Studies on the biology and productivity of the giraffe giraffa camelopardalis

[摘要] This study was carried out in the eastern Transvaal Lowveld in an area2with a giraffe population density of 2,6 per km . Lions are the only predatorsand it was estimated that 48% of the calves die in their firstyear. The sex ratio departs significantly from unity in favour of females.Plant fragments in the rumen were identified. Giraffe subsist on theleaves of trees and shrubs, though fruit, flowers, twigs and grass werealso utilised. Marked seasonal changes in the plant species selectedwere determined by availability and different habitats were utilisedaccordingly. Chemical analysis of rumen content showed correlations ofnutritional value with species eaten and seasonal phenological changesof the vegetation.Tooth eruption, wear and incremental layers in the cementum were foundto be suitable criteria for age determination. Total body mass was measured and carcasses dressed out at 61,9% for malesand 56,6% for females. Lower mass and lower proportion of fat was foundin the dry season. Meat yield was similar to other African ungulates,buttock and bone proportion was high, but fat was low.A gestation period of 457 d and birth mass of 102 kg (higher than in theliterature) was used to determine the age of foetuses whose growth wassimilar to other uniparous mammals. Postnatal increase in mass, height,length and chest girth followed the usual mammalian growth curve. Masscould be predicted from buttock or foreleg mass or from body measurements.There is evidence that hypertrophy of the foetal testis occurs. Parametersof male sexual function were correlated with age, but no seasonal effectswere apparent. Puberty was found to be dependant on physiological status.Androstenedione was the dominant testicular hormone in the foetus andtestosterone ·in the adult. Most conceptions occurred du~ing the humidmonths of the year when conditions are good for the females.Vesicular and haemorrhagic follicles and corpora lutea were common infoetal ovaries. Numerous corpora lutea were also found in immature ovaries,but they regressed at puberty. The corpus luteum of pregnancy underwent adecrease in size in early gestation followed by an increase to term. Bothovaries are equally active, implantation is ipsi1ateral and the placentais polycotyledonary of the syndesmochorial type. Gonadotrophic activitycould not be demonstrated in the urine of pregnant females. Lactationendured for about 13 months, the milk was relatively rich but its compositionchanges with time. There was a reduction in stomach fill in lategestation but lactating females had a significantly greater fill thanothers.

[发布机构] University of Pretoria