SUMMARYThe effects of severe food restriction and of protein supplementation on the apparent digestibility of a forage were studied on 12 wethers in 1992 at INRA, Theix. Ruminal digestion of the forage cell walls was studied in a second experiment carried out on four ewes fitted with rumen and duodenal cannulas, receiving the same diets as the wethers. The animals were fed on two different hay-based diets: hay only (58 or 25 g/kg BW0·75 per day) or hay supplemented with fish meal (48 or 20 g hay with 6·5 and 3·0 g fish meal respectively per kg BW0·75). The effects of fish meal supplementation on apparent digestibility of the hay cell walls were small, + 1·8 and + 2·3 units for neutral detergent fibre (NDF) and acid detergent fibre (ADF) respectively. In contrast, NDF and ADF digestibility was respectively 4·0 and 4·7 units higher at low than at high intake. Rumen fluid volume decreased by 2·4 1 with decreasing intake, while water concentration in rumen content increased slightly from 89·8 to 91·8%. The mean retention time of the hay particles in the foreguts increased concomitantly from 39·5 to 55·1 h. This was achieved by a higher retention time to a similar extent in both slow and fast compartments. The calculated in situ degradability of NDF and ADF increased respectively by 12·1 and 13·1 units with decreasing intake. This reflected the lower fractional outflow rate recorded at low intake. If a fractional outflow rate value of 4·1%/h (as measured in high intake diets) was applied to all dietary treatments, NDF and ADF in situ degradability would be greater at low than at high intake (31·7 v. 26·6% for NDF; 27·9 v. 22·1 % for ADF), indicating a higher microbial activity in restricted diets. Interactions between intake and fish meal supply were detected for in situ degradation parameters, indicating principally a reduction of the cell wall undegraded fraction in supplemented diets when intake declined. Ruminal fermentation was modified by the dietary treatments, the acetate: propionate ratio being higher at low intake. Fish meal increased concentrations of ammonia and of isoacids in rumen liquid. The relationship between apparent digestibility and in situ degradability of plant particles is discussed.

Link to this article: http://journals.cambridge.org/abstract_S0003356100007169How to cite this article: P. Kabré and M. Petit (1994). Fish-meal supplement for severely undernourished ewes: effects on apparent digestibility and utilization of the diet. AbstractEight non-pregnant, non-lactating adult ewes weighing 56 kg were fed for 26 days on a meadow hay (organic matter 937 g, crude protein 107 g, metabolizable energy (ME) 8-3 M] per kg dry matter) to satisfy half of their daily energy and protein maintenance requirements i.e. 200 kj ME and 1-3 g truly digestible protein per kg M 0 ' 75 . They were then allotted to two groups of four each. Control ewes continued to receive the initial diet for another 74 days while the others were supplemented with 60 g/day fish meal to receive 200 kj ME and 2-7 g truly digestible protein per kg initial M 0 ' 75 per day. In spite of its high nitrogen content, the digestibility of the hay was increased by the protein supplementation, e.g. from 0-56 to 0-60 for neutral-detergent fibre and from 0-54 to 0-59 for energy. The supplemented ewes lost significantly less body weight than the controls (96 v. 134 g/day) essentially because of their higher ME intake (272 v. 252 kj/kg average M 0 ' 75 during the experimental period). The measurements of blood metabolites suggest that the daily amounts of mobilized body protein increased with duration of underfeeding. The additional amino acids provided by fish meal were principally used as a source of energy and for wool growth.

Four ruminally cannulated ewes were used in a series of two crossover designs to investigate the effects of underfeeding and of supplementation with slowly degradable protein on polysaccharide and glycoside-degrading enzyme activities in rumen solid-adherent microorganisms. The ewes were fed twice daily on a hay based diet to satisfy either 1.2 or 0.5 maintenance energy requirements, with or without 125 and 65 g fish meal supplement for the high and the low intakes, respectively. Enzyme preparations were isolated from rumen solid contents 2, 6, and 12 h after feeding. Protein supplementation had no significant effect on the activity of any of the enzymes measured. The effects of feeding level on carboxymethycellulase and xylanase activities were small, the specific activity (expressed per mg microbial protein) being slightly increased at low intake (P < 0.10). However, B-D-galactosidase, B-D-glucosidase, B-D-xylosidase, and B-D-cellobiosidase activities were considerably increased with low feeding level ( + 5 6 to +70% for specific activities; +31 to +50% when expressed per g dry matter). The activities of all enzymes tested increased significantly with time after feeding. The extent of specific activity response to variation of feeding level was greater for late sampling times than 2 h post-feeding. Ruminal degradation of the dietary hay was not affected by fish meal supplementation, but increased with reduction of feeding level ( + 59.7 g kg-' for neutral detergent fibre during the first 12 h of rumen incubation; P < 0.001). The higher microbial efficiency associated with greater retention time of feed particles in the rumen may account for the increase in cell wall degradation usually observed when feeding level declines.

No abstract

Twenty-one Salers nearly-mature (4 -7 yr old) non-lactating cows were used during mid-pregnancy (from the 2nd to the 7th month) to