| 口試日期：2026 |
| 學位類別：碩士 |
| 指導教授：李滋泰 |
| 研究生：李士昕 |
| 摘要 |
| The present study evaluated the effects of reducing dietary crude protein content under balanced major limiting crystalline amino acid supply, with supplementation of distillers dried grains with solubles (DDGS), on growth performance, serum biochemical profiles, urinary and fecal nitrogen concentrations, daily nitrogen excretion, feed cost, and estimated greenhouse gas emission potential in nursery pigs. The core concept of low-protein feeding is not simply to reduce dietary crude protein content, but to reduce excess nitrogen supply while maintaining amino acid balance through supplementation of major limiting crystalline amino acids, including Lys, Trp, Thr, and Met, thereby reducing nitrogen metabolic burden without impairing growth performance. The study comprised two independent trials. In Trial 1, diets with different crude protein levels were used to evaluate the basic responses of nursery pigs to low-protein feeding. The results showed that, when major limiting amino acid supply was maintained, reducing dietary crude protein decreased serum urea nitrogen (SUN), urinary nitrogen concentration, and fecal nitrogen concentration, and significantly reduced total daily nitrogen excretion and estimated CO2e emission potential during the later nursery phase (P < 0.01). However, in Trial 1, average daily gain or average daily feed intake at selected growth phases still showed treatment differences (P < 0.05) or tendencies (0.05 ≤ P < 0.10), indicating that nursery pigs remain sensitive to the extent of crude protein reduction, amino acid balance, and diet composition. Separately, Trial 2 was conducted using diets formulated to meet the target levels of the major limiting amino acids. Pigs were assigned to a control group (CON), a low-protein group (LP), or a low-protein diet supplemented with 20% DDGS group (LPDDGS) to evaluate whether inclusion of 20% DDGS in the later-phase low-protein diet could maintain growth performance without weakening nitrogen-reduction responses. The results showed that low-protein and LPDDGS treatments did not significantly impair body weight, average daily gain, average daily feed intake, or gain-to-feed ratio during any phase (P > 0.05). SUN was significantly lower in the low-protein treatments during the later phase than in the CON group (P < 0.05), and urinary and fecal nitrogen concentrations were generally lower than those in the CON group. Daily nitrogen excretion, calculated from individual urinary wet weight, fecal dry matter output, and nitrogen concentrations, showed that LP and LPDDGS significantly reduced total daily nitrogen excretion during the 8- and 12-week metabolism collection periods (P < 0.01). At the 12-week collection period, LPDDGS reduced total daily nitrogen excretion by approximately 32.8% relative to CON. Estimated CO2e emission potential, calculated from daily total nitrogen excretion using the IPCC Tier 2 approach, was also lower in LP and LPDDGS than in CON (P < 0.01), indicating that low-protein diets can reduce relative greenhouse gas emission potential under the same manure management assumptions. Feed cost analysis showed that feed cost per kilogram of body weight gain was 21.12% lower in LPDDGS than in CON, although this result was descriptive. In conclusion, low-protein diets supplemented with major limiting crystalline amino acids reduced nitrogen metabolic burden, daily nitrogen excretion, and estimated CO2e emission potential in nursery pigs, and the use of 20% DDGS was suitable as a compatible co-product ingredient in later-phase low-protein formulations. Keywords: nursery pigs, low-protein diet, distillers dried grains with solubles, nitrogen utilization efficiency, sustainable feeding |