Ryegrass-based Pasture Research Articles

Effect of animal and diet parameters on methane emissions for pasture-fed cattle

Context Estimates of enteric methane emissions for agricultural emissions trading schemes or national inventories can be a simple single emission factor, but the accuracy of the predictions may be affected by other diet- and animal-related parameters. Aims Determine the animal and dietary factors that affect methane yield (methane per unit of dry-matter intake) in pasture-fed cattle. Methods Methane emissions and dry-matter intake (DMI) of cattle of various ages and in different physiological stages that were fed different-quality fresh-cut pastures were quantified in respiration chambers. The animals used in the various trials were post-weaned calves, heifers and steers of various ages and some older lactating dairy cows. Diet quality of the pastures offered was determined using near-infrared spectroscopy. Mixed linear modelling was used to assess the impacts of animal and diet parameters on methane emissions. Key results Our results indicated that diet quality does not have a major effect on methane production. For individual composition parameters, the correlation (Pearson’s r) with methane production was less than 0.25. Only estimates of metabolisable energy (ME) content showed a higher correlation (r = 0.43). However, despite this correlation, ME, like the other diet composition variables, was not a useful parameter to predict daily methane production, as indicated by the Akaike’s information criterion (AICc). Including data on concentrate supplementation at a level of 30% of the DMI did not improve the prediction of methane production. The resulting model indicated that besides DMI, bodyweight, physiological state and sex significantly affected methane production. Methane production was mostly explained by DMI. This was illustrated by the observation that when methane production is expressed per kilogram DMI (methane yield, g kg−1 DMI) none of the diet or animal related characteristics showed a significant correlation with methane yield. The model performed well, but needs to be validated with an independent dataset. Conclusions For ryegrass-based pasture dry-matter intake is the single most important factor that affects methane yield, while pasture composition has no effect and animal-related factors such as physiological stage and age only appear to modulate methane emissions. Implications Our findings have implications for methane accounting and national inventories in pastoral agricultural systems, which account for the majority of ruminant production systems.

Substituting ryegrass-based pasture with graded levels of forage rape in the diet of lambs reduced post-feeding variation in methane emissions

The temporal profile of methane (CH4) emissions from ruminants is affected by feed composition and forage type. This study aimed to 1) describe and compare the post-feeding pattern of CH4 emissions from lambs fed fresh ryegrass substituted with graded levels of forage rape, and 2) to evaluate the association between the magnitude of the variation in CH4 emission patterns and organic fermentation products quantified in pre- and- post- feeding rumen content samples. Methane emissions were measured at approximately 6 min intervals in respiration chambers from 70 lambs (n = 14 per treatment) fed ryegrass only (FR0) or as a proportion, 0.25 forage rape + 0.75 ryegrass (FR25), 0.50 forage rape + 0.50 ryegrass (FR50), 0.75 forage rape + 0.25 ryegrass (FR75), and forage rape only (FR100). The magnitude of the variability in CH4 emissions was defined as the ratio of maximum to minimum CH4 emissions in a 24 h period. This ratio was correlated (P < 0.05) with the proportions of major short chain fatty acids, and calculated hydrogen (H2) available per unit of glucose fermented (H2/GEF), quantified in rumen content samples collected pre- and- post- feeding. The CH4 emission profile after each feeding followed an asymmetrical positively skewed shape for FR0 to FR75, but not in lambs fed FR100. The lowest CH4 emission rates were observed before morning feeding which was followed by a CH4 peak within the 2 h after feeding, and then the CH4 emissions decreased until the next feeding. In FR100 lambs, the CH4 emission rate was, unexpectedly, relatively constant after feeding, without any clear CH4 peaks. The magnitude of the variability in the CH4 emission rate increased when the pH of rumen contents and H2/GEF measured in pre-feeding samples decreased. Including forage rape at 0.75, or greater proportion, in the diet of lambs drastically changed the CH4 emissions pattern, likely due to a continuous low pH in the rumen which is detrimental for methanogenesis. In conclusion, the daily variation in CH4 emissions decreased with increasing forage rape inclusion in the diet of sheep and this was associated with a decreasing acetate proportion in the rumen liquid.

