Sodium fertilizer application to pasture. 4. Effects on mineral uptake and the sodium and potassium status of steers

Mineral availability and status in body tissues was examined with four rumen-fistulated steers arranged in a Latin-square change-over design. The steers were fed perennial ryegrass herbage from a pasture fertilized with four Na treatments: 0 (Nil), 32 (Low), 66 (Medium) or 96 (High) kg Na ha^-1 yr^-1. Na fertilizer increased herbage contents and intakes of Na, Mg and Ca but did not affect intakes of K, P and S. Herbage K:Na and K:(Ca+Mg) decreased in direct proportion to the amount of Na fertilizer applied. With increasing dietary Na intake, the Na content of saliva increased and the K content decreased. There was an increase in Na and a reciprocal decrease in K contents of rumen fluid with increasing dietary Na. Blood plasma Na contents were greater when the Na-treated herbages were fed than in the Nil treatment. There was no effect of treatment on blood plasma K content. Increasing dietary Na increased urinary Na but did not affect urinary K. Faecal mineral concentrations of Na, Ca, P and S were increased by increasing dietary Na, whereas K content was reduced and the Mg content was unaffected. There was no difference between treatments in the proportion of mineral rapidly solubilized, except Na which increased with increasing dietary Na content. The fractional rate of degradation was greater for Na, K, and Mg than for Ca and P. Based on effective solubilization, minerals were ranked in the order K > (Mg = Na) > Ca > P, and treatments were in the order Medium > (High = Low) > Nil. Increasing Na intake increased Ca but not P or Mg availability and increased the uptake of all three minerals.     

Sodium fertilizer application to pasture. 1. Direct and residual effects on pasture production and composition

Results are given on the effect of sodium (Na) fertilizer applied as NaNO₃ in five application sat 0 (Nil), 32 (Low) or 64 (High) kg Na ha ^-1yr^-1 and the residual effect of sodium chloride(NaCl) fertilizer applied in the previous year on the growth rate and the chemical composition of herbage cut at fortnightly intervals over the grazing season. Na fertilizer at Low and High rates increased herbage Na contents by 20 and 40% respectively. Magnesium (Mg) content in herbage was increased at Low Na fertilizer application rate but there was no difference between the Nil and the High Na treatments. Calcium (Ca) content was increased in proportion to Na fertilizer level. Potassium (K) content of Nil Na herbage exceeded that of Low and High, but there was no effect of treatment on total harvested K yields. The contents of phosphorus (P), sulphur (S), true protein (TP) and modified acid detergent fibre (MADF) in herbage were not affected, but the dry matter digestibility (DMD) was increased with increasing Na fertilizer level. Applying Na fertilizer at the Low and High levels gave similar increases in water-soluble carbohydrates (WSC) and ash contents and decreased crude protein (CP) and non-protein nitrogen (NPN) contents. Net herbage accumulation(fresh and dry weight) was increased by 15 and 26% at the Low and High Na fertilizer application rates respectively. NaCl fertilizer residues from the previous year increased herbage Na, DM, DMD and WSC contents, reduced K contents and did not affect Ca, P, S, CP, TP and NPN contents. Residues from Na fertilizer decreased MADF and ash contents at the Low and High Na application rates. The main and residual effects of Na fertilizer were generally maximal in early season and diminished as the season progressed, with many of the effects eliminated by late season. Proportionally 0·70 of Na applied was recovered in the first two grazing seasons after application. The effects of Na fertilizer on mineral ratios are also described, together with the implications for animal health.     

Sodium fertilizer application to pasture. 5. Effects on herbage digestibility and mineral availability in sheep

The effects of feeding herbages fertilized with 0 (nil), 32 (low), 66 (medium) or 96 (high) kg of sodium per hectare per year to sheep on herbage digestibility and mineral availability were examined. Modified acid detergent fibre (MADF), ash, magnesium (Mg) and phosphorus (P) contents were increased by the application of sodium (Na) treatments, while potassium (K), sulphur (S) and true protein (TP) contents were reduced. Dry matter (DM) and MADF intakes were increased in the low and medium treatments and DM and MADF digestibility increased in all Na-treated herbages. The medium- and high-sodium treatments increased salivary Na content and Na/K ratio and decreased K content. Blood K content was not affected by treatment. Intake, faecal output, apparent availability, urinary output and balance of Na were increased by the application of Na treatments. Potassium intake, balance, apparent retention and urinary output were increased by the low, unaffected by the medium and reduced by the high sodium treatment. The low and medium Na treatments increased the intake and apparent availability of Mg; Mg balance and apparent retention were increased by all Na treatments. Feeding the Na-treated herbages increased intakes, apparent availability, balance and apparent retention of Ca, P and total cations.
The low and medium Na treatments increased S intake, faecal output and apparent retention. It is suggested that through increasing the balance and apparent retention of minerals, the application of sodium fertilizer to pasture will improve the mineral status of sheep, particularly at the low and medium application rates employed in this experiment.     

