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. 9. The effects of combined or separate applications of sodium and sulphur fertilizers on herbage composition and dairy cow production

An experiment was conducted to examine the response of herbage grazed by dairy cows to sodium fertilizer applied with or without sulphur fertilizer. The residual effects of applying sodium fertilizer in the previous year were also evaluated. The application of sodium or sulphur fertilizer did not affect herbage growth or height, but the application of sulphur fertilizer increased crude protein content of herbage. The increase in sodium content with application of sodium fertilizer was small, but was greater when sodium fertilizer had also been applied in the previous year. Herbage potassium was increased when sodium fertilizer was applied in the year of the experiment, but only if sodium had not been applied in the previous year. Application of sulphur fertilizer increased herbage sulphur content and reduced the contents of boron, chromium, molybdenum and nickel. Cows grazing pasture that had received sodium fertilizer had increased milk yields and the content of lactose in milk, whereas those grazing pasture that had received sulphur fertilizer application had reduced milk yields and the content of milk fat.     

Sodium fertilizer application to pasture. 3. Rumen dynamics

The objective of the present experiment was to examine the effects of 0 (Nil), 32 (Low), 66 (Medium) or 96 (High) kg sodium (Na) ha^-1 yr^-1, applied as fertilizer to zero-grazed perennial ryegrass pasture, on rumen digestion and feed and water intake of steers. Herbage Na contents increased with increasing Na up to the Medium Na treatment and no further at the High. Dry matter (DM) contents were increased by Na fertilizer but not affected by the level. Herbage crude protein (CP), true protein (TP) and non-protein nitrogen (NPN) fractions were not affected by treatment. Application of Na fertilizer increased the modified acid detergent fibre (MADF) and ash and total cation content of herbage, particularly at the Medium and High treatments. Faecal DM and TP contents were not affected by treatment, but the CP, NPN, MADF and ash and total cation contents were increased by Na fertilizer. Herbage DM intake increased in proportion to dietary Na content. Water intake increased with increasing Na fertilizer level. Rumen pH was increased by Na fertilizer but ammonia concentration was not affected. The rapidly (a), slowly (b) and potentially (a + b) soluble fractions of degradable DM and the effective degradability (P) of DM increased in direct proportion to amount of Na fertilizer applied up to the Medium level, above which b was reduced and a, a + b and P did not increase further. Solid and total outflow rates were not affected by treatment. Liquid outflow rates were greater in the Medium and High treatments than in the Nil and Low treatments. The immediately soluble fraction of MADF was increased in the Na-applied treatments but the increase declined with each additional Na level. The degradability of MADF increased with increasing dietary Na, particularly in the High treatment. Na increased the proportion of small particles and those with a high specific gravity. It is suggested that the high dilution rates that accompanied the high water intakes and the increased rumen pH are essential factors enabling increased DM intake and rumen digestion when high Na herbages are fed to steers.     

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. 6. Effects of combined applications with sulphur on herbage production and chemical composition in the season of application

The effect of sulphur and sodium fertilizers on the response of a perennial ryegrass ( Lolium perenne ) sward was examined over 2 years. Sulphur fertilizer was applied as ammonium sulphate at 0 or 97·5 kg S ha⁻¹ year⁻¹ and sodium fertilizer as sodium nitrate at 0 (nil), 31 (low), 62 (medium) or 94 (high) kg Na ha⁻¹ year⁻¹, with nitrogen input balanced across all treatments. Both sulphur and sodium increased herbage yield. Sodium fertilizer increased herbage sulphur concentration and sulphur fertilizer slightly increased herbage sodium concentration, but there were no major interactions between the two fertilizers on herbage yield or composition in the season of application. Sodium fertilizer increased dry-matter digestibility, water-soluble carbohydrate concentration and the live proportion of the herbage. Herbage sodium and magnesium concentrations were increased and potassium concentration decreased by sodium fertilizer. Sulphur fertilizer increased herbage dry-matter digestibility and water-soluble carbohydrate concentration. Sulphur and potassium concentrations were also increased and non-protein nitrogen, magnesium and phosphorus concentrations decreased in response to sulphur fertilizer. It is concluded that, although there was evidence of facilitation of sodium uptake by sulphur fertilizer and vice versa, this was not sufficient to produce synergistic effects on herbage growth in the season of application.     

