Prediction of Lactation Yield by Multiple Regression in Pleven Blackhead Dairy Sheep
G. DIMOV1, D.GEORGIEV2 and G.GETOV2
1 Institute of Animal Science, BG – 2232 Kostinbrod, Bulgaria
2 District Breeding Center, BG – 5800 Pleven, Bulgaria
DIMOV, G., D. GEORGIEV and G. GETOV, 1999. Prediction of lactation yield by multiple regression in Pleven blackhead dairy sheep. Bulg. J. Agric. Sci., 5: 641-646
Officially approved method (OAM) for control of lactation milk yield in sheep was based on seven or eight test days. A simplified method was developed aiming to reduce farm visits and so the cost of recording. The obtained reduced test days yield (RTDY) is convenient for intraherd selection in reproductive part of population. That simplified method was based on two test day yields.
Development of simplified method and its comparison with actual lactation milk yield was based on 805 first and 556 second lactations of Pleven Black head dairy ewes. The accuracy of RTDY prediction was 66-69%. Comparative analysis of two data sets indicated that stage of lactation was more important in prediction than season. The best model accounted for real length of lactation period (L), daily yields corresponded to third (K3) and fifth (K5) test day of the OAM. Prediction equations for first (I1) and second (I2) lactations were correspondingly:
I1 = L (0.358+0.386K3+0.255K5); I2 = L (0.285+0.411K3+0.305K5).
Appropriate time for first test day was 80-90 day after parturition and for second test day – 150-160 day of lactation.
Key words: dairy sheep, test day yield, prediction, lactation yield
Abbreviations: OAM – officially approved method; RTDY – reduced test days yield