Dry and wet conditions during the prepartum forage growing season affect offspring feedlot performance and carcass composition in beef cattle

Abstract Text: We hypothesize that dry and wet conditions during the prepartum forage growing season impact cow nutrient availability during pregnancy, resulting in altered fetal growth and development, and affecting subsequent feedlot performance and carcass composition. Steers (n = 7,439) and heifers (n = 2,380) finished in southwestern Iowa feedlots through the Tri-County Steer Carcass Futurity Cooperative were used for a retrospective analysis. Cattle were born in the Midwest (Iowa, Missouri, Indiana, Illinois, and Minnesota) in February, March, or April of 2002 to 2013. Feedlot performance and carcass data were measured for each animal. Palmer Drought Severity Index (PDSI) values were obtained for each dam during the prepartum forage growing season (April through October) on a monthly basis. Conditions were classified as dry (mean PDSI value ≤ -2.00), normal (mean PDSI value > -2.00 and < 2.00), or wet (mean PDSI value ≥ 2.00) during this period. Data were analyzed using the MIXED procedure of SAS with PDSI drought classification, birth year, feedlot, and calf sex included as fixed effects. Feedlot delivery BW was greatest (P < 0.01) for calves born to dams in the wet class, intermediate (P < 0.01) for normal, and least (P < 0.01) for dry. Feedlot ADG was greater (P < 0.01) for calves from cows in the dry class compared with normal and wet, suggesting compensatory growth. Calves born to dams in the normal class had a greater (P = 0.02) number of days on feed than wet. Calculated yield grade was improved (P < 0.01) for calves from normal and wet classes compared with dry, partially because calves born to cows in the normal class had greater (P ≤ 0.01) LM area than dry and wet. Calves born to cows in the dry class had the most (P < 0.01) 12^th rib fat and marbling, normal were intermediate (P ≤ 0.03), and calves from wet had the least (P ≤ 0.03). Despite this, drought classification did not affect (P ≥ 0.39) final pre-slaughter BW, HCW, or dressing percent. In conclusion, prepartum forage growing season precipitation likely impacts offspring post-weaning growth and carcass characteristics by altering nutrient intake of cows throughout gestation due to grazing during the growing season and consumption of stored forage in winter. More research is necessary to investigate the impacts of dry and wet conditions during specific periods of fetal development on subsequent calf performance.

Keywords: developmental programming, drought, post-weaning