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.     

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. 10. A comparison of the responses of dairy cows with high and low milk yield potential

Current recommendations for the intake of sodium of lactating dairy cows are related to milk yield. A study was conducted to compare the responses of cows of high and low milk production potential to the application of sodium fertilizer to grazed perennial ryegrass pasture. The application of sodium fertilizer increased the intake of herbage dry matter (DM), the time that cows spent grazing and the biting rate. It also increased the concentration of sodium, magnesium and calcium in herbage and decreased the concentration of potassium. Applying sodium fertilizer increased milk yield and milk fat concentration and decreased somatic cell count in the milk of cows of low-production potential only, whereas it increased persistency of milk production in the cows of high-production potential. The concentration of lactose in milk increased in both groups after the application of sodium fertilizer. It is concluded that the optimum dietary sodium concentration for grazing cows does not increase with milk yield, and that most immediate advantage will be gained from increasing the sodium concentration in herbage for low-yielding cows.     

The effects of sodium chloride application to pasture, or its direct supplementation, on dairy cow production and grazing preference

The experiment aimed to examine the effects of sodium chloride (NaCl) application to pasture on dairy cow production, distinguishing the effects of Na supply on pasture production from the direct effects on animal production, and also to examine the preference of dairy cows for sodium-fertilized pasture. Twenty-four dairy cows were grazed in six treatment areas with three fertilizer levels—all (A), one-half (H) or none (N) of the area fertilized with 50 kg NaCl ha⁻¹, and with or without 50 g cow⁻¹ day⁻¹ NaCl supplementation (+, −) offered in concentrate feed. The experiment was a changeover design with four 3-week periods. NaCl fertilization increased herbage growth rate and Na, Cl and calcium (Ca) contents and reduced K content. Milk yield and liveweight gain were increased by NaCl application to pasture but not by direct supplementation. Milk fat content was increased with increasing Na concentration in the diet. Grazing time was increased by NaCl application to pasture, but only cows not receiving direct NaCl supplementation preferred NaCl-fertilized pasture. Ruminating time was increased both by NaCl application to pasture and by direct supplementation. It is concluded that in the warm, dry conditions of this experiment, increasing Na supply to natrophilic herbage increased both pasture and animal production, and that within the range 3–8 g Na kg⁻¹ dietary DM, increasing Na supply to the cow increased milk fat content.     

The influence of strain of Holstein-Friesian dairy cow and pasture-based feeding system on grazing behaviour, intake and milk production

A comparative study of grazing behaviour, herbage intake and milk production of three strains of Holstein‐Friesian dairy cow was conducted using three grass‐based feeding systems over two years. The three strains of Holstein‐Friesian cows were: high production North American (HP), high durability North American (HD) and New Zealand (NZ). The three grass‐based feeding systems were: high grass allowance (MP), high concentrate (HC) and high stocking rate (HS). In each year seventy‐two pluriparous cows, divided equally between strains of Holstein‐Friesian and feeding systems were used. Strain of Holstein‐Friesian cow and feeding system had significant effects on grazing behaviour, dry matter (DM) intake and milk production. The NZ strain had the longest grazing time while the HD strain had the shortest. The grazing time of cows in the HC system was shorter than those in both the HS and MP systems. There was a significant strain of Holstein‐Friesian cow by feeding system interaction for DM intake of grass herbage and milk production. The NZ strain had the highest substitution rate with the HP strain having the lowest. Hence, response in milk production to concentrate was much greater with the HP than the NZ strain. Reduction in milk yield as a consequence of a higher stocking rate (MP vs. HS system) was, however, greater for the HP and HD strains compared with the NZ strain. The results suggest that differences in grazing behaviour are important in influencing DM intake and milk production.     

