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.     

Herbage intake and milk production by grazing dairy cows 1. The effects of variation in herbage mass and daily herbage allowance in a short-term trial

Twenty-four British Friesian cows were allocated between six grazing treatments (two levels of herbage mass x three levels of daily herbage allowance) in a balanced change-over design with four periods of 12 d each at monthly intervals. Herbage OM mass ranged from 3790 to 5770 kg ha^-1 measured to ground level and daily herbage DM allowances were 30, 60 and 90 g per kg animal live weight. Herbage OM intake was lower at high than at low herbage mass (24·6 vs 26·3 g per kg LW), and was 26·9, 26·6 and 22·9 g per kg LW respectively at daily herbage DM allowances of 90, 60 and 30 g per kg LW. Milk yield was not affected by herbage mass but was depressed at the low herbage allowance.     

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.     

The effects of cereal supplementation of grass and maize silages

Grass and maize silages were fed alone and with two levels of a barley supplement to Friesian steers of about 300 kg liveweight. The organic matter (OM) intakes of grass and maize silage were similar although the OM digestibilities of the silages were 0·722 and 0·649 respectively. For both silages, barley supplementation increased total OM intake and total digestible OM intake by 0·46·0·08 and 0·37·0·06 g per g OM of supplement respectively. Liveweight gains on grass and maize silage diets were 1·38 and 1·20 kg d^-1 respectively, but the differences were not significant (P> 0·05).     

A STUDY OF THE UTILIZATION OF SILAGES OF DIFFERENT DRY–MATTER CONTENT BY YOUNG BEEF CATTLE WITH OR WITHOUT SUPPLEMENTARY BARLEY

Three Uages containing 18.7, 35.2 and 51.0% DM were given to young beef cattle without supplementary barley or with a daily allowance of 1.8 or 3.6 kg air-dry fortified barley. Each diet was given to 9 individually fed animals, the mean fasted liveweight of which at the start of the experiment was 304 kg. The dafly voluntary DM intake was recorded for a 10-day period for the 9 animals on each silage without supplementary barley. The mean DM intakes per kg W^0.73 were 58.4, 94.6 and 104.1 g for Silages 1, 2 and 3 and the intakes increased curvilinearly with the DM content of the silage. The mean daily liveweight gains on Silages 1, 2 and 3 were 0.63,0.73 and 0.75 kg, respectively; the relationship was significantly linear (P <0.01). The barley supplement also had a significantly linear CP <0.01) effect on daily gains. The mean daily gains for 0, 18 and 3 6 kg fortified barley per day were 0.54, 0.74 and 0.84 kg, respectively. The DM and digestible organic matter required per kg liveweight gain were not significantly affected by the DM of the silage, but were significantly (P < 0.01) affected by supplementation. The metabolizable energy (ME) values of Silages 1,2 and 3 were 2.46, 2.52 and 2.50 Meal/ kg DM, respectively. The supplementary concentrate increased the ME concentration significantly (P < 0.05), although the overall increase was small. The mean values were 2.49, 2.54 and 2.61 Meal/ kg DM, respectively, for 0, 1.8 and 3.6 kg fortified barley per day. The digestibilities of DM and organic matter were not significantly affected by the type of silage, but there was a significant increase with increasing intake of supplementary barley.     

A comparison between barley and groundnut as supplements for dairy cows at pasture

In two 12-week grazing experiments using twelve and eighteen spring-calved cows in 1976 and 1977 respectively, the effects of feeding either a barley or a groundnut concentrate supplement were investigated. The mean yield of herbage DM on offer was 2330 and 2030 kg ha^-1, with crude protein concentrations of 192 and 193 g per kg DM in 1976 and 1977 respectively. Grazed herbage was the sole feed in the control treatment. In the other two treatments the herbage was supplemented with 3 kg per cow per d of a concentrate containing either 82·2% barley or groundnut with mean crude protein concentrations of 109 and 409 g per kg DM respectively. Similar results were obtained in both experiments with average daily milk yields of 18·3, 19·8 and 19·9 kg per cow on the control, barley and groundnut treatments respectively. The supplements had no significant effects on either milk composition or liveweight change. It is concluded, that with an ample supply of herbage of high crude protein concentration, a supplement of groundnut had no advantages over one of barley.     

