Sward Height Research Articles

Ingestive behavior of supplemented Nellore heifers grazing palisadegrass pastures managed with different sward heights.

Three sward heights (15, 25 and 35cm) and three supplement types (energy, energy-protein, and a mineral mix supplement) were evaluated in a 3×3 factorial arrangement distributed in a completely randomized design to study changes in forage search patterns in Nellore heifers in a continuous grazing system. Pasture data were collected using two replicates (paddocks) per treatment over four periods during the rainy season. The behavior assessments were made in the first and fourth grazing seasons. It was hypothesized that supplements and pasture management would modify ingestive behavior, considering that animals would require less time grazing if they had energy requirements met through higher digestibility of better managed paddocks, or use of supplements high in energy. Total and green forage masses along with green:dead material ratio were greater in treatments managed with higher sward heights. Sward managed with 35cm height resulted in lower leaf:stem ratio compared with 15cm sward height treatments. The animals on the 15cm pastures spent more time grazing overall and during each meal, but there were no differences observed in meal numbers in comparison to 35cm treatments. Heifers fed protein and/or energy supplements spent less time grazing in the early afternoon, but overall grazing time was the same for all animals.

Effects of sheep stocking on the plant community and agricultural characteristics of upland Anthoxanthum odoratum–Geranium sylvaticum meadow in northern England

AbstractIn the UK, upland hay meadows (Anthoxanthum odoratum–Geranium sylvaticum grassland) with high plant biodiversity are rare and confined to submontane areas of northern England. We report results from a 5‐year experiment to test suggestions that recent biodiversity declines were attributable to increased sheep‐stocking density and a longer spring stocking period, thus delaying the shut up date for the growth of the hay crop. Longer stocking periods and higher stocking densities decreased the forage mass at 8 July, but they increased herbage N content and digestibility, reduced plant species diversity and reduced populations and seed production of Rhinanthus minor. Compared with unstocked swards, the similarity of the vegetation to Anthoxanthum odoratum–Geranium sylvaticum grassland was reduced by 16·9% when stocking with sheep continued until 27 May each year, and by 8·3% when sward heights were maintained at 3 cm compared with 5 cm. Increased mean sward height and height of R. minor were positively correlated with accumulated temperatures. Results support suggestions that recent reductions in the nature value of these grasslands might be a consequence of high stocking densities persisting until later in the spring, carried out during a 1‐year period with warmer temperatures.

Effect of ewe prolificacy potential and stocking rate on primiparous flock performance

The objective of this study was to investigate the effect of ewe prolificacy potential (PP; predicted number of lambs born/ewe/year) as dictated by sire breed type, stocking rate (SR; ewes/ha), and their interaction on animal performance in a primiparous flock. The study had a 2×3 factorial design, consisting of two PP levels and three SR incorporating 360 primiparous ewes, comprising of two ewe genotypes (180 medium prolificacy potential (MP – Suffolk crossbred ewes) and 180 high prolificacy potential (HP – Belclare crossbred ewes)). Stocking rates were low (LSR; 10ewes/ha), medium (MSR; 12ewes/ha), and high (HSR: 14ewes/ha). There were 60 ewes per treatment and each treatment was assigned to an individual farmlet of five paddocks for the duration of the study. There was no PP by SR interactions observed for ewe body weight (BW) and body condition score (BCS; P>0.05). Medium prolificacy potential ewes had a higher BW and BCS at initial mating, pregnancy scanning, 6 weeks post-lambing and weaning (P<0.001). At lambing and second mating ewe BCS did not differ by PP (P>0.05). Lambs born to HP ewes achieved a lower average daily gain (ADG) up to 6 weeks of age, but a higher ADG from 10 to 14 weeks of age compared to MP lambs (P<0.01). Post-weaning, and lifetime lamb ADG, carcass traits (weight, conformation, fat score), and days to slaughter (DTS) did not differ by PP. Low SR ewes had a higher BW than ewes at the MSR and HSR, which did not differ from each other at second mating (P<0.001). Lower lamb ADG was recorded at the MSR and HSR pre- and post-weaning (P<0.01) compared to LSR, with MSR and HSR lambs subsequently requiring longer to reach slaughter (P<0.001). Total herbage utilisation was highest at the HSR and lowest at the LSR (with the MSR not differing from either; P>0.05), above the post-grazing sward height of 4.0cm pre-weaning and 3.5cm post-weaning (P<0.05). Carcass output per hectare increased as both PP and SR increased (P<0.001). In summary, Primiparous flock performance was significantly reduced as SR increased from 10ewes/ha to 12ewes/ha and 14ewes/ha, with no further decrease in performance from 12 to 14ewes/ha. Increased carcass output per hectare is achievable through the use of greater PP and SR levels within a temperate grass-based lamb production system.

