ABSTRACT The interaction between pasture and supplementation in dairy production systems constitutes a very important part of the efficiency of dairy. This study evaluated the effect of the herbage mass (HM) on the milk production and solid concentration. Twenty Holstein cows were distributed into two groups, 10 assigned 2200 kg DM ha-1 (low herbage mass, LHM) and 10 with 2800 kg DM ha-1 (medium herbage mass, MHM). Herbage mass was measured above 5 cm. The experiment lasted 8 wk. The variables evaluated were DM intake (DMI), milk production and composition (fat and protein concentration). Effects of treatments on variables were evaluated using a repeated measure analysis over time. The results showed nonsignificant differences in the pasture DMI between LHM and MHM for weeks 1, 2, 3 and 5 (P > 0.05). During week 4, pasture DMI was 3 kg greater for LHM than MHM (P < 0.05). The milk production did not differ between treatments per week, but the average was 2.4 kg greater for LHM compared to MHM (P < 0.05). In conclusion, changes in the pasture availability increased milk production at LHM, but not enough to cause changes in solids concentration. This clearly shows that, LHM can increase milk and solids production.

ABSTRACT Various studies have evaluated the use of electronic devices to automatically record the grazing behavior of dairy cows. Linking individual grazing behavior of dairy cows with the modifications in grazing behavior across the grazing session through the use of automatically registered indicators, would allow the development of decision-making tools in grazing management. The objective of the present study was to evaluate the use of the activity level (AL) recorded with an accelerometer during the grazing-down process of a pasture grazed by dairy cows as a possible criterion for decision-making related to grazing management. A completely randomized design was used to evaluate the AL of dairy cows in two contrasting pasture-based dairy production systems: A pasture-based system with high concentrate supplementation level and high herbage mass (HM), using high-yielding dairy cows (GRAZSUP), and a pasture-based system with minimal concentrate supplementation level and medium HM, using Holstein New Zealand strain (GRAZ). Pre-grazing HM was higher in GRAZSUP than in GRAZ (+750 kg DM ha-1), while forage removed was higher in GRAZ than in GRAZSUP (+1.9 kg DM cow-1 d-1). Although the production system influenced the characteristics of the pasture and the ingestive behavior of the dairy cows, when AL was evaluated as the proportion of the initial AL recorded at a time-point of the grazing-down process, there were no differences in each of the times evaluated. In conclusion, AL of grazing dairy cows was significantly affected during the grazing-down process, reflecting the modifications in grazing behavior across grazing session.

ABSTRACT Pastures dominated by native and naturalized species account for a large portion of the total grassland area in southern Chile. However, information on these ecosystems is scarce, particularly with respect to the seeds of the species that compose them. The objective of this study was to evaluate the physical and germinative characteristics of Bromus valdivianus Phil., Paspalum dasypleurum Kunza ex Desv., Holcus lanatus L., Agrostis capillaris L. y Arrhenaterum elatius L. spp. bulbosus (Wild), collected from two geographical areas of southern Chile and classified into two contrasting sizes. The areas evaluated were the foothills (Coastal Mountain Range) of the commune of La Unión and the foothills (Los Andes Mountain Range) of the commune of Lago Ranco. Seed germination percentage, germination rate, diameter, length, and 1000 seed weight were determined. Subsequently, germination vigor was determined by measuring leaf length, aerial weight, root weight and total weight of the species. In addition, a pot experiment was conducted under controlled conditions of temperature, light and humidity to determine establishment vigor, measuring the same parameters as for germination vigor. The data were analyzed under a completely randomized nested design. Bromus valdivianus Phil. was the species that showed the best performance in all the evaluated variables (P < 0.05). In terms of locality of origin, Lago Ranco recorded larger seeds, while La Unión presented better germination. In terms of size, large seeds proved to be more vigorous and had better germination performance. It was concluded that germination percentage and rate as well as vigor of germination and establishment vary between seed size and locality of origin within the same species.

