Response of Holstein cows to corn gluten meal used to increase undegradable protein in early or later lactation

Supplemental corn gluten meal was used to raise CP by 1.1 to 1.5 percentage units and undegradable intake protein from 35 to 39% of CP in the corn-based diet of parity 1 or greater Holstein cows to study effects of undegradability, parity, stage of lactation, and interactions on DMI, milk yield and composition, BW, and related traits during complete lactations. Cows were assigned at calving to treatments (n = 30, 8 primiparous): control, supplement wk 1 to 8 postpartum (early), or supplement wk 9 to 44 postpartum (late). Total lactation means were not affected significantly by treatments. Supplementation with undegradable protein enhanced forage and, thus, total DMI in later lactation by pluriparous cows; it apparently spared BW loss wk 1 to 8 postpartum and enhanced BW recovery thereafter in first lactation cows with no effect in older cows. Effects of supplementation on milk yield were small, and they were negative in early lactation and generally positive in late lactation; effects were positive on fat test in early lactation for both parity categories but distinctly negative for parity 1 cows in late lactation. Supplementation of undegradable protein in late lactation also decreased milk protein content in parity 1 cows and raised it in older cows. Data suggest that Lys may have been first-limiting, followed by Ile in early lactation and Met in late lactation, and that AA adequacy may be more important than undegradability in ration protein balancing. For most traits measured, treatment by parity interactions were significant, indicating that parity 1 cows did not respond in the same way as older ones to protein supplementation.