Carolina Bremm

Relações planta-animal em ambiente pastoril heterogêneo: processo de ingestão de forragem

Com o objetivo de avaliar o efeito da estrutura de uma pastagem nativa nos parâmetros que compoem o processo de ingestao de forragem de ovelhas e bezerras em pastejo, foram estabelecidas quatro alturas de pasto (4, 8, 12 e 16 cm), em delineamento estatistico inteiramente casualizado, com quatro tratamentos e duas repeticoes no tempo e no espaco. A massa do bocado e a taxa de ingestao foram estimados por diferenca de peso vivo corrigido para a perda de peso metabolico, durante 45 minutos. Os movimentos mandibulares de apreensao e mastigacao foram registrados pelo aparelho IGER Behaviour Recorder. A profundidade do bocado foi obtida em 40 perfilhos marcados por unidade experimental, em medicoes realizadas antes e apos o pastejo. Observou-se correlacao positiva entre a altura do pasto e a massa de forragem, e negativa com a densidade de forragem. A profundidade de bocados apresentou relacao linear e positiva com o aumento da altura do pasto e nao diferiu entre especies animais. Acima de 9,5 cm de altura do pasto, a profundidade do bocado das ovelhas nao compensou a pouca densidade de forragem nos estratos mais superiores, o que reduziu a massa do bocado. A mesma resposta foi observada a partir da altura do pasto de 11,4 cm para as bezerras. Com o aumento da massa do bocado, houve diminuicao na taxa de bocados e aumento na taxa de mastigacao. A taxa de ingestao foi maior nas alturas em que a massa de bocados foi tambem superior, o que evidencia a correlacao positiva entre as duas variaveis. Nessas condicoes, para aumentar o consumo de ovelhas e bezerras em campo nativo, a estrutura ideal de manejo requer manutencao de altura do pasto entre 9,5 e 11,4 cm, respectivamente.

Efeito de níveis de suplementação sobre o comportamento ingestivo de bezerras em pastagem de aveia (Avena strigosa Schreb.) e azevém (Lolium multiflorum Lam.)

Foi avaliado o comportamento ingestivo de bezerras de corte submetidas a diferentes niveis de suplementacao energetica. Os niveis testados foram (0; 0,5; 1,0; 1,5% do peso vivo), em pastagem de aveia preta (Avena strigosa Schreb.) e azevem (Lolium multiflorum Lam.). O suplemento foi farelo de trigo, fornecido diariamente as 14h. Para registro das atividades de pastejo, ruminacao, ocio e permanencia no cocho, adotou-se a observacao visual, feita a cada dez minutos, durante 24 horas, em quatro datas. Para cada nivel de suplementacao, foram observados seis animais dos grupos geneticos Charoles, 3/4 Charoles/Nelore e 5/8 Nelore/Charoles, com aproximadamente oito meses de idade e peso inicial de 158 kg. Os animais que receberam suplementacao diminuiram o tempo de pastejo em relacao aos nao-suplementados, sem alteracao no consumo estimado de forragem. Os animais que receberam suplementacao a 1,5% do PV permaneceram mais tempo no cocho, aumentando a frequencia de retorno ao cocho nos maiores niveis de suplementacao. Os niveis de suplementacao nao interferiram nos tempos de ruminacao e ocio.

Forage Allowance as a Target of Grazing Management: Implications on Grazing Time and Forage Searching

