Graduate Thesis Or Dissertation

 

Perennial ryegrass nonstructural carbohydrates in dairy cattle nutrition Public Deposited

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  • Ruminal microorganisms require nitrogen and energy for microbial crude protein (MCP) synthesis. High-quality grass provides an excess of readily available proteins relative to available carbohydrates which reduces the conversion efficiency of grass protein to MCP. Nonstructural carbohydrates (NSC) are the primary source of readily available energy. Objectives of trial 1 were to study the effects of perennial ryegrass NSC on milk yield and composition, dry matter intake (DM1), and rumen fermentation in dairy cows. Two perennial ryegrasses, one with a relatively high NSC content (HNSC; Elgon®) and one commonly grown in Oregon (CNSC; Linn) were fed as green chop. Twelve Holsteins and two Jerseys were blocked by milk yield and assigned at random to a treatment. Cows were supplemented with a total mixed ration (TMR) for 1 h twice daily. Grasses were cut, sampled, and offered ad-libitum twice daily after the TMR. Individual grass and TMR intake and milk yield were collected twice daily for 21 d. Milk samples were collected d 0 of the treatment adaptation period and d 7 and 21 of the treatment period. On d 9 and 21 of the treatment period, rumen samples were collected at 0, 1, 2, 3, 4, 6, 8, 10, and 12 h relative to each TMR feeding and analyzed for pH, volatile fatty acids (VFA), and ammonia (NH3). Data were analyzed with the MIXED procedure of SAS. For grass DM1, treatment by wk interaction was significant (P<O.Ol). For HNSC, grass DM1 was greater wk 2 (P<O.O1) and tended to be greater wk 3 (P<O.lO). Total mixed ration DM1 tended to be greater for HNSC treatment (P0.06). Milk yield and yield of milk fat and protein were greater for the HNSC treatment (P<O.05). Milk urea nitrogen and ruminal VFA and NH3 did not differ between treatments. Grass composition was different than expected. High NSC grass was lower in NSC (P<O.05) and higher in crude protein (P<O.O1). Grass neutral detergent fiber and acid detergent fiber were similar. In this study, milk and component yields for HNSC were greater than CNSC treatment; however, effects were not due to grass NSC. Well-preserved grass silage is the result of the controlled fermentation of fresh grass; characterized by low pH, high lactic acid, and low NH3. Nonstructural carbohydrates are the primary fermentation substrate. Objective of trial 2 was to determine if differences exist between fermentation characteristics of three high NSC grasses and one control NSC grass ensued in vacuum sealed bags. Perennial ryegrasses, three with a relatively high NSC concentration (HNSC; AberAvon®, AberDart®, and Elgon®) and one commonly grown in Oregon, control NSC (CNSC; Linn) were selected. Three replicates of each grass were ensiled at the a.m. and p.m. harvests. Each bag was packed, vacuum sealed, and ensued for 60 d. Fresh grass samples were taken from each bag. Fresh grass NSC was greater for 1-INSC grasses versus Linn. Final pH was lower, total acids was higher, and lactic acid tended to be higher for HNSC grasses. Final pH, lactic acid, acetic acids, total acids, and NH₃ were lower for p.m. versus a.m. cutting. Ensuing was most efficient for HNSC grass varieties harvested at the p.m. cutting.
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