Analysis of Genotype × Environment Interaction for milk production in dairy cow

Abstract

Genotype by environment interaction was studied with 526 lactation milk records of Red Steppe dairy cows maintained at State Enterprise “Breeding reproducer “Stepove” (Mykolayiv region, Ukraine). The analyses in this study were based on the milk yields of cow per 1st–10th month (M1–M10) and per 305 day for complete lactations (Y305). We tested the hypotheses that milk performance were influenced by the sire (factor “Sire”), by number of lactation (factor “NoL”), by of cow’s year of born (factor “Generation”) and by the season of calving (factor “SoC”). The data were analysed with the “Variance components” and the “ANOVA/MANOVA” modules of statistical software STATISTICA (StatSoft Inc, USA). Experimental cows originated from five sires. The effect of the sire was significantly expressed in milk yield from the 2nd to 7th month of lactation (in all cases: P < 0.001–0.024) and Y305 (P = 0.011). The 12-year period studied (year of cow’s birth from 2001 to 2011) was classified into four periods as follows: G1 – 2001–2003, G2 – 2004–2006, G3 – 2007–2009 and G4 – 2010–2011. Year of birth (factor “Generation”) had significant (in all cases: P < 0.001–0.044) effect on all traits studied (but not on M7–M8). All cows were divided according to the season of calving (SoC): winter (December to February), spring (March to May), summer (June to August) and autumn (September to November). The production of milk for M1–M2, M4–M8 and M10 (but not for 305 day lactation) statistically differed according to the season of calving (in all cases: P < 0.05). From the study results, a significant relationship was found between the milk yield and lactation number, with the maximum milk yield occurring in the third lactation cows (pattern 1 < 2 < 3 = 4+). Milk yields from the M1 to M6 month of lactation (in all cases: P < 0.001–0.017) and Y305 (P < 0.001) were statistically different between cows according to the number of lactation. Cow’s lactation number, year of birth and calving season causes differences in the shape and persistency of lactation curve. Genotype by environment interactions for lactation number and cow’s year of birth can be result in re-ranking of sire between the different environments.