Search

The goals of this study were to evaluate the length of time grazing which should be monitored over a 24-h period to predict the grazing behavior of beef heifers within a season and determine the patterns of foraging activity over 24 h. A database was constructed between 2010 and 2012 for beef heifers managed under rotational grazing in a natural grassland. Grazing, rumination, and other activity times were assessed visually during 24 h on 15 occasions. Data were classified according to climatic seasons, generating 12 replicates in summer, 18 in spring, 24 in autumn, and 36 in winter. Treatments were the evaluation of four distinct periods: from sunrise to sunset (DAY-SUN), daylight duration from dawn to nightfall (DAYLIGHT), DAYLIGHT plus 2 h (DAYLIGHT+2), DAYLIGHT to midnight (DAYLIGHT to 0), and the entire 24 h period (CONTROL). Differences for grazing, rumination, and other activities were found in all seasons for the evaluation periods. Sampling sufficiency was reached only with the DAYLIGHT to 0 and CONTROL for all four climatic seasons. The DAYLIGHT to 0 treatment covered 75% of a 24-h period and 95% of the mean foraging time took place during this time interval. Considering grazing distribution during a day, in the warm seasons, the major grazing period during mornings occurred earlier than in the cool seasons, and in cool seasons, the grazing peak was observed during the afternoon. Visual observations from dawn until midnight represented the total grazing time and natural behavior of heifers and could be used to represent grazing activities for the entire day.

ABSTRACT: This study aimed to evaluate the effect of two rest intervals between grazing on the structural characteristics of pasture and performance of beef heifers in Campos grassland under rotational grazing. The treatments were two intervals between 375 and 750 DD (degree-days) grazing, based on the cumulative thermal sum for leaf expansion of native grasses belonging to capture and conservation groups of resources dominant in a natural grassland. The experiment was conducted during 151 days from October 2015 to March 2016, and twenty-four Braford heifers tests mean age = 12 months; mean body weight = 220kg (± 27.8) were used. The pre-grazing total forage mass (FMt) was on average 3791 kgMSha-1 and did not differ between treatments and season, the same occurred with the non-tussock FM. The average stocking rate was 469 kg ha-1 in both treatments. The average daily gain varied only between seasons, 0.102 kg animal-1 day-1 during spring and 0.372 kg animal-1 day-1 during summer. During the 151 evaluation days, the gain per area was a 103 kgha-1. The use of rest intervals between grazing based on the leaf elongation of dominant grasses, when applied to the areas of Campos grasslands, provided nutritional conditions to reach the target body weight for breeding 24 months old beef heifers.

The aim of this study was to evaluate the performance of beef heifers in natural grassland under continuous and rotational grazing during the autumn-winter period. The treatments were distributed in a completely randomized design and conducted using the forage mass above eight cm and 50% of the leaf blades mass of tussocks. The animals were Brangus beef heifers with initial body weight of 258kg. The variables evaluated were available forage mass (FMa), leaf blades mass of tussocks (LBMt), real forage allowance (FAr), sward height of the lower stratum (HLS), crude protein (CP), neutral detergent fiber (NDF), organic matter digestibility (OMD), total digestible nutrients (TDN), average daily gain (ADG), body condition score (BCS), reproductive tract score (RTS) and stocking rate (SR). FMa, HLS, OMD and TDN decreased while FAr, CP and NDF were similar during the experimental period. The ADG was positive only at third experimental period while BCS, RTS and SR decreased over time. The natural grassland management under continuous and rotational grazing during the autumn-winter period, using the forage mass above 8cm and 50% of the leaf blades mass of tussocks, does not allow the adequate corporal development for breeding the beef heifers at 24 months old.