Effect of cattle grazing a species-rich mountain pasture under different stocking rates on the dynamics of diet selection and sward structure

Abstract

Although stocking rate is a key management variable influencing the structure and composition of pastures, only few studies have simultaneously analysed the seasonal patterns of pasture use by cattle, and the adjustments the animals make to maintain intake of a high-quality diet over the grazing season. Therefore, over a 3-year study, we recorded diet selection, plot use and impact of heifers on sward structure and quality under three different stocking rates (0.6, 1.0 and 1.4 livestock units (LU) per ha) in a species-rich mountain pasture of central France. Measurements were made on three occasions between early June and the end of September each year. Overall, heifers selected for bites dominated by legumes or forbs, and against reproductive grass, whatever the stocking rate or season. Selection for tall mixed (P , 0.05), short mixed (P , 0.05) and short pure grass bites (P , 0.01) was more pronounced in plots grazed at the lowest stocking rate. Although heifers' selection for short patches decreased at the end of the season (P , 0.001), they continued to graze previously grazed areas, thus exhibiting a typical 'patch grazing' pattern, with the animals that grazed at the lowest stocking rate tending to better maintain their selection for short patches in September (treatment 3 period: P 5 0.078). Neither diet quality nor individual animal performance were affected by the different stocking rate treatments despite high variability in the quantity and quality of herbage offered and differences in diet selection. However, at the 1.4 LU per ha stocking rate, the quantity of forage available per animal at the end of the season, 0.79 t dry matter (DM) per ha of green leaves with the median of sward height at 4.6 cm, approached levels limiting cattle's ability to compensate for the effects of increasing stocking rate. In plots grazed at 0.6 LU per ha, the total herbage biomass remained higher than 3 t DM per ha with more than 30% of plot area still covered by reproductive grass patches at the end of the grazing season, which in the medium term should affect the botanical composition of these pastures. Sward heterogeneity was high in plots grazed at 1.0 LU per ha, with sufficient herbage availability (1.1 t DM per ha of green leaves) to maintain animal performance, and more than 15% of plot area was kept at a reproductive stage at the end of the grazing season. Hence, it could represent the optimal balance to satisfy both livestock production and conservation management objectives.

Podolian beef production on pasture and in confinement

“…Accordingly, in response to high ambient temperature (Table 1) walking (P , 0.001) and standing (P , 0.05) were lower in summer, whereas inactivity was higher (P , 0.05). Dumont et al (2007) observed that daily distance walked by cattle either increased or remained relatively constant over the grazing season for animals at a low stocking rate, which suggests that they kept on exploring the grazing area. However, these results are not necessarily in contrast with our results, as in this experiment the higher supplementation given to the grazing animals could have reduced the motivation to explore and ingest material of poor quality from pasture (Table 3).…”

“…According to this theory, grazing herbivores make a series of short-term decisions (e.g. about which plants or plant portions to select and how long to search) in order to ingest a diet adequate to satisfy their nutrient requirements for maintenance, growth and reproduction (Gordon, 1995;Dumont et al, 2007). No significant effect of source was detected for the other chemical components.…”

“…Therefore, as a consequence of a higher bite rate during spring, intake rate was higher in spring than in summer (P , 0.05). Cattle usually exhibit very typical selectivity patterns preferentially selecting against reproductive grass patches (Wallis De Vries and Daleboudt, 1994;Dumont et al, 2007), especially as these become more mature (Ginane et al, 2003). Herbage height tended (P , 0.10) to be higher in summer.…”

Screening of plants from diversified natural grasslands for their potential to combine high digestibility, and low methane and ammonia production

“…Besides a number of ecosystem services, grassland plant diversity helps to strengthen the resilience of ruminant production by securing the feeding system against seasonal and long-term climatic variability, so maintaining animal performance (Dumont et al, 2007). Plants from diversified grasslands can potentially contain bioactive compounds such as secondary metabolites that may interfere, especially with methane production (Patra and Saxena, 2010) and proteolysis in the rumen (Selje et al, 2007).…”

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

“…However, an increase in sward height by means of this management may result in a decrease in herbage digestibility (Hirata, 1993;Dumont et al, 2007;Da Silva et al, 2013), because infrequent or lenient defoliation allows the sward to accumulate low-quality materials (e.g. aged leaves, stems and dead material; Hirata and Ueno, 1993;Hirata et al, 2010a).…”