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Iger-2003 26/6/2003 9:02 AM Page 31 I G E R I N N O VA T I O N S 2003 New Methods for Identification and Evaluation of Intake Characteristics o f G r a s s Va r i e t i e s Robert Orr and James Cook Grass breeding and testing 30 Measuring grass intake potential 31 Correlation of intake with plant characteristics 31 Measuring bite mass 32 Iger-2003 26/6/2003 9:02 AM Page 32 2003 I G E R I N N O VA T I O N S NEW METHODS FOR IDENTIFICATION AND EVALUATION OF INTAKE CHARACTERISTICS OF GRASS VARIETIES NEW METHODS FOR IDENTIFICATION AND EVALUATION OF INTAKE CHARACTERISTICS OF GRASS VARIETIES Robert Orr and James Cook P lant breeding priorities at IGER have gradually changed since the establishment of grass breeding at the former Welsh Plant Breeding Station in 1919, reflecting the changing needs of the farming community and society at large. The current Livestock production systems based on grazing offer a greater probability of long-term environmental sustainability than those based on high levels of concentrate supplementation or using housed animals. 30 interest in and emphasis on grazing is based, in part, Grass breeding and testing on a need to reduce the costs of livestock production Ideally, grass varieties should be bred to satisfy the in order to sustain a viable UK agriculture which can particular requirements of specific grazing systems operate in world markets. There is a need to produce and be evaluated using appropriate methodologies. meat and milk using welfare-friendly methods in This may not necessarily mean breeding for pastoral systems that consumers perceive to be increased intake and production, if it is at the 'natural'. There is also a need to minimise pollution. expense of other desirable traits. 26/6/2003 9:02 AM Page 33 I G E R I N N O VA T I O N S 2003 Measuring grass intake potential grasses consider 'simulated grazing' yield (measured In order to investigate the extent of any differences using frequent cutting), midseason digestibility, in grass intake potential under grazing, 15 ground cover, winter hardiness and disease intermediate-heading perennial ryegrass varieties, resistance. We propose that for varieties destined for with five replicate paddocks of each variety, were grazing use, identifying grazing-related traits would compared under continuous variable stocking facilitate the development of varieties for grazing management with sheep (Figure 5.1). Daily herbage with reliable selection criteria. Screening varieties intake was measured using alkane markers in grass for intake characteristics would also identify those and faeces, along with eating time which was which are best suited to particular grazing systems. measured using the IGER Behaviour Recorder (http://www.ultrasoundadvice.co.uk), and mean Large-scale grazing trials for routine variety intake rate was calculated. There were marked assessment are expensive in terms of land, animal differences (Figure 5.2) in intake rate amongst the and labour resources, and require quantities of seed diploid (d), tetraploid (t) and tetraploid hybrid (th) that may not be available in the early stages of varieties tested with some having values nearly 20 variety development. In addition, the potential value % higher or more than 20 % lower than the control of grass cultivars under grazing cannot necessarily variety for this heading group (Fennema). be drawn from feeding value assessments with ) (th rm xc el ( th) erE Ab Sto ) t) n( Tw ins (t e( t) sali Ro qu e( t) ion Fet Au bis d) d) a( elg Sp (d) Mo rga na ( (d) mo Gla n (d) ilo ri ( d) (d) (d) lan Ag Be lra describes some of the methods under development. erS sheep and cattle grazing at a field scale. This article Ab traits that are correlated with herbage intake by ov e subsequent evaluation for the identification of plant 0 -5 -10 -15 -20 -25 erE both during the breeding programme and the 15 10 5 Ab scale, low-cost screening methods that are required 20 erD At IGER, therefore, we are developing rapid, small- Intake rate % of Fennema housed animals. NEW METHODS FOR IDENTIFICATION AND EVALUATION OF INTAKE CHARACTERISTICS OF GRASS VARIETIES Current UK national testing procedures for forage Ab Iger-2003 Fig 5.2 Intake rate as a percentage of that for the control variety Fennema in diploid (d), tetraploid (t) and tetraploid hybrid (th) intermediate-heading perennial ryegrass varieties when grazed by sheep