Residual Sward Height Research Articles

The effects of stocking rate, residual sward height, and forage supplementation on forage production, feeding strategies, and productivity of milking dairy cows

The intensification process in Uruguayan dairies over the last 30 years has involved increases in stocking rate (SR) and individual milk production. This research aimed to compare biophysical indicators along with the associated feeding strategies for Holstein–Jersey crossbred dairy cow systems. The comparison was conducted in farmlets representing a typical Uruguayan pasture-based dairy system on a grazing area. The study spanned from 2017 to 2019, combining 1.5 or 2.0 milking cows per hectare (SR), with two different residual sward heights (RH)—low (LR) and high (HR). These combinations resulted in four treatments: 1.5 LR, 1.5 HR, 2.0 LR, and 2.0 HR. A total of 96 cows were randomly allocated to each treatment based on parity, body weight (BW), and body condition score (BCS) for the years 2017, 2018, and 2019. The response variables per hectare were analyzed using a linear mixed model, including SR, RH, their interaction effect, year, and paddock as a repeated measurement. Results show that forage production did not differ between treatments, and forage directly harvested by cows was affected by SR, as well as milk and solids productivity. An interaction effect was detected between SR and RH on milk and milk solids production where 2.0 HR was higher than 2.0 LR, but treatments on SR 1.5 were not different between them. The consumption of concentrate, forage, and conserved forage per hectare was influenced by the level of SR. However, individual milk production was not influenced by SR or RH. Dry matter intake were affected by SR where 2.0 HR had higher consumption than 1.5 LR and 1.5 HR but was not different from 2.0 LR. The concentrate DMI per cow was not different between treatments, while the conserved forage DMI per cow was affected by SR and higher for SR 2.0 than that for SR 1.5. These combinations of feed determined varying proportions of time allocated for grazing, which were influenced by the SR and RH. This research highlights different approaches to enhance the competitiveness of Uruguayan grazing systems through improvements in forage harvest.

Endophytic Fungal Infection of Meadow Fescue in the Driftless Area of the Upper Mississippi River Valley: Impacts on Agronomic Fitness

Meadow fescue, Schedonorus pratensis (Huds.) P. Beauv., has recently been discovered as a common but previously unknown pasture grass in the Driftless Area of the upper Mississippi River Valley, USA. Preliminary data also indicated that many meadow fescue pastures were infected with an endophytic fungus, Epichloë uncinata (W. Gams, Petrini & D. Schmidt) Leuchtm. & Schardl. Therefore, the objective of this study was to determine if the endophyte impacts agronomic fitness of the host meadow fescue. Meadow fescue plants from eight farm sites were intensively sampled, and endophyte infection levels were determined to range from 82 to 95%. Paired endophyte-infected (E+) and endophyte-free (E−) meadow fescue subpopulations from each collection site were then created, and were subsequently compared for greenhouse and field drought tolerance, forage mass, and persistence under frequent defoliation. There was no impact of the endophyte under a wide range of drought conditions for either greenhouse or field studies. Furthermore, there was a small forage-mass-enhancement effect in the E+ subpopulation for only one of the eight collection sites. The only consistent effect was an average of 9% increased ground cover (persistence) in endophyte-infected meadow fescue under frequent defoliation. As per other studies, enhanced root growth, fungal-disease resistance, and/or reduced insect feeding could be mechanisms for this increased survivorship. We conclude that the meadow fescue endophytes present in the Driftless Area do not help protect their host from drought or provide any consistent forage-growth enhancement; however, we found evidence that the endophyte provides some protection against frequent defoliation at low residual sward heights.

Field indicators of leaf nutritive value for perennial ryegrass and tall fescue pastures under different growing and management conditions

