Genetic regulation of prepartum dry matter intake in Holstein cows.

The objective of this study was to estimate genetic parameters for dry matter intake (DMI) in prepartum nonlactating and in lactating Holstein cows. Measurements were recorded on cows from Iowa State University (ISU) and the University of Florida (UF) dairy herds. Individual feed intake data were recorded daily at ISU from approximately 30 d prepartum through 150 d in milk (DIM). Individual intakes from cows at UF were recorded for approximately 42 d pre- and postpartum. Prepartum DMI traits were defined as DMI on d -15 (multiparous) or d -8 (primiparous) relative to calving date (DRYDMI), DMI on d -1 before parturition (CALVEDMI), and the negative of the slope of a regression line fitted through the last 14 (multiparous) or 7 (primiparous) days before calving (DEC). Lactation DMI traits were defined as DMI at 30 DIM (DMI30) and 100 DIM (DMI100; ISU data only). The final data set included 245 primiparous and 221 multiparous cows from ISU, and 125 multiparous cows from UF. Heritability estimates were 0.43, 0.64, 0.32, and 0.62 for DRYDMI, CALVEDMI, DEC, and DMI30, respectively. The estimate of heritability for DMI100 (ISU only) was 0.52. The genetic correlation between DRYDMI and DMI30 was 0.97. Thus, DMI prepartum is a moderately heritable trait that is highly correlated with intake during early lactation. Genetic correlations between DEC and DMI during lactation were lower and similar to standard error estimates (-0.24 ± 0.22 for DEC and DMI30 for combined data, and -0.13 ± 0.27 for DEC and DMI100 in ISU data). Thus, selection for altered DMI during lactation may not dramatically affect the depression in intake that occurs before parturition.