It is accepted that the best economic results, informed by the yearly peak milk, is a one-year calving interval (CI), which includes a 10-month lactation and a two-month dry period. However, as a consequence of this cycle, cows experience several transitions during the year, including drying-off, calving and the start of the next lactation. During these transitions, large changes in both physiology and management are associated with an increased risk of diseases and disorders, such as clinical mastitis, milk fever and ketosis. In total, about 75% of disease incidences within herds occur within the first month of lactation. One possible solution to reduce the frequency of transitions is to extend the lactation length and CI. With an extended CI, the risk of diseases per year can be expected to reduce as there will be fewer calving events per year and it has been shown that cows with an extended period between calving and first insemination (EPCF) had a lower incidence of metabolic disorders, lower veterinary costs and lower culling rates than cows with the normal period. Furthermore, cows in the one-year cycle usually dry off at still a high level of production, which probably has a negative effect on udder health. However, as all the implications of EPCF on udder health are not well described, the purpose of the study by the authors cited was to evaluate the effect thereof on SCC, SCC elevations and clinical mastitis incidence during the complete lactation and the first six weeks of the next lactation.
A total of 154 Holstein-Friesian cows were blocked for lactation number, expected milk yield, calving season and breeding value for persistency and were randomly distributed across three EPCF treatments of respectively 50, 125 or 200 days (EPCF-50, EPCF-125 and EPCF-200). The cows were monitored from calving until six weeks into the next lactation, or until culling. Am elevation of SCC in milk was defined as SCC of equal to or more than 200 000 cells per ml after two previous weeks with milk SCC being less than 200 000 cells per ml.
The results showed that over the complete lactation, extending the EPCF did not affect SCC elevations and the occurrence of clinical mastitis per lactation per cow per year. There was also no clear effect of EPCF length on SCC in the complete lactation, except that multi-lactation cows in EPCF-125 had a higher SCC compared with multi-lactation cows in EPCF-50. Dry-off antibiotic usage per cow per year was lower in EPCF-200 compared to EPCF-50 in multi-lactation cows. In the first six weeks of the next lactation, cows in in EPCF-200 had a higher SCC compared with cows in EPCF-50, with no effect of EPCF on the number of elevations of SCC or the occurrence of clinical mastitis.
It was concluded that extending EPCF is an option to reduce the frequency of transition periods and the associated use of dry-off antibiotics, with limited impact on udder health, and a similar occurrence of SCC elevations and clinical mastitis per year. Overall though, milk yield, management costs, disease incidence, animal welfare, antibiotic resistance and total economy implications need to be taken into account, before embarking on such a revolutionary approach.