Abstract This work aimed to evaluate the following hypotheses: 1) the daily grazing time (GT) and 2) forage searching are more associated with the sward structure than with the levels of daily forage allowance (FA). To this end we proposed a model that was tested through an analysis of the sward structure, grazing time, and displacement in grazing by heifers on the natural grassland of the Pampa Biome (southern Brazil), which has been managed by FA levels since 1986. For three seasons, between January 2009 and February 2010, we evaluated the effect of FA on the main descriptors of the sward structure (herbage mass, sward height, and tussocks frequency) and the effect of these on the GT, displacement rate (DR), and daily displacement (D) in grazing. The data were analyzed with the use of regression and descriptive analyses from three-dimensional contour graphs with the data of the sward structure and GT. The DR was not associated with the FA levels or sward structure; however, the DR presented a positive linear relationship with the D and GT. The incremental change in the GT was accompanied by an increase in the D. Lastly, independently of the level of the FA and season evaluated, the lower values of GT were always associated with the following structural configuration: forage mass between 1 400 and 2 200 kg DM · ha−1, sward height between 9 and 13 cm, and tussock levels not exceeding 35%. Outside these limits, a penalty occurred in the GT and displacement patterns of the heifers. We found evidence that a better understanding of the cause–effect relationships between the sward structure and the ingestive behavior of the animals demonstrates the possibility of increasing the performance of domestic herbivores with important economic and ecological consequences. Resumen El objetivo del estudio fue evaluar las siguientes hipótesis: (i) si el tiempo de pastoreo diario (TP) y (ii) la búsqueda de forraje están más estrechamente relacionados a la estructura del pasto que a los niveles diarios de oferta de forraje (OF). Con este fin, propusimos un modelo que se puso a prueba en base al análisis de la estructura del pasto, el tiempo de pastoreo y el desplazamiento en pastoreo en terneras sobre un pastizal natural del Bioma Pampa (sur de Brasil) que, desde 1986, se ha manejado con distintos niveles de OF. En tres épocas, entre Ene/2009 y Feb/2010, se evaluó el efecto de la OF sobre los principales descriptores de la estructura del pasto (biomasa de forraje, altura y frecuencia de matas) y el efecto de éstos sobre el tiempo de pastoreo (TP), la tasa de desplazamiento (TD) y el desplazamiento diario (D). Los datos fueron analizados mediante regresión y por análisis descriptivos a partir de gráficos de contorno tridimensionales en base a los datos de estructura del pasto y TP. La TD no tuvo relación con OF ni con la estructura del pasto, pero mostró una relación lineal positiva con D. Incrementos en TP estuvieron asociados a incrementos en D. El estudio demostró la importancia de la estructura del pasto al constatar que, independientemente del nivel de OF y de la época del año evaluada, los valores más bajos de TP siempre estuvieron asociados a estructuras del pasto caracterizadas por una masa de forraje de 1 400 a 2 200 kg MS · ha−1, alturas de 9 a 13 cm y frecuencia de matas en el pastizal menores al 35%. Fuera de estos límites hubo una penalización en el TP y en el patrón de desplazamiento en pastoreo de las vaquillas. Encontramos evidencias de que el mejor entendimiento de las relaciones causa-efecto entre la estructura del pasto y el comportamiento en pastoreo harían posible incrementar el rendimiento de los herbívoros domésticos, con importantes consecuencias económicas y probablemente ecológicas.

Effect of sward surface height and level of herbage depletion on bite features of cattle grazing Sorghum bicolor swards1

To maximize herbage DMI, pregrazing sward surface height (SSH) and level of herbage depletion (HD) must be such that variables determining short-term herbage intake such as bite mass (BM) and bite rate (BR) are optimized. The objective of this study was to determine a SSH target and the level of HD as a proportion of the SSH that optimizes BM and BR of beef heifers grazing Sorghum bicolor swards. Two experiments were conducted using 2 S. bicolor swards and 4 beef heifers (25 mo old; 322 kg BW). Experiment 1 compared the effect of 6 pregrazing SSH, 30, 40, 50, 60, 70, and 80 cm, on BM, BR, and jaw movements. Experiment 2 assessed the effect of HD level as a proportion of SSH (0.17, 0.34, 0.50, 0.67 and 0.84) on BM, BR, and jaw movements using the optimal pregrazing SSH defined in Exp. 1. Short-term herbage DMI was estimated using a double-weighing technique and corrected for insensible BW loss. Herbage DMI was subsequently used to calculate the BM. Net eating time and jaw movements for apprehension and manipulation + mastication during grazing as well as total jaw movements were determined using the IGER (Institute of Grassland and Environmental Research) behavior recorders. Bite rate and the number of total jaw movements per gram herbage DMI were derived from jaw movement count and measurements of herbage DMI. The results of Exp. 1 showed low and high SSH constraint the ease of herbage harvesting. Greater BM are maintained until a SSH of 50 cm is reached (P < 0.05) and then decline at greater SSH due to herbage dispersion. The nonbiting jaw movement rate increased at greater SSH whereas BR decreased (P < 0.05). For both variables, the turning point was close to a SSH of 50 cm. Experiment 2 showed that such an optimization of BM and BR was maintained until an HD level of 0.34 was reached (P < 0.05). There was a linear increase in both the total jaw movements per unit herbage DMI and the nonbiting jaw movements rate (manipulation + mastication) subsequent to levels of HD greater than 0.34 (P < 0.05). These studies provide, for the first time, sward feature targets to manage grazing and optimize BM and BR, aiming to maximize the short-term herbage DMI of cattle grazing S. bicolor swards.

