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Weaning and post-weaning performance by fall-born beef calves weaned on different dates in the spring from Neotyphodium coenophialum-infected tall fescue pastures

Caldwell, James D., Coffey, Kenneth P., Coblentz, Wayne K., Jennings, John A., Hubbell, Donald S., III, Kreider, David L., Looper, Michael L., Galloway, Douglas L., Kegley, Elizabeth B., Rosenkrans, Charles F., Jr.
Livestock science 2011 v.135 no.1 pp. 44
Festuca arundinacea subsp. arundinacea, Neotyphodium, antioxidant activity, beef cattle, birth weight, bovine viral diarrhea, breeding, calves, carcass weight, cows, early weaning, eosinophils, forage, grazing, heifers, infectious bovine rhinotracheitis, mycotoxins, parturition, pastures, shipping, spring, steers, weight gain
Fall-born calves grazing Neotyphodium coenophialum-infected tall fescue [E+; Lolium arundinaceum (Schreb.) Darbysh.] pastures 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±4.7days of age; MarW), 2) April 13 (204±4.7days of age; AprW), 3) May 11 (236±4.7days of age; MayW), and 4) June 8 (264±4.8days 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 14days. After the weaning period, calves were weighed, blood samples were collected, and then calves were moved to pastures containing non-toxic forages. Birth weight and calf weights on MarW, AprW, and MayW weaning dates did not differ (P≥0.21) across weaning date treatments. However, calf weaning weights on their respective weaning dates, weight on JuneW and on June 22 (14days 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: i) total antioxidant potential and eosinophils at weaning; ii) changes in antibody titers to BVD and IBR, total antioxidant potential, and serum Zn during the 14-day post-weaning period; and iii) 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, and heifer weight at breeding, but those benefits in steers may be mitigated through the feedlot period.