AbstractField indicators of forage nutritive value could help farmers with rapid management decisions to optimize timing and intensity of grazing and meet objectives regarding animal nutrition. The objective of this research was to evaluate the likely relationships among leaf blade nutritive value, herbage mass and leaf stage of pasture regrowth under different growing seasons and residual sward heights. Experiments were performed on perennial ryegrass (Lolium perenne L.) and tall fescue (Festuca arundinacea Schreb.) pastures during spring and summer of 2016. In both pastures, three residual sward height treatments (3, 6 and 12 cm) were imposed on plots arranged in a split plot design, replicated in three blocks. Sward plots were harvested 5–6 times at intervals spaced 7–10 days apart to measure herbage mass, plant morphology, neutral detergent fibre (NDF), and the 24‐hr in vitro digestibility of NDF (NDFD) and dry matter (DMD) of leaf blades. Pastures showed strong (R2: .62 to .70), but variable, negative relationships between NDFD and herbage mass that varied with the rate at which pasture grew in each season of experimentation. Although there was a consistent NDFD decline as leaf stage of regrowth progressed (R2: .75 to .97), the NDFD also decreased as residual sward height increased, most notably in tall fescue. Additionally, findings indicate that the greater leaf length plasticity of tall fescue compared to residual sward heights may offer opportunities to manage both post‐ and pre‐grazing targets to achieve tall fescue forages with a similar high nutritive value as perennial ryegrass. However, the evaluation of this hypothesis at the farm level and its impacts on animal intake and performance warrants further careful investigations.

Assessing the importance of plant, soil, and management factors affecting potential milk production on organic pastures using regression tree analysis

Certified organic dairies are required to utilize pastures for a portion of forage intake. Pasture species composition, management, and soil fertility are known to influence milk production, but have not been studied concurrently. We evaluated agronomic and management variables on 20 organic dairies in the upper midwestern United States to determine factors associated with potential pasture milk production. At each farm, two pastures were sampled just prior to grazing in June and September for species composition, productivity, and forage nutritive value. Soil samples and management information were collected in October. Potential milk production was calculated based on forage productivity, cell wall concentration and digestibility, and estimated dry matter intake by a 500 kg cow. A regression tree prioritized the factors associated with potential milk production. Improved legume cover exceeding 40% in June increased potential milk production by 97%. Non-improved grass cover <70% in June and September increased potential milk production by >75%. Maintaining residual sward height at 9 cm or greater throughout the year was also associated with increased milk production. Soil fertility explained little of the variability in milk production. Our results suggest prioritizing management of residual height and improved legume and non-improved grass cover are critical for high milk production from organic pastures in the Upper Midwest.

Plane of nutrition during the rearing phase for replacement ewes of four genotypes: II - effects on performance during first pregnancy and to weaning, and of their progeny

Plane of nutrition (PN) offered to ewe replacements during the rearing phase (8 to 17 months) and first pregnancy may affect reproductive and progeny performance when replacements are joined at ~19 months. The effects of PN offered to spring-born ewe replacements during their first winter (winter_1), second summer (summer_2) and subsequent winter (mid and late pregnancy; winter_2) were evaluated, over 3 consecutive years, using 287 ewe lambs of four genotypes: Charmoise×Scottish Blackface (C×SBF), Belclare×SBF (Bel×SBF), Belclare (Bel) and Belclare×SBF (heterozygous for a gene, either FecGH or FecXG mutations, that increases ovulation rate: BelMG×SBF). Ewe lambs were offered, daily, a deferred-grazed herbage allowance (HA) of either 0.75 or 1.75 kg dry matter during winter_1. During summer_2 the replacements were set-stocked to maintain sward heights of 4 or 6 cm. Ewes were housed during mid and late pregnancy (winter_2) and offered either medium or high-feed-value grass silage, thus yielding a 2×2×2 factorial design. Increasing HA during winter_1 and residual sward height during summer_2 increased ewe BW post joining (P<0.001) and at lambing (P<0.01), but had no effect (P>0.05) on number of lambs reared. Increasing HA during winter_1 increased lamb BW at birth (P<0.05) and reduced carcass fat score (P<0.05). There was a significant interaction between PN offered during winter_1 and summer_2 for average daily gain (ADG) from birth to 5 weeks (P<0.01) and from 5 to 10 weeks (P<0.05): progeny of replacements that experienced either a high or low PN throughout the rearing phase had lower ADG than lambs born to the replacements that experienced a low PN only during winter_1 or summer_2. Increasing PN during winter_2 increased ewe BW (P<0.001), lamb BW at birth (P<0.001) and weaning (P<0.05) and reduced the proportion of ewes that failed to lamb (P<0.01). Ewe genotype had a significant (P<0.001) effect on litter size (1.48 to 2.45), number of lambs reared, lamb BW at birth and weaning, lamb ADG and age at slaughter. It is concluded that, among the nutrition treatments examined, increasing PN during mid and late pregnancy had the greatest effect on ewe and progeny performance. Although increasing PN offered during winter_1 increased lamb birth BW, PN offered during summer_2 had no effect on lamb performance. There were no significant interactions between PN and ewe genotype.

