|Hubbell, iii, Donald|
Submitted to: Livestock Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/10/2010
Publication Date: 1/7/2011
Citation: Caldwell, J.D., Coffey, K.P., Coblentz, W.K., Jennings, J.A., Hubbell, III, D.S., Krieder, D.L., Looper, M.L., Galloway, D.L., Kegley, E.B., Rosenkrans, C.F. 2011. Weaning and Post-Weaning Performance by Fall-Born Beef Calves Weaned on Different Dates in the Spring from Neotyphodium Coenophialum-Infected Tall Fescue Pastures. Livestock Science. 135:44-52. Interpretive Summary: Endophyte-infected tall fescue complicates management of beef cattle throughout the Upper South. This occurs because toxins produced by the endophyte cause poor performance in cattle grazing these forages. While cattle performance may be affected negatively, the endophyte also is beneficial to the host fescue plant, specifically improving persistence through a variety of physiological mechanisms. Theoretically, fall-born beef calves raised in Arkansas on endophyte-infected tall fescue pastures should benefit from early weaning (March or April) because toxin levels within the forage typically peak later (in late-spring or early-summer). However, in a previous study, fall-born calves that grazed endophyte-infected pastures and were weaned in mid-April had reduced post-weaning performance compared with calves managed similarly but weaned in early June. Therefore, a three-year study was conducted to assess four weaning dates in the spring (March, April, May, and June) for fall-born calves and to determine which date supported the optimum post-weaning performance for beef steers and heifers. Based on the results of this study, as well as those from previous work, producers grazing fall-born calves on endophyte-infected tall fescue pastures in the spring should be discouraged from weaning early unless the objective is for increasing cow performance. Weaning late led to heavier calf weights, which is beneficial to producers selling to a cash market and may offset declining market prices as spring progresses. However, these benefits for steers may not persist through the feedlot period. Animal immune function appeared to be greater in late-weaned calves than in early-weaned calves, thereby providing a significant potential benefit to subsequent calf owners. Theoretically, this allows healthier animals to be marketed, possibly increasing the return per head, and certainly increasing the reputation of the producer as society moves toward permanent records of ownership.
Technical Abstract: Fall-born calves grazing Neotyphodium coenophialum-infected tall fescue [E+; Lolium arundinaceum (Schreb.) Darbysh.] should benefit from early weaning because of reduced exposure to fungal toxins. However, fall-born calves that grazed E+ and were weaned in mid-April had reduced post-weaning performance compared with calves managed similarly but weaned in early June. Gelbvieh × Angus calves (n = 238) were used in a 3-year study to determine the optimal time to wean fall-born calves grazing E+. Cow/calf pairs were allocated randomly to one of four weaning date treatments: 1) March 16 (177 ± 4.7 days of age; MarW), 2) April 13 (204 ± 4.7 days of age; AprW), 3) May 11 (236 ± 4.7 days of age; MayW), and 4) June 8 (264 ± 4.8 days of age; JuneW). On their assigned weaning date, calves were weighed, vaccinated, blood samples were collected, and calves were moved to 3.2-ha pastures adjacent to their dams for 14 days. After the weaning period, calves were weighed, blood samples were collected, then calves were moved to pastures containing non-toxic forages. Birth weight and calf weights did not differ (P = 0.21) across weaning date treatments on the MarW, AprW, and MayW weaning dates. However, calf weaning weights on their respective weaning date, weight on JuneW and on June 22 (14 days following the JuneW), daily gain between birth and June 22, and weight change between MarW and JuneW increased linearly (P < 0.05) across weaning dates. Linear decreases (P < 0.05) across weaning dates were noted for antibody titers to bovine virus diarrhea (BVD) and infectious bovine rhinotracheitis (IBR), serum Cu, and platelets at the time of actual weaning. Linear increases (P < 0.05) across weaning dates were noted for total antioxidant potential and eosinophils at weaning, changes in antibody titers to BVD and IBR, total antioxidant potential, and serum Zn during the 14-day post-weaning period, and changes in BVD and BRSV titers and serum Cu between actual weaning date and June 22. Heifer weight at breeding increased (P < 0.05) and steer weight at shipping, hot carcass weight and backfat thickness tended (P = 0.10) to increase linearly across weaning dates. Final feedlot weight and gain did not differ (P = 0.18) among weaning dates. Therefore, delaying weaning of fall-born calves grazing E+ pastures until early June may be beneficial for calf weight and immune function at weaning, but those benefits may be mitigated through the feedlot period.