Effects of Nutrition and Time of Weaning on Dry Season Liveweight Loss of Breeder Cows

In the seasonally dry tropics of northern Australia, breeder cows may lose up to 30% liveweight during the dry season when pasture is of low nutritive value. This is a major cause of low reproductive rates and high mortality. Weaning early in the dry season is effective to reduce this liveweight loss of the breeder (Holroyd et al. 1988). An experiment examined the dry season liveweight loss of breeders for a range of weaning times and levels of nutrition. From April to October through the dry season, 209 Bos indicus x Shorthorn cross cows 4-6 years of age grazed speargrass pastures in north Queensland. The cows had been joined with bulls from late January until April. Twenty-nine breeders had not suckled a calf during the previous wet season (DRY cows). In addition 180 cows lactating in April were weaned in late April, mid July or early September. The cows were allocated by stratified randomisation based on lactational status, stage of pregnancy and body condition to 15 x 40 ha paddocks. Five paddocks with low fertility soils provided LOW nutrition, while 10 paddocks with medium fertility soils and no supplementation or with supplementation provided MEDIUM and HIGH nutrition, respectively. The supplement consisted of molasses containing 14% urea offered ad libitum. Liveweight was measured at intervals and conceptus-free liveweight (CF-LW) calculated. Data were analyses by AOV within groups of paddocks. Animal production for a consuming world : proceedings of 9th Congress of the Asian-Australasian Association of Animal Production Societies [AAAP] and 23rd Biennial Conference of the Australian Society of Animal Production [ASAP] and 17th Annual Symposium of the University of Sydney, Dairy Research Foundation, [DRF]. 2-7 July 2000, Sydney, Australia.

Influence of nitrogen based supplements on live weight, fertility and mortality of heifers grazing dry season native pasture

Supplements containing urea or biuret were fed in the dry season to yearling and two year old pregnant heifers grazing native spear grass pastures in north Queensland. Liveweight change and survival during the dry season and fertility in the following year were measured. In the first experiment during a relatively favourable dry season, supplementation significantly (P<0.01) reduced liveweight loss in yearling heifers (5 vs. 32 kg). In the following year during a drought, supplement significantly (P<.01) reduced liveweight loss in yearling heifers (32 vs. 41 kg) and significantly (P <0.01) reduced mortalities (23.5% vs. 5.2%) in pregnant and lactating heifers. The supplement had no significant effect on subsequent fertility in either experiment. 14th Biennial Conference.

Defining and predicting the 'break of the season' for north-east Queensland grazing areas

For pasture growth in the semi-arid tropics of north-east Australia, where up to 80% of annual rainfall occurs between December and March, the timing and distribution of rainfall events is often more important than the total amount. In particular, the timing of the 'green break of the season' (GBOS) at the end of the dry season, when new pasture growth becomes available as forage and a live-weight gain is measured in cattle, affects several important management decisions that prevent overgrazing and pasture degradation. Currently, beef producers in the region use a GBOS rule based on rainfall (e. g. 40mm of rain over three days by 1 December) to define the event and make their management decisions. A survey of 16 beef producers in north-east Queensland shows three quarters of respondents use a rainfall amount that occurs in only half or less than half of all years at their location. In addition, only half the producers expect the GBOS to occur within two weeks of the median date calculated by the CSIRO plant growth days model GRIM. This result suggests that in the producer rules, either the rainfall quantity or the period of time over which the rain is expected, is unrealistic. Despite only 37% of beef producers indicating that they use a southern oscillation index (SOI) forecast in their decisions, cross validated LEPS (linear error in probability space) analyses showed both the average 3 month July-September SOI and the 2 month August-September SOI have significant forecast skill in predicting the probability of both the amount of wet season rainfall and the timing of the GBOS. The communication and implementation of a rigorous and realistic definition of the GBOS, and the likely impacts of anthropogenic climate change on the region are discussed in the context of the sustainable management of northern Australian rangelands.

Genetics of heifer performance in 'wet' and 'dry' seasons and their relationships with steer performance in two tropical beef genotypes.

