mammary gland, particularly in lactating ruminants fed concentrate-based diets. There is evidence that the nutritional status of the animals might also affect their response to insulin. This is largely untested in early lactating ruminants fed fresh forage. To investigate nutritional effects on insulin response, 12 lactating sheep, housed indoors, were allocated to one of two treatment groups (hyperinsulinaemic euglycaemic clamp (HEC) or control) in a randomised block design and fed perennial ryegrass (Lolium perenne)/white clover (Trifolium repens) pasture. Mammary amino acid (AA) net uptake from plasma and utilisation for milk protein synthesis was measured during the 4th day of the HEC using arterio-venous concentration differences, and 1-13C-leucine was used to estimate whole body and mammary gland leucine kinetics. There was no change in feed intake, milk protein output and mammary blood flow during the HEC (P > 0.1). The HEC decreased (P < 0.1) the arterial concentrations of all essential AA (EAA) except histidine. The mammary net uptake of some EAA (isoleucine, leucine, methionine and phenylalanine) was reduced by the HEC (P < 0.1). Leucine oxidation in the mammary gland was not altered during the HEC (P > 0.1) but mammary protein synthesis was reduced by the HEC (P < 0.05). These results show that sheep mammary gland can adapt to changing AA precursor supply to maintain milk protein production during early lactation, when fed fresh forage. How this occurs remains unclear, and this area deserves further study.

Intestinal amino acid absorption in lambs fed fresh Lucerne (Medicago sativa) during an established Trichostrongylus colubriformis infection

The effects of an established Trichostrongylus colubriformis infection on amino acid (AA) absorption from the small intestine and their availability to other tissues were determined in lambs 48 days post infection. The lambs were fed fresh Lucerne (Medicago sativa; 800 g dry matter (DM)/day) and dosed with 6000 L3 T. colubriformis larvae for 6 days (n = 5) or kept as parasite free controls (n = 6). Faecal egg production was monitored every second day from day 22 to day 48. A nitrogen (N) balance was conducted on days 35 to 43 after infection, and digesta flow and AA concentration measurements were made on day 44. On day 48 after infection, blood was continuously collected from the mesenteric artery and vein, plasma harvested and AA concentrations measured. Faecal egg production peaked on the 26th day after infection (P < 0.001) and intestinal worm burdens on day 48 were greater (P < 0.001) in the infected lambs. Feed intake and liveweight gain were similar (P > 0.10) between control and infected lambs. Digestibility and flow of DM and N through the digestive tract were also unaffected (P > 0.10) by parasite infection. Despite a trend towards higher abomasal AA flux in the parasitised lambs (P < 0.10), apparent AA absorption from the small intestine and AA availability to other tissues were unaffected (P > 0.10) by infection. These results suggest that an established parasite infection had little effect on the intestinal absorption and availability of AA to other tissues in lambs fed fresh Lucerne.

Protein synthesis in mammary epithelial cells harvested from cows treated with growth hormone or atropine

Mammary epithelial cells, harvested from either mammary tissue or milk from cows treated with growth hormone or atropine, were cultured in vitro. Protein synthesis in these cells was determined by measuring the incorporation of [3,4,5]-3H-leucine into protein secreted into the cell culture medium. Incorporation was measured between 0 and 11 h after addition of labelled leucine to the cell culture medium. No difference in incorporation was observed between epithelial cells isolated from milk compared to those from mammary tissue, nor was there any difference in incorporation in epithelial cells derived from the milk of control, growth hormone or atropine-treated cows.