Effects of reduced time on pasture caused by prolonged walking on behaviour and production of Mpwapwa Zebu cattle

In many African countries, cattle are often allowed to graze only during the daytime and the daily walk to pasture limits time for foraging. Two groups of cattle were allowed access to pasture for 9 h or 5 h associated with a daily walk of 0·5 h or 4·5 h respectively. Each treatment period lasted for 14 days in a cross‐over design. Observations of behaviour were carried out for 8 days in each treatment period. When only 5 h were allowed at pasture, the animals grazed less (0·61 vs. 0·66 of time) compared with the first 5 h of the 9 h treatment. The average daily milk yield was 323 g (0·078) higher when 9 h were allowed on pasture (P < 0·05 during the second week of treatments). There were no differences in milk yield after the end of the treatments. The daily liveweight gain was 250 g higher when the animals were on pasture for 9 h. These differences could be due to the limited time on pasture or to energy requirements for the walk to pasture. It is concluded that increasing the walking time and reducing time on pasture may compromise animal welfare and performance under the experimental conditions, i.e. on poor quality pastures in a warm humid climate where the main period at pasture is in the middle of the day.     

Pasture‐based dairy farm systems increasing milk production through stocking rate or milk yield per cow: pasture and animal responses

A 2‐year whole‐farm study compared pasture‐based systems increasing milk production per ha by increasing either stocking rate (from 2·5 to 3·8 cows ha^?1) or milk yield per cow (from 6000 to 9000 kg cow^?1 lactation^?1) or both. Four treatments (systems), comprising 30 cows each, were compared under the same management and grazing decision rules. The diet was based on grazed pasture, whereas pellets and conserved fodder were fed when deemed necessary. Milk production per ha increased by 0·49, 0·1 and 0·66 in the systems that increased either stocking rate, milk yield per cow or both respectively. Cows in the ‘high milk yield per cow’ systems had a significantly higher body condition score throughout the lactation, but reproductive performance was similar among all groups. Total pasture utilized (11 t DM ha^?1 year^?1) and pasture nutritive value were similar across all systems. This was associated with the grazing rules applied and the ability of accurately supplementing to meet deficits in available pasture. At the whole‐system level, there was a higher marginal efficiency of supplement use when increasing stocking rate than when increasing milk yield per cow or increasing both (0·18, 0·07 and 0·12 kg milk MJ^?1 of metabolizable energy of supplements respectively).     

Effects of fertilizer application to grasslands in Greece

Grasslands in Greece are composed of a large variety of plant species, but they have relatively low productivity due to their misuse by domestic animals for thousands of years, and also to soil and climatic factors. Fertilizer application can improve productivity by affecting herbage yield, botanical composition, earliness of spring growth and quality. The application of N and P generally alters species composition and increases dry matter and crude protein yields, while the addition of K is often not effective. Also, NP fertilizer increases the in vitro digestibility while N often decreases P, Ca, Mg and Zn contents of herbage. It appears that Greek grasslands cannot utilize as much N as their temperate counterparts and that their soils are usually deficient in P. This indicates that NP fertilizer is necessary to secure increased yields with P being important in achieving a balanced grass-legume composition in the plant cover.     

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.     

Operational nitrogen fertilizer management in dairy farming systems: identification of criteria and derivation of fertilizer application rates

Fertilizer‐nitrogen (N) management is a decisive factor in grass‐based, intensive dairy farming, as it strongly influences economic and environmental performance but little attention has been paid to providing guidance on N‐fertilizer management at an operational level to meet these criteria of performance. Essential criteria in operational N‐fertilizer management were identified as target dry matter (DM) yield of herbage, growth period per cut, herbage N concentration, N use efficiency (NUE), amounts of unrecovered N and marginal N response. Statistical relationships between fertilizer‐N application rates per cut and these criteria were derived from field experiments. These relationships were then used to explore the effects of the criteria on optimum fertilizer‐N applications. Optimum fertilizer‐N rates depended strongly on target levels for NUE, amounts of unrecovered N, growth period and DM yield of herbage. Calculations showed that target DM yield of herbage and growth period per cut are essential in estimating the effect of applied N on marginal N response, NUE and amounts of unrecovered N. The derived relationships can be used to explore the effects of changes in target levels of the criteria on optimum fertilizer‐N applications. The study showed that operational fertilizer‐N management set constraints to the decisions made at strategic and tactical management levels and vice versa.     

