Influence of food deprivation on intravenous glucose tolerance test traits in Holstein Friesian heifers

Abstract

Glucose is essential for numerous cellular functions due to its involvement in energy supply from early development to adulthood. In the lactating cow, glucose demands by the mammary gland significantly increase to support milk production when compared with other tissues. Thus, insufficient blood glucose levels might predispose dairy cows to metabolic disturbances. The intravenous glucose tolerance test (ivGTT) is a suitable tool to characterize glucose metabolism and insulin responses, but results must be reliable and repeatable. One factor influencing ivGTT is food deprivation period, which has been considered as an obligatory requirement before conduction of glucose tolerance studies in monogastric species, whereas it has been permissive in ruminants. The objective of this study was to determine the influence of 5 fasting periods (0, 12, 24, 36, and 48 h) on ivGTT traits and insulin responses in German Holstein heifers. A total of 140 tests were conducted in 28 females aged 12 to 19 mo. Blood samples were collected every 7 min within 1 h. Assessed glucose and insulin parameters included basal serum glucose and insulin concentration, maximum glucose and insulin concentration obtained between min 7 to 21, and concentrations at min 63 (last sampling) relative to glucose administration, glucose area equivalent (GA), glucose area under the curve (GAUC), insulin area equivalent (InsA), insulin area under the curve (InsAUC), and blood glucose half-life time (GHLT). Serum glucose and insulin concentration were measured according to the hexokinase colorimetric method and solid phase radio immunoassay, respectively. The generalized linear mixed model was used to test for significant differences in all glucose traits and insulin responses at different fasting periods. The model used season and weight as confounding variables. Glucose and insulin concentrations at 0, 7 to 21 (maximum concentration), and 63 min were affected by the duration of food deprivation. The GA, InsA, GAUC, InsAUC, and especially GHLT were also affected by fasting period. A positive linear relationship between GHLT and length of food deprivation was found. Significantly higher GA, GAUC, GHLT values, and glucose and insulin concentration at min 63 were obtained at increasing fasting periods. High intraclass correlation coefficient (0.48) was found for GHLT. The results demonstrate that GHLT might be used to reliably characterize an individual's glucose metabolism and the importance of standardizing food deprivation schedules when performing an ivGTT in nongestating Holstein heifers.

Evaluation of glucose dose on intravenous glucose tolerance test traits in Holstein-Friesian heifers

“…From all ivGTT traits assessed, only GMAX was influenced by BW, which could be related to higher glucose amounts applied as weight increased. The lack of influence of BW on ivGTT traits and insulin responses is in agreement with our previous study on fasting times (González-Grajales et al, 2017). Other studies found an association between degree of obesity and insulin maximum responses (McCann and Reimers, 1986).…”

“…Individual factors influencing a metabolic response (e.g., age, breed, and physiological status) should be carefully revised to obtain reliable results (Kaneko, 1997). Additionally, the effects of fasting (González-Grajales et al, 2017), stress, and diet composition on ivGTT traits in Holstein heifers have also been investigated (Görner, 2011). Surprisingly, little attention has been paid to the effects of glucose dose on ivGTT despite its wide implementation.…”

“…Furthermore, Pieper et al (2016) found high heritability for some ivGTT traits, such as glucose half-life time (GHLT) in young Holstein bulls, which is related to glucose clearance times from the body. Other parameters derived from the test are influenced by numerous factors besides individual variation (González-Grajales et al, 2017). As suggested by Pieper et al (2016), GHLT might be used in the future as a selection criterion to predict animal health due to the development of numerous conditions in dairy cattle as a result of impaired carbohydrate and lipid metabolism (Drackley et al, 2005).…”

Short communication: Repeatability of intravenous glucose tolerance test traits in young Holstein-Friesian cattle

“…Therefore, test standardization is important to obtain repeatable and reliable data. We have reported about test standardization including fasting times (González-Grajales et al, 2017), glucose dose (González-Grajales et al, 2018), and management and nutritional measures (Görner, 2011). However, test repeatability in young Holstein-Friesian cattle is unknown.…”

Effects of auditory and visual stimuli on glucose metabolism in Holstein dairy cattle

“…The information obtained from these responses is routinely used to assess conditions such as insulin resistance [11], diagnose diabetes, although its incidence in cattle is very low [12], determine the impact of certain compounds on insulin sensitivity [13] among other applications. Despite the wide implementation of ivGTT in cattle, careful data interpretation is always recommended because test standardization is lacking [14]. Recently, the effects of food deprivation times [14] and glucose dose [15] on ivGTT and insulin traits have been demonstrated.…”