Prediction of reproductive performance of ewes based on the early production data, ewe birth rank, dam age, and dam birth rank.

Abstract

This research aimed to analyze whether ewes' total reproductive performance up to the fourth year of life (RP4) can be predicted based on the data available at an early stage of a ewe's productive life. The RP4 of 133 Romanov ewes was measured in terms of the total number of lambs born per ewe (TNLE) and total birth weight of lambs per ewe (TBLE). Multiple regression was used to analyze whether early reproductive performance indicators (first litter size - FLS, age at first lambing - AFL, first lambing interval - FLI), ewe birth rank, dam age, and dam birth rank can be used as the predictors of RP4. Predicted $R^2$ and 95 % prediction intervals were used as indicators of the precision of prediction. Average TNLE and TBLE at the end of fourth year of ewe life were 11.84 lambs and 37.96 kg, respectively. FLS and FLI significantly ( $P<0.05$ ) influenced TNLE and TBLE, while AFL was not a significant ( $P>0.05$ ) variable. Ewes with shorter FLI had significantly ( $P<0.05$ ) higher TNLE (10.94 lambs) and TBLE (36.17 kg) than ewes with long FLI (TNLE  $=$  9.12 lambs and TBLE  $=$  28.05 kg). $R^2$ predicted for TNLE and TBLE was 7.54 % and 11.49 %, respectively. The ewe's birth rank and the dam's birth rank significantly ( $P<0.05$ ) influenced TNLE and TBLE. Ewes born as singletons and ewes from singleton-born dams had significantly ( $P<0.05$ ) lower TNLE and TBLE than ewes born as triplets and ewes from triplet-born dams. $R^2$ predicted for TNLE was 16.76 %, and 25.69 % for TBLE. FLS and FLI are better predictors of RP4 than AFL. The birth rank of ewe and dam also proved significant predictors of RP4. For both sets of predictors (early reproductive indicators and birth rank data), low values of $R^2$ predicted indicate that precise prediction of RP4 cannot be made.