Plane of nutrition during the rearing phase for replacement ewes of four genotypes: I – effects on growth and development, and on ovulation rate at first joining

Plane of nutrition (PN) offered to ewe replacements during the rearing phase (8 to 17 months) affects BW at joining and may affect reproductive performance when joined at ~19 months. The effects of PN offered to ewe replacements during their first winter (winter_1) and second summer (summer_2) were evaluated over 3 consecutive years, using 287 spring-born ewe lambs, representing four genotypes (Belclare (Bel), Charmoise×Scottish Blackface (C×SBF), Bel×SBF (Bel×SBF), Bel×SBF that were heterozygous either FecGH or FecXG mutations that increase ovulation rate (OR) (BelMG×SBF)). During extended (deferred) grazing in winter_1 (November to March) the lambs were offered herbage DM allowances (HA) of 0.75 (L) or 1.75 (H) kg/day. During summer_2 (March to August) the replacements were set stocked to maintain sward heights of 4 (L) or 6 (H) cm, thus yielding a 2×2 factorial design for the nutrition treatments (71 to 73 animals/treatment). Increasing HA during winter_1, and residual sward height during summer_2, increased (P<0.001) BW and body size at joining (19 months) but had no effect (P>0.05) on OR. Mean BW at joining was 53.3, 56.8, 56.6 and 61.7 (SEM 0.74) kg for ewes offered the LL, LH, HL and HH treatments, respectively. Mean OR of C×SBF and BelMG×SBF differed (P<0.001) from that of Bel×SBF by −0.58 and +0.47, respectively. Correlations between linear measurements (LMs) of body size and BW at 7, 12 and 17 months were all positive and significant (P<0.001). The precision of the set of LMs as a predictor of BW at joining improved with age (R2 0.46, 0.54 and 0.74 at 7, 12 and 17 months) but BW at a given age was a better predictor at all age time points. Chest girth was the best predictor, among the LMs, of BW at joining and its explanatory power increased with age. Equations developed using LMs at 7, 12 or 17 months, to predict BW at joining exhibited biases of −2.1, −1.5 and +0.9 kg, respectively. It is concluded that whilst altering PN during the rearing phase changed BW by 16% it had no effect on OR. There was no interaction (P>0.05) between the PN offered during winter_1 and summer_2, or PN and ewe genotype for BW at joining or OR. LMs, either at 7, 12 or 17 months of age, are useful predictors of BW at joining.

Long-term assessment of a new rotational-grazing management strategy called PUP-grazing (proportion of un-grazed pasture)

A new rotational-grazing management strategy called PUP-grazing (proportion of un-grazed pasture, which is the estimated percentage of pasture vegetation without signs of being consumed) was compared with the traditional rotational-grazing management strategy (TGMS, which is based on residual sward height) using Brahman cross steers on Axonopus catarinensis over two periods (2013/14 and 2015/16) in Misiones, Argentina. The proportion of un-grazed pasture for PUP and TGMS was 11.5 and 3.4%, respectively, of the pasture area. Average daily liveweight gain/animal was significantly higher for PUP than for TGMS (606 vs. 420 g/d; P&lt;0.05) while liveweight gain per hectare was 35% greater for PUP (194 vs. 144 kg/ha/period). The gross margin per hectare was much higher for PUP than for TGMS (US$ 85.7 vs. 8.4/ha/period). These results indicate that on A. catarinensis pastures PUP-grazing has the potential for greater animal and economic performance than the TGMS.Keywords: Cattle, forage consumption, grazing management, gross margin, liveweight gain.DOI: 10.17138/TGFT(6)53-57

Efecto de la frecuencia de defoliación en el rendimiento y composición nutricional de Pennisetum clandestinum Hochst.ex Chiov

In Colombia at 2,560 m.a.s.l. the effect of three defoliation frequencies (3, 4.5 and 6 leaves tiller-1) was evaluated, during four months (August - November), on growth and nutritional quality of Kikuyu (Pennisetum clandestinum Hochst.ex Chiov). Nine plots of 6 x 4 m were established, which were distributed in a complete randomized block repeated measures design. Data were subjected to analysis of variance. A significant interaction between defoliation frequency and the month of utilization on total herbage mass yield and crude protein concentration was observed. The highest values for both variables were obtained at 6 leaves tiller-1 in October (herbage mass) and OctoberNovember (crude protein). Defoliation frequency did not modify yield components (proportion of blades, sheath, stems and dead material). Neutral Detergent Fiber and Acid Detergent Fiber were not affected by defoliation frequency. In conclusion, grazing of kikuyu swards, under similar environmental conditions of this study should be performed at stage of 4.5 to 6 leaves tiller-1 with a residual sward height of 5 cm.

