Models for lucerne quality grading

[摘要] English: A study was conducted to develop and identify an evaluation system (model) to predictlucerne hay quality. Two hundred and ten lucerne hay samples for chemical analyses and invitro digestibility determinations were obtained from different cuttings during two seasons(100 samples for 1998/1999 and 110for 1999/2000), at different times in a season and fromdifferent lucerne producing areas (sites) in the Northern Cape, South Africa. One hundredand eighteen of these samples were used for essential amino acid analysis. Thirty of the 210samples and an additional 42 lucerne hay samples were obtained during one season(1999/2000) to estimate protein degradation (in sacco). Twelve Dorper lambs fitted with arumen cannula were used in the degradation study.The variation in nutritive value of South African lucerne hay was evaluated as an initialstudy. The highest moisture content recorded (9.35%) was safely below the criticalmoisture level of 15% for effective storage. The coefficient of variation (CV = ± 15%) ofcrude fibre (CF), acid detergent fibre (AD F) and neutral detergent fibre (NDF) emphasizedthe need for analysis to ensure accurate diet formulation. This also applied for ash (CV =22.11 %), crude protein (CP) (CV = 11.6%), non-fibre carbohydrate (NFC) (CV = 34.0),effective ruminal protein degradability (ERPD) (CV = 18.9%) and essential amino acids(EAA) (CV = 14.5% - 27.1%). The effective protein degradation parameters a, b and cshowed the highest CV (106.8% - 306.4%). The mean in vitro organic matter digestibility(IVOMD) value (67.6%) seems to be representative (CV = 5.4%) of the IVOMD for thelucerne hay population used.Lower ERPD values (average 47.7%) than usually reported, were observed. The influenceof acid detergent fibre nitrogen (ADF-N) on the rumen undegradable protein (RUP) oflucerne hay was negligible. Heat damage occurred to a small percentage (3.5%) of thesamples. Lucerne hay had a high lysine (4.55g/100g CP) and low methionine (0.44g/100gCP) content. Methionine, lysine and isoleucine were, in a descending order, the leastdetectable in lucerne hay for milk synthesis.A second study was conducted to include protein quality, according to the United Kingdommetabolizable protein system (MP), into the total forage index (TFI) system to determine thequality of lucerne hay more accurately. This model (lucerne quality index) was compared tothe chemical analysis and existing models for the determination of lucerne hay quality. Thefollowing models were used to estimate lucerne hay quality:a) Relative feed value (RFV) = % digestible dry matter (DDM) x dry matter intake as a% of body weight (DMI) x 0.775b) Total forage index (TFI) = RFV + % CP x 6c) Adjusted total forage index (ATFI) = RFV + adjusted crude protein (ACP) x 6.d) Lucerne quality index (LQI) = IVOMD x DMI + MP x 6, expressed as an index.NDF (r2 = 0.57) compared to ADF (l = 0.48) was a more accurate estimator of IVOMD.The NDF content of lucerne hay also played an important (P<0.0001)role in regressionequations to predict the quality models RFV (r2 = 0.86), TFI (r2 = 0.82) and ATFI (r2 = 0.84)respectively as well as IVOMD (r2 = 0.57) and ERPD (r2 = 0.50). A high relationshipoccurred between these various models (r2>0.90). A moderate correlation (P<0.0001) washowever observed between LQI and respectively ADF (r2 = 0.50), NDF (r2 = 0.50), IVOMD(r2 = 0.56), CP (r2 = 0.50), RFV (r2 = 0.51), TFI (r2 = 0.56) or ATFI (r2 = 0.55). Nosignificant (P>0.05) predictor for the ERPD fractions (a, b and c) were observed. LQI couldbe predicted from ADF (r2 = 0.50) or ADF, ERPD and CP (r2 = 0.94) in a multipleregression equation.The results of the present study clearly indicated that a large variation occur in the energyand protein composition as well as the utilization of nutrients in South African lucerne hay.This emphasizes the need for a rapid and accurate quality evaluation system for lucerne hayin practice. LQI seems to be a better quality evaluation system than to those currentlyavailable. The relationships with LQI in the present study is based on a relatively smallnumber (n = 30) of lucerne hay samples. Further research with a larger number of lucernehay samples is needed to confirm these results. The usage of near infrared reflectancespectroscopy (NIRS) for the rapid nutritional evaluation of lucerne hay (LQI) also needsurgent investigation.

[发布机构] University of the Free State