Lidiane Fonseca

Influência da luminosidade no comportamento de onze espécies forrageiras perenes de verão

Objetivou-se avaliar o comportamento de especies forrageiras (Brachiaria decumbens cv. Basilisk, Brachiaria brizantha cv. Marandu, Panicum maximum cvs. Tanzânia, Aruana e Mombaca, Hemarthria altissima cv. Florida; Paspalum notatum cv. Pensacola, Axonopus catharinensis, Cynodon sp. hibrido Tifton-85; Arachis pintoi cvs. Alqueire e Amarillo) submetidas a diferentes niveis de luminosidade produzidos por arvores de Pinus taeda (ceu aberto; 9 m entre linhas e 3 m entre arvores; e 15 m entre linhas e 3 m entre arvores). Avaliaram-se a producao de MS, a relacao lâmina foliar:colmo (L:C), o nivel de florescimento das plantas, os teores de PB e FDN e as variaveis meteorologicas e do solo, na projecao da copa e no meio da entrelinha de arvores, de cada parcela. A producao de MS foi afetada negativamente pelo sombreamento, por outro lado, o teor de PB foi maior nas parcelas sombreadas em relacao ao pleno sol. Alem da menor radiacao, a velocidade do vento e a temperatura do solo nas parcelas sombreadas foram menores naquelas a sol pleno. O teor de FDN nao diferiu significativamente entre os niveis de luminosidade, embora a relacao L:C tenha sido maior na entrelinha do 9 × 3 em relacao aquela a ceu aberto. As especies forrageiras mais produtivas e com maior potencial para utilizacao em ambiente silvipastoril foram: Axonopus catharinensis e Brachiaria brizantha cv. Marandu.

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.

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.

Desempenho de forrageiras hibernais sob distintos níveis de luminosidade

Possible effects of brightness restriction, obtained by different Pinnus taeda tree densities, on the production and quality of black oat (Avena strigosa Schreb) cv. Common, white oat (Avena sativa L.) cv. FAPA 2, annual ryegrass (Lolium multiflorum L.) cv. Common, hairy vetch (Vicia villosa), wheat (Triticum aestivum L.) cv. dual purpose BRS Taruma were studied. It was evaluated three brightness levels: 1 - full sunlight with no trees; 2 - 30% of radiation restriction, using 15 × 3 m spacing between trees (222 trees/ha), and; 3 - 60% of radiation restriction, using 9 × 3 m between trees (370 trees/ha). It was performed evaluations of forage production, chemical composition and structural component of plants, water potential of the plants, soil moisture, microclimate variables and production of needles. The experimental design was completely randomized blocks, in split-plots and three replicates. Ryegrass was the most productive species at all brightness levels, although hairy vetch showed the lowest reduction on production under shading. There was higher water potential in the plants and higher soil moisture under shading, however, forage production was significantly reduced in the most intense shading (81%). Chemical composition and structural components of all studied forage species are also affected by brightness restriction increase.

Diet Switching by Mammalian Herbivores in Response to Exotic Grass Invasion

Invasion by exotic grasses is a severe threat to the integrity of grassland ecosystems all over the world. Because grasslands are typically grazed by livestock and wildlife, the invasion is a community process modulated by herbivory. We hypothesized that the invasion of native South American grasslands by Eragrostis plana Nees, an exotic tussock-forming grass from Africa, could be deterred by grazing if grazers switched dietary preferences and included the invasive grass as a large proportion of their diets. Bos taurus (heifers) and Ovis aries (ewes) grazed plots with varying degrees of invasion by E. plana in a replicated manipulative experiment. Animal positions and species grazed were observed every minute in 45-min grazing session. Proportion of bites and steps in and out of E. plana tussocks were measured and used to calculate several indices of selectivity. Both heifers and ewes exhibited increasing probability of grazing E. plana as the proportion of area covered by tussocks increased, but they behaved differently. In agreement with expectations based on the allometry of dietary preferences and morphology, ewes consumed a low proportion of E. plana, except in areas that had more than 90% E. plana cover. Heifers consumed proportionally more E. plana than ewes. Contrary to our hypothesis, herbivores did not exhibit dietary switching towards the invasive grass. Moreover, they exhibited avoidance of the invasive grass and preference for short-statured native species, both of which should tend to enhance invasion. Unless invasive plants are highly palatable to livestock, the effect of grazing to deter the invasion is limited, due to the inherent avoidance of the invasive grass by the main grazers in the ecosystem, particularly sheep.