Body condition indices of impala Aepyceros melampus : effect of age class, sex, season and management

Four indices of body condition : visual body condition (VBC), packed cell volume (PCV), marrow dry weight (MDW), and kidney fat index (KFI) were examined in impala over a 12-month period in a managed area and an unmanaged, overpopulated area in the Mlawula-Mbuluzi-Simunye Nature Reserve and Protected Area complex in north-eastern Swaziland. All of the body condition indices were significantly (p < 0,05) higher in adults (g 24 months of age) than in lambs (≤ 12 months) and yearlings (13 to 24 months). There was a significant seasonal variation in PCV and MDW in lambs, but not in the yearlings and adults. KFI varied with the reproductive status of adults, but there was only a slight seasonal variation in lambs and yearlings (p ≈ 0,1). VBC was poor in lambs, yearlings and adult males in the winter and spring, and good in the summer. In adult females VBC was fair / good in the winter and poor in the summer when they were nursing. VBC and PCV were lower in lambs in the unmanaged area than the managed area, and VBC, PCV, MDW and KFI were lower in yearlings in the unmanaged area. Only a combined index, MDW < 85% and KFI < 20%, differed significantly between areas in the adults. Despite significant differences between areas, the body condition indices were not sensitive indicators of habitat condition. The indices may provide information on the relative condition of individuals, but habitat effects may be restricted to small segments of the population, and can only be assessed when there is a proper control group. Vier indekse van liggaamskondisie : sigbare liggaamskondisie (SLK) verpakte selvolume (VSV), murg-droe-gewig (MDG) en niervetindeks (NVI), is oor 'n tydperk van 12 maande by rooibokke in 'n bestuurde gebied en 'n onbestuurde, oorbevolkte gebied in die Mlawula-Mbuluzi-Simunye Natuurreservaat- en Bewaarde Gebied-kompleks in noordoos-Swaziland, ondersoek. Al die indekse was betekenisvol (p < 0,5) hoer by volwassenes (g 24 maande ouderdom) tenoor lammers (≤ 12 maande) en jaarlinge (13-24 maande). Daar was betekenisvolle seisoenale variasie in VSV en MDG by lammers, maar nie by jaarlinge en volwassenes nie. NVI het gewissel na gelang van die voortplantingstatus van volwassenes, maar daar was slegs 'n geringe seisoenale variasie by lammers en jaarlinge (p ≈ 0,1). SLK was swak by lammers, jaarlinge en volwasse ramme gedurende die winter en lente en goed tydens die somer. By volwasse ooie was SLK gemiddeld / goed gedurende die winter en swak gedurende die somer terwyl hulle gesoog het. SLK en VSV was laer by lammers in die onbestuurde gebied teenoor die in die bestuurde gebied en SLK, VSV, MDG en NVI was laer by jaarlinge in die onbestuurde gebied. Slegs 'n gekombineerde indeks, MDG < 85% en NVI < 20% het betekenisvol tussen gebiede by die volwassenes verskil. Ten spyte van betekenisvolle verskille tussen gebiede was liggaamskondisie-indekse nie sensitiewe aanduiders van omgewingskondisie nie. Die indekse kan inligting aangaande die relatiewe kondisie van individue verskaf, maar omgewingsinvloede mag beperk wees tot klein gedeeltes van die bevolking en kan slegs bepaal word indien daar 'n geskikte kontrolegroep is.