Genotype × Environment Interactions in Conventional versus Pasture-Based Dairies in Canada

Abstract

The objective of this study was to evaluate effects of genotype x environmental interaction (GxE) on dairy traits among herds in Canada that practice intensive rotational grazing versus conventional methods that rely on stored feeds. Based on responses to questionnaires, 22 herds were selected for the grazing group and the conventional group consisted of 34 large free-stall dairies. Production data consisted of 6,749 lactations of 2,817 cows in the grazing herds and 29,371 lactations of 12,774 cows in the control herds. Subsets of data for reproduction and conformation also were created. Per cow production was greater in the conventionally managed herds (9,947 kg of milk) than in the grazing herds (9,400 kg). Phenotypic data were regressed on sire predicted transmitting abilities (PTA) and genetic correlations for all traits were estimated between environments. A scaling effect was observed across environments for yield traits, as phenotypic differences among cows were greater than predicted by sire PTA in conventional herds and consistent with sire PTA in grazing herds. Heritabilities for yield also were greater in conventional herds. Other effects of GxE were minor, with genetic correlations of near 0.90 or greater for all traits. Among yield traits, genetic correlation was lowest for fat (0.88 with SE = 0.04). These results demonstrate that effects of GxE are small between the two types of management systems analyzed and that graziers can accurately select sires based on national rankings.

Genotype by feeding system interaction in the genetic evaluation of Jersey cattle for milk yield

“…This agrees with the reported phenotypic means from confinement and grazing of our study (Table 1) and with studies that have shown less genetic variation in lower production herds (Cromie et al, 1998;Cienfuegos-Rivas et al, 1999;Kearney et al, 2004). Boettcher et al (2003) estimated higher heritability using herds in confinement than in grazing, and suggested that genetic differences among animals were better expressed in herds under confinement. The difference could result from a more complete expression of the true genetic value in a 'better' environment (Ceró n-Muñ oz et al, 2004).…”

“…The estimate of our genetic correlation was lower than those of the studies already mentioned. This might be explained mainly by the differences in the production level per cow between confinement and grazing systems (Boettcher et al, 2003). In this study, cows yielded 64% more milk in confinement than in grazing (Table 1), whereas this difference was only 6% to 16% in other studies (Weigel et al, 1999;Boettcher et al, 2003;Kearney et al, 2004;Fahey et al, 2007).…”

“…Therefore, the problem would be to transfer correctly the genetic progress from high-input level farms to low-input level farms in temperate climate. Boettcher et al (2003) reported higher breeding values when predicted from confinement data and attributed it to a scaling effect. When herds in two environments show differences in additive genetic variances, Carabañ o et al (1989) mentioned that a scaling effect is expected.…”

“…In confinement and grazing Holstein systems in the United States (Weigel et al, 1999) and Canada (Boettcher et al, 2003) the estimated values of r g for MY were 0.92 and 0.93, respectively, indicating that GEI was not important (r g 5 1.0, P , 0.05). Kearney et al (2004) and Fahey et al (2007) estimated r g in grazing v. confinement of US Holstein herds with data divided into variance quartiles based on variance of MY.…”

“…The results have varied depending on the specific genotypes and environments studied (Ceró n et al, 2001;Boettcher et al, 2003;Valencia et al, 2008). Thus, knowing the magnitude of some specific GEI could be important to identify the best genotypes for specific environments.…”