Sward height management, desiccation time of Urochloa ruziziensis and nitrogen fertilization of soybean under crop-livestock system

The integration of soybean crop with pastures is an important strategy to diversify the grain production systems in Brazil. The objective of this research was to evaluate the effect of grazing intensities in Urochloa ruziziensis, desiccation time of the pasture in relation to soybean sowing and crop fertilization with mineral nitrogen on the growth and yield of soybean, cultivar NK 7059 RR. Three grazing intensities of U. ruziziensis (15, 35 and 50 cm of plant height), were grazed continuously for six months, plus a no grazing paddock, making four experiments, were evaluated. In each experiment a randomized complete block design with three replications in a split plot design was used. In the plots were allocated four desiccation time of the pasture (35, 28, 20 and 8 days before soybean sowing) and in the subplots, nitrogen fertilization in soybean (without N or with 30 kg N ha-1 at sowing). Initially, analysis of each experiment was performed and subsequently a joint analysis was performed. The grazing intensities did not significantly affect the soybean growth and the yield. The increased interval between pasture desiccation and soybean seeding and the nitrogen fertilization on crop promoted increments in the growth and N accumulation by soybean in early development cycle. On the other hand, in the reproductive phase, these differences were negligible and did not affected the yield.

Grazing intensities affect weed seedling emergence and the seed bank in an integrated crop–livestock system

Integrated crop-livestock systems (ICLS) are widespread worldwide. Although weeds can result in several types of losses, essential information regarding weed seedling emergence and seed banks is lacking in these systems for integrated weed management planning. This study investigated the effects of different grazing intensities (no grazing and grazed swards maintained at 10-, 20-, 30- and 40-cm sward heights) on weed seedling emergence and seed banks in a winter cover crop during the 15th year of an ICLS experiment under no-tillage management in subtropical Southern Brazil. We hypothesized that low grazing intensities would reduce weed interference and weed seed banks size in an ICLS. We determined treatment effects on weed species richness, seed bank population density, and seedling emergence during winter and summer. Higher sward heights in the winter-grazed cover crop reduced the number of weed species, the density of emerged weed seedlings, and the weed seed bank size compared with the non-grazed control. With a sward grazing height of 10cm, the seed bank contained an average of 3151 seeds m−2, and the weed population densities during the summer and winter were 11.8 and 21.7 plants m−2 greater, respectively, compared with the sward grazing height of 40cm. Fifteen years after adopting low grazing intensities (30- and 40-cm sward heights) in the ICLS, the size of the weed seed bank was reduced by 42.1% compared with the non-grazed treatment. Decreasing the grazing intensity reduced the number of weed species, the density of emerged weed seedlings, and the weed seed bank density; therefore, integrated weed management strategies should consider minimizing grazing intensities in an ICLS.

