Genotype Environment interactions for milk production traits in Holstein and crossbred Holstein-Zebu cattle populations estimated by a character state multibreed model

- The environmental effects are not the same in Holstein and Holstein×Zebu cattle.
- The G×E is a real problem for milk production in the tropics.
- The use of a multicharacter model allows us to quantify the importance of G×E.
- The effects of G×E are not the same in Holstein and Holstein×Zebu cattle.
- The use of eigen decomposition of genetic correlation matrix is a useful tool.

A total of 478,555 lactation records from 203,825 cows calving from January 1984 to December 2003 were used to quantify the importance of the genotype-environment interaction (G×E) on milk production in a large population of Holstein and Holstein-Zebu crossbred animals under Cuban tropical conditions. These cows were distributed in a total of 1288 herds, daughters of 1565 Holstein (H) sires and 831 Holstein crossbred sires (HZ) with female Zebu (Z). Due to the dramatic political crisis in eastern countries at the end of the 1980s, all economical activities in Cuba were affected, and particularly the resources available for the dairy sector were marginalize; therefore two contrasted environmental periods of time were created: the first one was the calving from 1984 to 1990 and the second from 1991 to 2003. This division was made to estimate the magnitude of the G×E. Data were analyzed with different character state multi-breed sire models. Accordingly to the genetic correlation between the same traits across the time periods, the G×E was negative and highly significant but with more intensity in H sires with regard to HZ sires. A very important genetic variation was found in plasticity and a group of robust or generalist sires were identified showing a very good performance in the two time-period environmental conditions. The importance of the use of a Character State Multi-breed Model and the plasticity concept for breeding programs in the tropics are highly suggested.