Poor growth during parasitic infection may be due to a redistribution of amino acids away from skeletal muscle protein synthesis to the intestinal site of infection. The effect of a Trichostrongylus colubriformis infection on whole-body amino acid kinetics and tissue fractional protein synthesis rates were determined in lambs fed fresh Sulla (Hedysarum coronarium; 800 g DM/d). Lambs were dosed with 6000 L3 Trichostrongylus colubriformis larvae daily for 6 d (n 6) or kept as parasite-free controls (n 6). On day 45 post-infection, the lambs received an intravenous injection of 2H2O and infusions (8 h) of [35S]sulphate to measure the size of the whole-body water and sulphate pools, respectively. On day 48, the lambs were continuously infused for 8 h with [3,4-3H]valine into the jugular vein as well as with [1-13C]valine and [35S]cysteine into the abomasum. After the 8 h infusions, the lambs were killed and tissue samples collected from the duodenum, ileum, mesenteric lymph nodes, liver, spleen, thymus, muscle and skin. Feed intake (769 v. 689 (sd 47) g DM/d) was not affected by infection, whereas liveweight gains (50 v. -50 (sd 70) g/d) were lower and intestinal worm burdens (240 v. 18,000 (sd 7000) worms) higher in the infected lambs. Parasitic infection increased the fractional protein synthesis rates in the small intestine, mesenteric lymph nodes and liver but did not affect skin and skeletal muscle fractional protein synthesis rates during the established parasitic infection.

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.

SUMMARYFive Romney wethers, fitted with rumen fistulae, were each fed five pelleted diets high in starch (30–50%) containing 0·72, 1·22, 1·72, 2·47 and 3·72% N respectively. Samples of rumen liquor were incubated with glycerol-tri-[1-14C]oleate or with [1-14C]- linoleic acid. The rates of lipolysis or hydrogenation of these substrates were measured. In addition rumen contents of the sheep when fed the 1·22% N diet were incubated with radioactive substrates plus 0, 100 and 200 mg finely ground casein.It was found that there was an approximately linear increase in the rate of lipolysis between 0·7 and 2·5% N. The rate of hydrogenation did not increase below l·2% N and tended to decrease above 2·5% N. The potential for hydrogenation of unesterified linoleic acid was calculated to be 4–6 times greater with all diets except that containing 1·2% N. This may be one explanation for the elevated concentration of the rumen unsaturated fatty acids in sheep fed diets containingca.1–1·5% N.It was also established that the addition of finely ground casein to the incubate was without effect.It was concluded that microbial composition is important in regulating the relative rates of lipolysis and hydrogenation which determined the amount of unsaturated dietary fatty acid present in the rumen.

An arterio-venous preparation was developed which allowed infusion into, and/or sampling from, branches of the deep circumflex iliac artery and vein supplying and draining a discrete area of skin on the abdominal flank of Romney sheep.Measurements of blood flow (using dye dilution techniques), utilization or output of energy metabolites (oxygen, glucose, lactate and acetate) and amino acid metabolism were made in relation to whole body protein and energy metabolism.Measurements on the patch suggested that blood flow to the total skin was about 6% of cardiac output but that only 1-2% of whole body oxygen utilization occurred in the skin. This was partly accounted for by a significant proportion of glucose uptake (1.15 g day-1) being anaerobically oxidized to lactate (0.41 g day-1). Measurements of protein synthesis in the patch showed that between 10 and 16% of whole body protein synthesis occurs in the skin.Results from the preparation demonstrate that it is a useful procedure to study metabolism in a defined patch of skin in the intact animal.

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.