Defoliation patterns and their implications for the management of vegetative tropical pastures to control intake and diet quality by cattle

AbstractThis study assessed the use of pasture attributes to control daily intake and diet quality during progressive defoliation on pastures of Axonopus catarinensis. Three consecutive 12‐day grazing treatments of progressive defoliation were conducted with Brahman cross‐steers. Daily forage intake and defoliation dynamics were assessed using a pasture‐based method. The treatments differed in initial sward height (33, 44 and 61 cm) and herbage mass (1030, 1740 and 2240 kg ha−1). The post‐grazing residual sward height, at which forage intake decreased, appeared to increase with the initial sward height (12·3, 14·6 and 15·5 cm). Steers grazed up to four distinctive grazing strata in all treatments. The depth and herbage mass content of the top grazing stratum were at least five times higher than the lower grazing strata in all treatments. This explains why forage intake decreased when the top grazing stratum was removed in approximately 93% of the pasture area in all treatments, equivalent to approximately 7% of the pasture area remaining ungrazed. We conclude that the residual ungrazed area of the pasture, rather than residual sward height, can be used to develop grazing management strategies to control forage intake and diet quality in a wide range of pasture conditions.

Residual Sward Height Effects on Growth and Nutritive Value of Grazed Temperate Perennial Grasses

ABSTRACTResidual sward height (RSH) has a significant impact on temperate perennial grass growth, but its effect is rarely studied under grazing. We determined RSH effects on forage harvested (FH), seasonal yield distribution, nutritive value, and persistence of meadow fescue {Festuca pratensis Huds. subsp. pratensis [syn. Schedonorus pratensis (Huds.) P. Beauv.]}, orchardgrass (Dactylis glomerata L.), quackgrass [Elymus repens (L.) Gould], and reed canarygrass (Phalaris arundinacea L.). Grasses were rotationally stocked with dairy heifers (Bos taurus) at vegetative stage (32‐cm height) to a 16‐, 8‐, or 2‐cm RSH or at mature stage (48‐cm height) to a 24‐, 12‐, or 4‐cm RSH in each of 2 yr. Grass FH and nutritive value were measured for each grazing event. Annual FH of grasses grazed at vegetative stage to a 2‐ or 8‐cm RSH was greater than that grazed to a 16‐cm RSH when precipitation was limiting, but few differences existed when precipitation was abundant. Annual FH of grasses grazed at mature stage increased as RSH decreased. As RSH increased, the mean grazing interval decreased, which increased the number of seasonal grazing events of vegetative but not of mature‐stage grasses. There was no apparent relationship between forage nutritive value and RSH. The primary risks incurred by grazing vegetative‐stage grasses to a shorter RSH (&lt;8 cm) were reduced persistence in a dry year and delayed date of first grazing event the following spring. Little or no advantage in growth was gained by intentionally leaving a tall RSH when grazing mature‐stage grasses.

Increasing milk solids production across lactation through genetic selection and intensive pasture-based feed system

