Indices of heart rate variability as potential early markers of metabolic stress and compromised regulatory capacity in dried-off high-yielding dairy cows

High performing dairy cows experience distinct metabolic stress during periods of negative energy balance. Subclinical disorders of the cow’s energy metabolism facilitate failure of adaptational responses resulting in health problems and reduced performance. The autonomic nervous system (ANS) with its sympathetic and parasympathetic branches plays a predominant role in adaption to inadequate energy and/or fuel availability and mediation of the stress response. Therefore, we hypothesize that indices of heart rate variability (HRV) that reflect ANS activity and sympatho-vagal balance could be early markers of metabolic stress, and possibly useful to predict cows with compromised regulatory capacity. In this study we analysed the autonomic regulation and stress level of 10 pregnant dried-off German Holstein cows before, during and after a 10-h fasting period by using a wide range of HRV parameters. In addition heat production (HP), energy balance, feed intake, rumen fermentative activity, physical activity, non-esterified fatty acids, β-hydroxybutyric acid, cortisol and total ghrelin plasma concentrations, and body temperature (BT) were measured. In all cows fasting induced immediate regulatory adjustments including increased lipolysis (84%) and total ghrelin levels (179%), reduction of HP (−16%), standing time (−38%) and heart rate (−15%). However, by analysing frequency domain parameters of HRV (high-frequency (HF) and low-frequency (LF) components, ratio LF/HF) cows could be retrospectively assigned to groups reacting to food removal with increased or decreased activity of the parasympathetic branch of the ANS. Regression analysis reveals that under control conditions (feeding ad libitum) group differences were best predicted by the nonlinear domain HRV component Maxline (L MAX, R 2=0.76, threshold; TS=258). Compared with cows having L MAX values above TS (>L MAX: 348±17), those with L MAX values below TS (<L MAX: 109±26) had higher basal blood cortisol levels, lower concentrations of insulin, and respond to fasting with a shift of their sympatho-vagal balance towards a much stronger dominance of the sympathetic branch of the ANS and development of stress-induced hyperthermia. The data indicate a higher stress level, reduced well-being and restricted regulatory capacity in <L MAX cows. This assumption is in accord with the lower dry matter intake and energy corrected milk yield (16.0±0.7 and 42±2 kg/day) in lactating <L MAX compared with >L MAX cows (18.5±0.4 and 47.3 kg/day). From the present study, it seems conceivable that L MAX can be used as a predictive marker to discover alterations in central autonomic regulation that might precede metabolic disturbances

Effects of Feeding Milk Replacer Ad Libitum or in Restricted Amounts for the First Five Weeks of Life on the Growth, Metabolic Adaptation, and Immune Status of Newborn Calves

The pre-weaning period is critical for calf health and growth, and intensive milk feeding programs may assist postnatal development by improving body growth and organ maturation. The aim of the present work was to study the effects of ad libitum milk replacer (MR) feeding on the growth, metabolic adaptation, health, and immune status of newborn calves. Twenty-eight newborn Holstein and Holstein x Charolais crossbred calves were fed ad libitum (ADLIB) or in restricted amounts (6 liters per day; RES) during the first five weeks of life. The MR intake in the ADLIB treatment was gradually reduced at weeks 6 and 7, and all calves then received 6 liters of MR per day until day 60. Blood samples were collected to measure the plasma concentrations of metabolites, insulin, insulin-like growth factor (IGF)-I and IGF binding proteins (IGFBP), immunoglobulins, and acute phase proteins. The expression of mRNA associated with both the somatotropic axis and gluconeogenic enzymes was measured in the liver on day 60. Intensive feeding improved MR intake and growth in ADLIB without influencing concentrate intake. Carcass weight, perirenal fat, and muscle mass were greater in ADLIB. Plasma concentrations of glucose, triglycerides, insulin, and IGF-I were greater, whereas plasma concentrations of β-hydroxybutyrate, total protein, albumin, urea, IGFBP-2 and -4, and fibrinogen were lower at distinct time points in ADLIB. The hepatic mRNA expression of cytosolic phosphoenolpyruvate carboxykinase was greater in ADLIB. Most metabolic and endocrine differences occurred during the MR feeding period, but a slightly greater concentrate intake was associated with increased plasma IGF-I and insulin at the end of the study. The immune and health status of the calves were not affected by MR feeding. However, increased plasma fibrinogen in the RES group suggested differences in the acute phase response

Composition of Milk Replacer (MR) and the Concentrate.

