83 Canola fat supplementation for mid-late gestating beef cows and the effects on progeny backgrounding and finishing performance.

Abstract This study aimed to identify the optimal level of supplemental canola fat in gestating beef cow diets to enhance progeny performance during the backgrounding and finishing phases. Seventy-two Angus-cross, multiparous, pregnant beef cows were randomly assigned to 1 of 3 replicated (n=4) dietary treatments fed during mid-late gestation for 149 ± 3 d. Dietary treatments included control (CON), low fat (LF), and high fat (HF) supplemented with 0, 150, or 300 g of canola fat/head/day, respectively. Following parturition, cow-calf pairs were pastured, and progeny were later weaned and arrived to the feedlot at 175 ± 9 days of age. In yr 1 and 2, 63 and 65 progenies, respectively, were allocated into 1 of 6 pens/yr by sex and dam treatment. A similar backgrounding ration (14.4% CP; 67.7% TDN) was fed for 146 ± 2 d. To follow, a similar finishing ration (13.2% CP; 76.3% TDN) was fed for 114 ± 11 d including an initial 25 d transition period. Body weights (BW) were obtained over 2 d at start and end of each feeding phase and every 28 d. Data was analyzed in a complete randomized design with the mixed procedure of SAS (9.4). Progeny pen was the experimental unit, dam treatment was the fixed effect, and year was the random effect. During backgrounding phase for heifer progeny, there were no differences (P > 0.05) in initial shrunk BW (ISBW) (232 ± 25 kg), final shrunk BW (FSBW) (407 ± 34 kg), DMI (8.0 ± 0.2 kg/d) and gain to feed efficiency (GF) (0.150 ± 0.007). Increased supplemental fat in dam diets, linearly decreased (P=0.05) heifer background ADG in CON, LF, and HF treatments (1.25, 1.18, and 1.17 kg/d, respectively). In background phase for steer progeny, ISBW (236 ± 28 kg), FSBW (426 ± 39 kg), ADG (1.3 ± 0.1 kg/d), DMI (8.4 ± 0.3 kg/d), and GF (0.155 ± 0.002) did not differ (P > 0.05). In finishing phase for heifer progeny, there were no differences (P > 0.05) in FSBW (598 ± 43 kg), ADG (1.7 ± 0.2 kg/d), DMI (11.4 ± 0.4 kg/d), GF (0.145 ± 0.007), and post-weaning cumulative ADG (1.4 ± 0.1 kg/d). During finishing phase for steer progeny, FSBW (637 ± 40 kg), ADG (1.9 ± 0.2 kg/d), DMI (12.3 ± 0.4 kg/d), and post-weaning cumulative ADG (1.6 ± 0.1 kg/d) did not differ (P > 0.05). However, increased supplemental fat in dam diets caused a linear increase (P=0.03) of GF in finishing steer progeny in CON, LF, and HF treatments (0.144, 0.157, 0.159, respectively). These results of supplementing canola fat in mid-late gestating beef cow diets suggest reduced heifer progeny performance during background phase but improved steer performance during finishing phase.