Short communication: Variance and autocorrelation of deviations in daily milk yield are related with clinical mastitis in dairy cows.

Daily milk production, and fluctuations therein, can provide information on health and resilience of dairy cows. We studied variance and autocorrelation of deviations in daily milk yield in relation to the occurrence of clinical mastitis (no, early or later in lactation). Individual lactation curves were fitted to 305-d lactations of 414 dairy cows using quantile regression. Log-transformed variance (lnVar) and autocorrelation of the quantile residuals of daily milk yield (predicted - observed) were evaluated for intervals until 30 and until 305 days in milk (DIM). Cows were classified as having no mastitis (n = 249), early mastitis that first occurred before 30 DIM (n = 29); or later mastitis (n = 136). Subsequently, linear models were used to assess effects of mastitis and parity class (primiparous or multiparous) on lnVar and autocorrelations; and logistic regression analyses were performed to predict mastitis from lnVar or autocorrelation and parity. From 10 to 30 DIM, lnVar was greater for cows with early mastitis than for cows with no or late mastitis, and autocorrelation tended to be lower for cows with early mastitis than for cows with no mastitis. The lnVar and autocorrelation from 10 to 30 DIM were not predictive of late mastitis. From 10 to 305 DIM, lnVar was greater and autocorrelation was lower for both cows with early and late mastitis than for cows with no mastitis; and both were predictive of having mastitis in the 305-d lactation. Primiparous cows had lower lnVar than multiparous cows. In cows without mastitis, autocorrelation values were positively correlated with lnVar. Results confirm that increased lnVar is associated with clinical mastitis.

Extended lactation in high-yielding dairy cows. I. Effects on reproductive measurements.

The objective of this prospective field study was to evaluate the effects of extending the lactation period on various reproductive measurements of high-yielding Holstein cows. On 40 d in milk (DIM), cows were gynecologically examined (transrectal palpation, sonography, vaginoscopy). Cows without signs of clinical endometritis were blocked by parity and were randomly allocated to 1 of 3 experimental groups with a voluntary waiting period (VWP) of 40, 120, and 180 d, respectively (G40, n = 135; G120, n = 141; G180, n = 139). Cows of G120 and G180 were reexamined at the end of the VWP. If natural estrus was detected within 46 d after the end of the VWP, an artificial insemination was performed. If no estrus was detected, the respective cows were synchronized by applying the classical Ovsynch protocol. We found no difference in the proportion of cows in which estrus was detected between 40 to 86 DIM or in the days to first estrus between the 3 groups. Estrus detection in this period was lower in cows with body condition score <3 on 90 DIM compared with body condition score ≥3 (61.5 vs. 76.0%) and in cows with high energy-corrected milk production (ECM) on 92 DIM [58.6 vs. 70.1%, for cows with higher and lower than the median (39.9 kg) ECM, respectively]. The proportion of cows that estrus was detected within 46 d after the VWP was greater in G120 (88.9%) and G180 (90.8%) compared with G40 (70.4%). These effects were more apparent in cows with high ECM. The rate of estrus detection and of becoming pregnant in this period was greater for G120 (hazard ratio = 2.2 and 1.6, respectively) and for G180 (hazard ratio = 2.4 and 1.8) compared with G40. Cows in both groups with extended lactation had greater overall first service conception rates (G120 = 48.9%; G180 = 49.6%) and a lower number of services per pregnant cow (G120 = 1.56 ± 0.1; G180 = 1.51 ± 0.1) compared with G40 (36.6%; 1.77 ± 0.1). We observed no difference in pregnancy loss or in the proportion of cows culled up to 305 d of lactation between the 3 groups. The number of Ovsynch protocols per 1,000,000 kg of ECM was reduced by 75% in G180 and by 74% in G120 compared with G40 (5.9 vs. 7.1 vs. 25.1). In conclusion, extending the lactation of dairy cows can improve main reproductive measurements in high-yielding cows.

Extended lactation in high-yielding dairy cows. II. Effects on milk production, udder health, and body measurements.

The objective of this prospective field study was to evaluate the effects of extending the lactation period of high-yielding dairy cows on milk production, udder health characteristics, and development of body condition. On 40 d in milk (DIM), an examination of the genital tract (transrectal palpation, sonography, vaginoscopy) was performed. Cows without signs of clinical endometritis were blocked by parity and were randomly allocated to 1 of 3 experimental groups with a voluntary waiting period of 40, 120, and 180 d, respectively (G40, n = 135; G120, n = 141; G180, n = 139). Mean daily milk and energy-corrected milk production did not differ between the 3 groups regarding the first 305 d or for the whole lactation (d 1 and up to dry off, culling, or 600 DIM). In late lactation (306 to 600 DIM), G40 had lower average productivity (23.8 kg) compared with G120 (26.5 kg), with G180 showing intermediate values (25.7 kg). The extended lactation groups showed greater persistency, as the rate of decline based on a Wilmink function was lower for G120 (c = -0.063 and -0.045 for milk and energy-corrected milk, respectively) and G180 (c = -0.061 and -0.047) compared with G40 (c = -0.071 and -0.056). We found no difference between the 3 groups regarding the evaluated udder health characteristics (somatic cell count, incidence of mastitis, and days off milk due to mastitis). More cows in G180 (7.9%) were culled due to low productivity compared with G40 (0.7%) and as a tendency compared with G120 (2.8%). Moreover, cows of G180 showed higher median body condition score at the time of dry off compared with cows of both G40 and G120 (3.50 for G180 vs. 3.25 for both G40 and G120). At the time of dry off, G180 cows also had greater backfat thickness (25.0 mm) compared with both G40 (22.2 mm) and G120 cows (21.6 mm). Based on our results, the extension of the voluntary waiting period of high-yielding cows up to 120 d has no adverse effects regarding milk production, involuntary culling, udder health, or BCS gain.