Grazing behaviour,intake and performance of dairy ewes with restricted access time to berseem clover (Trifolium alexandrinum L.) pasture

The effects of restricted access time to pasture (2, 4 or 6 h d^?1; 2H, 4H or 6H) on ingestive behaviour and performance were assessed on four occasions per target grazing day (D1, initial day; D4, intermediate day; and D7, final day) in dairy ewes rotationally grazing berseem clover with a 7‐day grazing period and a 21‐day recovery period. A randomized block design with two replicates per treatment was used. All ewes were supplemented daily with 700 g per head of concentrates and 700 g per head of ryegrass‐based hay. Pasture subplot and animal group data were analysed by a factorial model including access time (AT), grazing day (D) and their interaction as fixed factors. Sward height decreased from D1 (P < 0·001) and green leaf mass from D4 (P < 0·001) onwards during the grazing period. Grazing time as a proportion of AT was higher in 2H than in 4H and 6H ewes on D1 and D4 but not on D7 (P < 0·05 for AT × D). Herbage intake rate was higher in 2H than in 4H and 6H ewes (P < 0·001). Herbage and total intakes were higher in 4H and 6H than in 2H ewes (P < 0·001), with herbage intake varying non‐linearly during the grazing period (P < 0·05). Milk yield was higher in 4H and 6H than in 2H ewes (P < 0·01). To conclude, despite the evidence of compensatory behaviour, restricting access time to 2 h d^?1 constrained intake and performance of dairy ewes rotationally grazing berseem clover.     

Effects of the amount of barley and time of access to grass silage on the voluntary intake, eating behaviour and production of dairy cows

Three separate changeover experiments were conducted to investigate the effect of the amount of rolled barley and time of access to silage on the voluntary intake, eating behaviour and production of dairy cows. In Experiment 1, twenty-four milking cows were used to compare the effect of 4 1 and 6 1 kg d⁻¹ rolled barley on voluntary intake and milk production. In Experiment 2, fourteen cows were used in a comparison of the effect on voluntary intake and milk production of 5- and 22-h access to silage. Experiment 3 measured the effects on intake of silage of 2 and 4 kg d⁻¹ rolled barley and of 5- and 22-h access to silage. In Experiment I, increasing the amount of barley eaten reduced intake of silage by 0–50 kg dry matter (DM) per kg barley DM but in Experiment 3 with 5-h access to silage there was no significant difference between the amounts of silage eaten with 2 and 4 kg d⁻¹ barley. However, in Experiment 3 when allowed 22-h access to silage, the replacement rate was 0–53 kg DM silage per kg DM barley. Increasing access from 5 to 22 h increased silage intake by 37% in Experiment 1 and by 27% in Experiment 3. Milk yield was significantly increased by 4% when extra barley was given in Experiment 1 but there was no significant effect in Experiment 3. Increasing the time of access to silage led to an 11% increase in milk yield in Experiment 2 but there was no significant effect in Experiment 3. There was much variation between cows in the depression of silage intake per kg change in barley DM eaten with coefficients of variation of 131% and 109% in Experiments 1 and 3, respectively. When allowed access to silage for 22 h daily, on average, each cow spent 180 min eating silage in ten meals, although there was appreciable variation between cows in eating behaviour. The amount of barley did not affect the cows' rate of eating silage nor the duration of eating.     

