Quantitative analysis of behaviour of grazing dairy cows

This research thesis describes the quantitative analysis of behaviour of grazing dairy cows in terms of sward height (SH) in combination with the length of the grazing session (grazing duration, GD), the time of allocation of fresh pasture and the type of carbohydrate supplement offered. A review of the literature (Chapter 2) identified that there was limited information on the combined affects of SH and GD on behaviour, herbage dry matter intake (DMI) and intake rate (IR) of dairy cows grazing sub-tropical pastures and how these interact to influence sward structure. Also, there was limited information on how SH x GD, time of allocation of fresh pasture and type of carbohydrate supplement offered affects the temporal patterns of behaviour and the subsequent time-dependent probabilities. In this current study, 2 levels of SH (10 and 13cm) and 5 levels of GD (1, 2, 4, 8 and 15h) were used to quantify the effects of SH and GD on dairy cow grazing behaviour, IR and herbage DMI. Sward height significantly (P70% of their total herbage DMI within the first 4h GD. Quantification of the sward profiles after each SH x GD combination showed that dairy cows grazing kikuyu using the management described in this current study did not graze at random. ... The results from this current thesis highlight the factors that either encourage or discourage grazing by dairy cows and should also help to improve decision tools used for pasture rotation, supplementary feeding and stocking density

Search for dark matter produced in association with bottom or top quarks in √s = 13 TeV pp collisions with the ATLAS detector

A search for weakly interacting massive particle dark matter produced in association with bottom or top quarks is presented. Final states containing third-generation quarks and miss- ing transverse momentum are considered. The analysis uses 36.1 fb−1 of proton–proton collision data recorded by the ATLAS experiment at √s = 13 TeV in 2015 and 2016. No significant excess of events above the estimated backgrounds is observed. The results are in- terpreted in the framework of simplified models of spin-0 dark-matter mediators. For colour- neutral spin-0 mediators produced in association with top quarks and decaying into a pair of dark-matter particles, mediator masses below 50 GeV are excluded assuming a dark-matter candidate mass of 1 GeV and unitary couplings. For scalar and pseudoscalar mediators produced in association with bottom quarks, the search sets limits on the production cross- section of 300 times the predicted rate for mediators with masses between 10 and 50 GeV and assuming a dark-matter mass of 1 GeV and unitary coupling. Constraints on colour- charged scalar simplified models are also presented. Assuming a dark-matter particle mass of 35 GeV, mediator particles with mass below 1.1 TeV are excluded for couplings yielding a dark-matter relic density consistent with measurements

Application of the Double-Normal Distribution to Measurements of Sward Height for Kikuyu Pastures Grazed by Dairy Cows at Different Grazing Durations

Sward height (SH) distributions are frequently summarised by the sample mean and standard error. This is most appropriate when the population distribution is approximately symmetrical. However, in continuously grazed swards a combination of relatively 'short' and 'tall' patches in pasture are created and maintained by cattle through selective grazing (Edwards et al. 1997). The relative proportions of 'short' and 'tall' areas are largely affected by management factors such as grazing intensity and the length of the grazing session. Sward heterogeneity is important for a number of reasons. It will affect subsequent utilisation by grazing animals which may in turn affect patterns of nutrient return and treading damage. It may also affect inter-plant competition and potentially the species composition of the sward in the long term. Frequencies of SH usually show a skewed distribution and the representation of a single mean SH is potentially misleading (Gibb and Ridout 1986). Sward height data from an experiment designed to measure the behaviour of dairy cows grazing kikuyu pastures at two different sward heights (SH: 10 and 13 cm) and grazing durations (1, 2, 4, 8 and 15h) was used to determine the ability of a double-normal (DN) distribution to describe changes over the grazing treatments in the mean heights of the 'short' and 'tall' components of the sward