RESUMEN Las praderas dominadas por especies nativas y naturalizadas constituyen un porcentaje significativo de la superficie total de praderas en el sur de Chile. Sin embargo, la información sobre estos ecosistemas es escasa, particularmente en lo que respecta a las semillas de las especies que los componen. El objetivo de este estudio fue evaluar las características germinativas y de establecimiento de Bromus valdivianus Phil., Paspalum dasypleurum Kunza ex Desv., Holcus lanatus L., Agrostis capillaris L. y Arrhenaterum elatius L. spp. bulbosus (Wild), provenientes de dos zonas geográficas del sur de Chile y clasificadas en dos tamaños de semilla contrastantes. Las zonas evaluadas fueron el sector precordillerano (Cordillera de la Costa) de la comuna de La Unión y el sector precordillerano (Cordillera de los Andes) de la comuna de Lago Ranco. Se realizó un análisis de germinación para determinar el porcentaje y tasa de germinación, diámetro, longitud y peso de 1000 semillas. Posterior a ello, se determinó el vigor de germinación, cuantificando longitud foliar, peso aéreo, radical y total de cada especie para cada tratamiento. Además, se realizaron ensayos en macetas bajo condiciones controladas de temperatura, luz y humedad para determinar el vigor de establecimiento, cuantificándose los mismos parámetros evaluados para el vigor de germinación. Los datos fueron analizados bajo un diseño completamente al azar anidado. B. valdivianus fue la especie que presentó mejor desempeño en todas las variables evaluadas (P < 0,05). En cuanto a la localidad, Lago Ranco dio origen a semillas más grandes y La Unión a semillas de mejor germinación. En términos de tamaño, las semillas grandes demostraron ser más vigorosas y tener un mejor desempeño germinativo. Se concluyó que el porcentaje, la tasa de germinación, el vigor de germinación y de establecimiento varían entre tamaño de semilla y localidad de origen dentro de la misma especie.

ABSTRACT Accumulated herbage mass (AHM) availability is a determining criterion for efficient pasture management and use. The Rising Plate Meter (RPM) is a tool for estimating this parameter; to do so, equations need to be developed for the pasture conditions in which it will be used. The objective of this study was to develop a calibration equation for the RPM to determine AHM in mixed pastures of Lolium perenne L. and Cenchrus clandestinus. The experiment was carried out at the San Pedro farm located in the municipality of Cota, Cundinamarca Department, Colombia. Sixteen experimental paddocks were used, composed of 30% L. perenne and 70% C. clandestinus; 25 samples per paddock were taken on a daily basis throughout the experimental period. A linear regression analysis was performed for compressed height (CH) and AHM expressed in kg DM ha1. The resulting equation for the RPM calibration showed a high level of precision and indicated that AHM (kg ha1) is highly dependent on CH. Given the level of accuracy of the regression equation developed in this study (R2 = 0.85), the RPM can be a useful tool for estimating AHM at a field level for mixed grasslands composed of L. perenne and C. clandestinus.

RESUMEN La acumulación de materia seca (AMS) disponible es un criterio determinante para el eficiente uso y manejo de la pradera. El plato medidor de praderas (PMP) es una herramienta disponible para estimar este parámetro; para esto, es necesario desarrollar ecuaciones para las condiciones de la pradera donde será utilizado. El objetivo de este estudio fue desarrollar una ecuación de calibración para determinar AMS en praderas mixtas compuestas por Lolium perenne L. y Cenchrus clandestinus con el PMP. El experimento se realizó en la finca San Pedro ubicada en el municipio de Cota, departamento de Cundinamarca, Colombia. Diez y seis potreros experimentales fueron usados, compuestos de 30% L. perenne y 70% C. clandestinum, y 25 muestras fueron tomadas diariamente durante el periodo experimental por cada potrero. Un análisis de regresión lineal fue corrido entre altura comprimida (AC) y MSA expresada en kg MS ha1. El resultado de la ecuación de calibración para el PMP mostró que existe una gran dependencia de la MS disponible expresada en kg MS ha1 in función de la AC con un alto nivel de precisión. Dado el nivel de exactitud de la ecuación de regresión desarrollada en este estudio (R2 = 0,85), el PMP pude ser una herramienta útil para estimar la MSA a nivel de campo para praderas mixtas compuestas por L. perenne y C. clandestinus.