Methane emissions from sheep grazing pearl millet (Penissetum americanum (L.) Leeke) swards fertilized with increasing nitrogen levels

This study aimed at quantifying methane emissions from sheep grazing pearl millet swards (Penissetum americanum (L.) Leeke) as affected by nitrogen (N) fertilization doses (50, 100, 200 and 400kgNha−1). The experimental period was 70days of pasture use, from February to April 2011. The grazing method was continuous stocking with variable stocking rate, so pasture structure was intended to be similar (30cm sward height) among treatments. Thirty six tester animals aging 5 months and initially weighing 20±1.6kg were used for evaluations. Intake (OMI) was estimated by their relationship with N content on faeces. The sulfur hexafluoride (SF6) technique was used for two sampling periods of five consecutive days each to quantify daily methane (CH4) production. Parameters related to sward structure was not affected by N fertilization, but herbage accumulation increased linearly (P<0.05). Greater (P<0.05) stocking rate, weight gain per area and CP content were observed with higher fertilization levels. N doses did not affect (P>0.05) OMI, and methane emissions expressed as a ratio of OMI. Results indicated that increasing nitrogen doses decrease methane emissions per animal. When expressed as grams of methane per kilogram of organic matter ingested or energy converted into methane, no difference was observed. However, emissions per unit area increase as a consequence of higher stocking rates allowed by the increase in forage production. Sheep emitted 16.3g of methane per kg of ingested organic matter and converted 5.1% of ingested gross energy into methane.

Acúmulo de forragem e valor nutritivo do híbrido de Urochloa 'BRS RB331 Ipyporã' sob pastejo intermitente

Resumo: O objetivo deste trabalho foi avaliar o acúmulo de forragem e o valor nutritivo do híbrido de Urochloa 'BRS RB331 Ipyporã' (Urochloa brizantha x Urochloa ruziziensis) submetido à pastejo intermitente. Os tratamentos corresponderam às combinações entre as condições de pré-pastejo, interceptação de 95% da luz incidente e máxima interceptação de luz, e as de pós-pastejo, 10 e 15 cm de altura de resíduo, em delineamento de blocos ao acaso, em arranjo fatorial 2x2, com quatro repetições. Pastos manejados com 95% de interceptação da luz apresentaram maior taxa de acúmulo de forragem, proporção de folhas, relação folha:colmo, teor de proteína bruta e densidade populacional de perfilhos basilares (DPPb), em comparação àqueles manejados com máxima interceptação da luz. Pastos manejados com 15 cm de altura do resíduo apresentaram maior DPPb do que os manejados com 10 cm e apresentaram pequena variação de DPPb entre as estações do ano avaliadas, independentemente do tratamento. Pastos do híbrido interespecífico de Urochloa 'BRS RB331 Ipyporã' apresentam maior acúmulo de forragem e maiores teores de proteína bruta e digestibilidade in vitro da matéria orgânica e menores teores de fibra em detergente neutro na fração folha, quando manejados com 95% de IL nas condições de pré-pastejo, com 30 cm de altura do dossel, associada com 15 cm de altura de resíduo.

Forage sward structure of Mulato grass (Brachiaria hybrid ssp.) subjected to rotational stocking strategies

The pasture structure is the point of origin and convergence of plants and grazing animal responses, which makes its knowledge essential in the planning of grazing management strategies. The objective of this study was to evaluate and describe the variation in sward structure of mulato grass subjected to stocking strategies. The treatments corresponded to combinations between the postgrazing height (15 and 20 cm) and the pre-grazing targets (95% and maximum light interception during regrowth: LI95% and LIMax). Sward height, light interception, forage mass, morphological composition, and vertical structure were evaluated. There was no difficulty maintaining the set post-grazing heights in the pastures managed with the LI95% target, which was not observed in the pastures managed with the LIMax target, especially for the post-grazing of 15 cm. For pre-grazing, the LI95% and LIMax targets corresponded to the heights of 30 and 40 cm, respectively. Overall, the pastures managed with the LI 95% target showed a lower height and a lower forage mass with a greater percentage of leaves pre-grazing. For post-grazing, the pastures managed with the LI95% target displayed a greater light interception and a lower forage mass with a higher percentage of leaves, as well as a lower percentage of dead material than the pastures managed under the LIMax. Based on the results, we conclude that grazing performed according to the LI95% pre-grazing target (30 cm), irrespective of the adopted post-grazing height (15 or 20-cm), resulted in adequate control of the sward structure, and this management strategy provides good pasture growth with important features for maximum forage intake and nutrients by grazing animals.

