The effects of high-concentrate diets and pasture on the concentration of conjugated linoleic acid in beef muscle and subcutaneous fat

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.     

Effects of the proportions of high or medium digestibility grass silage and concentrates in the diet of beef cattle on liveweight gain, carcass composition and fatty acid composition of muscle

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.     

The effect of a silage additive and level of concentrate supplementation on silage intake, animal performance and carcass characteristics of finishing beef cattle

An experiment was carried out to examine silage fermentation, effluent production and aerobic stability in unwilted grass silage, which was either ensiled without additive or with a commercially available blend of ammonium hexamethanoate, ammonium hexapropionate and octanoic acid (6 l t^?1, Maxgrass, BP Chemicals Ltd., Northwich, UK) and to determine alternative approaches to obtaining the same performance in finishing beef cattle. Seventy‐two Limousin × Friesian and Charolais × Friesian steers (mean initial live weight 424 kg s.d. 28·3) were blocked into groups of nine according to live weight and previous performance and offered silage, either with or without the additive, and supplemented with 0, 1·5, 3·0 or 4·5 kg d^?1 of a concentrate with a crude protein content of 150 g kg^?1 DM or allocated to a pre‐experimental slaughter group to enable calculation of daily carcass gain. Daily silage intakes were recorded for 112 days. At the end of the experiment, all cattle were slaughtered and daily carcass gain, omental, mesenteric, perinephric and retroperitoneal fat depots [kidney‐knob and channel fat (KKCF)], fatness, conformation, subcutaneous fat depth over M. longissimus dorsi muscle and carcass fat, protein and bone contents were assessed. Across all levels of supplementation, cattle offered the silage with the additive showed significantly (P < 0·001) higher daily DM intakes than those offered the silage without additive. Cattle offered the silage with the additive but unsupplemented had significantly (P < 0·001) higher daily carcass gains than those offered the silage without additive and unsupplemented. The response in carcass gain was 76 and 35 g kg^?1 additional concentrate for the silages with and without the additive respectively.     

Ingestive behaviour of beef cattle grazing alfalfa (Medicago sativa L.)†

Development of simulation models of grazing beef cattle requires measurement of the components of the ingestive process and the establishment of relationships between these components and the structure of the sward. The ingestive behaviour of eight half-sib Angus steers (live weight (LW), x?= 270 kg) grazing alfalfa (Medicago sativa L.) was studied at three stages of maturity (26, 40 and 47 days of regrowth) and at four allowances of herbage dry matter (DM) (1·0, 1·5, 20 and 2·5 kg per 100 kg LW) at each of two daily grazing sessions. A tethering system of grazing was used in which the experimental unit was a tethered steer and its plot for one grazing session. Grazing sessions commenced at 08.00 and 14.00 h EDT. Intake (DM) increased linearly from 1·98 kg per steer session at a DM allowance of 1 kg (100 kg LW)^?1 to 2 89 kg steer session at an allowance of 2·5 kg (100 kg LW) ^?1 as utilization of herbage declined linearly from 0·69 to 0·43. Herbage DM in take per bite increased from 1 0 g at 1 kg (100 kg LW) ^?1 allowance to 1·5 g at 2·5 kg (100 kg LW) ^?1 allowance. Rates of biting were not affected by herbage allowance and averaged 21 bites min^?1. Dry matter intake increased from 1·77 to 3 41 kg per steer session as the alfalfa matured and herbage mass changed from 1500 to 4656 kg ha^?1. Mean rates of biting were 24 bites min^?1 for steers grazing the youngest alfalfa and 16 bites min^?1 for steers on the oldest forage. Herbage DM intakes per bite were 1·1 g and 1·7 g at the same stages. Rates of DM intake approached 2 kg h^?1 and maximum daily DM intake was estimated at 2 75 kg (100 kg LW) ^?1. Intake of alfalfa was limited by allowance and mass of herbage above a canopy horizon of 20 cm and, to a lesser extent, by the length of fast.     