The genetics of heifer performance in tropical 'wet' and 'dry' seasons, and relationships with steer performance, were studied in Brahman (BRAH) and Tropical Composite (TCOMP) (50% Bos indicus, African Sanga or other tropically adapted Bos taurus; 50% non-tropically adapted Bos taurus) cattle of northern Australia. Data were from 2159 heifers (1027 BRAH, 1132 TCOMP), representing 54 BRAH and 51 TCOMP sires. Heifers were assessed after post-weaning 'wet' (ENDWET) and 'dry' (ENDDRY) seasons. Steers were assessed post-weaning, at feedlot entry, over a 70-day feed test, and after similar to 120-day finishing. Measures studied in both heifers and steers were liveweight (LWT), scanned rump fat, rib fat and M. longissimus area (SEMA), body condition score (CS), hip height (HH), serum insulin-like growth factor-I concentration (IGF-I), and average daily gains (ADG). Additional steer measures were scanned intra-muscular fat%, flight time, and daily (DFI) and residual feed intake (RFI). Uni- and bivariate analyses were conducted for combined genotypes and for individual genotypes. Genotype means were predicted for a subset of data involving 34 BRAH and 26 TCOMP sires. A meta-analysis of genetic correlation estimates examined how these were related to the difference between measurement environments for specific traits. There were genotype differences at the level of means, variances and genetic correlations. BRAH heifers were significantly (P < 0.05) faster-growing in the 'wet' season, slower-growing in the 'dry' season, lighter at ENDDRY, and taller and fatter with greater CS and IGF-I at both ENDWET and ENDDRY. Heritabilities were generally in the 20 to 60% range for both genotypes. Phenotypic and genetic variances, and genetic correlations, were commonly lower for BRAH. Differences were often explained by the long period of tropical adaptation of B. indicus. Genetic correlations were high between corresponding measures at ENDWET and ENDDRY, positive between fat and muscle measures in TCOMP but negative in BRAH (mean of 13 estimates 0.50 and -0.19, respectively), and approximately zero between steer feedlot ADG and heifer ADG in BRAH. Numerous genetic correlations between heifers and steers differed substantially from unity, especially in BRAH, suggesting there may be scope to select differently in the sexes where that would aid the differing roles of heifers and steers in production. Genetic correlations declined as measurement environments became more different, the rates of decline (environment sensitivity) sometimes differing with genotype. Similar measures (LWT, HH and ADG; IGF-I at ENDWET in TCOMP) were genetically correlated with steer DFI in heifers as in steers. Heifer SEMA was genetically correlated with steer feedlot RFI in BRAH (0.75 +/- 0.27 at ENDWET, 0.66 +/- 0.24 at ENDDRY). Selection to reduce steer RFI would reduce SEMA in BRAH heifers but otherwise have only small effects on heifers before their first joining.

Intake, growth and carcass characteristics of lambs consuming low digestible hay and cereal grain

The influence of barley and oat grain supplements on hay dry matter intake (DMI), carcass components gain and meat quality in lambs fed a low quality basal diet was examined. Thirty five crossbred wether lambs (9 months of age) were divided into four groups. After adaptation to a basal diet of 85% oat hay and 15% lucerne hay for one week, an initial group of 11 was slaughtered. The weights of carcass components and digesta-free empty body weight (EBW) of this group was used to estimate the weight of carcass components of the other three experimental groups at the start of the experiment. The remaining three groups were randomly assigned to pens and fed ad libitum the basal diet alone (basal), basal with 300 g air dry barley grain (barley), basal with 300 g air dry oat grain (oat). Supplements were fed twice weekly (i.e., 900 g on Tuesday and 1200 g on Friday). After 13 weeks of feeding, animals were slaughtered and, at 24 h post-mortem meat quality and subcutaneous fat colour were measured. Samples of longissimus muscle were collected for determination of sarcomere length and meat tenderness. Hay DMI was reduced (P<0.01) by both barley and oat supplements. Lambs fed barley or oat had a higher and moderate digestibility of DM, and a higher intake of CP (P<0.05) and ME (P<0.01) than basal lambs. Final live weight of barley and oat lambs was higher (P<0.05) than basal, but this was not reflected in EBW or hot carcass weight. Lambs fed barley or oat had increases in protein (P<0.01) and water (P<0.001) in the carcass, but fat gain was not changed (P>0.05). There were no differences in eye muscle area or fat depth (total muscle and adipose tissue depth at 12th rib, 110 mm from midline; GR) among groups. The increased levels of protein and water components in the carcass of barley and oat fed lambs, associated with improved muscle production, were small and did not alter (P>0.05) any of the carcass/meat quality attributes compared to lambs fed a low quality forage diet. Feeding barley or oat grain at 0.9–1% of live weight daily to lambs consuming poor quality hay may not substantially improve carcass quality, but may be useful in maintaining body condition of lambs through the dry season for slaughter out of season

