Effect of pre-grazing herbage mass and daily herbage allowance on perennial ryegrass swards structure, pasture dry matter intake and milk performance of Holstein-Friesian dairy cows

A I Roca-Fernandez,J Curran,A Gonzalez-Rodriguez,M A O’Donovan

doi:10.5424/sjar/20110901-126-10

Abstract

To maximize milk output and milk solids per hectare from grazing dairy cows it is necessary to identify the level of grazing swards in order to achieve high pasture dry matter intake (PDMI). The aim of this study was to investigate the effect of pre-grazing herbage mass (HM) and daily herbage allowance (DHA) on perennial ryegrass (Lolium perenne L.) swards structure, PDMI and milk performance. Sixty-four spring-calving Holstein-Friesian dairy cows were balanced and randomly assigned to one of four (n = 16) grazing groups (LL, LH, HL and HH) in a 2 × 2 factorial design. The treatments consisted on two pre-grazing HM, low (L- 1,600 kg DM ha–1) or high (H- 2,400 kg DM ha–1) and two DHA, low (L- 15 kg DM cow–1day–1) or high (H- 20 kg DM cow–1 day–1). Swards structure, PDMI and milk performance were examined across the grazing season. The low HM groups completed 9.5 rotations of average 22 days length compared to 6.5 rotations of 32 days for the high HM groups. Herbage utilization was greater (p < 0.001) when animals offered the low DHA (98.0%) compared to the high DHA (89.9%). Stem and dead DM yield (> 4.0 cm) were lower (p < 0.001) for the low HM (221 and 170 kg ha–1, respectively) than for the high HM (388 and 303 kg ha–1, respectively). The high DHA had higher (p < 0.001) milk output (19.5 kg day–1) and milk solids (1.46 kg cow–1). The highest milk output per ha and per cow was achieved by LH, with low post-grazing residuals and high sward quality.

Highlights

Irish milk production systems are mainly pasturebased spring-calving dairy cows in order to maximize milk performance per hectare and per cow by increasing the organic matter digestibility (OMD) of the swards and the pasture dry matter intake (PDMI) of the cows (Stakelum and Dillon, 2007)
Understanding the important role that pre-grazing herbage mass (HM) and daily herbage allowance (DHA) plays on swards morphological composition, PDMI and milk performance of dairy cows at pasture is a key tool for a better knowledge of the interaction between swards and animals to improve future grassland management practices which can be implemented at farm level with the aim of reducing feeding cost of production and increasing both swards and milk quality and quantity
In the current research a more approximated situation to the main effects of grazing perennial ryegrass swards with different HM and DHA has been realized with the aim of establishing the sward canopy response and milk output per ha of springcalving dairy cows throughout the grazing season, which can be really extrapolated in the future to on farm grazing management system

Summary

Introduction

Irish milk production systems are mainly pasturebased spring-calving dairy cows in order to maximize milk performance per hectare (ha) and per cow by increasing the organic matter digestibility (OMD) of the swards and the pasture dry matter intake (PDMI) of the cows (Stakelum and Dillon, 2007). With the abolition of European milk quotas in 2015 and the feeding costs projected to rise, the major purpose for the Irish dairy industry is to increase the efficiency use of grazed grass in the diet of the lactating dairy cows (McEvoy et al, 2009). Understanding the important role that pre-grazing herbage mass (HM) and daily herbage allowance (DHA) plays on swards morphological composition, PDMI and milk performance of dairy cows at pasture is a key tool for a better knowledge of the interaction between swards and animals to improve future grassland management practices which can be implemented at farm level with the aim of reducing feeding cost of production and increasing both swards and milk quality and quantity. Maintaining a proper balance between optimizing dairy cows’ milk performance and improving swards feeding value is a dual purpose for using more efficiently farm resources and to increase profitability of sustainable dairy systems worldwide (Kennedy et al, 2007; González et al, 2008; McEvoy et al, 2009; Roca et al, 2009)

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