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The objective of the study was to investigate selected key regulatory pathways of milk protein biosynthesis in primary bovine mammary epithelial cells ( MECs) of dairy cows during the first 155 days of lactation. In addition, cows were exposed to feed restriction for a short period ( FR) during different stages of lactation (week 4 and 21 pp) to study adjustment processes of molecular protein biosynthesis to metabolic challenge. Morning milk samples from twenty-four Holstein- Friesian cows were collected throughout the experimental period ( n = 10 per animal). MEC from raw milk were purified using an immunomagnetic separation technique and used for real-time quantitative PCR analyses. As was seen in transcript abundances of all major milk proteins, m RNA levels of E74-like factor 5 ( ELF5), an enhancer of signal transducer and activator of transcription ( STAT) action, concomitantly decreased towards mid-lactation. Expression of ELF5 as well as of all milk protein genes showed a similar increase during FR in early lactation. Occasional changes in expression could be seen in other Janus kinase ( JAK)/ STAT factors and in mammalian target of rapamycin (m TOR) pathway elements. Amino acid transfer and glucose transporter and the β-casein expression were also partially affected. In conclusion, our findings suggest a pivotal role of the transcription factor ELF5 in milk protein m RNA expression with complementary JAK/ STAT and m TOR signalling for the regulation of protein biosynthesis in the bovine mammary gland. [ABSTRACT FROM AUTHOR]

The objective of this experiment was to study milk productivity, metabolic adaptation and effect of a short-term feed restriction (FR) on key performance indicators during early lactation in cows classified according to energy-corrected milk (ECM) yield and milk protein concentration. Twenty-three multiparous Holstein-Friesian cows were categorized in four groups according to respective averaged values on Days 23-25 postpartum: high ECM yield and high protein concentration; low ECM yield and low protein concentration; high ECM yield and low protein concentration and low ECM yield and high protein concentration. Dry matter intake was reduced to 68.3% for three subsequent days. Our results showed that short-time FR in early lactation succeeded in enhancing energy deficit of cows in all groups. Milk fat, milk protein and lactose concentrations as well as milk fat yield were not influenced by FR. Several hepatic genes encoding for enzymes involved in catabolism of amino acids, β-oxidation, gluconeogenesis and ketogenesis as well as mRNA encoding for insulin receptor showed increased transcript abundances after FR, primarily in cows with high milk yield and low milk protein concentration. [ABSTRACT FROM AUTHOR]