No description available.

No description available.

Digitized by Kansas Correctional Industries

No description available.

Three experiments were conducted to study dietary effects on urea-nitrogen (N) recycling as a strategy to improve the efficiency of N utilization in ruminants. Experiment 1 examined the effects of feeding diets containing two levels of dietary crude protein (CP; 10.8 vs. 14.0%) and ruminally-degradable protein (RDP; 73.4 vs. 76.0% of CP) on urea-N recycling to the gastro-intestinal tract (GIT), N balance, and microbial protein production in beef heifers. Feeding the low CP diet decreased N intake (P < 0.01), ruminal ammonia-N (NH3-N) concentration (P < 0.01) and urinary N excretion (P <0.01). Endogenous urea-N production increased (P = 0.03) with increasing dietary CP level, as did urinary urea-N loss (P = 0.04). However, urea-N transfer to the gastro-intestinal tract (GIT) was similar across diets, with most of this N returned to the ornithine cycle. Microbial N supply was unaffected (P > 0.05) by dietary treatment. Experiment 2 examined the effects of feeding diets containing two levels of ruminally-degradable starch (RDS; 28.6 vs. 69.2% of total starch) and RDP (48.0% vs. 55.0% of CP) on urea-N recycling to the GIT, N balance, duodenal nutrient flow, and ruminal microbial protein production in beef heifers fed low CP (10%) diets. Ruminal NH3-N concentration was greater (P = 0.01) in heifers fed high RDP as compared with those fed low RDP, and it was also greater (P = 0.01) in heifers fed low RDS as compared with those fed high RDS. Microbial N flow to the duodenum increased as RDP level increased on the high RDS diet, but was not affected by RDP level on the low RDS diet (interaction; P = 0.04). Urea-N entry rate and urea-N transfer to the gastro-intestinal tract were similar (P > 0.05) across diets. The amount of recycled urea-N that was incorporated into microbial N increased as RDP level increased on the high RDS diet, but the opposite was observed on the low RDS diet (interaction; P = 0.008). Experiment 3 examined the effects of feeding diets containing two levels of CP (14.9 vs. 17.5%) and RDP (63.0 vs. 69.0% of CP) on urea-N recycling to the GIT, microbial protein production, N balance, omasal nutrient flow, and milk production in lactating dairy cows. Nitrogen intake (P < 0.01) and both urinary N (P < 0.01) and urea-N (P < 0.01) output were greater for cows fed the high compared with those fed the low CP diet. Ruminal NH3-N concentration tended to be greater in cows fed the high than those fed the low CP diet (P = 0.06), and was greater in cows fed high RDP as compared with those fed the low RDP diet (P < 0.01). However, N balance, milk yield, and microbial N supply were unaffected (P > 0.05) by dietary treatment. The proportion of endogenous urea-N that was recycled to the GIT (i.e., GER: UER) was greater (P = 0.02) in cows fed the low CP compared with those fed the high CP diet. In summary, the results of this thesis show that reducing dietary CP level in beef and dairy cattle reduces urinary N excretion whilst maintaining microbial N supply. In addition, judicious combinations of RDP and RDS when feeding low CP diets can potentially enhance the efficiency of microbial N production. These data show that through careful dietary manipulation, overall efficiency of N utilization can be improved leading to a reduction in N excretion into the environment.

Thesis (Ph.D.)--University of Wyoming, 2008. / Title from PDF title page (viewed on Dec. 4, 2009). Includes bibliographical references.

No description available.

No description available.

No description available.

The doubly labelled water technique (DLW) allows the estimation of the carbon dioxide production (r<SUB>co2</SUB>) of a free-living animal from which, with knowledge of the respiratory quotient (RQ), energy expenditure may be predicted. The aim of this project was to assess the performance of this technique in ruminant animals using sheep as a model. In a series of preliminary experiments physiological processes which may affect this technique were examined. It was found the administered isotopes equilibrated throughout the body water after 6 hours following either an oral or intravenous dosing. <SUP>2</SUP>H lost in the form of methane was estimated to lead to errors in r<SUB>co2</SUB> of between -3.27 and -6.54% and may be corrected for by use of a methane to urine enrichment ratio of 0.6536. Losses of <SUP>2</SUP>H in exchangeable sites in faeces were estimated to lead to errors in r<SUB>co2</SUB> of between -5.35 to -6.54%, again corrections factors were proposed. Sequestration of <SUP>2</SUP>H into carcase fat was also quantified, a maximum error of 0.67% was estimated on r<SUB>co2</SUB>, although more <SUP>2</SUP>H was detected in the fat free carcase this was assumed to be exchangeable <SUP>2</SUP>H. A maximum error of -2.39% on water turnover (r<SUB>H20</SUB>) was estimated to arise from the recycling of <SUP>2</SUP>H due to the catabolism of labelled body solids, although this was probably an overestimate. No convincing evidence was found to suggest the fractionation factors applied to human subjects are not equally applicable to ruminant animals. The baseline body water enrichment was altered by a change in diet from synthetic concentrates to fresh chopped grass. Isotopic estimates of r<SUB>co2</SUB> were compared with respiration chamber measurements of r<SUB>co2</SUB>. A number of curve fitting procedures were considered together with three multi-point, three ratio plot and three two-point estimations of r<SUB>co2</SUB>. Using a multi-point calculation and after making corrections for fractional water loss, loss of <SUP>2</SUP>H in methane and faecal solids, r<SUB>H20</SUB> was underestimated by 16.24%. The isotopic r<SUB>co2</SUB> estimates were on average 1.52% (SD 15.31) lower than the chamber measurements, although one animal was markedly different from the others, omitting this animal led to an average error of + 5.95% (SD 4.34). In applying this technique to animals in the field the influence of a free-living existence on the performance of the method was assessed. A number of r<SUB>co2</SUB> calculation procedures were again considered. Preliminary chamber measurements were used to estimate methane production and faecal dry matter output in the field. Estimates of r<SUB>H2O</SUB> in the field (mean 7.218.1. day<SUP>-1</SUP>) were lower than those measured in the chambers (mean 9.812 1.day<SUP>-1</SUP>). From predictions of dry matter intake in the field RQ was estimated (mean 1.067), using the isotopic r<SUB>co2</SUB> estimates (mean 590 1.day<SUP>-1</SUP>) energy expenditure was then predicted (mean 11586 kJ.day<SUP>-1</SUP>). In the light of this work it was concluded the DLW technique may be usefully applied to ruminant animals and a number of practical suggestions were made.