Factors associated with subclinical hypocalcemia at calving on multiparous Jersey cows

Abstr. n° 366 <br/>Abstr. n° 366<br/>Abstr. n° 366

anglais. The objective was to evaluate factors associated with calcemic statusat calving on 527 multiparous Jersey cows from 2 commercial dairies.Study variables included: lactation number (Lact; continuous, or 2,3, ≥ 4); previous lactation 305-d mature equivalent milk production(Pr305ME) and somatic cell count (PrSCC); calving body conditionscore (BCS; ≤ 2.5, 2.75, ≥ 3) and locomotion score (LS; ≤ 2, 3, ≥ 4);calf number, sex, and stillbirth; and dry period length (dDry). Bloodsamples for serum Ca analysis were collected from the coccygeal vessels3 h 14 min (±2 h 04 min) after calving. Previous lactation informationand calving outcomes were obtained from DairyComp305 herd records.Based on serum Ca concentration at calving cows were classified ashypocalcemic (SHC; Ca ≤8.5 mg/dL; n = 347) and normocalcemic (NC;Ca >8.5 mg/dL; n = 180). Associations among variables were studiedusing spearman rank correlations and mixed models for continuous,and chi-squared and exact fisher tests for categorical data (CORR,MIXED, GLIMMIX and FREQ procedures of SAS). A significantpositive correlation was observed between Lact and BCS, and bothwere negatively correlated with serum Ca concentration at calving.Cows with SHC had greater (P < 0.001) Lact (3.6 vs. 2.7), frequencyof Lact ≥4 (40.4 vs. 14.4%), dDry (68.8 vs. 64.6 d), and BCS (43.4 vs.58.2%, 31.2 vs. 27.7% and 25.4 vs. 14.1% for BCS ≤2.5, 2.75 and ≥3,respectively; P = 0.02[N1]) than NC cows. Twinning rate was higherfor SHC than NC (5.8 vs.1.1%; P = 0.01). The frequency of male calves(n = 98) was higher for SHC than NC cows (22.4 vs. 14.0%, P = 0.02),however, sexed semen was selectively used on both dairies and theseresults may derive from herd reproductive management. There was noassociation of Pr305ME, PrSCC, LS at calving or frequency of stillbirthwith calcemic status. These complex associations among SHC, Lact,BCS, dDry, twinning and calf sex, could be used for the decision-makingconcerning prophylactic SHC treatment at calving.