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The deep-sea benthic community at the Porcupine Abyssal Plain (NE Atlantic) is a highly food limited system. The annual input of sedimenting phytodetritus, which reaches the sea floor around May/June, is the major input of energy. The relative trophic position of the most abundant components of the benthos (90 species or higher taxonomic groups), including meiofaunal, macrofaunal, and megafaunal organisms, was evaluated by stable isotope analysis. The majority of the macro-and megafaunal organisms investigated were deposit feeders (N=35), less numerous were suspension feeders (N=17) and predators/scavengers (N=29). Stable nitrogen values overlap and cover a large range within feeding types, indicating a strong overlap in food sources and a high degree of competition for food. Suspension feeders, mainly cnidarians, have a broad trophic spectrum through feeding on resuspended material as well as capturing pelagic prey; thus during the greater part of the year they can compensate for any shortage in sedimenting fresh POM. Benthic deposit feeders use a variety of feeding strategies to exploit their common food resource. The holothurians, the dominant megabenthic group at PAP, included some highly mobile species, which seem to be quite efficient in tracing and exploiting localised patches of nutritious phytodetritus. Other holothurian species, however, forage successfully on more refractory material, possibly assisted by enteric bacteria. Predators/scavengers fall into two groups, representing two major trophic pathways. Firstly, several of the invertebrate predators prey on deposit-feeding organisms and so are the end consumers of an exclusively benthic food web. Secondly, there are highly mobile benthopelagic predators/scavengers, which are a major link with the benthopelagic food web through their feeding on pelagic prey.Generally, within the benthic community at PAP competition for food is reduced by two alternative evolutionary adaptations: (1) specialization on slightly different food sources and (2) vertical expansion of the trophic spectrum. This leads to a rather complex food web, covering a total δ 15 N range of at least 10‰. 

Effects of structural and non-structural carbohydrates on the development of rumen fermentation and ruminal mucosa in calves were examined during the weaning period. Barley/soybean meal (SBM) group was fed a concentrate starting from 2 weeks of age, whereas alfalfa group received a mixture of concentrate and alfalfa hay in which the proportion of the latter was gradually increased from 20% to 70% between weeks 2 and 9 of age. The total volatile fatty acid concentration in rumen fluid of calves increased with age, but at 9 weeks there were no significant differences between the two diets (barley/SBM group 153 mmol/l, alfalfa group 150 mmol/l). Rumen papillae at 9 weeks of age, as compared to 6 weeks of age, were longer and fewer in number per square centimetre mucosa, with larger cut surface. This resulted in a higher surface of papillae per square centimetre mucosa at 9 weeks (barley/SBM group 286 mm2/cm2, alfalfa group 245 mm2/cm2) than at 6 weeks of age (barley/SBM group 217 mm2/cm2, alfalfa group 198 mm2/cm2). At 9 weeks of age, the pH (barley/SBM 5.0, alfalfa 5.7), the acetate to propionate ratio (barley/SBM 2.2, alfalfa 3.2) as well as the length of the papillae in the ventral ruminal sac (barley/SBM 1.96 mm, alfalfa 2.37 mm) were increased in the alfalfa group when compared to the barley/SBM group (P < 0.1). In the former group, the proportion of butyrate revealed significantly increased values at 4 and 6 weeks of age. In animals of the barley/SBM group at 9 weeks of age, characteristic protrusions with proliferated thick epithelium occurred on the papillae and increased the surface for absorption. On the epithelium (Stratum corneum) desquamating cells with parakeratosis could be observed. In the alfalfa group the papillae of the ventral ruminal sac were longer, without protrusions. The morphotypes of the adhering rumen microflora differed between the groups. It can be concluded that feeding greater amounts of non-structural carbohydrates increases the surface for absorption of the rumen epithelium in calves. The absence of hyperkeratosis and rumenitis in the barley/SBM group indicated that there is no reason to limit high starch diets in the early weaning period of calves.