Effects of different levels of fertilizer application to veld on growth of steers and chemical composition of the herbage

The effects of different levels of N fertilization (no N, 40 kg N and 80 kg N ha^?1 year^?1), P fertilization (no P, 21 kg P ha^?1 year^?1 and 21 kg P plus 53 kg K ha^?1 year^?1) and stocking rates (0·52 large stock units (LSU) ha^?1, 0·78 LSU ha^?1 and 1·56 LSU ha^?1) on the chemical composition and in vitro dry matter digestibility of the herbage and the liveweight gains of steers were determined in the western variant of the Bankenveld in South Africa. The average daily liveweight gains (ADLGs) of the steers increased with increasing level of N fertilization. Fertilization with P had a positive effect on ADLG only when 53 kg of K was applied with 21 kg of P ha^?1. Higher stocking rates reduced ADLGs. The liveweight gains ha^?1 increased as the rates of N and P fertilization increased. The medium stocking rate (0·78 LSU ha^?1) gave a higher liveweight gain ha^?1 than the lowest stocking rate (0·52 LSU ha^?1), but the highest stocking rate (1·56 LSU ha^?1) reduced liveweight gain ha^?1. In general, in terms of chemical components, a higher nutritive value of the veld herbage resulted from N fertilization. The higher crude protein (CP) content of the herbage, resulting from higher stocking rates, should be seen against the background of lower liveweight gains ha^?1 at the highest stocking rate. On pasture with similar contents of CP and acid detergent fibre (ADF), higher ADLG of steers was found as a result of P and K fertilization, especially for herbage with a lower CP and a higher ADF content, implying better utilization of the nutrients in such herbage with P and K fertilization, although P was also supplemented through a lick.     

Effect of nitrogenous fertilizer on production per animal and per unit area by beef cattle offered similar daily allowances of herbage

An experiment repeated in 3 consecutive years in which 0, 200, 400 and 600 kg ha^?1 fertilizer N was applied annually is described. Cattle on all treatments were offered the same constant daily amount of 2.0 kg herbage DM per 100 kg liveweight above a 3.4 cm height of defoliation. Digestible OM intakes and daily rates of gain were in general not significantly different between treatments. Area required to support these intakes and gains however differed significantly between treatments (P < 0.001) and resulted in high outputs of liveweight gain per hectare on all treatments when compared with other published studies. These outputs together with other actual and theoretical outputs were used to predict optimum fertilizer N applications for grazing beef cattle and the predictions discussed in relation to commercial practice.     

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.     

Effect of stage of maturity of whole-crop barley on intake and liveweight gain by dairy steers differing in initial live weight

The effect of maturity at harvest of whole-crop barley for ensiling on intake and liveweight gain of dairy steers differing in initial live weight (LW) was evaluated in an experiment over two years. Light (104–120 kg) and heavy (402–419 kg) dairy steers were fed diets containing predominantly whole-crop barley silage harvested at the milk stage [dry matter (DM) content of 284 g kg⁻¹ and neutral-detergent fibre (NDF) concentration of 526 g kg⁻¹ DM] or the dough stage of maturity (DM content of 328 g kg⁻¹ and NDF concentration of 445 g kg⁻¹ DM) and supplemented with up to 1 kg of concentrate. Dry matter intake (g kg⁻¹ LW) was higher for whole-crop barley harvested at the dough stage than at the milk stage of maturity and the difference was greater in heavy than in light steers ( P <  0·001). Liveweight gain was higher and feed conversion ratio was lower for dough-stage compared with milk-stage silage ( P  <   0·05) but there was no interaction with size of steer. Whole-crop barley harvested at the dough stage of maturity promoted higher liveweight gains in dairy steers compared with whole-crop barley harvested at the milk stage due to a higher DM intake.     

