Submitted to: Arkansas Experiment Station Research Series
Publication Type: Experiment Station
Publication Acceptance Date: 8/31/2006
Publication Date: 12/2/2006
Citation: Kreider, D.L., Coffey, K.P., Whitworth, W.A., Montgomery, T.G., Coblentz, W.K., Caldwell, J.D., Mcnew, R.W., Ogden, R.K. 2006. Effect of Supplement Timing on Blood Measurements and Reproductive Performance in Beef Heifers Grazing Annual Ryegrass in the Spring. Research Series 545. Arkansas Animal Science Department Report. 9:196-198. Interpretive Summary: Cattle grazing winter-annual pastures in Arkansas often gain weight rapidly; however, heifers grazing these pastures often exhibit poor reproductive performance. In some cases, this has been associated with the high crude protein concentrations of these forages, poor nitrogen-use efficiencies by heifers consuming these forages, and high concentrations of urea-nitrogen in the blood. Supplementation with energy sources as been suggested as a possible technique for improving nitrogen-use efficiency in these grazing ruminants, and for reducing urea-nitrogen within the blood. In this study, heifers received no supplement, or a corn-based supplement beginning 60 or 30 days before breeding. The preliminary results from this study indicate that serum urea-nitrogen concentrations in all heifer groups grazing annual ryegrass in the early spring were greater than those shown to cause a decrease in pregnancy rates. The 60-day group had moderately lower serum urea nitrogen concentrations than the other two treatment groups in early spring, suggesting that supplementation of this group at 60 d prior to timed artificial insemination was beneficial in reducing serum urea-nitrogen concentrations. Numerical differences were observed across supplementation strategies for both conception rate following timed artificial insemination and overall pregnancy rate, but these differences were not statistically significant. This study will need to be repeated over several years before clear conclusions can be established.
Technical Abstract: Forty Gelbvieh x Angus heifers (443 lb initial BW) were allocated randomly by weight to one of eight bermudagrass pastures overseeded with annual ryegrass to determine the impact of providing degradable carbohydrates at different intervals prior to breeding on conception rates, growth rates, and serum urea N concentrations. Two replicates received no supplement (C); 3 replicates each received 3.0 lb/head of supplement (32.5% ground corn, 32.5% cracked corn, 30% wheat middlings, and 5% liquid molasses) at approximately 0930 h daily beginning either 60 (60S) or 30 (30S) d prior to timed insemination (May 7).Heifers were weighed without prior removal from pasture and water at the initiation of the study and at approximately 28-day intervals. Blood samples were collected 7 d following the start of supplement and the day prior to timed insemination at 1230 and 1530 h. Available forage was measured and forage samples were clipped from each pasture on or immediately following weigh days. Total gains (avg 192 lb) did not differ (P > 0.10) among treatments. Serum urea nitrogen was lower (P < 0.05) from 60S than 30S on March 15, but not on April 13 or May 6. Serum glucose was not affected by treatment (P > 0.94), but was different among months (P < 0.05). Glucose increased between March and April (P < 0.01) and between April and May (P < 0.05). First-service conception rates were 33, 50, and 46% (P > 0.10) from C, 30S, and 60S, respectively. Overall conception rate from timed artificial insemination and natural service combined was 88.9, 79.6, and 61.5% for C, 30S, and 60S treatments, respectively, but was not different among treatments (P > 0.14). Preliminary results after yr 1 of the study suggests that timing supplementation strategically may alter blood measurements that have been previously shown to affect reproductive performance.