Development of insulin resistance in dairy cows by 150 days of lactation does not alter oocyte quality in smaller follicles

Abstract

The objective of this study was to test the hypothesis that high-producing dairy cows become increasingly resistant to insulin throughout lactation and that, consequently, oocyte quality is compromised. We used Holstein cows at 50 (51.5±3.7; n=30), 100 (102.3±9.4; n=30), and 150 (154.5±18.9; n=30) days in milk (DIM). We measured circulating insulin and glucose and performed a glucose tolerance test (GTT) after 5h of fasting. To evaluate oocyte quality, we performed ovum pickup on the day before the GTT (581 oocytes). We performed statistical analyses using the MIXED procedure of SAS. The model included the fixed effects of DIM, period, time, parity, and an interaction between DIM and time. We observed no difference in the GTT between groups for any variable related to circulating glucose (for example, glucose peak=203.3±7.2, 208.8±6.3, and 194.3±5.9mg/dL). However, various measures of circulating insulin were different in cows at 150 DIM compared with 50 or 100 DIM: higher basal insulin (8.8±0.9, 8.8±0.8, and 11.9±0.8 µIU/mL), peak insulin (61.9±6.2 69.1±5.7, and 89.0±6.1 µIU/mL), delta maximum insulin (51.1±5.5 59.4±5.0, and 73.5±5.4 µIU/mL), and area under the curve 5-60 (1,874.8±171.0 2,189.5±157.8, and 2,610.5±174.0 µIU/mL × min). Nevertheless, we observed no difference among groups in the number of viable oocytes (3.2±0.7, 3.9±0.7, and 3.6±0.7 per cow per ovum pickup) or percentage of viable oocytes (49.3, 52.2, and 51.8%). Increased circulating insulin before and throughout the GTT in cows at 150 DIM indicates that cows develop increasing insulin resistance with increasing DIM; however, increased insulin resistance was not associated with a detectable alteration in the quality of oocytes aspirated from small and medium-sized follicles.

Associations of insulin resistance later in lactation on fertility of dairy cows

“…Moreover, ovum pick up in vitro embryo production (OPU-IVEP) may not be the most adequate method to assess the impact of insulin resistance on fertility. In fact, although lactating cows at 150 DIM were insulin resistant at the GTT, it did not reflect on quality of oocytes aspirated from small-and mediumsized follicles [20].…”

“…This state is characterized by increased mobilization of body reserves to overcome a shortfall in dietary intake, decreased circulating concentrations of insulin, IGF-I, and glucose, and elevated concentrations of nonesterified fatty acids (NEFA) and b-hydroxybutyrate (BHBA) [19]. However, if cows in later stages of lactation are submitted to prolonged intervals of high feed intake with reduced milk yield, BCS will increase, which might lead to development of hyperinsulinemia [20].…”

“…It was recently hypothesized that dairy cows become increasingly insulin resistant as they proceed through lactation [20]. This hypothesis was tested by performing the glucose tolerance test (GTT) on high-producing dairy cows at various DIM.…”

“…Within time, an asterisk (*) represents an effect of treatment (P 0.05). Adapted from Oliveira et al[20].…”

Adipose tissue lipolysis and remodeling during the transition period of dairy cows

“…Despite this evidence, the role of periparturient AT remodeling in the development of IR is still a matter of debate, as Mann and colleagues did not observe any changes in insulin signaling pathways in over-conditioned cows with excessive lipolytic rates [123]. Furthermore, throughout lactation the degree of IR is dynamic and was shown to increase during late lactation, a period characterized by reduced lipolytic activity [124]. These reports underscore that lipolysis regulation by insulin signaling and AT remodeling is a complex process that requires further characterization.…”