Vaccination with an Insulin-like Growth Factor Binding Protein-1 (IGFBP-1)-bBased Vaccine Improves Growth in Feed-Restricted Brahman Steers

Dry-season weight loss in grazing cattle in northern Australia has been attenuated using a number of strategies (Hunter and Vercoe, 1987, Sillence et al. 1993, Gazzola and Hunter, 1999). Furthermore, the potential to improve efficiency of feed utilisation (and thus, dry-season performance) in ruminants through conventional modulation of the insulin-like growth factor (IGF) axis (Oddy and Owens, 1997, Hill et al., 1999) and through immunomodulation of the IGF axis (Hill et al., 1998a,b) has been demonstrated. The present study investigated the use of a vaccine directed against IGFBP-1 in Brahman steers which underwent a period of nutritional restriction followed by a return to wet-season grazing.

Isolation of Pseudomonas pseudomallei from clay layers at defined depths

Twelve strains of Pseudomonas pseudomallei were isolated from the soil and water of a sheep paddock over a two-year period. The organism was recovered from the clay layer of the soil profile as well as from water that seeps into this layer during the "wet" season. Five isolates were obtained before the commencement of the "wet" season; environmental factors appear to play an important role in the survival of Ps. pseudomallei during the "dry" season. Lower isolation rates were recorded than those indicated by workers in southeast Asia and Iran.

Seasonal resource availability and use by an endangered tropical mycophagous marsupial

This study highlights the importance of considering how seasonality of rainfall affects availability of resources and consequently species distributions within tropical ecosystems. The endangered northern bettong, Bettongia tropica Wakefield is thought to be restricted to habitats where seasonal availability of hypogeous fungi, their principal food resource, remains high. To test this hypothesis fungal abundance was quantified in the early wet, late wet, early dry and late dry seasons within known bettong habitat. A relationship was found between precipitation and fungal availability, with the abundance of hypogeous fungi being significantly lower in the late dry season. Fungal availability correlated strongly with the seasonal rainfall pattern determined from 74-year monthly means. This contrasts with a previous study where mycophagy, measured by faecal analysis, remained high across seasons presumably because of aseasonal rainfall during that study period. Alloteropsis semialata R.Br. (cockatoo grass) use by bettongs increased significantly during the period of low fungal availability. This suggests that the importance of cockatoo grass as an alternative food resource during annual and extended dry periods has previously been underestimated. With the frequency and intensity of drought expected to increase with global climate change, these findings have significant implications for bettong management. The important and possibly equivalent dependence of B. tropica on both hypogeous fungi and A. semialata helps to explain their habitat preference and identifies this species as a true ecotonal specialist.

Incidence and pathogenicity of Phytophthora palmivora and Pythium vexans associated with durian decline in far northern Queensland

In recent years, dieback of durian has become a major problem in mature orchards in the northern Queensland wet tropics region. A survey of 13 durian orchards was conducted during the dry season (July-September 2001) and following wet season (February-April 2002), with roots and soil from the root zone of affected trees being sampled. Phytophthora palmivora was recovered from the roots of affected trees on 12 of the 13 farms in the dry season, and all farms in the wet season. Pythium vexans was recovered from all 13 farms in both seasons. P. palmivora and P. vexans were recovered from diseased roots of 3-month-old durian seedlings cv. Monthong artificially inoculated with these organisms.

