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SUMMARYIn a 15-week animal-house experiment, 24 steers were offered one of six diets based on molasses andad libitumbarley straw. Three levels of dietary nitrogen (N) and three levels of dietary phosphorus (P), in factorial combination, were formulated by the addition of urea, formaldehyde-treated wheat gluten and monosodium orthophosphate. Food intake, liveweight gain, plasma metabolites and P kinetics were measured under dietary regimens similar to those experienced by cattle grazing Australia's northern semi-arid rangelands.The adverse effect of the low dietary N on both liveweight change and feed intake was greater and more immediate than that of the dietary P deficiency. The reduction in feed intake due to the P deficiency approached that caused by the N deficiency after 10 weeks. Under conditions of adequate dietary N, there was a trend for the effects of P deficiency on liveweight gain to be exacerbated. Dietary N and P deficiency reduced the concentrations of plasma urea-N and inorganic P respectively. Dietary N deficiency had no effect on cortical rib bone thickness but P deficiency markedly decreased bone thickness. Faecal endogenous loss of P and P absorption efficiency ranged from 9 to 21 mg/kg LW and 0·63 to 0·82 respectively for P intakes from 6 to 41 mg·kg LW. Faecal endogenous losses were closely related to dry matter intake and plasma inorganic P together. Dietary N deficiency affected the efficiency of absorption of P.The results of this experiment indicate that cattle consuming diets containing low levels of N and P require supplementary N and P in combination to avoid severe depletion since an increase in N intake alone exacerbated the P deficiency. The results are also discussed in relation to the published findings regarding P metabolism and the implications for the calculation of P requirements.

Rectal temperatures of a flock of 151 Merino ewes from the semi-arid tropics of northern Australia were measured in March 1991 (Year 1). Two sub-groups of ewes, with different abilities to thermoregulate body temperature, were then classified according to rectal temperature at 16:00 h on 3 consecutive hot summer days: low body temperature status (LBT) ewes had a rectal temperature of ≤39.8 °C on each of the 3 days, and high body temperature status (HBT) ewes had a rectal temperature of ≥39.9 °C. These ewes were mated 20 months later and exposed to a hot summer gestation under typical field conditions. In February 1993 (Year 3) rectal temperatures of ewes were measured again to confirm body temperature status, and on the following day, at 107 ± 0.3 days of gestation, placental and fetal weights were determined at post mortem. Weight (20%, P < 0.01), DNA content (14%, P < 0.05) and protein content (15%, P < 0.05) of the placenta of LBT ewes were greater than for HBT ewes, whereas there was no significant difference in DNA or protein concentrations (mg per g tissue) or DNA:protein ratio. Fetal thoracic girth and fetal heart weight of HBT ewes were lower (P < 0.05) than for LBT ewes, but there was no significant difference in fetal body weight or fetal crown-rump length. We conclude that placental growth is restricted in sheep which do not thermoregulate well (i.e. HBT) when exposed to a hot environment. The ability of flock managers to identify HBT ewes, which will subsequently experience restricted placental growth, can be used to identify low producing individuals early in their commercial life.

SUMMARYThe aim of this experiment was to determine whether the thermal responses ofsheep exposed to a hot environment were similar in different years. Rectal temperaturesofsheep were measured during the hot months (between November and March) of three consecutive years (1990/91, 1991/92, 1992/93) in a flock of Merino sheep (n = 151) in the semi–arid tropics of northern Australia. Mean daily maximum temperatures in these months were 36±0·4, 39±0·3 and 37±0·3°C in Years 1, 2 and 3, respectively. In Year 1, rectal temperatures were measured on 3 consecutive days;the repeatability was 0·47 at 08·00 h and 0·64 at 16·00 h. In Year 1, two sub-groups were identified according to measurements of rectal temperature, low body temperature(LBT; n = 35) sheep, whose rectal temperature was ≤ 39·8°C at 16·00 h on each of the 3 consecutive measurement days, and high body temperature (HBT; n = 32) sheep, whose rectal temperature was ≥ 39·9°C. The rectal temperatures of LBT and HBT sheep were then measured during the subsequent 2 years. Rectal temperatures of HBT sheep were significantly higher than those of LBT sheep at both 08·00 and 16·00 h, in both Year 2 and Year 3. Rectal temperatures at 16·00 h in Year 1 were correlated (P < 0.001) with rectal temperatures at 16·00 h in both Year 2 (r = 0·79) and Year 3 (r = 0.82), respectively. It was concluded that measurement of rectal temperature in sheep exposed to a hot environment in any oneyear is an accurate index of their rectal temperatures during subsequent years.

