Summary. Two experiments were conducted on feeding grain supplements to dairy cows during summer. In experiment 1, dairy cows in mid–late lactation were offered one of 2 pasture allowances (about 20 and 40 kg DM/cow.day) with and without a supplement of a grain mix (5 kg of a 70 : 30 mixture of barley and lupins). This experiment was conducted twice over 2 consecutive summer–autumn periods (years 1 and 2). Milk yields were higher at the high pasture allowance and with grain feeding. The marginal response to grain feeding (kg milk/kg grain DM consumed) was 0.7 at both pasture allowances in year 1, and 1.1 and 0.8 at the low and high pasture allowance, respectively, in year 2. Diet had no significant effect on milk composition. Pasture intake was reduced by supplementary feeding and the level of substitution depended on pasture allowance. The alkane-based and sward sampling techniques were used to estimate pasture intake and diet digestibility. Estimates of pasture substitution, based on measurements made with the alkane technique, were 0.3 and 0.6 kg DM reduction in pasture/kg DM grain consumed at the low and high pasture allowance, respectively, in both years. In year 1, the pasture substitution measured with the pasture difference method was 1 kg pasture DM/kg grain DM at both pasture allowances. In year 2, estimates of substitution calculated using the pasture difference method were 0.2 and 0.5 kg pasture DM/kg grain DM at the low and high pasture allowance respectively. In the second experiment (year 3), the effects of level of feeding barley on pasture intake, diet digestibility and milk production were measured during summer. The 4 levels of grain consumed were 0, 1.8, 3.4 and 6.7 kg barley DM/cow. day. Higher grain intake resulted in higher milk yield, higher protein concentration and yields of fat, protein and lactose. Milk yield responses per kilogram of barley diminished from 1.6 at the low barley intake to 0.8 kg milk/kg barley DM at the highest barley intake. It is suggested that higher levels of substitution and a potentially less efficient use of grain contributed to the poorer production responses at higher levels of grain feeding.

Monensin, a polyether ionophore antibiotic, is potentially an important agent for bloat relief in dairy cows grazing temperate legume-based pasture. A series of studies was undertaken to determine the effect of monensin, when delivered continuously in the rumen of lactating dairy cows by means of controlled-release capsules (monensin CRC). Such devices release approximately 300 mg/head/day for 100 d. A short-term pilot study made at Ruakura, New Zealand, tested monensin CRC in cows selected for high susceptibility to bloat and grazing lucerne (Medicago sativa) or red clover (Trifolium pratense). Treatment significantly reduced the incidence of bloat, while milk yield and protein yield were increased. There was no effect on fat yield. Following the pilot study, 6 large-scale field experiments involving a total of 368 lactating dairy cows, were made in Australia and New Zealand to confirm the effectiveness of monensin CRC for bloat control and to measure the effect of such treatment on milk production and composition. A severe bloat problem occurred in 2 experiments, mild bloat occurred in 2 others, while no visual signs of bloat were observed in the remaining 2 experiments. Bloat was significantly (P less than 0.05) reduced by monensin CRC treatment when data was pooled over the 4 experiments in which bloat occurred. Daily milk yield was increased in all experiments from a mean of 17.7 in untreated groups to 18.8 kg/head/day (P less than 0.05) in monensin CRC-treated cows. Protein percentage was not affected by treatment, while there was a decrease from 4.29 to 4.10% fat, although total fat yield was not affected.(ABSTRACT TRUNCATED AT 250 WORDS)

Background Marked increases in atmospheric CO2 concentrations are largely associated with the release of sequestered carbon in fossil fuels. While emissions of green‐house gasses (GHG) from cattle have significant global warming potential, these are biogenic sources and substantially involve carbon in natural cycles, rather than fossil fuel. Cattle use human inedible feeds and by‐products of human food production to produce nutrient‐dense foods of great value to humans. Interventions to reduce GHG production Reductions in land clearing and burning of grasslands and increased carbon sequestration in soils and trees have potential to substantially reduce GHG emissions. Increased efficiencies of production through intensified feeding and enteric modification have markedly reduced intensity of GHG emissions for cattle in Australia. Genetic selection for lower emissions has modest, but cumulative potential to reduce GHG (mostly CH4) emissions and intensity. Improved reproductive performance can reduce intensity of GHG emissions, especially in beef production. Feeds and technologies that reduce GHG production and intensity include improved pastures, grain feeding, dietary lipids, nitrates, ionophores, seaweed, 3‐NOP, hormonal growth promotants in beef, and improved diets for peri‐parturient dairy cattle. There is considerable potential to further reduce emissions from cattle using the technologies reviewed. Interventions to reduce heat stress Cattle are susceptible to heat stress and ameliorating interventions include tree and shelter belts, shade, housing, cooling with fans and water and dietary manipulations. Conclusions Numerous interventions can reduce GHG emissions and intensity from cattle. There are opportunities to increase carbon capture and maintain biodiversity in Australia's extensive rangelands, but these require quantification and application. We can reduce the intensity of CH4 emissions for cattle in Australia and simultaneously improve their well‐being.

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