Twenty-four Quarter horse weanlings (120 d +/- 10 d) were blocked by age into 4 groups (n = 6) for a 56 d trial to evaluate the influence of methionine on growth and nitrogen retention. Weanlings were housed by block and individually fed 1 of 4 concentrate diets twice daily at 1.5% BW (as fed). Weanlings were randomly assigned to 1 of 4 treatments: basal (0.20 MET), basal + 0.03% methionine (0.23 MET), basal + 0.07% methionine (0.27 MET), and basal + 0.11% methionine (0.31 MET). Diets were formulated to be isonitrogenous, isocaloric, and contain equal amounts of LYS and THR. Coastal bermudagrass hay was individually fed at 0.75% BW (as fed). Growth measurements, body weight, rump fat, and plasma were obtained every 7 d. The final 4 days consisted of total collection of urine and feces. Feed, fecal, and urine samples were analyzed for nitrogen content and nitrogen balance was calculated. Urine was analyzed for urea and ammonia concentration. Plasma was analyzed for urea concentration. Grain, hay, and fecal samples were analyzed for nutrient composition. Data were analyzed using the PROC MIX procedure of SAS. Linear, quadratic, and cubic effects were tested in the form of contrasts. There was no influence of treatment on growth measurements, nitrogen balance, or urinary urea or ammonia. Intake of LYS and THR (g/d) did not differ among treatments (P = 0.78 and P = 0.38 respectively). Plasma urea nitrogen (PUN) was influenced by treatment (P = 0.005) exhibiting quadratic (P = 0.04) and cubic (P = 0.002) effects. An unexpected peak in PUN was observed with 0.27 MET. Upon analysis, 0.20 MET contained more lysine than formulated, and 0.27 MET contained the least lysine. Treatments 0.20 MET and 0.31 MET contained more threonine compared to formulations. These differences may explain unexpected values of PUN concentration. Results suggest future studies that more closely isolate methionine as the only dietary variable are necessary to better explain the methionine requirements of weanling horses.

<p>Successful management of nitrogen (N) excretion is important for sustainable pork production. Two experiments were conducted and their objectives were to study the effect of dietary protein and fibre on N excretion patterns and to relate plasma urea (PU) to urinary N excretion.</p> <p>In the first experiment, three dietary protein contents (high, 197; medium, 169; low, 138 g kg^-1 ) and two levels of fibre (low and high) were tested. Diets (wheat, barley, soybean meal; oat-hulls as the fibre source) were formulated to an equal digestible energy (DE) content (3.25 Meal DE kg^-1) and at least 2.18 g digestible lysine per Meal DE, and were supplemented with Lys, Met, Trp, Thr, Ile, or Val. Pigs (32 ± 3.4 kg; n = 42) were housed in confinement-type metabolism crates for 19 d. On d 10 or 11, catheters were installed by cranial vena cava venipuncture. Daily feeding rates were adjusted to three times maintenance and daily rations were halved to two equal meals. Faeces and urine were collected from d 15 to 19. Five blood samples were collected in two-h intervals on d 16 and 19. Faecal N, urinary N, and total N excretion were reduced linearly with a reduction of dietary protein content (P < 0.001). Reduction was greater for urinary (48%) and total N excretion (40%) than for faecal N (23%) excretion. The ratio of urinary N to faecal N was reduced linearly with a reduction of dietary protein content (P < 0.001). Retention of N (g d^-1) was reduced linearly but N retention as percentage of intake was increased linearly with a reduction of dietary protein content (P < 0.001). Addition of oat hulls did not affect N excretion patterns (P > 0.10). Dietary treatments did not affect average daily gain (ADG) or feed efficiency (P > 0.1 0). Plasma urea increased after feeding, peaked at 4 h and then decreased toward pre-feeding concentrations. A linear relationship of urinary N to PU concentration (R² = 0.66) was observed.</p> <p>In the second experiment, effects of dietary protein content (high, 185; and low, 157 g kg^-1) and fibre sources on N excretion patterns were studied in a 2x3 factorial arrangement. The three fibre sources were control, soybean hulls (SH; 15% ), and sugar beet pulp (SBP; 20%). Diets were formulated to 3.3 Meal DE kg^-1 and 2.4 g digestible Lys per Meal DE, and were supplemented with Lys, Met, Trp, Thr, lie, or Val. Pigs (30.5 ± 3 kg; n = 36) were housed in confinement-type metabolism crates, with restricted access to feed (3 x maintenance DE) from d 1 to 18, and free access to feed from d 19 to 26. Faeces and urine were collected from d 15 to 18 and d 23 to 26, and blood samples on d 17 and 25. With restricted access to feed, faecal N (as % of N intake) was increased 3 percentage units for low compared to high protein content, and increased 4 percentage units for SH and 6.5 percentage units for SBP compared to control (P < 0.05). Urinary N was reduced 5 percentage units for low compared to high protein content, and reduced 9 percentage units for SBP compared to control (P < 0.05). Retention of N (g d^-1) was reduced 12% for low compared to high protein content (17.9 compared to 20.4 g d^-1 ; P < 0.05), and was similar among fibre treatments (P > 0.10). With free access to feed, faecal N (as % of N intake) was increased 2.5 percentage units for low compared to high protein content, and increased 5 percentage units for SH and 9 percentage units for SBP compared to control (P < 0.05). Urinary N was reduced 5 percentage units for low compared to high protein content, and reduced 9 percentage units for SH and 10 percentage units for SBP compared to control (P < 0.05). Retention of N (g d^-1) was similar for dietary protein content (30.5 g d^-1 ; P > 0.10), and reduced for SH (27 g d^-1; P < 0.05) compared to control (31 g d^-1), while was intermediate for SBP (29 g d^-1). A linear relationship of urinary N to PU concentration was observed with both restricted (R² = 0.66) and free access to feed (R²= 0.71).