Flower abundance and vegetation height as predictors for nectar-feeding insect occurrence in Swedish semi-natural grasslands

With steadily shrinking areas of species-rich semi-natural grasslands in Europe, the management of the remaining fragments becomes ever more crucial for the preservation of key elements of biodiversity in the agricultural landscape. Detailed knowledge about species-wise, as well as group-wise, relationships can provide guidelines for conservation management and a basis for predictions about different management scenarios. In the present study, we related the occurrence of species of bumblebees (N=12), butterflies (31) and day-flying moths (4) and their total richness in 424 sites in southern Sweden to three grass sward attributes, (i) flower abundance, (ii) height of the grass sward and (iii) within-site variation in height of vegetation. The abundance of nectar-bearing flowers proved overall the best predictor of richness and in most of the occurrence-based species-wise models. However, both high grass sward height and high variation in grass sward height contributed significantly to species richness and occurrence of individual species. There was a tendency for bumblebees to respond less positively to flower abundance and vegetation height than butterflies and moths. One expectation was that grassland specialists, red-listed species, or species decreasing in other part of Europe, would be more responsive to tall vegetation or flower abundance but there was no support for this in the data. Hence, management strategies that promote common species will also benefit all, or most of, the rare ones as well.

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

AbstractThe 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 &lt; 0·001) and green leaf mass from D4 (P &lt; 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 &lt; 0·05 for AT × D). Herbage intake rate was higher in 2H than in 4H and 6H ewes (P &lt; 0·001). Herbage and total intakes were higher in 4H and 6H than in 2H ewes (P &lt; 0·001), with herbage intake varying non‐linearly during the grazing period (P &lt; 0·05). Milk yield was higher in 4H and 6H than in 2H ewes (P &lt; 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.

GRAZING BEHAVIOUR OF DAIRY COWS AND BODY CONDITION SCORE ASSOCIATED WITH SWARD CHARACTERISTICS OF FOUR PASTURE TYPES

SUMMARYThe objectives were to assess the following: (1) the relationship between sward height and chemical composition of four pasture types in association with grazing behaviour and body condition score (BCS) of dairy cows, and (2) the possibility of developing predictive equations of the nutrient intake and grazing behaviour within a continued grazing system. Pasture type had a significant (p &lt; 0.01) effect on nutrient supply from January to June for all pastures investigated. Ryegrass–white clover pasture (RW) had the highest metabolizable protein and metabolizable energy, followed by kikuyu pasture (KP), which was significantly (p &lt; 0.001) higher than native pastures 1 and 2 (NP1 and NP2). The highest values for effective grazing time, bite rate and BCS were found when dairy cows grazed RW followed by KP, NP2 and NP1. The results suggested that pasture type and sward height influenced grazing behaviour and BCS of dairy cows during the dry season. In the same vein, RW showed higher effective grazing time, bite rate, nutrient intake and BCS than the other three pastures suggesting that RW pastures that appear to be more expensive than native pastures could result in superior cow performance.

