Grain source and chromium supplementation: Effects on health, metabolic status, and glucose-insulin kinetics in Holstein heifer calves.

The nutritional and pharmacological advantages of chromium (Cr) for animals and humans have been well established. Trivalent Cr is a component of chromodulin which is involved with insulin regulation, and thereby associated with the metabolism of carbohydrates, protein and lipids. The signs of Cr deficiency include impaired nutrient metabolism, lower sensitivity of the peripheral tissues to insulin, compromised immunity and decreased weight gain and health status, specifically under stressful conditions. When stressed or when fed diets rich in carbohydrates urinary excretion of Cr increases dramatically, implying the need for Cr supplementation. However, it is not clear how grains with different ruminal fermentation and therefore different rates of carbohydrate supply, especially in Cr-supplemented diets, affect the dairy calf’s energy metabolism. The study of Dr Z. Habibi and colleagues was therefore aimed at determining the effects of grain type and Cr supplementation in the starter diets on the health, circulatory concentration of selected metabolites and hormones related to energy metabolism, and sensitivity to insulin in Holstein heifer calves. Their results were published in the Journal of Dairy Science, Volume 102 of 2019, page 8941 to 8951. The title of the paper is: Grain source and chromium supplementation: Effects on health, metabolic status, and glucose-insulin kinetics in Holstein heifer calves. 

The authors examined the effect of type of grain (maize vs. barley) and Cr-methionine supplementation on health-related variables, blood levels of metabolites and hormones related to energy metabolism, and insulin sensitivity. Forty-eight newborn heifers (3 day of age) were assigned randomly to 4 diets in a 2 × 2 factorial arrangement. The experimental diets were either maize-based (MBD) or barley-based (BBD), supplemented with 0 or 0.05 mg per kg of metabolic body weight. Chromium was provided in the milk before weaning (day 3 to 73 of age) and in pre-warmed water after weaning at 74 to 94 days of age. 

There was no interaction between the type of grain and Cr on the health-related variables, blood metabolites and hormones. The type of grain did not affect faecal score, respiration rate, and rectal temperature. However, there were tendencies for higher diarrhea occurrence and lower chance of having pneumonia in calves fed BBD versus MBD despite longer duration of diarrhea (0.54 days) and shorter days with pneumonia (0.63 days) in the calves fed BBD. The calves supplemented with Cr had lower faecal scores during the pre-weaning and overall periods, and respiration rate throughout the study. Chromium supplementation decreased the duration (0.63 days) and chance of having pneumonia. Calves fed BBD had lower blood levels of urea N during the post-weaning period, with no changes in other blood variables between MBD and BBD. Tendencies were detected for lower blood levels of β-hydroxybutyric acid (ßHBA) during the pre-weaning and overall periods and higher cortisol in Cr-supplemented calves. Chromium supplementation increased insulin clearance rate and decreased the time to half-maximal concentration and the area under the curve in BBD but not MBD calves. The calves were generally healthy, and the type of grain did not affect the health and blood variables related to energy metabolism. However, Cr supplementation increased faecal consistency, decreased respiration rate and days with pneumonia, and increased insulin sensitivity when added to BBD. 

In conclusion, the study indicated that neither the health related variables nor the blood levels of metabolites and hormones related to energy metabolism were affected by the type of grain, implying that maize and barley grains might replace each other in dairy calf starter diets until 3 months of age. Chromium supplementation increased faecal consistency, decreased respiration rate and days with pneumonia, and thereby improved the health status of the calves. Although tendencies for lower blood levels of βHBA and higher levels of cortisol were detected, Cr had no effect on energy metabolism. However, the data substantiated the beneficial effect of Cr supplementation on increasing insulin sensitivity in BBD but not MBD.