The performance of beef cattle given silages made from perennial ryegrasses of different maturity groups, cut on different dates

Two experiments were carried out to examine the interaction between early and late-heading varieties of ryegrass and date of harvesting of primary growths for silage in terms of the performance of beef cattle. A sward containing equal proportions of three early heading varieties (Cropper, Premo and Frances) (50% ear-emergence on 18 May) was harvested on 20 May (T1), 28/29 May (T2) and 5/6 June (T3) and a sward containing three late-heading varieties (Perma, Preference and Parcour) (50% ear-emergence on 12 June) was harvested on 28/29 May (T4), 5/6 June (T5) and 12/14 June (T6) in 1985 and 1987. In each year the six silages were harvested without wilting and were ensiled in trench silos. In Experiment 1 they were offered ad libitum and unsupplemented to 48 steers (407 kg live weight (LW)) for 101 days and in Experiment 2 they were offered with 2 kg concentrates per head daily to 48 heifers (392 kg LW) for 105 days. In Experiment 1 in vivo digestible organic matter (DOMD) concentrations in dry matter were 717, 671, 643, 709, 672 and 640 (s.e. 8·4) g (kg DM)^?1; silage DM intakes 7·1, 6·6, 6·6, 7·2, 7·3 and 6·7 (s.e. 0·15) kg d^?1; LW gains 0·94, 0·74, 0·62, 0·90, 0·82 and 0·57 (s.e. 0·047) kg d^?1; for T1 to T6 respectively. For Experiment 2, DOMD concentrations were 732, 699, 636, 734, 686 and 663 (s.e. 9·6) g (kg DM)^?1; silage DM intakes 6·4, 5·7, 6·0, 6·0, 5·5 and 5·0 (s.e. 0·22) kg d^?1; LW gains 1·12, 0·92, 0·99, 1·14, 0·88 and 0·76 (s.e. 0·078) kg d d^?1; and carcass gains 0·66, 0·56, 0·51, 0·68, 0·55 and 0·48 (s.e. 0·048) kg d d^?1; for TI to T6. It is concluded that silages made from early and late-maturing swards of perennial ryegrass sustained similar levels of performance in beef cattle when they were harvested at equal digestibility, and the digestibility declined at similar rates for the two sward types when harvesting of the primary growths was delayed. Under the conditions of these experiments the same level of animal performance was sustained by silages made from the two swards when the late-maturing varieties were harvested 7 days after the early varieties. This compares with an interval of 25 days between the early and late-maturing varieties reaching 50% ear-emergence.     

The effect of stage of perennial ryegrass maturity at harvesting, fermentation characteristics and concentrate supplementation, on the quality and intake of grass silage by beef cattle

Abstract Two experiments were carried out in consecutive years to examine the influence of cutting date and restricting fermentation by carboxylic acid treatment on the nutrient intake from grass silage by beef cattle. In year 1, four cutting dates during July and August after a primary growth harvest and, in year 2, five cutting dates of primary growth between mid‐May and early July were examined. Herbage was ensiled either untreated or treated with high levels of acid additive (‘Maxgrass’, mean 8·6 l t^?1). Ninety‐six (year 1) or forty‐eight (year 2) continental cross steers were used in partially balanced changeover design experiments with each silage type either unsupplemented or supplemented with 4·5 (year 1) or 5·5 (year 2) kg concentrates head^?1 d^?1. Silage digestibility declined significantly between initial and final harvest dates (P < 0·001), whereas silage dry‐matter (DM) and digestible energy (DE) intakes were significantly higher in the initial compared with final harvest dates in both years of the study (P < 0·01). Similarly, silage DM and DE intakes, and total DM intakes, of acid‐treated and unsupplemented silages were greater than those of untreated and concentrate supplemented silages, respectively (P < 0·001). The results indicate that earlier cutting dates, and addition of acid to herbage before ensiling, can increase silage DM intake by beef cattle.     