Sodium fertilizer application to pasture. 2. Effects on dairy cow production and behaviour

Fifty-four lactaling dairy cows were grazed for 24 weeks on pasture receiving 0 (Nil), 32 (Low) or 64 (High) kg Na ha^-1 yr^-1 and with (+) or without (-) 100g NaHCO₃ buffer included in a maize gluten concentrate supplement. Cattle grazed the Na-fertilized pasture to a lower height, particularly in the High treatment. Cows grazing pasture with Na fertilizer produced more milk, and milk fat concentration increased in direct proportion to amount of Na fertilizer applied and with NaHCO₃. This increase was greatest in early season. Milk protein concentration was not affected by Na fertilizer application or NaHCO₃ buffer addition. Milk lactose concentration was increased by Na fertilizer application but not by NaHCO₃ supplementation. Cows in the Na-applied treatments gained more live weight but there was no effect of treatment on condition score change. Grazing time and drinking frequency increased linearly with increasing pasture Na. Ruminating time and biting rate were similar at the Low and High treatments and greater than the Nil treatment. NaHCO₃, supplementation increased drinking frequency and decreased the rate of concentrate intake. Cow reproductive performance was not significantly affected by Na fertilizer application. During the residual period, cows that had previously grazed the Na-fertilized pasture had reduced milk fat and protein contents.     

Intake, rumen fermentation, degradability and digestion kinetics in beef cattle offered autumn grass herbage differing in regrowth interval

The effects of a 10-d increase in regrowth interval (35 and 45 d) of a predominantly perennial ryegrass sward harvested in two periods in the autumn in Ireland on feed intake, rumen fermentation, in situ degradability and rumen digesta kinetics was examined using six ruminally cannulated Holstein–Friesian steers in three replicates of a 2 × 2 crossover design. The longer regrowth interval had a higher grass dry-matter (DM) yield of herbage by 615 kg DM ha⁻¹ and a lower crude protein (CP) concentration of herbage by 27 g kg⁻¹ DM. There was no effect of regrowth interval on DM intake, rumen pH, total volatile fatty acid concentration or the molar proportions of acetate, propionate or butyrate in the rumen but the concentration of rumen ammonia (NH₃-N) was lower on the longer regrowth interval. The longer regrowth interval had a lower apparent total tract digestibility of DM, organic matter (OM), N and neutral-detergent fibre (NDF). There was no effect of regrowth interval on the in situ degradability of DM, OM, N or NDF. The passage rates ( k _p) of DM and OM were higher while the rate of digestion ( k _d) of DM and NDF was lower with the longer regrowth interval. The results indicated that, although increasing the regrowth interval by 10 d in autumn reduced the apparent digestibility of the grass herbage, there was no adverse effect on DM intake, rumen fermentation pattern or in situ rumen degradability. The reduction in rumen NH₃-N concentrations, reflecting the lower herbage CP concentration in herbage for the longer regrowth interval, may potentially reduce nitrogen excretion to the environment.     

Digestion and nitrogen metabolism in beef cattle and in vitro rumen fermentation of autumn grass differing in fertilizer nitrogen application rate

