The factors associated with postpartum body condition score change and its relationship with serum analytes, milk production and reproductive performance in dairy cows

Objectives were to (1) identify factors associated with postpartum body condition (BCS) maintenance/gain, (2) determine the optimum pre-calving BCS predictive of postpartum BCS maintenance/gain, and (3) evaluate the relationship between postpartum BCS change categories, serum analytes and performance in dairy cows. The BCS were determined in 271 primiparous and 640 multiparous cows from 11 dairy herds in Alberta, Canada at (mean +/- SD) 9.0 +/- 2.3 d pre-calving and at 34.6 +/- 4.0 d post-calving, using a 5-point scale with 0.25 increments. Cows were grouped into BCS change categories according to BCS change between post- and precalving as follows: lost >= 0.75 units (extreme loss; EL; n = 343), lost either 0.25 or 0.50 units (moderate loss; ML; n = 390), no change in BCS (maintained; M; n = 104), or gained >= 0.25 units (gained; G; n = 74). In a subset of 178 cows, the concentrations of glucose, beta-hydroxybutyrate, non-esterified fatty acids, urea, cholesterol, haptoglobin and aspartate aminotransferase were measured in serum at 9.0 +/- 2.3 d pre-calving and at 8.2 +/- 3.7 d post-calving. The proportion of cows grouped into EL, ML, M and G categories were 38, 43, 11 and 8%, respectively. Precalving BCS, season of calving and sickness were identified as factors associated with BCS maintenance/gain. The optimum pre-calving BCS predictive of postpartum BCS maintenance/gain was 3.25 for primiparous cows and 3.00 for multiparous cows. Mean serum concentration of beta-hydroxybutyrate, urea, cholesterol and haptoglobin did not differ among BCS change categories. However, G cows tended to have greater mean serum concentration of glucose compared with ML cows, and mean serum concentration of aspartate aminotransferase tended to be greater for EL cows compared with other BCS change categories. Mean serum concentration of nonesterified fatty acids was greater post-calving for EL cows compared with other BCS change categories. Milk yield by 25 and 90 days in milk (DIM) did not differ among BCS change categories; however, peak and 305-d mature equivalent milk yields were greater for EL compared with G cows. Overall, EL cows had reduced fertility compared with other BCS change categories, including a smaller proportion of cows with a corpus luteum by 35 DIM, reduced pregnancy to first AI and pregnancy by 150 DIM, and reduced hazard ratio of pregnancy risk up to 250 DIM. In summary, EL cows had reduced fertility compared with other BCS change categories and increased milk yield compared with G cows. Ensuring cows calve at an appropriate BCS to promote BCS maintenance, or only moderate loss, will improve fertility without sacrificing milk yield.