Allowance-intake relations of cattle grazing vegetative tall fescue†

Herbage allowance is one of the important pasture factors in the determination of intake by grazing livestock. Ingestive behaviour of 12 adult Angus cows (Bos taurus) was measured over a range of allowances (0·25 to 0·72 kg dry matter (DM) per 100 kg live weight (LW) for a 1-h period) of vegetative tall fescue (Festuca arundinacea Schreb.). A balanced change-over design was used to estimate direct, residual and permanent effects of herbage allowance on rate of DM intake, rate of biting and herbage DM intake per bite. In Experiment 1, herbage DM intake per meal increased linearly from 0·68 to 1·72 kg (100 kg LW)^?1 as DM allowance increased from 0·25 to 0·72 kg (100 kg LW)^?1 h^?1. Cows grazed at ·30 kg (100 kg LW)^?1 h^?1 and stopped grazing when the sward was reduced to a height about 10 to 12 cm above the soil surface, approximately defined by the tops of pseudostems. In Experiment 2, herbage DM intake rates of 0·29, 0·47 and 0·42 kg (100 kg LW)^?1 h^?1 were recorded as cows grazed allowances of 0·43, 0·70 and 0·90 kg (100 kg LW)^?1 h^?1 for most of the 1-h grazing period. Limiting herbage DM allowances in Experiment 2 were associated with small reductions in rate of biting and herbage DM intake per bite as allowance declined. Sward DM density (>5 cm) was an important variable in the determination of herbage DM intake rates at lower herbage allowances.     

Effect of early turnout to grass in spring on dairy cow performance

This experiment examined the effects of grazing severity and degree of silage restriction during early turnout of dairy cows to pasture in spring on animal performance. Forty late‐winter‐calving Holstein Friesian dairy cows were allocated to one of five treatments between 7 March and 17 April 1997. The treatments involved early turnout of cows to grass for 2 h per day at two residual sward heights and two silage allowances, plus a control treatment, in a randomized block design. Dairy cows on the control treatment remained indoors throughout the experiment and were offered grass silage ad libitum. Dairy cows on all treatments were also offered 6 kg d^–1 of a concentrate on a flat‐rate basis, split equally between the morning and afternoon milkings. Offering cows access to pasture in early spring for 2 h per day resulted in increases in both milk (P < 0·001) and protein yield (P < 0·01). On average, over all grazing treatments, cows produced an additional 2·6 kg milk per day compared with the control treatment (28·5 vs. 25·9 kg d^–1, s.e.m. 0·43). Furthermore, these increases in milk yield were obtained even when silage was restricted indoors (28·4 vs. 25·9 kg d^–1) and cows grazed down to a residual sward height of 40 mm (28·1 vs. 25·9 kg d^–1). Protein yield was higher (P < 0·01) with dairy cows grazing pasture compared with cows indoors (848 vs. 707 g d^–1, s.e.m. 28·9). Silage intake was significantly (P < 0·001) reduced when cows were turned out to pasture. In conclusion, early turnout of dairy cows to pasture in spring for 2 h per day reduced silage intake and increased milk yield and protein yield relative to those fully housed and offered grass silage with a low level of concentrates.     

Effect of increasing plant maturity in timothy‐dominated grass silage on the performance of growing/finishing Norwegian Red bulls

An investigation was made of the potential for attaining high daily live weight (LW) gain, high feeding efficiency and carcass quality in Norwegian Red (NRF) bulls fed grass silage harvested at early stages of maturity, supplemented with minimal amounts of concentrates. Roundbale silage was produced from timothy‐dominated swards harvested at three stages of maturity: stages 1 and 2 were dominated by tillers in stem elongation with two and three visible nodes, respectively, and stage 3 by tillers at early heading, with visible heads, but without head stems. Crops were wilted rapidly and a formic acid‐based additive applied. All silages were preserved with restricted fermentation. Silage DOMD values were 0·747, 0·708 and 0·647 for harvesting time (H) 1, 2 and 3 respectively. Silages were fed ad libitum as sole feed, or supplemented with 2–4 kg concentrate at increasing LW, to six bulls per treatment from age 7 months (288 kg) to slaughter at 575 kg. Daily LW gain for bulls fed unsupplemented silage was 1423, 1262 and 936 g, respectively, for H1, H2 and H3, and 1570, 1567 and 1357 g for supplemented bulls. For concentrate‐supplemented bulls, higher energy intake increased proportions of carcass fat more for H1 (0·163) than for H2 (0·134) but the same amount of energy was retained in the carcass per MJ net energy growth intake for these two groups. It is concluded that, apart from milk and concentrate fed to calves during the first months, an intensive beef production with NRF bulls finished before 15 months of age may be based entirely on local grass resources.     

