The objective of this study was to evaluate serum concentrations of nonesterified fatty acids, glucose, insulin, and progesterone in nonlactating dairy cows according to nutritional balance and glucose infusion. Ten nonlactating, ovariectomized Gir x Holstein cows were stratified by body weight (BW) and body condition score (BCS) on d -28 of the study, and randomly assigned to 1) negative nutrient balance (NB) or 2) positive nutrient balance (PB). From d -28 to d 0, cows were allocated according to nutritional treatment (5 cows/treatment) into 2 low-quality pastures with reduced forage availability. However, PB cows individually received, on average, 3 kg/cow per day (as-fed) of a concentrate during the study. All cows had an intravaginal progesterone releasing device inserted on d -14, which remained in cows until the end of the study. Cow BW and BCS were assessed again on d 0. On d 0, cows within nutritional treatment were randomly assigned to receive, in a crossover design containing 2 periods of 24h each, 1) intravenous glucose infusion (GLU; 0.5 g of glucose/kg of BW, as a 5% glucose solution administered, on average, at 32 mL/min over a 3-h period), or 2) intravenous saline infusion (SAL; 0.9% solution infused on average at 32 mL/min over a 3-h period). Prior to the beginning of each period, all cows were fasted for 12h. Blood samples were collected, relative to the beginning of the infusion, at -12 and -11.5h (beginning of fasting), and at -0.5, 0, 0.5, 1, 2, 3, 4, 5, and 6h. Following the last blood collection of period 1, cows received (PB) or not (NB) concentrate and were returned to their respective pastures. Changes in BCS and BW were greater in NB cows compared with PB cows (-0.60 and -0.25+/-0.090 for BCS, respectively; -22.4 and 1.2+/-6.58 kg for BW, respectively). Cows receiving GLUC had greater glucose concentrations from 0.5 to 3h relative to infusion compared with SAL cows. Insulin concentrations were greater in PB cows assigned to GLUC compared with SAL cohorts at 0.5 and 3h following infusion, whereas NB cows assigned to GLUC had greater insulin concentrations compared with SAL cohorts at 0.5, 1, 2, and 3h. Progesterone concentrations were greater in PB cows assigned to GLUC at 2, 3, and 4h following infusion compared with SAL cohorts. In conclusion, the effects of glucose infusion on serum concentrations of insulin and progesterone in nonlactating dairy cows were dependent on cow nutritional status.

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.

-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.

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