The introduction of low heat unit corn varieties in western Canada has led to questions on how this crop might fit into an extensive backgrounding program. Therefore, a 3-yr study was conducted to evaluate the effects of grazing standing whole-plant corn (Zea mays L. 'Pioneer P7443R') or swathed whole-plant barley (Hordeum vulgare 'Ranger') compared with barley hay fed in drylot pens on beef steer performance during backgrounding and feedlot phases. The effect of backgrounding system was also assessed during finishing when steers were fed diets based on barley grain or corn grain. Each yr, 120 Angus steers (BW = 250.5 ± 1.8 kg) were allocated to 1 of 3 replicated (n = 2) backgrounding systems: (1) field grazing swathed whole-plant barley (BSG; 11.2% CP, 60.6% TDN); (2) field grazing standing whole-plant corn (CG; 8.7% CP, 64.6% TDN); or (3) drylot (DL) bunk feeding of processed barley hay (10.9% CP, 57.2% TDN) for an average 78 d (42 to 95 d) trial. All calves received 2.5 kg/d of a range pellet supplement (16% CP, 78% TDN). Treatment groups were similar (P > 0.05) in final BW (295.8 ± 5.0 kg), ADG (0.59 ± 0.03 kg/d), and G:F ratio (0.187 ± 0.03 kg/kg).

A 2-yr study was conducted to evaluate the effects of level and source of fat in the diet of gestating beef cows on their prepartum performance and birth weight of progeny. Each year, 75 multiparous (≥3 calving) pregnant Angus cows were stratified by BW (663 ± 21.5 kg) and BCS (2.6 ± 0.12; 1 to 5 scale) and randomly assigned to 1 of 15 outdoor pens. Subsequently, each pen was randomly assigned to 1 of 3 (n = 5) treatments: a low-fat diet (LF; 1.4 ± 0.12% EE) consisting of grass-legume hay, barley straw, and barley grain, or 1 of 2 high-fat diets (HF; 3.3 ± 0.20% EE) that included either a canola seed (CAN) or a flaxseed (FLX) based pelleted feed. Diets were formulated to meet the requirements of pregnant beef cows during the last 2 trimesters of gestation (0.183 ± 4.8 d), adjusted for changes in environmental conditions, and offered such that each pen on average received similar daily amounts of DE (31.2 ± 2.8 Mcal/cow), CP (1.36 ± 0.13 kg/cow), and DM (12.9 ± 1.0 kg/cow). Data were analyzed as a randomized complete block design with contrasts to separate the effects of level (LF vs. HF) and source (CAN vs. FLX) of fat. After 160 d on trial, conceptus corrected-BW (CC-BW) of LF cows (708 kg) and the proportion of overconditioned cows (13.2%) were greater (P ≤ 0.04) than those of HF, with no difference (P ≥ 0.84) between CAN and FLX for CC-BW (697 kg) and proportion of overconditioned cows (3.6% vs. 2.9%). Feeding FLX diet during gestation resulted in cows with a greater (P ≤ 0.01) concentration of conjugated linolenic acid (0.12% vs. 0.05%) and n-3 (0.58% vs. 0.37%) fatty acids, and a tendency (P = 0.09) for conjugated linoleic acid concentration (1.05% vs. 0.88%) to be greater in subcutaneous adipose tissue (SCAT) when compared with cows fed the CAN diet. By the end of gestation, serum NEFA concentration of LF cows (592 µEq/L) was lower (P < 0.01) than that of HF cows, and FLX cows had greater (P < 0.01) serum NEFA concentration than CAN cows (636 vs. 961 µEq/L). Cows receiving the LF diet during gestation gave birth to lighter (P < 0.01) calves compared with those receiving the HF diets (40.2 vs. 42.9 kg), with no difference (P = 0.24) between calves born to CAN (42.4 kg) and FLX (43.3 kg) cows. In conclusion, these results suggest a partitioning of the ME in pregnant beef cows that is dependent on the type of dietary energy, resulting in heavier calves at birth for cows fed high-fat diets. Also, the type of fatty acid in the diet of gestating beef cows affected the fatty acid profile in SCAT and serum NEFA concentration.

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