Loss of patch-scale heterogeneity on secondary productivity in the arid shrubland of Western Australia

General models of degradation suggest soil and nutrients are lost and conversion of rainfall into primary productivity is diminished when rangeland is degraded. These models are supported by studies on non-resilient landscapes, where loss of primary productivity also translated into loss of secondary productivity, but have not been tested on resilient landscapes. Elsewhere we showed that loss of chenopod shrubs from a landscape characterized as resilient was associated with declines in plant productivity and efficiency of conversion of rainfall into plant mass. To explore whether these differences in primary productivity translated into differences in secondary productivity, we grazed sheep at five rates of stocking for 10 years on 2000 ha of this landscape. The experiment was necessarily replicated in time not space (i.e. pseudo-replicated), which limits confident extrapolation of results to other landscapes. Productivity of sheep at all except highest rates of stocking varied little between sites where shrubs were abundant or scarce. From an animal production point of view, greater rates of stocking were unsustainable through dry years on the degraded site, but animal performance was generally unaffected on the non-degraded site, where shrubs were abundant. While these results provide evidence of economic penalties associated with degrading a resilient landscape, important ecological penalties were only partially explored

Divergent breeding values for fatness or residual feed intake in Angus cattle. 4. Fat EBVs

The productivity of 500 Angus cows, divergently selected for either rib fat or residual feed intake (RFI) based on BREEDPLAN estimated breeding values (EBVs) and managed under two levels of nutrition (stocking rates), was evaluated. The study examined the effects of genetic line, nutrition and weaning history on profiles for weight, rib fat depth, fatness (rib fat depth adjusted for weight) and supplementary feed requirements from just before the first joining as heifers through to the weaning of their third calf. Cows gained both weight and fat as they grew older. Observed fluctuations in weight and rib fat depth, within each year, were associated with pasture availability and physiological demands. Cows that did not wean a calf in a given year became heavier and fatter than cows that did; and they remained so when they calved the following year. High-fat and High-RFI were always fatter and lighter than Low-fat and Low-RFI cows, respectively. The difference in rib fat and fatness between High- and Low-RFI lines (P 0.05). Supplementary feeding threshold was reached earlier by Low-fat and Low-RFI cows than their counterparts. Calculations based on the data in the present paper estimate that if cows lose condition at a rapid rate (1 condition score/month), then a cow with an extra 1 mm rib fat EBV would take 7.5 days longer to reach the same supplementary feeding threshold. Fat EBVs can, therefore, be a useful tool in assisting beef producers to match genotype to their production system

Divergent breeding values for fatness or residual feed intake in Angus cattle. 1. Pregnancy rates of heifers differed between fat lines and were affected by weight and fat

The pregnancy rate of heifers affects the efficiency and profitability of beef herds. Heifers extreme in rib fatness (Fat) or post-weaning residual feed intake (RFI) estimated breeding values (EBVs) were evaluated for their pregnancy rates at two locations in the southern agricultural regions of Australia (Struan and Vasse) as part of the Beef Cooperative Research Centre Maternal Productivity Project. Heifers divergent in Fat (High-Fat and Low-Fat) had differences in fat depth pre-joining at the 12/13th rib (4.4 mm vs 3.5 mm) and P8 rump site (6.1 mm vs 4.8 mm). This was associated with significant differences in pregnancy rates over a 9-week joining period (91.5% vs 83.0%) and an even larger difference when calculated over a 6-week joining period (77.3% vs 65.0%). Heifers divergent in RFI (Vasse only) also differed in rib fat (7.6 mm vs 6.4 mm) and P8 fat (11.0 vs 9.2 mm), but not significantly in pregnancy rates between the two RFI (High-RFI and Low-RFI) genotypes following a 9-week (92.4% vs 88.5%) or 6-week (81.2% vs 73.7%) joining period. The phenotypic analysis of the Fat and RFI heifers together indicated that weight and fat depth were the largest contributing factors to variation in pregnancy rates, and age and pre-joining weight gain were not significant. These phenotypic characteristics indicated that producers can manage heifers to particular weight and fat combinations to improve heifer conception rates. Associations of BREEDPLAN EBVs with heifer fertility showed that a shorter days-to-calving EBV had the biggest impact (P < 0.001) on heifer pregnancy rates and rib fat and scrotal size EBVs were close to significant (P < 0.10)

Divergent genotypes for fatness or residual feed intake in Angus cattle. 2. Body composition but not reproduction was affected in first-parity cows on both low and high levels of nutrition

