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The effects of the type of grass silage and dietary inclusion of fish oil (FO) on the fatty acid profile of bovine intramuscular and subcutaneous adipose tissue were investigated. Eighty Friesian steers were assigned (n10) to unwilted or wilted silage, and to one of four rations which contained, per kg, 80 g of sunflower oil and either 0, 10, 20 or 40 g of FO replacing lard. Animals were slaughtered after 108 d and the fatty acid profile of the neutral, polar and total lipid fractions of theM. longissimus dorsi, and the total lipid fraction of the subcutaneous adipose tissue were determined. Wilting of grass prior to ensiling increased the concentration of conjugated linoleic acid (CLA) in intramuscular total lipid (P n-6:n-3 PUFA ratio. Increasing FO supply linearly increased (P cis-9,trans-11 andtrans-10,cis-12 isomers of CLA andtrans-11 18 : 1 predominantly in the neutral lipid fraction of intramuscular total lipid, and linearly decreased then-6:n-3 PUFA ratio. Wilting of grass prior to ensiling increased the concentration of CLA in subcutaneous adipose tissue (P cis-9,trans-11 CLA. From a human nutrition perspective, increasing the level of FO in the ration or wilting of grass prior to ensiling appear to modify the fatty acid composition of beef muscle favourably. However, the health implications of associated increases intransfatty acids remain to be elucidated.

Duodenally and ruminally fistulated steers were offered grass silage and one of three concentrates at a ratio of 60: 40 (forage: concentrate on a dry-matter basis) : F0, F1 or F4 at 14 g/kg live weight. The concentrates were designed to be iso-lipid and to provide the same amount of sunflower oil but increasing amounts of fish oil : 0, 1 and 4 g per 100 g, respectively. Ruminal characteristics were measured along with fatty acid intakes and duodenal flows to determine the effect of fish oil on : ruminal pH, ammonia-N concentration, volatile fatty acid (VFA) concentration and polyunsaturated fatty acid (PUFA) metabolism. Fish oil had no significant effect on ruminal pH, ammonia-N concentration or the molar proportions of the major VFA, although total VFA concentration was significantly reduced at the highest level of fish oil inclusion. Fish oil significantly increased the flow of long chain PUFA, total conjugated linoleic acid and vaccenic acid to the duodenum and decreased the flow of stearic acid. Biohydrogenation, as determined by the net loss of fatty acid between the mouth and duodenum, of oleic and linolenic acid was not affected by fish oil inclusion and averaged 0·64 and 0·92, respectively. There was a small increase in the biohydrogenation of linoleic acid with increasing fish oil from 0·89 to 0·92 (P< 0·01) on F0 and F4, respectively. Biohydrogenation of the long chain PUFA C20 : 5(n-3) and C22 : 6(n-3) increased from 0·49 and 0·74 to 0·79 and 0·86 (P< 0·01), respectively when fish oil in the concentrate increased from 1 to 4 g per 100 g. The net effect of fish oil on lipid metabolism appears to inhibit the transition of vaccenic acid to stearic acid in the rumen resulting in a build up of this intermediate in the biohydrogenation pathway of C18 PUFA.

The aim of this experiment was to quantify the relationship between autumn grass supply and concentrate supplementation level on grass intake and animal performance. One hundred and ten continental steers (567 kg) were assigned to 10 treatments. The experimental design was a three grass allowances (6, 12 and 18 kg dry matter (DM) per head daily) by three concentrate levels: (0, 2·5 and 5 kg per head daily) factorial with a positive control group offered concentrates ad libitum and no grass. Grass allowance was offered daily and concentrates were given individually. The experiment began on 22 August and all animals were slaughtered after a mean experimental period of 95 days. Grass intake was calculated using the n-alkane technique and diet digestibility using ytterbium acetate as an indigestible marker. There was an interaction (P < 0·05) between grass allowance and concentrate level for grass intake. At the low grass allowance there was no effect of offering animals supplementary concentrates on grass intake, at the medium and high grass allowances, supplementary concentrates reduced grass intake by 0·43 and 0·81 kg DM respectively per kg DM concentrate offered. Increasing grass allowance increased (P < 0·001) complete diet organic matter (OM) digestibility at all concentrate levels and supplementary concentrates increased (P < 0·001) complete diet OM digestibility only at the low grass allowance. Both offering animals supplementary concentrates (P < 0·001) and increasing daily grass allowance (P < 0·001) increased their carcass growth rate. Relative to the animals offered the low grass allowance and no concentrate, supplementing with concentrate increased carcass growth by 116 g/kg concentrate DM eaten whereas increasing the grass allowance, increased carcass growth by 38 g/kg DM grass eaten. As a strategy for increasing the performance of cattle grazing autumn grass, offering supplementary concentrates offers more scope than altering grass allowance.

