|dc.description.abstract||A two-year study (2007, 2008) was conducted to evaluate the effects of two calving systems, early (March; Early Calving System (ECS)) vs. late (June; Late Calving System (LCS)) on cow, pre-weaning calf performance and feeding system management and costs. Both early and late calving systems were managed at three locations on the Canadian Prairies: Agriculture and Agri-food Canada (AAFC)-Brandon Research Centre (Brandon, Manitoba); AAFC-Semi arid Prairie Agricultural Research Centre (Swift Current, SK); and Western Beef Development Centre (Lanigan, SK). Four feeding management systems (drylot (DL), pasture (PG), swath-windrow (SG) and bale grazing (BG)) were utilized at all three locations to maximize grazing systems.
Management of animals through the four different feeding systems was found to meet or exceed protein and energy requirements according to NRC (2000). Differences in cow body weight (BW) (P=0.001; location) were observed across locations at pre-calving and weaning periods although there were no obvious patterns when comparing across calving systems. A significant three way interaction was observed for cow BW at breeding (P=0.003), and for cow body condition score (BCS) at breeding (P=0.002). Body condition score at breeding indicated there was a significant (P=0.002) three way interaction, where there were no significant interactions when comparisons across calving system within the same year (Y) and location (L) were performed for Brandon and Lanigan in 2007 and for Lanigan in 2008 also, therefore no improvements in one calving system compared to the other. At Brandon in 2007, ECS cow BCS were similar to LCS cows. In 2007 and 2008, the inverse occurred at SC where LCS cows had greater BCS compared to the ECS. The same two way (Calving System x Location) interaction was significant at pre-calving and weaning for both cow rib (P=0.003; P=0.007) and rump fat (P=0.002; P=0.02) where Lanigan had significantly lower rib and rump fat for the LCS as compared to the ECS. Rib and rump fat measurements did not follow a typical pattern. Fluctuations in body fat reserves varied depending on the calving system and location. Even though differences (P<0.05) occurred in cow BW and fat reserves, there was no significant difference (P>0.05) in reproductive performance between the two calving systems within the management of the current study. Pregnancy rate, calving rate, calving span and weaning rate were similar for both early and late calving systems.
In 2007, calf mortality on average was higher for LCS (5%) vs ECS (1.7%) and the inverse occurred in 2008, where LCS had lower calf mortalities than did ECS, 3.3% and 4%, respectively. Most calf mortalities were born dead or weak. There appeared to be no negative impact on calf mortality with early or late calving systems. A significant two way (Calving System x Year) interaction was observed for calf BW at birth (P=0.002) (Table 4.4). Treatment (Calving System) (P<0.0001) main effect was significant for ADG (Table 4.4). The average values for calf birth weights for ECS in 2007 and 2008 were 42.1 and 41.2 ± 0.45 kg and for LCS in 2007 and 2008 were 41.4 and 44.1 ± 0.47 kg, respectively. Birth weights in 2007 between ECS and LCS were not different but in 2008 calf birth weight for LCS was heavier (P<0.05) than ECS calves. As expected calf birth weights were affected by L (P<0.0001). Calf birth weights were 44.8, 40.5 and 41.5 ± 0.8 for BR, SC and LA. Weaning rate was not affected by calving system, location or year. Pre-weaning ADG was 1.13 and 0.96 ±0.01kg d-1 for ECS and LCS, respectively. Weaning weights were therefore significantly (P<0.05) heavier for ECS as compared to the LCS, 273 and 240 ±1.82 kg, respectively.
The results of cow and calf performance indicate that calving later in the year does not significantly affect cow performance or reproductive efficiency but calf growth rate is significantly affected largely due to the time of year. Labour and feeding system management and costs are typically lower for LCS because of the ability to manage the cow herd on pastures and extended grazing systems which reduces the need for stored feeds during periods of cold weather.||en_US