The objective of the study was to quantify the effect of genetic improvement using the Irish total merit index, the Economic Breeding Index (EBI), on overall performance and lactation profiles for milk, milk solids, body weight (BW), and body condition score (BCS) within 2 pasture-based systems of milk production likely to be used in the future, following abolition of the European Union's milk quota system. Three genotypes of Holstein-Friesian dairy cattle were established from within the Moorepark dairy research herd: LowNA, indicative of animals with North American origin and average or lower genetic merit at the time of the study; HighNA, North American Holstein-Friesians of high genetic merit; and HighNZ, New Zealand Holstein-Friesians of high genetic merit. Animals from within each genotype were randomly allocated to 1 of 2 possible pasture-based feeding systems (FS): 1) The Moorepark pasture (MP) system (2.64 cows/ha and 344kg of concentrate supplement per cow per lactation) and 2) a high output per hectare (HC) system (2.85 cows/ha and 1,056kg of concentrate supplement per cow per lactation). Pasture was allocated to achieve similar postgrazing residual sward heights for both treatments. A total of 126, 128, and 140 spring-calving dairy cows were used during the years 2006, 2007, and 2008, respectively. Each group had an individual farmlet of 17 paddocks and all groups were managed similarly throughout the study. The effects of genotype, FS, and the interaction between genotype and FS on milk production, BW, and BCS across lactation were studied using mixed models with factorial arrangements of genotype and FS accounting for the repeated cow records across years. No significant genotype by FS interaction was observed for any of the variables measured. Results show that milk solids production of the national average dairy cow can be increased across lactation through increased EBI. High EBI genotypes (HighNA and HighNZ) produced more milk solids per cow and per hectare than the LowNA genotype (2.7 and 4.1%, respectively). The results also suggest that when concentrate supplementation is used to facilitate increased stocking rates, increased herbage utilization and decreased substitution of concentrate for herbage can be achieved. When implemented, the HC FS could increase the overall productivity of pasture-fed dairy farming systems where land availability is the primary limiting factor of production.

Meadow Fescue, Tall Fescue, and Orchardgrass Response to Defoliation Management

Meadow fescue [Schedonorus pratensis (Huds.) P. Beauv.] represents an alternative to temperate grasses typically used in forage‐livestock systems. Our objective was to compare the productivity, nutritive value, and persistence of diverse meadow fescue cultivars with that of tall fescue [Lolium arundinaceum (Schreb.) Darbysh.] and orchardgrass (Dactylis glomerata L.) when harvested by regimes representing lax and severe hay production and rotational grazing. ‘Azov’ (plant introduction strain cross), ‘Bartura’ (commercial cultivar), and ‘Hidden Valley’ (naturalized population) meadow fescue, ‘Barolex’ tall fescue, and ‘Bronc’ orchardgrass were harvested infrequently (40‐ to 65‐d harvest interval) or frequently (when plants reached 25‐cm sward height) to a 5‐ or 10‐cm residual sward height (RSH) at two Wisconsin locations in 2 yr. Annual dry matter (DM) yield of all grasses was greater when harvested infrequently (7.46 Mg ha−1) than frequently (5.92 Mg ha−1), or at 5 cm (7.52 Mg ha−1) than 10‐cm RSH (5.88 Mg ha−1). Tall fescue and orchardgrass annual yield was greater than that of all meadow fescues when harvested infrequently, but differences among grasses were relatively small when harvested frequently, particularly at 10‐cm RSH. Neutral detergent fiber digestibility (NDFD) of meadow fescue was 30 to 80 g kg−1 neutral detergent fiber (NDF) greater than that of tall fescue or orchardgrass at every harvest in all environments. Meadow fescue cultivars were less persistent than tall fescue after 2 yr, but were usually equal to or more persistent than orchardgrass. Meadow fescue should be considered as a viable alternative to tall fescue and orchardgrass in temperate, managed intensive rotational grazing systems due to its comparable yield and superior digestibility.

Carbon isotope discrimination as an index of tall fescue–endophyte association response to light availability and defoliation

Tall fescue [ Lolium arundinaceum (Schreb.) S.J. Darbyshire] is adapted to the diverse growing conditions of humid, temperate agro-ecosystems. A mutualistic endophytic symbiont ( Neotyphodium coenophialum, [Morgan-Jones et Gams] Glenn, Bacon, and Hanlin) contributes to this resilience, but at the same time compromises grazing livestock health. Novel endophytes that do not produce ergo-alkaloids were developed to circumvent livestock health issues, but the response of novel associations to site conditions and management practices, such as partial shade and repeated defoliation, is unclear. We conducted a field experiment with tall fescue to determine if carbon isotope discrimination ( Δ) could be used to characterize host–endophyte association responses to site and management. Plants infected with either the native or novel non-ergogenic endophyte, or that were endophyte free were clipped to typical pasture (5 cm) or silvopasture (10 cm) residual sward heights each time mean canopy height reached 20 cm. The Δ of tall fescue was inversely related to light availability. Greater variation in Δ occurred when plants were clipped to a 5 rather than a 10 cm residue height. This trend persisted throughout the growing season and was similar whether Δ was expressed relative to potential evapotranspiration (ET o), leaf dry matter content (LDMC) or an index of herbage nutritive value (expressed as energy relative to crude protein). Host–endophyte association did not affect Δ. This might be attributable to relatively mild growing conditions occurring in the central Appalachian region of the USA, irrespective of site conditions, or the minimal cost of hosting endophyte. Carbon isotope discrimination responses for tall fescue agree with previous observations on Δ and light availability, and might be a useful means to assess silvopastoral management practices.

