A systematic review and meta-analysis of impact of strongyle parasitism on growth rates in young cattle.

BACKGROUND: To identify any universal impact of strongyle parasite burden on the growth rate of young cattle. METHODS: A meta-analysis and meta-regression of the relationship between differences in strongyle parasite burden between cohorts and average daily weight gain was conducted. Publications were identified from a search of databases applying PRISMA 2020 principles. Eligible studies had at least two groups of growing cattle on the same farm that were identical in composition, management and diet except for parasite exposure and were subject to body weight gain or average daily gain and faecal egg count measurements across the common growing period. The reference group had the lowest growth-period faecal egg count. A meta-regression estimated the impact of strongyle parasitism. The dependent variable was the log of the ratio of average daily gain between comparison groups and the reference group with the predictor variable as the common logarithm of the difference in average faecal egg count (plus 1) between the comparison and the reference groups. RESULTS: 26 publications containing 85 groups and 59 comparison ratios were analysed. Papers included representatives from dairy and beef industries and from pasture and feedlot production systems and from all cattle-producing continents. The comparison group average daily growth rate was 0.89 (95%CI 0.81-0.97) that of the reference group. Meta-regression identified a 0.131 linear reduction in average daily weight gain ratio for every log10 increase in the difference between comparison and reference group faecal egg count. Direction of effect was consistent across all subset analyses (continent, class of stock and production system). Whilst small faecal egg count differences between the comparison and reference groups often provided similar rates of daily weight gain, the trend was negative with most comparison groups having lower daily weight gains than their reference group. CONCLUSIONS: Strongyle parasitism of growing cattle as measured by faecal egg count is associated with reduced growth across all production systems, geographies and classes of cattle.

Modeling the effects of steroid implant use on the environmental and economic sustainability of Brazilian beef production.

Brazilian beef systems contribute 14.9% of global beef production, therefore given climate change concerns, there is a clear need to reduce environmental impacts while maintaining economic viability. This study evaluated the hypothesis that steroid implant use in Brazilian beef cattle would reduce resource use, greenhouse gas (GHG) emissions and economic costs of production, thereby improving environmental and economic sustainability. A deterministic model based on beef cattle population demographics, nutrition and performance was used to quantify resource inputs and GHG emissions per 1.0 × 106 kg of hot carcass weight (HCW) beef. System boundaries extended from cropping input manufacture to cattle arriving at the slaughterhouse. Beef systems were modeled using herd population dynamics, feed and performance data sourced from producers in four Brazilian states, with additional data from global databases. Implants were used in calves, growing and finishing cattle at low (LI), medium (MI), and high (HI) levels of performance enhancement, compared to nonimplanted (NI) controls. Feed use results were used in combination with producer-derived input costs to assess the economic impacts of implant use, including production costs and returns on investment. Improved FCE, ADG, and carcass weights conferred by implant use reduced the number of cattle and the time taken to produce 1.0 × 106 kg HCW beef. Compared to NI controls, the quantities of feed, land, water and fossil fuels required to produce 1.0 × 106 kg HCW beef was reduced in implanted cattle, with reductions proportional to the performance-enhancing effect of the implant (HI > MI > LI). Implant use reduced GHG emissions per 1.0 × 106 kg HCW beef by 9.4% (LI), 12.6% (MI), or 15.8% (HI). Scaling up the MI effects to represent all eligible Brazilian cattle being implanted, revealed avoided GHG emissions equivalent to the annual exhaust emissions of 62.0 × 106 cars. Economic impacts of implant use reflected the environmental results, resulting in a greater margin for the producers within each system (cow-calf through to finishing). The 6.13% increase in kg of HCW beef produced generates a cost reduction of 3.76% and an increase in the return on invested capital of 4.14% on average. Implants offer the opportunity for Brazilian beef producers to demonstrate their dedication to improving environmental and economic sustainability through improved productivity, although care must be taken to avoid negative trade-offs.