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Dry period heat stress effects on calf health and metabolism

Jim Quigley Published on 06 May 2014

Research continues to show that prenatal stress can affect metabolism of the offspring. This appears to hold true for many different species of animals including cattle. One stress that consistently affects pregnant dairy cows is heat stress.

We know that heat stress can impair a cow’s reproduction and depress milk production. However, effects on calves – either before or after calving – are less well-defined.

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Previous research has shown that prenatal heat stress on the dam affects calf bodyweight (calves from heat-stressed cows are up to 11 pounds lighter than calves from cooled cows) and immune function. Calves born to non-cooled cows had lower IgG absorption.

The apparent efficiency of IgG absorption (AEA, an index of the calf’s ability to extract IgG from ingested colostrum) was 19 percent compared to 33 percent in calves born from cooled cows. The effect of impaired AEA was serum IgG concentrations were lower (10.6 versus 15.8 g per L at 24 hours old), which places calves at greater risk of disease.

Further, an evaluation of cell-mediated immunity (CMI, the ability of the calf’s immune cells to respond to an immune challenge) indicated that CMI was impaired in calves from heat-stressed cows.

Taken in total, these data clearly show that heat stress during the dry period can impair the immune response of newborn calves.

Effect on basal metabolism
A more recent publication from the University of Florida reported results of a study wherein researchers housed 20 dry cows in a cooled or non-cooled heat stress environment at drying off. When calves were born, they were immediately separated from their dams and fed 3.8 L of high-quality colostrum by one hour after birth and then 1.9 L of colostrum again in about 12 hours.

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From day two to day 42, calves were fed pasteurized milk (1.9 to 3.8 L per day) and decreasing amounts to weaning at day 49. Calf starter and water were available for ad-lib consumption from 2 days old. On day 55, calves were exposed to two different metabolic tests, a glucose tolerance test and an insulin challenge.

Descriptive statistics for cows exposed to cooled or heat stress environments and their calves on day 55 of age Response of calves to glucose tolerance and insulin sensitivity in calves from cows exposed to cooled or heat stress environments

The goal of the glucose tolerance test is to find out how calves respond when a dose of glucose is infused into the jugular vein. Typically, blood glucose will increase after administering the glucose into the vein, followed by an increase in blood insulin concentration.

The body secretes insulin into the circulation to regulate blood glucose; as glucose rises, insulin is secreted, which promotes uptake of the glucose from the circulation into many different body tissues. In this way, blood glucose can be closely regulated by the animal.

In the study, the concentration of both glucose and insulin in calves in both groups increased up to two hours after glucose infusion. Although there was no effect on insulin concentrations, the concentration of plasma glucose was lower in calves from heat-stressed cows.

This suggests that when glucose was infused, calves from heat-stressed cows were more efficient in moving glucose from the circulation into other body tissues, so the pool of circulating glucose remained lower.

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So it appears that other tissues, including fat cells, utilized glucose more efficiently when calves came from heat-stressed cows. Although we want calves and heifers to utilize glucose efficiently, we also want to avoid directing that glucose towards adipose tissue, when it may contribute to over-fattening instead of good growth.

Results of the insulin sensitivity test also showed little effect of insulin injection on blood insulin AUC (area under the curve, a measure of concentration over time). However, when insulin was injected, calves born from heat-stressed cows had lower-glucose AUC compared to calves from cooled cows.

Taken together, these data suggest that basal metabolism of calves is affected by the stress imposed on the mother during gestation. This study shows that the way calves use glucose is altered.

Whether this alteration in metabolism of glucose affects the animal’s predisposition is not completely clear; however, other data suggest that increased uptake of glucose in response to glucose tolerance test or insulin challenge does predispose animals to increased risk of adipose deposition.

Managing the environment of cows is important to their health and continued productivity. Results from this study suggests that cooling dry cows is also important for the health and, perhaps, future productivity of the calf. PD

References omitted due to space but are available upon request. Click here to email an editor.

Jim Quigley

Jim Quigley
Technical and Research Manager – Calf and Heifer
Provimi North America

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