Breeding heifers on wheat pasture
Many areas of the eastern twothirds of Oklahoma have grown some wheat pasture for use as winter feed. Some producers may have questions about the utilization of wheat pasture for growing replacement heifers before, during, and after their first breeding season.
Unsatisfactory breeding performance has occasionally been anecdotally reported when replacement heifers have been exposed to bulls or AI while grazing wheat forages. Therefore an Oklahoma State University study was conducted to compare reproductive performance of heifers grazing wheat pasture before, and during breeding, with heifers grazing wheat pasture until approximately three weeks before breeding.
In each of two years, 40 spring-born Angus and Angus crossbred heifers were placed on wheat pasture in December and randomly assigned to one of two treatment groups in mid-March. Group one (Wheat Pasture; n=20) remained on wheat pasture (26.6 percent mean crude protein) through estrus synchronization and fixed-time A.I.
Group two (Dry Lot; n=20) was placed in drylot and had free choice access to a corn-based growing ration (11.1 percent crude protein) through estrus synchronization and fixed-time A.I. The heifers were inseminated on about April 5 both years. Heifers were exposed to fertile bulls starting 10 days after fixed-time A.I. for 45 more days. Fixed-time A.I. conception was determined at 32 days after A.I. by ultrasonography.
The percentage of heifers cycling at the start of estrous synchronization was 75 percent and 55 percent for Wheat Pasture and Dry Lot, respectively. Weights of Dry Lot heifers were slightly heavier than Wheat Pasture heifers (897 vs. 867 pounds) at the time of A.I. but were similar at ultrasound (917 vs. 910 pounds). Conception rate to fixed-time A.I. was similar for Wheat Pasture (54 percent) and Dry Lot (43 percent) and final pregnancy rate was similar for Wheat Pasture (98 percent) and Dry Lot (88 percent).
Reproductive performance of heifers grazing wheat pasture during estrus synchronization and fixed-time A.I. was similar to heifers consuming a corn-based growing diet. Source: Bryant and co-workers. 2011. February issue. The Professional Animal Scientist. — Glenn Selk, Oklahoma State University Emeritus Extension Animal Scientist