PSV-A-8 Reduced Daylength pre-Calving Increases Milk Production Post-Calving

Abstract Exposing Holstein dry cows to short-day (SD) photoperiod of 8 hours per day can improve milk production post-calving by 3.2 kg per day, compared to cows exposed to long-day (LD) photoperiod of 16 hours per day during the same period. To date, no studies have evaluated the effect of altered photoperiod during the dry period on milk production in Jersey cows. Our objective was to study the effect of LD and SD during the dry period on milk production in both breeds. Holstein and Jersey cows (n=33) dried off 60 days prior to their due date were exposed to either SD (n=9 Holstein, n=8 Jersey) or LD (n=8 Holstein, n=8 Jersey) at 18.3 °C until calving. After calving, cows returned to ambient photoperiod and milk data was collected for 15 weeks. Lactation number, replicate, dry period feed intake and days of treatment were recorded. Data were analyzed using PROC MIXED in SAS 9.4. Overall average milk production differed by breed (P< 0.01), with Holsteins producing more (72.9 ± 6.2 kgs) than Jerseys (66.1 ± 7.3 kgs). Treatment differed (P=0.02) with SD cows producing more milk (71.0 ± 6.9 kgs) than LD cows (68.1 ± 6.7 kgs). Treatment and breed interaction significantly differed. Long-day Holsteins produced 73.9 kgs ± 6.2 kgs which was not different (P >0.10) from SD Holsteins (72.1 ± 6.4 kgs). Neither LD nor SD Holsteins differed significantly (P=0.16, P=0.60) from SD Jerseys which produced 70.0 ± 7.4 kgs. Long-day Jerseys averaged the least milk at 62.3 ± 7.3 kgs which was significantly different from all other groups (P< 0.01). This data suggests Jerseys’ milk production responds similarly to previous reported Holstein data. Factors causing the unexpected Holstein data could be elevated temperature-humidity index values post-calving, despite industry standard heat abatement.