The objective of this study was to determine the effects on animal performance and rumen digestion characteristics of supplementing cattle grazing autumn grass offered at two levels of allowance, with concentrates formulated from different carbohydrate sources. Seventy-two steers (494 (s.e. 38·4) kg) were assigned to one of six treatments which were arranged in a two grass allowances (5·5 or 11 kg grass dry matter (DM) per head per day) by three concentrate types (starch, starch + fibre or fibre-based diets) factorial design. The experiment commenced on 22 August and had a mean duration of 84 days. Concentrates were formulated to have similar metabolizable energy and crude protein and animals were offered 5 kg per head daily. Grass allowances were offered daily and concentrates were offered individually. Six rumen fistulated steers were used concurrently in a Latin square design to determine the effect of the diets on rumen digestion characteristics. Grass and concentrates degradabilities were measured using the nylon bag technique. The concentrate DM was degraded at 0·189, 0·102 and 0·094 per h for the starch, starch + fibre and fibre-based diets, respectively. Concentrate carbohydrate source and grass allowance did not affect (P> 0·05) degradation rate of grass DM or nitrogen in the rumen, rumen fluid pH, rumen fluid concentration of volatile fatty acids, total lactic acid or ammonia concentration or plasma concentration of glucose, urea or beta-hydroxybutyrate. Animals offered the low grass allowance had larger (P< 0·05) diurnal variation in the rumen fluid acetate: propionate ratio than those offered the high grass allowance. Increasing grass allowance increased (P< 0·01) carcass gain whereas concentrate type had no effect. There was no interaction between concentrate carbohydrate source and grass allowance on any of the production variables measured. It is concluded that the rumen environment in cattle grazing autumn grass buffered the effects of concentrate carbohydrate degradability such that similar productivity was achieved with each concentrate.

Ardacin is an antibacterial glycopeptide with ruminal activity. The objective of this study was to measure its effects on food intake and growth rate of growing and finishing steers. Two experiments were carried out simultaneously using the same foods and the same ardacin supplementation levels. In experiment 1, 72 growing steers (8 months old and 240 kg initial weight) in four treatment groups were individually offered a basal diet of grass silage ad libitum. In experiment 2, 44 finishing steers (19 months old and 463 kg initial weight), also in four treatment groups were individually offered a basal diet of grass silage ad libitum plus 3 kg (5 kg for the final 28 days) concentrates per head daily. The four treatments were 0, 50, 125 and 210 mg ardacin per head daily incorporated into 1 kg ground barley. This was offered in addition to the basal diet. The duration of the experimental period was 154 days after which 48 of the growing steers were put to pasture for a 196-day grazing season. The finishing steers were slaughtered following a withdrawal period of 7 days. Mean daily silage dry-matter intakes, and mean daily total metabolizable energy intakes for the treatments as listed above were 4·91, 5·15, 5·10 and 5·03 (s.e. 0·083) kg and 63, 66, 65 and 65 (s.e. 0·7) MJ (experiment 1), and 5·63, 5·62, 5·51 and 5·54 (s.e. 0·059) kg and 108, 108, 107 and 107 (s.e. 0·4) MJ (experiment 2), respectively. In the same order, mean daily live-weight gains during the treatment period were 612, 758, 784 and 798 (s.e. 25·2) g (experiment 1) and 911, 942, 851 and 860 (s.e. 40·0) g (experiment 2). In the growing steers proportionately 0·64 of the weight response to ardacin was retained to the end of the following grazing season. It is concluded that ardacin supplementation increased live-weight gain and improved the efficiency of conversion of food to live weight in growing steers but had no significant effect on finishing steers in this study.