Effect of maize grain and herbage allowance on estimated metabolizable energy intake and animal performance in beef cattle finishing systems

This study investigated the effects of levels of supplementation with maize grain and herbage allowance (HA) on grass herbage and maize intake, animal performance and grazing behaviour in two replicated grazing experiments with Angus beef cattle in Argentina. In Experiment 1, the response to increasing HA (2·5, 5·0 and 7·5 kg DM herbage 100 kg^?1 live weight (LW) d^?1 with and without 0·5 kg DM maize grain 100 kg^?1 LW d^?1) was investigated. In Experiment 2, the responses to level of maize grain offered (0, 0·5 and 1·0 kg DM maize grain 100 kg^?1 LW d^?1) at an HA of 2·5 kg DM herbage 100 kg^?1 LW d^?1 and an HA of 5·0 kg 100 kg^?1 LW d^?1 without maize grain were assessed. In Experiment 2, soyabean meal was added to control the crude protein concentration in the diet. Two methods were used for intake estimations: pre‐ and post‐feeding herbage mass difference, and the use of the n‐alkane and ¹³C technique. The latter predicted most accurately the metabolizable energy requirements calculated from live weights and liveweight gain of beef cattle attained in each treatment in both experiments. Increasing HA significantly increased herbage intake and liveweight gain (P < 0·01), and general quadratic relationships between these variables could be fitted across experiments despite differences in animal and pasture characteristics. Increasing the amount of maize grain offered significantly reduced herbage intake and grazing time, but increased liveweight gain and digestibility of the diet. Substitution rate increased with increasing HA in Experiment 1 but was not affected by level of maize supplementation in Experiment 2. These relationships will aid the development of grazing management models for Argentinean conditions.     

Effects of supplementation on the ingestive behaviour of grazing steers*

Herbage intake is usually depressed when beef cattle grazing abundant pastures are supplemented with energy-rich feedstuffs but relatively little is known about the effects of supplementation on the components of ingestive behaviour. An experiment was conducted to establish the effect of ground corn (Zea mays L.) on the ingestive behaviour of yearling Angus and Angus × Hereford steers (Bos taurus) (mean live weight (LW) of 323 kg) grazing autumn stockpiled Boone cocksfoot (Dactylis glomerata L.) using a tethered grazing system in which the experimental unit was the tethered steer and its grazing area (45 m²) for one grazing session. Herbage dry matter (DM) mass was 1662 kg ha^?1 and herbage DM allowance was 7–5 kg steer^?1 for each grazing session. Herbage DM intake was measured as the difference between herbage DM mass offered and refused. Grazing took place during two daily sessions each of about 2 h duration commencing at 08.00 and 14.00 h for 9 days. Ground corn (0, 1·5, 3·0 and 4·5 kg steer^?1) was fed each day at 12.00 h and had no significant (P < 0·05) effect on rate of DM intake, rate of biting or DM intake per bite. Mean DM intake was 6 2 kg steer^?1 d^?1 (87 mg (kg LW)^?1 min^?1). Steers averaged 4832 bites per grazing session, with a mean DM intake per bite of 644 mg (2·0 mg (kg LW)^?1) and a mean rate of 44 bites min^?1. Data obtained at the beginning and end of each grazing period on ingestive behaviour of one group of four steers (mean LW of 306 kg) fitted with oesophageal fistulae supported data for the two groups of normal steers and showed no response to supplementation. Mean values for rate of DM intake, DM intake per bite and rate of biting established for the fistulated cattle were 73 mg (kg LW)^?1 min^?1, 521 mg bite^?1 (1·7 mg (kg LW)^?1) and 39 bites min^?1, respectively.     

