a b s t r a c tThis experiment compared insulin resistance parameters, milk production, and reproductive outcomes in: (1) lactating dairy cows consuming adequate or excessive energy, and (2) lactating dairy cows consuming excessive energy and receiving or not Cr-propionate supplementation. Seventeen primiparous and multiparous, non-pregnant, lactating Holstein cows (initial days in milk ¼ 76 72) were assigned on d 0 to: (1) concentrate intake to meet their requirements of net energy for lactation (NE L ) without Cr supplementation (MAN; n ¼5), (2) concentrate intake to exceed their NE L requirements without Cr supplementation (HIGH; n ¼ 6), and (3) HIGH with 2.5 g/d of Cr propionate (HIGHCR; n ¼ 6). Throughout the experiment (d 0 to 210), cows were offered corn silage for ad libitum consumption, and individually received a corn-based concentrate twice daily. Concentrate intake was formulated to allow diets to provide 100% of daily NE L requirements of MAN, and 160% of daily NE L requirements of HIGH and HIGHCR cows. Cow BW, BCS, and milk production were recorded weekly. Blood samples were collected weekly, prior to and at 2 and 4 h after the morning concentrate feeding. Six glucose tolerance tests (GTT) were performed, every 42 d, by infusing cows with 0.5 g of glucose/kg of BW. Follicle aspiration for in vitro embryo production was performed via transvaginal ovum pick-up 2 d after each GTT. Increase in BCS from d 0 to 210 was greater (P r0.04) in HIGH and HIGHCR vs. MAN. Milk production was similar (P ¼0.92) between treatments. Within weekly samples, serum non-esterified fatty acids concentration were greater (P r0.05) for MAN vs. HIGH and HIGHCR. Serum insulin concentrations and insulin:glucose ratio were often greater (Pr 0.05) for HIGH, intermediate for HIGHCR, and lesser for MAN (treatment  day interaction, Po 0.01). During the GTT, serum insulin concentrations and insulin:glucose ratio were greater (P r0.05) for HIGH compared with HIGHCR and MAN from 10 to 60 min relative to the time of glucose infusion. Proportion of embryo produced per oocyte collected was greater (Pr 0.02) for MAN vs. HIGH and HIGHCR, and similar (P ¼0.59) between HIGH and HIGHCR. In conclusion, lactating cows consuming excessive concentrate and NE L experienced increased insulin resistance and reduced proportion of embryo produced per oocyte collected compared with cows consuming adequate amounts of energy, whereas Cr-propionate supplementation was effective in alleviating insulin resistance caused by excessive NE L intake.

The objective of this experiment was to evaluate the effects of glucose infusion on serum concentrations of glucose, insulin, and progesterone (P4), as well as mRNA expression of hepatic CYP2C19 and CYP3A4 in nonlactating, ovariectomized cows in adequate nutritional status. Eight Gir × Holstein cows were maintained on a low-quality Brachiaria brizantha pasture with reduced forage availability, but they individually received, on average, 3 kg/cow daily (as fed) of a corn-based concentrate from d -28 to 0 of the experiment. All cows had an intravaginal P4-releasing device inserted on d -14, which remained in cows until the end of the experiment (d 1). On d 0, cows were randomly assigned to receive, in a crossover design containing 2 periods of 24h each (d 0 and 1), (1) an intravenous glucose infusion (GLUC; 0.5 g of glucose/kg of BW, over a 3-h period) or (2) an intravenous saline infusion (SAL; 0.9%, over a 3-h period). Cows were fasted for 12h before infusions, and they remained fasted during infusion and sample collections. Blood samples were collected at 0, 3, and 6h relative to the beginning of infusions. Liver biopsies were performed concurrently with blood collections at 0 and 3h. After the last blood collection of period 1, cows received concentrate and returned to pasture. Cows gained BW (16.5 ± 3.6 kg) and BCS (0.08 ± 0.06) from d -28 to 0. Cows receiving GLUC had greater serum glucose and insulin concentrations at 3h compared with SAL cohorts. No treatment effects were detected for serum P4 concentrations, although mRNA expression of CYP2C19 and CYP3A4 after the infusion period was reduced for cows in the GLUC treatment compared with their cohorts in the SAL treatment. In conclusion, hepatic CYP3A4 and CYP2C19 mRNA expression can be promptly modulated by glucose infusion followed by acute increases in circulating insulin, which provides novel insight into the physiological mechanisms associating nutrition and reproductive function in dairy cows.

