Effect of environmental factors and of the proportion of Holstein blood onthe milk yield and lactation length of crossbred dairy cattle on smallholder farms in north-east Tanzania

A study was carried out on the lactation performance of crossbred dairy cat tle in a smallholder farming system in north-east Tanzania. Data were colle cted from the records for 6 years and the factors considered were district, proportion of Holsteins, season of calving, year of calving and herd size. The data were considered separately for animals with a single lactation re cord. The least-square means for first lactation length and yield were 331 days (SD 77.0) and 2332 L (SD 283.0), respectively, while for cows with dat a on more than one lactation record the yield was 2477 L (SD 840.1) in 324 days (SD 74.0). First lactation yield was significantly affected by year of calving. For repeated records the lactation yield was significantly affect ed by district, proportion of Holsteins and herd size, while lactation leng th was significantly affected by district and herd size. The calculated rep eatabilities for lactation yield and length were 0.27 and 0.12, respectivel y. For the pooled data the correlation between lactation length and yield g ave r = 0.569 (p < 0.0001).