Spatial and temporal patterns of feral pig diggings in rainforests of north Queensland

Feral pigs (Sus scrofa) are believed to have a severe negative impact on the ecological values of tropical rainforests in north Queensland, Australia. Most perceptions of the environmental impacts of feral pigs focus on their disturbance of the soil or surface material (diggings). Spatial and temporal patterns of feral pig diggings were identified in this study: most diggings occurred in the early dry season and predominantly in moist soil (swamp and creek) microhabitats, with only minimal pig diggings found elsewhere through the general forest floor. The overall mean daily pig diggings were 0.09% of the rainforest floor. Most diggings occurred 3-4 months after the month of maximum rainfall. Most pig diggings were recorded in highland swamps, with over 80% of the swamp areas dug by pigs at some time during the 18-month study period. These results suggest that management of feral pig impacts should focus on protecting swamp and creek microhabitats in the rainforest, which are preferred by pigs for digging and which have a high environmental significance.

Evaluation of a remote drafting system for regulating sheep access to supplement

Remote drafting technology now available for sheep makes possible targeted supplementation of individuals within a grazing flock. This system was evaluated by using 68 Merino wethers grazing dry-season, native Mitchell grass pasture (predominantly Astrebla spp.) as a group and receiving access to lupin grain through a remote drafter 0, 1, 2, 4 or 7 days/week for 8 weeks. The sole paddock watering point was separately fenced and access was via a one-way flow gate. Sheep exited the watering point through a remote drafter operated by solar power and were drafted by radio frequency identification (RFID) tag, according to treatment, either back into the paddock or into a common supplement yard where lupins were provided ad libitum in a self-feeder. Sheep were drafted into the supplement yard on only their first time through the drafter during the prescribed 24-h period and exited the supplement yard via one-way flow gates in their own time. The remote drafter operated with a high accuracy, with only 2.1% incorrect drafts recorded during the experimental period out of a total of 7027 sheep passes through the remote drafter. The actual number of accesses to supplement for each treatment group, in order, were generally less than that intended, i.e. 0.02, 0.69, 1.98, 3.35 and 6.04 days/week. Deviations from the intended number of accesses to supplement were mainly due to sheep not coming through to water on their allocated day of treatment access, although some instances were due to incorrect drafts. There was a non-linear response in growth rate to increased frequency of access to lupins with the growth rate response plateauing at similar to 3 actual accesses per week, corresponding to a growth rate of 72.5 g/head. day. This experiment has demonstrated the application of the remote drafting supplementation system for the first time under grazing conditions and with the drafter operated completely from solar power. The experiment demonstrates a growth response to increasing frequency of access to supplement and provides a starting point with which to begin to develop feeding strategies to achieve sheep weight-change targets.

Migration of feral pigs (Sus scrofa) in rainforests of north Queensland: fact or fiction?

The Wet Tropics bioregion of north Queensland has been identified as an area of global significance. The world-heritage-listed rainforests have been invaded by feral pigs (Sus scrofa) that are perceived to cause substantial environmental damage. A community perception exists of an annual altitudinal migration of the feral-pig population. The present study describes the movements of 29 feral pigs in relation to altitudinal migration (highland, transitional and lowland areas). Feral pigs were sedentary and stayed within their home range throughout a 4-year study period. No altitudinal migration was detected; pigs moved no more than a mean distance of 1.0 km from the centre of their calculated home ranges. There was no significant difference between the mean (+/- 95% confidence interval) aggregate home ranges for males (8.7 +/- 4.3 km², n = 15) and females (7.2 +/- 1.8 km², n = 14). No difference in home range was detected among the three altitudinal areas: 7.2 +/- 2.4 km² for highland, 6.2 +/- 3.9 km² for transitional and 9.9 +/- 5.3 km² for lowland areas. The aggregate mean home range for all pigs in the present study was 8.0 +/- 2.4 km². The study also assessed the influence seasons had on the home range of eight feral pigs on the rainforest boundary; home ranges did not significantly vary in size between the tropical wet and dry seasons, although the mean home range in the dry season (7.7 +/- 6.9 km²) was more than twice the home range in the wet season (2.9 +/- 0.8 km²). Heavier pigs tended to have larger home ranges. The results of the present study suggest that feral pigs are sedentary throughout the year so broad-scale control techniques need to be applied over sufficient areas to encompass individual home ranges. Control strategies need a coordinated approach if a long-term reduction in the pig population is to be achieved.

