Karin Hartung

Statistical aspects of on-farm experimentation

This paper reviews options for the design and analysis of on-farm experiments. It covers both older approaches that have been popular since the Green Revolution, and more recent developments made possible by the availability of online monitoring systems as used in precision farming. The roles of randomisation as well as of geostatistical methods of analysis for these kinds of experiments are critically discussed. Two case studies are provided for illustration.

Effects of long-term supplementation of chestnut and valonea extracts on methane release, digestibility and nitrogen excretion in sheep.

The long-term effects of adding chestnut (CHE; Castanea sativa) and valonea (VAL; Quercus valonea) tannin-rich extracts to sheep feed were investigated. In Experiment 1, sheep (65 kg BW) were fed 842 g/day of a ryegrass-based hay. The control-treated animals (CON) received 464 g/day of concentrate, and tannin-treated animals received the same amount of concentrate additionally containing 20 g of the respective tannin-rich extract. Hay and concentrates were offered together in one meal. After the onset of treatment, methane release was measured in respiration chambers for 23.5-h intervals (nine times) in a 190-days period. Faeces and urine were collected three times (including once before the onset of the tannin treatment) to assess digestibility and urinary excretion of purine derivatives. Based on the results obtained from Experiment 1, a second experiment (Experiment 2) was initiated, in which the daily tannin dosage was almost doubled (from 0.9 (Experiment 1) to 1.7 g/kg BW0.75). With the exception of the dosage and duration of the treatment (85 days), Experiment 2 followed the same design as Experiment 1, with the same measurements. In an attempt to compare in vitro and in vivo effects of tannin supplementation, the same substrates and tannin treatments were examined in the Hohenheim gas test. In vitro methane production was not significantly different between treatments. None of the tannin-rich extract doses induced a reduction in methane in the sheep experiments. On the 1st day of tannin feeding in both experiments, tannin inclusion tended to decrease methane release, but this trend disappeared by day 14 in both experiments. In balance period 3 of Experiment 1, lower dry matter and organic matter digestibility was noted for tannin treatments. The digestibility of CP, but not NDF or ADF, was reduced in both experiments. A significant shift in N excretion from urine to faeces was observed for both tannin-rich extracts in both experiments, particularly in Experiment 2. In balance period 2 of Experiment 2, an increased intake of metabolisable energy for VAL was observed. The urinary excretion of purine derivatives was not significantly different between treatments, indicating that microbial protein synthesis was equal for all treatments. Thus, we concluded that both tannin-rich extracts temporary affect processes in the rumen but did not alter methane release over a longer period.

Occurrence and Distribution of 13 Trichothecene Toxins in Naturally Contaminated Maize Plants in Germany

The objective of the present study was to monitor the occurrence and distribution of a spectrum of trichothecene toxins in different parts of maize plants. Therefore maize plants were sampled randomly from 13 fields in southwest Germany and the fractions kernels, cobs, husks, stalks, leaves and rudimentary ears were analyzed for eight A-type and five B-type trichothecenes. Each of the toxins was found in at least three of the total of 78 samples. The study revealed that both A-type and B-type trichothecenes may be present in all parts of the maize plant but may be unevenly distributed. For the contents of deoxynivalenol, 3- and 15-acetyldeoxynivalenol, nivalenol, scirpentriol, 15-monoacetoxyscirpenol, HT-2 and T-2 toxin significant differences (p < 0.05) were found between different parts of the maize plants whereas no significant differences were observed for fusarenon-X, 4,15-diacetoxyscirpenol, neosolaniol, T-2 triol and T-2 tetraol. Up to twelve toxins co-occurring in one sample were detected. As a group B-type trichothecenes dominated over A-type trichothecenes concerning incidences and levels. Contamination was strongest with rudimentary ears based on incidence and mean and maximum contents; mean contents with few exceptions tended towards a higher level than in other fractions with significant (p < 0.05) differences compared to leaves for seven toxins.

Comparison and evaluation of bone measurements for the assessment of mineral phosphorus sources in broilers

The main objective of this study was to compare different bone measurements in response to supplements of mineral P sources. Comparisons were also made with P retention and digestibility responses determined in a companion study and with blood inorganic phosphate (P(i)) responses. A corn-soybean meal-based basal diet was used (0.35% total P on DM basis). Anhydrous monosodium phosphate (MSP(a)) or anhydrous dibasic calcium phosphate (DCP(a)) was supplemented to increment the P concentration by 0.08%, 0.16%, or 0.24%. Each of the 7 diets was fed for 10 d starting 11 d (period 1) or 25 d posthatch (period 2). Bone ash and P were determined, and density criteria were measured using quantitative computed tomography. Responses were evaluated and compared based on linear regression analysis. In general, responses to MSP(a) had a greater slope than DCP(a) for all criteria studied. In period 1, differences between the slopes were significant (P < 0.05) for almost all bone criteria. In period 2, the slopes significantly differed for the amounts of ash and P of all bones studied, for tibia, tarsometatarus, and foot ash percentage, for total and cortical density of tibiae, but not for the other criteria. For the different bones, the ratio of slopes for MSP(a) and DCP(a) was very similar based on the amount of ash in both periods. Foot ash proved to be as sensitive as tibia ash for evaluation of mineral P sources in both periods. Ninety-four percent of the variance of the corticalis content based on quantitative computed tomography measurements could be explained by the amount of tibia ash in period 1. Blood serum P(i) and BW gain were not suitable for P evaluation. We concluded that the ranking of mineral P sources based on bone criteria differed from the ranking that was based on P retention or prececal digestibility. This underlines the need for developing a standard protocol of determination of available P in poultry.

