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Influence of Dietary Roughage Level on Reproductive Rate in Ewe Lambs^{1 ,6,}

University of Illinois, Urbana 61801

Abstract

Crossbred ewe lambs initially weighing approximately 90 lb (41 kg) were fed rations varying in roughage level prior to breeding to examine the influence of level of dietary energy upon subsequent reproductive performance when bred as lambs. In the two trials conducted over a 2-year period 200 spring-born lambs were placed in four lots of 25 lambs each year and received rations containing 12% crude protein and ground mixed hay at 10, 30, 50 or 70% of the diet. Average initial weights were 100.6 ± 14.8 and 83.8 ± 11.2 lb (45.7 ± 6.7 and 38.1 ± 5.1 kg), respectively. Average daily gains during the first trial of 56 days were .46, .31, .24 and .09 lb (.20, .14, .11 and .04 kg), respectively, for diets containing 10, 30, 50 and 70% roughage. During the second trial of 99 days average daily gains were .42, .40, .24 and .041b (.19, .18, .11 and .02 kg), respectively.

At the end of each feeding period five lambs from each treatment were slaughtered and carcass measurements collected. Weight and fat parameters were found to decrease (P<.05) with increasing dietary roughage level. The remaining ewes were pooled, exposed to rams for 40 days, and checked for pregnancy using echo analysis during the first 50 days of pregnancy. Pregnancy detection was accurate 75% of the time. Reproductive performance did not differ significantly among treatment groups (60, 65, 75 and 70; 44, 74, 83 and 75% of the ewes lambed corresponding to 10, 30, 50 and 70% roughage diets during the first and second trial, respectively). Lambing percentages based upon 100 ewes lambing were 116.7, 107.7, 113.3 and 109.4 and based upon ewes exposed were 70, 70, 85 and 70, respectively, in the first trial, and 150.0, 121.4, 113.3 and 106.7, and 67, 89, 94 and 80, respectively, in the second trial. Reproductive performance (the highest lambing percent and the greatest number of lambs per ewe exposed) tended to be highest for ewes bred as lambs and fed the 50% roughage diet.

¹ The authors wish to express their appreciation to H. W. Norton for his assistance with statistical analysis and Ray Hankes and Doug Parrett for their assistance in the collection of data.

⁶ Supported in part by funds from the Illinois Agricultural Experiment Station.

² Graduate Assistant in Animal Science, research completed in partial requirement for the M.S. degree in Animal Science, 1975.

³ Professor of Animal Science, Urbana.

⁴ Associate Professor of Animal Science, Dixon Springs Center, Simpson, IL 62985.

⁵ Assistant Animal Scientist, Dixon Springs Center.