SummaryIdentifying the genetic and physiological background of phenotypic variability between animals of different nutrient turnover is a well recognised prerequisite for efficient breeding strategies. Published results relevant for our recently initiated project on properties of the nutrient transformation in cattle with respect to secretion type and accretion type are reviewed. For a deeper insight into the genetic and physiological background of both types, an experiment has been initiated using segregating F 2 offspring's of crosses of Charolais bulls and German Holstein cows. It will be shown that, with respect to their phenotypic and physiological properties, these two breeds are especially suitable for a study of the accretion and secretion type. The basis of the experimental design and the intended investigations are described.

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Sheep fitted with a PVC cannula in the dorsal rumen, a silastic infusion tube in the abomasum, and single 'T'-shape PVC cannulas in the proximal duodenum @I), distal duodenum (D2), mid-jejunum (J), and terminal ileum (I), were fed on diets varying in crude protein (Nx6.25) and fibre contents. Reducing the environmental burden of livestock production systems is a major objective for current nutrition research. To achieve this objective the first option is to replace the external inputs of concentrate feeds and by-products grown elsewhere by home-grown feeds of a comparable nature. If this is not a viable option, including a larger proportion of home-grown alternative feeds in the diet constitutes a second possibility. Hence, increasing the utilization of home-grown feeds has been identified as one of the keys. For ruminant production, particularly in Western Europe, this implies that a larger part of the diet should be fibrous feeds, such as grass or grass-maize silages. However, for higher levels of production, especially of milk, only part of the nutrients can be derived fiom roughages. Concentrate supplements are needed to meet energy requirements, to optimize m e n conditions and to manipulate the amount and composition of the nutrient mixture rendered available for intermediary metabolism.Livestock production systems geared towards longer-term sustainability aim at the reduction of the environmental burden in terms of nutrient losses, particularly of N and P. In other words, they aim to optimize (1) the conversion of nutrients into product and (2) the

An experiment was initiated to evaluate the glucose-dependent insulin response in relation to milk production in F2 crossbred cattle with respect to secretion type (Holstein) and accretion type (Charolais). For this purpose, F2 offspring were generated by mating Charolais bulls with German Holstein cows and a following intercross of the F1 individuals. In 52 dairy heifers of 5 F2 half-sib families, glucose-dependent insulin responses were investigated during first lactation to test the hypothesis that the different genetic disposition for milk production within the F2 population would affect the insulin response to glucose. Heifers received intravenous glucose infusions (1 g/kg of BW(0.75)) 10 d before, and 30 and 100 d after parturition. Blood samples were taken before and at 7, 14, 21, and 28 min after glucose challenge. Glucose and insulin concentrations were measured in blood, and glucose half-life as well as areas under the curve for glucose (AUC(gluc)) and insulin (AUC(ins)) were calculated. Milk yield was low but differed among F2 families. Before parturition, insulin concentrations after glucose challenge showed no between-family differences for AUC(ins). In contrast, on d 30 and 100 of lactation, glucose half-life and AUC(ins) differed among families. Calculated correlations revealed a significant negative relationship between AUC(ins) and milk yield as well as glucose half-life on d 30 and 100 of lactation. In conclusion, milk production as well as the glucose-dependent insulin response of F2 Charolais x German Holstein crossbred dairy heifers differed between half-sib families, with both parameters displaying an inverse relation to each other.

A new method has been developed which permits the crude protein digestibility of feedstuffs in the intestine of cattle to be measured with little effort in terms of samples and experimental work. It consists of welding 0.4 ... 0.8 g of the feedstuff (particle size: 125 ... 1000 micron) into polyamide fabric bags (25 X 40 mm) which are inserted via cannulae into the digestive tracts of fistulated cows from the abomasum/duodenum to the ileum or from the abomasum/duodenum to the faeces. The mean retention time of the bags in the animal was 8.5 +/- 2.7 h from the abomasum to the end of the ileum and (13.3 +/- 1.9 h from the abomasum to the faeces. Up to 15 bags per day and cow may be used. The random error of the method is 1.3% (absolute) when the measurements are performed on two animals using two bags each. Intestinal digestibilities of over 90% were measured for concentrate proteins (except linseed meal) and of 72 ... 95% for forage proteins. Post-ruminal digestion was virtually finished at the end of the small intestine.