ABSTRACT In temperate milk production systems, it is important to study the effect of grazing strategies in both the quantity and quality of the diet, resulting in potential impacts on animal metabolism. The aim was to evaluate the effect of timing of herbage allocation and herbage mass on blood indicators. Forty Holstein-Friesian cows were grouped according to milk production (24.7 ± 2.8 kg cow-1), body weight (580.6 ± 51.7 kg) and days in milk (74 ± 17.1 d). The groups were randomly allocated to one of four treatments: 1) L-AM, access to new herbage allocation after morning milking with herbage mass of 2000 kg DM ha-1; 2) L-PM; access to new herbage allocation after afternoon milking with herbage mass of 2000 kg DM ha-1; 3) H-AM; access to new herbage allocation after morning milking with herbage mass of 3000 kg DM ha-1; 4) H-PM; access to new herbage allocation after afternoon milking with herbage mass of 3000 kg DM ha-1. Milk production was only different for H-PM in 1.1 kg higher than L-PM. Urea in milk was affected by treatments, being 22% higher for L-AM than other treatments. ß-Hydroxybutyrate and blood urea concentrations were 47% and 30% higher, respectively, for AM compared to PM treatments. Plasma albumin concentration was lower for H-PM compared to other treatments at week 3 of blood sampling. PM treatments modify the herbage composition and animal metabolism, while combining it with a high herbage mass impacts positively in production and milk composition.

Abstract: Restricting plant available water in the soil can negatively affect pasture growth. Lolium perenne L. (Lp) and Bromus valdivianus Phil. (Bv) are important components of the permanent pastures in southern Chile. The aim of this study was to investigate the growth response of Lp and Bv when subjected to soil water restriction, contrasting soil structure conditions and growing as a single species pasture or in a mixture. The treatments were two soil physical conditions (undisturbed (US) and disturbed soil (DS)), two soil water restriction levels (optimum PAW and very-dry PAW), and three pastures (Bv, Lp and Bv+Lp). The US provided more water to plants regardless of the soil water restriction, and Bv and Lp presented more development (highest accumulated herbage mass) in US than in DS, under a similar soil water restriction. The soil structure and soil water restriction did not modify the tiller number of Bv, although Lp showed different tiller numbers under each condition, soil structure and soil water restriction. The conservation of the soil structure (undisturbed soil) has an important role in pasture productivity by providing a continuous pore system, which certainly improved the water accessibility for the growing species.

Abstract The cumulative effects of daily herbage allowance (DHA) restriction on pasture characteristics and the sustainability of pasture-based dairy systems were evaluated. Sixty-four dairy cows were randomly assigned to one of two grazing treatments (20 and 30 kg DM cow-1 day-1). Milk yield and pre- and post-grazing herbage mass were recorded for every grazing event. Botanical and chemical compositions of the pasture were evaluated. Low DHA increased the stocking rate by 0.7 cows ha-1 and consequently increased grazing efficiency from 41 to 47%. Daily herbage allowance restriction did not affect pasture characteristics or milk production per cow, but DHA restriction increased milk production per hectare (+27%). The results suggest that restriction on daily herbage allowance ensures a higher level of herbage utilization and milk output per ha than high DHA, without affecting pasture characteristics. Therefore, DHA might be a useful grazing management tool for improving the profitability and sustainability of grazing-based dairy systems.

Resumen El estudio evaluó el efecto acumulado de la restricción en la oferta diaria de pradera sobre las características de la pradera y sobre la sustentabilidad de los sistemas lecheros pastoriles. Se utilizaron 64 vacas lecheras que fueron asignadas aleatoriamente a dos tratamientos de pastoreo (20 y 30 kg MS vaca-1 día -1). En cada evento de pastoreo se registró la fitomasa de pre y post-pastoreo y la producción diaria de leche por vaca. Se evaluó la composición botánica y composición nutricional de la pradera. La baja oferta diaria de pradera aumentó la carga animal en 0,7 vacas ha-1 y consecuentemente aumentó la eficiencia de de pastoreo de 41 a 47%. La restricción en la oferta diaria de pradera, no modificó las características de la pradera ni la producción de leche por vaca, incrementando la producción de leche por hectárea en 27%. Los resultados de este estudio sugieren que la restricción en la oferta diaria de pradera por vaca, aumenta la eficiencia de utilización de la pradera y la producción de leche por hectárea respecto de una alta oferta de pradera sin afectar negativamente las características y sustentabilidad de la pradera. Por lo tanto, la oferta diaria de pradera puede ser una herramienta útil de manejo del pastoreo para mejorar la rentabilidad y sustentabilidad de los sistemas lecheros basados en pastoreo.

