Beef calves raised in intensive cow-calf production systems encounter different physiological and environmental challenges than calves raised in traditional, extensive cow-calf production systems. This research examined the effects of a partial-intensive and extensive cow-calf production system on post-weaning calf growth and greenhouse gas emissions. Compared to calves from the extensive cow-calf system, calves raised in the partial-intensive cow-calf system required an additional 27 d on feed to reach the targeted backfat thickness before harvest, and produced more total methane and CO2. An experiment was conducted over 2 yr to measure performance and greenhouse gas (GHG) emissions of weaned calves from two cow-calf production systems. Crossbred steers and heifers (n = 270, initial body weight (BW) = 207 kg, SD = 35) were used in a randomized complete block design, with treatments applied to the cow-calf system. Treatments were: 1) a traditional system consisting of April to June calving with smooth bromegrass pasture and grazed corn residue as forage resources (TRAD); 2) an alternative system consisting of July to September calving utilizing partial-drylot feeding, summer-planted oats, and corn residue grazing (ALT). Calves from both production systems were weaned at the same age and grown (diet NEg = 1.05 Mcal kg(-1)) for approximately 117 d. The calves then transitioned to a high-grain finishing diet (year 1: NEg = 1.32 Mcal kg(-1); year 2: NEg = 1.39 Mcal kg(-1)) and fed to a targeted 1.52 cm backfat. Growth performance in the grower phase resulted in greater (P < 0.01) average daily gain (1.39 vs. 1.22 +/- 0.02 kg), greater gain:feed (P < 0.01; 0.157 vs. 0.137 +/- 0.003) for ALT calves compared to TRAD calves, However, a lower initial BW (P < 0.01; 185 vs. 229 +/- 4.9 kg) resulted in a lower ending BW (P < 0.01; 347 vs. 371 +/- 2.9 kg) for ALT calves compared to TRAD calves in spite of improved growth performance. In the finisher phase, ALT calves gained less (1.52 vs. 1.81 +/- 0.218 kg; P = 0.02), were less efficient (0.139 vs. 173 +/- 0.0151; P = 0.01) but exhibited similar hot carcass weights (HCW) (388 vs. 381 +/- 3.8 kg; P = 0.14) compared to TRAD calves. Each pen of calves was put into a large pen-scale chamber that continuously measured carbon dioxide (CO2) and methane (CH4) for 5 d during the grower and finisher phases. The average CH4 and CO2 production per unit of feed intake was used to calculate total GHG emissions over the entire grower and finisher phase. Overall, there were no differences (P >= 0.17) between treatments for CH4 per day and per kilogram dry matter intake (DMI). However, ALT calves tended to produce less (P <= 0.10) CO2 per day and per kilogram DMI than TRAD calves. Overall, methane emissions were greater in ALT calves (110.7 vs. 92.2 +/- 8.3 g CH4 kg(-1) HCW; P = 0.04) than TRAD calves. The ALT calves required 27 additional days on feed to market, which resulted in more total CH4 per animal across the entire feeding period (P = 0.02) than TRAD calves. Production systems that reduce days to market to achieve similar HCW may reduce GHG emissions. Lay Summary There are many reasons (i.e. drought, limited perennial forage, calving) for using intensive or partially intensive production practices (e.g. drylotting or confinement) in a cow-calf enterprise. These practices may impact subsequent calf growth and feedlot performance. In addition, limited data are available comparing the environmental impacts (i.e., greenhouse gas (GHG) emissions) from different cow-calf production systems. This experiment evaluated the effects of a partial-intensive cow-calf production system on post-weaning calf growth performance, carcass characteristics, and GHG emissions. Calves from the partial-intensive cow-calf system had improved growth compared to calves from the extensive cow-calf system during the grower phase. During finishing, calves from the partial-intensive cow-calf system had poorer growth performance resulting in calves from the partial-intensive cow-calf system requiring an additional 27 d on feed to reach finish as calves from the traditional cow-calf system. These differences are likely due to compensation from lower gain periods resulting in better gain in the subsequent growth period. Cow-calf production system did not alter methane and carbon dioxide emissions per kilogram of intake. However, because calves in the partial-intensive cow-calf system required additional days on feed, absolute methane and carbon dioxide emissions were greater per animal for the partial-intensive cow-calf system compared to the extensive cow-calf system suggesting that reducing days to market may reduce emissions from beef systems.
