2 results
A compartmental model describing changes in progesterone concentrations during the oestrous cycle
- Susanne Meier, John R Roche, Eric S Kolver, Ray C Boston
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- Journal:
- Journal of Dairy Research / Volume 76 / Issue 2 / May 2009
- Published online by Cambridge University Press:
- 13 March 2009, pp. 249-256
- Print publication:
- May 2009
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The objective of this study was to develop a mathematical model that accurately describes the rise and decline in plasma progesterone concentrations, and is able to define parameters describing progesterone appearance and disappearance during the bovine oestrous cycle. Daily plasma progesterone data from 27 cows were used to develop a compartmental model consisting of an appearance function and an appearance modulating function. Model outputs included an apparent appearance or secretion duration, appearance rate and an average disappearance rate (expressed as arbitrary units per day; units/d). Shape-based clustering identified three common shape-based groups (or clusters) of progesterone profiles defined as either ‘peaked’ profile, with the profile reaching a distinguishable peak, 'structured', with the profile exhibiting a wave-like pattern, or ‘flat top’, with the profile reaching a plateau. Differences in the model parameters for the three different shapes of progesterone profiles were examined: peaked (n=13), flat top (n=7) and structured (n=7). The mean duration of apparent appearance was 11·49 (sd 0·17 d) for all 27 profiles. The model estimates for total appearance of progesterone (area under the curve; ng/ml per cycle), mean appearance rate and maximum appearance rate were 69·04 ng/ml per cycle (sd 15·2 ng/ml per cycle), 3·19 ng/ml per cycle (sd 0·7 ng/ml per d) and 6·70 ng/ml (sd 1·31 ng/ml), respectively. The average disappearance rate was 1·0 units/d (sd 0·04 units/d). The apparent appearance duration was greatest (P<0·01) in the flat top profiles (12·54, sd 0·41 d) followed by the structured (11·77, sd 0·66 d) and the peaked (10·80, sd 0·30 d) profiles. Total and mean progesterone appearance, maximum progesterone appearance rate, and the progesterone disappearance rates were not different between the profiles. The model successfully simulated all components of the progesterone profile and was able to define specific parameters of different shaped progesterone profiles. A simple model able to estimate parameters describing progesterone appearance and disappearance can be used to explore the relationships between profile shapes and reproductive outcomes.
A new approach to the quantitative estimation of nitrogen metabolic pathways in the rumen
- Yoav Aharoni, Haim Tagari, Ray C. Boston
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- Journal:
- British Journal of Nutrition / Volume 66 / Issue 3 / November 1991
- Published online by Cambridge University Press:
- 09 March 2007, pp. 407-422
- Print publication:
- November 1991
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Rumen nitrogen metabolism values were estimated by the use of a single injection of 15(NH4)2SO4 into the rumen of sheep and consecutive 15N enrichment measurements in the rumen ammonia pool, rumen non-NH3-N (NAN) pool, rumen purine pool and blood urea-N (BUN) pool for a period of 24 h. Synthesis and degradation of N compounds in the rumen and passage of N to and from the rumen were evaluated on a chemical rather than a microbial basis; microbial fractions were not separated. This model was examined in two experiments. In Expt 1 a ram (55 kg) was given a semi-synthetic diet (1067 g dry matter (DM), 22.8 g N) in which soya-bean meal provided over 90% of the N. In Expt 2, two rams (45 kg) were given in three consecutive periods a semi-synthetic basal diet containing: (1) roasted soya-bean meal (SBM, 725 g DM, 14.8 g N/d); or (2) fishmeal (FM, 728 g DM, 15.5 g N/d); or (3) raw soya-bean meal (RSBM, 724 g DM, 13.8 g N/d). In all these rations, the main protein source provided over 90% of the N. In Expt 1, 68.3% of N intake was degraded directly to NH3 in the rumen, 21.2% escaped rumen degradation and 10.5% was incorporated into stable N compounds in the rumen. Net NH3 transfer to the blood was 30.4%, NH3 flow from the rumen was 6.6% and rumen NAN output was 63% of N intake. In Expt 2, rumen NAN output was larger (7.67, 14.36 and 8.89 g N/d for diets containing SBM, FM and RSBM respectively; P < 0.05) and net NH3 loss to the blood was smaller (6.1, 0.39 and 4.17 g N/d for diets SBM, FM and RSBM respectively; P < 0.05) for diet FM as compared with the soya-bean diets. The percentage of rumen NAN that was synthesized from NH3 was larger for diet RSBM (36.4, 40.3 and 49.1 for diets SBM, FM and RSBM respectively; P < 0.05) than for the other two rations. NH3 pool sizes (g N) were 0.463, 0.385 and 0.301 for diets SBM, FM and RSBM respectively (P < 0.05), while their hourly turnover rates were 15.8, 26.1 and 5.12 for diets SBM, FM and RSBM respectively (P < 0.01), indicating no correlation between pool size and its turnover rate. The existence of a small and rapidly turning over NAN pool to which NH3 is first bound (SNAN1) was indicated by the difference in the shape of the NAN and purines 15N-enrichment curves in the first 3 h after label injection. The fact that the rate of NH3 initial binding to SNAN1 pool was related neither to ammonia pool size nor to SNAN1 pool size suggests the existence of an unknown control mechanism at this site.