Effect of astaxanthin supplementation on Holstein cows subjected to IVP of embryos during the summer.

To evaluate whether astaxanthin supplementation improves dairy Holstein cows' performance in IVP programs, lactating females (n = 45) were supplemented with 0, 0.25, or 0.50 mg of astaxanthin kg-1 day-1 for 70 days during the summer before OPU. Mixed and generalized linear mixed models were used. The compost barn microclimate was hot and partially humid. Haircoat surface temperature differed by day (p = 4.38 × 10-7) but not by the astaxanthin. Rectal temperature remained within normal range and showed no astaxanthin effect; heart rate varied by day (p = 0.0030) but stayed within reference limits; respiratory rate showed a dose effect (p = 0.041), with the 0.50 mg kg-1 day-1 group exhibiting higher rates than control (p = 0.018). Total leukocytes and subsets were unchanged: lymphocytes showed a near-significant interaction with transient increases at 0.25 mg on days 42-56; neutrophils showed a mild day × dose tendency at day 28. Cortisol did not differ by dose or day. Astaxanthin at 0.50 mg kg-1 day-1 increased milk DPPH activity. The highest dose increased the total of recovered oocytes compared to 0.25 mg (p = 0.0254) and improved recovery of morphologically viable oocytes (p = 0.0006); however, cleavage and blastocyst rates remained unchanged. Seasonally, blastocyst rate was higher in winter than summer (26.8 % vs 15.7 %; p = 0.0399). Under summer compost barn conditions, astaxanthin at 0.50 mg kg-1 day-1 enhanced oocyte yield but did not improve embryo development, physiological heat stress indicators, leukogram, or cortisol levels. Seasonal heat remains a major constraint on IVP outcomes.