Endocrine and metabolic responses to glucose, insulin, and adrenocorticotropin infusions in early-lactation dairy goats of high and low milk yield

Abstract

This experiment aimed to examine endocrine and metabolic responses to glucose, insulin, and adrenocorticotropin (ACTH) infusions in early-lactation dairy goats of different levels of milk production (LMP). Goats were grouped as either high (HY; 4.0 L/d, n = 13) or low milk yield (LY; 2.4 L/d, n = 13). Individual milk yield (L/d) and dry matter intake (DMI; kg/d) were measured daily. Concentration (mM) of glucose, fatty acids, and β-hydroxybutyrate, percent of milk fat and protein, body weight (BW; kg), and body condition score (BCS) were assessed weekly (from 2-6 wk postpartum). An intravenous glucose tolerance test (IVGTT), an insulin tolerance test (ITT), and an ACTH stimulation test were carried out at 43, 44, and 45 ± 0.7 d in milk, respectively. The HY goats had greater milk yield (+67%), energy-corrected milk (ECM; +70%), DMI (+28%), ratio of ECM output to metabolic BW (+67%), and feed efficiency (+25%), but lesser BCS than LY goats (2.4 vs. 2.6). The DMI (% of BW) was moderately correlated with ECM (r = 0.70) and negatively correlated with BCS (r = −0.57). At the time of the IVGTT, HY goats had lesser basal insulin and glucose than LY goats. However, results from IVGTT and ITT indicate that the sensitivity of peripheral tissues to insulin was unaffected by LMP. Compared with LY, HY goats had lesser insulin secretion (−52%) and greater insulin clearance rate (+47%) after glucose infusion. The ITT and ACTH stimulation test results show that both the growth hormone response to insulin and the cortisol response to ACTH were unaffected by LMP. Also, basal plasma concentrations of GH and cortisol were not correlated with glucose and fatty acids concentrations or any performance traits. Collectively, our results suggest that differences between HY and LY goats, concerning milk yield and feed efficiency, were probably more closely related to differences in insulin secretion and clearance than to differences in peripheral tissue responsiveness to the effects of catabolic and anabolic hormones.

Comparison of measures of insulin sensitivity in early-lactation dairy goats

“…For instance, we observed a positive correlation between RQUICKI and ECM (r = 0.56), which is similar to previous observations in dairy goats (r = 0.45, P < 0.001; Zamuner et al, 2020b). By applying the medical interpretation of RQUICKI values, one may be misled to believe that increasing milk production is associated with decreasing degree of IR, even though the most plausible explanation is that the observed positive relationship was due to decreased insulin and increased fatty acids concentration in animals of higher milk production, as demonstrated in Zamuner et al (2020a). Indeed, several studies in dairy cows have suggested that RQUICKI is a better reflection of energy status than of IR itself (Schoenberg and Overton, 2011;Cincović et al, 2017;Hasegawa et al, 2019).…”

“…At first glance, the direction and strength of these correlations could be interpreted as compensatory hypersecretion of insulin in response to lower insulin sensitivity. However, these results should be interpreted with caution because in Zamuner et al (2020a) we found no difference in peripheral tissue response to insulin between goats of different basal insulin levels (5.6 vs. 12.9 mU/L, P = 0.008). Therefore, the observed large interindividual variations in insulin production and secretion could be attributed to genetic differences, as has been demonstrated in humans (Hansen et al, 2020), or to differences in milk production and energy status (Zamuner et al, 2020a).…”

“…Conversely, in Zamuner et al (2020b), we observed that the increase in fatty acids concentration in postpartum goats (+188%) was accompanied by a more pronounced decrease in insulin concentration (−312%) compared with antepartum goats. Similarly, in Zamuner et al (2020a), we observed that greater fatty acids concentration in high-yielding goats (+20%) was accompanied by a much lower insulin concentration (−130%) compared with low-yielding goats.. Schoenberg and Overton (2011) pointed out the weaknesses of using RQUICKI to measure IR in ruminants, suggesting that interpretation of results between cows of different metabolic status or stage of lactation should be done with caution. Apparently, the same principle can be applied to comparisons between goats and cows.…”

“…Indeed, several studies in dairy cows have suggested that RQUICKI is a better reflection of energy status than of IR itself (Schoenberg and Overton, 2011;Cincović et al, 2017;Hasegawa et al, 2019). Furthermore, comparisons between studies in goats and cows suggest that RQUICKI values are usually lower in postpartum cows compared with antepartum cows (Cincović et al, 2014;Marinković et al, 2019), whereas a retrospective analysis of data from our previous studies showed that RQUICKI values were lower in antepartum goats than in postpartum goats (0.43 vs. 0.49, P < 0.001, data not shown; Zamuner et al, 2020b) and lower in low-yielding goats than in high-yielding goats in early lactation (0.42 vs. 0.50; P = 0.01, data not shown; Zamuner et al, 2020a).…”

“…F. Zamuner, 1 * A. W. N. Cameron, 2 B. J. Leury, 1 and K. DiGiacomo 1 presented in Zamuner et al (2020a). Briefly, goats were kept in individual stalls (15 m 2 ) from 11 to 45 ± 4.2 d postpartum (mean ± SD) and ad libitum fed a TMR once daily at around 0900 h.…”