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Association of subclinical hypocalcemia at calving with productive outcomes in multiparous Jersey cows.

A. Valldecabres



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Association of subclinical hypocalcemia at calving with productive outcomes in multiparous Jersey cows.
A. Valldecabres*, N. Silva-del-R�o. Veterinary Medicine Teaching and Research Center, University of California-Davis Tulare, CA.

The most appropriate blood calcium (Ca) threshold to define subclinical hypocalcemia (SCH) is still under study. Currently, there is a wide range of suggested definitions, and variability on its reported associations with productive outcomes, which have not been described in Jersey cows. Our aim was to evaluate the association of SCH at calving with subsequent lactation milk and energy-corrected milk (ECM) yield, fat% and protein%, in 609 multiparous Jersey cows from 2 commercial herds fed acidifying prepartum diet. Blood samples for total serum Ca concentration determination were collected from the coccygeal vessels at 3 h 10 min (�2 h 17 min) after calving. Monthly test milk yield, fat% and protein% information up to the 10th test was obtained from the Dairy Herd Improvement Association. Milk yield, ECM, fat% and protein% were analyzed with SAS (version 9.4); with multiple linear regression, using a 2-piece linear function for days in milk and cow as the subject in the repeated statement. Considered covariates for all outcomes were: parity, herd, previous lactation length and 305-d mature equivalent milk yield, dry period length, calving body condition and locomotion scores, calving easiness, oral Ca supplementation, and somatic cell linear score at test. Milk yield was also considered in the fat% and protein% models. Serum Ca thresholds among 1.80 and 2.20 mmol/L at 0.02 mmol/L intervals were used to define SCH. The Ca threshold significant for the type 3 test of fixed effects, and leading to the smallest P-value and most extreme β coefficient for the solution for fixed effects, was chosen to define SCH. Subclinical hypocalcemia (Ca ≤ 2.18 mmol/L) was associated with 1.52 and 1.88 kg/d more of milk and ECM, respectively (P < 0.001). For milk fat%, SCH (Ca ≤ 1.96 mmol/L) was associated with 0.12 units of milk fat%/d more (P = 0.01); and SCH (Ca ≤ 1.80 mmol/L), with 0.06 units of milk protein%/d less (P = 0.03). Similar effects were observed for additional thresholds evaluated. Further studies are needed to elucidate the applicability of a SCH definition.

Keywords: dairy cow, hypocalcemia, transition cow.