Abstract Improved plantain (Plantago lanceolata L.) and chicory (Cichorium intybus L.) are attractive forage species for finishing lambs and contain compounds that might protect sheep from gastrointestinal nematodes. This study compared the live weight gain and parasite burden of weaned lambs finished on a plantain-chicory mix (Pl-C) or a permanent grass-based pasture (PP) and treated with or without an endectocide. From mid-November, weaned lambs (n=72, average live weight 32 kg) were distributed into three paddocks per sward type for 30 d. Half of the lambs were initially treated with ivermectin. Fecal egg counts (FEC), larvae genera and the presence of infective larvae (L3) in pastures were evaluated. No differences (P>0.05) were obtained between the pastures for the initial (ca. 80 epg) or final FEC (322 epg) or type of eggs (Strongylid- or Nematodirus-type). Ivermectin treatment reduced (P<0.01) the total FEC (482 vs. 158 epg) and the Strongylid- (418 vs. 148 epg) and Nematodirus-type eggs (64 vs. 9 epg). No significant effects (P>0.05) of pasture type or anthelmintic treatment and no interactions were detected on the cultured larvae genera, except for Cooperia, which decreased with the anthelmintic treatment. By day 30, the number of L3 recovered from the pastures increased (P<0.05) in the PP (62 to 280 L3 kg-1 DM), while the number was unchanged (P>0.05) in the Pl-C (average 63 L3 kg-1 DM). The parasite load estimated by the FEC reached low infection levels (<400 epg), preventing clinical signs. The live weight gain of lambs was similar (P>0.05) among treatments (average 173 g d-1), reflecting an adequate nutritional quality of both pastures and a moderate parasitism status of the lambs.

Resumen Variedades mejoradas de plantago (P. lanceolata L.) y achicoria (Cichorium intybus L.) son interesantes para engordar corderos y pueden protegerlos del parasitismo interno por sus metabolitos secundarios. Este estudio comparó la ganancia de peso y carga parasitaria de corderos destetados terminados en una mezcla de plantago-achicoria (Pl-C) o una pradera permanente basada en gramíneas (PP), tratados o no con un endectocida. Setenta y dos corderos con peso promedio de 32 kg se distribuyeron en tres potrerillos por cada tipo de pradera, por 30 días desde mediados de noviembre. La mitad de los corderos se trató inicialmente con ivermectina. Se evaluó recuento fecal de huevos (FEC), géneros larvarios y recuento de larvas L3 en las praderas. La carga de FEC inicial (ca. 80 hpg) o final (322 hpg) fue similar (P>0.05) entre praderas. El tratamiento con ivermectina logró menor (P<0.01) recuento total (482 vs. 158 hpg), huevos tipo estrongílidos (418 vs. 148 epg) y Nematodirus (64 vs. 9 epg). Las cargas parasitarias finales estimadas fueron bajas (<400 hpg). No hubo efecto del tipo de pradera, antihelmíntico o su interacción, para el número de larvas obtenidas del cultivo de fecas, excepto para Cooperia que disminuyó con la ivermectina. Las larvas L3 en la pradera aumentaron (P<0.05) durante el estudio para PP (62 to 280 L3 kg-1 MS) pero no para Pl-C (promedio 63 L3 kg-1 MS). La ganancia de peso fue similar (P>0.05) entre tratamientos (promedio 173 g d-1) reflejando una calidad nutricional adecuada de ambas praderas y un parasitismo moderado.