In situ degradation of fresh and frozen-thawed 15N-labelled alfalfa and ryegrass

Alfalfa and perennial ryegrass were labeled with 15N during growth in a glasshouse, harested at s milar growth phases and samples (either fresh (F) or frozen and thawed (FT)) were incubated in situ in the rumen. The results were fitted to a model describing the degradation of DM and total N with time. There c as no difference between forage species for the instantly soluble fraction (a) and the insoluble but potentially degradable fraction (b) estimates for DM and N disappearance over time but alfalfa 15N value. for a and b were significantly (

Probability of Transition in Behaviour of Grazing Dairy Cows

Improving our knowledge of the pasture-animal interface will help farmers make better decisions on the timing of allocation of new grazing areas and the type and amount of supplements offered to grazing dairy cows. Understanding why and what motivates grazing dairy cows to change their grazing behaviour will also help improve these decisions. Hence, improving feed allocation systems to maximise intake of pasture and supplements more efficiently. Dutilleul et al. (2000) calculated the time-dependent transitions for chewing behaviour in sheep using transition probabilities at each sampling time point. To determine the time-dependent probabilities (TDP) of grazing dairy cows, data collected in an experiment designed to investigate the effects of sward height (SH, 10 v 13cm) and grazing duration (GD, 1, 2, 4, 8 and 15h) on grazing behaviour (Dobos et al. 2009) was used. Briefly, 6 dairy cows were randomly allocated to one of 2 SH x 5 GD treatments on kikuyu pastures over a 15h grazing period (1600h to 0700h) for 3 days (replicates). Cows were observed at 20-minute intervals for the first 2 hrs after entering their experimental paddocks at 1600h and thereafter at 30 minute intervals until 0700h the next day. Within 'time-dependent transition probabilities' are incorporated three types of probabilities: the probabilities of (1) being in a given state, (2) staying in the same state, and (3) changing of state, although being in a given state is not a transition per se. These probabilities are calculated at multiples of a 'sampling interval' (Δt) in discrete time, from the raw data collected in continuous time. The grazing TDP of cows in the 10cm SH treatment was similar to their ruminating and idling/resting TDP (0.37 grazing v. 0.31 ruminating v. 0.32 idling). However, the grazing TDP of cows in the 13cm treatment was almost twice that of them either ruminating or idling/resting (0.49 grazing v. 0.25 ruminating v. 0.26 idling). Therefore, 13cm SH treatment cows are more likely to be grazing than either ruminating or idling. The total time spent grazing for these cows was found to be 45min longer (

Spectral Analysis of Dairy Cow Grazing Behaviour Patterns Relative to Sward Height

Cattle and sheep graze 4 to 5 times in each 24h with the longest and most intense periods occurring in the early morning and between late afternoon and dusk. When the daytime temperature exceeds their thermal comfort zone, cows tend to increase their night grazing and graze less during the day. Interspersed between the periods of grazing are periods of idling/resting and ruminating. Understanding the factors that affect grazing behaviour and the subsequent behaviour patterns will help in the development of more efficient feed allocation systems and improve our understanding of how both behavioural and physiological processes control feeding (Fulkerson et al. 2005). Data on time spent grazing, ruminating and resting (min/h) were collected during an experiment designed to investigate the effects of sward height (SH, 10 v 13cm) and grazing duration (GD, 1, 2, 4, 8 and 15h) on grazing behaviour (Dobos et al. 2009). These were subjected to spectral analysis to determine if SH influenced grazing cyclicity. Spectral analysis enables the calculation of periodicities (cycles) within time series data and has been used successfully to determine differences in feeding behaviour due to selection for residual feed intake (Dobos and Herd 2008). Briefly, 6 dairy cows were randomly allocated to one of 2 SH x 5 GD treatments on kikuyu pastures over a 15h grazing period (1600h to 0700h) for 3 days (replicates). Cows were observed at 20-minute intervals for the first 2 hrs after entering their experimental paddocks at 1600h and thereafter at 30 minute intervals until 0700h the next day. Both SH treatment cows had similar patterns of grazing, that is two cycles of grazing 7.5h apart. The 10cm SH treatment cows had significantly (

Estimation of Effective Protein Degradability of Fresh Forage in situ: Correction for Microbial Contamination using 15N-Labelled Plant Material

