Effect of year and cutting on equations for estimating net energy of alfalfa forage
1999
Belyea, R. | Restrepo, R. | Martz, F. | Ellersieck, M.
The net energy of lactation (NE(L)) concentration of forages is important for formulating diets. The equations presently used to estimate NE(L) of alfalfa are based on limited data. Our objective was to determine whether a larger database would provide more relevant equations. One hundred eighty samples of alfalfa were taken over four cuttings and 2 yr, combined into 45 composites and analyzed for neutral detergent fiber, acid detergent fiber (ADF), and in vitro true digestibility. Finally, NE(L) values were estimated using neutral detergent fiber and in vitro true digestibility. Prediction equations were obtained by regressing NE(L) upon ADF concentration. Changes in NE(L) with age of alfalfa at harvest differed with year and cutting. Estimation of NE(L) would be more accurate with equations specific for cutting and year, but such an approach would be difficult to use in practice. When data were pooled across years, four cutting-specific equations were obtained; these had different intercepts and slopes and gave different NE(L), values for a given ADF content. Differences among estimates of NE(L) increased as ADF increased. Data were combined across years and cuttings to give an overall equation that was similar to published prediction equations. Compared with NE(L) values from the cutting-specific equations, the overall equation under-estimated NE(L) for first cutting alfalfa and overestimated NE(L) of second cutting alfalfa. A lack of precision in estimating NE(L) could equate to 1.5 to 2.5 kg of milk/d. Cutting specific equations should be used to estimate the NE(L) of first- and second-cutting alfalfa; NE(L) of the third and fourth cuttings could be estimated using an overall equation.
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