Beef cattle partition dietary nitrogen (N) into meat or excrete it mainly in faeces and urine, which can contribute significantly to water and air pollution. The effects of two inorganic nitrogen (N) fertilizer application rates—15 (LN) or 80 (HN) kg N/ha—to Lolium perenne‐dominant swards in autumn, on herbage chemical composition, intake, digestion and N balance in beef cattle, and in vitro fermentation and methane production were studied. Four growing beef steers used in a 2 × 2 crossover design experiment were offered zero‐grazed grass harvested 21 days post‐N application between July and October. The same grasses were incubated in an eight‐vessel rumen simulation technique in a randomized complete block experiment. Grass dry‐matter (DM) concentration was 26 g/kg lower and crude protein (CP) concentration was 35 g/kg DM higher for HN compared to LN. There was no difference in herbage DM intake or in vivo DM digestibility between treatments. Nitrogen intake and the digestibility of N were higher for HN compared to LN. Total and urine N loss were 41 and 45 g/day greater, respectively, for HN compared to LN, but faecal N loss did not differ between treatments. The quantity of N retained and therefore N‐use efficiency did not differ between LN and HN (25% vs. 22%). In vitro rumen pH and ammonia‐N concentrations were higher for HN compared to LN, whereas volatile fatty acid concentrations and molar proportions did not differ between treatments. In vitro methane and total gas production were 0.9 mmol/day and 280 ml/day lower for HN than LN respectively. Under the particular conditions of this experiment, reducing fertilizer N application rate reduced total and urinary N excretion, which has potential environmental benefits; however, methane output measured in vitro was increased.     

Sodium fertilizer application to pasture. 8. Turnover and defoliation of leaf tissue

The effects of application of sodium fertilizer on the turnover and defoliation of leaf tissue were investigated in a perennial ryegrass (Lolium perenne) pasture grazed by dairy cows. Eight plots were allocated to treatments either with or without sodium fertilizer, with the former receiving 32 kg Na ha^–1 applied in five applications of NaNO₃ over the grazing season. An equivalent amount of nitrogen was given to the controls as ammonium nitrate, the application of which was reduced in the sodium treatment to equate nitrogen fertilizer applications for the two treatments. In nine periods between April and September, marked tillers were recorded to measure leaf turnover, leaf lamina growth and specific leaf weight and, when combined with tiller density measurements, gave an estimate of herbage flux for the sward. The defoliation and net growth of the marked tillers were monitored at 3-day intervals and the data were combined with tiller density and specific leaf weight data to determine the intake of the expanding, penultimate and oldest live leaf laminae. Sodium fertilizer application did not affect the rate at which leaves appeared, but it retarded their rate of disappearance. The extension rate and the specific weight of green laminae were both increased by sodium fertilizer application and therefore the net gravimetric growth rate was increased. Tiller density was not affected by sodium fertilizer application and hence the estimated herbage growth and net herbage flux were increased by sodium fertilizer application. Application of sodium fertilizer did not affect lamina length, and in both treatments the penultimate laminae were approximately twice as long as expanding and oldest live laminae. Defoliation frequency decreased from the expanding to the oldest live laminae in the control treatment without sodium. Sodium fertilizer application increased the frequency of defoliation of the oldest live leaf and also increased the length of the expanding leaf that was defoliated. For penultimate leaf laminae sodium fertilizer application reduced the defoliation frequency and length of foliage grazed. The dry-matter (DM) intake of the oldest live laminae was increased by the application of sodium fertilizer. It is concluded that sodium fertilizer application increases net herbage growth both by increased extension rate of leaf laminae and specific leaf weight and by delayed laminae senescence, and that it increases herbage DM intake by increasing the defoliation frequency of the oldest live leaf laminae.     

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 effect of adding surface water to herbage on its digestion by ruminants

In two experiments the effects of adding surface water to herbage on its digestion by ruminants were examined. In experiment 1, with sheep, adding water to silage reduced DM intake and the diet DM digestibility. Offering a high DM alternative forage, hay, increased DM digestibility with the wetted silage, but tended to decrease it with the dry silage. More hay was eaten with the wetted than dry silage. In experiment 2, with steers, adding water to fresh herbage reduced DM intake but had no effect on rumen pH or ammonia levels. Adding water to the herbage reduced the rate of DM disappearance from nylon bags placed in the rumen and the proportion of rumen liquor particles of low specific gravity. The proportion of very short and very long particles in the rumen liquor was also reduced by adding water to the herbage.     

Effects of applying a bacterial inoculant to silage immediately before feeding on silage intake, digestibility, degradability and rumen volatile fatty acid concentrations in growing beef cattle