Padrões de uso do tempo por novilhos em pastagem consorciada de azevém anual e aveia-preta

Aiming to assess the steer grazing behavior, an experiment was carried out with pastures composed by italian ryegrass (Lolium multiflorum Lam.) and black oat (Avena Strigosa Schreb) submitted to different sward heights (10, 20, 30, and 40 cm). The sward heights were distributed in an experimental randomized block design with three replicates. Data was recorded by visual assessment, from sunrise until sundown, in three evaluation dates, two in the vegetative stage and one in the reproductive stage. The evaluated variables were grazing time, rumination time, idling time, number and length of meals, and number and length of meals intervals. Results indicated that with increasing sward height the animals reduced grazing time and the meal length as well, however, the ruminating time increased. The variables such as idling time, number of meals and number/length of intervals were not influenced by the sward surface height. The results showed changes in the animal grazing behavior due to the variations in sward height management.

Produção animal e vegetal em pastagem nativa manejada sob diferentes ofertas de forragem por bovinos

In this research it was evaluated the influence of different forage allowances and combinations of forage allowances along the year on the pasture accumulation dynamic and animal performance. The experiment was conducted in a natural pasture area with yearling beef heifers maintained in continuous grazing with variable stocking rate. The treatments utilized with fixed forage allowances during the year were 4; 8; 12 e 16kg 100kg-1 of live weight; and the treatments of forage allowance combinations were 8 on Spring and 12 on Autumn-Winter-Summer (8-12%); 12 on Spring and 8 on Autumn-Winter-Summer (12-8%); 16 on Spring and 12 on Autumn-Winter-Summer (16-12%), constituting a experimental design in randomized blocks with two replicates of area. The primary and secondary productions were evaluated on the accumulation period of 2007-2008. The results proved that in situations of very low forage allowances, e.g. 4%, the individual performance of animals and per area were prejudiced. Management of forage allowance combination of 8-12% promoted increase of 35% on the individual performance of animals (0,345kg animal-1), and of 20% on the production per area (209kg ha-1 of LW) when compared to a management of 12% over the year.

Can animal performance be predicted from short-term grazing processes?