Effect of feeding fresh forage plantain (Plantago lanceolata) or ryegrass-based pasture on methane emissions, total-tract digestibility, and rumen fermentation of nonlactating dairy cows

Plantain (Plantago lanceolata) is an herb used to reduce the forage deficit of ryegrass-based pastures during the summer. This herb is being promoted for its reduced environmental impact in terms of nitrogen emissions, particularly reducing urinary nitrogen. However, the effect of plantain on emissions of enteric CH4, the main greenhouse gas produced from ruminant-based production systems, is not known. The aim of the present trial was to determine CH4 emissions and rumen fermentation characteristics of nonlactating dairy cows fed 100% plantain (PLT) or 100% perennial ryegrass (RG; Lolium perenne) in 2 experiments (E1 and E2). The forages were in a vegetative growth stage in E1 and were in a reproductive growth stage in E2. Methane emissions from 16 cows in each experiment were measured in respiration chambers for 2 d. Methane emissions per unit of dry matter intake (CH4 yield) were 15 and 28% less for cows fed PLT than those fed RG in E1 and E2, respectively. Dry matter digestibility of PLT was 7 and 27% less than that of RG in E1 and E2, respectively, and CH4 per unit of dry matter digested was similar for PLT and RG in both experiments. There were only minor (but some significant) differences in rumen fermentation characteristics between cows fed PLT and RG in both experiments. In conclusion, CH4 yield was lower for cows fed PLT compared with those fed RG in both experiments and this reduction was largely explained by the lesser dry matter digestibility of PLT.

Substituting ryegrass-based pasture with graded levels of forage rape in the diet of lambs decreases methane emissions and increases propionate, succinate, and primary alcohols in the rumen.

Feeding 100% forage rape to sheep consistently lowers methane emissions per unit of intake (CH4/DMI) compared to those fed 100% ryegrass pasture. However, forage rape is usually supplemented with other feeds, which might impact the mitigation potential provided by forage rape. The objective of this study was to determine the effect of substituting ryegrass with graded levels of forage rape in the diet of lambs on methane emissions and rumen fermentation characteristics. Seventy wether lambs (n = 14/treatment) were fed a ryegrass-based pasture substituted with 0%, 25%, 50%, 75%, and 100% of forage rape (Brassica napus; FR0, FR25, FR50, FR75, and FR100, respectively) on a dry matter basis. Methane emissions and dry matter intake were measured for 48 h in respiration chambers and a rumen fluid sample was collected. CH4/DMI decreased (P < 0.01) with increasing forage rape inclusion in the diet so that sheep fed FR100 and FR75 emitted 34% and 11% less, respectively, than those fed FR0. CH4/DMI differences for lambs fed FR25 and FR50 were much smaller (<6%) relative to FR0. The pH of rumen fluid decreased (P < 0.01) at higher levels of forage rape inclusion in the diet (FR75 and FR100) compared to low levels of inclusion (FR0, F25, and F50). The proportion of ruminal acetate was least in FR100 (30%) followed by FR75 (10%), FR50 (8%), and FR25 (4%) compared with FR0 (P < 0.001). The proportion of propionate plus succinate was greater for FR100 (+40%), FR75 (+28%), and FR50 (+29%) compared with FR0, with FR25 intermediate (P < 0.001). The methanol concentration, and ethanol and propanol proportions in rumen fluid were greater for FR100 compared with any other treatment (P < 0.001). In conclusion, CH4/DMI decreased at high levels of forage rape inclusion in the diet and especially feeding FR100 was associated with a pronounced shift in rumen fermentation profile, with a significant presence of succinate, ethanol, propanol, methanol, valerate, and caproate.

Progress towards delivering high metabolisable energy ryegrass

A method developed at AgResearch to increase leaf fatty acids (FA) and plant growth called ‘High metabolizable energy’ (‘HME’) could elevate the nutritional quality and productivity of perennial ryegrass-based pastures. The industry strategy has been to perform HME ryegrass field trials offshore to test whether the herbage FA, gross energy (GE) and yield enhancing traits observed in containment translate into field swards. To complement the field testing programme, we have also characterised the growth and nutritional profile of HME miniswards under simulated grazing in containment. The results from one such trial are presented. The major changes measured in HME miniswards; increased FA (+0.8–1.4 %DW), increased GE (+0.3–0.5 MJ/kgDM), and generally similar herbage DW production, closely mirror data from field trials with hemizygous HME populations in the Midwest USA. Changes in other HME nutritional components were generally minor, although WSC was reduced late in the diurnal cycle. Secondary effects of HME on photosynthesis appear to be diminished in swards, suggesting that HME yield benefits may be limited to specific environment and management scenarios. The primary benefit of HME technology is thus expected to come from increasing the energy density of pasture, and animal feeding trials using homozygous HME material are now required.

Substituting a pasture-based diet with plantain (Plantago lanceolata) reduces nitrogen excreted in urine from dairy cows in late lactation.

