A grading system for Medicago sativa hay in South Africa

Abstract

English: The purpose of this study was to develop a national grading system for lucerne hay in South Africa by identifying the most appropriate sampling, as well as sample handling and preparation procedures, the most accurate NlRS - nutrient calibrations and an accurate, cost effective quality model. Six hundred lucerne hay samples were obtained from different cuttings at different times in the seasons and from different commercial irrigation areas (sites) in South Africa. The 600 samples were scanned and screened through a NlR Systems Model 5000 monochromator (Foss). One hundred and sixty- eight samples representing the spectral characteristics of the South African lucerne hay population were selected and chemical analysed. The variation in nutritive value of South African lucerne hay was evaluated as an initial study. The highest moisture content recorded (13.54%) was safely below the critical moisture level of 16% for effective storage. The coefficient of variation (CV) ranged from 1.2% for dry matter (DM) up to 66.2% for acid detergent fibre-crude protein (ADF-CP). The average ash content was 12.97% (7.3 to 29.5%), indicating soil contamination. Relatively high average values were recorded for calcium (Ca) (l.35%), potassium (K) (2.53%) and iron (Fe) (874 ppm). The fibre fractions varied as follows: acid detergent fibre (ADF) (2l.26 to 47.28%), neutral detergent fibre (NDF) (28.89 to 65.93%), lignin (4.32 to 16.25%), cellulose (16.29 to 36.44%) and hemicellulose (5.26 to 19.86%). The mean NOMD for both 24 and 48hr (69.26 and 73.19% DM, respectively), was representative (CV = ± 8%) of the lucerne hay population. Crude protein (CP) (average = 20.7%DM) consists of 76.9% true protein. According to ADFCP, 6% of the samples were heat damaged. A second study was conducted to determine the effect of the grinding procedure on the moisture and CP content of the ground sample. Variance of analyses revealed significant (P<0.0001) differences in moisture concentration between ground (CV = 16.1%) and unground (CV = 27.4%) samples ranging from 14.7 up to 4l.1% (of the unground sample). However, the grinding process had a non-significant (P>0.05) influence on the CP content of the final ground product. Even though r2 between measured moisture results on unground samples and values predicted by electronic moisture tester (EMT) seems to be significantly high (r = 0.79; P<0.0001), individual predicted values for higher moisture samples (>10%) failed to accurately predict moisture content around the moisture area of critical concern (16%) and higher. In a third study, the accuracy of near infrared reflectance spectroscopy (NIRS) to predict chemical and digestibility parameters was investigated. Values for r2 and ratio of prediction to deviation (RPD) used as estimates of calibration accuracy for chemical and digestibility parameters were considered as follows: good for DM (r2 = 0.97; RPD = 4.84), CP (r2 = 0.97; RPD = 4.57), ADF (r2:;; 0.95; RPD;;;; 3.97), NDF (r2 <= 0.0.95; RPD = 3.99), lignin (r2 = 0.94; RPD = 3.61), ash (r2 = 0.93; RPD = 3.12) and chloride (Cl) (r2 = 0.95; RPD = 3.74); intermediate for neutral detergent fibre-crude protein (NDF-CP) (r2 = 0.91; RPD = 2,96), sugar (r2 = 0.91; RPD = 2.82), in vitro organic matter digestibility at 24 hr (IVOMD24) (r2 = 0.90; RPD = 2.84) and NOMD at 48hr (IVOMD48) (r2 = 0.89; RPD = 2.70); and low (RPD<2.31 ) for soluble protein (SP), acid detergent fibre-crude protein (ADF-CP), fat, starch, neutral detergent fibre digestibility (NDFD) and the macro minerals (Ca, P, Mg, P, Na and S). The results recorded in the present study indicated that the NIRS technique is acceptable for DM, CP, ADF, NDF, lignin, ash and Cl analysis and for inclusion in quality models. Milk yield (MY) derived from the CNCPS model, by replacing the average lucerne hay in a complete diet with the rest of the 168 samples, was used as a criterion to evaluate and/or develop models for lucerne hay quality grading. The best single predictor of MY was the ADF content of lucerne hay, which explained 67% of the measured variation. The relatively poor performance of CP (r2 = 0.04) and other protein related parameters (r2< 0.25; ACP, ADF-CP, NDF-CP and SP) in predicting MY suggest that protein content of lucerne hay is an unreliable indicator of lucerne hay quality. The developed empirical equation named lucerne milk value (LMV), including ADF, ash and lignin (Y = 64.18 - 0.23ADF - 0.53ash - 0.90lignin), accurately predict MY. Application of the theoretically-based summative TDNlig model of Weiss et a/. (1992), using lignin to determine truly digestible NDF, explained almost all of the variation in MY (r2 = 0.98). However, several of its components were poorly predicted by NIRS and therefore, not suited for quality assessment. Current available models for assessing lucerne hay quality revealed lower accuracies, especially when protein was included in the model. The results of the present study clearly indicated that large variations occur in the energy and protein composition as well as the utilisation of nutrients in South African lucerne hay. This emphasises the need for a rapid and accurate quality evaluation system for lucerne hay in practice. The developed LMV proved to be a practical, simplistic, economical and accurate quality evaluation model for commercial application.