Repeated application of anaerobic digestate,undigested cattle slurry and inorganic fertilizer N: Impacts on pasture yield and quality

The growth of on‐farm anaerobic digestion (AD) has generated significant quantities of digestate for use as a soil amendment. However, relative to other organic and inorganic fertilizers, only limited field trial data exist on the effect of repeated applications of digestate to temperate grasslands. Here, we compare yields and grass quality (protein and digestibility) from a field trial of a mixed pasture ley (ryegrass and clover), following the application of five different fertilizer types (liquid digestate generated from anaerobically digested slurry, dry fibre digestate, undigested slurry, ammonium nitrate and an NPK compound fertilizer) in comparison with a no‐fertilizer control. Application rates were normalized in terms of nitrogen (N) and were added as a split dose, with 100 kg N/ha added prior to the first harvest and an additional 50 kg N/ha supplied after the first harvest, every year for 3 years. Overall, our results showed that applying both forms of digestate or undigested slurry gave grass yields that matched those obtained with one compound inorganic fertilizer, and better than those from a straight N inorganic fertilizer. No differences were found with regard to digestibility or sward N‐content (hence calculated protein) between any treatments. Although the trial was conducted at only one site, the results indicate that inorganic fertilizers can potentially be replaced by digestate without compromising grassland productivity.     

Defoliation pattern, foraging behaviour and diet selection by lactating dairy cows in response to sward height and herbage allowance of a ryegrass-dominated pasture

The effects of sward surface height (SSH) and daily herbage allowance (HA) on the defoliation pattern and grazing mechanics of early lactation dairy cows grazing on irrigated perennial ryegrass–white clover pasture were studied. The hypothesis tested was that SSH and HA affect intake and diet selection through their effects on the pattern of defoliation which is influenced by the resistance to prehension bites. Factorial combinations of two initial SSH (14 and 28 cm) and two daily HA (35 and 70 kg DM cow^?1 d^?1) were examined in a replicated experiment. The peak longitudinal tensile force required to break the sward portion encompassed in a 100 cm² area [bite fracture force (BFF₁₀₀)] was measured as an index of the resistance to prehension. The volume of herbage defoliated and herbage intake increased with SSH (P < 0·05) and HA (P < 0·01). Corresponding to an increase in HA from 35 to 70 kg DM cow^?1 d^?1, there was a proportional increase in the total defoliation area (TDA) and intake by 0·24 and 0·55 in the short sward compared with 0·16 and 0·32 in the tall sward respectively. The results of this experiment suggest that a consistent spatial pattern of reduction of the canopy exists during defoliation by cows and that the volume of sward canopy defoliated is the major variable affecting herbage intake. The BFF increased down the sward profile at a rate that was higher (P < 0·05) for the taller sward than for the shorter sward. It is proposed that a relatively lower resistance to prehension in the short sward compared with the tall sward explains the greater proportionate increase in TDA and intake corresponding to an increase in HA. The rate at which BFF₁₀₀ increases down the sward profile is suggested as a sward physical variable that can influence the defoliation process. The estimated time and energy costs of prehension bites are discussed in the context that larger bites are handled more efficiently than smaller bites.     

Effect of feed space allowance and period of access to food on dairy cow performance

Two experiments were conducted to examine the ‘long‐term’ effect of feed space allowance and period of access to feed on dairy cow performance. In Experiment 1, three horizontal feed space allowances (20, 40 and 60 cm cow^?1) were examined over a 127‐d period (14 cows per treatment). In Experiment 2, 48 dairy cows were used in a continuous design (10‐week duration) 2 × 2 factorial design experiment comprising two horizontal feed space allowances (15 and 40 cm cow^?1), and two periods of access to feed (unrestricted and restricted). With the former, uneaten feed was removed at 08·00 h, while feeding took place at 09·00 h. With the latter, uneaten feed was removed at 06·00 h, while feeding was delayed until 12·00 h. Mean total dry‐matter (DM) intakes were 19·0, 18·7 and 19·3 kg cow^?1 d^?1 with the 20, 40 and 60 cm cow^?1 treatments in Experiment 1, and 18·1 and 18·2 kg cow^?1 d^?1 with the ‘restricted feeding time’ treatments, and 17·8 and 18·1 kg d^?1 with the ‘unrestricted feeding time’ treatments (15 and 40 cm respectively) in Experiment 2. None of milk yield, milk composition, or end‐of‐study live weight or condition score were significantly affected by treatment in either experiment (P > 0·05), while fat + protein yield was reduced with the 15‐cm treatment in Experiment 2 (P < 0·05). When access to feed was restricted by space or time constraints, cows modified their time budgets and increased their rates of intake.