Recent research has demonstrated that grazing cows fed diets including plantain (Plantago lanceolata) express reduced urinary nitrogen (UN) concentration relative to cows fed perennial ryegrass, while milk production is similar or improved. This study explored the effect of increased substitution of ryegrass-based pasture with plantain for cows fed ad libitum in late lactation on intake, nitrogen (N) excretion and partitioning. Sixteen mixed age (4.1 ± 0.5 y) multiparous Holstein-Friesian cows were randomly allocated to four dietary treatments, which comprised ryegrass only (RG), or ryegrass substituted with 15 (15PL), 30 (30PL) and 45% (45PL) plantain. In an incomplete cross over design cows were adapted to a dietary treatment over 14 days prior to a six-day measurement period, then reallocated to another dietary treatment for a second six-day measurement period following 14 days adaptation. Cows offered 45PL consumed 2.6 kg DM/day more than cows fed RG (P = 0.021). Milk and milk solids yield were greater (P < 0.01) when plantain comprised 30% of the diet or more. Daily mean urinary N (UN) concentration followed a quadratic response to increasing plantain content (R2 = 0.62; P < 0.001). Cows fed 30PL and 45PL excreted urine with 19 and 41% less N (g/100 g) respectively, relative to cows fed RG or 15PL. The mechanisms for reduced UN concentration of cows fed diets including plantain included dilution of urine through greater total daily urine volume and alteration of dietary N partitioning. Cows fed 45PL produced 9 L (~25%) more urine per day than cows on other diets; but between 0800 and 1600 h there was a progressive increase in the cumulative volume of urine as the percentage of plantain in the diet increased, due to increased urination frequency rather than individual urination volume which was similar between diets. Regression analyses indicated that cumulative urine volume was correlated with water intake (r = 0.61; P < 0.001), largely from water in the feed of the plantain diets. Nitrogen intake was similar across diets (545 ± 23 g N/cow/day) but N output in urine was reduced by 39 and 66 g/cow/d (15 and 25%) from cows fed 30PL and 45PL compared to those fed RG diets. Evaluation of N partitioning indicated that dietary N is partitioned away from urine and into milk and faeces when plantain is included in a ryegrass-based diet. The results confirm that at least 30% plantain in the diet is required to reduce urinary N excretion and concentration, without reducing dry matter intake or milk production.

The performance and profitability of plantain/clover pasture mixtures in East Coast farming systems

Yield and animal performance data from plantain/clover and resident ryegrass-based pastures were collected over several years from six properties on the East Coast of the North Island. This information was used in a FARMAX® model developed for a hypothetical farm based on data collected by the Beef + Lamb Economic Service. The hypothetical farm was 495 ha with 50 ha of flats used for silage and/or winter forage crop. The base model had a gross margin of $703/ha. The 50-ha flat block was modelled as if in a plantain rotation with two thirds in plantain and one third in annual ryegrass each year. The higher yields and better-quality feed on the plantain block improved animal performance and carcass weights. Early mating of one-year ewes for feeding on plantain provided a very high-returning enterprise. More ewes and lambs were killed early at heavier carcass weights with a premium before the onset of summer-dry conditions. This became a force multiplier across the entire farm as more feed was available for other stock and lamb carcass weights increased across the farm. Highest returns were generated by using the extra quality feed to increase ewe liveweights by 8 kg. Whilst ewe numbers had to be decreased, this was more than compensated for by the higher lambing percentage and greater number of lambs from mated hoggets. The combined effect was an increase in farm gross margin by around $200/ha and in farm returns of $100,000.

Excreta emissions in progeny of low and high enteric methane yield selection line sheep fed pasture of different qualities

