Alternatives to treatment of all quarters with antibiotics at dryoff are of interest in the dairy industry. The objective was to evaluate intramammary casein hydrolysate (CH), alone or in combination with antibiotic dry cow treatment (DCT) and/or teat sealant (TS) at dryoff (FDA and animal use committee sanctioned). Dairy cows (n = 32) from 6 commercial farms comprised 2 study groups: 16 pregnant cows estimated 60 d prepartum and 16 non-pregnant cows > 300 d in milk (DIM). A split udder design was used, with each udder half assigned a treatment and the contralateral half administered DCT + TS as a control. There were 4 treatments: 1. CH, 2. CH + DCT, 3. CH + TS, 4. CH + DCT + TS. Pregnant cows had quarter milk samples collected, with time “0” the time of dryoff: 0 d, 2 d, 4 d, 7 d, 10 d dry for SCC and biomarkers of involution pH, lactoferrin and serum albumin. Milk culture was at −4 d, 0 d, and 1–7, 8–14, and 15–21 DIM. Milk production was measured in udder halves before dryoff and again 3 DIM for proportion of total-cow milk production by each half. Cull cows were euthanized 2 d (n = 8) or 7 d (n = 8) after dry treatment and mammary tissue was sampled from ventral, mid, and dorsal regions of each quarter. Histopathology and tissue staining for degree of involution were performed. All 32 cows had no clinical signs or milk leakage at dryoff, and all 64 quarters of pregnant cows resumed milk production after calving. All milk was Delvotest SP-NT-negative for antimicrobial residues at 3 DIM. Treated and control halves’ proportion of milk production were 47%:53% at dryoff, 51%:49% at 3 DIM (P = 0.38, 0.39, t-test). Involution was more evident histologically in all CH treated quarters than in controls; biometry measurements of % involuted tissue are in progress. Bacterial cure rates and new infection (NI) rates during dry period by treatment were: 1. 0%, 75%; 2. 100%, 0%; 3. 0%, 25%; 4. No infections to cure, 75%; controls 0%, 56% (P = 0.66 for cures, P = 0.61 for NI, chi-squared). Casein hydrolysate may be useful as an adjunct to other treatments, or possibly as a non-antibiotic alternative at dryoff of dairy cows.