Effects of feeding stockpiled tall fescue versus tall fescue hay during late gestation on pre-weaning calf performance

Abstract Text:

We hypothesized that cows grazing stockpiled tall fescue (STF) during late gestation have increased nutrient intake compared with cows fed summer-baled hay, which would result in improved fetal development and subsequent calf performance. Forty-eight multiparous, spring-calving crossbred beef cows (683 + 16 [SE] kg, BW) were allocated by BW, BCS, age, and expected calving date to either strip-graze endophyte-infected STF (59.7% NDF, 12.3% CP; DM basis) in 4.05 ha pastures (n = 4) or consume ad libitum endophyte-infected tall fescue hay (HAY; 64.9% NDF, 6.2% CP; DM basis) in uncovered drylots (n = 4) beginning on d 188 ± 2 of gestation. Cow BW, BCS, and 12^th rib fat thickness (RF) changes were determined after 35 d (ending period 1) and at 3 d before initiation of calving (ending period 2). Cows remained on their respective treatments until calving, but STF cows were moved to drylots at 7.0 ± 1.0 d pre-calving and fed ryelage (58.6% NDF, 12.3% CP; DM basis). Within 1 wk post-partum, cow-calf pairs were moved to a single pasture for common pre-weaning management. Data were analyzed with treatment as a fixed effect; calf date of birth (cow and calf measures) and sex (calf measures) were included when P < 0.25. There were no differences (P ≥ 0.44) in initial cow measures. Late gestational treatment did not affect (P ≥ 0.14) cow BW change during period 1 or overall. During period 2, cow BW change was affected by treatment (P = 0.02) where cows fed HAY lost BW and STF cows gained BW. Although treatment had no effect (P = 0.76) on period 2 BCS change, treatment affected (P ≤ 0.02) period 1 and overall BCS change where STF cows gained BCS and HAY cows lost BCS. Cow RF change was not affected (P ≥ 0.11) by treatment. Calves born to STF cows tended (P = 0.08; 38.3 vs. 34.6 ± 1.3 kg) to weigh more at birth, suggesting fetal growth was restricted in HAY cows. This trend continued, and calves born to STF cows tended (P = 0.07) to have greater BW at 80 d than HAY. There were no differences in calf pre-weaning ADG (P > 0.22) weaning BW (P = 0.37), or dam age-adjusted weaning BW (P= 0.29). In conclusion, cow performance and calf birth weight suggest that cows grazing STF during late gestation had increased nutrient intake leading to improved fetal development.

Keywords:  developmental programming, forage systems, pregnancy