<p>Composition of Milk Replacer (MR) and the Concentrate.</p

Feed Intake and Growth Performance.

<p>Colostrum and milk replacer (MR) (<b>A</b>) and concentrate intake (<b>B</b>), total metabolizable energy (ME) intake, body weight (<b>D</b>), and average daily gain (<b>E</b>) in calves fed MR either <i>ad libitum</i> (ADLIB, black square, straight line) or restrictively (RES, white circle, dashed line) for the first five weeks of life. MR intake in ADLIB was gradually reduced during weeks 6 and 7 to amounts fed in RES. The data are presented as the least squares means ± standard error. ^†Trend between groups <i>P</i> < 0.1; *different between groups <i>P</i> < 0.05; **different between groups <i>P</i> < 0.01; and ***different between groups <i>P</i> < 0.001.</p

Carcass Composition.

<p>The weight of the hot carcass, liver, pancreas, fat depots, and distinct muscle cuts<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0168974#t003fn002" target="_blank">¹</a> and the size of the musculus longissimus dorsi (MLD) in calves fed milk replacer (MR) either <i>ad libitum</i> (ADLIB) or restrictively (RES) for the first five weeks of life.</p

Total Protein and Immune Status in Blood Plasma.

<p>Plasma concentrations of total protein (<b>A</b>) and immunoglobulins (Ig) G1 (<b>B</b>), IgG2 (<b>C</b>), and IgM (<b>D</b>) in calves fed milk replacer (MR) either <i>ad libitum</i> (ADLIB, black square, straight line) or restrictively (RES, white circle, dashed line) for the first five weeks of life. MR intake in ADLIB was gradually reduced during weeks 6 and 7 to amounts fed in RES. The data are presented as the least squares means ± standard error. *Different between groups <i>P</i> < 0.05.</p

Endocrine Status in Blood Plasma.

<p>The plasma concentrations of insulin (<b>A</b>), insulin-like growth factor 1 (IGF-I; <b>B</b>), and IGF-binding proteins (IGFBP)-2 (<b>C</b>), -3 (<b>D</b>), and -4 (<b>E</b>) in calves fed milk replacer (MR) either <i>ad libitum</i> (ADLIB, black square, straight line) or restrictively (RES, white circle, dashed line) for the first five weeks of life. MR intake in ADLIB was gradually reduced during weeks 6 and 7 to amounts fed in RES. The data are presented as the least squares means ± standard error. ^†Trend between between groups <i>P</i> < 0.1, *different between groups <i>P</i> < 0.05, **different between groups <i>P</i> < 0.01, and ***different between groups <i>P</i> < 0.001.</p

Metabolic Status in Blood Plasma.

<p>The plasma concentrations of glucose (<b>A</b>), lactate (<b>B</b>), beta-hydroxybutyrate (BHB; <b>C</b>), non-esterified fatty acids (NEFA; <b>D</b>), triglycerides (<b>E</b>), and cholesterol (<b>F</b>) in calves fed milk replacer (MR) either <i>ad libitum</i> (ADLIB, black square, straight line) or restrictively (RES, white circle, dashed line) for the first five weeks of life. MR intake in ADLIB was gradually reduced during weeks 6 and 7 to amounts fed in RES. The data are presented as the least squares means ± standard error. ^†Trend between groups <i>P</i> < 0.1, *different between groups <i>P</i> < 0.05, **different between groups <i>P</i> < 0.01, and ***different between groups <i>P</i> < 0.001.</p