Despite all the biotic and abiotic factors affecting foraging by ruminants, there is a common and fundamental process, which is bite gathering. We hypothesised that because the mechanics of bite formation dominate the foraging process, changes in short-term bite mass are reflected in longer-term animal performance across a wide range of sward conditions. We focus at the meal level of foraging, using experiments in which the effect of abiotic factors and digestive constrains are minimised, making intake rate the main currency. We estimated bite mass across a wide range of structural challenges to large-herbivore foraging in a long-term experiment with heterogeneous native grasslands. A conceptual model was developed for average daily gain, where energy gain and energy costs were proximate causal variables. Energy gain was a function of diet quality and components of daily intake rate, where bite mass was the main component estimated. In turn, components of intake rate were determined by sward structure and bodyweight. Energy costs were a function of bodyweight and abiotic conditions. Finally, sward structure, bodyweight and abiotic conditions were determined by experimental treatments, seasons and years. Then, the conceptual model was translated into statistical models that included variables measured or estimated, and coefficients representing all links in the conceptual model. Weight gain was a function of bite mass, forage characteristics, and animal and abiotic conditions. Models were set up to test whether forage and stocking conditions affected monthly gain beyond the effects through bite mass, after correcting for abiotic factors. Forage mass, height and disappearance did help predict monthly gain after bite mass was included in the model, which supported our hypothesis. However, stocking treatments and season had significant effects not incorporated in bite mass. Although the model explained 77.9% of liveweight gain variation, only 35.2% was due to fixed effects, with 10.8% accounted by bite mass and its interactions. Concomitant experiments showed that sward structure (first with sward height and the second with tussock cover) does determine bite mass and short-term intake rate in the complex native grasslands we studied. Yet, other temporal varying components of monthly gain not correlated with bite mass, temperature or wind, added most of the observed variation in monthly animal performance. Part of the model failure to account for variation in performance may be related to a significant and temporally variable grazing of tussocks. We used a bite mass model that assumed no tussock grazing. In light of these results and a parallel experiment, we conclude that tussock grazing must be incorporated in future versions of the model.

Aspectos metodológicos do comportamento ingestivo de bovinos em pastejo

It was evaluated grazing times of heifers in natural pasture, obtained by visual assessment in 5-minute intervals. By using the original data, it was calculated observation intervals of 10, 15 and 20 minutes. It was used four crossbreed Angus × Nellore heifers, with average weight of 249 ± 6 kg BW. The completely randomized block design was used with four treatments (forage allowance of 4, 8, 12 and 16 kg DM/100 kg BW) and two replicates, and type of soil was the blocking factor. The grazing method was continuous stocking with variable stocking rate. Grazing time, ruminating time and time of other activities did not differ among scales tested, therefore, they can be observed at every 20 minutes, but the number and duration of meals and its intervals presented variations according to observation scale. Only the observation scale of 5 minutes allowed the detection of daily modifications which compose meal dynamics upon the ingestive behavior of grazing animals. Estimates proved overestimation of 20 minutes in meal duration when observed at every 10 minutes in relation to the observation at every 5 minutes.

Comportamento ingestivo de ovelhas e cordeiras em pastagem de azevém-anual sob níveis crescentes de suplementação

It was evaluated the ingestive behavior of lactating ewes and ewe lambs before and after weaning receiving different supplement levels (0; 0.5; 1.0, and 1.5% of body weight), grazing on a Italian ryegrass (Lolium multiflorum Lam.) pasture, under continuous variable stocking. The experimental design was completely randomized with repeated measures in time with four supplement levels and two replicates. The supplement utilized was a commercial ration, daily supplied at 2 p.m. It was evaluated the diurnal grazing time, rumination time, idle time and trough permanence time (min/day), and biting rate (bite/min), from 8:30 a.m. to 5:30 p.m. in four dates, being two dates by category (ewes/lambs and weaned lambs). Bite mass (g OM/bite) was obtained by the division of daily forage intake by daily total bites. Increasing supplementation levels provided reduction on diurnal grazing time and increase on permanence time of ewes and ewe lambs near troughs. Ingestive behavior patterns of ewes and ewe lambs were variable with structural and bromatologic characteristics of Italian ryegrass pasture. The differences observed in the grazing process of lactating ewes and ewe lambs happened mainly in function of sward structure and quality of pasture.

Consumo de forragem por cordeiras suplementadas em pastagem de milheto

This research evaluated the influence of different levels of supplement (0.0; 0.5; 1.0 and 1.5% in relation to the live weight (LW)) on the forage intake of beef lambs, in Pearl millet (Pennisetum americanum (L.) Leeke) pasture. The forage intake was conditioned by the levels of supplement only at the beginning of the pasture utilization (days 1-21), with maximum ingestion of dry matter when lambs received supplement at the ratio of 0.84% of the LW. The influence of the levels of supplement on the daily weight gain and live weight gain was observed only in the half and in the end of the cycle of the pasture (days 22-64).The intake and performance of lambs in Pearl millet are more dependent on the phenological stage of the pasture rather than the level of supplement received.