The influence of sward canopy structure on foraging decisions by grazing cattle. I. Patch selection

Abstract

Patch selection by grazing dairy cows in response to simultaneous variation in combinations of sward structural characteristics was examined in three experiments in which four mature dairy cows were offered a choice of patches (typically 0.9 m × 0.9 m) of perennial ryegrass (Lolium perenne) presented in a linear arrangement. Treatments involved combinations of variations in sward height, stubble height and/or depth of regrowth, prepared by preliminary cutting treatments. They were arranged in balanced sets of four to nine treatments, which were arranged in linear sequences of eighteen to twenty‐seven patches. Within experiments, sequences were balanced across replicate sets of patches, which were grazed separately by individual cows. The number of bites removed and the residence time for each patch were highly correlated in all three experiments, and the results are reported using number of bites per patch as an estimator of foraging behaviour. In the first experiment, with vegetative swards, cows preferentially selected the tallest swards. When swards comprising reproductive stem were offered in Experiment 2, cows selectively grazed short‐stubble swards rather than tall‐stubble swards, although both offered a similar depth of regrowth. Cows did not exhibit preference for swards comprising the greatest quantity of leaf mass, indicating that the spatial distribution of plant components assumed greater importance. In the third experiment, the number of bites removed increased with increasing depth of regrowth, and was negatively correlated with sward height. The three patch‐appraisal cues investigated were broadly ranked in order of importance as (i) depth of regrowth, (ii) sward maturity and (iii) sward height. There was no evidence, at least at a short temporal scale, that patch behaviour was influenced by conditions in adjacent patches, suggesting that the cows assessed grazing opportunities on a patch‐by‐patch basis.

Características do processo de ingestão de forragem por novilhas holandesas em pastagens de capim-mombaça

“…A redução na taxa de bocados com o aumento da altura do dossel também foi registrada por Griffiths et al (2003) e pode ser explicada pelo aumento significativo no tempo de formação de bocados maiores, que variou de 1,95 a 3,99 segundos neste experimento (Figura 1d), ou seja, houve acréscimo de 100% no tempo para realização de cada bocado entre a menor e a maior altura avaliada, incremento superior ao de 40% verificado por Carvalho et al (2001a), em pastagem de capim-tanzânia pastejada por ovinos.…”

Canopy structure, ingestive behavior and displacement patterns of beef heifers grazing warm-season pastures

“…There was a correlation of number of feeding station with LSR of 30-45 cm stratum (ρ=0.88; P=0.0213) and canopy height (ρ=0.44; P=0.0015) in Coastcross. These correlations show that more important than the total availability of forage or the presence of leaf lamina is the proportion of leaf lamina allowance and the vertical architecture of the sward (Griffiths et al, 2003). According these authors, the spatial distribution of leaf lamina was more important than leaf lamina mass, highlighting the importance of the structural composition of the grazed horizon.…”

“…The morphological composition per strata of sward (Stobbs, 1975) was evaluated on three areas of the sward in each experimental unit. The stocking adjustment was made through forage disappearance method (Heringer and Carvalho, 2002). The considered structural descriptors of the sward were: forage mass (kg of DM/ha), leaf lamina mass and stem mass (kg of DM/ha), canopy height (cm), forage accumulation rate (kg of DM/ha), forage allowance (kg DM/100 kg BW), leaf lamina allowance (kg DM/100 kg BW) and average leaf lamina:stem ratio and per strata of the sward (0-15cm; 15-30cm; 30-45cm; >45cm).…”

Padrões de deslocamento e procura por forragem de novilhas leiteiras em pastagem de capim-mombaça

“…No entanto, esse mecanismo é controverso na literatura pois, conforme Trevisan et al (2003) e Griffiths et al (2003a), mais que a massa de forragem disponível, a distribuição das Figura 2 -Relação altura do dossel (cm) × número de passos entre estações alimentares de novilhas holandesas em pastagem de capim-mombaça. Passos entre estações alimentares…”

“…Mesmo em sistemas mais intensivos de produção, em que a oportunidade de utilização dessas estratégias é limitada, os animais escolhem em curto prazo (Griffiths et al, 2003a) o local onde pastejar e onde efetuar um simples bocado.…”