Effects of dietary antioxidants and modulators of immune response on animal performance and metabolism of Holstein cows during heat stress.

Abstract:

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Effects of dietary antioxidants and modulators of immune response on animal performance and metabolism of Holstein cows during heat stress.
A. Ruiz Gonzalez*^1,2, W. Suissi², L. H. Baumgard³, P.-Y. Chouinard¹, R. Gervais¹, D. E. Rico². ¹Universit� Laval Quebec, QC, Canada, ²CRSAD Deschambault, QC, Canada, ³Iowa State University Ames, IA.

Twelve multiparous Holstein cows (42.2 � 5.6 kg milk/d; 83.4 � 27.1 DIM) were used in a split-plot design testing the effects of mineral and vitamin supplementation on animal performance and metabolism during heat stress. The main plot was the level of dietary vitamin E and Se (HVE: 200 IU/kg and 1.2 ppm; LVE 20 IU/kg and 0.3 ppm; respectively). Within each plot, cows were randomly assigned to 1) Heat stress (HS), 2) Pair-feeding (PF), or 3) HS with Vitamin D and Ca supplementation (HS+DCa; 1820 IU/kg and 1.5% Ca) in a Latin square design with 14-d periods. Milk components were analyzed by mid-infrared spectroscopy from samples taken on d 0, 3, 7, 10, and 14. This statistical model included the random effects of cow and period, and the fixed effects of plot, treatment, day and their interactions. No 3-way interactions were detected for any variable. Heat stress progressively decreased dry matter intake (DMI) before stabilizing on d 7 (30% reduction; Time P < 0.001) and was not affected by treatment. Milk yield decreased progressively in all treatments and was higher in PF relative to both HS and HS+DCa cows from d 3 to 14 (−10%; P < 0.05). There was a treatment by day interaction for milk fat and protein concentrations (P < 0.05). Milk fat was 10% lower in HS relative to PF on d 10 and 14, but not different between PF and HS+DCa, whereas milk protein was 7.5% lower in HS and HS+DCa relative to PF from d 3 to 14. Pre-prandial NEFA were 64% lower, whereas pre-prandial insulin was 58% higher in HS and HS+DCa than in the PF on d 7 and 14 (P < 0.05). Mineral and vitamin supplementation seems to have a moderate effect on the performance and metabolic responses of cows to heat stress.

Keywords: heat stress, dairy cows, nutrition.