Decades of research has identified how much of individual nutrients prepartum cows need and how best to formulate and deliver that diet during the last few weeks of gestation, but the optimal number of days to feed prepartum diets has not been clearly defined. Nor do we know if the number of days spent in the prepartum group should be the same or different for nulliparous (having their first calf) and multiparous cows. New research from the University of Florida provides some answers.
The observational and epidemiological study tracked performance of 18,657 cows on 2 California dairies over multiple years. Cows with a gestation length shorter than 256 days, longer than 296 days or those that spent 0 days in the prepartum group were excluded. That left 18,021 cow records to analyze for associations between the number of days spent in the prepartum group with milk production, health, reproduction and survival. Results clearly demonstrate that the number of days in the prepartum group impacts milk production, cow health, reproduction and survival. The data also indicate there is a range of optimal number of days that cows should spend in the prepartum group.
Both farms grouped nulliparous and multiparous cows separately during the prepartum and lactation periods. All cows received a similar prepartum diet. The one difference was that multiparous cows were fed an acidogenic product to minimize the risk of hypocalcemia, which was not offered to nulliparous cows. After calving, all cows were fed the same early-lactation and lactation diets.
Increasing the days spent in the prepartum group from 7 to 28 increased daily milk yield by 3.3 lbs/day for nulliparous cows and by 7.7 lbs/day for multiparous cows. However, when days in the prepartum group increased from 28 to 42, milk yield decreased. The plateau for daily milk yield was reached when nulliparous and multiparous cows spent 24 and 25 days in the prepartum group, respectively.
In terms of total milk yield for the 300-day observation period, increasing days in the prepartum group from 7 to 28 increased total milk yield by 736 lbs for nulliparous cows and by 2,321 lbs for multiparous cows. Total milk yield reached a plateau when nulliparous and multiparous cows spent 21 and 24 days in the prepartum group, respectively.
Interactions between days in the prepartum group and parity/diet were observed for retained placenta, metritis, lameness and morbidity. Incidence rates varied with the number of days spent in the prepartum group. For retained placenta, the smallest incidence was observed when cows spent 27 days in the prepartum group. For metritis, the smallest incidence for nulliparous and multiparous cows occurred with 9 and 26 days spent in the prepartum group, respectively. The smallest incidence of lameness in nulliparous and multiparous cows occurred with 9 and 25 days spent in the prepartum group, respectively. Morbidity during the first 90 days in milk was smallest in nulliparous cows with 9 days in the prepartum group compared to 23 days for multiparous cows.
Days in the prepartum group also impacted reproduction. At 300 DIM, the proportion of pregnant cows was greatest when the days spent in the prepartum group was 19. And in terms of survival, culling decreased as days in the prepartum group increased until reaching a nadir at 20 days for both groups.
For most of the responses evaluated, a quadratic association with days in the prepartum group was observed. These data suggest that there is an optimal number of days cows should spend in the prepartum group that is somewhere between 21 and 28 days. Any greater, or fewer days in the prepartum group might have detrimental impacts on postpartum performance.