|Abstract or Summary
- 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.