The multi-year cumulative effects of alternative stocking rate and grazing management practices on pasture productivity and utilization efficiency

Abstract

The production and utilization of increased quantities of high quality pasture is of paramount importance in pasture-based milk production systems. The objective of this study was to evaluate the cumulative effects of alternative integrated grazing strategies, incorporating alternative stocking rate (SR) and grazing severities, on pasture productivity and grazing efficiency over multiple years within farm systems using perennial ryegrass dominant pastures. Three whole-farm SR treatments were compared over 4 complete grazing seasons (2009 to 2012 inclusive): low (2.51 cows/ha; LSR), medium (2.92 cows/ha; MSR), and high (3.28 cows/ha; HSR). Each system had its own farmlet containing 18 paddocks and remained on the same treatment for the duration of the study. Stocking rate had a significant effect on all grazing variables with the exception of soil fertility status and sward density. Increased SR resulted in increased total annual net pasture accumulation, improved sward nutritive value, and increased grazed pasture utilization. Total annual net pasture accumulation was greatest in HSR [15,410kg of dry matter (DM)/ha], intermediate for MSR (14,992kg of DM/ha), and least for LSR (14,479kg of DM/ha) during the 4-yr study period. A linear effect of SR on net pasture accumulation was detected with an increase in net pasture accumulation of 1,164.4 (SE=432.7) kg of DM/ha for each 1 cow/ha increase in SR. Pregrazing pasture mass and height and postgrazing residual pasture mass and height were greatest for LSR, intermediate for the MSR, and lowest for the HSR. In comparison with the LSR, the imposition of a consistently increased grazing severity coupled with increased whole farm SR in MSR and HSR treatments arrested the decline in sward nutritive value, typically observed during mid-season. Incorporating the individual beneficial effects of SR on pasture accumulation, nutritive value, and utilization efficiency, total proportional energy (unité fourragère lait) utilization per hectare increased significantly with increasing SR (+0.026 and +0.081 for MSR and HSR, respectively). These results quantify the significant effect of grazing management practices on the feed production capability of modern perennial ryegrass pastures for intensive grazing dairy production systems. Furthermore, these results highlight the importance of consistently imposing grazing treatments over multiple years, and within integrated whole farm systems, to accurately assess the longer term effects of alternate grazing management practices on pasture productivity.

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

“…Although no SR effect was noted in the present study, the seasonal effects observed on sward quality in the current study follow a similar trend to that reported by McCarthy et al. (), with herbage CP, OMD and UFL highest in the spring period which is a possible explanation for the greater pre‐weaning CP content observed. The decrease in herbage OMD and UFL content from grazing rotation one to seven highlights the seasonal reductions in herbage quality, particularly from the spring to summer and into the autumn grazing period.…”

“…production, utilization and sward structure (Fariña, Garcia, Fulkerson, & Barchia, 2011;Macdonald et al, 2008). The grazing management applied in this study is similar to that of Macdonald et al (2008) and McCarthy et al (2016) for dairy systems and aimed to optimize herbage utilization within each SR, with a different target PGSH applied to each SR. Results therefore represent the likely implications on herbage of increasing ewe PP through selection of genetically higher PP ewe genotypes of a lighter mature live weight and increased SR when associated with an increase in grazing severity within a temperate grass-based lamb production system.…”

Review: New considerations to refine breeding objectives of dairy cows for increasing robustness and sustainability of grass-based milk production systems

“…Robust grazing cows: adapting to changes in feed supply and quality Economically robust grazing systems are defined by the high levels of pasture utilisation and a reduced exposure to external price fluctuations (Ramsbottom et al, 2015). Pasture utilisation is primarily determined by stocking rate (Macdonald et al, 2008a;McCarthy et al, 2016), with high stocking rates resulting in a high proportion of the pasture being directly harvested by the cow and low stocking rates resulting in either lower pasture utilisation or a greater proportion of pasture utilised via silage or hay. High stocking rates increase the likelihood of short-term feed deficits, particularly in the change between winter and spring and between autumn and winter.…”

External validation of the GrazeIn model of pasture dry matter intake and milk yield prediction for cows managed at different calving dates and stocking rates

“…A recent review of several SR experiments, for which there was no additional supplement fed at the highest SR, reported a 0.20 increase in milk production per ha arising from a one cow per ha increase in SR (McCarthy et al, 2011). In addition to SR, CD is an important determinant of feed utilization through its impact on the alignment between cow requirements and pasture supply (McCarthy et al, 2013), and altering the mean CD may have a relevant role in reducing the reliance of dairy farms on purchased feeds, particularly at high SR in early lactation (McCarthy et al, 2016). However, few studies (McCarthy et al, 2012a,b;2014) have attempted to quantify the effect of mean CD in spring on PDMI and MY or elucidate any potential interactions with SR.…”

“…Productivity within such grazing dairy systems depends on achieving a balance between the competing objectives of high pasture dry matter intake (PDMI) and milk yield (MY) per animal by maximizing pasture production per hectare, sward quality and pasture utilization (McCarthy et al, 2014;2016). This increase in milk production may be achieved by an increase in stocking rate (SR) in conjunction with the optimization of mean calving date (CD) at farm level (Dillon et al, 2008).…”