Typescript (photocopy). / Digitized by Kansas Correctional Industries

No description available.

Thesis (Ph. D.)--University of Missouri-Columbia, 2002. / Typescript. Vita. Includes bibliographical references (leaves 103-104). Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 2002. / Typescript. Vita. Includes bibliographical references (leaves 103-104). Also available on the Internet.

Postpartum LH and GH secretory patterns were evaluated with mature Brangus cows group fed either 50%M (n = 8) or 100%M (n = 7) NRC maintenance energy requirements starting two months prepartum and continuing for three months postpartum. Feed level was adjusted at 14 day intervals. Weights of cows and (or) calves were taken every 14 days before and after calving. Sequential blood samples were taken every 15 min for 8 h at biweekly intervals starting 14 days postpartum and continuing until 100 days. Serum LH and GH were determined by a validated double antibody RIA. A peak-detection algorithm was used to summarize hormone data into 5 variables for each cow at each bleeding period. Data were analyzed by GLM and regression using SAS procedures. Cows in the 100%M group were heavier (P<0.01) at calving time and at the end of the trial. There were no significant differences for weight of calves at birth or at the end of the study for the two energy levels. Total release of LH during secretory episodes was 5 fold greater (27 vs 5 ng/ml x min P<0.05) in cows receiving 100%M vs 50%M energy. Basal concentration and peak height of LH increased linearly with time postpartum in 50% but not 100% energy groups. For GH, cows receiving 50%M energy had more secretory spikes (2.6 vs 2.1 per 8 h; P<0.05), and higher basal concentration (14 vs 8 ng/ml; P<0.05), and a shorter duration of secretory episodes (82 vs 95 min; P<0.05) compared with cows on 100%M energy. Maximum release of GH occurred earlier postpartum in cows receiving 100%M energy (30-39 d) vs cows receiving 50%M energy (90+d). Number of GH peaks increased linearly with time postpartum in cows on 100% energy, but not in the 50% group. Dietary energy restriction of mature beef cows significantly alters several parameters of LH and GH secretion during the early postpartum period.

No description available.

No description available.

Several hypotheses concerning the role of fishes in influencing nutrient dynamics in freshwater ecosystems were examined in Lake Memphremagog (Quebec-Vermont). Phosphorus excretion by fishes provides a negligible amount (< 0.33%) in comparison to the quantity taken up by the seston. The phosphorus pools present in the seston and fish community were approximately equal and both were twice the phosphorus content in the zooplankton. Part of this nutrient reservoir is released during the decomposition of fish carcasses. The potential is dependent upon post-spawning mortality rate, the fate of phosphorus in decomposing fish tissue, and the concentrations of allochthonous phosphorus entering the lake. Daily losses of epilimnetic phosphorus from the seston due to fish (up to 40%) and enhancement of nutrient excretion by zooplankton due to size-selective predation are important when open water fish populations are mainly planktivores. When benthic, detrital, or faculative consumers predominate, as in Lake Memphremagog, the effect of fishes on nutrient dynamics through foraging pressure is probably small.

No description available.

Phytic acid (PA) reduces nutrient digestibility in pigs and poultry, and has been shown to increase endogenous nutrient losses (ENL) in poultry. However, there is lack of information on the effect of PA on ENL in pigs, and mechanisms by which PA increases ENL. Three experiments were conducted to determine the effects of PA on ENL in pigs and to establish mechanisms by which PA increases the ENL. The first experiment investigated the effect of PA on ileal digestibility and ileal endogenous nutrient flows. Phytic acid decreased the apparent ileal sodium digestibility to a negative value (-18%). The second experiment investigated the effect of PA on gut enzyme activities, histomorphology and sodium-dependent glucose transporter 1 (SGLT1) gene expression. Phytic acid did not affect the gut villous height, villous height to crypt depth ratio, and jejunal SGLT1 gene expression, but decreased gastric pepsin activity and tended to decrease jejunal Na-K-ATPase activity. In the third experiment, the effect of PA on piglet performance and ion uptake in jejunum mounted in Ussing chamber, and jejunal SGLT1 protein level was evaluated. Phytic acid did not affect jejunal SGLT1 protein expression, but lowered piglet performance and jejunal active ion uptake. In conclusion, results from this study show that PA can reduce the apparent ileal digestibility of sodium to a negative value, indicating that PA can increase ileal endogenous sodium loss. The results also show that PA can reduce the pepsin activity and ion uptake in the gut. The reduced pepsin activity implies increased secretion of the enzyme plus hydrochloric acid and hence increased secretion of sodium bicarbonate that neutralizes the acid. The reduced ion uptake by PA implies reduced nutrient absorption. Because sodium is absorbed partly by co-transportation with other nutrients, the reduced ion uptake by PA implies reduced sodium absorption. Thus, it appears that PA increases ileal endogenous sodium flow partly through reduced pepsin activity and ion uptake in the small intestine. Overall, the results show that phytase (a PA-hydrolysing enzyme), which is added in pig diets to improve phosphorus availability, does not only improve phosphorus availability, but alleviates ant-nutritional effects of PA as well.