Short-term foraging dynamics of cattle grazing swards with different canopy structures1

Abstract

The objective of the present experiment was to describe the sward canopy structures of 3 different wheat (Triticum aestivum L.) pastures and relate them to short-term herbage intake rate and foraging dynamics by steers. Pastures were sampled for leaf and stem fractions at the bottom, middle, and top canopy strata. Sward surface heights and tiller and bulk densities were measured. Herbage was separated into stem and leaf, and leaves were then ranked phenologically. Three steers grazed (grazing sessions) 3 different pastures in a Latin square design. Ruminal contents were emptied and weighed before and after grazing sessions to assess herbage intake rate and bite mass. All grazing sessions were video recorded and analyzed for feeding stations (eating steps demarking the potential area of herbage consumption), bites per feeding station, and feeding stations per minute. Bite depth, bite area, and area grazed per feeding station were calculated. Morphological components and tiller density did not differ (P > 0.05) between the pastures, but sward surface height (P < 0.05) and leaf proportions in the middle and top canopy strata did differ. The herbage intake rate, bite mass, and bite area differed between treatments (P < 0.05). Steers grazing the tallest pasture with the greatest leaf accessibility ate faster, navigated slower, and grazed more efficiently (P < 0.05). The area grazed per feeding station differed between treatments (P < 0.05), being 87% for the tallest pasture with the greatest leaf accessibility and the least, 31%, for the pasture with the least leaf accessibility. Pastures with greater leaf accessibility may lead grazing cattle to reach the same herbage intake amount in less time while grazing more efficiently per unit area. Therefore, it may be logical to reduce the area and time allocations in pastures with taller swards where a leafy upper canopy stratum is found.

Foraging behavior and ruminal fermentation of dairy cows grazing ryegrass pasture alone or with white clover

“…This result shows that under strip-grazing management the time spent grazing is a poor indicator of the intensity of ruminal fermentation, which could be associated to sward structural traits and to their effects on the intake rate (Baumont et al, 2004) and the chemical composition of herbage (Noziere et al, 2011). Under rotational stocking, the influence of sward height and of the leaf/stem ratio on bite mass is more highly correlated with green leaf mass than with sward surface height or total herbage mass (Gregorini et al, 2009). Likewise, the intake rate declines progressively as leaves are removed, and the pseudostem corresponds to a greater proportion of the ingested material (Drescher et al, 2006).…”

“…This reduction could be associated to a lower intake rate (Gregorini et al, 2009) and to a lower proportion of green leaf at the end of the paddock in the oldest swards. These data are in agreement with Williams et al (2005), who concluded that the lower rumen fluid pH level observed was a function of the higher intake rate of cows grazing at high herbage allowance.…”

“…Changes in ingestive behavior with a reduction in sward height have been associated to short-term adaptations, such as bite mass and intake rate reductions (Gregorini et al, 2009). In pure legume swards, higher intake rates may be related to differences in the morphological composition of the defoliated strata, when compared to ryegrass swards (Chapman et al, 2007).…”

Seasonal and interannual variations in feeding station behavior of cattle: effects of sward and meteorological conditions

“…The animal is considered to move to a new feeding station at the cost of taking steps when intake rate from the current feeding station falls below the threshold level under repeated bites (Searle et al, 2005;Gregorini et al, 2011). Bite number, residence time and intake per feeding station, feeding station number per unit foraging time and step number between feeding stations are major feeding station behavior variables, which reflect profitability or unprofitability of feeding stations (Ruyle and Dwyer, 1985;El Aich et al, 1989;Roguet et al, 1998b;Gregorini et al, 2007Gregorini et al, , 2009Gregorini et al, and 2011Hirata et al, 2008;Shingu et al, 2010). The cost-benefit concept of the feeding station behavior is useful for a better understanding of foraging behavior of animals (Roguet et al, 1998b) and adjusting management strategies of various grazing systems ranging from an intensively managed small paddock of a sown pasture to an extensive rangeland across a landscape (e.g.…”

“…Ruyle and Dwyer, 1985;El Aich et al, 1989;Gregorini et al, 2011). However, previous studies have focused mainly on relatively short-term (<1 day to about 30 days) variations in feeding station behavior in order to investigate the effects of forage availability (Ruyle and Dwyer, 1985;Roguet et al, 1998b), sward structure (Gregorini et al, 2009), plant species (Hirata et al, 2008), grazing management (Gregorini et al, 2011), animal species (Shingu et al, 2010) and rumen fill (Gregorini et al, 2007). Relatively little information has been reported on how grazing animals modify feeding station behavior seasonally and interannually in response to varying environmental conditions (El Aich et al, 1989;Jiang and Hudson, 1993).…”