Effects of Forage Management on Pasture Productivity and Phosphorus Content

The objectives of the current study were to determine the amounts of above- and below-ground plant biomass production, P uptake by forage, and P concentration of cool-season grass forage as influenced by management and season. Five forage management treatments were evaluated over 3 years in smooth bromegrass (Bromus inermis Leyss) pastures. Management practices were: ungrazed (U), hay harvest/fall stockpile grazing (HS), rotational stocking to residual sward heights of 10 (10R) or 5 (5R) cm, and continuous stocking to maintain sward height at 5 cm (5C). Forage samples were hand-clipped within and outside grazing exclosures monthly from April through November of each year and analyzed for mass and P concentration. Root samples were collected at the initiation and completion of the study for determination of root length density (RLD) and root surface area density (RSAD). Phosphorus concentrations of forage outside the grazing exclosures did not differ among 5C, 5R, and 10R treatments, which were greater than U paddocks in April and August and less than HS paddocks in June. Mean annual forage productivity was greater in HS, 10R, 5R, and 5C paddocks (6 744 ± 62 kg · ha−1 mean ± SE) than in the U paddocks (1 872 ± 255 kg · ha−1). Mean P concentration of forage outside exclosures was greatest during the spring (0.21 ± 0.01%), and lowest during the fall (0.13 ± 0.01%). Mean annual P uptake by forage followed the same trend as forage production, being greater in the HS, 10R, 5R, and 5C paddocks (13.9 ± 2.0 kg · ha−1) than in the U paddocks (3.7 ± 0.5 kg · ha−1). After 3 years, RLD decreased in the ungrazed paddocks, but was unchanged in the HS, 10R, 5R, and 5C paddocks. Forage production and P uptake by forage is stimulated by forage harvest, either by grazing or hay harvest in smooth bromegrass pastures.

Understanding foraging behaviour in spatially heterogeneous environments

The role of stochasticity and spatial heterogeneity in foraging systems is investigated. We formulate a spatially explicit model which describes the behaviour of grazing animals in response to local information using simple stochastic rules. In particular the model reflects the biology in that decisions to move to a new location are based on visual assessment of the sward height in a surrounding neighbourhood, whilst the decision to graze the current location is based on the residual sward height and olfactory assessment of local faecal contamination. It is assumed that animals do not interact directly, but do so through modification of, and response to a common environment. Spatial heterogeneity is shown to have significant effects including reducing the equilibrium intake rate and increasing the optimal stocking density, and must therefore be taken into account by resource managers. We demonstrate the relationship between the stochastic spatial model and its non-spatial deterministic counterpart, and in the process derive a moment-closure approximation to the full process, which can be regarded as an intermediate, or pseudo-spatial model. The role of spatial heterogeneity is emphasized, and better understood by comparing the results obtained from each approach. The relative efficiency of random and directed searching behaviour in spatially heterogeneous environments is explored for both clean and contaminated pastures, and the impact of faecal avoidance behaviour assessed.

Effect of nitrogen fertiliser rates and defoliation regimes on the vertical structure and composition (crude protein content and digestibility) of a grass sward

AbstractThe vertical sward structure (proportions of lamina and sheath) and sward composition (crude protein and digestibility) have an effect on animal behaviour and performance, but their variation through management is not well known. We studied the effect of defoliation regime and nitrogen supply on these sward characteristics. There were six treatments, two nitrogen fertiliser rates combined with three defoliation regimes. Two of the latter mimicked a long growth duration (up to 7 weeks) and one mimicked a short period of regrowth (2 weeks). The swards were cut 7 cm from ground level. We found that there was a single relationship between sheath length and sward height, regardless of treatment and sampling date. For the treatments which mimicked a long growth duration, crude protein and digestibility decreased linearly from the top to the base of the sward when these decreases were expressed per unit of herbage mass. Conversely, for the treatments which mimicked a short growth duration, crude protein and digestibility fell quickly between the upper layers and those close to the ground. This discontinuity was the result of a smaller number of laminae per tiller than for the other treatments, whereas the composition of the sheath was the same. For resting periods longer than 20 days a model was proposed to simulate the effect of sward defoliation depth on the chemical composition of the diet selected by grazing animals according to available herbage mass before and during grazing. From a practical point of view the sward height alone could not be used to predict the sward composition from the top to the base of the sward and its effect on diet selection by grazers. The length of the resting period needs to be known in addition to the residual sward height. Copyright © 2003 Society of Chemical Industry

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 &lt; 0·001) and protein yield (P &lt; 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 &lt; 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 &lt; 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.