Effect on upland beef production of incorporating winter feeding of red clover silage or summer grazing of Molinia-dominated semi-natural pastures

Management systems for finishing beef cattle, designed to meet environmental goals in the Less Favoured Areas (LFAs) of the UK, often rely on the integration of grazing of semi‐natural pastures with sown permanent pasture. In this experiment, three management options were compared: (i) permanent pasture for grazing and silage production (treatment PP), (ii) permanent pasture for grazing and silage and grazing of Molinia‐dominant semi‐natural pasture in summer from June to August inclusively (treatment PP + SNP) and (iii) permanent pasture for grazing and silage and red clover (RC) silage for 0·25 of the silage requirement in winter (treatment PP + RC). The performance of spring‐born Welsh Black steers was measured from turnout in spring 2002 until finishing in summer 2003. During summer 2002, the liveweight gain of steers grazing the semi‐natural pasture was significantly lower than that of steers grazing the permanent pasture. There was a trend for the liveweight gains of the steers on the PP + SNP treatment to be higher from housing in autumn 2002, and live weights on all treatments were similar at the start of the red clover‐feeding phase. Steers offered red clover silage had a significantly higher liveweight gains than those offered grass silage, but there was only a trend for a higher live weight at the end of the winter‐feeding period. During summer 2003, liveweight gains were again higher on the permanent pasture. Finishing system significantly affected the fatty‐acid profile of the meat produced, but there was no difference in the colour of meat in relation to shelf‐life. Lipid oxidation was less for the meat from steers on the PP + SNP treatment than on the PP treatment, which, in turn, was less than for meat from the steers on the PP + RC treatment, and was in inverse proportion to the vitamin E concentration in the loin muscle. There were no significant differences in sensory panel scores for texture, juiciness or flavour of the meat.     

The effect of sugar beet pulp-based silage additives on effluent production, fermentation, in-silo losses, silage intake and animal performance

First-harvest direct-cut, double-chopped grass (190 and 164g DMkg^?1 in Experiments 1 and 2 resptectively) was ensiled without an additive or, in Experiment 1, with 30 kg t^?1 grass of an absorbent additive based on sugar beet pulp (Sweet ‘n’ Dry) or with 3·441 t^?1 grass of formic acid and, in Experiment 2, with 30, 50 and 70 kg t^?1 grass of Sweet ‘n’ Dry or with 50kg t^?1 grass of unmolassed sugar beet pulp. The preservation and nutritive value of the silage, in-silo losses (including silage effluent production), silage intake and animal performance of adult and growing cattle were examined. In Experiment 1 all three silages were well preserved, although the formic acid-treated silage displayed significantly lower pH, ammonia nitrogen (NH₃N) [g kg^?1 total nitrogen (TN)] and volatile fatty acids (VFAs) than the other two silages. In Experiment 2 absorbent-treated silages displayed significantly lower pH, buffer capacity (Bc), NH₃N (gkg^?1 TN), CP, modified acid detergent fibre (MADF) and VFAs than untreated silage. Treatment of grass with the absorbent additives at ensiling resulted in reduced effluent production. In Experiment 1 each kilogram of Sweet ‘n’ Dry retained approximately 11 effluent, and in Experiment 2 silages made with Sweet ‘n’ Dry applied at 70kgt^?1 and sugar beet pulp applied at 50 kg t^?1 produced similar volumes of effluent and each kilogram of absorbent retained 1·0 and 1·31 of effluent respectively. In Experiment 1 sixty beef cattle [mean initial live weight (LW) 460 kg] were grouped according to LW and allocated to treatment at random. For untreated silage (unsupplemented or with 1 or 2 kg supplement head^?1 day^?1), absorbent-treated silage (unsupplemented or with 1 or 2 kg supplement head^?1 day^?1) and formic acid-treated silage (1 kg supplement head^?1 day^?1) the daily silage DM intakes were 6·12, 6·21, 6·40, 7·65, 7·45, 7·11 and 7·85 (s.e. 0·280) kg respectively, the daily liveweight gains were 0·22, 0·56, 0·81, 0·59, 0·74, 0·81 and 0·75 (s.e. 0·071) kg respectively and daily carcass gains were 0·31, 0·47, 0·67, 0·47, 0·61, 0·70 and 0·57 (s.e. 0·043) kg respectively throughout a 75-day feeding period. In Experiment 2, fifty-six growing cattle (mean initial weight 312 kg) were grouped according to LW and allocated to treatment at random. For untreated silage (unsupplemented or with 1·5 kg Sweet ‘n’ Dry or 1·5 kg commercial concentrates head^?1 day^?1), silage treated with Sweet ‘n’ Dry at 30, 50 and 70 kg t^?1 grass and silage treated with 50kg sugar beet pulp t^?1 grass the daily silage DM intakes were 5·46, 5·28, 5·33, 6·21, 6·27, 6·60 and 6·62 (s.e. 0·154) kg respectively and daily liveweight gains were 0·39, 0·75, 0·81, 0·63, 0·76, 0·94 and 1·75 (s.e. 0·052) kg respectively throughout a 122-day feeding period. In this experiment 360g kg^?1 more absorbent was required when it was included at ensiling rather than offered as a supplement to untreated silage to achieve the same individual animal performance.     

