The effect of rumen liquid volume, pH and concentration of volatile fatty acids (VFA) on the rates of absorption of acetic, propionic and butyric acids from the rumen was examined in lactating dairy cows. Experimental solutions introduced into the emptied, washed rumen comprised two different volumes (10 or 30 I), four levels of pH (4.5, 5.4, 6.3, 7.2) and three levels of individual VFA concentrations (20, SO or 100 mM-acetic, propionic or butyric acid). All solutions contained a total of 170 mM-VFA and an osmotic value of 400 mOsmol/l. Absorption rates were calculated from the disappearance of VFA from the rumen corrected for passage with liquid phase to the omasum. An increase in initial fluid pH caused a reduction in fractional absorption rates of propionic and butyric acids. Increasing the initial pH from 4 5 to 7.2 reduced fractional absorption rates of acetic, propionic and butyric acids from 0.35, 0.67 and 0.85 to 0.21, 0.35 and 0.28/h respectively. The fractional absorption rates of all VFA were reduced (P < 0.05) by an increase in initial rumen volume. The fractional absorption rate of acetic acid was lower (P < 0.05) a t an initial concentration of 20 mM than of 50 mM. The fractional absorption rate of propionic acid tended (P < 0.10) to decrease as the level of Concentration increased while fractional absorption rate of butyric acid was not affected by butyric acid concentration. These results indicate that relative concentrations of VFA in rumen fluid might not represent relative production rates and that attempts to estimate individual VFA production from substrate digestion must take account of pH and VFA concentration.Volatile fatty acids: Dairy cows -________.

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

In animal production, endogenous protein losses associated with the digestion process are important losses, but difficult to measure. Measuring methods include feeding N-free diets, regression techniques based on amino acid profiles, and separating feed protein and endogenous protein by markers like homoarginine, hydrolysed casein or stable isotopes like 15N. Endogenous losses arise from saliva, digestive enzymes, bile, shedded epithelial cells and mucins and may be extra stimulated by the presence in feeds of antinutritional factors (ANF) such as lectins, trypsin inhibitors (TI), tannins and fibre. The impact of such factors may differ between non-ruminants and ruminants. The magnitude of the effect of the different factors is quantified and some of the consequences for protein deposition and nitrogen losses to the environment are discussed.

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The potential forage value and appropriate length of study on intake and relative palatability ranking of 40 multipurpose tree species (MPTs) were determined using 24 sheep blocked on live weight and age. As the MPTs had different dry matter contents, intakes were also expressed as a ratio of quantity offered (A/D3. Using daily Eragrostis tef straw offer (TD) and intake (T), relative palatability indices were calculated as R i = (A]DI)/(Ti/TDi).There was a significant (P < 0.0001) decrease in correlation of intake measured in day 1 and subsequent days (r = 0.88, 0.81 and 0.79 for days 2-4, days 5-8 and days 9-12, respectively). A similar trend was observed on corresponding palatability indices. Individual animal preference and blocking did not affect intake and palatability indices significantly (P > 0.05), however significant (P < 0.0001) tree species differences were observed. Results on linear regression, correlation coefficients, palatability ranking and standard errors of means (adjusted palatability indices) indicate that, if palatability is done to predict long-term intake of MPTs, at least 5 days are appropriate in palatability assessment for sheep.Using mean palatability index (days 2-12), the MPTs were grouped into four clusters. The MPTs such as Leucaena leucocephala and Sesbania sesban which are known to have good nutritive value had high palatability. In the same classification group, there were less known species such as Acacia venosa, A. persiciflora, A. melanoxylon, A. hockii, A. polyacantha, Tamarindus indica, Chamaecytisus palmensis, Tipuana tipu, Indigofera arrecta and Atriplex nummularia. and Erythrina burana had poor palatability. These species seem to have little forage value for animals with short-term adaptation periods. Gliricida sepium and Calliandra calothyrsus although currently being used by farmers had a medium palatability ranking.