Bibliothek

Notizen: Abstract An experiment was carried out over 2 years to evaluate the effects of increasing the proportion of cereal-based concentrates in diets containing high-digestibility and conventional medium-digestibility grass silages on the dry-matter (DM) intake, liveweight gain and carcass composition of beef cattle, and to examine the effects of grazed grass and the ratio of grass silage:concentrates in the diet on the fatty acid composition of selected muscle tissues. Late-maturing steers (n = 231) were offered diets based on high-digestibility (HD) (0·743 digestible organic matter (DOM) in DM) or medium-digestibility (MD) (0·643 DOM in DM) grass silages supplemented with barley/soyabean meal-based concentrates. The concentrates constituted 0·20, 0·40, 0·60 and 0·80 of total DM of the diets, which were offered ad libitum (AL). The two diets, which contained 0·80 concentrates, were also offered at 0·80 of AL intake. A further group of fourteen animals were given the medium-digestibility silage only for 5 months and then grazed perennial ryegrass pastures for a further 5 months (silage/pasture treatment). For the diets containing HD silage and 0·20, 0·40, 0·60 and 0·80 concentrate, and 0·80 concentrate at 0·8 of AL intake, the DM intakes were 9·4, 10·2, 10·4, 10·2 and 8·1 (s.e. 0·16) kg d−1, respectively, and daily carcass gains were 0·67, 0·78, 0·77, 0·79 and 0·62 (s.e. 0·029) kg d−1, respectively; for those containing MD silage and 0·20, 0·40, 0·60 and 0·80 concentrate, and 0·80 concentrate at 0·8 of AL, the DM intakes were 8·2, 9·3, 10·1, 10·1 and 8·0 (s.e. 0·16) kg d−1, respectively, and daily carcass gains were 0·38, 0·48, 0·64, 0·77 and 0·56 (s.e. 0·029) kg d−1 respectively. Increasing the proportion of concentrates in silage-based diets decreased the concentration of omega-3 (ω-3) polyunsaturated fatty acids (PUFA) (P 〈 0·001) and increased the concentration of ω-6 PUFA (P 〈 0·001) in muscle. Cattle on the silage/pasture treatment had the highest concentration of ω-3 PUFA in muscle (51 g kg−1 lipid), this value being over three times that for animals given diets containing MD silage and 0·80 concentrate in the diet. These results demonstrate the potential of HD silage made from perennial ryegrass relative to high concentrate diets. The consumption of pasture-finished beef could make a significant contribution towards increasing the intake of ω-3 PUFA in the human diet.

Notizen: This study reviews the volatility coefficients used to convert the oven dry-matter (DM) content of grass silage to an accepted true DM base, volatile-corrected oven dry matter (VCODM). The revised coefficients quoted for DM determination at 60°C, 85°C and 100°C are based on 18 grass silages with DM contents in the range 153–365 g kg–1. The volatility coefficients for drying at 60°C, 85°C and 100°C were 0·090, 0·224 and 0·375 for lactic acid and 0·554, 0·716 and 0·892 for total volatile fatty acids respectively. The volatilities of ammonia and total alcohols remained unchanged from previous work and showed no temperature dependences in the range 60°C to 100°C. These revised coefficients were validated using 36 grass silages from three harvests in 1996 and 1997, and no significant differences were found among absolute dry matter (GCDM), alcohol-corrected toluene dry matter (ATDM) and VCODM contents based on the three drying temperatures (VCODM100, VCODM85 and VCODM60). A series of regression equations relating absolute DM content to oven DM content determined at different temperatures gave coefficients of 1·024, 1·013 and 1·000 and constants of 12·67, 11·43 and 11·16 for oven drying at 60°C, 85°C and 100°C respectively. Mathematical manipulation of these equations enables interconversion of DM contents at the three drying temperatures. A new method is described for the analysis of volatile fatty acid, lactic acid and alcohol concentrations in grass silage by gas–liquid chromatography using a single injection in an automated procedure that makes the routine estimation of VCODM a practical proposition to satisfy routine high-volume requirements. Finally, in a separate study over 4 years using 2381 grass silages from research and commercial farms throughout Ireland, a simple regression is described, which, for advisory purposes, allows true silage DM content to be estimated from oven dry matter content (ODM) for silages in which ODM is 〉200 g kg–1.