This experiment tested the hypothesis that relocating cattle is detrimental to their growth. The study examined the effect of having relocated cattle mixed with, or segregated from, the local acclimatised cattle at the destination property. Bos indicus cross steers (120) were allocated to three groups and were relocated, in two separate cohorts, 980 km from northern Queensland to improved pastures in central Queensland. At the start of Phase 1, the control group (C) was moved 3 months before the other two groups. The remaining two groups grazed native pastures; one group was supplemented (SR) to increase growth rate similar to that expected from improved pasture in central Queensland and the other was not supplemented (R). At the end of Phase 1, C was significantly (P < 0.05) heavier than SR, which was significantly (P < 0.05) heavier than R. At the start of Phase 2, the SR and R groups were relocated and after transportation the R and SR groups lost 12 kg or 4.4% of liveweight and 18 kg or 5.7% of liveweight, respectively; this weight loss was recovered after 5 days. All steers were reallocated to segregated (SEG) or mixed (MIX) treatment groups forming six treatments (SEG.C, SEG.R and SEG.SR and MIX.C, MIX.R and MIX.SR). There were no significant differences in liveweights within the SEG treatments by 57 days or within the MIX treatments by 106 days after relocation. There were few if any significant differences in the plasma constituents and differential leucocyte counts of the steers and most results were within physiologically normal ranges. We conclude on the basis of these results and of other experiments that the anecdotal poor performance of cattle after relocation appears to be unfounded.

Variation in the composition of eastern Australian molasses was examined. Data on molasses composition for 1997–2001 were collected from all 28 eastern Australian sugar mills. Since the last detailed study in 1975, there have been decreases in the concentration of reducing sugars (–6.2%), sucrose (–0.9%), total sugars (–2.5%), other organic matter (–11%) and calculated metabolisable energy (ME) (–2.8%). Dry matter (DM, +0.1%) and ash (+29%) concentrations have increased. Differences between milling regions were observed for DM (P

During 1996 and 1997, a survey examined the business activities of 375 selected northern Australian beef producers during the 1991 and 1992 to 1995 and 1996 financial years. The producers represented a broad cross-section of the northern beef industry in terms of geographical location, size of enterprise and herd, and ownership structures. The survey examined the enterprise structures and herd productivity of the participating properties. A diverse range of production activities were carried out with breeding and finishing, of which breeding stores and live cattle export being the most common activities. About 50% of the survey properties were run in conjunction with another property, both of which tended to be located in the same survey region. The additional properties served various purposes, depending on their location. There was evidence of specialist roles for the additional properties. The purchase of store cattle tended to be an opportunistic activity with younger cattle (

Breeding herd performance and husbandry were surveyed on 375 northern Australian beef properties in 8 regions during 1996 and 1997. Mean branding rates ranged from 62.6% in the Northern Territory to 77.1% in the Maranoa South West regions of Queensland with considerable variation within regional herds. The proportion of herds using controlled mating was highest in the Central Coastal, Central Highlands and Maranoa South West. Mean mating period across all regions varied from 5.6 to 11.8 months. Calving was seasonal with peak activity in the August–December period. Calving commenced earlier in the south (August) than it did in northern regions (September–November). Rainfall influenced the timing of commencement of calving and peak calving activity. The use of pregnancy testing was widespread but selective and often not all females were pregnancy tested. About 97% of properties used weaning strategies with a peak in calf weaning in April–July, and a minor peak in September–October. Although mean weaner ages were similar across regions (5.9–6.9 months), mean weaner liveweight varied markedly with weaners in the more northern regions being lightest (200 kg. Culling criteria for cows and heifers focused on temperament, conformation and reproductive failure; age was also important for cows with a common culling age of 10 years. Bulls were more commonly culled at 7–8 years of age. In addition to age, bulls were culled for physical defects, reproductive problems, temperament and poor quality/performing calves. Four to 5 criteria were commonly used to select bulls. Structural soundness and temperament ranked highest followed by conformation, weight for age, Breedplan and colour. Producers using Breedplan tended to use structural soundness and temperament also as selection criteria. The results suggest that producers associated increasing turn-off weight or decreasing turn-off age more with pasture improvement than with bulls of higher genetic merit for growth. Supplementation of the breeding herd increased in the last half of the calendar year. Supplements containing molasses, urea, phosphate source, salt, and sulphate of ammonia were the most commonly supplied supplementary nutrients. Vaccination for botulism was quite common (>30% of regional survey groups) in all regions except Central Coastal and Maranoa South West regions of Queensland. Comparisons with previous surveys show that there have been marked improvements in breeding herd performance and management over an extended period. The results are discussed in relation to scientific developments over the last 2 decades and future development of the northern Australian beef industry.

Ninety young Merino ewes, depastured on Mitchell (Astrebla spp.) grass pastures in North West Queensland, were used in a hormonal growth promotant implantation study. The ewes were given 1 implant of Compudose, Ralgro, Revalor or Synovex-H, either at lamb marking (mid-dry season) or the start of the following summer wet season, which was ~180 days post-marking. The hormonal growth promotant implanted groups had greater (P

Summary. Thirty-two mature recently shorn wethers (mean liveweight 52.1 kg) were implanted with 1 of 4 different hormonal growth promotants (Ralgro, Compudose, Revalor-S and Synovex-H) to determine animal production responses on dry season pastures. The wethers were grazed for a period of 135 days on dry season native Mitchell grass (Astrebla spp.) pastures infested with Acacia nilotica. The wethers were weighed monthly. Four months after commencement of the experiment, the wethers were shorn to determine wool characteristics (micron, yield and staple length). At 2 weeks post-shearing the wethers were slaughtered to determine carcass attributes. Serial rumen ammonia concentrations indicated that diet quality was declining throughout the experiment. Relative to the controls, the Compudose implant had increased (P