Kob (Uganda kob) (Kobus kob)

Order: Artiodactyla

Family: Bovidae

1) General Zoological Data

The Uganda kob is a grazer and a close relative of the waterbucks; it is still fairly abundant in western Uganda but has become rare or extinct in Kenya and Tanzania. Two possible subspecies with somewhat different phenotypes and mtDNA findings exist (formerly "Adenota" : Kobus kob; Kobus vardoni [or puku] see Nowak, 1999). Adult males weigh around 95 kg, females are 60 kg. Males are generally larger and darker than females and possess lyre-shaped horns. Kobs live gregariously in "leks" or "arenas". The longevity of various kob species has been summarized by Weigl (2005); that of Kobus kob is given as 18-21 years. "Kobus" is said to be an African native name (Gotch, 1979).

The evolution of the Neotraginae is poorly understood because of the paucity of African fossils (Thenius & Hofer, 1960).

Male Uganda kob at San Diego Zoo.

2) General Gestational Data

Gestation is from 235 to 240 days and produces single neonates that weigh around 5 kg (Buechner et al., 1966). Longer gestations are quoted by Mentis (1972).

3) Implantation

Hradecky et al. (1988) described the early attachment (dorsal curvature – close to the mesometrium) of ruminant cotyledons and their future development as well as the histiotrophic nutrition of the fetus. They also depicted the implanted cotyledons of an Uganda kob. Of the various species studied by these authors they considered the kob to have the "simplest" placentome structure. Implantation is always in the right horn (Buechner, 1961; Mossman & Duke, 1973), as this is always the larger uterine horn.

4) General Characterization of the Placenta

This is a polycotyledonary, epitheliochorial placenta and the only specimen available came from a pregnant animal that was euthanized because of severe trauma. The female fetus weighed 1,550 g, had a 33 cm CR length and was located in the right uterine horn. There were approximately 35 cotyledons in this gestation and the cotyledons had the "flat" appearance, as suggested by Mossman (1987). The corpus luteum was also on the right but the placenta extended into the left horn with smaller cotyledons. The cotyledons were arranged in four rows and the largest measured 5 x 4 cm. The entire placenta measured 50 x 20 cm and weighed 1,250 g with the uterus attached.

Pregnant uterus with left horn at left and cervix bottom left.

Position of fetus after first opening the uterus.

The right horn is occupied by fetus and most of the placenta; the left horn has smaller and fewer cotyledons. Cervix is at bottom, left.

Single attached cotyledon with uterus below.

Edge of the implanted placenta; uterus below.

Chorionic surface of this implanted placenta with somewhat loosely structured villi and more compact endometrium.

Implantation over the "compact zone" of the endometrium with indenting villi above.

5) Details of fetal/maternal barrier

This is a typical epitheliochorial relationship with the slender and non-branching villi interdigitating with the endometrium of maternal caruncles. Binucleate cells are abundant but there was no "hemophagous zone".

Trophoblast with binucleate cells (arrows) on the fetal surface with indenting maternal endometrium.

6) Umbilical cord

The umbilical cord of this immature gestation was 13 cm long, had four vessels and an allantoic duct as well as diminutive callosities (squamous metaplasia). The cord had no twists but contained numerous smaller blood vessels, some of which surrounded the allantoic duct.

Squamous metaplasia on the surface of the umbilical cord.

Centrally positioned allantoic duct in the umbilical cord.

7) Uteroplacental circulation

This has not been described in detail.

8) Extraplacental membranes

Hradecky et al. (1988) depicted the allantoic vascularization in kobs (their Fig. 4) where "milky patches" were produced in the early membranes from caruncular absorption. The allantoic sac was "sausage-shaped" and was filled with urine.

Membranes between cotyledons. The trophoblast (bottom) is positioned over the endometrium.

9) Trophoblast external to barrier

There is no "invasion" of the uterus by trophoblast.

10) Endometrium

There is no decidualization but the endometrium has a "compact zone".

11) Various features

Mossman & Duke (1973) described "two classes of luteal cells" in the corpora lutea of kob and some other species. They were skeptical of these being different developmental stages as described by Morrison (1971). Moreover, while this (and some other) species have smaller left uterine horns, their ovaries are bilaterally symmetrical.

12) Endocrinology

No endocrine studies are known to me.

13) Genetics

The Uganda kob has 50 chromosomes, as first identified by Taylor et al. (1967). Defassa and Ellipsen waterbucks have higher numbers as described by Kingswood et al (1998). Later, these authors described the extensive Robertsonian fusion system occurring in the kob species (Kingswood et al., 2000). Matthee & Davis (2001) studied nuclear DNA of Bovidae and concluded that the "problematic Reduncinae" appeared to be earliest diverging of the Caprinae/Alcelaphinae/Hippotraginae clade. Mitochondrial DNA studies by Birungi & Arctander (2000) disclosed significant differences in the mtDNA cytochrome b gene control region between the two presumed subspecies' colonies. The most comprehensive review of phylogenetic relationships in the Ruminantia comes from Hernandez Fernandez & Vrba (2005). Hybridization has taken place with Defassa waterbuck (K. defassa) and the Nile Lechwe (K. megaceros) according to Gray (1972).

Male and female chromosome sets from Hsu & Benirschke (1969).

Giemsa-banded male karyotype from CRES.

C-banded male karyotypes from Kingswood et al. (2000).

14) Immunology

I am not aware of any type of immunological study in this species.

15) Pathological features

Baumeister et al. (1983) identified rotaviruses in the stools of waterbucks and many other zoo ruminants. A new species of Onchocerca(O. hamoni) was described to occur by Denke & Bain (1981). Trauma and perinatal deaths were the commonest entries in Griner's large experience (1983). Occasional other maladies cited were splenitis, malnutrition, cataracts, brachygnathia, uterine "adenoma" and pulmonary hemangiomas. Infectious causes of death were not mentioned.

16) Physiologic data

Hagey et al. (1997) have described the composition of bile acids in Kobus and other Artiodactyla. Pospisil et al. (1984) have described hematological values of several kob species and other artiodactyla. Kupper et al. (1981) reported on medicines used for immobilization of these animals that these are quickly reversed with nalorphine, although this was less successful than in hartebeest. Data on the composition of the "fetal fluids" of two waterbuck species may be found in Hradecky (1984).

17) Other resources

A wide variety of fibrous tissue cell strains from the Reduncinae is available from CRES by contacting Dr. O. Ryder (oryder@ucsd.edu).

18) Other remarks – What additional Information is needed?

The study of early stages of implantation is highly desirable.

Acknowledgement

The animal photograph in this chapter comes from the Zoological Society of San Diego. I am also grateful to the pathologists at the San Diego Zoo for allowing me to obtain this specimen.