ABSTRACT In Chile, high moisture corn (Zea mays L. [HMC]) has been included mainly in diets for grazing dairy cows on pastures with high crude protein, and is an alternative that improves nutrients supply and rumen synchrony between energy and protein provided by the diet. In addition, supplementation with HMC results in an increase of fatty acids (FA) in milk, desirable for human health. The aim of this study was to evaluate the effect of herbage allowance (HA) and type of supplement on milk FA composition in grazing dairy cows during spring. Thirty-two multiparous Holstein-Friesian dairy cows (533 ± 71 kg BW; 53 ± 4 d in milk [DIM[ and milk yield 23.8 ± 4.2 kg d-1) were randomly assigned to four dietary treatments resulting from the combination of two HA levels (low 20 vs. moderate 30 kg DM cow1 d-1) and two types of supplements HMC and cracked wheat [Triticum aestivum L., CW]) offered at 3.5 kg DM cow-1 d-1. Total FA intake was greater for moderate HA (547.8 g d-1) than low HA (527.2 g d-1) (P < 0.05); but did not affect milk yield, milk constituents and milk FA composition (P > 0.05). Supplementation with HMC increased milk production by 2.3 kg d-1 compared with CW. Cows supplemented with HMC showed a greater intake of total FA (564 g d-1) and had greater concentrations of long-chain monounsaturated FA in milk (27.13 g 100 g-1) compared to cows supplemented with CW (511.0 g d-1 total FA intake and 25.39 g 100 g-1 in milk, respectively) (P < 0.05). It is concluded that grazing dairy cows supplemented with HMC during spring produced milk with higher concentrations of desirable FA, independently of the HA level.

Winter grazing provides a useful means for increasing the proportion of grazed herbage in the annual diet of dairy cows. This season is characterized by low herbage growth rate, low herbage allowance, and low herbage intake and hence greater needs for supplements to supply the requirements of lactating dairy cows. The aim of this study was to determine the influence of herbage allowance (HA) offered to autumn calving dairy cows grazing winter herbage on milk production, nutritional status, and grazing behavior. The study took 63 d using 32 multiparous Holstein-Friesian dairy cows. Prior to experimental treatment, milk production averaged 20.2 ± 1.7 kg d-1, body weight was 503 ± 19 kg, and days in milking were 103 ± 6. Experimental animals were randomly assigned to two treatments according to HA offered above ground level: low (17 kg DM cow-1 d-1) vs. high HA (25 kg DM cow¹ d¹). All cows were supplemented with grass silage supplying daily 6.25 and 4.6 kg DM of concentrate (concentrate commercial plus high corn moisture). Decreasing HA influenced positively milk production (+25%), milk protein (+20 kg), and milk fat (+17 kg) per hectare; however no effects on milk production per cow or energy metabolic status were observed in the cows. In conclusion, a low HA showed to be the most significant influencing factor on milk and milk solids production per hectare in dairy cows grazing restricted winter and supplemented with grass silage and concentrate; but no effect on the milk production per cow was found.

Corn (Zea mays L.) silage (CS) is a nutritious food that can be used as a supplement in dairy cows. The aim of this study was to determine the effect of supplementation with two amounts of CS on milk production and composition, live weight and body condition, as well as on some blood indicators for energy and protein metabolism on dairy cows in early lactation and grazing low mass pasture during autumn. The study was carried out in 40 Holstein Friesian cows over 57 d. Prior to experimental treatment, milk production and days of lactation averaged 24.1 ± 2.8 kg d-1 and 62 ± 14 d, respectively. The dietary treatments consisted of two levels of supplementation with CS; 4.5 and 9 kg DM cow-1 d-1 (treatments LCS and HCS, respectively). Additionally, all the cows received a pasture allowance of 21 and 3 kg DM cow-1 d-1 of concentrate. Milk composition was determined using infrared spectrophotometry, while blood indicators were obtained using an autoanalyzer. There were not differences between treatments regarding milk production or composition, total DM or energy intake. Herbage and protein intake was higher for LCS treatment (P < 0.001). Increasing supplementation decreased (P < 0.001) daily weight gain but did not affect body condition. Plasma concentrations of βOH-butyrate were lower (P = 0.038) for the LCS treatment; while urea concentrations were higher (P = 0.003), with no differences for non-esterified fatty acids (NEFA) concentrations. Supplementation with 4.5 kg d-1 of CS was sufficient to meet the production requirements of the cows.

