GENETIC AND NON-GENETIC ANALYSIS OF LIFETIME TRAITS OF CROSSBRED DAIRY CATTLE IN THE CENTRAL HIGHLAND OF ETHIOPIA

Abstract

Lifetime traits are some of the important traits used to compare the performance and profitability of dairy cattle. The objective of this study was to estimate the genetic and non genetic performance of lifetime traits of crossbred dairy cattle in the central highland of Ethiopia. Birth year records of 502 cows maintained at Holetta Agricultural Research Centre from 1974 to 2015(42 years) were used to estimate total life, herd life, productive life, lifetime milk yield, lifetime calf crop, lifetime milk yield per total life (LTMYTL), lifetime milk yield per productive life (LTMYPL) and lifetime milk yield per herd life (LTMYHL). The fixed effects considered were genetic groups, the season of birth, and birth year groups. Least squares mean analyses were performed by applying the general linear model procedure of SAS 2016 version 9.4. In addition, VCE (6.0.2) and PEST (4.2.5) software were also employed for genetic parameters analysis. Genetic parameters considered were heritability, genetic and phenotypic correlation for lifetime traits of crossbred dairy cows. The overall means for total life, herd life, productive life, lifetime milk yield, lifetime calf crop, LTMYTL, LTMYHL, and LTMYPL were 3294.6±54.16days, 2046.2±47.19days, 1367.8±37.7days, 9314.14±314.2kg, 4.5±0.10, 2.71±0.06kg, 4.45±0.08kg, and 6.56±0.10kg, respectively. Both genetic group and birth year group were found to be the factors that significantly influenced all studied traits. However, birth seasons did not influence all the traits. The heritability estimates for lifetime traits observed in the present study were medium to high ranging from 0.19±0.04 to 0.62±0.06. The estimates of heritability for total life, productive life, herd life, lifetime milk yield, LTMYTL, LTMYPL, LTMYHL and lifetime calf crop were 0.25 ±0.05, 0.20±0.04, 0.19±0.04, 0.21±0.04, 0.31±0.05, 0.31±0.06, 0.27±0.07 and 0.62±0.06, respectively. The genetic correlation estimates among the traits vary in magnitude from lower to high, ranging from 0.02 between lifetime calf crop and LTMYPL to 0.94 between LTMYTL and lifetime milk yield. The phenotypic correlation estimates between the traits also vary from lower to high, ranging from 0.02 between lifetime calf crop and LTMYHL to 0.94 between herd life and total life. The study revealed that the first generation F1, ¾, and 62.5% Friesian x Borana crossbred dairy cows had performed better than later generations (F2 and F3) which means that first-generation crossbred cows exceeded cows with later generation for both 50% and 75% crosses. It can be noted from estimated heritabilities that including the lifetime trait in the selection program can bring genetic progress in this herd. The genetic and phenotypic correlations between total life, productive life, herd life, and lifetime milk yield were high and imply that selection on total life and lifetime milk yield would bring positive improvement on most of the lifetime traits. Therefore, the result indicated that the performance of most crossbred genotypes in lifetime milk yield and other longevity traits were good. However, enhancing the farm husbandry practices and optimizing breeding programs that encompass the lifetime traits are essential to reduce the effect of environmental factors, reduce segregation, and further genetic improvement.