Notizen: Abstract In view of the evidence indicating several potential benefits of high intakes of conjugated linoleic acid (CLA) on human health, an experiment was conducted to examine the effects of the diet of beef cattle on the total CLA concentration in muscle and subcutaneous fat. High-concentrate [steers consumed 515 g concentrates and 485 g grass silage kg−1 dry matter (DM) for 8 weeks followed by 887 g concentrates and 113 g grass silage kg−1 DM for 14 weeks until slaughter] and high-forage (steers consumed 803 g grass silage and 197 g concentrates kg−1 for 8 weeks followed by grass silage only for 10 weeks and then grazed perennial ryegrass-based pasture for 23 weeks until slaughter) treatments were imposed on 48 steers, which were crosses of continental beef breeds (initially 414 kg live weight) The concentrates were based on barley, extracted soyabean meal, molassed sugarbeet pulp and maize meal. The silages were of medium to low digestibility and contained 117–137 g crude protein kg−1 DM and 83–158 g ammonia-N kg−1 total N. The pasture was of high quality and contained 168 g crude protein, 234 g acid-detergent fibre and 222 g water-soluble carbohydrate kg−1 DM. Samples of muscle were taken post slaughter from the m. semimembranosus, m. gluteobiceps, m. longissimus and m. deltoideous muscles, and subcutaneous fat was taken from over the m. longissimus. Concentrations of total CLA in the tissues were for the high-concentrate and high-forage treatments, respectively (mg 100 g−1 fresh tissue), m. gluteobiceps 18 and 47 (s.e. 3·5); m. semimembranosus 9 and 20 (s.e. 1·6); m. longissimus 15 and 35 (s.e. 3·2), m. deltoideous 20 and 59 (s.e. 4·3); subcutaneous fat 584 and 1975 (s.e. 138·7). It is concluded that muscle and subcutaneous fat tissue from grass-fed cattle contained three times as much CLA as those from concentrate-fed cattle, and that the consumption of beef from grass-fed cattle should be effective in increasing the intake of CLA by humans.

Notizen: Plasma melatonin synthesis in juvenile Atlantic salmon Salmo salar decreased with increasing light intensity. Melatonin profiles reflected accurately the photoperiod under which the salmon were maintained. Groups maintained at 12°C showed significantly higher (P 〈 0·01) levels of dark phase plasma melatonin compared with the groups maintained at 4°C.

Notizen: There is increasing public, governmental and commercial interest in the welfare of intensively farmed fish and stocking density has been highlighted as an area of particular concern. Here we draw scientific attention and debate to this emerging research field by reviewing the evidence for effects of density on rainbow trout. Although no explicit reference to ‘welfare’ has been made, there are 43 studies which have examined the effects of density on production and physiological parameters of rainbow trout. Increasing stocking density does not appear to cause prolonged crowding stress in rainbow trout. However, commonly reported effects of increasing density are reductions in food conversion efficiency, nutritional condition and growth, and an increase in fin erosion. Such changes are indicative of a reduced welfare status—although the magnitude of the effects has tended to be dependent upon study-specific conditions. Systematic observations on large scale commercial farms are therefore required, rather than extrapolation of these mainly small-scale experimental findings. There is dispute as to the cause of the observed effects of increasing density, with water quality deterioration and/or an increase in aggressive behaviour being variously proposed. Both causes can theoretically generate the observed effects of increasing density, and the relative contribution of the two causes may depend upon the specific conditions. However, documentation of the relationship between density and the effects of aggressive behaviour at relevant commercial densities is lacking. Consequently only inferential evidence exists that aggressive behaviour generates the observed effects of increasing density, whereas there is direct experimental evidence that water quality degradation is responsible. Nevertheless, there are contradictory recommendations in the literature for key water quality parameters to ensure adequate welfare status. The potential for welfare to be detrimentally affected by non-aggressive behavioural interactions (abrasion, collision, obstruction) and low densities (due to excessive aggressive behaviour and a poor feeding response) have been largely overlooked. Legislation directly limiting stocking density is likely to be unworkable, and a more practical option might be to prescribe acceptable levels of water quality, health, nutritional condition and behavioural indicators.

Notizen: Abstract Consumption of carrot by third-instar larvae of Sericesthis nigrolineata was measured under conditions of constant temperature. Consumption increased curvilinearly with increasing temperature between 4° and 30°. Larvae stopped feeding at the lower threshold, but at the upper threshold larval mortality prevented further feeding. Larval relative growth rate peaked at 17.5°, with zero growth at 5° and 32°, and the proportion of food converted to growth was greatest at 14° with a value of 11%. Late third-instar larvae lost weight but continued feeding, except for a short non-feeding period, before entering the prepupal stage. There was no evidence for a diapause by mature larvae.