The objectives of this project were to investigate the effects of dietary lysine restriction on (1) the plasma concentrations of selected metabolites, free AAs, and three growth-related hormones, (2) the gene expression profile in longissimus dorsi muscle growing pigs. Twelve individually penned young barrows (Yorkshire × Landrace; 22.6 ± 2.04 kg) were randomly assigned to two dietary treatments (a lysine-deficient, LDD, and a lysineequate, LAD) diets, respectively. Pigs had ad libitum access to water and their respective diets for 8 weeks, and the ADG, ADFI, and G:F were determined. At the end of the trial, jugular vein blood was collected, and plasma was separated for the analysis of plasma parameters. Also, the longissimus dorsi muscle samples were collected from each pig for gene expression profile analysis. The ADG of LDD pigs was lower than that of LAD pigs, and so was the G:F since there was no difference in the ADFI between the two groups of pigs. The plasma concentrations of lysine, methionine, leucine, and tyrosine were lower, while that of β-alanine was higher, in the LDD pigs. The total plasma protein concentration was lower in the LDD pigs, whereas no differences were observed for the other metabolites, and the plasma concentrations of GF, insulin, and IGF-1 between the two groups. While gene expression profile results showed that sixty-nine genes were found differentially expressed (Benjamin-Hochberg corrected P-value < 0.05) in Diet I vs. Diet II pigs, of which 29 genes were down-regulated (Log₂ fold change (FC) < - 0.58) and 40 genes were up-regulated (Log₂ FC > 0.58). Furthermore, bioinformatic analyses revealed that the upregulation and downregulation of the DEGs may negatively affect the muscle protein turnover, structural development, and lipid metabolism of skeletal muscle. In conclusion, these results indicate that the lack of lysine including other two EAA as protein building block must be the primary reason for the compromised G:F ratio and ADG. The changes in the performance might be associated with some cell signaling and metabolic pathways suggested from the Bioinformatic results; however, may not involve the GH/IGF-1 axis.

The decrease in productivity caused by fescue toxicosis has been estimated to cost the United States livestock industry more than $1 billion per year due to reduced growth and diminished reproductive efficiency. This goal of the research presented in this dissertation is to enhance the knowledge base concerning the underlying physiological changes that occur during fescue toxicosis that lead to reduced intake and weight gain in cattle. As one of the factors associated with fescue toxicosis is a reduction in feed intake, achieving a consistent and adequate intake of toxins can be a complication. Results from experiment 1demonstrate that ruminal dosing of ground seed and a seed extract are able to mimic the classic symptoms of fescue toxicosis in cattle. This model whereby seed or extract is directly dosed into the rumen eliminates the possibility of reduced alkaloid intake due to refusal of feed by the animal. This model allows for more precise and repeatable dosing of alkaloids in fescue research. Experiment 2 results indicate that ingestion of endophyte-infected tall fescue leads to decreased fasting heat production in cattle. This is indicative of a reduction in maintenance energy requirements and may be related to a decrease in liver size or other metabolic activity in animals grazing endophyte-infected pastures. In addition, a reduction in basal metabolic rate may cause the compensatory gain often observed in cattle entering the feedlot after grazing endophyte-infected pastures. Data from experiment 3 provides evidence that whole body nitrogen and energy metabolism are not altered by fescue alkaloid ingestion. Experiment 3 also addresses the rate of feed degradation and ruminal passage rates in cattle ingesting endophyte infected fescue. While ruminal VFA profile is altered, this is likely due to reduced absorption, not increased production. The data from this experiment indicate that the reduction in weight gain and productivity seen during fescue toxicosis is primarily a function of reduced intake and not secondary effects of alkaloid ingestion.

A 2-year grazing study was conducted to evaluate the growth performance, ruminal fermentation, carcass characteristics, and fatty acid compositions in subcutaneous adipose tissue of beef steers grazing tall fescue (Festuca arundinacea Shreb.; TF) pastures without or with N fertilization. Nitrogen fertilization increased crude protein concentration of TF pasture and average daily gain of beef steers. Increase in total volatile fatty acids (VFA) and ammonia-N (NH3-N) concentrations were detected in steers grazing fertilized TF. In comparison with steers on feedlot, pasture-finished steers had greater proportions of cis-9, trans-11 CLA and C18:3 n-3, but lower n-6:n-3 ratio in adipose tissue. In the first in vitro study using 2 energy supplements [corn or dried distillers grains with solubles (DDGS)] and 4 pasture mixture forages [TF without or with N fertilizer (TF˗NF or TF+NF), TF-alfalfa mixture (TF+AF), and TF-birdsfoot trefoil mixture (TF+BT)], we found that corn supplementation increased total VFA and propionate concentrations, while DDGS supplementation decreased total VFA concentrations. Lower NH3-N concentration and methane (CH4) production were observed due to energy supplementation, in particular when corn grain was supplemented. Similar NH3-N:VFA ratios were detected in the cultures fed the TF+NF and the TF+BT. This result indicates that the TF+BT had similar fermentation efficiency on in vitro ruminal metabolism compared with the TF+NF. The second in vitro study was performed to investigate the effects of grass-to-legume ratios of 3 different TF-legume mixed diets on in vitro fermentation characteristics in continuous cultures. Propionate concentration increased with the increasing of legume proportion in the mixed diets. The greatest propionate concentration was shown by cultures fed the TF+CM, while the TF+AF and the TF+BT maintained a similar propionate concentration. Increasing legume proportion in the forage diets also increased NH3-N concentration, but decreased CH4 production in the cultures. Further decrease of CH4 production was recorded when the TF+BT was fed to the cultures. Overall results from the grazing study demonstrate that N fertilizer can improve nutrient quality of TF as well as growth performance of grazing steers, while the in vitro studies showed positive effects of grass-legume mixture diets on in vitro microbial metabolism by improving ruminal fermentation and reducing CH4 production.