In an experiment, involving twelve male cattle (initially 235 kg live weight), the effects of applying lactic acid bacteria [Lactobacillus plantarum; 10⁹ colony-forming units (g fresh silage)^?1] to grass silage, immediately prior to that silage being fed, on dry-matter (DM) intake of the silage, degradability of nitrogen (N) and fibre in the rumen, total tract digestibility and composition of rumen fluid in the animals were examined. A grass silage, which had been made from the primary growth of a predominantly perennial ryegrass sward, was offered as the sole diet. The inoculant was applied to the silage at the rate of 2 g of freeze-dried powder reconstituted in 12 ml of water (kg fresh silage)^?1 immediately prior to that silage being fed and an equivalent amount of water was applied to the silage in the control treatment. The two diets were compared in a change-over design. The silage was well preserved, having a pH and concentrations of ammonia N and butyrate of 3.72, 74 g (kg total N)^?1 and 0.11 g (kg DM)^?1 respectively. Application of the inoculant significantly increased true protein, acid-insoluble N and water-soluble carbohydrate concentrations (P < 0.001) in the diet. Silage DM intake was not significantly increased (P= 0.072) by this of inoculant treatment, which had no significant effect (P > 0.05) on rumen degradability or total tract digestibility of DM, N, neutral detergent fibre or modified acid detergent fibre. Rumen pH, ammonia concentration or the molar proportions of volatile fatty acids were not altered (P>0.05) by inoculant treatment. It is concluded that application of the inoculant to the silage prior to silage being fed did not significantly affect silage DM intake, total tract digestibility, or degradability or fermentation in the rumen of cattle offered grass silage as the sole diet. It is also concluded that the results of this experiment provide no evidence that the mode of action of L plantarum, applied as an additive to grass at ensiling in previous studies, is through ‘direct’ effects in the rumen.     

Effect of extent and rate of wilting on nitrogen components of grass silage

Wilting grass prior to ensiling generally increases the dry matter (DM) intake but the effect of wilting on animal performance is still poorly understood. There is a need to improve understanding of the effects of wilting on the nutritional components and chemical composition of grass silage. This study focused on the effects of the extent and rate of wilting on N components of grass silage. Meadow grass was wilted to four DM contents (200, 350, 500, 650 g kg^?1) at two different rates (fast, slow), creating a total of eight silages. Crude protein (CP) fractions were measured using the Cornell Net Carbohydrate and Protein System. Utilizable CP at the duodenum (uCP), a measure of feed protein value, was estimated using the modified Hohenheim gas test. Ruminally insoluble, undegraded feed CP (RUP) was measured using an in situ technique. Amino acid (AA) composition prior to and after rumen incubation was also investigated. Utilizable CP at the duodenum, RUP and true protein fractions B2 and B3 were increased by rapid wilting and high DM content (DM > 500 g kg^?1), although the increase with DM was only mild for uCP, probably due to lower ME content in the DM‐650 silages. Non‐protein‐N decreased with increasing DM and rapid wilting. The higher RUP content from both DM‐650 silages leads to a higher total AA content after rumen incubation. Treatment also influenced the AA composition of the ensiled material, but the AA composition after rumen incubation was similar across treatments. Rapid and extensive wilting (DM > 500 g kg^?1) improved protein value and reduced CP degradability. Increased uCP may result in higher milk protein yield, while reduced degradability may reduce N lost from urinary excretion. The primary effect of wilting on post‐ruminal AA supply from RUP appeared to be quantitative, rather than qualitative.     

Effects of gamma irradiation on ruminal DM and NDF degradation kinetics of alfalfa hay

The effects of gamma irradiation on ruminal dry matter, Neutral Detergent Fiber (NDF) degradation of alfalfa hay were investigated. Alfalfa hay samples were irradiated by gamma irradiator at doses of 50, 100 and 150 kGy under identical conditions of temperature and humidity. Nylon bags of untreated or irradiated samples were suspended in the rumen of three Taleshi bulls for up to 96 h and resulting data were fitted to non-linear degradation model to calculate degradation parameters. Results indicated that the washout fractions of dry matter and NDF increased linearly (p < 0.001) with increasing irradiation dose. The b fraction and the degradation rate of the b fraction (c) of DM and NDF were the highest at 50 kGy dose. Effective degradability of DM and NDF increased linearly with increasing irradiation dose. Gamma irradiation at doses of 50, 100 and 150 kGy increased the effective NDF degradability of alfalfa hay at rumen outflow rate of 0.05 h(-1) by about 8, 11 and 12%, respectively. Gamma irradiation affects on the hydrogenic bonds and with theirs breakdowning causes the wander-valls power weaken, that results in the degradation of cellulose and increasing of DM and NDF degradability.     