Grass silage as a basic feed for store lambs. 3. Effect of barley supplementation of silages varying in chop length on silage intake and lamb performance

An experiment was carried out to study the effect of silage chop length and barley supplementation on silage intake and the performance of store lambs. The silages were cut from a perennial ryegrass regrowth at a relatively mature stage of growth in early July. Different types of harvester were used to produce a long silage (L), single-chopped (S), double-chopped (D), medium precision-chopped (MP) or a short precision-chopped (SP) silage. The chop length of the silages averaged 37.4, 12.4, 8.4, 7.0 and 2.9 cm respectively. All silages were treated with formic acid at 2.51 t^?1grass. They were well preserved and of a good quality with a dry-matter (DM) digestibility of 720–760 g kg^?1 DM. The silages were fed ad libitum to Suffolk crossbred store lambs over a period of 10 weeks. Each silage was fed either alone or was supplemented with whole barley at 400 g lamb^?1 d^?1. When offered silage alone, intakes were 738, 679, 773, 980 and 910 (± 30) g DM d^?1 for silages L, S, D, MP and SP respectively. Similar relative differences in intakes between the silages were evident when supplemented with barley. Liveweight gain on silage alone was higher on the precision-chopped silages (85–93 g d^?1) than the long or flail-chopped silages (28–49 g d^?1). Liveweight gain on the precision-chopped silages was also better when supplemented with barley (150 vs. 90–112 (± 90) g d^?1). Silage intake and lamb performance were similar for the MP and SP silages, despite the difference in chop length. Barley supplementation reduced silage intake to a similar extent for all silages (-9%) and increased total DM intake (+ 30%) and metabolizable energy intake (+ 37%). The substitution rates of silage for barley were similar for all silages and averaged 0.24 g silage DM g^?l barley DM. The response in weight gain per 100g of barley fed was similar for all silages and averaged 20.0 g liveweight gain and 13.4 g carcass gain. Feed conversion efficiency of the total diet was similar for the Mail-chopped and precision-chopped silages but was less for the long silage. The results of this study show that the benefit in weight gain due to the higher intake of precision-chopped silage was maintained when the silage was supplemented with a moderate level of barley. Such silage required supplementation with barley (400 g d^?l) to achieve a rate of liveweight gain of 150g d^?1.     

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.     

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.     

Concentrate supplementation of grazing dairy cows

Two experiments are described in which twenty-four spring-calving Dutch Friesian cows were allocated between six grazing treatments (two levels of daily herbage allowance × three levels of daily concentrate intake) in a 2 × 3 factorial design. The swards consisted predominantly of perennial ryegrass. A two-machine sward-cutting technique (with correction for herbage accumulation during grazing) was used for estimating herbage intake by cows which grazed swards for 3 or 4d. Experiment 1 was carried out for 16 weeks of the grazing season of 1981 and experiment 2 for 18 weeks in 1982.
Daily herbage OM allowances in both experiments were 16 and 24 kg per cow above 4 cm cutting height. Daily concentrate OM intake ranged from 0.8 to 5.6 kg per cow. The effect of concentrates on herbage intake differed significantly between allowances. At the low allowance level and at daily concentrate OM intakes of 0.8, 3.2 and 5.6 kg per cow daily herbage OM intake was 10.9, 10.6 and 10.4 kg per cow respectively and the mean substitution rate of herbage by concentrates was only 0.1. At the high allowance level and at daily concentrate OM intakes of 0.8, 3.2 and 5.6 kg per cow daily herbage OM intake was 14.8, 13.6 and 12.4 kg per cow respectively and mean substitution rate was 0.5 kg herbage OM (kg concentrate OM)⁻¹.     

Unwilted and prewilted grass silage for finishing bulls*

Three silages were prepared from perennial ryegrass; unwilted without additive (UW), unwilted treated with 3·5 litres commercial (85%) formic acid (UWA) and prewilted without additive (WN) with dry matter (DM) concentrations of 189, 209 and 328 g kg⁻¹ respectively. The three silages were offered ad libitum in a 348-d feeding experiment to three groups of eight Belgian white-blue bulls with an initial live weight (LW) of 277 kg. The concentrate (47 g digestible crude protein (CP) kg⁻¹) supplementation was 7·5 g (kg LW)⁻¹. Acid treatment (UWA) slightly improved digestibility of all silage nutrients except CP, whereas wilting generally slightly decreased digestibility of the nutrients except DM and ether extract. The daily LW gain averaged 912 g and was not significantly different on the three different treatments. DM intake per (kg LW)^0.75 was higher with the UWA silage, 69·3 g, and with the WN silage, 71·6 g, than with the UW silage, 65·8 g. However, this difference in DM intake was not reflected in either daily LW or carcase gain. The DM of UW silage was more efficiently utilized than DM of UWA or WN silage.     

