Bioperformance evaluation of various summer pasture and winter feeding strategies for cow-calf production

Legesse, G., Small, J. A., Scott, S. L., Kebreab, E., Crow, G. H., Block, H. C., Robins, C. D., Khakbazan, M. and McCaughey, W. P. 2012. Bioperformance evaluation of various summer pasture and winter feeding strategies for cow-calf production. Can. J. Anim. Sci. 92: 89-102. Bioperformance of two summer pasture and four winter feeding cow-calf production strategies in the western Canadian Parkland was evaluated. Diet composition and animal data were collected over 5 production years. Each production year began with fixed-time artificial insemination (TAI) of cows and turnout of cow-calf pairs (n = 288 yr(-1) including 76 primiparous replacement cows) assigned to either alfalfa-grass (AG, n = 9 paddocks) or grass (G, n = 9 paddocks) pastures until weaning. Post-weaning, pregnant cows (n =240 yr(-1)) were assigned to either extended-grazing (EG, n = 120) of dormant regrowth of perennial pastures and swathed annual crops, or one of three diets fed in a drylot (DL): hay (HY, n = 40), straw/barley (SB, n = 40; 70% oat straw:30% steam-rolled barley grain DM), and silage/straw (SS, n = 40; 40% barley silage:60% oat straw DM). Common diets were used for all treatment groups between the weaning and winter feeding period, as well as between the pre-calving and summer grazing period. Cow and calf body weight (BW) gains were higher (P < 0.05) for AG than G pasture until the third production year and the advantage diminished as the carrying capacity declined. The latter may be attributed to a lack of spring/summer moisture. Further, G pastures required more nitrogen fertilizer to achieve the same level of bioperformance as that of AG pastures in years 4 and 5. Cows in the EG treatment maintained BW better than those in the DL treatment (especially those cows receiving the SS diet) except in year 5 (P < 0.05) in which drought resulted in lower body weights for cows in the EG treatment. On all treatments, cows maintained BCS that supported reproductive function; however, fertility to TAI was lowest (P < 0.05) in years 4 and 5. Cows in the DL group had a 1.8 times greater risk of being culled before turnout and as a result lower (P < 0.05) rates of calf survival to weaning. In conclusion, AG pastures and EG are important alternatives to further develop for cow-calf production in western Canada.