This paper reports a subset of results from the Beef Cooperative Research Centre-funded Maternal Productivity Project. This research aimed to describe the response of Angus cows of different and divergent genotypes to variable nutritional environments over five breeding seasons. Cows selected for a divergence in either fat depth (HFat vs LFat) or residual feed intake (RFI: HRFI vs LRFI) based on mid-parent estimated breeding values (EBV) for those traits were allocated in replicate groups to either high or low nutritional treatments at two different sites, namely the Vasse Research Centre in Western Australia and the Struan Research Centre in South Australia. The traits reported in this paper include output traits (birth and weaning weight of calves, liveweight change of cows), change traits (change in Rib Fat, P8 fat, eye muscle area and liveweight between specified time points) and reproductive traits [pregnancy rates, percentage calves born alive and days to calving at the days to calving at the second calving opportunity (DC2)]. Having had their first calf, the vulnerability of these young cows to nutritional restriction and how it may adversely affect rebreeding was examined. HFat and HRFI cows were fatter, heavier and had greater eye muscle area than LFat and LRFI, respectively, at all times during the breeding cycle on both levels of nutrition. There was no difference in either days-to-calving or pregnancy rates after the second mating between genotypes. Equally, nutritional treatment had no effect on these traits in this cohort of cows. There was evidence for an implied genetic correlation between Rib Fat EBV, DC2 and pregnancy rates of –0.38 that suggests that selection for leanness may result in reduced fertility of the herd but the effect was not significant herein. As long as producers record the phenotype for both traits and select cows with favourable DC2 as well as low fatness, these problems can be avoided, owing to only 22% of variation in pregnancy rates being explained by DC2 and Rib Fat EBV. Producers can largely be confident that selection for leanness, or increased feed efficiency, has little impact on productivity as long as cows are in adequate body condition to remain healthy and productive

Divergent genotypes for fatness or residual feed intake in Angus cattle. 3. Performance of mature cows

This experiment evaluated the productivity of 500 Angus cows that differed in genetic merit for either subcutaneous rib fat depth (Fat) or residual feed intake (RFI) based on estimated breeding values (EBVs) and managed under two levels of nutrition. Reproductive rate over four calving opportunities in mature cows and growth performance of progeny to weaning was assessed. Level of nutrition significantly affected all body composition traits for both Fat and RFI line cows. Cows on High-Nutrition were 14–16% heavier (P < 0.001) than those on Low-Nutrition. Differences in EBVs for fatness were reflected in phenotypic fatness at maturity. High-RFI line cows were fatter for both scanned rump (P8) and rib (RIB) fat depth relative to their Low-RFI contemporaries. Of those cows that were lactating, there was no significant effect of line or nutrition on pregnancy rate or days to calving (DC). There was, however, a trend (P < 0.1) in the Low-Fat line cows towards longer DC compared with the High-Fat line cows. There was no significant effect of either line or nutrition on calf birthweight. Calves with mothers on High-Nutrition were 8% heavier at weaning (P < 0.001) than those on Low-Nutrition. Lower EBVs for RFI was associated with higher 200-day growth EBV and heavier calves at weaning. Current carcass BREEDPLAN EBVs can be used to select for changes in cow body composition if desired. In this experiment, Angus cows selected for lower RFI or with below-average fatness EBV and had raised a calf at every previous opportunity were not compromised in pregnancy rate or DC at maturity under varying nutrition such as can be experienced during normal seasonal conditions in southern Australia. However, selection for lower RFI was associated with lower weaning rate (P < 0.05), which warrants further investigation to confidently predict the implications for commercial cattle production

Divergent genotypes for fatness or residual feed intake in Angus cattle. 7. Low-fat and low-RFI cows produce more liveweight and better gross margins than do high-fat and high-RFI cows when managed under the same conditions

The present paper focuses on the economic evaluation of the observed differences in maternal productivity of different genetic lines in Angus cattle that were managed under contrasting nutritional regimes typical of southern Australia. Five hundred Angus cows were managed concurrently at two locations in southern Australia. On each site, the cows were managed under the following two different nutritional treatments: High and Low, to simulate different stocking rates. Cows selected for a divergence in either carcass rib-fat depth or residual feed intake based on mid-parent estimated breeding values for those traits, were allocated in replicate groups to either High- or Low-nutrition treatments. By design, the supplementary feeding regime was the same for the High and Low genetic lines to ensure genetic differences were not confounded with management differences. Animal productivity results from the experiment were used as input data to evaluate the economic performance of the four genetic lines under the two nutritional treatments. Two methods were used; the first was a gross-margin calculation of income minus variable costs as AU$ per breeding cow for a 1000-cow herd; the second was a whole-farm linear programming model maximising the gross margin. Stocking rates were optimised by matching the energy requirements for the whole herd with the energy available from pasture and supplementary feed on a representative 700-ha farm. Using the two methods of calculating gross margin (per cow and optimised per hectare), including examination of sensitivity to changes in prices of cattle and supplementary feed, the present study demonstrated that genetically leaner cows due to selection of low fat or low residual feed intake, had gross margins superior to those of genetically fatter cows. They generated more income by selling more liveweight due to heavier weights and higher stocking rates. The results are affected by the management system utilised and some confounding with growth (leaner genetic lines had higher growth estimated breeding values), but will assist producers to make more informed decisions about how to manage animal breeding and nutritional interactions

Genesis, design and methods of the Beef CRC Maternal Productivity Project

Australian seedstock cattle breeders have expressed concerns that while there has been genetic improvement in feedlot and abattoir performance of cows, it could have led to a decline in maternal productivity, especially under variable nutritional conditions. This paper describes a substantial project with two components designed to address these issues. The first sub-project was to monitor bodyweight and composition of 7760 young Angus and Hereford cows as they experience variable physiological states (pregnancy and lactation) and seasons. This was conducted on large numbers in seedstock herds. The second sub-project was to monitor more regularly bodyweight, body composition, and calf rearing performance of 500 Angus cows that are genetically divergent for either fat or residual feed intake at two research centres. This also included two levels of nutrition and recording of weekly feed intake of small groups of cows for at least three parities to allow reporting of genotype × nutrition effects on maternal productivity and efficiency. Results from the project are reported in a series of papers with each one having a defined focus