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Context. Heat stress is an increasing concern for the Australian dairy industry. Aims. This study aimed to evaluate the effect of temperature-humidity index (THI) on rumination time (RT), milk yield and quality, and milking frequency in a pasture-based voluntary-movement automatic milking system (AMS). Methods. Data were collected from the University of Melbourne Dookie College AMS farm for 3 years (June 2016 to March 2019). Daily RT was collected through the transponder collar (Qwes-HR, Lely). Climatic data (maximumambient temperature and relative humidity) were obtained fromthe Dookie Meteorological station to calculate daily maximumTHI (THImax). Key results. Daily milk yield increased with a rising THImax to 65, then declined after THImax 65. Milking frequency was highest at THImax 90, followed by a steady decline afterwards. Rumination time was maximum at mid-range THImax and declined for high and low values. Conclusions. The findings of this study clearly indicated that under pasture-based voluntary-movement AMS, high THI resulted in a drop in the milk yield, milking frequency and RT. Implications. With the provision of automation of data collection from AMS, further study with mathematical modelling describing the daily patterns and thresholds in conjunction with the different heat stress levels can be useful for assessing animal welfare and to mitigate heat stress and seek alternative management strategies. [ABSTRACT FROM AUTHOR]

Tall fescue pastures have an increasing potential to be used worldwide. The purpose of this study was to test the ability and flexibility of the model Dairy Mod to represent herbage mass accumulation ( HMA) of tall fescue pastures from Argentina under several environmental conditions, including different seasons, fertilizer nitrogen levels and irrigation. Species-specific responses were obtained by customizing particular parameters (i.e. number of living leaves per tiller, leaf appearance interval, optimum plant N concentration and the response of leaf gross photosynthesis to temperature). Additionally, a simulation experiment to compare the model assumption that optimum N concentration stays constant through HMA with the application of a reference critical N dilution curve verified for temperate forage grasses (N% = 4·8 HMA−0·32) was conducted. Application of Dairy Mod simulated with reasonable accuracy the HMA of tall fescue pastures under a wide range of climatic and management conditions; however, the model tended to underestimate HMA where pastures grew under high N availability. The use of a reference critical N curve substantially improved this bias, indicating that a further analysis on the N issue of the model is necessary. Results from this study provide support for further evaluations of the model under other scenarios and conditions. An upgrade of the model to improve simulation of N nutrition is suggested to enhance its performance to predict growth dynamics at high N availabilities as well as its value to address the effectiveness of N-management practices. [ABSTRACT FROM AUTHOR]

The estimated metabolisable energy (ME) concentration of pasture has a significant influence on the profit of farm systems that rely on pasture as a dietary component. However, breeders of pasture plants have traditionally focussed on improving herbage yield over nutritive characteristics or ultimately feeding value. Pasture intake from two contrasting dairy farm experiments in temperate Australia over multiple years was used to estimate the potential economic benefit of changes in the ME concentration of pasture consumed by lactating dairy cows. Barley prices were used to calculate the worth or 'replacement cost' of the ME within perennial ryegrass (Lolium perenne L.). The economic values for changes in ME concentration of pasture in each year of the experiments were estimated using a deterministic model. Then Monte Carlo (stochastic) simulation was conducted, incorporating distributions of changes in pasture intake, ME concentration and replacement cost of ME to derive a distribution of the economic benefits of an increase in ME concentration of pasture. The mean stochastic results of a one unit increase in ME concentration across the year for perennial ryegrass were AU$191/ha (Terang-'medium rainfall' in Victoria) and AU$459/ha (Elliott-'high rainfall' in Tasmania). In both farm experiments the largest seasonal contribution to the annual economic value was in the spring. In comparison, when economic values were estimated using changes in ME concentration achieved in experiments (1.74 MJ/kg DM higher in spring and 1.44 MJ/kg DM higher in summer), the economic values were AU$141/ha in spring and AU$74/ha in summer for Terang and AU$266/ha in spring and AU$187/ha in summer for Elliott. The economic values for changes in ME concentration of pasture provide an indication of potential feed cost savings for these farms. The savings estimated using Monte Carlo simulation for Terang was 9% of total variable costs for a one unit increase in ME concentration and 20% of total variable costs for Elliott. The magnitude of the economic benefits that genetic improvement in the ME concentration of pasture plants could have on Australian dairy farms warrants consideration by plant breeders developing breeding programmes. [ABSTRACT FROM AUTHOR]