</p> <p>Reduction of dietary protein content is an efficient way to reduce total and urinary N excretion, which may reduce ammonia emission. Inclusion of fibre sources high in fermentable fibre shifted N excretion from urine N to faeces N while fibre sources resistant to fermentation did not have any effects on N excretion patterns. Combined effects of dietary protein content and fibre reduced urinary N excretion further than single effects. Level of feed intake is an important consideration when effectiveness of a nutrient management strategy is studied. Diets with a low protein content and containing synthetic AA should be studied using pigs with free access to feed to verify that N retention is maintained. A linear relationship of urinary N to PU concentration was observed under both restricted and free access to feed indicating that urinary N excretion could be predicted from PU concentration.</p>

<p>Successful management of nitrogen (N) excretion is important for sustainable pork production. Two experiments were conducted and their objectives were to study the effect of dietary protein and fibre on N excretion patterns and to relate plasma urea (PU) to urinary N excretion.</p> <p>In the first experiment, three dietary protein contents (high, 197; medium, 169; low, 138 g kg^-1 ) and two levels of fibre (low and high) were tested. Diets (wheat, barley, soybean meal; oat-hulls as the fibre source) were formulated to an equal digestible energy (DE) content (3.25 Meal DE kg^-1) and at least 2.18 g digestible lysine per Meal DE, and were supplemented with Lys, Met, Trp, Thr, Ile, or Val. Pigs (32 ± 3.4 kg; n = 42) were housed in confinement-type metabolism crates for 19 d. On d 10 or 11, catheters were installed by cranial vena cava venipuncture. Daily feeding rates were adjusted to three times maintenance and daily rations were halved to two equal meals. Faeces and urine were collected from d 15 to 19. Five blood samples were collected in two-h intervals on d 16 and 19. Faecal N, urinary N, and total N excretion were reduced linearly with a reduction of dietary protein content (P < 0.001). Reduction was greater for urinary (48%) and total N excretion (40%) than for faecal N (23%) excretion. The ratio of urinary N to faecal N was reduced linearly with a reduction of dietary protein content (P < 0.001). Retention of N (g d^-1) was reduced linearly but N retention as percentage of intake was increased linearly with a reduction of dietary protein content (P < 0.001). Addition of oat hulls did not affect N excretion patterns (P > 0.10). Dietary treatments did not affect average daily gain (ADG) or feed efficiency (P > 0.1 0). Plasma urea increased after feeding, peaked at 4 h and then decreased toward pre-feeding concentrations. A linear relationship of urinary N to PU concentration (R² = 0.66) was observed.</p> <p>In the second experiment, effects of dietary protein content (high, 185; and low, 157 g kg^-1) and fibre sources on N excretion patterns were studied in a 2x3 factorial arrangement. The three fibre sources were control, soybean hulls (SH; 15% ), and sugar beet pulp (SBP; 20%). Diets were formulated to 3.3 Meal DE kg^-1 and 2.4 g digestible Lys per Meal DE, and were supplemented with Lys, Met, Trp, Thr, lie, or Val. Pigs (30.5 ± 3 kg; n = 36) were housed in confinement-type metabolism crates, with restricted access to feed (3 x maintenance DE) from d 1 to 18, and free access to feed from d 19 to 26. Faeces and urine were collected from d 15 to 18 and d 23 to 26, and blood samples on d 17 and 25. With restricted access to feed, faecal N (as % of N intake) was increased 3 percentage units for low compared to high protein content, and increased 4 percentage units for SH and 6.5 percentage units for SBP compared to control (P < 0.05). Urinary N was reduced 5 percentage units for low compared to high protein content, and reduced 9 percentage units for SBP compared to control (P < 0.05). Retention of N (g d^-1) was reduced 12% for low compared to high protein content (17.9 compared to 20.4 g d^-1 ; P < 0.05), and was similar among fibre treatments (P > 0.10). With free access to feed, faecal N (as % of N intake) was increased 2.5 percentage units for low compared to high protein content, and increased 5 percentage units for SH and 9 percentage units for SBP compared to control (P < 0.05). Urinary N was reduced 5 percentage units for low compared to high protein content, and reduced 9 percentage units for SH and 10 percentage units for SBP compared to control (P < 0.05). Retention of N (g d^-1) was similar for dietary protein content (30.5 g d^-1 ; P > 0.10), and reduced for SH (27 g d^-1; P < 0.05) compared to control (31 g d^-1), while was intermediate for SBP (29 g d^-1). A linear relationship of urinary N to PU concentration was observed with both restricted (R² = 0.66) and free access to feed (R²= 0.71).</p> <p>Reduction of dietary protein content is an efficient way to reduce total and urinary N excretion, which may reduce ammonia emission. Inclusion of fibre sources high in fermentable fibre shifted N excretion from urine N to faeces N while fibre sources resistant to fermentation did not have any effects on N excretion patterns. Combined effects of dietary protein content and fibre reduced urinary N excretion further than single effects. Level of feed intake is an important consideration when effectiveness of a nutrient management strategy is studied. Diets with a low protein content and containing synthetic AA should be studied using pigs with free access to feed to verify that N retention is maintained. A linear relationship of urinary N to PU concentration was observed under both restricted and free access to feed indicating that urinary N excretion could be predicted from PU concentration.</p>