The effects of altering the glucogenic potential of the diet of wether lambs (initial body weight 56·4 kg) offered an energy allowance of 0·25 that required for maintenance on body-weight loss, nitrogen retention and blood and rumen fluid parameters were examined. Whole barley was offered alone or substituted on an isoenergetic basis with 40 or 120 g of a blend of glucose precursors (polyhydric alcohols, propylene glycol, sodium propionate) absorbed on to palm kernel meal (acetona meal), to 36 lambs (no. = 12 per treatment) for 8 weeks. Substituting barley with 40 g acetona meal had a small but non-significant effect in decreasing body-weight loss and plasma aspartate amino transferase activity and in increasing plasma insulin concentration. Increasing the glucogenic potential of the diet by substituting barley with 120 g acetona meal decreased body-weight loss in the early phase of the study, decreased plasma concentrations of non-esterified fatty acids and increased the proportion of propionate in volatile fatty acids in rumen fluid, plasma aspartate amino transferase and gamma-glutamyl transferase activities and plasma insulin concentrations. Increasing the glucogenic potential of the diet did not affect nitrogen retention or plasma glucose concentration. It is concluded that increasing the glucogenic potential of the diet of lambs resulted in an increase in metabolic efficiency at the onset of negative energy balance which was mediated through a change in plasma insulin concentration. The absence of a significant difference in body-weight loss between the diets in the latter part of the study reflects the lack of sustained ketosis.

The myriad putative health benefits of conjugated linoleic acid (CLA) and in particular the cis-9, trans-11 isomer, have stimulated interest in increasing its concentration in food. Ruminant fat is the main dietary source of CLA for humans and CLA is produced in the rumen by incomplete biohydrogenation of dietary linoleic acid (LA). It is now accepted that most CLA is synthesised post-ruminally by desaturation of vaccenic acid (VA) produced during ruminal biohydrogenation of (LA) and linolenic acid (LNA) (Griinari et al., 2000). Enhancement of VA synthesis in the rumen is therefore an important element of strategies to increase CLA concentration in tissue. The objective of this experiment was to determine the effect of controlling the rate of release of oil from camelina seeds, a novel source of both LA and LNA, on the accumulation of intermediates during ruminal biohydrogenation.

Some studies have shown a synergistic effect of supplementing dairy cow diets with a blend of fish and soya oil on the concentration of conjugated linoleic acid (CLA) in milk. This is apparently due to increased accumulation of ruminal and tissue concentrations of vaccenic acid (VA), the main substrate for ∆-9 desaturase catalysed, de novo tissue synthesis of the cis 9, trans 11 isomer of CLA. Furthermore, recent in vitro studies suggest that the dietary ratio of linoleic acid to the omega-3 polyunsaturated fatty acids (ω-3 PUFA), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) may be an important mediator of this synergism (AbuGhazaleh and Jenkins, 2004). Additionally, dietary supplementation with ω-3 PUFA can shorten the shelf life of meat. The objectives of the current study were to examine level and duration of dietary PUFA supplementation on tissue fatty acid concentrations and on lipid oxidative stability of beef cattle.

Satisfying consumer preferences is an important element in ensuring the sustainability of the beef industry. An array of feed ingredients are available to beef producers but the effects of pre-slaughter ration composition on determinants of consumers’ decisions to purchase beef, such as appearance and sensory characteristics, are unclear. Previous research has shown that the diet of cattle can influence fat colour, but that concentrates per se had little effect on sensory attributes of beef when compared with a grass silage or grass-based ration (French et al., 2000). The objective of the current study was to examine the effect of silage fermentation and concentrate composition on the appearance and eating quality characteristics of beef.

The costs associated with indoor finishing, i.e. ensiling grass, storage of silage and slurry, providing animal accommodation and disposal of slurry are substantial. Thus, where possible animals approaching slaughter should be finished at pasture rather than indoors. However, the seasonal decline in grass growth often results in insufficient grass in autumn to attain satisfactory performance with finishing animals. Finishing animals at pasture will involve less ensilage thereby permitting grass to accumulate on pastures as autumn approaches. Such grass could be supplemented with the concentrate allowance normally offered indoors. The objectives of this study were to determine the effect on performance of heifers of offering supplementary concentrates at pasture, and to compare pasture finishing with finishing on grass silage and concentrates.