Determination of fibre and protein content in heterogeneous pastures using field spectroscopy and ultrasonic sward height measurements

Feeding of livestock on pastures requires constant monitoring of diet composition to ensure consistent levels of animal production. The widely used but conventional techniques to measure the components of feed are impractical to obtain in-field forage quality status for making real-time decisions. Assessment of forage quality parameters using proximal sensing is of particular interest. The present study aimed to demonstrate the potential of using a combination of ultrasonic and canopy reflectance data to predict forage quality variables of heterogeneous pastures. A field experiment with pastures continuously grazed by cows with three stocking density treatments (moderate, lenient and very lenient stocking) was used to calibrate ultrasonic and hyperspectral reflectance sensors. Hyperspectral analysis by a modified partial least square regression (MPLSR) resulted in maximum accuracy for the prediction of acid detergent fibre (ADF) and crude protein (CP) (R2calibration=0.63–0.85). Any reduction of hyperspectral data into vegetation indices based on few specific narrow wavebands or satellite broadbands reduced prediction accuracy significantly. However, prediction of ADF and CP was improved by a combined analysis of ultrasonic sward height and vegetation indices or satellite broadbands, so that most calibration models exceeded an RPD (ratio of standard deviation and standard error of prediction) value of 1.4, which is considered as an acceptable predicting capability for variable field condition. Our findings showed that combined sensing systems using reflectance and ultrasonic sensors may provide acceptable prediction accuracies for practical application even under extremely heterogeneous pasture conditions.

Productive responses of breeding Cashmere goats and their kids to different stocking rates on improved upland pastures.

Although goat meat production could be an option for diversification in improved upland pastures in northern Spain, precise information on the optimal grazing management to enhance goat performance and maximize production per unit land area is lacking. The objective of this study was to compare the effects of 3 stocking rates, high stocking rate (HSR; 20 goats/ha), medium stocking rate (MSR; 15 goats/ha), and low stocking rate (LSR; 10 goats/ha), on gastrointestinal (GI) nematode infections and productive responses of Cashmere goats grazing such pastures. Treatments were replicated twice on 6 paddocks sown with and and with a high presence of the native grass . The experiment lasted 3 grazing seasons (from spring to autumn). Pastures were sampled for sward height and botanical and proximate composition. Body weight and BCS changes of goats were monitored and GI nematode infections were assessed by fecal egg counts (FEC). The established treatments resulted in lower mean sward height in the HSR than in the MSR and LSR (9.6, 11.5, and 14.4 cm, respectively; < 0.001). Pasture botanical composition and nutritive quality did not differ between treatments. The mean FEC of does across the 3 grazing seasons were greater ( < 0.05) in the HSR than in the LSR. spp., , and were the most prevalent nematode species identified in coprocultures. Does showed more favorable ( < 0.001) BW and BCS changes in the LSR than in the MSR and HSR (-14, -30, and -52 g/d and -0.1, -0.3, and -0.7 BCS units [scale 1 to 5], respectively). Greater ( < 0.001) kids' BW gains were observed in the LSR and MSR (average 94 g/d) compared with the HSR (70 g/d). Inversely, kid output per unit land area was greater in the HSR than in the MSR and LSR (320, 258, and 192 kg∙ha∙yr, respectively; < 0.001), whereas daily kids' BW gains per hectare were greater ( < 0.001) in the HSR and MSR (average 1.37 kg∙d∙ha) compared with the LSR (0.98 kg∙d∙ha). A medium stocking rate of 15 goats/ha could represent the best compromise between animal health, performance, and productivity per unit land area in this type of upland pastures, but stricter controls of parasite levels during the grazing season would be necessary to avoid production losses, unless alternative nutraceuticals are provided.

Animal performance and sward characteristics of two cultivars of Brachiaria brizantha (BRS Paiaguás and BRS Piatã)