It is difficult to make field measurements of the effective degradability (ED) of fresh forage ingested by grazing ruminants. The in situ or nylon bag technique is often used for estimating ruminal protein digestibility of forage samples, but microbial attachment to feed residues in the bags causes true degradability coefficients to be underestimated (Nocek and Grant 1987). In addition, the forage samples are often dried or frozen before being placed in the bags and this may affect microbial attachment. Internal and external microbial markers have been used to correct for microbial 'contamination' (Nocek and Grant 1987). In this study, we have used an alternative approach, i.e. labelling the plant material (perennial ryegrass, 'Lolium perene' L.) with 15N to determine the extent of microbial 14N contamination in situ and, from this, the errors in predicting ED

Effect of Nitrate on Variability of Methane Production in Sheep Fed Every 2 Hours

Rumen microbes ferment feed organic matter to obtain energy for microbial growth and generate endproducts including volatile fatty acids, H₂ and CO₂. H₂ and electrons from NADH are used by Archaea to reduce CO₂ to CH₄. Therefore, methane represents a loss of digestible energy as well being a potent greenhouse gas and the search for practical methods to reduce CH₄ release is a current priority. Nitrate salts inhibit methanogenesis (Allison et al 1981) and Leng (2008) has concluded that the inclusion of nitrate salts in feed supplements offers a feasible means of reducing CH₄ emissions from ruminant livestock. The study reported here was undertaken to provide a better understanding of the effect of NO₃⁻ on the rate of and variability in CH₄ production in the rumen of sheep. Twelve sheep were slowly acclimated over 2 weeks to a diet of chaffed oaten hay (1 kg/d as fed) containing no KNO₃ (n=4), or 2% (n=4) or 4% KNO₃ (n=4). CH₄ production was then measured over a 22h period while the sheep were in respiration chambers (Bird et al. 2008) and given 1/12th of their daily ration every 2h. Concentrations of CH₄ in each chamber were recorded automatically at regular (c. 14 min) intervals. These concentrations were subjected to serial correlation and spectral analysis to determine if rhythmic variations CH₄ production could be detected. Figure 1 shows the serial correlation coefficients for the mean CH₄ concentrations in the chambers for 4 sheep receiving the control diet or the same diet with 4% added KNO₃⁻. ... There are strong rhythmical cycles of 2h duration in the original signal for both control and nitrate supplemented sheep. Mean CH₄ concentration was 27.5% lower for sheep offered the diet containing 4% KNO₃⁻ (207± 1.6 vs 150 ± 2.4 ppm). This result is similar to that found by Mathers and Walters (1982) in sheep offered feed every 2h. As well as reducing ruminal CH₄ production, the addition of NO₃⁻ to the diet altered the patterns of chamber CH₄ concentrations relative to those for the control diet. Even with addition of NO₃⁻ to the diet to reduce CH₄ production and frequent feeding, there was considerable deviation from steady state in the rate of fermentation in the rumen. Further analysis of this type of data will help improve our understanding of the rumen fermentation mechanisms leading to variations in CH₄ production

The persistence over time of divergent methane production in lot fed cattle

Steers (12) previously screened using the SF₆ measurement technique and found to have either high or low methane yield (MY: gCH₄/MJ DEI) were re-tested on the same diet. Several steers changed their MY, but the group characteristic of High (1.3 g/MJ) or Low (0.8 g/MJ) MY persisted between the measurement periods as did differences in propionate concentration and protozoal density. This suggests that one or more innate animal attributes must affect MY. The need to consider intake variation of cattle in extrapolating short term measures of methane measurements to annual emission estimates was also highlighted

Degradation of dietary nitrate in the rumen and its use as a potential nitrogen source for rumen micro-organisms

Inclusion of nitrate (NO3⁻) instead of urea in the diet of ruminants provides non-protein nitrogen for rumen micro-organisms and, at the same time, has the potential to reduce rumen methane production (Leng, 2008). However, there is little information on whether NO3⁻ is taken up as such by rumen micro-organisms or is reduced to ammonia (NH3) before assimilation