Contraceptie als methode in het beheer van hoefdierpopulaties

Bezorgdheid over dierenwelzijn en praktische problemen met lethale methoden hebben geleid tot de ontwikkeling van contraceptiemiddelen om hoefdierpopulaties te beheren. Vroege studies hebben enkele chemische sterilisatiemiddelen getest, maar de meeste daarvan zijn niet geschikt gebleken om in het wild levende hoefdieren mee te behandelen. Sommige zijn onpraktisch vanwege de noodzaak van herhaalde toediening of de grote volumes die geïnjecteerd moeten worden om effect te verkrijgen (o.a. (synthetische) hormonen), terwijl andere afvallen vanwege negatieve bijwerkingen op de gezondheid van behandelde dieren (o.a. DES, levonorgestrel). Een ander probleem van de meeste chemocontraceptiemiddelen is hun resistentie tegen biologische afbraak, waardoor de middelen via de voedselketen overgedragen kunnen worden of zich ophopen in het milieu. Het meest veelbelovende chemocontraceptiemiddel is waarschijnlijk de GnRH-agonist leuprolide, dat wel biologisch afbreekbaar is

Digestive strategies in ruminants and nonruminants

Of the 176 species of ungulates in the world the great majority (146 species) are ruminants. The more recent ruminants probably have displaced the older nonruminants because of their superior digestive system in combination with the ruminantion mechanism leading to significant advantageous differences in important life history traits. Nonruminants like hippos, equids, elephants and tapirs reach sexual maturity at a later age and produce fewer young per year than ruminants, relative to body size.Within the ruminants three different adaptive syndromes in feeding style are distinguished and expected differences in digestive physiology between members of the various feeding styles were tested. Nonruminants are poorer fibre digesters than ruminants while the large bovid 'grass and roughage feeders' have superior capacity for digesting fibre.In some areas in the world, notably in East Africa, species-rich ungulate communities can be found. Various guilds of species occupying different habitats and feeding niches can be distinguished and the species belonging to different guilds are sufficiently dissimilar as not to compete with each other. Within guilds frequently groups of species of similar body weight and with similar ecology occur sympatrically. The apparent peaceful co-existence of these species yet has to be explained

Digestive strategies in two sympatrically occurring lagomorphs

Separation of low digestible fibres and fermentation of the digestible part of the food in the caecum is an adaptation of some small herbivores to cope with low-quality forage. The caecum content is later re-ingested as soft faeces so that the herbivore can benefit from this protein-rich material. This is known as caecotrophy and is a common phenomenon in species of leporids, although differences exist between hares and rabbits. Hares have amorphous soft faeces and the amount of soft faeces produced is smaller compared to that of rabbits. Both factors suggest that hares have smaller benefits from re-ingestion of the caecal contents compared with rabbits and, as a consequence, have a less efficient digestion (mainly of nitrogen) compared to rabbits. The assertion was tested whether digestive efficiency is different between the two herbivores and how this affects the choice of food plants in a natural situation. A feeding trial was conducted using hares and rabbits fed with diets with a range of fibre contents. Dry matter digestibility was not different, but nitrogen digestibility was lower in hares than in rabbits, indicating a less efficient digestion of protein. Both taxa showed a different response to increased fibre content in the diet. Rabbits maximized digestibility by increasing retention time of the food, hares maximized digestion rate by increasing the passage rate of the food through the digestive tract. The daily digestible nitrogen intake was higher in hares Lepus europaeus than that in rabbits Oryctolagus cuniculus, indicating that hares compensated for their lower nitrogen digestibility. Hares were predicted to select for higher quality plant species in a natural situation, but they had, on average, a lower nitrogen and higher total fibre content in their diet compared to sympatrically occurring rabbits. This indicated that hares did not compensate for their lower digestive efficiency by selecting higher quality food plants. The present experiment shows that hares and rabbits have different digestive strategies to cope with low quality forage. Rabbits had a higher N-digestibility by increasing the retention time, whereas hares appeared to compensate for their lower N-digestibility by increasing the processing rate, when food quality deteriorated

Begrazingsonderzoek in Nederland : samenhang, prioriteiten en samenwerking

Ten behoeve van een optimale planning van het begrazingsonderzoek wordt: - een overzicht gegeven van het lopende en recent afgesloten begrazingsonderzoek; - een analyse gegeven van de hiaten in de huidige kennis en worden prioriteiten aangeduid voor toekomstig onderzoek; - de mogelijkheid onderzocht tot verbetering van de organisatie van het begrazingsonderzoe

Distributional congruence of mammalian herbivores in the Trans-Himalayan Mountains

Large-scale distribution and diversity patterns of mammalian herbivores, especially less charismatic species in alpine environments remain little understood. We studied distributional congruence of mammalian herbivores in the Trans-Himalayan region of Ladakh to see if the distributions of less prominent and smaller herbivores can be determined from those of larger and more prominent herbivores like ungulates. Using a similarity index, we assessed shared distributions of species in 20x20 km2 grid-cells in an area of about 80,000 km2. We used the Unweighted Pair-Group Method with Arithmetic Average (UPGMA) to classify mammalian herbivores into groups with similar distributions. We then used the G-test of independence to look for statistical significance of the groups obtained. We identified six groups of mammalian herbivores with distributions more similar than expected at random. The largest group was composed of nine species whereas the other large group comprised six species. Canonical Correspondence Analysis (CCA), used to relate the groups with environmental features, showed that the largest group occurred in higher and flatter areas, while the other large group occurred in lower and steeper areas. Large herbivores like ungulates can be used as surrogate for less prominent small herbivores while identifying areas for latter’s protection in the inaccessible mountainous regions of the Trans-Himalay