In reproductive swards, stems appear to act as vertical or horizontal barriers to bite formation, influencing instantaneous intake rate (IIR). The hypothesis was tested that the stems' barrier effect is determined by the physical properties and density of stems. Artificial microswards, consisting of 20-cm leaves and 15-cm stems of Panicum maximum, were offered to three steers (362 kg) in a factorial combination of three stem densities (0, 100 and 400 stems m )2 ) and two levels of stem tensile resistance [low (LTRS) and high tensileresisting stems (HTRS)]. LTRS were not a barrier to defoliation and did not affect bite depth and bite mass. HTRS acted as both a horizontal barrier and a vertical barrier depressing bite depth (13AE4, 13AE6 and 5AE1 cm for 0, 100 and 400 stems m )2 , respectively), bite area (89AE3, 50AE8 and 47AE6 cm 2 for 0, 100 and 400 stems m )2 , respectively), bite mass (0AE51, 0AE29 and 0AE11 g for 0, 100 and 400 stems m )2 , respectively) and IIR (23AE8, 10AE5 and 3AE6 g sec )2 for 0, 100 and 400 stems m )2 , respectively). The results confirmed the importance of the density and physical properties of stems as determinants of the stems' barrier effect on bite dimensions and IIR.

This study assessed the use of pasture attributes to control daily intake and diet quality during progressive defoliation on pastures of Axonopus catarinensis. Three consecutive 12‐day grazing treatments of progressive defoliation were conducted with Brahman cross‐steers. Daily forage intake and defoliation dynamics were assessed using a pasture‐based method. The treatments differed in initial sward height (33, 44 and 61 cm) and herbage mass (1030, 1740 and 2240 kg ha−1). The post‐grazing residual sward height, at which forage intake decreased, appeared to increase with the initial sward height (12·3, 14·6 and 15·5 cm). Steers grazed up to four distinctive grazing strata in all treatments. The depth and herbage mass content of the top grazing stratum were at least five times higher than the lower grazing strata in all treatments. This explains why forage intake decreased when the top grazing stratum was removed in approximately 93% of the pasture area in all treatments, equivalent to approximately 7% of the pasture area remaining ungrazed. We conclude that the residual ungrazed area of the pasture, rather than residual sward height, can be used to develop grazing management strategies to control forage intake and diet quality in a wide range of pasture conditions.

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The effects of stem density of tropical swards and age of cattle on their foraging behaviour were evaluated using artificial microswards, consisting of leaves of 20 cm in height and high tensile-resisting stems of 25 cm in height of Panicum maximum. The treatments consisted of a factorial combination of four stem densities of swards (0, 100, 200 and 400 stems m )2 ) and two ages of cattle (1-and 3-year-old steers). There was a significant interaction between stem density of sward and age of cattle for bite area (BA), bite mass (BM) and instantaneous intake rate (IIR). Stem density had a significant negative effect on these variables describing ingestive behaviour which was particularly strong for older steers. In leaf-only swards, mature cattle achieved a much greater BA (106AE5 vs. 57AE9 cm 2 ), BM (0AE88 vs. 0AE47 g DM) and IIR (46AE9 vs. 17AE2 g DM min )1 ) than did young cattle. However, these variables were very similar across ages of cattle at the highest stem density of sward. These results show the importance of the high tensile-resisting stems as deterrents of the grazing process in tropical pastures, particularly in older cattle.

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The effect of lucerne pasture allocation on defoliation dynamics, pasture intake and animal production was investigated in a subtropical partial mixed-ration dairy system. The study took place at the Gatton Research Dairy, south-eastern Queensland, with a 28-day adaptation period followed by an 8-day treatment period during November and December 2016. Twenty-four multiparous Holstein Friesian dairy cows were offered 11 kg of dry matter (DM)/cow.day as partial mixed-ration dairy system, and four levels of daily pasture allocation measured to 5-cm residual pasture height (averaging 30.6, 20.5, 15.1 and 10.9 kg DM/cow.day). Cows with lower allocations were forced to graze further down the vertical plane and pasture intake and milk yield significantly (P < 0.001) declined. Cows grazed the top grazing stratum (TGS) across 80% of the pasture area before re-grazing another area of the paddock, regardless of the allocation level. Pasture intake (kg DM/ha) of the TGS was at least 2.9 times higher than that of the lower strata, regardless of allocation level. Therefore, the decline in pasture intake is explained by the transition from grazing the TGS to grazing lower strata. When the horizontal utilisation of the TGS approached 100%, the proportion of ungrazed, uncontaminated pasture approached 0% of the area, and intake and milk production declined. Grazing management strategies for lucerne should allocate pasture to lactating dairy cows to achieve horizontal utilisations approaching 0% for proportion of ungrazed, uncontaminated pasture to maximise intake and production. Secondary grazing herds or mechanical methods should be used to remove residual pasture to the ideal height for pasture regrowth.

Determining the phosphorus (P) status of cattle grazing P-deficient rangelands in northern Australia is important for improving animal production in these areas. Plasma inorganic P concentration is currently the best diagnostic marker of dietary P deficiency in growing cattle but is not suitable for assessing the P status of breeder cows, which often mobilise substantial bone and soft tissue reserves in late pregnancy and lactation. Markers of bone turnover offer potential as markers of P status in cattle, as they reflect bone mobilisation or bone formation. Recent experiments investigating the physiology of beef breeder cows during diet P deficiency have indicated that the ratio of plasma total calcium concentration to plasma inorganic P concentration might be suitable as a simple index of P deficiency. However, a more specific measure of increased bone mobilisation in P-deficient breeders is plasma concentration of C-terminal telopeptide of Type 1 collagen. Also, plasma concentration of bone alkaline phosphatase is a marker of defective bone mineralisation in dietary P deficiency. These candidate markers warrant further investigation to determine their predictive value for P deficiency in cattle.