Establishing fertility benchmarks for in-line automated milk progesterone monitoring in postpartum dairy cows

Abstract Text: Milk progesterone (MP4) concentrations in postpartum dairy cows are indicative of ovarian cyclicity. The adoption of automated in-line MP4 monitoring on farm has created the need for benchmarks to better understand MP4 data across cows, parities, farms, etc. The objective was to establish useful fertility benchmarks for in-line MP4 records. MP4 records (n=135,588) from an automated milk progesterone sampling system (Herd Navigator; DeLaval International, Tumba, Sweden) were used. The records were from 1,224 lactations of 1,505 lactating cows in 4 European herds from January 2014 to December 2015. Farms started monitoring MP4 by 20 d postpartum. Excluded cows did not have MP4 samples before 30 d postpartum, lacked a defined ovulation (MP4 < 3ng/mL followed consecutively by MP4 > 3ng/mL), or lacked consistent MP4 records. The LIFETEST and GLM procedures of SAS 9.4 (Cary, NC) were used to test for differences among farm, parity, and milk yield for commencement of luteal activity (CLA) and length of postpartum estrous cycle. CLA was defined by MP4 >3ng/mL on 20 to 22 d for initial samples or by a defined ovulation thereafter. Length of estrous cycle was the difference between the two ovulations. Cows were classified as primiparous, mature (2 to 4 lactations), or aged (>4 lactations). The UNIVARIATE procedure was used to classify daily milk yield (Q1: < 25 kg/day, Q2: 25 to 33 kg/day, Q3: 34 to 41kg/day, Q4: > 41kg/day). The mean interval to CLA was 28.7±14.6 d for all farms. Farm 4 had more cows (103/308 cows) not achieving CLA by 50 d postpartum than the other farms (P < 0.001). Aged cows (28/114, 25%) failed to achieve CLA by 50 d postpartum compared with primiparous cows (13/148; P < 0.05). Highest producing cows (Q4) failed to achieve CLA by 40 d postpartum compared with cows producing less than 33kg/day (P < 0.001). Length of estrous cycle was shorter for farms 1 and 2, (21.8±0.4d) compared with 22.7±0.4 and 23.0±0.4d for farms 3 and 4, respectively (P < 0.05). Length of estrous cycle differed (P< 0.001) for primiparous, mature, and aged cows, 21.3±0.2d, 22.7±0.2d, and 23.0±0.5d, respectively. Strategic sampling of MP4 concentrations using an automated system identified differences between herds, parities, and milk production with respect to ovarian cyclicity. Establishing benchmarks based on these data will enable producers to assess ovarian function and the underlying causes of infertility in their herds. 

Keywords: , fertility, in-line milk progesterone, ovulation