The effect of silage energy concentration and price on finishing decisions for young dairy bulls

This study focuses on the effect of grass silage energy concentration and price on the decisions about concentrate level, slaughter age and carcass weight in the finishing of young dairy bulls. The three main steps were as follows: (i) the adaption of a daily liveweight (LW) gain simulation model to young dairy bulls of the breed Norwegian Red; (ii) the comparison of the model key output to experimental data; and (iii) model‐based maximization with respect to the profitability of the finishing period, and stochastic simulations with respect to prediction error and variation as derived from the experimental data. In general, the model adequately simulated the LW gain of the bulls, but tended to overestimate the LWs of the bulls that received very high energy rations and underestimated the LWs of the bulls fed with the lowest energy diets. Model‐based maximization of profit was conducted for three silage energy concentrations, expressed as feed unit beef (FUb), combined with three silage prices. Taking into account the risk associated with model prediction error and the empirical variation and correlation among key variables, we concluded that under the prevailing Norwegian economical conditions, finishing of young dairy bulls with an early harvested silage having an energy concentration of slightly above 0·90 FUb kg^?1 dry matter, 10% FUb concentrate of the total FUb ration and an average daily LW gain of 1·2–1·3 kg LW d^?1 will offer the highest profit.     

THE EFFECT OF INCLUDING DRIED GRASS IN THE SUPPLEMENT GIVEN TO LACTATING COWS AT PASTURE

An investigation into the effect of including dried grass in the supplement given to dairy cows at pasture is reported. Supplements containing 0, 50 and 100% dried grass were used in the investigation which was carried out in two parts. In the first part 12 high-yielding cows with unrestricted access to pasture were used in an experiment with a change over design to assess the effects of feeding 5 kg/day of each supplement on milk yield and composition. In the second part 8 steers, housed in stalls and given cut herbage from the same sward as that grazed hy the cows, were used in a change over experiment to assess the effects of the three supplements on herhage and total DM intake. No significant differences in milk yield between supplements were ohtained, the mean yields being 23·9, 24·5 and 23·9 kg/day for the supplements containing 0, 50 and 100% dried grass, respectively. Milk composition was also not significantly affected by including dried grass in the supplement. In the indoor feeding trial using the steers, the addition of 3·5 kg DM from the supplement resulted in an increase in total DM intake of only 1·3 kg/day. There was no significant difference hetween supplements on herbage and total DM intake.     

Effects of incorporating cowpea in a subtropical grass pasture on forage production and quality and the performance of cows and calves

