174. ATMOSPHERIC OXYGEN ALTERS THE EMBRYONIC METABOLOME AS QUANTIFIED BY CARBOHYDRATE UPTAKE AND AMINO ACID UTILISATION

Oxygen regulates embryo development at both the cleavage and post compaction stages. In this study we investigated the effects of atmospheric oxygen during the preimplantation stages, on the post-compaction embryonic metabolome through quantification of glucose consumption and amino acid utilization. Zygotes obtained from F1 hybrid mice (C57BLxCBA) were randomly allocated to either 5 or 20% oxygen. In the first experiment, following the first 48 h of culture, embryos were cultured individually in 1 μL drops of modified G2 medium (0.5 mM glucose) and moved to fresh drops of medium every 24 h. The glucose concentration in the spent media samples, including controls containing no embryo, was determined by microfluorimetry. In the second experiment, embryos which had developed to the early blastocyst stage after 72 h were cultured for a further 24 h in groups of 10 in 2 μL drops of G2. Analysis of amino acid utilization was performed using liquid chromatography-triple quadrupole mass spectrometry. Glucose consumption by embryos cultured in 5% oxygen was significantly greater on day 4 and day 5 (4.89 ± 0.29 and 6.13 ± 0.41 pmol/embryo/h) compared to embryos cultured in 20% oxygen (2.59 ± 0.40 and 5.09 ± 0.28 pmol/embryo/h; P < 0.05). In contrast amino acid utilisation by embryos cultured in 5% oxygen was significantly less than embryos cultured in 20% oxygen (P < 0.05). The data generated will help to determine the aetiology of oxygen toxicity to the preimplantation embryo. Higher glucose utilisation by embryos in 5% oxygen is consistent with their improved development. Conversely, the increased utilisation of amino acids by blastocysts in 20% oxygen may reflect an adaptation to increased oxidative stress as a result of culture in a non-physiological oxygen concentration. This study demonstrates that atmospheric oxygen during the preimplantation period perturbs the embryonic metabolome which results in a compensatory increase in amino acid utilisation.

Nematodes and nutrient partitioning

Subclinical infection of sheep with gastrointestinal nematodes results in the diversion of nutrients from growth and development towards the repair of damaged intestinal tissues and to sustain the metabolic shifts (nutritional, hormonal and immune) occuring in tissues affected by the parasites. These metabolic effects include decreased nitrogen retention; increased amino acid utilisation and oxidation in the gastrointestinal tract; increased endogenous protein loss and altered protein synthesis in the gastrointestinal tract; increased amino acid utilisation and protein synthesis in the liver and activation of the immune system. These observations strongly suggest that there is competition between the key tissues involved in parasitism and that metabolic decisions are made resulting in the re-prioritisation of nutrient utilisation between the tissues in this inter-organ system. Nutritional status of the host can influence the pathogenesis of parasitic infection and well-nourished animals generally withstand parasitism better than those less adequately fed. Recent studies have focused on the effect of restricting intake on the acquisition of immunity in sheep selected either for resistance or susceptibility to nematodes. The major outcome of these studies was the increase of peripheral eosinophil counts in resistant animals infected with Trichostrongylus colubriformis when fed on an ad libitum diet compared with similar animals fed the same diet at a maintenance level. This was inversely correlated to the numbers of adult parasites recovered. Intake seems to be the primary determinant of the expression of immunity in sheep selected for resistance against nematodes.

Effects on growth rate and utilisation of amino acids in weaner pigs fed diets containing whole proteins and free amino acids in combination with different energy sources

This experiment was designed to determine the effects of 3 protein and 3 energy (carbohydrate) sources on the growth rate of weaner piglets and their eciency of nutrient utilisation. All 3 energy sources and 2 of the protein sources [casein plus free amino acids (casein), free amino acids alone (FAA)] were chosen because they were suitable for studies measuring amino acid utilisation. The third protein source, based predominantly on peptide protein, was a combination casein-fish meal-soyabean meal (CFS). The combinations of carbohydrates tested were sucrose alone, sucrose plus 150 g lactose/kg, and wheat starch plus 150 g sucrose plus 150 g lactose/kg. The experiment was a randomised complete block design based on a 33 factorial arrangement with 5 blocks and 9 pigs per block. Piglets given CFS as the protein source exhibited greater (P < 0·001) weight gain than those consuming casein or FAA (494 v. 415 and 345 g/day) and deposited protein more eciently (P < 0·001) (e.g. crude protein retention/ileal-digestible protein intake, 0·65 v. 0·56 and 0·49). The apparent digestibility of nitrogen (N) and amino acids was lower for the CFS-fed piglets (0·83 and 0·88) than for those given casein (0·92 and 0·95) or FAA (0·94 and 0·96). The daily weight gains of piglets given diets containing starch, sucrose, and lactose were 9-10% lower (P < 0·05) than those consuming either sucrose or sucrose plus lactose (391 v. 433 and 430 g/day). The energy sources, however, had no effect on ileal digestibility of amino acids or empty body composition. Neither casein nor FAA diets were found to be acceptable sources of amino acids for studies on amino acid utilisation. Sucrose and sucrose plus lactose were excellent energy sources for piglets. In contrast, wheat starch was found to be unsuitable for inclusion in synthetic weaner diets for piglets with a liveweight of 5-20 kg.