Selection of sheep with low enteric methane (CH4) emissions is a greenhouse gas (GHG) mitigation option suitable for pastoral systems. However, the effect of breeding sheep with low enteric CH4 emissions on excreta output and associated CH4 and nitrous oxide (N2O) emissions and therefore total GHG emissions are not known. The objective of the current experiments were to determine excreta output, and estimate associated GHG emissions, from progeny of low and high enteric CH4 per unit of dry matter intake (DMI) selection line sheep (CH4/DMI). The animals were fed two qualities of cut perennial ryegrass-based pasture (very mature vs. vegetative, 12 animals per CH4/DMI line) in Exp. 1 and cut pasture in two repeated seasons (autumn and winter; 15 animals per CH4/DMI line × 2 seasons) in Exp. 2. Total faecal and urine output was determined on individual animals, followed by enteric CH4 emission measurements in respiration chambers. GHG emissions from urine (N2O) and faeces (CH4 and N2O) were estimated based on New Zealand Agricultural GHG Inventory methodology. There was no interaction between CH4/DMI selection line and diet quality in Exp. 1 or seasons in Exp.2. Total daily faecal output of DM, organic matter (OM) and neutral detergent fibre (NDF; all g/d) and associated calculated faecal CH4 emissions were greater for low compared to high CH4/DMI sheep in Exp. 1 (P < 0.05), while being similar between CH4/DMI selection lines in Exp. 2. Nitrogen (N) excretion and N partitioning into urine, faeces and body retention, and calculated excreta N emissions, were mostly similar between CH4/DMI selection line sheep in both experiments. Except, faecal N output (g/d and per unit of N intake) and associated calculated direct faecal N2O-N emissions (g/d) were greater in low compared to high CH4/DMI sheep in Exp. 1 (P < 0.05). Enteric CH4 emissions were numerically 8% less (P = 0.15) in Exp.1 and 10% less (P = 0.004) in Exp. 2 and total animal level GHG emissions (CH4 and N2O) were numerically 7% less (P = 0.21) in Exp. 1 and 8% less (P = 0.006) in Exp.2 for progeny of the low compared to the high CH4/DMI line sheep. In conclusion, the magnitude of difference in enteric CH4 (expressed as CO2-equivalent) between low and high CH4/DMI selection line sheep were still present when CH4 from faeces and N2O emissions from urine and faeces were also accounted for. The animal genetic traits were expressed independent of environmental factors, i.e. pasture quality and season.

Feeding a marine-based rumen buffer increases milk production and decreases time of low reticulo-rumen pH in grazing dairy cows offered perennial ryegrass-based pasture

Dairy cows grazing highly digestible perennial ryegrass-based pastures are reportedly susceptible to low rumen pH. This experiment investigates the effect of feeding a novel marine-based rumen buffering product on milk production, milk composition and reticulo-rumen pH in dairy cows grazing perennial ryegrass-based pasture supplemented with concentrates. Three primiparous and twenty-one multiparous spring calving dairy cows (58 ± 12.6 days in milk) were blocked by parity (3.2 ± 1.56) and pre-experimental milk yield (36.0 ± 6.55 kg) and randomly assigned to three experimental treatments in a three-period crossover-design experiment. Dietary treatments consisted of Control; 8 kg of a commercial cereal-based compound, BUF1; control diet +70 g of a novel marine-based buffer (a mix containing only calcified seaweed and a marine source of magnesium oxide: see detailed analysis provided) and BUF2; control +140 g of the same marine-based buffer in a changeover design experiment. Experimental periods lasted for 35 d with 21 d for diet adaptation and a 14 d measurement period. In-dwelling reticulo-rumen pH probes recorded reticulo-rumen pH and temperature during d 58–63 (Period 2) and d 93–98 (Period 3) of this experiment. Cows fed BUF1 and BUF2 showed an increased milk yield of 1.20 kg/d and 1.07 kg/d respectively when compared to the Control diet (P = 0.004 and P = 0.012). There were increases in energy corrected milk yield (ECM) of 1.53 kg/d (P = 0.02) and 3.5% and 4% fat corrected milk (FCM) of 1.87 kg/d and 1.76 kg/d, respectively (P = 0.012), when cows were fed BUF2 compared to cows fed the Control. Number of minutes per treatment per day at reticulo-rumen pH < 5.8 and < 6.0 was significantly greater for cows fed Control compared to cows fed BUF2 (P<0.001). Results of this experiment suggest that supplementation with a novel marine-based rumen buffering product increased milk production and reduced the amount of time the reticulo-rumen was below pH 5.8 and 6.0 in grazing dairy cows supplemented with a cereal-based concentrate.

Estimation of spatial and temporal variability of pasture growth and digestibility in grazing rotations coupling unmanned aerial vehicle (UAV) with crop simulation models.

