The influence of the environment on feed intake of cattle in semi-arid Africa

In our observation, continuous efforts to improve the yield potential of dairy cattle have not been accompanied by a concomitant increase in gut capacity. It therefore comes as no surprise that in all production systems, the nutrient intake is constrained by the ingestion capacity of an animal. This situation calls for better insight into the regulatory mechanisms of feed intake in ruminants. The determination of the daily ration of an individual animal is difficult enough; even more complex is the question of why an animal eats a certain quantity and then stops grazing. Of all the factors involved in regulating feed intake, this chapter primarily deals with satiety (level of gut fill), abiotic (e.g. temperature, water balance, seasonality) and biotic aspects (e.g. feed, nutritional status and activity of the animal). Metabolic factors will only be touched upon briefly. Feed intake in the study area is governed principally by physical factors, since, for most of the year, the digestibility of pastoral biomass is significantly below 67%. Levels around 67% are encountered only briefly at the start of the rainy season, at which point it is assumed that physical factors interact with physiological ones to govern feed intake. Nomads traditionally attempt to synchronize the lactation period of their animals with times of maximum reed availability; even then, only a considerable increase in the level of feed intake can guarantee an adequate supply of nutrients. High temperatures, insufficient water supply, long distances to be covered and meagre pasture biomass supplemented by agricultural by-products rich in neutral detergent fibre (NDF), all help to constrain the performance of livestock in semi-arid Africa. The simultaneous occurrence of these constraining factors throughout: most of the year has favoured the selection of autochthonous ruminants, which are ideally adapted to prevailing conditions. In this chapter, data on the quantitative and qualitative feed intake of these adapted animals over the seasonal cycle will be presented.