Evaluation of corn and barley varieties in extensive winter grazing systems for beef calves

Two experiments were conducted to determine the suitability of whole plant corn as an alternative forage to whole plant barley for winter grazing and the subsequent effect of extensive winter grazing systems on performance and carcass characteristics of beef steers during feedlot finishing. Experiment 1 evaluated the in vitro digestibility of dry matter (IVDMD) and neutral detergent fibre (IVNDFD) of whole plant corn (COR), whole plant barley (BAR) and processed barley hay (CON) collected on October and February sampling dates over 2 yrs. COR forage had similar (P>0.05) IVDMD and IVNDF to both CON or BAR forage. The IVDMD and IVNDFD also remained similar (P>0.05) between the October and February sampling date for COR and BAR forages and processed barley hay. Experiment 2 evaluated the effects of grazing either swathed whole plant barley, standing whole plant corn, or drylot fed barley hay on forage quality, estimated intake, calf performance and backgrounding production costs over 2 years. In each year, 120 spring born Angus calves (263.3 ± 5 kg; 169 d of age) were fall weaned, stratified by body weight and randomly allocated to 1 of 3 replicated (n = 2) backgrounding systems: 1) field grazing standing whole plant corn (COR); 2) field grazing swathed whole plant barley (BAR); or 3) dry lot (CON) bunk fed processed barley hay. Calves fed COR and BAR were limit grazed in 4-ha paddocks for a 3-d grazing period using electric fencing for an average of 97 d over 2 yr, with all calves receiving a pelleted supplement (78% TDN, 16% CP) daily at 0.8% BW. A randomized complete block design (RCBD) was used to analyze crop yield, crop quality, dry matter intake (DMI), body weight (BW), average daily gain (ADG), total system cost and cost of gain (COG) over the 2 yr trial. Forage samples were collected every 21 d to determine forage quality. Protein content was greater (P<0.01) for CON (11.1%) compared to BAR and COR forage (10.1 and 7.9%, respectively). Neutral detergent fibre was greater (P=0.03) for BAR (63.3%) compared to CON (60.3%), while COR forage (62.9%) was not different (P>0.05) from either CON or BAR forage. Acid detergent fibre was not different (P>0.05) between the 3 forage types. Total digestible nutrients and net energy for gain were greater (P<0.01) for the COR forage (62.3% and 0.36 Mcal/d, respectively) compared to CON (57.8% and 0.30 Mcal/d, respectively) and BAR (59.0% and 0.32 Mcal/d, respectively). Calcium was greater (P<0.01) for CON and BAR (0.39 and 0.37%) compared to COR (0.20%) forage. Phosphorus content was greater (P<0.01) for CON (0.27%) then BAR (0.23%) and COR (0.20%) forage. There was no difference (P>0.05) in DMI, BW, ADG or COG between the 3 backgrounding systems. Total cost of production was greatest (P<0.05) for CON calves ($2.57/calf/day) compared to COR and BAR calves (1.40 and 1.48 $/calf/day). Net return was greatest for COR and BAR calves (65.03 and 61.60 $/hd, respectively) compared to CON calves ($-28.85/hd). After backgrounding, replicates of calves were divided into 2 groups and placed in a feedlot each year of the trial. Calves were fed a barley silage based diet with either barley or corn grain for 203 d to a weight of 667.8 ± 5 kg, at which point they were slaughtered and carcass data was collected. A RCBD split plot was used to analyze DMI, BW, ADG, dressing %, hot carcass weight (HCW), ribeye area, and marbling score while quality and yield grade data were analyzed using the GLIMMIX macro with a binomial error structure and logit data transformation. Dressing % was greatest for both COR and CON steers fed the corn grain diet (58.9%) and HCW was greatest (P<0.05) for COR steers fed a corn grain diet (397.5 kg). There was no difference (P>0.05) in BW, DMI, ADG, yield grade or carcass characteristics among systems, suggesting that backgrounding calves by field grazing either standing whole plant corn or swathed barley is a viable option to decrease winter feeding costs without having an effect on finishing performance