Systematic monitoring of pasture quantity and quality is important to match the herd forage demand (pasture removal by grazing or harvest) to the supply of forage with adequate nutritive value. The aim of this research was to monitor, assess and manage changes in pasture growth, morphology and digestibility by integrating information from an Unmanned Aerial Vehicle (UAV) and two process-based models. The first model, Systems Approach to Land Use Sustainability (SALUS), is a process-based crop growth model used to predict pasture regrowth based on soil, climate, and management data. The second model, Morphogenetic and Digestibility of Pasture (MDP), uses paddock-scale values of herbage mass as input to predict leaf morphogenesis and forage nutritive value. Two field experiments were carried out on tall fescue- and ryegrass-based pastures under rotational grazing with lactating dairy cattle. The first experiment was conducted at plot scale and was used to calibrate the UAV and to test models. The second experiment was conducted at field scale and was used to test the UAV’s ability to predict pasture biomass under grazing rotation. The Normalized Difference Vegetation Index (NDVI) calculated from the UAV’s multispectral reflectance (n = 72) was strongly correlated (p < 0.001) to plot measurements of pasture biomass (R2 = 0.80) within the range of ~226 and 4208 kg DM ha-1. Moreover, there was no difference (root mean square error, RMSE < 500 kg DM ha-1) between biomass estimations by the UAV (1971±350 kg ha-1) and two conventional methods used as control, the C-Dax proximal sensor (2073±636 kg ha-1) and ruler (2017±530 kg ha-1). The UAV approach was capable of mapping at high resolution (6 cm) the spatial variability of pasture (16 ha). The integrated UAV-modeling approach properly predicted spatial and temporal changes in pasture biomass (RMSE = 509 kg DM ha-1, CCC = 0.94), leaf length (RMSE = 6.2 cm, CCC = 0.62), leaf stage (RMSE = 0.7 leaves, CCC = 0.65), neutral detergent fiber (RMSE = 3%, CCC = 0.71), digestibility of neutral detergent fiber (RMSE = 8%, CCC = 0.92) and digestibility of dry matter (RMSE = 5%, CCC = 0.93) with reasonable precision and accuracy. These findings therefore suggest potential for the present UAV-modeling approach for use as decision support tool to allocate animals based on spatially and temporally explicit predictions of pasture biomass and nutritive value.

Temporal fermentation and microbial community dynamics in rumens of sheep grazing a ryegrass-based pasture offered either in the morning or in the afternoon

Eight ruminally-fistulated wethers were used to examine the temporal effects of afternoon (PM; 1600h) v. morning (AM; 0800 h) allocation of fresh spring herbage from a perennial ryegrass (Lolium perenne L.)-based pasture on fermentation and microbial community dynamics. Herbage chemical composition was minimally affected by time of allocation, but daily mean ammonia concentrations were greater for the PM group. The 24-h pattern of ruminal fermentation (i.e. time of sampling relative to time of allocation), however, varied considerably for all fermentation variables (P⩽0.001). Most notably amongst ruminal fermentation characteristics, ammonia concentrations showed a substantial temporal variation; concentrations of ammonia were 1.7-, 2.0- and 2.2-fold greater in rumens of PM wethers at 4, 6 and 8h after allocation, respectively, compared with AM wethers. The relative abundances of archaeal and ciliate protozoal taxa were similar across allocation groups. In contrast, the relative abundances of members of the rumen bacterial community, like Prevotella 1 (P=0.04), Bacteroidales RF16 group (P=0.005) and Fibrobacter spp. (P=0.008) were greater for the AM group, whereas the relative abundance of Kandleria spp. was greater (P=0.04) for the PM group. Of these taxa, only Prevotella 1 (P=0.04) and Kandleria (P<0.001) showed a significant interaction between time of allocation and time of sampling relative to feed allocation. Relative abundances of Prevotella 1 were greater at 2h (P=0.05), 4h (P=0.003) and 6h (P=0.01) after AM allocation of new herbage, whereas relative abundances of Kandleria were greater at 2h (P=0.003) and 4h (P<0.001) after PM allocation. The early post-allocation rise in ammonia concentrations in PM rumens occurred simultaneously with sharp increases in the relative abundance of Kandleria spp. and with a decline in the relative abundance of Prevotella. All measures of fermentation and most microbial community composition data showed highly dynamic changes in concentrations and genus abundances, respectively, with substantial temporal changes occurring within the first 8h of allocating a new strip of herbage. The dynamic changes in the relative abundances of certain bacterial groups, in synchrony with a substantial diurnal variation in ammonia concentrations, has potential effects on the efficiency by which N is utilised by the grazing ruminant.