under continuous stocking management. Correlation of characteristics intake with plant To relate these differences in intake to plant characteristics which could be targeted in grass breeding programmes, intake measurements were Figure 5.1 Aerial view of the grass variety evaluation grazing trial with sheep made on five grass varieties (AberDove, Belramo, Glen, AberExcel and Twins) along with a suite of detailed chemical (digestibility, nitrogen and water 31 Iger-2003 26/6/2003 9:02 AM Page 34 I G E R I N N O VA T I O N S 2003 MORPHOLOGICAL MEASUREMENTS NEW METHODS FOR IDENTIFICATION AND EVALUATION OF INTAKE CHARACTERISTICS OF GRASS VARIETIES Morphological measurements included: extended tiller and sheath tube lengths; partition of herbage mass into leaf, pseudostem and dead fractions; number of tillers per unit ground area; leaf area index (leaf area per unit ground area); leaf weight per unit leaf area and the vertical distribution of leaves within the swards using an inclined point quadrat (Figure 5.3a, 5.3b). Fig 5.3a An inclined point quadrat with the pin mounted at 32.5o to the horizontal. The height of each contact with plant parts is recorded as the pin travels from the sward surface to the ground. This allows the calculation of a number of sward parameters. (mm) 60 - 65 AberDove Belramo Glen AberExcel Fig 5.4. Measuring leaf area using a planimeter. Twins 55 - 60 50 - 55 45 - 50 40 - 45 35 - 40 30 - 35 25 - 30 20 - 25 15 - 20 10 - 15 5 - 10 0-5 0.00 0.50 1.00 0.00 0.50 1.00 0.00 0.50 1.00 0.00 0.50 1.00 0.00 0.50 1.00 No. of leaf contacts per descent Fig 5.3b. Number of leaf contacts – this is a measure of leaf density and plant architecture obtained using an inclined point quadrat instrument. Fig 5.5.Measuring plant dimensions. soluble 32 carbohydrate concentrations) and Measuring bite mass morphological factors (see box above). Currently, short-term, small scale assessment There were significant differences between the five methodologies are being developed to measure bite contrasting varieties in ingestive and ruminative mass. Evaluations used boxes (dimensions 85 x 44 x behaviour, in plant morphology and in plant 14 cm) containing compost growing medium sown chemistry. An example of potentially important with either Belramo, Glen, AberExcel or Rosalin morphological data is shown in Figure 5.5b. Work is varieties at a sowing rate of 1600 seeds m-2 (Figure now in progress to identify plant traits that are 5.6). The boxes were kept in a glasshouse and the correlated with grass intake. grass cut to 6 cm from the soil surface at 5 and 8 Iger-2003 26/6/2003 9:02 AM Page 35 I G E R I N N O VA T I O N S 2003 Fig 5.8 Measuring bite mass weeks after sowing. They were moved outdoors to an arena before each test, in which each variety was The tests were recorded on video and the actual offered to one of four yearling Simmental x Holstein number of bites was determined (Figure 5.8). The heifers 11 weeks after sowing in an experiment with heifers ate the grass readily from the boxes and the a Latin-square design. mean time between the 'before' and 'after' weighings Each box was weighed accurately (± 0.1 g) before was 8 min. A mean number of 51 g 3.9 bites was and after a period in which the heifer was allowed to taken. Bite mass tended to be higher for Glen than take approximately 50 bites (Figure 5.7). Samples of Belramo (diploids) and higher for AberExcel than the grasses were weighed, dried and then weighed Rosalin (tetraploids), similar to rankings for intake again in order to calculate bite mass (dry matter). rate when these varieties were grazed in the field by NEW METHODS FOR IDENTIFICATION AND EVALUATION OF INTAKE CHARACTERISTICS OF GRASS VARIETIES Fig 5.6 Sward boxes sown with ryegrass continuously-stocked sheep (Figure 5.2). The technique provided a relatively quick assessment of intake characteristics of the four grass varieties. In 2003, ingestive behaviour will be measured for groups of heifers rotationally stocked in 1-day paddocks on these same varieties and compared with data from the short-term methods. If successful, the methodologies developed in this project could be used by plant breeders and variety evaluators to identify useful genetic material and produce grass varieties optimised for grazing systems for a range of circumstances/managements. This work has been funded by DEFRA. Contact; [email protected] or [email protected] Fig 5.7 Weighing sward box 33