Prairies are a main source for livestock feeding in southern Chile. The aim of this research was to define how grazing events and natural wetting and drying cycles (WD) affect the spatial and temporal variability of the soil’s structural properties. The investigation was conducted in a Duric Hapludand, Valdivia Series. Penetration resistance (PR) and volumetric water content (WC), measured in situ, were used to prepare maps which show i) temporal (1383 to 3047 kPa for 46 to 16% WC) and spatial changes, and ii) grazing events as an important factor influencing spatial changes in PR (differences of 3421 kPa between max and min values). Grazing and WD cycles induced changes in the soil’s mechanical stability and pore functions, which indicate that structure-dependent properties are dynamic. During the study, variations between 0.3 and 0.9 log µm² were detected for air permeability (k a), whereas air capacity (ACp) ranged between 5 and 18%. Soil mechanical strength also varied over time and showed changes in PR. The same instrument, however, cannot be used to identify changes in soil pore functions. Generally, after grazing events, soil deformation induced a reduction of air capacity and permeability; however, after WD cycles, soil pores were able to recover their functional integrity.

Las praderas son la principal fuente de alimentación del ganado en el sur de Chile. El objetivo de esta investigación fue definir cómo afectan los eventos de pastoreo y ciclos naturales de mojado y secado (WD), la variabilidad temporal y espacial de las propiedades estructurales del suelo. La investigación fue realizada en un Duric Hapludand, Serie Valdivia. La resistencia a la penetración (PR) y el contenido volumétrico de agua (WC) determinados in situ fueron usados para preparar mapas que muestran i) que ellas cambian en el tiempo (PR: 1383-3047 kPa para WC: 46-16%) y espacio, y ii) que los eventos de pastoreo son un factor importante que influye sobre la variación espacial de PR (diferencias de 3421 kPa entre los valores max y min). El pastoreo y WD inducen cambios en la estabilidad mecánica y la función de los poros indicando que las propiedades estructurales son dinámicas. En permeabilidad de aire (k a) se detectaron variaciones entre 0,3 y 0,9 log mm² durante el período de estudio, mientras que la capacidad de aire osciló entre 5 y 18%. La estabilidad mecánica también varió en el tiempo reflejando los cambios en PR. Este instrumento, sin embargo, no puede ser usado para identificar variaciones en las funciones de los poros del suelo. Generalmente, después de los eventos de pastoreo, la deformación del suelo provocó una reducción en la capacidad y permeabilidad de aire, sin embargo, después de WD, los poros del suelo fueron capaces de recuperar su integridad.

The objective of this study was to determine, under the soil and climatic conditions of Southern Chile, the effect of the ploidy of perennial ryegrass (Lolium perenne L.) cultivars on herbage production, nutritive value, grazing preference and utilization of pasture produced. This study was conducted in southern Chile, Valdivia Province, and was evaluated for 3 years. The tetraploid cultivars used were Quartet (4n), Gwendal (4n), Pastoral (4n) and Napoleon (4n). The diploid cultivars were Anita (2n), Jumbo (2n), Aries (2n), and Yatsyn 1 (2n).When the average sward height reached 20 cm, all plots were simultaneously grazed by dairy cows for a period of 24 h. Before and after grazing, sward height, dry matter availability and nutritive value were evaluated. Grazing preference was visually assessed every 5 min for a period of 2.5 h after the afternoon milking. During the 3-year period 20 grazing events were evaluated. A randomized complete block design, with eight cultivars and three replicates, was used. Diploid cultivars showed greater herbage mass accumulation than tetraploid cultivars (P ≤ 0.05). No significant differences were obtained in the annual average crude protein content. Nevertheless, tetraploid cultivars showed a greater D value than diploid cultivars, except during the third year when the difference was not statistically significant. Dairy cows grazed more time on tetraploid cultivars. Considering, additionally, the residual herbage mass after grazing and the percentage of pasture utilization, diploid cultivars were less intensively grazed, suggesting a lower consumption by the cows.

