Effect of date of harvest on the nutritional quality of native grass hay

Native grass hay meadows in three Kansas Flint Hills counties were sampled at 2-week intervals during the growing season to determine the effect of harvest date on forage quality. Each sample was analyzed for crude protein (CP), acid detergent fiber (ADF), and phosphorus (PHOS). CP and PHOS contents declined, and ADF increased as harvest date progressed into the growing season. Both CP and ADF were related highly to harvest date. PHOS content was associated only moderately with harvest date. Harvest date of native grass hay can significantly influence supplemental protein needs for beef cows.


Introduction
Native grass hay serves as an important are dominant in the Flint Hills region of Kanroughage source for wintering beef cattle in sas.Kansas.Harvest date is the most important management factor for native grass hay mead-A 35 ft.long by 3 ft.wide plot was estabows, because it has a major impact on dry lished at each county location.Within each matter (DM) yield, forage quality, and plant plot, 12 blocks corresponding to harvest date vigor in the following year.Native hay harvest were established.A 30-in.×30-in.sample was in the Flint Hills region normally occurs in hand-clipped from the center of each block mid-July, although it can take place from late leaving a 4-in.stubble height.Samples were June through September.
harvested from each block at 2-week intervals Because forage quality declines and DM yield per acre increases with advancing plant

Experimental Procedures
Cowley, and Marion counties were used in this study.Meadows consisted of mixed species of perennial, warm-season grasses and forbs that beginning on June 3, 1997 and concluding on November 4, 1997.
Immediately after clipping, forage samples were sealed in an airtight bag and submitted to a commercial forage testing laboratory for chemical analysis.Samples for each harvest date were analyzed for DM, crude protein (CP), acid detergent fiber (ADF), and phosphorus (PHOS) contents and regression equations were developed to describe their relationship with harvest date.Julian calendar date (JCD) was included as the independent variable (June 3 = day 155, November 4 = day 309).Feed costs were estimated for lactating beef cows consuming native grass hay of various CP content.

Results and Discussion
Individual county data were pooled into one overall regression equation for each indicator of forage quality evaluated.Harvest date accounted for the majority of the variation for CP (R 2 =.89) and ADF (R 2 = .81).As anticipated, CP content declined with advancing maturity throughout the growing season (Figure 1), where % CP = 30.13-(.1753 x JCD)+(.00029x JCD 2 ).Conversely, ADF content increased by 1 percentage unit every 12 days (% ADF = 21.75 + .0836xJCD) within the window of the sampling period (Figure 2).Harvest date was less effective for predicting PHOS content (R 2 = .36) (Figure 3).However, the PHOS content of the native grass hay sampled in this study did tend to decline with advancing maturity and ranged from .18 to .05%(% PHOS = .1822-[.00036xJCD]).
The CP content of the base forage influences the amount of supplemental protein needed to meet nutritional requirements.Therefore, beef cows or stockers that consume forages harvested beyond the optimum date will require more supplemental protein to attain requirements.Table 1 illustrates the influence of harvest date and CP content of native hay on the supplemental protein requirements for a 1,100 lb lactating beef cow.In this example, cows consuming 4.0% CP native grass hay would require an additional .88lb of supplemental protein at an added cost of $.30/day, compared to cows consuming 8.0% CP hay.Represented another way, there is an approximate cost savings of $4.43 per cow per percentage unit improvement in CP from 4.0 to 8.0% in the native grass hay.Based on the results of this study, native hay meadows should be harvested by mid-July in order to optimize forage quality, while allowing adequate time for range grasses to replenish root carbohydrate reserves prior to fall dormancy.

Figure 1 .
Figure 1.Crude Protein Content of Native Grass Hay.

Figure 2 .
Figure 2. Acid Detergent Fiber Content of Native Grass Hay.

Figure 3 .
Figure 3. Phosphorus Content of Native Grass Hay.