Assessment of variability in biomass yield and quality: what is an adequate size of sampling area for miscanthus?

To diversify energy crop production and improve its biodiversity and sustainability, there is currently a search for alternative energy crops. Many of the newly arising alternatives are perennial species such as the C4 grass miscanthus. The assessment of reliable data is a prerequisite for understanding the performance of these crops and developing corresponding management systems. However there is great uncertainty concerning research methodology for these crops. When data are collected from small plots of perennial crops, such as miscanthus or short rotation coppice plantations, a larger variability is expected than for cereals. A square meter cut, corresponding to harvest practice in cereals, is not sufficient for perennial C4 grasses and is not recommended for these species. The aim of this research was to identify an adequate size of sampling area for miscanthus to estimate the true biomass yield or quality. For this purpose, whole plots of 10‐ and 14‐year old miscanthus stands were divided into smaller subplots. These were used to calculate variances for various sizes of simulated plots. The variances for all traits in the experiments were rather high when the sampling area was smaller than 2 m². A cutting regime of more than 5.6 m² would be advisable, but an area of 3 m² is sufficient to eliminate approximately 90% of the variances and is therefore an adequate size of sampling area.

Effect of monensin on in vitro fermentation of silages and microbial protein synthesis

The objective of the study was to investigate the effects of monensin on silage fermentation and microbial net protein synthesis. In Experiment 1, monensin (0.5, 1, 2, 4, 6, or 10 µg) was added to syringes that contained 120 mg of grass silage (GS), grass silage and concentrate (GS + C), or maize silage (MS), resulting in concentrations of 4.2, 8.3, 16.7, 33.3, 50.0 and 83.3 mg monensin/kg feed. Samples were incubated for 24 h to determine the monensin concentration that resulted in the maximum reduction in methane production without effects on the total gas production. In Experiment 2, GS and GS + C were incubated in a rumen simulation technique (Rusitec) to assess the monensin effects (133 and 266 mg/kg feed) on the production of total gas, methane and volatile fatty acids (VFA), degradation of nutrients and microbial net protein synthesis. In Experiment 1, methane production was reduced without significant effects on the total gas production; the reductions were 17% (GS), 10% (GS + C) and 13% (MS) with 16.7 (GS), 50.0 (GS + C) and 33.3 (MS) mg monensin/kg feed. Monensin reduced the total gas and methane production in GS and GS + C in Experiment 2. Propionate production was enhanced by monensin, accompanied by a decrease in acetate production. Along with a reduction in crude protein (CP) degradation, monensin reduced the ammonia nitrogen concentration in the effluent of both treatments. While the protein produced by liquid-associated microbes increased with monensin, protein production by solid-associated microbes was reduced. Total microbial net protein synthesis increased in the presence of monensin. Monensin influenced the production of total gas, methane and VFA from the silages without an effect on the degradation of organic matter (OM). Different microbial fractions were affected differently by monensin supplementation. If monensin is used as a tool to reduce methane emission, the supplementation level must be carefully chosen to avoid negative effects on overall fermentation in the rumen.

Response of imidazolinone-tolerant and -susceptible volunteer oilseed rape (Brassica napus L.) to ALS inhibitors and alternative herbicides.

BACKGROUND Imidazolinone-tolerant oilseed rape (Brassica napus L.) varieties are currently grown in Canada, North America, Chile and Australia with high acreage. A Europe-wide introduction has started and will be pushed further for both spring and winter varieties. The primary aim of this study was to evaluate the impact of imidazolinone tolerance for future volunteer oilseed rape control in subsequent crops, particularly winter wheat. RESULTS A greenhouse bioassay showed cross-tolerance of imidazolinone-tolerant oilseed rape towards sulfonylureas, triazolopyrimidines and sulfonylaminocarbonyltriazolinones (resistance factors between 5 and 775), with a homozygous variety expressing a much higher tolerance level compared with a heterozygous variety. Calculated ED90 values suitable for controlling tolerant plants were always much higher than the recommended herbicide dose. Generally, results were confirmed under field conditions, but with higher efficacies than expected in some cases (e.g. florasulam). Herbicides with an alternative mode of action were found to be effective in controlling imidazolinone-tolerant volunteers in subsequent winter wheat crops. CONCLUSION Herbicide strategies have to be adjusted for volunteer control in subsequent crops if imidazolinone-tolerant oilseed rape varieties are to be grown. However, agronomic tools (harvest date, harvest technique, tillage) should be used conscientiously in the first place to keep volunteer oilseed rape densities at the lowest possible level.