Supplementary forage for grazing sheep. 2. Effects on weaned lambs

In two experiments weaned entire ram lambs were offered either pasture alone or pasture plus ad libitum conserved forage for 7–12 weeks during the finishing period. Herbage height was maintained at 3·2 cm on both treatments by manipulation of stocking rate in the twenty-four plots (twelve per treatment) used for the experiment. In experiment 1 silage, which was of lower metabolizable energy (ME) and crude protein (CP) content than the grazed herbage, was consumed at an average of 194 g DM head⁻¹ d⁻¹, providing approximately 40% of total DM intake requirements. In experiment 2 a strawmix, containing (g k g ⁻¹ freshweight) 450 g barley straw, 300 g concentrate and 250 g molasses and again with a lower ME and CP content than the grazed herbage, was consumed at an average of 57 g DM head⁻¹ d⁻¹, providing approximately 11% of total DM intake requirements. In both experiments stocking rate was increased by 20–25% by providing forage, but lamb growth rate was not affected.     

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.     

Relationship of physicochemical characteristics and hydrolyzed hydroxycinnamic acid profile of barley varieties and nutrient availability in ruminants

The objectives of this study were to (1) investigate the relationship between physicochemical characteristics (mean/median particle sizes, physical hull content) and hydrolyzed hydroxycinnamic acid profile (ferulic acid (FA), para-coumaric acid (pCA), and their ratio) of barley varieties and in situ rumen degradability in dairy cattle; and (2) investigate rumen degradation kinetics of FA and pCA of CDC barley varieties grown in western Canada. Barley variety had a significant effect (P < 0.05) on rumen undegradable fraction of DM, FA, pCA, neutral (NDF) and acid detergent fiber (ADF) at 12 and/or 24 h of rumen incubation. FA in barley grain was more degradable than the pCA (P < 0.05). There were no differences (P > 0.05) in effective degradability of DM (EDDM) and EDFA, but significant differences in EDpCA (P < 0.05). Barley hull was strongly correlated to NDF, ADF, ADL, hemicellulose and cellulose (R > 0.78, P < 0.001) and correlated to FA (R = 0.57, P < 0.05) but not to pCA (R = 0.42, P > 0.05) in original samples. FA and pCA were highly and positively correlated to NDF, ADF, ADL, hemicellulose, cellulose, mean/median particle sizes, and rumen indigestible DM, NDF and ADF at either 12 or 24 h (P < 0.05). Mean/median particle size of barley grain positively influenced the rumen indigestible DM, but not others (FA, pCA). The results implied that reduction of barley hull, FA and pCA contents could increase the degradability of barley grain in rumen. Multi-regression with best model variable selection analysis revealed that FA was the factor most inhibiting to DM degradability of barley in rumen, and was the most effective factor to predict DM degradability, while hull was the most effective factor to determine NDF degradability in rumen. Both hull and FA affected ADF degradability in the rumen. The results indicate that breeding or identifying barley varieties with lower hull and FA contents would result in higher degradability, higher energy density and higher quality barley and improve nutrient availability of barley.     

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.     

Use of the in situ technique in the study of degradation of lucerne and smooth bromegrass genotypes

Six lucerne ( Medicago sativa ) genotypes (Beaver, Vernal and four other strains being developed at the University of Alberta) and five smooth bromegrass ( Bromus inermis ) genotypes (Carlton, Magna and three genotypes being developed) were examined in terms of forage dry matter (DM) yield and degradability, as determined by the rate and amount of material which disappeared from bags suspended in the rumen of cattle. Dry matter yield did not differ ( p > 0·05) between lucerne genotypes at first cut. The smooth bromegrass strain 517 had a proportionately Oil higher ( P < 0·05) DM yield than did the Magna strain. No differences ( P < 0·05) were detected within either smooth bromegrass or lucerne genotypes for 48 or 60 h in situ DM degradability. The 416E smooth bromegrass genotype, however, had a significantly higher ( P < 0·05) rate of DM degradation in the rumen than the other genotypes and also exhibited a longer ( P < 0·05) lag period before a significant amount of DM degradability occurred. In the in situ technique, approximately eighteen bags would have been needed to obtain DM degradability measurements with a confidence interval of 0·04 for DM degradability of a probability of 0·95. Further in vivo studies with the bromegrass genotypes are warranted to ascertain if the differences in digestion rates and lag times are related to meaningful differences in animal intake and digestibility.     