The objective was to compare insulin resistance parameters in cows with adequate or excessive energy intake as well as in cows with excessive energy intake receiving Cr supplementation as chromium propionate. Thirteen multiparous, nonlactating Gir × Holstein cows were ranked by BW and BCS and assigned to 1 of 3 dietary treatments on d 0: 1) diet to meet their ME requirements without Cr supplementation (MAN; n = 4), 2) diet to exceed their ME requirements without Cr supplementation (HIGH; n = 4), and 3) HIGH with 2.5 g/d of chromium propionate (HIGHCR; n = 5, with 10 mg of Cr/cow daily). Diets were formulated to provide 100% of daily ME requirements of MAN and 177% of daily ME requirements of HIGH and HIGHCR cows and offered twice daily via individual self-locking head gates from d 0 to 88. Cow BW and BCS were recorded on d 0 and 88 of the experiment. Blood samples were collected before and 2 h after the morning feeding twice weekly. Preprandial revised quantitative insulin sensitivity check index (RQUICKI) was determined using serum glucose, insulin, and NEFA concentrations obtained before feeding. Glucose tolerance tests (GTT) were performed on d 32 and 88 by infusing cows with 0.5 g of glucose/kg of BW whereas blood samples were collected at -15, 0, 10, 20, 30, 45, 60, and 90 min relative to infusion. Change in BCS tended to be greater in HIGH and HIGHCR (P = 0.09) compared with MAN cows. Within samples collected twice weekly, serum concentrations of glucose, insulin (beginning on d 14 of the experiment), and NEFA (preprandial samples only) were greater (P ≤ 0.05) in HIGH compared with HIGHCR cows and tended to be greater in HIGH compared with MAN cows (P ≤ 0.10) but did not differ (P ≥ 0.52) between HIGHCR and MAN cows. Moreover, HIGH cows had reduced RQUICKI compared with MAN (P = 0.02) and HIGHCR cows (P = 0.05) whereas RQUICKI was similar between MAN and HIGHCR cows (P = 0.53). Within samples collected during the GTT, mean serum insulin concentrations and insulin:glucose ratio were greater (P < 0.01) in HIGH compared with HIGHCR cows, tended (P ≤ 0.09) to be greater in HIGH compared with MAN cows, and were similar (P ≥ 0.16) between HIGHCR and MAN cows. Serum glucose concentrations were greater (P < 0.01) for HIGH compared with MAN and HIGHCR cows 20 min relative to infusion. In conclusion, chromium propionate supplementation prevented the increase in insulin resistance caused by excessive energy intake in nonlactating dairy cows.

-Forty-five non-lactating, pregnant Holstein animals (18 heifers and 27 multiparous cows; BW = 561±114 kg; BCS = 2.9±0.3; days pregnant = 110±56 d) were stratified by initial BW and BCS, and randomly assigned to receive daily (as-fed basis) 0.50 kg of ground corn plus 0.22 kg of kaolin (CON), calcium salts of saturated fatty acids (SFA) or polyunsaturated fatty acids (PF) for 14 d. Blood samples were collected on days 0, 7 and 14, immediately prior to (0 h) and 3, 6, 9 and 12 h after feeding, to determine the serum concentrations of P 4 and insulin. No treatment effects were detected for serum concentrations of P 4 (5.52, 6.13 and 5.63±0.41 ng/mL for CON, SFA and PF, respectively). No treatment effects were detected for serum concentrations of insulin (11.5, 10.5 and 10.1±1.43 µIU/mL for CON, SFA and PF, respectively). Heifers had greater serum concentrations of P 4 than multiparous cows (6.35 vs. 5.16±0.42 ng/mL), but lower serum concentrations of insulin (7.0 vs. 14.4±1.49 µIU/mL). Feeding 0.22 kg of calcium salts of polyunsaturated fatty acids is not sufficient to increase the serum concentrations of P 4 and insulin of non-lactating, pregnant dairy cows.

The objective of this experiment was to evaluate the effects of bovine somatotropin administration on serum concentrations of glucose, insulin, NEFA, IGF-I, and progesterone (P4) in ovariectomized non-lactating dairy cows receiving exogenous P4, as a model to estimate treatment effects on hepatic P4 degradation. Ten non-lactating, non-pregnant, and ovariectomized Gir  Holstein cows were assigned to the experiment (d À 14 to 27). On d 0, cows were ranked by BW and BCS, and randomly assigned to one of two treatments: (1) bovine somatotropin (BST; n ¼ 5) or (2) saline control (control; n ¼ 5). Cows assigned to the BST treatment were administered s.c. injections containing 500 mg of sometribove zinc on d 0, 9, and 18 of the experiment, whereas control cows concurrently received a 10-mL s.c. injection of 0.9% saline. On d À 2, cows were inserted with an intravaginal releasing device containing 1.9 g of P4, which remained in the cows until the end the experiment (d 27). Cow BW and BCS were assessed on d À 14, 0, and 27. Blood samples were collected daily from d 0 to d 27, at 0 (immediately before), 1, and 2 h relative to concentrate feeding for determination of serum glucose, insulin, NEFA, P4, and IGF-I concentrations. Concentrations of glucose, NEFA, and insulin obtained prior to feeding (0 h) were used to determine pre-prandial revised quantitative insulin sensitivity check index (RQUICKI). No treatment effects were detected for BW (P ¼ 0.72) and BCS change (P ¼ 0.79) during the experiment. Beginning on d 2 of the experiment, BST cows had greater (P≤0.01) serum IGF-I concentrations compared with control cohorts (treatment  day interaction; P o 0.01). Cows receiving BST had greater (P≤0.05) insulin concentrations compared with control cohorts from d 8 to d 11, d 16 and 17, as well as from d 19 to d 21 of the experiment (treatment  day interaction; Po 0.01). Cows receiving BST had greater (P≤0.01) mean glucose and NEFA concentrations, as well as reduced (P o0.01) mean RQUICKI during the experiment compared with control cohorts. No treatment effects, however, were detected (P ¼ 0.73) for serum P4 concentrations. In conclusion, results from this experiment indicate that hepatic P4 catabolism is not directly regulated by circulating IGF-I, whereas BST administration decreases insulin sensitivity in non-lactating dairy cows in adequate nutritional status.