Studies on the nutritive value of lucerne for dairy cows

[摘要] ENGLISH ABSTRACT:An experiment was conducted to determine whether the quality of lucerne hay could beimproved by artificial drying in a forced air bulk dryer (FABD) in comparison to lucernehay produced by natural drying in the field. Lucerne fields were divided into four blocksof equal size and blocks were randomly assigned to each of the two treatments (natural orartificial drying). Lucerne was harvested at an early to mid flowering stage on sixoccasions. In two blocks, cut lucerne was left in the field to dry. Material in theremaining two blocks were left in the field for an initial drying period of no longer than24 hours, after which it was transferred to a FABD. Samples oflucerne were taken at thetime of harvest and then at regular intervals (on average 0, 4, 8,22,26,29,47,50,53, 56,58,69, 72, 76 and 80 hours after cutting) in the field and in the FABD until the materialwas dry enough for baling (ca. 15-18% moisture). Collected lucerne samples were driedin a forced draught oven until constant mass to determine moisture content. The rate ofmoisture loss was compared. Samples of the lucerne hay in the field and in the FABDwere taken after baling to determine forage quality by means of chemical analysis.Samples were analysed for crude protein (CP), total digestible nutrients (TDN), digestibleorganic matter (DOM), acid detergent fibre (ADF) and neutral detergent fibre (NDF)content. Good weather conditions for natural drying during the trial period resulted inlucerne hay of similar chemical composition. Naturally dried lucerne hay had CP, ADFand NDF contents of 17.3, 41.2 and 48.0%, respectively, while values for artificiallydried lucerne were 17.6, 40.6 and 47.3%. It was concluded that artificial drying oflucerne does probably not produce lucerne of a better quality than field drying undergood weather conditions.In the following trials eight ruminally cannulated cows (four Jerseys and four Holsteins)were used to compare protein and fibre degradability of lucerne harvested at differentstages of maturity (ie. 4, 5 and 6 weeks' regrowth), and of different lucerne products (ie.lucerne hay, lucerne leaves and 8% leaves added to hay), dried in a forced air bulk dryer.All cows received a total mixed lactation diet for the duration of the trial period. The firstin situ rumen degradability trial was conducted with lucerne harvested at three stages ofmaturity namely after 4,5 and 6 weeks' regrowth. Bags were incubated in the rumen fortime intervals of 0, 2, 4, 8, 16, 24, 48 and 72 hours. Samples were analysed for dry matter(DM), crude protein (CP) and neutral-detergent fibre (NDF) content.The effective DM, protein and NDF degradabilities of lucerne hay did not differ (P>0.05)between Holstein and Jersey cows. In Holsteins, DM degradability values calculated atan outflow rate of 0.05/h for lucerne harvested after 4, 5 and 6 weeks' regrowth were63.1, 57.1 and 55.0%, respectively. Values of 64.6, 58.6 and 55.7% were obtained inJerseys. CP degradability values for lucerne harvested after 4, 5 and 6 weeks' regrowthwere 81.7, 77.2 and 77.6% in Holsteins and 81.3, 78.2 and 79.4% in Jerseys. NDFdegradability values for lucerne harvested after 4, 5 and 6 weeks' regrowth were 35.8,45.5 and 23.2% respectively in Holsteins and 35.1, 45.9 and 24.8% in Jerseys.Analysis of the effective DM, protein and NDF degradabilities across breeds indicateddifferences between lucerne harvested after 4, 5 and 6 weeks' regrowth. Rumendegradability of DM and protein was the highest for lucerne harvested after 4 weeks'regrowth. DM degradability values oflucerne harvested after 4,5 and 6 weeks' regrowthcalculated at a flow rate of 0.05/h were 63.9, 57.9, 55.4%, respectively, while proteindegradability values were 81.5, 77.7 and 78.5%. The lowest ruminal NDF degradabilityvalues were found for lucerne harvested after 6 weeks' regrowth. Values for NDFdegradability calculated at a flow rate of 0.05/h for lucerne harvested after 4, 5 and 6weeks' regrowth were 35.5, 45.7 and 23.7%, respectively. These results indicated thatlucerne quality decreased in terms of DM, protein and NDF degradability as the plantsmature.The second in situ rumen degradability trial was conducted with three different lucernecomponents dried in a forced air bulk dryer, namely lucerne hay, lucerne leaves andlucerne hay + 8% leaves. The procedure followed was the same as in the first in situ trial.Dacron bags, containing samples of the lucerne components were incubated in the rumenfor time intervals of 0, 2, 4, 8, 16,24,48 and 72 hours. Samples were also analysed forDM, CP and NDF content and compared both between breeds and across breeds.DM and protein degradability values (rate and effective degradability) of the artificiallydried lucerne hay were higher in Jerseys than in Holsteins. DM degradability valuescalculated for Holsteins at a flow rate of 0.05/h for lucerne hay, lucerne leaves andlucerne hay + 8% leaves were 57.6, 66.5 and 61.4%, respectively, while proteindegradability values of 76.9, 75.5 and 77.9% were obtained. DM degradability valuescalculated for Jerseys were 62.9, 69.1 and 61.7%, respectively, while proteindegradability values of 82.4, 77.6 and 78.5% were obtained.Analysis of the mean disappearance values across breeds indicated that proteindegradability of lucerne hay in the rumen was higher than that of lucerne leaves. Proteindegradability values calculated at a flow rate of 0.05/h for lucerne hay and lucerne leaveswere 80.1 and 76.5% respectively. The NDF degradability of lucerne hay was, however,lower than what it was for lucerne leaves (24.6 vs. 29.7%).

[发布机构] Stellenbosch University