Biomedical subjects

J C MacRae

Publications and source records attributed to J C MacRae.

At least 55 records · Page 3Linked to original sources

PubMed1983

Threonine metabolism in sheep. 2. Threonine catabolism and gluconeogenesis in pregnant ewes.

The irreversible loss rate (ILR) of glucose, bicarbonate and threonine were determined in six twin- and triplet-bearing ewes on three occasions during the last 6 weeks of gestation. Three of the ewes (group S) were given conventional rations of hay plus concentrates so that their blood ketone levels did not rise over this period. The other three ewes (group H) were given a fixed intake of hay throughout; their blood ketone levels rose, but remained at subclinical levels. The results are presented in the form of three-pool open-compartment models for each period. There was an increase in the glucose ILR for both groups over the 6-week period, but the over-all increase (mean +/- SE) was much greater (P less than 0.001) in group S (35.1 +/- 2.43 g carbon/d) than in group H (11.3 +/- 1.28 g C/d). Similarly, increases in bicarbonate ILR were also higher in group S (161 +/- 11.2 g C/d) than in group H (63 +/- 21.7 g C/d). However, whereas with group S ewes, receiving supplementary feed, this increase was progressive throughout the 6 weeks, with the group H ewes the increase which occurred over the last 3 weeks of gestation (56 +/- 26.3 g C/d) was much greater than that which occurred over the preceding 3 weeks (7 +/- 4.7 g C/d). This pattern was also evident in the oxidation of glucose to CO2. In contrast to the previously mentioned findings, neither threonine ILR nor the amount of threonine converted to glucose or catabolized to CO2 changed significantly over the 6-week period. The results are discussed in the light of findings presented in the previous paper that the amount of threonine used in catabolic processes can alter if a glucose-only sink is created in wether sheep.

3-Hydroxybutyric Acid↗

PubMed1983

Glucose production and utilization in non-pregnant, pregnant and lactating ewes.

By using continuous infusions of 3H- and 14C-labelled substrates, three-pool models, incorporating rumen propionate, plasma glucose and blood carbon dioxide were constructed to determine the contribution of propionate to glucose in non-pregnant, pregnant (mid and late) and lactating hill ewes. Although the intakes of non-pregnant and pregnant ewes were the same (1200 g dried grass/d) and resulted in similar levels of propionate production (33 g C/d), glucose production rate (GPR) increased from 44 g C/d in the non-pregnant ewes to 62 g C/d in the ewes carrying twins in late pregnancy. In lactating ewes given 2500 g dried grass/d, propionate production increased to 56 g C/d and GPR increased to 93 and 104 g C/d in ewes suckling single and twin lambs respectively. There was an increase in the percentage of the propionate resource which was diverted to glucose, from 37% in the non-pregnant ewes and ewes in mid-pregnancy, to 55% in late pregnancy and 60% in lactation. In spite of this apparent metabolic adaptation to the additional requirements for glucose, approximately 55% of the glucose-C was supplied by metabolites other than propionate and CO2. From the determination of plasma glycerol concentrations it was estimated that the maximum possible contribution of glycerol-C to glucose was only 8-12 g C/d. The remaining 40% of the glucose-C could not be accounted for and could have been derived from non-essential amino acids (NEAA). In the non-pregnant and pregnant ewes only 62% of the GPR was oxidized to CO2. In the lactating ewes only 49 and 30% of the GPR was oxidized to CO2 in the ewes suckling single and twin lambs respectively. In the majority of cases there was a marked similarity between the amounts of glucose-C apparently derived from NEAA and the amount of glucose-C which was not oxidized to CO2.

Animals↗

PubMed1982

Effects of gastrointestinal cannulation and jugular vein catheterization on the metabolism of sheep.

1. Certain digestive and metabolic criteria were examined in mature wethers before and following (1) a simple exploratory laporotomy (two sheep), (2) establishment of a rumen cannula plus simple ('T'-shaped) cannulas in the duodenum and ileum (six sheep), (3) establishment of a rumen cannula plus two cannulas in the caecum (four sheep), (4) establishment of a rumen cannula plus re-entrant cannulas in the duodenum and ileum (four sheep) and (5) insertion of catheters into both external jugular veins (four sheep). 2. Metabolizability of a standard ration and nitrogen balance and rumen retention time of the sheep were not significantly changed by any of the surgical procedures carried out. 3. The amount of heat produced per unit metabolic weight of the sheep prepared with re-entrant cannulas increased significantly (21 +/- 5.6%; P less than 0.001). 4. The use of the different preparations in digestive and metabolic studies is discussed.

Animals↗

PubMed1979

Nitrogen digestion in sheep given poor-quality indigenous hill herbages.

1. In two experiments, the sites of digestion of non-ammonia nitrogen (NAN) and the amounts of urea N recycled to the rumen were measured in mature wether sheep given diets of indigenous hill herbage (Agrostis-Festuca and heather). 2. Duodenal and ileal flow values were obtained using 103Ru-phenanthroline and 51Cr-EDTA markers in animals prepared with simple (T-shaped) cannulas. Amounts of urea N recycled to the rumen were estimated from measurements of the transfer of plasma urea carbon into rumen bicarbonate and the production rate of rumen bicarbonate using 14C-labelled urea and bicarbonate respectively. 3. The flows of NAN at the duodenum and ileum were linearly related to the intake of herbage (P less than 0.001). There was a net gain of non-ammonia N anterior to the duodenum on both diets (at an intake of 460 g organic matter (OM)/d, 3.7 g NAN/d on Agrostis-Festuca and 3.3 g NAN/d on heather). 4. Net digestibility of NAN entering the small intestine was within a normal range on the Agrostis-Festuca (0.58 at 460 g OM intake) diet but low on the heather diet (0.43 at 460 g OM intake). 5. It was calculated that at 460 g OM intake only 0.9 and 1.1 g/d respectively of the duodenal NAN on the Agrostis-Festuca and heather diets could have been derived from urea-N recycled to the rumen. Thus 2.8 g and 2.2 g/d had to be accounted for as non-urea endogenous NAN.

Animal Feed↗

PubMed1978