Submitted to: Arkansas Agricultural Experiment Station Research Series
Publication Type: Experiment Station
Publication Acceptance Date: 8/15/2007
Publication Date: 12/15/2007
Citation: Kreider, D.L., Coffey, K.P., Caldwell, J.D., Whitworth, W.A., Montgomery, T.G., Rorie, R., Mcnew, R.W., Coblentz, W.K., Ogden, R.K. 2007. Reproductive performance, blood urea nitrogen, and blood glucose concentration in beef heifers grazing annual ryegrass in the spring and supplemented at different intervals prior to timed AI. Arkansas Animal Science Research Series 553. Arkansas Animal Science Department Report 2007. 10:41-44.
Technical Abstract: In successive years, 76 Gelbvieh x Angus heifers [n = 36 (year 1) and n = 40 (year 2)] at 12 to 14 months of age were stratified by weight and randomly allocated to one of three treatments to determine the impact of rumen degradable carbohydrates at different intervals prior to breeding on conception rate (CR) to timed artificial insemination (TAI), overall pregnancy rate (PR), serum urea nitrogen (SUN), and serum glucose (GLU). Heifers grazed bermudagrass pastures interseeded with annual ryegrass pastures during March, April, and May. Two replicates were provided no supplement (C); 3 replicates each were provided 3 lb/hd of supplement (32.5% ground corn, 32.5% cracked corn, 30% wheat middlings, and 5% liquid molasses), beginning either 60 (60S) or 30 (30S) d prior to TAI. Supplement for 60S was discontinued at the time 30S was initiated. Heifers were weighed unshrunk at the initiation of the study and at 28-d intervals. Serum was collected at 1230 h and 1530 h on d 7 after the start of supplementation and 1 d prior to TAI. Conception rate to TAI did not differ between treatments (P = 0.31; 42, 62, and 48% for C, 30S, and 60S, respectively). Overall PR was 92, 86, and 78% for C, 30S, and 60S, respectively, and did not differ among treatments (P = 0.42).Mean SUN was not altered by treatment (P = 0.95), or time of day (P = 0.68), but was affected by month (P < 0.001).Mean SUN was 24.1 ± 2.5, 15.5 ± 2.4, and 10.5 ± 2.4 mg/dl for March, April, and May respectively. Serum GLU differed among months, averaging 90.8 ± 3.8, 90.5 ± 3.2 and 101.6 ± 3.3 mg/dl for March, April, and May, respectively. Supplementation and supplement timing in this study did not affect CR to TAI or overall PR.