RESUMO
Among the commonly implemented strategies developed to support calcium (Ca) metabolism postpartum, oral Ca supplementation is within the most studied. However, research shows varying responses to treatment in regard to production and reproduction. Our objectives were (1) to identify and synthesize the literature evaluating the associations between postpartum oral Ca supplementation as bolus and milk yield and risk of pregnancy to first service using a systematic review, and (2) to quantify these associations using meta-analytical methods. Nine relevant studies published between January 2010 and September 2021 were identified after systematic search of 4 databases (Biosis, CAB Abstracts, Medline, Scopus). The studies were conducted in commercial confined and grazing farms. Eight of the 9 studies reported feeding low to negative dietary cation-anion difference diets prepartum. Oral Ca bolus supplementation strategies varied among studies but were predominantly centered on the first 24 h postpartum. Milk yield and pregnancy to first service were evaluated in 9 and 6 of the studies, respectively. Other productive (energy-corrected milk yield, peak milk yield, or fat and protein concentrations) and reproductive (estrus cyclicity, days from calving to first service, or pregnancy by 150 or 210 days in milk) outcomes were evaluated in 4 of the studies. The meta-analyses revealed a lack of evidence for associations between prophylactic blanket postpartum oral Ca bolus supplementation and milk yield (including 8 studies) or risk of pregnancy to first service (including 6 studies). Some of the evaluated studies reported statistically significant associations after data stratification. However, not enough studies reported estimates for the evaluated conditional factors to perform a meta-analysis among the identified subgroups. In conclusion, future research should study and report the production, reproduction, and health estimates of cow-level conditional factors of interest for the evaluated response, and investigate alternative regimes of oral Ca bolus supplementation.
RESUMO
The aim of the present study was to describe the dynamics of serum IgG (determined with radial immunodiffusion) and total protein (TP; determined with refractometry) concentrations during the first 16 d of life. Secondary objectives were to evaluate the transfer of passive immunity (TPI) classification at d 1 of life as a conditional factor for the aforementioned dynamics, and to describe over time changes on calves' TPI classification. At a commercial raising operation, 36 calves (19 Holstein, 17 Jersey) were sampled immediately after arrival (d 1) and at d 4, 8, 12 and 16 of life, for serum IgG and TP concentration, and hematocrit determination (HCT). Transfer of passive immunity was categorized based on serum IgG (IgG-Poor: IgG <18 g/L; IgG-Good: IgG 18 to <25 g/L; IgG-Excellent: IgG ≥25 g/L) and TP concentrations (TP-Poor: <5.8 g/dL; TP-Good: 5.8 to <6.2 g/dL; TP-Excellent: ≥6.2 g/dL). Multiple linear regression was used to evaluate serum IgG and TP changes over time, considering the effects of time after birth, breed, HCT, and TPI classification at d 1 of life. At d 1, median serum IgG and TP concentrations were 29.9 g/L and 6.3 g/dL, respectively (interquartile ranges: 21.3-42.3 g/L and 5.6-6.7 g/dL, respectively). Dynamics of serum IgG and TP concentrations were conditional to TPI at d 1 of life. Serum IgG concentration declined over time for IgG-Excellent and IgG-Good calves (18.1 and 4.6 g/L, respectively), but remained constant for IgG-Poor calves. Serum TP concentration declined over time in the 3 TPI groups but it was more marked for TP-Excellent (27%) and TP-Good (19%) than for TP-Poor (14%) calves. At d 1, 83.3% of the calves were classified as IgG-Excellent or IgG-Good, whereas 77.8, 55.6, 41.7, and 58.3% of calves were classified within these categories at d 4, 8, 12, and 16 of life, respectively. Similarly, at d 1, 66.7% of calves were classified as TP-Excellent or TP-Good, whereas 47.2, 36.1, 25.0, and 2.8% were classified within these categories at d 4, 8, 12, and 16 of life, respectively. In summary, our results indicate that serum IgG and TP concentrations decline over 16 d of life, and the decline is associated with TPI classification at d 1 of life. Further studies are needed to determine the biological implications of serum IgG and TP decline after d 1 of life, and to elucidate the factors determining the different dynamics. Our results suggest that current thresholds for TPI classification should be interpreted carefully when the age of calves is unknown or outside the age range used to define those thresholds (>24 h to 7 d).