Effects of perennial ryegrass (Lolium perenne L.) cultivars on herbage production, nutritional quality and herbage intake of grazing dairy cows

Four perennial ryegrass (Lolium perenne L.) cultivars were compared for differences in herbage production, nutritive value and herbage intake of dry matter (DM) during the summers of 2002 and 2003. Two paddocks were sown with pure stands of four cultivars in a randomized block design with three replicates. Each plot was subdivided into fourteen subplots (22 m × 6 m) which were grazed by one cow during 24 h. Twelve lactating dairy cows were assigned to one cultivar for a period of 2 weeks in a 4 × 4 Latin square experimental design; the experiment lasted 8 weeks in each year. Sward structure (sward surface height, DM yield, green leaf mass, bulk density and tiller density) and morphological characteristics were measured. The ash, neutral‐detergent fibre, acid‐detergent lignin, crude protein and water‐soluble carbohydrate concentrations, and in vitro digestibility of the herbage were measured. The sward was also examined for infestation by crown rust (Puccinia coronata f. sp. lolii). Herbage intake of dairy cows was estimated using the n‐alkane technique. Cultivar differences for all sward structural characteristics were found except for bulk density and tiller density in 2003. Cultivars differed for proportions of pseudostem, stem (in 2003 only) and dead material. The chemical composition of the herbage was different among cultivars, with the water‐soluble carbohydrate concentration showing large variation (>0·35). Cultivars differed in susceptibility to crown rust. Herbage intake differed among cultivars in 2002 (>2 kg DM) but not in 2003. Herbage intake was positively associated with sward height, DM yield and green leaf mass. Canopy morphology did not affect herbage intake. Crown rust affected herbage intake negatively. It was concluded that options for breeders to select for higher intake were limited. High‐yielding cultivars and cultivars highly resistant to crown rust were positively related with a high herbage intake.     

Effects of length of grazing session, rumen fill and starvation time before grazing on dry-matter intake, ingestive behaviour and dry-matter rumen pool sizes of grazing lactating dairy cows

The effects of the length of allowed grazing time (Experiment 1) and length of starvation period before grazing (Experiment 2) on dry-matter (DM) intake, ingestive behaviour and changes in DM rumen pool sizes during the first grazing bout were investigated in lactating Holstein-Friesian dairy cows. In Experiment 1, four lengths of allowed grazing time (1, 1·75, 2·50 and 3·25 h) after overnight starvation were compared. Increasing the length of the allowed grazing time significantly increased DM intake ( P < 0·01), the proportion of time spent actively eating ( P < 0·01) and DM rumen pool size after grazing ( P < 0·05). However, DM rumen pool size after grazing was smaller than that measured immediately before the start of starvation ( P < 0·01). Bite mass during the first hour of grazing was greater than in the following grazing time. Experiment 2 consisted of a factorial combination of two durations of starvation before grazing (16·5 h and 2·5 h) and the presence or absence in the rumen of 12·5 kg of a synthetic indigestible material. DM intake, as well as grazing time, were greater after a starvation period of 16·5 h and were reduced by the presence in the rumen of indigestible material ( P < 0·01). The interaction between factors on grazing time, although not significant ( P < 0·06), supports the idea of a combination of signals controlling meal size under grazing conditions. Bite mass was not significantly modified by the period of starvation. DM rumen pool size after grazing was reduced by the placement in the rumen of synthetic indigestible material ( P < 0·05) and tended to be lower in cows with the larger period of starvation ( P < 0·058). In both experiments, bite rate declined as the grazing session progressed, but bite rate was not affected by treatments.     

Effects of electron beam irradiation on dry matter degradation of wheat straw in the rumen

The effect of electron beam irradiation at doses of 100, 200 and 300 kGy on ruminal dry matter degradation kinetics of wheat straw was investigated. Samples were irradiated by electron beam irradiator under identical conditions of temperature and humidity. Nylon bags of untreated or irradiated wheat straw were suspended in the rumen of three Taleshi steers for up to 96 h and resulting data were fitted to non-linear degradation model to calculate degradation parameters of dry matter. Results show that the washout fractions of dry matter increased linearly (p<0.001), but potentially degradable fraction and degradation rate decreased linearly (p<0.001) by electron beam irradiation. As a consequence, the effective degradability of dry matter increased linearly (p<0.001) with increasing irradiation dose. Electron beam irradiation at doses of 100, 200 and 300 kGy increased the effective degradability of dry matter at rumen outflow rate of 0.05/h by about 7, 15 and 18%, respectively. In the condition of this study, electron beam irradiation at dose of 200 kGy appeared to be a suitable dose for improving dry matter degradability of wheat straw in the rumen.