Item

Evaluation of perennial ryegrass cultivars for dairy production under different pasture management

Chen, Ao
Date
2017
Type
Thesis
Fields of Research
ANZSRC::0702 Animal Production , ANZSRC::070306 Crop and Pasture Nutrition
Abstract
The main objective of this thesis was to evaluate perennial ryegrass (Lolium perenne L.) cultivars for dairy production under different pasture management. Five experiments were conducted in Canterbury, New Zealand to evaluate perennial ryegrass in terms of morphology (experiment 1), nutritive value (experiments 1 and 2), rumen degradation (experiment 3), dietary preference (experiment 4) and milk production (experiment 5). Pasture management included growing perennial ryegrass cultivars with and without white clover (Trifolium repens L.) (experiments 1, 2, 3 and 4) and defoliating at different times of day (experiments 2 and 5) during pasture regrowth (experiment 2). In experiment 1, morphology and nutritive value of eight perennial ryegrass cultivars (AberMagic, Alto, Base, Bealey, Commando, Kamo, One50 and Prospect) growing with and without white clover were evaluated in a split-plot design at three phenological stages (pre-heading vegetative, reproductive and post-flowering vegetative). Pastures were managed under dairy grazing with irrigation and the annual nitrogen (N) fertiliser application rate was 325 kg N/ha. Compared with diploid cultivars, the tetraploid cultivars, Base and Bealey, had less dead material proportion (16.0% vs. 18.0% at the pre-heading vegetative stage; 22.0% vs. 27.0% at post-flowering vegetative stage) and greater lamina proportion (51.7% vs. 45.1% at the pre-heading vegetative stage; 55.0% vs. 50.7% at post-flowering vegetative stage) at the vegetative stages. The high-sugar diploid cultivar, AberMagic, had the greatest water-soluble carbohydrates (WSC) concentration at all stages in both lamina and pseudostem. Organic matter digestibility in dry matter (DOMD) was greater in Base, Bealey and AberMagic (mean = 75.9%) than other cultivars (mean = 73.8%). However, the differences in morphology was not the root cause of the variation in chemical composition and digestibility among cultivars. White clover had little effect on morphology of perennial ryegrass but significantly increased the crude protein (CP) concentration of accompanying perennial ryegrass at the pre-heading vegetative stage from 162 to 170 g/kg dry matter (DM). Interactions between perennial ryegrass cultivar and the presence of white clover were found for herbage WSC, acid detergent fibre (ADF) and neutral detergent fibre (NDF) concentrations and DOMD at the reproductive stage only. In experiment 2, herbage nutritive value variation of three perennial ryegrass cultivars (AberMagic, Bealey and Prospect) harvested at different times of day (from sunrise to sunset) during pasture regrowth (from 7 to 28 days after defoliation) was evaluated in monocultures and mixtures with white clover. AberMagic had a greater WSC concentration (162 g/kg DM) than Bealey (144 g/kg DM) and Prospect (112 g/kg DM). White clover proportions in perennial ryegrass swards (4 cm above ground level) increased during pasture regrowth from 6.5% on day 7 to 13.8% on day 28. The presence of white clover led to a greater overall herbage CP concentration (260 vs. 286 g/kg DM) and a lower NDF concentration (421 vs. 397 g/kg DM) in all cultivars. Herbage WSC concentration increased from 87 to 186 g/kg DM during the 4-week regrowth and was greater in the herbage harvested at sunset (180 g/kg DM) than sunrise (93 g/kg DM). In contrast, herbage CP concentration decreased during pasture regrowth from 292 g/kg DM to 242 g/kg DM and was lower in the herbage harvested at sunset (263 g/kg DM) than sunrise (293 g/kg DM). Herbage NDF concentration increased during pasture regrowth from 394 g/kg DM to 436 g/kg DM but dropped during the day from 439 g/kg DM to 378 g/kg DM. DOMD showed an opposite pattern to the NDF concentration, decreasing during pasture regrowth from 81.4% to 75.1% and increasing during the day from 76.4% to 81.2%. The interaction between perennial ryegrass cultivar and growth stage indicated that the cultivar ranking by CP and NDF concentration and DOMD changed during pasture regrowth and the differences in the WSC concentration among perennial ryegrass cultivars increased as regrowth proceeded. In experiment 3, four rumen-fistulated Friesian × Jersey dairy cows were used in two Latin square designs to investigate in sacco rumen degradation characteristics of perennial ryegrass cultivars in monocultures and in mixtures with white clover at different proportions. Perennial ryegrass cultivars included AberMagic, Bealey and Prospect, and white clover proportions in the mixtures were 0%, 16.7%, 33.3% and 100% on a fresh weight basis. The tetraploid cultivar, Bealey, had a greater soluble fraction a and a faster insoluble-degradable fraction b of both DM (0.305 and 0.621/h, respectively) and organic matter (OM, 0.280 and 0.647/h, respectively). Regarding CP degradation, Prospect had a greater soluble fraction, a (0.132), than AberMagic (0.082) and Bealey (0.062). Bealey had the lowest accumulative and instantaneous N release rate relative to OM disappearance, indicating it had the best rumen N/energy balance and synchrony among cultivars. As white clover had a greater effective degradability of CP (76.6% vs. 60.5%) and effective rumen degradable protein (ERDP) concentration than perennial ryegrass (237 vs. 118 g/kg DM), the effective degradability and ERDP concentration of the mixtures increased proportionally as white clover proportion increased. Consequently, white clover exerted a negative effect on rumen N/energy balance and synchrony. However, the impact was limited when the white clover proportion was low (16.7% on a fresh weight basis). In the mixtures, white clover interacted with perennial ryegrass for DM and OM predicted potential rumen degradability but did not the effective degradabilities. In experiment 4, dietary preference and selection of dairy cows for eight perennial ryegrass cultivars (AberMagic, Alto, Base, Bealey, Commando, Kamo, One50 and Prospect) growing with and without white clover was examined in a split-plot design at three phenological stages (pre-heading vegetative, reproductive and post-flowering vegetative). The dietary preference was defined as the decreasing rate of sward surface height at the beginning of grazing with minimum environmental constrains. The selection index was calculated based on pre-grazing herbage mass availability and post-grazing herbage mass residual of each cultivar. Results showed that the tetraploid perennial ryegrass cultivars, Base and Bealey, and the high-sugar diploid cultivar, AberMagic, were most preferred and selected by dairy cows. The proportion of perennial ryegrass, herbage WSC concentration and DOMD were positively correlated with dietary preference and selection indices, while negative correlations were found with the proportion of dead material and herbage ADF and NDF concentration. Although white clover had limited effect on sward structure and morphology of perennial ryegrass pastures, its presence (4.9% to 6.8% on a DM basis above ground level) increased overall herbage CP concentration (154 vs. 171 g/kg DM at pre-heading vegetative stage; 230 vs. 249 g/kg DM at post-flowering vegetative stage). The interaction between the presence of white clover and perennial ryegrass cultivar for dietary preference index indicated that the presence of white clover reduced the differences in dietary preference for perennial ryegrass cultivars. However, it did not lead to a significant re-ranking of cultivars preference order. In experiment 5, the effect of perennial ryegrass cultivar (AberMagic and Prospect) and the timing of herbage allocation (in the morning at 0830 h or afternoon at 1630h ) on herbage nutritive value and milk production of mid-lactation dairy cows were examined in a randomised block design. Twelve groups of four Friesian × Jersey cows were allocated to three replicates of four treatments over 10 days. There were no significant differences in sward structure and morphological characteristics between cultivars, except Prospect having a lower average tiller mass (43.1 mg DM/tiller) than AberMagic (48.4 mg DM/tiller). The concentration of WSC and DOMD was greater in AberMagic (180 g/kg DM, 74.2%) than Prospect (153 g/kg DM, 71.4%). Herbage DM percentage, WSC concentration and DOMD were lower in the morning compared with in the afternoon (22.3% vs. 18.8%; 154 vs. 179 g/kg DM; 72.1% vs. 73.5%). Herbage DM intake (mean = 12.0 kg/cow/day), milk yield (mean = 17.2 kg/cow/day) and milksolids yield (mean = 1.60 kg/cow/day) did not differ significantly among treatments. Milk urea nitrogen (MUN) concentration decreased when Prospect was allocated in the afternoon compared with in the morning (8.39 vs. 9.33 mmol/L), while MUN concentration remained similar whether AberMagic was allocated in the morning or afternoon (8.95 vs. 8.96 mmol/L). This interaction suggested that the effects of allocation timing may potentially be different for different perennial ryegrass cultivars. Pasture management exerted more pronounced and consistent effects than the effects of perennial ryegrass cultivar on herbage nutritive value. Interactions were found between perennial ryegrass cultivar and mangement for herbage nutritive value (the regrowth stage) and dietary preference (the presence of white clover). Therefore, pasture management could potentially be a more effective way to manipulate herbage nutritive value than perennial ryegrass cultivar. Additionally, the evaluations of perennial ryegrass cultivars should be conducted under a defined and consistent condition to exclude the management effects and cultivar × management interactions for herbage nutritive value. Further, in order to achieve a higher herbage feeding value, management could be adjusted to benefit a particular cultivar, and cultivars, in turn, could be selected to fit a certain management system better.
Source DOI
Rights
https://researcharchive.lincoln.ac.nz/pages/rights
Creative Commons Rights
Access Rights