The effect of by-product inclusion and concentrate feeding rate on milk production and composition, pasture dry matter intake, and nitrogen excretion of mid-late lactation spring-calving cows grazing a perennial ryegrass-based pasture

Interest is growing in the use of by-products as economical sources of nutrients that complement grazed grass, particularly at times when grass supply is insufficient to meet the nutritional demands of lactating dairy cattle. The objective of this research was to assess the effect of the amount of by-product inclusion and concentrate feeding rate on pasture dry matter intake, milk production and composition, and N excretion from spring-calving cows grazing summer pasture during mid-late lactation. Forty-eight Holstein Friesian dairy cows were randomly assigned to 1 of 4 dietary treatments in a 2 × 2 factorial design. Cows were grazed in one group on a perennial ryegrass-based sward, with pelleted concentrates offered twice daily during milking over a 63-d experimental period. The dietary treatments were 3 kg of concentrate containing 35% by-products; 6 kg of concentrate containing 35% by-products; 3 kg of concentrate containing 95% by-products; and 6 kg of concentrate containing 95% by-products on a fresh matter basis. The by-products used were soybean hulls, palm kernel expeller, and maize dried distillers grains with solubles, included in equal proportions on a dry matter basis. Pasture dry matter intake (14.5 kg/d) was not affected by the amount of by-product inclusion or feeding rate. By-product inclusion had no effect on milk yield (27.1 kg/d) or milk solids (MS) yield (2.0 kg/d). Cows offered 6 kg of concentrate had a greater milk (+1.6 kg/d) and MS (+0.13 kg/d) yield, consumed more N (+0.08 kg/d), and excreted a lower proportion of N in the milk (0.25 vs. 0.27) and feces (0.39 vs. 0.41) and a higher proportion in the urine (0.39 vs. 0.32) compared with cows offered 3 kg of by-product-based concentrate. In conclusion, by-products can be included at up to 95% of the concentrate fed to cows grazing pasture without affecting pasture dry matter intake, milk production or composition, or N excretion. Cows offered 6 kg of concentrates produced more milk and MS than cows offered 3 kg but had higher urinary N excretion. Economics of this yield response will depend on milk and concentrate prices.

Digestion and nitrogen excretion by Holstein–Friesian cows in late lactation offered ryegrass-based pasture supplemented with fodder beet

Recent changes in New Zealand dairying have included incorporation of fodder beet (FB) into rations. The present trial explored the impact of substituting different proportions of ryegrass-based pasture with FB for cows fed ad libitum in late lactation. The objective was to measure effects of FB on intake, digestion and urinary nitrogen (N) excretion using 16 Holstein–Friesian cows with a permanent rumen fistula. Before the 9-day indoor measurement period, cows were adapted to feeding 0%, 20%, 40% or 60% FB (bulbs and tops) with medium quality ryegrass-based pasture (191 g CP and 517 g neutral detergent fibre (aNDF)/kg DM; DM digestibility 0.634) over 2 weeks. However, it became apparent that a diet of 60% FB was detrimental to cow health, with two cows developing acidosis. The allocation of FB was reduced and the actual intakes were 23% and 45% of DM intake during the trial. Feeding FB substantially reduced N intake and urinary N excretion. The lower level (23%) of FB resulted in greater DM digestibility, albeit with a small reduction in N and aNDF digestibility. However, the higher level (45%) of FB reduced N and aNDF digestibility by 7.1 and 12.1 percentage units respectively, relative to pasture. Daily creatinine excretion was lower than published measurements from cattle fed dry diets, and circadian variation in urinary N:creatinine ratios suggests a need for caution when attempting to predict daily urinary N excretion from spot samples.

Genetic parameters of methane emissions determined using portable accumulation chambers in lambs and ewes grazing pasture and genetic correlations with emissions determined in respiration chambers1

Methane (CH4) emission traits were previously found to be heritable and repeatable in sheep fed alfalfa pellets in respiration chambers (RC). More rapid screening methods are, however, required to increase genetic progress and to provide a cost-effective method to the farming industry for maintaining the generation of breeding values in the future. The objective of the current study was to determine CH4 and carbon dioxide (CO2) emissions using several 1-h portable accumulation chamber (PAC) measurements from lambs and again as ewes while grazing ryegrass-based pasture. Many animals with PAC measurements were also measured in RC while fed alfalfa pellets at 2.0 × maintenance metabolizable energy requirements (MEm). Heritability estimates from mixed models for CH4 and CO2 production (g/d) were 0.19 and 0.16, respectively, when measured using PAC with lambs; 0.20 and 0.27, respectively, when measured using PAC with ewes; and 0.23 and 0.34, respectively, when measured using RC with lambs. For measured gas traits, repeatabilities of measurements collected 14 d apart ranged from 0.33 to 0.55 for PAC (combined lambs and ewes) and were greater at 0.65 to 0.76 for the same traits measured using RC. Genetic correlations (rg) between PAC in lambs and ewes were 0.99 for CH4, 0.93 for CH4 + CO2, and 0.85 for CH4/(CH4 + CO2), suggesting that CH4 emissions in lambs and ewes are the same trait. Genetic correlations between PAC and RC measurements were lower, at 0.62 to 0.67 for CH4 and 0.41 to 0.42 for CH4 + CO2, likely reflecting different environmental conditions associated with the protocols used with the 2 measurement methods. The CH4/(CH4 + CO2) ratio was the most similar genetic trait measured using PAC (both lambs and ewes, 63% and 66% selection efficiency, respectively) compared with CH4 yield (g/kg DMI) measured using RC. These results suggest that PAC measurements have considerable value as a rapid low-cost method to estimate breeding values for CH4 emissions in sheep.

