Abstract
Vitamin D supports several physiological functions, from mineral homeostasis to immune activity. The aim of this study was to provide 25-hydroxyvitamin D(3) [25(OH)D(3)] to late gestation and early lactation dairy cows and evaluate the impact on lactational performance. Holstein cows (n = 100) that finished their first or greater lactation were enrolled in a randomized block design with a 2x2 factorial arrangement of treatments (n = 25 cows per treatment group). Prepartum treatments were 0 or 3 mg of 25(OH)D(3) per cow daily from 28 d before expected calving until calving. Postpartum treatments were 0 or 1.5 mg of 25(OH)D(3) per cow daily from calving until 63 d after calving. Treatments were top-dressed at feed delivery using a cornmeal carrier. The 25(OH)D(3) source was Hy· D100. Prepartum [30 IU/kg body weight (BW)] and lactation (40 IU/kg BW) rations also provided a basal amount of cholecalciferol fed to NASEM 2021 recommendations. Dry cows were fed individually, and group housed in a bedded pack. Lactating cows were fed individually, group housed in a freestall, milked 3x/d, and milk sampled 6x/wk. Data were analyzed by ANOVA with repeated measures using the MIXED procedure of SAS (v. 9.4). The model contained fixed effects [prepartum treatment (PRE), postpartum treatment (POST; removed for prepartum data) week, and their interactions] and a random effect (block). Prepartum dry matter intake (DMI) averaged 16.3 kg/d and 2.04% of BW, was not affected by prepartum treatment (P ≥ 0.89) and was decreased closer to calving (P ≤ 0.01). As expected, week after calving affected (P ≤ 0.05) lactational performance. Postpartum DMI was greater for cows fed 3-1.5 mg than those fed 0 to 1.5 mg (Table 1). Colostrum yield and quality were not affected by prepartum treatment (P ≥ 0.91) and averaged 5.7 kg with an IgG content of 75.6 g/L. Actual milk yield was not affected by prepartum or postpartum treatments. Interestingly, there was a carryover effect of prepartum treatment on yield of 4% fat-corrected milk (FCM) and energy-corrected milk (ECM). Cows fed 3 mg during late gestation produced more than those fed 0 mg. Postpartum treatment did not affect component-corrected milk yield. Providing additional vitamin D in the form of 25(OH)D(3) to late gestation cows improved lactational performance by increasing intake and the yield of component-corrected milk.