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For tropical forage grasses, leaves are the main morphological component accumulated at the beginning of regrowth, and as leaf area index increases, plants change their growth pattern, allocating more resources to stem elongation as a means of optimising light capture. We hypothesised that, for Mombaça guineagrass, stem elongation and leaf senescence rate play a major role in determining net herbage accumulation rate (NHAR) and that senescence would be the key factor driving the reduction in NHAR when regrowth is interrupted beyond the critical leaf area index, that is, when canopy light interception (LI) exceeds 95%. Treatments corresponded to all combinations of two levels of pre-grazing canopy LI during regrowth (LI95% and LIMax) and two post-grazing heights (30 and 50 cm), and were allocated to experimental units according to a randomised complete block design with four replications. Measurements were performed throughout contrasting climatic conditions during four seasons from January 2001 to February 2002. Overall, spring and the two summers were the seasons when rates of leaf appearance, leaf elongation and leaf growth rate were higher, and leaf lifespan was smaller; the inverse occurred during autumn–winter. Despite the lack of statistically significant differences in NHAR between LI treatments during some seasons of the year, the ratio of leaf growth rate to NHAR was consistently higher for LI95% than LIMax. The pre-grazing target of LI95% was also efficient for decreasing stem elongation and leaf senescence rate. Increased senescence on individual tillers was the key driver generating modifications in the patterns of variation in NHAR beyond the critical leaf area index, suggesting that there is no advantage in extending the regrowth period when the main objective is to maximise leaf growth rate or NHAR. Herbage production is an important feature of pastoral systems of animal production because it determines stocking rate. Herbage production depends on the turnover of tillers and on the turnover of tissues on living tillers. This is the second of two companion papers that deal separately with tiller and tissue turnover, providing complementary strategic knowledge for defining grazing management targets for Mombaça guineagrass (Megathyrsus maximus cv. Mombaça). [ABSTRACT FROM AUTHOR]

In rotationally grazed pastures, the canopy light environment can be modulated through both grazing frequency and severity, and the magnitude of sward responses may differ according to forage species and its ability to use available resources. We hypothesised that the tall, tufted, fast-growing, tussock-forming species Mombaça guineagrass (Megathyrsus maximus (Jacq.) B.K.Simon & S.W.L.Jacobs cv. Mombaça) can modulate its tillering dynamics and change its persistence pathway according to grazing strategy and the availability of growth factors. Treatments corresponded to all combinations of two levels of pre-grazing canopy light interception during regrowth (95% and maximum) and two post-grazing heights (30 and 50 cm), and were allocated to experimental units according to a randomised complete block design with four replications. Measurements were performed throughout contrasting climatic conditions during four seasons from January 2001 to February 2002. A quite stable tiller population density presented regardless of the range of grazing frequency and severity used in the study. However, tiller appearance and death were strongly influenced (P < 0.001) by season of the year, with highest rates recorded during the two summers and lowest during autumn–winter. There was no conclusive evidence that the persistence pathway of Mombaça guineagrass changes within the grazing management strategies studied. Herbage production is an important feature of pastoral systems of animal production because it determines stocking rate. Herbage production depends on the turnover of tillers, and on the turnover of tissues on living tillers. This is the first of two companion papers that deal separately with tiller and tissue turnover, providing complementary strategic knowledge for defining grazing management targets for Mombaça guineagrass (Megathyrsus maximus cv. Mombaça). [ABSTRACT FROM AUTHOR]

Trees in the production systems can effectively reduce hot weather-induced stress in the Brazilian Midwest. High temperatures cause changes in animals daily routine, and trees into pastures can promote benefits. The aim of this research was to evaluate the behavior of dairy heifers in silvopastoral systems in the state of Mato Grosso, Brazil. A herd of 24 crossbreed heifers (3/4 and 7/8 Holstein/Zebu), 350kg average weight, was evaluated over three seasons. Piatã grass was managed under three shade levels: full-sun, moderate-shade, and intensiveshade provided by 10 to 12m high Eucalyptus trees. Behavior data were collected every 15 minutes from 8:30h to 16h. Shade availability significantly impacted heifer behavior, mainly affecting grazing frequency and time during the hottest hours. Grazing behavior was affected by shade levels during the different seasons. Heifers showed preferred grazing times. Heifers in the intensive-shade system visited shady areas during the hottest hours throughout the seasons. Heifers in the full sun-system avoided grazing during the warmer times, ceasing feeding activities. Our results from the Brazilian Midwest showed that shade availability causes breed heifers to change their daily routine. [ABSTRACT FROM AUTHOR]