EFFECTS OF CHROMIUM SUPPLEMENTATION ON EARLY LACTATION PERFORMANCE OFHOLSTEIN COWS

Two experiments were conducted to evaluate the effects of chromium (Cr ) supplementation on early lactation performance of Holstein cows. Exp eriment 1 involved 12 primiparous (PP) and 22 multiparous (MP) cows, w hile exp. 2 involved 18 PP and 22 MP cows. In each trial, cows were fe d total mixed rations (TMR) and assigned to one of two treatments: con trol or 0.5 mg kg(-1) supplemental chelated Cr from week 6 prepartum t o week 16 postpartum. The cortisol response to synthetic adrenocortico tropin (ACTH) intramuscular (i.m.) and the luteinizing hormone (LH) re sponse to synthetic gonadotropin-releasing hormone (GnRH) i.m. were ev aluated as well, during weeks 2 and 6 postpartum in exp. 2. During the first 16 wk of lactation, supplemental Cr tended to increase milk yie lds in PP cows by 13% (P = 0.06) and increased milk production by 7% ( P < 0.05) in exps. 1 and 2, respectively, but had no effect in MP cows . Despite increased milk yield, Cr supplementation had no adverse effe ct on milk composition, reproductive performance, or health status. Fu rthermore, Cr supplementation tended to increase the milk lactose cont ent in PP cows. Supplemental Cr reduced serum beta-hydroxybutyrate lev els and may reduce subclinical ketosis in MP cows. In addition, in ove rconditioned, aged cows, Cr supplementation may reduce the incidence o f certain other metabolic disorders. Peak values and production rates of cortisol in Cr-supplemented cows tended to be greater (P < 0.10) th an in control cows at week 6 Basal LH concentrations did not differ be tween the two treatments for either week. However, the Cr-supplemented cows released less (P < 0.05) LH than did control cows at week 6. Res ults from hormone-stimulation tests suggest that the Cr-supplemented c ows may have experienced a greater stress with their increased milk pr oduction. However, the time in postpartum anestrus and the time to con ception were similar, suggesting that Cr supplementation may have miti gated the slower return to fertility usually seen in higher producing PP dairy cows. Further study is needed to determine the effects of Cr supplementation on reproductive performance, health status, and metabo lic disorders in dairy cows.