EVALUATION OF WINTER FEEDING SYSTEMS FOR CROP YIELD AND AGRONOMY, BEEF COW PERFORMANCE, METABOLISM AND ECONOMICS
Two experiments were conducted during the winters of 2012-13 (yr 1) and 2013-14 (yr 2), to evaluate 3 winter feeding systems: (i) field grazing standing whole plant corn (SC) cv. ‘DKC 26-25’ (yr 1, CP = 9.5%, TDN = 66.1%; yr 2, CP = 9%, TDN = 69.8%), (ii) field grazing swathed barley hay (SB) cv. ‘Ranger’ (yr 1, CP = 13.2%, TDN = 56.8%; yr 2, CP = 10%, TDN = 61.9% and (iii) barley hay bales fed in drylot pens (DL) cv. ‘Ranger’ (yr 1, CP = 13.1%, TDN = 53.2%; yr 2, CP = 8.2%, TDN = 55.2%). Forages were allocated on a 3-4 d interval in SC and SB systems. The specific objectives were to compare crop yield and agronomy, beef cow performance, reproductive efficiency and system costs in experiment 1 (EXP 1); and ruminal pH, SCFA and ammonia concentration in experiment 2 (EXP 2). In EXP 1, 60 dry, pregnant Black Angus cows (yr 1, 644 kg ± 72 kg; yr 2, 672 kg ± 66 kg) at mid-gestation, stratified by body weight (BW) were allocated to 1 of 3 replicated (n=2) winter grazing treatments for 77 d in yr 1 and 78 d in yr 2. Increases in rib fat were greater (P = 0.02) for SC cows compared to SB cows (1.6 vs 0.3 mm, respectively). Estimated DMI was lower (P < 0.01) for SC cows (9.1 kg/d) compared to SB and BH cows (14.3 and 13.0 kg/d, respectively) which did not differ (P > 0.05) from each other. Calves born to cows grazing SC were heavier (P ˂ 0.01) at birth compared to calves from SB and BH cows (43, 40 and 40 kg, respectively). Changes in cow BW and average daily gain (ADG) were lower (P < 0.01) and negative in year 2 (BW change, 23.8 and -4.9 kg; ADG, 0.3 and -0.1 kg for yr 1 and 2, respectively). The number of calves born in first 21 d was 44% higher (P < 0.01) in yr 1 compared to yr 2. Economic analysis revealed that total costs were greatest for BH ($2.75/cow/d) compared to SC and SB ($2.06 and $2.00 cow/d, respectively) systems. In EXP 2, 9 cannulated beef heifers were cycled through the 3 winter systems concurrently within EXP 1, in a replicated 3 × 3 Latin square design, for 63 d to evaluate effect of forage type and day of allocation on rumen fermentation. Results from EXP 2 indicated an increase (P < 0.01) in minimum pH of cannulated heifers from d 1 to d 3 of forage allocation in SC and SB systems. Lower (P < 0.01) minimum and mean pH and increased duration and area (P < 0.01) under pH 5.8 were observed in yr 2 in SC and yr 1 in SB. In yr 2, total SCFA, acetate and propionate concentration increased (P < 0.01) in SB heifers, but butyrate concentration increased (P < 0.05) in SC heifers compared to yr 1. Ruminal fermentation was unaffected (P > 0.05) by day of forage allocation and yr of study in BH system. Results from EXP 1 and EXP 2 suggest that both SC and SB systems are cost effective alternatives to BH system, and do not negatively affect cow reproductive performance following winter grazing. However, yearly differences in weather and seeding date of forages can have a profound effect on nutrient composition of forages, and can cause variations in cow performance and rumen metabolism during the period of extensive winter grazing.
winter grazing, extensive grazing
Master of Science (M.Sc.)
Animal and Poultry Science