Herbage intake and milk production by grazing dairy cows 2. The effects of level of winter feeding and daily herbage allowance

Two experiments are described in which two levels of winter feeding and three levels of herbage allowance during the grazing season were imposed upon March/April calving British Friesian dairy cows. The winter treatments resulted in differences in live weight and milk yield at turnout of 35 and 53 kg and 3·4 and 3·2 kg d^-1 for the two trials. Subsequently, when grazed at generous herbage allowances, the cows were able to compensate for much of this difference but when herbage was restricted the milk yield differences were accentuated. Groups of cows from each winter treatment were offered 25, 50 or 75 (Experiment 1) and 30, 50 or 70 (Experiment 2) g herbage DM per kg LW daily during the grazing season. Daily herbage intakes on the three allowances in each trial were 14·1, 13·3, 10·7 and 12·5, 12·1, 11·5 kg OM and milk yields were 16·0, 15·3, 12·5 and 15·2, 14·3, 11·8 kg SCM respectively. Both intake and milk production were depressed once the cows were forced to consume more than 50% of herbage on offer or to graze the sward down to a mean height of less than 8–10 cm. Grazing behaviour observations indicated that under rotational managements the cows did not compensate for restrictions in available herbage by grazing longer. Highest levels of milk production per unit area were observed in both trials when production per cow was depressed by 20–25%.     

THE EFFECT ON FATTENING STEERS OF SUPPLEMENTING SILAGE WITH DRIED GRASS OR ROLLED BARLEY

Eighteen crossbred Aberdeen-Angus and six Shorthorn steers with an average liveweight of 382 kg were given silage (DM content 22.3%) ad lib., supplemented with 0, 1.2, 2.4 and 3.6 kg artificially dried grass, or 1.8 kg rolled barley, per day. A digestibility study carried out on the silage and dried grass showed that the concentration of the metabolizable energy was 52.7 and 45.6 kcal/100 kcal of food, respectively. Live-weight gain increased with each level of supplementation. Supplementation did not significantly affect the intake of silage DM, but differences in the intake of total DM were significant. The killing-out percentages of the steers were similar. The results suggest that dried grass pellets may be a usefid supplement for a silage diet. It was shown that 1.12 kg of dried grass was equivalent to 1.80 kg rolled barley as a supplement for silage.     

Ingestive behaviour of beef cattle offered different forms of lucerne (Medicago sativa L.)†

A change-over design was used to establish the ingestive behaviour of twelve adult Angus cows (Bos taurus), live weight (LW) of 475 ± 18 kg, while grazing luceme (Medicago sativa L.) (T₁), eating from a swath of freshly cut lucerne (T₂), or eating wilted lucerne from a swath (T₃). In the first experiment, the herbage dry matter (DM) allowance was 4-7 kg h^?1 and in T₁ the available herbage DM mass (>5 cm) was 2892 kg ha^?1. Herbage DM intake was 2.5, 1.6 and 2.0 kg h^?1 (0.53,0.35 and 0.41 kg (100 kg LW)^?1h^?1) for T₁, T₂ and T₃, respectively. Cattle grazed at 29 bites min^?1 and ate the swathed lucerne at 6 bites min^?1. Herbage DM intake per bite was 1-2, 4-9 and 6-7 (2-5,104 and 14-4 mg(kg LW)^?1)for T₁, T₂ and T₃, respectively. The DM content of the luceme was 227, 263 and 309 g kg^?1 for the same sequence. In a second experiment with luceme of available herbage DM mass of 5321 kg ha^?1 and an allowance of 7- 3 kg h^?1 cows grazed lucerne at 2-9 kg h^?1, ate freshly cut material at 21 kg h^?1 and wilted herbage at 25 kg h^?1 (0.61, 0.45 and 0.52 kg (100 kg LW)^?1h^?1), respectively. Leaf accounted for 80%, 68% and 54% of intake for T₁, T₂ and T₃, respectively. Swathing lucerne reduced the diet selectivity by forcing cattle to take large bites that required many jaw movements to form a bolus that could be swallowed. It appeared that the mechanics of bolus formation determined ingestive behaviour of cattle eating swathed herbage.     

