Date of Award
Master of Science
Lance H. Baumgard
Multiparous (n = 79) and primiparous (n = 68) Holstein cows were blocked by 305 previous mature equivalent milk yield and parity and assigned to one of three dietary treatments. Treatments differed in Zn content as follows: 1) 75 mg/kg of DM supplemental Zn provided entirely as Zn sulfate (CON); 2) 33.3 mg and 15.5 mg of Zn sulfate/kg of DM in the control close up and lactation diets respectively were replaced by a Zn amino acid complex (Availa®Zn; MED); and 3) 66.6 mg and 40 mg of Zn sulfate/kg of DM in the control close up and lactation diets were replaced by a Zn amino acid complex (Availa®Zn; HIGH). Cows were housed at the Iowa State University Dairy farm, and were individually offered a TMR containing dietary treatments beginning at 28 ± 15 d prior to expected calving date and continued until 250 DIM. Compared to controls, multiparous cows (but not heifers) fed OZn had increased (20%) colostrum IgG. Feeding increasing levels of OZn did not affect prepartum DMI, but compared to CON-fed cows decreased (P < 0.01) DMI during lactation (5.1 and 3.2 %, respectively). Feeding increasing levels of OZn improved (P < 0.01) services per conception (38 and 24 %, respectively), and tended (P = 0.08) to increase NEFA concentration (455 vs. 409 μEq/L). Feed efficiency measured as MY/DMI, FCM/DMI, and SCM/DMI increased (P < 0.05) 6.2, 5.8, and 5.9 % in HIGH OZn vs. CON-fed cows. MED-fed cows had reduced overall milk fat content (3.0%) compared to CON and HIGH-fed cows. Cows fed HIGH OZn had increased (P < 0.01) SCC compared to the CON and MED-fed cows (35%), but less (P < 0.05; 17%) LnSCC than CON-fed cows. Feeding increasing levels of OZn reduced feed intake without affecting overall milk production and therefore improved feed efficiency.
Nayeri, Amir, "Transition Performance and Metabolic Variables in Periparturient Holstein Cows Fed Increasing Amounts of Organic Zinc" (2012). Graduate Theses and Dissertations. 12565.