Analysis of Genebank Evaluation Data by using Geostatistical Methods

Genebanks often characterize accessions based on evaluation trials. This paper evaluates geostatistical methods as a tool to increase the utility of evaluation data. These methods were selected to overcome limitations resulting from a relative lack of replication and the scarcity of standards or check varieties. The data employed in the present study comprise nine characteristics of spring and winter barley, evaluated mostly as ratings. Ratings with quasi-metric scales were transformed by using the folded exponential transformation. To estimate the genetic component of the total effect, we compared two methods: Method 1 whereby a variogram is fitted by non-linear regression, and subsequently the implied spatial correlation is embedded into a mixed model analysis, which estimates the genetic effect by Best Linear Unbiased Prediction (BLUP); and Method 2 where each data value is re-estimated by kriging to correct for spatial effects and then the corrected data are submitted to a mixed model analysis. For practical application we propose Method 1 (though occasionally we met convergence problems): Fit the short range of the empirical variogram, visually choose the suitable covariance model. Use this and the initial values from non-linear regression fit with the mixed model, fixing the spatial parts at their starting values from non-linear regression, and estimate genetic effects by BLUP by using the fitted mixed model. To improve performance, we recommend that more standard or check varieties be used and, wherever possible, replace rating scales with metric scales or free-percentage scales (without categories).

Changes in fatty acid composition of various full fat crushed oilseeds and their free oils when incubated with rumen liquor in vitro.

The fatty acid pattern of dietary lipids can be modified during rumen biohydrogenation (BH). The objective of the present study was to assess changes in the FA pattern of different oilseed products supplied either as crushed full fat oilseed or as free oil after in vitro incubation with buffered rumen liquor. The FA patterns were determined at the beginning and compared with those measured after 24 h of incubation. The contents of fatty acids (FA) < C18 increased (p < 0.05) in nearly all treatments, eventually due to microbial de novo synthesis and fermentation of carbohydrates and proteins during incubation. In contrast, the contents of the dominating C18 FA, (oleic acid – C18:1c9, linoleic acid – C18:2c9,12, linolenic acid – C18:3c9,12,15) were reduced due to BH, resulting in the accumulation of characteristic BH intermediates, such as conjugated linoleic acid (CLA) isomer C18:2c9t11 (rumenic acid). However, both for crushed full fat oilseeds and their free oils the process of BH was not completed at the end of incubation. The disappearance was highest for C18:3c9,12,15, followed by C18:2c9,12 and C18:1c9. The rate of BH of unsaturated FA was higher in the crushed form compared to the oil form. Higher amounts of BH intermediates accumulated in the crushed form. Obviously, the physical form affects the degree of BH in vitro. The current results suggest that feeding crushed full fat seeds instead of their free oils to dairy cows might stimulate the formation of beneficial BH intermediates such as CLA in the rumen.

Effects of different forms and origins of oilseeds on dynamics of ruminal biohydrogenation of long-chain fatty acids in vitro.

Dietary unsaturated fatty acids (FA) are intensively hydrogenated in the rumen, resulting in reduced amount of poly-unsaturated fatty acids (PUFA) and accumulation of several biohydrogenation (BH) products. In this study, BH of PUFA originating from different oilseeds (linseed, soya beans, sunflower seed and rapeseed) present in crushed oilseeds or their free oils were assessed in vitro. The assay substrates were incubated in buffered rumen fluid for 0, 6, 12 and 24 h. After incubation, the FA pattern of the incubated samples was analysed using gas chromatography. Biohydrogenation is defined as disappearance of double bonds (DB) calculated from the contents of unsaturated FA. After 24-h incubation, the DB contents of all oilseeds were reduced (p < 0.001) by 40-60%. The reduction was higher (p < 0.001) for the crushed form compared with the oil form. In addition, linseed and sunflower seed known as oilseeds with high contents of linolenic acid C18:3 c9,12,15 (LNA) and linoleic acid C18:2 c9,12 (LA), respectively, showed a higher (p < 0.001) accumulation of the BH intermediates conjugated linoleic acid (CLA, isomer C18:2 c9t11) and vaccenic acid (C18:1 t11) for the crushed form, when compared with the oil. These results suggest an inherent effect of the physical form of the assay oilseeds on in vitro BH. Changes in FA pattern during BH in vitro can be attributed to both source and physical form of the assay oilseeds. However, further investigations are warranted to ensure whether the observed in vitro effects on ruminal BH can be confirmed in vivo.