Abstract #476

# 476
Effects of timing of chromium propionate supplementation on metabolic and production responses of Holstein cows in early lactation.
Michael S. Allen*1, Richard Longuski1, 1Michigan State University, East Lansing, MI.

Forty-eight multiparous Holstein cows were used in a randomized block design experiment with 4 treatments and 12 cows per treatment to determine effects of timing of chromium propionate (CrPr) supplementation on metabolic and production responses in early lactation. Treatments were chromium propionate (C) or control (N), supplemented according to 4 schedules: 1 to 65 d PP (CC); 1–22 d PP (CN); 23–65 d PP (NC); no CrPr supplementation (NN). Supplements were top-dressed at 20 g per cow/d to provide 8 mg of chromium per cow/d for C (KemTRACE Chromium, 0.04% chromium, Kemin Animal Nutrition and Health) or no additional chromium for N (feed-grade limestone). Cows were blocked by calving date, body condition score (BCS) and previous milk yield, and randomly assigned to treatment. Cows were offered a fresh diet (FR) from 1 to 22 d PP and a peak diet (PK) from 23 to 68 ± 3 d PP. CrPr increased daily DMI (2.75 kg/d) and milk yield (4.5 kg/d, both P < 0.01), tended to decrease milk fat concentration (P = 0.07), and did not affect fat yield compared with control when supplemented during FR only. There were no interactions of the main effects of timing of CrPr supplementation; effects of CrPr supplementation were sustained through most of the experiment when supplementation ceased at 22 d PP and starting supplementation at 23 d PP did not benefit production. Although CrPr supplementation during FR increased milk yield, the effect diminished by 68 d PP, even when supplementation continued during PK. Plasma metabolites and hormones indicate possible effects of CrPr on insulin sensitivity with a reduction in plasma concentrations of NEFA (P = 0.08) and BHBA (P = 0.02), lower milk fat concentration (P = 0.07), and greater BCS over time (interaction P = 0.06) during FR compared with control. Supplementation of CrPr during FR increased DMI and milk yield but effects on production diminished over time with no effects of CrPr by 10 weeks PP, even when supplementation continued during PK. Initiating supplementation at 23 d PP did not benefit production in this experiment.

Key Words: postpartum, chromium, insulin sensitivity