Afrikaans: Die studie het ten doel gehad om 'n nasionale graderingstelsel vir lusernhooi in Suid-Afrika te ontwikkel deur die mees toepaslike monstememing-, sowel as monsterhanterings en - voorbereidingsprosedures, die mees akkurate NIRS-kalibrasies en 'n akkurate, koste-effektiewe kwaliteitsmodel te identifiseer. Seshonderd lusernhooi monsters is vanaf verskillende snysels gedurende verskillende tye van die seisoen vanaf verskillende kommersiële besproeiingsgebiede in Suid-Afrika ingesamel. Hierdie 600 monsters is met die hulp van 'n Nabyinfrarooispektrofotometer (NlRS), Model 5000 monochromator (Foss) geskandeer. Eenhonderd agt-en-sestig monsters verteenwoordigend van die spektrale karakter van die Suid-Afrikaanse lusernhooi populasie is geselek-teer en chemies ontleed. Die vanaste ill die voedingswaarde van Suid-Afrikaanse lusemhhooi is in 'n eerste studie geevalueer. Die hoogste verkreë voginhoud, (13.54%), was veilig onder die kritiese vogvlak van 16% wat nodig is vir effektiewe opberging. Die koëffisiënt van variasie (KV) het vanaf 1.2% vir droëmateriaal (DM) tot 66.2% vir suurbestandevesel-protein (SBV-RP) gewissel. Die gemiddelde asinhoud was 12.97% (7.3 tot 29.5%) wat grondbesoedeling aangedui het. Relatiewe hoë gemiddelde waardes is vir kalsium (Ca) (1.35%), kalium (K) (2.53%) en yster (Fe) (874 ppm) verkry. Die veselfraksies het as volg gevarieer: suurbestandevesel (SBV) (21.26 tot 47.28%), neutraalbestande vesel (NBV) (28.89 tot 65.93%), lignien (4.32 tot 16.25%), sellulose (16.29 tot 36.44%) en hemisellulose (5.26 tot 19.86%). Die gemiddelde in vitro organiesemateriaalverteerbaarheid (NOMV) vir beide 24 en 48 uur (69.26 en 73,19% DM, respektiewelik) was verteenwoordigend (KV = 8%) van die lusernhooi populasie. Ru-protein (RP) (gemiddeld = 20.7% DM) het uit 76.9% ware protein bestaan. Volgens suurbestandeonoplosbare- protein, was 6% van die monsters aan hitte beskadiging blootgestel. 'n Tweede studie is uitgevoer om die effek van maalprosedure op die vog en die RP inhoud van die gemaalde monster te bepaal. 'n Variansie-analise het betekenisvolle (P<0.0001) verskille in vogkonsentrasie tussen gemaalde (KV == 16.1%) en ongemaalde (KV ;: 27.4%) monsters aangetoon wat van 14.7 tot so hoog as 41.1% (van die ongemaalde monster) gewissel het. Daarenteen het die maalproses 'n nie-betekenisvolle (p>O.05) invloed op die RP inhoud van diefinale gemaalde produk gehad. Alhoewel r2 tussen die voginhoud van die ongemaalde monsters, en die waardes deur die elektroniese vogmeter (EVM) voorspel beduidend hoog was (r = 0.79; P<O.OOOl), was die voorspelling vir hoër vogmonsters (>10%) rondom die van kritiese voginhoud (16%) onakkuraat. In 'n derde studie is die akkuraatheidondersoek van 'n N1RS om die chemiese en verteerbaarheids