The objective of this study was to investigate if a reduced milking frequency altered the effect of dietary energy restriction on the hepatic transcriptome of grazing dairy cows during early lactation. Multiparous Holstein-Friesian and Holstein-Friesian × Jersey cows (n = 120) were milked twice daily (2×) from calving until 34 ± 6 days in milk (mean ± SD). Cows were then allocated to one of four treatments in a 2 × 2 factorial arrangement. Treatments consisted of two milking frequencies [2× or once daily (1×)] and two feeding levels for 3 wk: adequately fed (AF) or underfed (UF, 60% of AF). Liver tissue was biopsied from 12 cows per treatment after 3 wk of treatment, and the hepatic transcriptome was profiled with an Agilent 4 × 44k bovine microarray. Over 2,900 genes were differentially expressed in response to the energy restriction; however, no effects resulted from changes to milking frequency. This may indicate that after 3 wk of 1× milking, any changes to the liver transcriptome that may have occurred earlier have returned to normal. After 3 wk of energy restriction, gene expression patterns indicate that glucose-sparing pathways were activated, and gluconeogenesis was increased in UF cows. Genes involved in hepatic stress were upregulated in response to the energy restriction indicative of the pressure energy restriction places on liver function. Other pathways upregulated included "cytoskeletal remodeling," indicating that a 3 wk energy restriction resulted in molecular changes to assist tissue remodeling. Overall, 1× milking does not modify the hepatic transcriptome changes that occur in response to an energy restriction.
Keywords: homeorhesis; negative energy balance; once-daily milking.