Genetics of heifer puberty in two tropical beef genotypes in northern Australia and associations with heifer- and steer-production traits

A total of 2115 heifers from two tropical genotypes (1007 Brahman and 1108 Tropical Composite) raised in four locations in northern Australia were ovarian-scanned every 4-6 weeks to determine the age at the first-observed corpus luteum (CL) and this was used to de. ne the age at puberty for each heifer. Other traits recorded at each time of ovarian scanning were liveweight, fat depths and body condition score. Reproductive tract size was measured close to the start of the first joining period. Results showed significant effects of location and birth month on the age at first CL and associated puberty traits. Genotypes did not differ significantly for the age or weight at first CL; however, Brahman were fatter at first CL and had a small reproductive tract size compared with that of Tropical Composite. Genetic analyses estimated the age at first CL to be moderately to highly heritable for Brahman (0.57) and Tropical Composite (0.52). The associated traits were also moderately heritable, except for reproductive tract size in Brahmans (0.03) and for Tropical Composite, the presence of an observed CL on the scanning day closest to the start of joining (0.07). Genetic correlations among puberty traits were mostly moderate to high and generally larger in magnitude for Brahman than for Tropical Composite. Genetic correlations between the age at CL and heifer- and steer-production traits showed important genotype differences. For Tropical Composite, the age at CL was negatively correlated with the heifer growth rate in their first postweaning wet season (-0.40) and carcass marbling score (-0.49), but was positively correlated with carcass P8 fat depth (0.43). For Brahman, the age at CL was moderately negatively genetically correlated with heifer measures of bodyweight, fatness, body condition score and IGF-I, in both their first postweaning wet and second dry seasons, but was positively correlated with the dry-season growth rate. For Brahman, genetic correlations between the age at CL and steer traits showed possible antagonisms with feedlot residual feed intake (-0.60) and meat colour (0.73). Selection can be used to change the heifer age at puberty in both genotypes, with few major antagonisms with steer- and heifer- production traits.

Calf wastage - how big an issue is it?

What is calf wastage. Breeding female cattle in north Australia contribute best to business success by producing a heavy weaner each year at the first weaning round. This maximises increase in value by the cow unit over the year, generally from mid-year to mid-year. The ability to cycle in both maiden heifers and lactating cows is the primary limitation to achieving this. Wastage of a calf at any stage between conception and weaning also substantially limits fertility and value increase at a herd level. Embryo loss may result in later calves as cows re-conceive; the calves produced are smaller at weaning and have to be weaned later into the dry season. Late calf wastage usually results in breeders missing a calf for the year. Late calving often also results in failure to cycle, thus cows rear a calf in the subsequent year.

Using Trichogramma Westwood (Hymenoptera: Trichogrammatidae) for insect pest biological control in cotton crops: an Australian perspective.

Trichogramma Westwood egg parasitoids alone generally fail to suppress heliothine pests when released in established cotton-growing regions. Factors hindering their success include indiscriminate use of detrimental insecticides, compensation for minimal pest larval hatch due to their activity via reduced larval cannibalism or mortality in general, singly laid heliothine eggs avoiding detection and asynchronous development benefiting host over parasitoid. Yet, despite these limitations, relatively large Trichogramma pretiosum Riley populations pervade and effectively suppress Helicoverpa (Hardwick) pests in Australian Bt (Bacillus thuringiensis Berliner)-transgenic cotton, Gossypium hirsutum L., crops, especially in the Ord River Irrigation Area (ORIA) of tropical northern Australia, where their impact on the potentially resistant pest species, Helicoverpa armigera (Hubner), is considered integral to the local insecticide resistance management (IRM) strategy for continued, sustainable Bt-transgenic cotton production. When devoid of conventional insecticides, relatively warm and stable conditions of the early dry season in winter grown ORIA Bt-transgenic cotton crops are conducive to Trichogramma proliferation and biological control appears effective. Further, there is considerable scope to improve Trichogramma's biological control potential, in both the ORIA and established cotton-growing regions, via habitat manipulation. It is proposed that Trichogramma may prove equally effective in developing agricultural regions of monsoonal northern Australia, and that environmental constraints on Trichogramma survival, and those of other natural enemies, require due consideration prior to their successful application in biological control programs.