The objective of the present study was to evaluate live weight gain per animal and per area and its relationship with the characteristics of pastures of Brachiaria brizantha cv. Paiaguas and Piata. A randomized blocks experimental design was used, with two treatments and six replicates. The experimental area was 8.0 ha, divided into twelve paddocks of 0.67 ha. The grazing method used was continuous stocking, with variable stocking rate. Three tester steers were used per paddock. Sward heights were measured once a week, and the stocking rate (SR) was adjusted using regulator steers to maintain the sward height at 30 cm. Pasture samples were collected once a month, and herbage accumulation rate (HAR), percentage of leaves (PL), leaf:stem ratio (LSR), and nutritive value (NV) were determined. Animals were weighed every 28 days. No differences between the two cultivars were observed during the wet season for any of the evaluated parameters. However, cv. Paiaguas presented higher HAR and, consequently, higher SR than cv. Piata during the dry season. As a result of its higher regrowth, cv. Paiaguas pastures presented significantly higher PL, LSR, and NV and, consequently, significantly higher average daily live weight gain. These differences resulted in higher live weight gain per area for Paiaguas grass (695 kg/ha per year) than for Piata grass (645 kg/ha per year). Thus, Brachiaria brizantha cv. Paiaguas is a good alternative to decrease the temporary forage shortage and for the diversification of pastures in the Cerrado biome region.

Variation in Elevation and Sward Height Facilitate Coexistence of Goose Species through Allometric Responses in Wetlands

Allometric scaling law predicts that herbivores respond differently to the availability of resources, mediated by body size. However, studies of allometric responses have often focused on animals with a relatively large difference in body size. Here, using a correlative field study, habitat use by two herbivorous species, the Bean Goose (Anser fabalis) and the Greater White-fronted Goose (A. albifrons), with a relatively small difference in body size was investigated during the wintering period. Both a generalized linear mixed model and a mixed logistic regression model showed that both species selected lower lying areas that were recently exposed, and, as expected, the smaller Greater White-fronted Goose showed a stronger selection of foraging habitat than the larger Bean Goose. Sward height also influenced habitat selection by both species, and the smaller species selected shorter swards than the larger species. In terms of forage quality, both models failed to detect a significant effect of nitrogen content on goose habitat selection. A logistic regression model showed that structural heterogeneity of the sward negatively correlated with the patch selection of the smaller species, but for the larger species such a correlation was not found. In agreement with our hypotheses, our results provide some preliminary indication that coexistence of the two goose species studied here might be mediated by an allometric response even if the difference in body size is relatively small.

Light grazing of saltmarshes increases the availability of nest sites for Common Redshank Tringa totanus, but reduces their quality

The breeding population of Common Redshank Tringa totanus on British saltmarshes has reduced by >50% since 1985, with declines linked to changes in grazing management. Conservation initiatives have encouraged low-intensity grazing of 0.5 cattle ha−1y−1 but even light grazing can lead to high rates of nest mortality. To avoid predators, Redshank nest in patches of tall vegetation, but the effects of grazing on the availability and quality of habitat selected by Redshank remain unclear. We investigated Redshank nest site selection in relation to cattle grazing and asked (a) which nest vegetation conditions do Redshank select and (b) does grazing limit the availability of higher quality nest sites? We characterised vegetation height and composition at nests and control locations on six saltmarshes grazed between 0 and 0.55 cattle ha−1y−1, which falls within or near the UK Environment Agency definition of light grazing. Redshank selected nest locations in the tallest vegetation available (26±13cm with no grazing), but grazing limited the availability of such tall vegetation (11±7cm at 0.55 cattle ha−1y−1). However, Redshank also selected nest locations dominated by the grass Festuca rubra, which increased with higher livestock densities. By causing Redshank to nest in shorter vegetation, but with more of their preferred grass species, grazing presented a trade-off for Redshank. As previous work has shown that nesting in shorter vegetation results in higher nest predation rates, results of this study suggest that even light conservation grazing can result in Redshank nesting in lower quality habitat. Reducing saltmarsh grazing levels below 0.55 cattle ha−1y−1 may therefore increase Redshank populations by maintaining a vegetation structure with patches of F. rubra but with longer sward heights for nesting.