The increasing cost of N fertilizer has stimulated an interest in sourcing protein from warm‐season legumes among beef cattle producers in the tropical/subtropical areas of the world. The objective of this study was to evaluate effects of two strategies of incorporating cowpea [Vigna unguiculata (L.) Walp.] into bahiagrass (Paspalum notatum Flügge) pastures on the herbage characteristics and performance of grazing cow–calf pairs. The study was conducted in Ona, Florida, USA, from May to August in 2007 and 2008. Experimental units were 1·0 ha. Treatments were bahiagrass pasture alone (control), 50:50 bahiagrass–cowpea pasture (cowpea), bahiagrass pasture with a cowpea creep grazing area (0·1 ha, creep grazing) and bahiagrass pasture with a creep‐fed concentrate [(creep feeding; 10 g kg^?1 body weight (BW)]. The cowpea pastures had lower herbage mass [HM, 1·8 vs. 3·7 t ha^?1] and herbage allowance [HA, 0·8 vs. 1·4 kg DM kg^?1 live weight (LW)] compared with the other treatments. Cowpea had greater CP (CP, 160 g kg^?1) and in vitro digestible organic matter (IVDOM), (600 g kg^?1) than bahiagrass (110 and 490 g kg^?1 respectively); however, cowpea HM was only 0·9 t ha^?1 in May and 0·7 t ha^?1 in June, but it did not persist in July and August. Calves receiving the creep feeding treatments had greater average daily gain (0·8 vs. 0·7 kg d^?1) than calves in other treatments. Further research is necessary to exploit the superior nutritive value of cowpea in grazing systems in the south‐eastern USA.     

A COMPARISON BETWEEN SPRING AND AUTUMN PASTURE FOR BEEF CATTLE AT EQUAL GRAZING PRESSURES

Two comparisons between spring and autumn pasture for beef cattle were made. Animals used in all comparisons were of similar breed and weight and were subjected to the same feeding regime for 6–8 weeks before turn-out. The pastures were grazed on an equal grazing pressure basis between season comparisons. The pastures received similar rates of fertilizer N between seasons and had similar lengths of rest period for regrowth. Intakes of digestible OM were greater per unit of metabolic liveweight in spring than in autumn. Daily liveweight gains in spring were high, being 1·09 and 1·37 kg (2·4 lb and 3·0 lb), but were lower from autumn pasture at 0·98 and 0·71 kg (2·2 lb and 1·6 lb). Weather was implicated as a factor affecting daily gain from autumn pasture. Greater herbage yields in spring supported 42 and 204 more grazing days per ha which together with the greater gains per animal supported 80–120% more liveweight gain/ha.     

The performance of summer-calving cows grazing perennial ryegrass swards

The objectives of this experiment were to study the effects of different grazing managements in spring on herbage intake and performance of summer-calving dairy cows and to examine the effects of regrowth in early June on herbage intake and cow performance. Four spring-grazing treatments were applied to predominantly perennial ryegrass swards: Control (C), sward grazed by cows to 6–8 cm sward surface height (SSH); CG16, sward grazed by cows to 3–4 cm SSH in May and allowed to regrow to a target SSH of 16cm in early June; CG8, sward grazed by cows to 3–4 cm SSH in May and allowed to regrow to 8cm in early June; and SG8, sward grazed by sheep to 2–3 cm SSH in May and allowed to regrow to 8 cm in early June, All swards were continuously stocked by summer-calving (May and July) primiparous and multiparous cows from 16 June to 7 September, to a target SSH of 8–10cm. Spring treatments bad marked effects on herbage intakes and milk production. Estimated in July by n alkane analysis, the mean herbage intake ± s.e.d. of cows on each treatment were 1·8, 1·4, 1·4 and 3·0 ± 0·31 kg dry matter (DM) 100 kg live weight (LW)^?1 d^?1 (P < 0·01) for treatments C, CG16, CG8 and SG8 respectively. Measured in August, intakes were 1·8, 20, 2·1 and 2·4 ± O·33kg DM 100kg LW^?1 d^?1 respectively. Severe spring grazing led to increased milk yield and reduced milk fat content from summer-calving cows fed 5·2 kg d^?1 of a proprietary concentrate. Average milk yields for the eleven experimental cows on each treatment were 24·3, 23·4, 26·2 and 29·0 ± 1·20 kgd^?1 (P < 0·01) for C, CG16, CG8 and SG8, and average milk fat contents were 45·4. 42·4, 43·9 and 40·9 ± 1·02gkg^?1 (P<0·05) respectively. The results suggest that severe grazing of swards in early season could improve herbage intake and milk yield of summer-calving cows in mid- and late season. The most favourable spring treatment in this respect was severe grazing by sheep. However, this advantage could be negated in midseason by lax grazing at that time.     