Milk yield and urinary-nitrogen excretion of dairy cows grazing forb pasture mixtures designed to reduce nitrogen leaching

The effect of including a mixture of forbs in a standard perennial ryegrass-white clover pasture, with or without Italian ryegrass was investigated in a two-period grazing study comparing urinary nitrogen (N) excretion and milk yield of dairy cows in late lactation. Forty-eight mixed age, Holstein Friesian x Jersey cows were assigned to replicated, balanced, groups of six and offered one of four pasture treatments. Pasture types were either a perennial ryegrass-based pasture (PRG) with white clover or a forb-containing mixed pasture (MIX) including perennial ryegrass, white clover, chicory, plantain and lucerne. A second factor was the inclusion of Italian ryegrass (PRG+I and MIX + I). During Period I, ten cows in each of the MIX and PRG treatments were fitted with urine sensors to measure urine N parameters (urination frequency, volume and N concentration). During Period II, milk yield was measured from cows on all four pasture types. In both the ryegrass and forb pasture types, legume content exceeded 30% of the DM and in forb pastures chicory and plantain accounted for over 30% of the DM. Italian ryegrass in the MIX + I and PRG+I was respectively 5% and 15% of the DM. Digestibility and crude protein was similar for all pasture types, but fibre content was lower for forb pastures. During Period I, there was no effect of pasture type on the amount of N per urination event (averaged 13gN/event) and daily urine-N excreted (190gN/cow/day). However, pasture type affected the diurnal pattern in urine-N excretion with MIX pastures having a lower urine N loading per event during the day and higher urine N loading at night compared with PRG pastures. During Period II, milk yield was greater for forb compared with ryegrass pasture types (1.66 vs 1.50kg MS/cow/d). There was no effect of Italian ryegrass on milk yield due to low botanical content. This study demonstrated that forb containing pastures altered the diurnal pattern in urine-N excretion and offers opportunities to mitigate N leaching from grazed pastures whilst supporting high milk production in late lactation.

Establishment year productivity, botanical composition and nutritive value of grass/lucerne/plantain dairy pasture mixtures

In the context of dairy grazing systems, pasture mixtures including tall fescue, lucerne and plantain have been identified by animal modelling as having potential to both improve milk production and reduce urinary nitrogen excretion. A grazed paddock-scale trial was established in the Waikato in September 2015 to test this in two short-term grazing trials including these species. This paper presents the pasture production, botanical composition and nutritive value data generated from four pasture mixtures sown in spring 2015 and sampled until autumn 2017 (18 months). The pasture mixtures represented a comparison between perennial ryegrass and tall fescue, with and without the herb narrow-leaved plantain. The inclusion of plantain in grass-lucerne mixtures had a positive effect on firstyear herbage dry matter (DM) production, by ~2.6 t DM/ha/year in ryegrass-based pastures and ~1.6 t DM/ ha/year in tall fescue-based pastures. Where plantain was included, the proportion of grass was reduced by more than half from autumn 2016 through to summer 2016-2017, while the proportion of lucerne was reduced to a lesser degree. The proportion of plantain was 35-70% through most of the first year, declining to

Milk fatty acid and protein profiles of late-lactation dairy cows as affected by time of allocation of a fresh strip of ryegrass-based pasture

Abstract Eighty late-lactation dairy cows were used to examine the effects of allocating a new strip of a perennial ryegrass-based sward in the morning (AM) or in the afternoon (PM) on milk fatty acid (FA) and protein profiles. Milk total polyunsaturated FA (PUFA) were greater from cows on AM herbage, whereas total saturated and monounsaturated FA (MUFA) were similar. Time of allocation only affected the milk protein α-casein, which was greater in milk from cows on PM herbage, in turn affecting the casein:whey ratio. Under the current conditions, timing of allocation altered the herbage nutrient supply to cows; a greater concentration of precursor FA in AM herbage resulted in a greater concentration of beneficial FA in milk compared with cows on PM herbage. Quantifying the composition of FA in herbage could potentially aid in the design of grazing strategies to increase precursors of beneficial FA in dairy products. Keywords: fatty acids, milk proteins, herbage composition, time of allocation

