Effects of feeding oscillating dietary ruminally-degradable protein levels on production, ruminal function, omasal nutrient flow, and N utilization in dairy cows
| dc.contributor.advisor | Mutsvangwa, Tim | |
| dc.contributor.committeeMember | Luby, Christopher | |
| dc.contributor.committeeMember | Buchanan, Fiona | |
| dc.contributor.committeeMember | McKinnon, John | |
| dc.contributor.committeeMember | Christensen, David | |
| dc.creator | Makurumure, Audrey Y | |
| dc.creator.orcid | 0000-0001-9645-9390 | |
| dc.date.accessioned | 2020-04-09T20:23:13Z | |
| dc.date.available | 2020-04-09T20:23:13Z | |
| dc.date.created | 2020-06 | |
| dc.date.issued | 2020-04-09 | |
| dc.date.submitted | June 2020 | |
| dc.date.updated | 2020-04-09T20:23:13Z | |
| dc.description.abstract | The objectives of this experiment were to determine the effects of feeding oscillating dietary ruminally-degradable protein (RDP) levels on: 1) feed intake, milk production and composition; and 2) ruminal fermentation characteristics, extent of ruminal nutrient digestion, omasal outflow of nutrients, and nitrogen (N) balance in lactating dairy cows. Eight Holstein dairy cows (days-in-milk = 110 ± 40; mean bodyweight = 734 ± 72 kg) were used in a replicated 4 × 4 Latin square design experiment with 4 dietary treatments. Each experimental period was 28 d long (14 d of dietary adaptation and 14 d of data and sample collection). Four cows in one Latin square were ruminally-cannulated and were used to study dietary effects on ruminal fermentation, nutrient digestion, and N balance. Heat-treated soybean meal (SoyPlus; Landus Cooperative, Ames, Iowa) and untreated soybean meal were used to manipulate dietary RDP levels of the experimental diets. The diets were initially formulated to be isonitrogenous at 16.5% CP; however, actual dietary CP contents ranged from 18.1 to 18.6% CP. Three diets were formulated to contain 9.34% (as % of dietary DM) RDP, 11.3% RDP, and 12.6% RDP. These three diets were then combined into 4 dietary treatments as follows: 1) feeding the 9.34% RDP diet on a continuous basis (designated LRDP); 2) feeding the 11.3% RDP diet on a continuous basis (MRDP); 3) feeding the 9.34 and 11.3% RDP diets on an oscillating (48-h) basis (LRDP/MRDP); and 4) feeding the 9.34 and 12.6% RDP diets on an oscillating (48-h) basis (LRDP/HRDP). Treatments 1 and 2 were designated STATIC RDP diets, whereas treatments 3 and 4 were designated OSC RDP diets. Experimental diets were offered to cows as total mixed rations (TMR) twice a day for ad-libitum intake. Dry matter intake (mean = 29 kg/d) was unaffected by diet (P ≥ 0.31). Milk yield was greater (P = 0.02) in cows fed the LRDP/ MRDP diet compared to those fed the LRDP/HRDP diet. Milk protein content was greater (P < 0.01) in cows fed the OSC RDP diets compared to those fed the STATIC RDP diets. Milk protein yield was greater (P = 0.02) in cows fed the OSC RDP diets compared to those fed the STATIC RDP diets. Milk urea-N content was greater (P < 0.01) in cows fed the MRDP diet compared to those fed the OSC RDP diets. Milk urea-N content was greater (P < 0.01) in cows fed the LRDP/HRDP diet compared to those fed the LRDP/MRDP diet. Plasma urea-N concentration tended to be greater (P = 0.10) in cows fed the OSC RDP diets compared to those fed the STATIC RDP diets. Nitrogen intake tended to be greater (P = 0.09) in cows fed the OSC RDP diets compared to those fed the STATIC RDP diets. Total urinary excretion was unaffected by diet (P ≥ 0.15). Urinary N excretion (expressed as g/d) was greater (P = 0.04) in cows fed the MRDP diet compared to those fed the OSC RDP diets. Also, urinary N excretion (expressed as g/d) was greater (P = 0.03) in cows fed the LRDP/MRDP diet compared to those fed the LRDP/HRDP diet. Urinary N excretion (expressed as % of N intake) was unaffected by diet (P ≥ 0.30). Urinary urea-N excretion (expressed as g/d) was unaffected by diet (P ≥ 0.11); however, urinary urea-N excretion (expressed as % of N intake) was greater (P = 0.05) in cows fed the LRDP/HRDP diet compared to those fed the LRDP/MRDP diet. Total N excretion (expressed as % of N intake) was unaffected by diet (P ≥ 0.23). Milk N secretion (expressed as g/d or % of N intake) was unaffected by diet (P ≥ 0.19). Apparent N balance (expressed as g/d) was unaffected by diet (P ≥ 0.13. Ruminal acetate concentration was greater (P < 0.01) in cows fed the OSC RDP diets compared to those fed the STATIC RDP diets. Ruminal concentrations of propionate were greater (P = 0.03) in cows fed the OSC RDP diets compared to those fed the STATIC RDP diets. Ruminal concentrations of total SCFA were greater (P = 0.01) in cows fed the OSC RDP diets compared to those fed the STATIC RDP diets. Ruminal ammonia-N concentration, acetate: propionate ratio and ruminal pH were not affected by diet (P ≥ 0.20). Intake, omasal flow and apparent digestion of DM were not affected by diet (P ≥ 0.14). Omasal flow of NH₃-N (expressed as g/d) was unaffected by diet (P ≥ 0.52). In conclusion, oscillating RDP levels of dairy cow diets improved milk protein yield and content and tended to increase plasma urea-N concentration and N intake. Total N excretion, milk N secretion, and apparent N balance were unaffected by feeding OSC RDP diet. Generally, the dietary changes did not improve NUE as expected. | |
| dc.format.mimetype | application/pdf | |
| dc.identifier.uri | http://hdl.handle.net/10388/12784 | |
| dc.subject | RDP | |
| dc.subject | oscillating | |
| dc.title | Effects of feeding oscillating dietary ruminally-degradable protein levels on production, ruminal function, omasal nutrient flow, and N utilization in dairy cows | |
| dc.type | Thesis | |
| dc.type.material | text | |
| thesis.degree.department | Animal and Poultry Science | |
| thesis.degree.discipline | Animal Science | |
| thesis.degree.grantor | University of Saskatchewan | |
| thesis.degree.level | Masters | |
| thesis.degree.name | Master of Science (M.Sc.) |