Effect of sward surface height on the performance of ewes and Iambs continuously grazed on grass/clover and nitrogen-fertilized grass swards

In three successive years, sward height was maintained at 3, 5, 7 or 9 cm on grass swards receiving a total of 300 kg N ha^?1 in six equal monthly dressings from April, and on grass/clover swards receiving 50 kg N ha^?1 as a single dressing in early spring. From turnout in April until weaning in July, 64 ewes and their lambs (mean litter size 1·5) were continuously grazed at the four sward surface heights on the two sward types. White clover content of grass/clover swards remained low throughout the experiment ranging from 0·2 to 7·4% of the herbage mass. During the first two years, lamb gains averaged over sward types were 204, 260, 285 and 308 g d^?1 up to weaning, while in the third year gains were 238, 296, 296 and 260 g d^?1 on 3, 5, 7 and 9 cm swards respectively. Ewes lost live weight on 3 cm swards but apart from this sward height had little effect on performance. During the autumn, weaned lambs gained — 27, 87, 147 and 167 g d^?1 on 3, 5, 7 and 9 cm swards respectively. Sward type had only a small effect on the performance of lambs up to weaning but in the autumn, mean gains of weaned lambs were lower on grass/N swards (73 g d^?1) than on grass/clover swards (115 g d^?1). Relative to 3 cm swards, carrying capacities of 5, 7 and 9 cm swards were 0·76, 0·57 and 0·52 respectively from turnout to weaning and 0·66, 0·52 and 0·44 respectively during autumn. Grass/clover swards carried 0·67 of the ewes carried by grass/N swards from turnout to weaning and 0·51 of the live weight carried by grass/N swards during autumn. The reaction of the two sward types to sward height did not appear to differ but in the third year there was evidence of a reduction in white clover content when swards were grazed at 9 cm. The data suggest that lamb growth rates will increase as sward height increases up to 9 cm and the evidence for this was stronger with weaned lambs in autumn than with suckling lambs in spring.     

Effect of formic acid and a bacterial inoculant on the amino acid composition of grass silage and on animal performance

An Italian ryegrass and hybrid ryegrass sward was harvested on 11 May 1994. The mean dry‐matter (DM) content of the herbage was 197 g kg^–1 fresh matter (FM), and mean nitrogen and water‐soluble carbohydrate contents were 20 and 272 g kg^–1 DM respectively. Approximately 72% of total nitrogen (TN) was in the form of protein‐nitrogen. The herbage was treated with either no additive, formic acid (3·3 l t^–1) (Add‐F, BP) or inoculant (2·3 l t^–1) (Live‐system, Genus) and ensiled in 100 t silos. Changes in effluent composition with time showed that silage fermentation and protein breakdown were delayed by treatment with formic acid. Formic acid and inoculant treatments also inhibited amino acid catabolism during ensilage. All silages were well fermented at opening with pH values < 4·0 and ammonia‐N concentrations of ≤ 50 g kg^–1 TN after 120 d ensilage. Treatment had an effect on protein breakdown as measured by free amino acid concentration, with values of 21·5, 18·2 and 13·2 mol kg^–1 N at opening (191 d) for untreated, formic acid‐treated and inoculated silages respectively. Amino acid catabolism occurred to the greatest extent in untreated silages with significant decreases in glutamic acid, lysine and arginine, and increases in gamma amino butyric acid and ornithine. The silages were offered ad libitum without concentrate supplementation to thirty‐six Charolais beef steers for a period of 69 d (mean live weight 401 kg). Silage dry‐matter intakes and liveweight gains were significantly (P < 0·05) higher on the treated silages. Silage dry‐matter intakes were 7·42, 8·41 and 8·23 kg d^–1 (s.e.d. 0·27) with liveweight gains of 0·66, 0·94 and 0·89 kg d^–1 (s.e.d. 0·058) for untreated, formic acid‐treated and inoculated silage‐fed cattle respectively. In conclusion, additives increased the intake of silage and liveweight gain by the beef steers, and it is suggested that this may be caused in part by the amino acid balance in these silages.