Herbage Volume per Animal: A Tool for Rotational Grazing Management

The objective of this study was to provide a tool for maintaining a high grazing efficiency. In a rotational grazing system, the residual sward height does not provide enough information in advance to make the recommendation. The grazing management of 4 commercial dairy farms which differed greatly in their stocking rate, was monitored over 3 spring seasons. Data were collected on the overall grazing area (sward height measurements, stocking rate, indoor feeding, nitrogen supply) and on 3 grazed fields (herbage mass, height, and nitrogen status). At the whole grazing area level, computed data were herbage volume per animal unit (HVAU). We show that the HVAU depends on the residual herbage height. Both criteria decreased when stocking rate increased. The HVAU reflects, at the whole grazing season and area levels, how the system works on grazed field over grazing cycle. The HVAU has 2 advantages: (i) It gives rough estimation of the size of the whole grazing area to achieve a high grazing efficiency; (ii) it is a means to assess a posteriori the efficiency of the grazing system regarding the consistency between stocking rate and nitrogen supply management. DOI:10.2458/azu_jrm_v53i4_duru

Evaluation of the effects of nematode parasitism on grazing behaviour, herbage intake and growth in young grazing cattle

Parasitic nematodes, even in the absence of any clinical disease, can cause a reduction in voluntary feed intake in housed ruminants. This trial examined these effects on young cattle grazing pastures. Twenty dairy heifer calves, born in the previous autumn, were blocked according to liveweight and allocated to one of two groups: either untreated or dosed with an IVOMEC ® (ivermectin) SR Bolus 10 days prior to turnout on 1 May 1998. The groups grazed separately on two paddocks on predominately ryegrass swards. Liveweights were recorded every 28 days and faecal samples taken for worm egg counts at the same time. In mid-May and mid-July, for two 14-day periods, animals were paired within treatment groups and transferred to one of 10 replicate paddocks of similar sward height and herbage mass. Grazing behaviour and herbage intake were measured during these periods. In mid-May, 2 weeks after turnout, treated and untreated animals showed no difference in grazing behaviour or daily intake of grass. By mid-July, 10 weeks after turnout, the untreated heifers spent on average 105 min less per day in grazing time and their daily herbage intake was 0.78 kg dry matter (DM) per day lower than that of the treated animals. Residual sward height, mass and composition in the trial paddocks reflected these differences. There were no clinical signs of gastrointestinal parasitism in the untreated group up to this time; in July, the mean worm egg count in this group was 120 eggs per gram (e.p.g.) of faeces. Faecal samples from several untreated animals were positive for lungworm larvae by July, mild clinical signs of bronchitis were observed in two of these animals in mid-July. Over the period from turnout until mid-July, the untreated heifers showed a reduction in mean daily liveweight gain of 150 g, compared to the treated animals.

Herbage volume per animal: A tool for rotational grazing management

The objective of this study was to provide a tool for maintaining a high grazing efficiency. In a rotational grazing system, the residual sward height does not provide enough information in advance to make the recommendation. The grazing management of 4 commercial dairy farms which differed greatly in their stocking rate, was monitored over 3 spring seasons. Data were collected on the overall grazing area (sward height measurements, stocking rate, indoor feeding, nitrogen supply) and on 3 grazed fields (herbage mass, height, and nitrogen status). At the whole grazing area level, computed data were herbage volume per animal unit (HVAU). We show that the HVAU depends on the residual herbage height. Both criteria decreased when stocking rate increased. The HVAU reflects, at the whole grazing season and area levels, how the system works on grazed field over grazing cycle. The HVAU has 2 advantages: (i) It gives rough estimation of the size of the whole grazing area to achieve a high grazing efficiency; (ii) it is a means to assess a posteriori the efficiency of the grazing system regarding the consistency between stocking rate and nitrogen supply management.