parameters te voorspel. Waardes vir r2 en die verhouding van voorspelling teenoor afwyking (RPD), as beramers van die akkuraatheid van kalibrasies vir chemiese en verteerbaarheidsparameters gebruik en was as volg goed vir DM (r2 = 0.97; RPD = 4.84), RP (r2 = 0.97; RPD = 4.57), SBV (r2= 0.95; RPD = 3.97), NBV (r2= 0.0.95; RPD = 3.99), lignien (r2 = 0.94; RPD = 3.61), as (r2 = 0.93; RPD = 3.l2) en chloried (Cl) (r2 = 0.95; RPD = 3.74); gemiddelde vir neutraalbestandevesel-ruprotein (NBV-RP) (r2 = 0.91; RPD = 2.96), suiker (r2 = 0.91; RPD = 2.82), in vitro organiesemateriaalverteerbaarheid op 24 uur (IVOMV24) (r2 = 0.90; RPD = 2.84) en IVOMV op 48uur (IVOMV48) (r2 = 0.89; RPD = 2.70); en laag (RPD<2.31) vir oplosbare protein (OP), SBV-RP, vet, stysel, neutraalbestandevesel verteerbaarheid (NBVV) en die makro minerale (Ca, P, Mg, P, Na and S). Die resultate van die huidige studie dui daarop dat die NIRS tegniek aanvaarbaar is vir DM, RP, ADF, NVB, lignien, as en Cl -analise sowel as vir insluiting in kwaliteitsmodelle. Melkproduksie (MP) voorspel deur die "Cornell Net Carbohydrate and Protein System" (CNCPS) model, deur lusern met gemiddelde waardes in 'n volledige dieët met die res van die 168 monsters te vervang, is as kriteria gebruik vir die evaluasie en/of ontwikkeling van modelle vir lusernhooi kwaliteitsbepaling. Die enkele beste voorspeller van MP was SBV-inhoud van lusernhooi, wat 67% van die gemete variasie verklaar het. Die relatiewe swak vertoning van RP (r2 = 0.04) en ander protein verwante parameters (r2<0.25; ACP, SBV-RP, NBV-RP EN OP) in die voorspelling van MP dui daarop dat proteininhoud van lusernhooi 'n onbetroubare aanduider van lusernhooikwaliteit is. Die empiriese ontwikkelde vergelyking genaamd lusernrnelkwaarde (LMW), wat insluit SBV, as en lignien (Y=64.l8 - 0.23SBV - 0.53as - 0.90lignien), het MP akkuraat voorspel. Die toepassing van die teoreties-gebaseerde "summative" TDNlig model van Weiss et al. (1992), deur van lignien gebruik te maak om ware verteerbare NBV te bepaal, het byna al die variasie in MP (r2= 0.98) verklaar. Verskeie van die komponente word egter swak deur NIRS voorspel en is nie geskik vir kwaliteitbepaling nie. Huidige beskikbare modelle vir die bepaling van lusernhooikwaliteit toon swak akkuraatheid veral wanneer protein by die model ingesluit word. Die resultaat van die huidige studie het duidelik aangetoon dat daar groot variasie in die energieen proteinsamestelling, asook benutting van voedingstowwe in Suid-Afrikaanse lusernhooi voorkom. Dit beklemtoon die noodsaaklikheid van 'n vmmge en akkurate kwaliteitsevalueringstelsel vir lusernhooi in die praktyk. Die ontwikkelde LMW blyk 'n praktiese, eenvoudige, ekonomiese en akkurate kwaliteitevalueringsmodel te wees, vu kommersiële gebruik.