Reducing the cost of overwintering beef cows is a major management goal in order to increase profitability within the cow-calf industry. Research from the University of Saskatchewan has shown that feed costs can be reduced by feeding pelleted feed products comprised of by-products from the western Canadian grain and oilseed industry. In ruminants, high-fat supplements have been shown to benefit the reproductive performance of beef cows, moreover, improving the nutritional status of the dam during gestation has been shown to benefit the performance of the offspring including ultimate carcass quality, potentially the result of epigenetic effects during fetal development. Based on this past research, our goal was to develop a high fat pelleted feed product that is comprised of by-products from the western Canadian grain and oilseed sectors that would allow feeding programs to be developed for gestating beef cows that are high in MUFA and/or PUFA in an effort to improve reproductive performance as well as the growth performance and carcass quality of the progeny.

The overall objective was to evaluate over two annual calving cycles the effects of fat and source of fat inclusion in the diet of pregnant beef cows during the second and third trimesters of gestation on the performance of the dam and the offspring. To accomplish these goals, in each year 75 multiparous (?3 calving) pregnant Angus cows entering the second trimester of pregnancy were housed in 15 outdoor pens (5 cows/pen) at the Western Beef Development Centre, Lanigan, Saskatchewan. Each pen was assigned to one of three (n=5) treatments: a low-fat diet (LF; 1.4±0.0% EE) consisting of grass-legume hay, barley straw, and barley grain, and two high-fat diets (HF; 3.3±0.0% EE) where barley grain was substituted with a canola seed (CAN) or a flaxseed (FLX) based pelleted feed. Following calving, all cow-calf pairs were managed similarly through weaning and during backgrounding and finishing phases at the University of Saskatchewan’s Beef Cattle Research and Teaching Unit in Saskatoon, Saskatchewan.

Some of the significant findings include the observation that after 160 d on trial, corrected BW of LF cows (708±2.9 kg) and proportion of over conditioned cows (16.3±8.8%) were greater than those fed HF, with no difference between CAN and FLX for corrected BW (696±4.8 vs. 698±3.8 kg) and proportion of over conditioned cows (4.2±3.3 vs. 6.2±4.3%). From calving to weaning, no differences were observed in ADG, BW, BCS, milk yield, and milk composition of cows. Pregnancy rate and calving to calving length did not differ among treatments. Birth weight of bull-calves from LF cows (41.5±0.5 kg) was lower than that from HF cows, while no difference in birth weight was observed between bull-calves from CAN (44.7±0.7 kg) and FLX (45.1±1.2 kg) cows. At weaning, ADG and standardized BW at 150 d of steer-calves from LF cows (1.16±0.02 kg/d and 216±3.1 kg) were similar to those from HF cows, while steer-calves from CAN cows had greater ADG (1.20±0.03 vs. 1.10±0.04 kg/d) and standardized BW (225±4.5 vs. 212±5.5 kg) than those from FLX cows. At slaughter, steers from LF cows had lower shrunk BW (597±9.5 kg) and carcass weight (352±5.2 kg) than those from HF cows, while no difference (P?0.12) was found between CAN and FLX for shrunk BW (639±6.1 vs. 617±13.6) and carcass weight (375±3.9 vs. 366±7.8). In contrast, performance and carcass attributes of heifer calves were not influenced by treatment. The possibility for these results to be a result of fetal programing/epigenetic effects during gestation is the subject of the last phase of our research which will be detailed in our final report to NSERC.

These results have important economic implications for both the cow/calf and feedlot industries. At a market price of $3.3 per kilogram (live weight basis; Canfax December 2017), the extra live weight gain of calves whose dams were fed canola meal based gestation diets translates into $135.00 more revenue per head for the producer. This has obvious positive implications for the cattle feeder, particularly if they can develop a supply chain of calves whose dams were on a high fat canola seed based gestation diet. These results also raise the potential for birth to slaughter programs where cow-calf producers would reap the benefits of the increased slaughter weight of their calves whose dams were fed under such a program by retaining ownership of the calves through slaughter. In conclusion, these data suggest a differential partitioning of ME by gestating beef cows which is dependent on the form of dietary energy during gestation, and points to the possibility that gestation diets can be developed from common by-product feeds that can not only meet the nutrient requirements of pregnant beef cows but positively affect the growth of the calf over the course of its life.