El objetivo de este estudio fue determinar, bajo las condiciones edafoclimáticas del sur de Chile, el efecto de la ploidía de cultivares de ballica perenne (Lolium perenne L.) sobre el rendimiento de fitomasa, calidad nutricional, preferencia de pastoreo y porcentaje de utilización del forraje producido. El ensayo se realizó en el sur de Chile, provincia de Valdivia, y se evaluó por 3 años. Se utilizaron los cultivares tetraploides Quartet (4n), Gwendal (4n), Pastoral (4n) y Napoleón (4n). Los cultivares diploides Anita (2n), Jumbo (2n), Aries (2n) y Yatsyn 1 (2n). Vacas lecheras pastorearon simultáneamente durante 24 h todas las parcelas cuando éstas alcanzaron una altura promedio de 20 cm. Previo y posterior a cada pastoreo se midió altura de la pradera, fitomasa y valor nutritivo. La preferencia de pastoreo fue evaluada visualmente cada 5 min durante un período de 2,5 h posterior a la ordeña de la tarde. Durante el período de 3 años se evaluaron 20 pastoreos. El diseño experimental fue de bloques completos al azar con ocho cultivares y tres bloques. Los cultivares diploides presentaron un mayor rendimiento de materia seca (P ≤ 0,05). No se detectaron diferencias significativas en el contenido de proteína. Sin embargo, los cultivares tetraploides presentaron un mayor valor D, aunque esta diferencia no fue significativa en el tercer año. Las vacas en lactancia pastorearon significativamente más tiempo sobre los cultivares tetraploides. Considerando la fitomasa residual pospastoreo y el porcentaje de utilización se puede indicar que las vacas pastorearon menos intensamente los cultivares diploides.

This research was conducted for two years to evaluate magnesium fertilizer application (0, 24, 48 and 96 kg ha-1 year-1 of Mg) on a permanent pasture composed by Lolium perenne and Trifolium repens as an agronomic alternative of hypomagnesaemia management in grazing herds. The effect on magnesium, calcium, potassium and sodium concentration in the pasture dry matter and the ratio between cations were evaluated. The research was carried out on an Hapludand (Valdivia serie) with an initial available magnesium content of 0.8 cmol c kg-1. Pasture dry matter production was not affected by magnesium fertilization, nevertheless, the concentration of magnesium in the pasture dry matter increased proportionally to the magnesium applied. A weighed average showed an increase of 0.006 and 0.012 g kg-1 of dry matter for each kg of magnesium applied during the first and second year, respectively. In addition, the magnesium fertilization decreased the calcium dry matter concentration, but it did not affect potassium and sodium dry matter concentration. The ratios between calcium/magnesium, potassium/magnesium and sodium/magnesium decreased with the increase of the magnesium fertilization rate.

Como una alternativa de manejo agronómico de la hipomagnesemia en rebaños a pastoreo se estudió, durante dos años, el efecto de la fertilización magnésica (0, 24, 48 y 96 kg ha-1 año-1 de Mg) sobre la concentración de magnesio, calcio, potasio y sodio y sus relaciones en la materia seca del forraje cosechado de una pradera permanente compuesta por Lolium perenne y Trifolium repens. El ensayo se realizó en un suelo Hapludand (Serie Valdivia) con un nivel inicial de 0,8 cmol c kg-1 de Mg. No se detectó un efecto de la fertilización magnésica sobre la producción de materia seca de la pradera, pero la concentración de magnesio en la materia seca se incrementó proporcionalmente a la dosis de magnesio aplicada. Considerando el promedio ponderado anual el aumento de la concentración de magnesio fue de 0,006 y 0,012 g kg-1 de materia seca por cada kg de magnesio aplicado, durante el primero y segundo año, respectivamente. La fertilización magnésica disminuyó la concentración de calcio, pero no afectó la concentración de potasio ni de sodio en la materia seca del forraje cosechado. Las relaciones entre Ca/Mg, K/Mg y Na/Mg en general disminuyeron en la medida que aumentó la dosis de fertilización con magnesio.