A modeling assessment of cow management decisions, sustainability and durability of beef production systems

Abstract Text: Sophisticated calculations of system durability should be incorporated into sustainability assessments. The objective of this study was to assess how cow herd management affected the environmental impact (EI), economic viability and stability of a simulated beef herd. A modeling approach was used incorporating dynamic simulation of cattle genetic improvement with cradle-to-farmgate EI and income over feed costs (IOFC). Two 15 yr systems were simulated, one looking at culling rates of 1%, 5%, 10%, 15% or 20% (CULL) and one assessing culling rate differences with a trauma (random removal of 30% of the breeding herd) occurring in the 5^th year (CULL+T). Yearly changes in genetic merit were simulated using Markov Chain Monte Carlo sampling, expected progeny differences and the Key equation. Changes in conception/birth rate, mature weight, offspring daily gain, birth weight, weaning weight and yearling weight were tracked. Land use, water use and greenhouse gas emissions (GHG) and IOFC per kg hot carcass weight beef (HCWb) produced were calculated annually and yearly change was compared across culling levels. Trauma effects were calculated by interpolating across the points where the trauma occurred and calculating the cumulative difference between the CULL+T and interpolated lines. In the CULL scenario, the 15% cull rate resulted in the largest average annual improvement in EI and IOFC. Average yearly reductions in land, water and GHG were 2.4±5.7 m²/kg HCWb, 29±77 L/kg HCWb and 0.26±0.53 kg CO₂-equivalents (CO₂e)/kg HCWb. Annual change in IOFC was $0.03±$0.09/kg HCWb. In the CULL+T scenario, a 2 year system depression occurred and IOFC and EI were compromised. Culling at 10% was the least stable option; beef produced during the 2 yr trauma period had greater land use, water use and GHG (4.0 m²/kg HCWb, 420 L/kg HCWb and 3.74 kg CO₂e / kg HCWb) compared with the no trauma line. Culling at 5% was the most stable treatment; environmental changes were only 3.4 m²/kg HCWb, 374 L/kg HCWb and 3.26 kg CO₂e/kg HCWb. Culling at 1% was the most economically stable treatment; IOFC decreased $0.27/kg HCWb, substantially lower than losses seen with 10% or 15% culling (-$0.32/kg HCWb). Management that best optimized EI and IOFC did not always result in the most durable system. This model presents one framework for assessing durability that is applicable to multiple cow management decisions.

Keywords:

Cow-Calf; Sustainability; Durability