Short dry period improves postpartum energy balance and reproduction but reduces milk yield in dairy cows.

The experiment evaluated the effects of dry period length (DPL) on postpartum energy balance (EB), reproduction, milk yield, and granulosa cell gene expression in Holstein cows. Forty-four cows were blocked by parity and previous lactation yield and randomly assigned to a traditional 60-day (TDP; n = 22) or short 30-day (SDP; n = 22) dry period at the University Dairy Research Unit, Pattoki-Pakistan. The dry matter intake (DMI) and EB were recorded from - 21 days before calving until 21 days after calving. Milk yield was recorded and presented daily for the first 21 days and weekly by 43 weeks postpartum, and components were assessed weekly for the first 15 weeks. The ovarian ultrasound was performed between 15 and 50 days postpartum to determine the resumption of cyclicity. Cows were bred on detected estrus between 50 and 70 days postpartum, and the remaining cows were synchronized with the G6G breeding protocol and timed inseminated. Cows returned to estrus after AI were bred on detected estrus. Pregnancy was diagnosed on 32 days after AI using ultrasonography. Open cows were rebred using the Ovsynch protocol, and reproduction was assessed for 300 days postpartum. The economic impact of the SDP was evaluated using data from income over feed cost (IOFC), 305-day total milk yield, and associated costs. Data was analyzed using MIXED, GLIMMIX, and PHREG procedures in SAS. The SDP cows had improved postpartum EB (3.29 vs. - 3.40 ± 1.15 Mcal/d) but produced 1518 kg less milk than TDP cows in 305-day lactation. The DMI and prepartum EB did not differ. Ovarian cyclicity resumption was unaffected, but SDP cows tended to have higher estrus response between 50 and 70 days postpartum. The SDP cows tended to have higher 21-day cycle insemination and pregnancy rates, reducing open days by 40 days. Gene expression in granulosa cells was unchanged. The IOFC was greater for TDP compared with SDP. However, after including the other variable costs in the economic calculations, the net profit and loss did not differ between the SDP and TDP. In conclusion, cows in SDP produced less milk but had improved postpartum EB and estrus expression, leading to earlier insemination and fewer open days without affecting the granulosa cell molecular signature in Holstein cows. The IOFC was reduced in SDP, but after accounting for the other variable costs, the net profit or loss was similar to TDP, indicating a potential strategy for dry period management.