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Understanding factors associated with grazing efficiency of perennial ryegrass
T. Tubritt, N. Byrne, T. Gilliland, Luc Delaby, D. Cummins, M. O’Donovan
To cite this version:
T. Tubritt, N. Byrne, T. Gilliland, Luc Delaby, D. Cummins, et al.. Understanding factors associ- ated with grazing efficiency of perennial ryegrass. 10. International Symposium on the Nutrition of Herbivores (ISNH), Sep 2018, Clermont-Ferrand, France. �hal-02165424�
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Session 5: Feed resources and sustainable dietsUnderstanding factors associated with grazing efficiency of perennial ryegrass
Tomas Tubritt1,2, Nicky Byrne1,2, Trevor Gilliland2,3, Luc Delaby4, David Cummins5, Michael O'Donovan1
1Teagasc, Animal and Grassland Research and Innovation Centre, Moorepark, Fermoy, Co. Cork, Ireland, 2Institute of Global Food Security, Queen's University Belfast, Belfast, UK, 3Agri-food and Biosciences Institute, Large Park, Hillborough, UK, 4INRA, UMR production du lait,, 35590 St. Gilles, France, 5Department of Agriculture, Food and the Marine, Crop Evaluation and Certification Division, Ballyderown Farm, Kilworth, Co. Cork, Ireland
E-mail: ttubritt@hotmail.com
Take home message This study showed that differences in grazing efficiency exist between perennial ryegrass varieties and identified traits that could be used by breeders as selection criteria for superior grazing varieties.
Introduction Grazing efficiency refers to the ease at which grass swards are grazed to a desired post-grazing height typically <4 cm.
Increased grazing efficiency of grass varieties is desirable as it affects the ease of management of grass swards and influences the level of grass utilisation on-farm. Current mechanical simulated grazing variety evaluation protocols do not take grazing efficiency into account. The objective of this study was to identify traits within perennial ryegrass (PRG) (Lolium perenne) that influence grazing efficiency.
Material & methods Fifty-five perennial ryegrass varieties with various heading dates were sown in August 2014 in a randomised complete block design in 3 replicates (165 plots). Each variety was sown in a 3m x 7m plot. Plots were rotationally grazed by lactating dairy cows from February to October in both 2015 and 2016. On average sixty-five cows grazed the 0.95 ha paddock by block when herbage mass was estimated to be 1300 kg DM ha-1. Dung pats were removed from the plots after each grazing and a total of 252 kg N ha-1, 47 kg N ha-1 and 197 kg N ha-1was applied to plots over both years. Prior to grazing pre-height measurements were taken in each plot using a Jenquip rising plate meter. Post-grazing residual heights (PGRH) were taken as a measure of grazing efficiency of each variety. Three selected herbage samples were taken from each plot cut at 4 cm with a garden hand shears (ACCU 60, Husqvarna AB, Sweden). A sub-sample (0.1 kg) was oven dried at 60˚C to obtain a dry matter value for each plot. Near infrared spectroscopy (NIRS) was used to obtain dry matter digestibility (DMD), water soluble carbohydrates (WSC) and crude protein (CP). Sward morphological characteristics were also quantified by collecting tillers from each plot. Fifty tillers were used to measure tiller mass and the pre-grazing extended tiller height (ETH) and extended sheath height (ESH). Free leaf lamina (FLL) was calculated by subtracting ESH from ETH. Data was analysed using the PROC MIXED and PROC GLM procedure (SAS) with sward height, sward quality and sward morphological characteristics used as variables in the model.
Results Tetraploids achieved lower PGRH than diploids, 3.8cm vs 4.1cm (Table 1). This is likely due to the contributory effects of the traits examined. Pre-grazing height was shown to have a significant negative effect (p<0.001) on PGRH and while tetraploids achieved lower PGRH, more herbage (0.3cm) was also removed from this group. FLL (+1.5), tiller mass (+0.02), DMD (13.4 g kg DM-1) and CP (+2.4 g kg DM-1) was greater for tetraploids than diploids and these characteristics were shown to have a significant positive effect (p<0.001) on grazing efficiency. FLL is a trait of interest as it is a reliable trait that is easily measured. Therefore, it is a trait that could be selected for improved grazing efficiency. Increased tiller mass is indicative of reduced tiller density due to less competition between plants for resources. It is easier for cows to graze such swards as reduced bulk density reduces the shear strength required to graze the sward. Swards with increased levels of green leaf, DMD and CP are shown to have greater grazing efficiency.
Table 1 Sward characteristic differences between ploidy and heading date groups under animal grazing.
Ploidy Heading date
Trait Diploid Tetraploid Significance Intermediate Late Significance s.e
Herbage removed 5.1 5.4 *** 5.3 5.2 ** 0.03
Post-grazing characters
Post-Grazing Residual (cm+) 4.1 3.8 *** 3.9 4.0 ** 0.03
Pre-grazing Characters
Pre-Grazing height (cm+) 9.4 9.0 *** 9.3 9.2 ** 0.14
Free leaf lamina (cm) 19.0 20.5 *** 20.0 19.5 NS 0.16
Tiller mass (g DM-1) 0.06 0.08 *** 0.07 0.07 NS 0.001
DMD (g kg-1 DM) 819.8 833.2 *** 824.0 829.0 *** 1.75
CP (g kg-1 DM) 176.4 178.8 ** 178.3 176.8 NS 1.82
+ Compressed height P > 0.05 NS P < 0.05 * P < 0.01 ** P < 0.001 ***
Conclusion Differences between variety ploidy and heading dates for sward canopy and quality traits influenced the grazing efficiency of these varieties with ploidy having the greatest effect. Some of these characteristics like sward quality are already tested for in routine variety evaluations. Others like FLL and tiller mass are shown in this study to be easily selected for. It is therefore possible in the future for plant breeders to develop varieties with higher grazing efficiency by selecting varieties with improved performance in the traits identified in this study.
