Relationships between fertility and postpartum changes in body condition and body weight in lactating dairy cows

Abstract

The relationship between energy status and fertility in dairy cattle was retrospectively analyzed by comparing fertility with body condition score (BCS) near artificial insemination (AI; experiment 1), early postpartum changes in BCS (experiment 2), and postpartum changes in body weight (BW; experiment 3). To reduce the effect of cyclicity status, all cows were synchronized with Double-Ovsynch protocol before timed AI. In experiment 1, BCS of lactating dairy cows (n = 1,103) was evaluated near AI. Most cows (93%) were cycling at initiation of the breeding Ovsynch protocol (first GnRH injection). A lower percentage pregnant to AI (P/AI) was found in cows with lower (≤ 2.50) versus higher (≥ 2.75) BCS (40.4 vs. 49.2%). In experiment 2, lactating dairy cows on 2 commercial dairies (n = 1,887) were divided by BCS change from calving until the third week postpartum. Overall, P/AI at 70-d pregnancy diagnosis differed dramatically by BCS change and was least for cows that lost BCS, intermediate for cows that maintained BCS, and greatest for cows that gained BCS [22.8% (180/789), 36.0% (243/675), and 78.3% (331/423), respectively]. Surprisingly, a difference existed between farms with BCS change dramatically affecting P/AI on one farm and no effect on the other farm. In experiment 3, lactating dairy cows (n = 71) had BW measured weekly from the first to ninth week postpartum and then had superovulation induced using a modified Double-Ovsynch protocol. Cows were divided into quartiles (Q) by percentage of BW change (Q1 = least change; Q4 = most change) from calving until the third week postpartum. No effect was detected of quartile on number of ovulations, total embryos collected, or percentage of oocytes that were fertilized; however, the percentage of fertilized oocytes that were transferable embryos was greater for cows in Q1, Q2, and Q3 than Q4 (83.8, 75.2, 82.6, and 53.2%, respectively). In addition, percentage of degenerated embryos was least for cows in Q1, Q2, and Q3 and greatest for Q4 (9.6, 14.5, 12.6, and 35.2% respectively). In conclusion, for cows synchronized with a Double-Ovsynch protocol, an effect of low BCS (≤ 2.50) near AI on fertility was detected, but change in BCS during the first 3 wk postpartum had a more profound effect on P/AI to first timed AI. This effect could be partially explained by the reduction in embryo quality and increase in degenerate embryos byd 7 after AI in cows that lost more BW from the first to third week postpartum.

Keywords: body condition score loss; body weight loss; embryo quality; fertility.

Figure 1

Schematic representation of the Double Ovsynch protocol used in experiments 1 and 2 (panel A), and diagram of sampling and the modified Double-Ovsynch protocol use in experiment 3 (panel B). PGF = PGF_2α; BS = blood sample; TAI = timed AI; P4 = progesterone.

Figure 2

Kaplan-Meier survival analysis of calving-to-pregnancy interval for cows with BCS ≤2.50 (closed circles) or BCS ≥ 2.75 (open circles) at first postpartum timed AI (TAI). Cows with BCS ≤2.50 at first postpartum TAI had a median calving-to-conception interval of 146 d compared with 113 d for cows with BCS ≥2.75. The symbols on each line represent a censoring event (cow removed from analysis due to death, culling, or designation as “do not breed”).

Figure 3

Kaplan-Meier survival analysis of calving-to-pregnancy interval for cows that gained (open triangles), maintained (closed circles), or lost (open circles) BCS between calving and 21 d postpartum. Cows gaining BCS between calving and 21 d postpartum had a median calving-to-conception interval of 84 d, compared with 113 d for cow maintaining BCS and 128 d for cows losing BCS between calving and 21 d postpartum. The symbols on each line represent a censoring event (cow removed from analysis due to death, culling, or designation as “do not breed”).

Figure 4

Percentage BW change from first week postpartum (panel A), NEFA concentrations during the first 3 wk postpartum and during the synchronization period (panel B), DMI (panel C), and ECM yield (panel D). Cows were ranked according to percentage BW change from the first to third week postpartum and divided into quartiles. Values are means ± SEM.