Effect of grazing severity on perennial ryegrass herbage production and sward structural characteristics throughout an entire grazing season

Abstract

The objective of this study, which was part of a larger grazing‐systems experiment, was to investigate the cumulative impact of three levels of grazing intensity on sward production, utilization and structural characteristics. Pastures were grazed by rotational stocking with Holstein–Friesian dairy cows from 10 February to 18 November 2009. Target post‐grazing heights were 4·5 to 5 cm (high; H), 4 to 4·5 cm (intermediate; I) and 3·5 to 4 cm (low; L). Detailed sward measurement were undertaken on 0·08 of each farmlet area. There were no significant treatment differences in herbage accumulated or in herbage harvested [mean 11·3 and 11·2 t dry matter (DM) ha−1 respectively]. Above the 3·5 cm horizon, H, I and L swards had 0·56, 0·62 and 0·67 of DM as leaf and 0·30, 0·23 and 0·21 of DM as stem respectively. As grazing severity increased, tiller density of grass species other than perennial ryegrass (PRG) decreased (from 3,350 to 2,780 and to 1771 tillers m−2 for H, I and L paddocks respectively) and the rejected area decreased (from 0·27 to 0·20 and to 0·10 for H, I and L paddocks respectively). These results indicate the importance of grazing management practice on sward structure and quality and endorse the concept of increased grazing severity as a strategy to maintain high‐quality grass throughout the grazing season. The findings are presented in the context of the need for intensive dairy production systems to provide greater quantities of high‐quality pasture over an extended grazing season, in response to policy changes with the abolition of EU milk quotas.

Comparison of perennial ryegrass,Lolium perenneL., ploidy and white clover,Trifolium repensL., inclusion for herbage production, utilization and nutritive value

“…Tetraploid and diploid swards in the current study were managed similarly, and postgrazing sward heights were maintained below 4.5 cm across the study, leading to similar total herbage DM production. Despite contrasting sward structures, both swards achieved a high level of herbage utilization, similar to that reported by McCarthy et al (2013) and Tuñon et al (2014).…”

The variation in morphology of perennial ryegrass cultivars throughout the grazing season and effects on organic matter digestibility

“…A tolerable amount of dead in sward is any amount that does not negatively affect animal production. The proportion of dead in the present study was less than previously reported, indicating that there was not an excessive amount of dead in the sward (Wims et al ., ; Tuñon et al ., ). The dead proportion in all cultivars remained stable throughout the year apart from an increase for Spelga in mid‐July and end‐July.…”

Evaluation of the effects of ewe prolificacy potential and stocking rate on herbage production, utilization, quality and sward morphology in a temperate grazing system

“…This demonstrates the positive effects of increasing SR and grazing severity on sward morphology and daily herbage growth rates, despite greater pre‐grazing herbage masses above the target PGSH. This improvement in sward morphology can be primarily attributed to the lower PGSH and increased penetration of light into the MSR and HSR swards (Tuñon et al., ) and highlights the potential to graze at higher SR and lower into the grazing sward while maintaining a high content of leaf for grazing ewes and lambs. This in turn may assist in alleviating declines in animal performance associated with increasing SR.…”

“…The quality of pasture offered to grazing animals plays a vital role in determining herbage utilization and animal performance within a grazing system (McCarthy et al, 2012). Increasing SR and grazing severity are commonly associated with improved sward quality (Lee, Donaghy, & Roche, 2008;Tuñon et al, 2013). A study by Macdonald et al (2008) observed an increase in herbage OMD and energy content but a quadratic decline in herbage NDF and ADF as both SR and grazing severity increased.…”