Effects of Concentrate Type and Chromium Propionate Supplementation on Insulin Resistance Parameters, Milk Production, and Reproductive Outcomes in Lactating Dairy Cows Consuming Excessive Energy

This experiment compared insulin resistance parameters, milk yield, and reproductive outcomes in lactating dairy cows consuming excessive energy, and receiving in a 2 x 2 Latin square design the following treatments: 1) concentrate based on ground corn (CRN; n = 13) or citrus pulp (PLP; n = 13), and 2) supplemented (n = 14) or not (n = 12) with 2.5 g/d of Cr-propionate. Twenty-six multiparous, non-pregnant, lactating Gir x Holstein cows (average 80 d in milk on d 0) were offered corn silage for ad libitum consumption (d 0 to 180). Cows individually received concentrate formulated to allow diets to provide 160% of their daily NE_L requirements. Weekly, BW, BCS, and milk production were recorded and blood samples were collected prior to feeding. GTT were performed on d 0, 60, 120, and 180, (0.5 g of glucose/kg of BW infusion). Ovarian pick-up for in vitro embryo production was performed on d 0, 80, and 160. No treatment differences were detected for BW and BCS (P >= 0.25), neither for milk yield, milk fat and solid (P >= 0.24). However, CRN had greater (P= 0.01) milk protein compared with PLP cows (3.54 vs. 3.14 %, respectively; SEM = 0.08). Within weekly samples, concentrations of serum insulin and glucose, as well as RQUICKI and insulin:glucose ratio were similar among treatments (P >= 0.40), whereas CRN had less serum NEFA concentrations compared with PLP cohorts (0.178 vs. 0.219 mmol/L; SEM = 0.008). No treatment differences were detected (P >= 0.35) on number of viable oocytes collected and embryos produced within each aspiration. During the GTT, no treatment differences were detected (P >= 0.16) for serum glucose concentration, glucose clearance rate, glucose half-life, and insulin:glucose ratio (P >= 0.16). Serum insulin concentrations were less (P = 0.05) in CRN cows receiving Cr-propionate compared with non-supplemented CRN cohorts (9.01 vs. 13.61 ng/mL, respectively; SEM = 1.73), whereas Cr-propionate supplementation did not impact serum insulin within PLP cows (P = 0.68). In summary, concentrate type altered milk protein content and serum NEFA concentrations in lactating dairy cows consuming excessive NE_L, impacted the effects of Cr-propionate supplementation on serum insulin response to a GTT, but did not influence milk yield or reproductive responses.