Steers production in integrated crop-livestock systems: pasture management under different sward heights

The aim of this study was to evaluate the effects of different grazing intensities on forage production and animal performance of yearling steers kept under permanent grazing in an integrated crop-livestock system. The treatments consisted of areas with sward heights of 10; 20; 30 and 40 cm, and one treatment with no grazing. The pastures were of bristle oat (Avena strigosa Schreb.) and annual ryegrass (Lolium multiflorum Lam.) following soybean (Glycine max (L.) Merr.). The variables forage mass, forage allowance and residual straw showed a positive and linear fit to the increasing sward height (P≤0.0001). Average daily gain of steers displayed a quadratic response (P = 0.0017), being optimal with increases in grazing height up to values of near 30 cm, showing a weight gain per animal of approximately 1.0 kg day-1. A similar response was seen for live weight at slaughter and carcass characteristics (P≤0.0305). The results suggest that sward heights close to 30 cm provide greater individual gains, due to the increase in forage available to each animal and the better quality of the consumed forage without compromising the residual straw destined for the following crop.

Control de intensidad de defoliación sobre la producción de forraje estacional y total en sistemas lecheros

This study aimed to determine the effect of controlling the intensity of defoliation (ID) on forage production and herbage disappearance in eight commercial farms, in a complete randomized block design. Two blocks were selected in each farm to compare, the grazing management routine of the farm (T0) vs. controlled management (T1, pre grazing height 15-20 cm and post grazing height 5-7 cm). Pre grazing sward height (SH), herbage mass (HM, kg DM ha-1) and daily growth rate (GR, kg DM ha-1 d-1) were determined. In average, SH was lower (p <0.05) in autumn (A) and winter (W) (15.5 ± 1.2 and 16.9 ± 1 cm) than in spring (Sp) and summer (Su) (19.8 ± 1.0 and 21.1 ± 1.2 cm). The same trend (p <0.05) followed HM (A: 1250 ± 164; W: 1476 ± 145; Sp: 1914 ± 140; Su: 2564 ± 167 kg DM ha-1). Average GR was 26.5% higher in T1 than in T0 (p <0.05), and significant differences remained throughout the seasons (A: 19.3 ± 4.3 vs 7.0 ± 3.9; W: 21.3 ± 3.4 vs 17.0 ± 3.0; Sp: 39.6 ± 9.0 vs 33.4 ± 2.5 Su: 43.5 ± 4.2 vs 39.7 ± 4, 0 kg DM ha-1 d-1; p <0.05, for T1 and T0 respectively). In average, T1 yielded 2336 kg DM ha-1 extra when compared to T0, 52% of that was produced in A (p<0.05). Herbage allowance (HA), HM, length of the grazing and SH explained most of the variation (R2 =0.75) of the disappeared forage per hectare (offered - rejected). Controlled grazing management increased herbage production and utilization by dairy cows.

Sward structure and relationship between canopy height and light interception for tropical C4 grasses growing under trees

The canopy height (CH) at 95% light interception (LI) is a valuable defoliation frequency strategy used to handle variability in herbage accumulation throughout the year, mainly in C4 grasses. Such a strategy has been adopted as an open pasture management index, but defoliation frequency and intensity remain unsolved issues for shade-grown forages. A field experiment was conducted for 2 years to determine the influence of tree canopy (Eucalyptus dunnii) shading and nitrogen availability (0 and 300 kg N ha–1 year–1) on CH at 95% LI of six perennial tropical forage species. The plots were cut at 95% LI, and the height of the residual sward was kept at 50% of the corresponding CH at 95% LI. The shade level ranged from ~40% at the beginning of the experiment to ~60% at the end of summer 2013. Variations in CH at 95% LI occurred because of shading and across seasons. The range of these variations was species-dependent. Overall, species growing under trees showed higher CH, except for Paspalum notatum and Megathyrsus maximus in the first year. There was a significant increase in the length of the sheaths and leaves, as well as a decrease in tiller density and leaf : stem ratio in plants growing under trees. Nitrogen also had an impact on CH; however, its application did not compensate the shade effect on CH. Therefore, our results suggest that greater CH should be considered in case of defoliated, shade-grown plants and that such strategy might change throughout seasons.

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.