In grass silage-based beef production systems, sugar cane molasses, of which the major carbohydrate is sucrose, is frequently an economically attractive supplement. However, the efficiency of utilisation of molasses appears to decline relative to barley, at high levels of dietary inclusion (Drennan, 1985) which may reflect differences in rumen fermentation. The objectives of this study were to (i) compare rumen fermentation in steers offered grass silage and a range of levels of a starch or sugar-based supplement, and (ii) since molasses has a low crude protein concentration, to determine the influence of the source of protein in a molasses-based supplement formulated to supply the same amount of nitrogen as a barley/soyabean mixture.

Due to its slower rate of rumen degradation, molassed sugar beet pulp (MBP) is considered to result in a higher pH in rumen fluid wnen compared with cereals and to be of benefit in diets where maximum fibre digestion is desired (Fahmy et al., 1984). Sodium hydroxide-treatment of MBP, by increasing feed pH may increase the value of MBP still further in these situations. The most common method of processing whole cereal grains is dry rolling. Sodium hydroxide pre-treatment has also been shown to increase the digestibility of whole cereal grains close to thai achieved by dry rolling (Orskov, 1979). Little information is available on the relative effects on rumen fermentation of both processing methods. The objectives of this study were to (1) determine the effects of treating MBP with NaOH and (2) compare the effects of rolfing (R) and S as processing methods for barley and wheat, on rumen fermentation and dry matter (DM) degradability (DMD) in steers offered grass silage.

Twenty-four steers of low iodine (I) status were selected from a group of 40 of similar weight and type. Changes in plasma inorganic iodide (PII) levels in steers treated with I were examined in a randomised block experiment (Part 1 below). Relationships between PII, plasma total I (TOTI) and thyroxine (T4) levels were examined also (Part 2 below).The trial began after a pre-treatment blood sampling (Pre) on Day 1. Selected steers (4 groups of 6 each) were assigned at random to individual stalls. Treatments were: C = no I supplement; D = a daily oral drench of 10 mg I (as potassium iodide)/100 kg liveweight (LW) on Days 1 to 7 inclusive; F = one application of 70 mg I (as Tincture of l)/100 kg LW to the flank fold on Day 1; L = intramuscular injection (1.1 ml/100 kg LW) of an oil-based iodine preparation (Lipiodol; 400 mg l/ml)) on Day 1.

The nutritive value of ensiled grass can be modified by the fermentation process. Compared to industrial fermentation, silage fermentation is still a relatively uncontrolled process. Consequently, considerable variation in the pattern of silage fermentation occurs on farms (Wilson and O'Kiely, 1990). This makes animal performance difficult to predict accurately and may alter the composition of the most appropriate concentrate to be fed with the silage. The objectives of the present experiment were (1) to compare the growth and rumen fermentation in cattle fed silage, where silage fermentation was altered using organic acids and (2) to determine the relative effects on growth when the silages were supplemented with two forms of concentrate.

Harvesting cereals in whole-crop form and conserving them by ensilage, has potential benefits compared to conventional cereal harvesting systems in terms of a lesser dependence on weather conditions and higher animal production per hectare. Three experiments were carried out to determine the performance of cattle offered whole-crop barley silage harvested at an immature stage of development.Whole-crop barley was harvested using a precision chop harvester in each experiment and intakes were recorded on a group basis in Experiments 2 and 3. In Experiment 1, winter barley was harvested either on June 17 (Cut 1 - grain at milky stage) or July 6 (Cut 2 -grain at mealy stage). Groups of seven Friesian steers (503 kg mean starting weight) were offered either Cut 1 or Cut 2 silage ad libitum for 95 days supplemented with one of the following supplements per head daily : (a) none, (b) 3 kg rolled barley, (c) 3 kg barley/soya (154 g crude protein (CP)/kg DM) and (d) 1 kg soyabean (470 g CP/kg DM).