Changes in nutritive characteristics associated with plant height, and nutrient selection by dairy cows grazing four perennial pasture grasses

Previous research has documented nutritive characteristics of perennial ryegrass-based pastures and subsequent nutrient-selection differentials when dairy cows graze such pastures, but there has been little comparable research on alternative pasture grasses. The aim of the present study was to compare the pre-grazing nutritive characteristics of four perennial grasses, how nutrients vary with plant height, and selection differentials achieved by dairy cows grazing these grasses in late winter and late spring. The study utilised an established field experiment, with four replicates of monoculture swards of perennial ryegrass (Lolium perenne L.), tall fescue (Festuca arundinacea Schreb.), cocksfoot (Dactylis glomerata L.) and prairie grass (Bromus willdenowii Kunth.), in western Gippsland, Victoria. Eighty individual tillers per replicate were sampled to ground level immediately pre- and post-grazing in late winter (July–August, vegetative tillers only) and late spring (November–December, vegetative and reproductive tillers sampled separately), dissected into three height categories (0–5 cm, 5–10 cm and 10+ cm) and analysed for nutritive characteristics. For vegetative tillers in both seasons, perennial ryegrass had the highest estimated metabolisable energy concentration and lowest neutral detergent fibre concentration of all species. In spring, reproductive tillers had consistently lower nutritive characteristics than did vegetative tillers. Selection differentials, calculated as the ratio of nutritive characteristics selected by the herd to that available pre-grazing, showed that cows selected herbage with higher crude protein concentration but there was little evidence for selection of higher metabolisable energy concentration. The selection differentials reflected the vertical distribution of nutrients in the tillers. The present results have provided new information to assist in developing grazing guidelines for alternative perennial grasses.

The effect of by-product inclusion level on milk production, nutrient digestibility and excretion, and rumen fermentation parameters in lactating dairy cows offered a pasture-based diet

The objective of this study was to investigate the effects of replacing barley and soybean meal with increasing levels of by-products on production, digestive, and metabolic parameters in early-mid lactation dairy cows offered perennial ryegrass-based pasture. Forty-eight (32 multiparous and 16 primiparous) dairy cows that were 64 ± 24 d in milk were assigned to 1 of 4 pasture-based dietary treatments (n = 12) in a randomized block design experiment that ran for 70 d. Treatments consisted of a perennial ryegrass-based pasture and 1 of 4 supplementary concentrates: BP35, BP55, BP75, and BP95 containing 35, 55, 75, and 95% by-products, respectively, in the concentrate on a dry matter basis. The by-products used were soyhulls, dried distillers grains, and palm kernel extract in equal proportions. Barley and soybean meal were replaced as by-product inclusion level increased. In this study, intakes of pasture dry matter (15.7 kg) and total dry matter (21.1 kg) were not affected by treatment. Similarly, milk production parameters (milk yield, milk composition, somatic cell count, and urea) were not different between treatments. Unsaturated fatty acids were lower in the milk of cows offered BP35 and BP55 compared with those offered BP75 and BP95. Concentrations of β-hydroxybutyrate, nonesterified fatty acids, and other blood metabolites were within normal range and did not differ between treatments, and cow body condition score and body weight were also not different. Equally, N was unaffected by diet. Blood urea N was lower in the BP75 group compared with BP35. This study demonstrated that barley and soybean meal can be replaced with soyhulls, dried distillers grains, and palm kernel extract without affecting milk production, digestive, or metabolic parameters in dairy cows offered a pasture-based diet.

Herb-clover mixes increase lamb live weight gain and carcass weight in the autumn period

Two experiments were carried out in two consecutive autumns to examine whether herb-clover mixes would improve lamb production compared with a ryegrass-based pasture. The three herbage treatments were: (1) ‘pasture mix’—perennial ryegrass (Lolium perenne L.) and white clover (Trifolium repens); (2) ‘plantain mix’—plantain (Plantago lanceolata), white clover and red clover (Trifolium pratense); (3) ‘chicory mix’—plantain, chicory (Cichorium intybus L.), white and red clover. Individual lamb live weight gain, final lamb live weights, carcass weights and GR tissue depths were greater (P < 0.05) in both of the herb-clover mixes in both experiments compared with the pasture mix. However, environmental conditions in the second year resulted in lower stocking rates on the plantain mix. This result suggests that in a dry environment, of the three mixes examined, the chicory mix is the best option for finishing lambs in the autumn.