Herbage intake and liveweight gain of bulls and steers continuously stocked at fixed sward heights during autumn and spring

Two experiments were conducted to examine the relationship between sward surface height, herbage intake and liveweight gain in beef cattle grazed on pasture. In Experiment 1, two 'animal types' (18 Charolais × Angus steers and 18 Friesian bulls) were continuously grazed for 22 days during the late autumn on replicated swards maintained at sward surface heights of 6, 10 and 15 cm. Herbage intakes, assessed from the faecal concentration of chromium delivered from an intraruminal controlled release capsule and the in vitro digestibility of hand-plucked herbage samples, were curvilinearly related to sward height (r = 0·76, p <0·0·01). Average liveweight gains were 0·02, 0·61 and 1·31 kg d^-1 ( P <0·05) and increased linearly ( r = 0·84, P <0·001) with sward height. The maintenance organic matter intakes of the steers and bulls, with initial mean (± s.e.) live weights of 225 ± 15 kg and 172 ± 15 kg respectively, were estimated to be 3·6 and 3·5 kg d^-1 respectively. In Experiment 2 (spring) 36 cattle, including 35 of those used in Experiment 1, were reallocated to sward heights of 5, 10 and 15 cm using the same design as for Experiment 1. Average liveweight gains were 0·94, 1·57 and 1·68kg d^-1 ( p 0·05) and were curvilinearly related to sward height ( r = 0·093, p <0·05). Maintenance intakes could not be reliably extimated for the cattle in Experiment 2 because few animals had liveweight gains close to zero. These trials confirm that liveweight gain in continuously grazed finishing steers and bulls increases with sward surface height to maximum of 8–10cm with spring ryegrass/white clover pastures while, in autumn, swards of 12–15cm height are required to achieve maximum performance.     

Liveweight gains of lambs from Caucasian clover/ryegrass and white clover/ryegrass swards on soils of high and low fertility

The high nutritive value and persistence under a wide range of climatic and soil fertility conditions make Caucasian clover a potentially useful forage legume but there is little information about the performance of livestock grazing Caucasian clover/grass swards. This study compared liveweight gains of lambs grazing Caucasian clover/perennial ryegrass and white clover/perennial ryegrass swards on high fertility (Olsen P 20 mg L^?1, SO₄‐S 12 mg kg^?1) and low fertility (Olsen P 11 mg L^?1, SO₄‐S 7 mg kg^?1) soils from 1998 to 2001 in the South Island of New Zealand. Mean annual liveweight gains were 1178 kg ha^?1 for Caucasian clover/perennial ryegrass and 1069 kg ha^?1 for white clover/perennial ryegrass swards at high fertility compared with 1094 kg ha^?1 and 1015 kg ha^?1, respectively, at low fertility. There was a higher mean proportion of clover in Caucasian clover/perennial ryegrass (0·19) than white clover/perennial ryegrass (0·11) swards, but there were no differences in total herbage production between the two clover/perennial ryegrass swards. The mean concentration of crude protein in the herbage of Caucasian clover (302 g kg DM^?1) was higher than that in white clover (287 g kg DM^?1) and grass herbage (227 g kg DM^?1). Estimated mean metabolizable energy concentrations in the herbage were 12·5 MJ kg DM^?1 for the two clovers and 11·6 MJ kg DM^?1 for grass herbage. The difference in liveweight gain between swards on soils of high and low fertility was associated with an increase in total herbage production of similar composition and nutritive value, giving a greater number of grazing days for the swards on soils of high than low fertility.