Epidemiologic approach to antibiotic dry cow therapy in dairy herds

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The nonlactating period is a critically important time for dairy cow health and optimal subsequent milk yield. Regarding udder health, at the beginning and end of this period, cows are most susceptible to new intramammary infections. In addition, dry-off is also the optimal time to cure any existing mammary-gland infections. Hence, intramammary-infused antibiotic dry cow therapy (DCT) after final milking is an important and widely used mastitis control measure. DCT can be administered either to all quarters of all cows or only to infected cows or quarters. The global antibiotic resistance problem causes an increasing need to reduce antibiotic use in livestock, but a shift in management should not harm animal welfare or impair farm profitability. Although selective treatment of only infected cows is a more sustainable approach, accurate and cost-effective identification of cows or quarters in need of medication is a challenge. The objective of this epidemiologic study was to determine ideal drying-off practices to maintain good udder health and productivity while implementing prudent use of antibiotics. The specific focus of interest was on DCT, and an additional aim was to examine risk factors for post-calving udder health problems and reduced milk yield.

The three cohort studies comprised retrospective herd- and cow-level dairy-herd-recording data registered from conventional, commercial Finnish dairy farms. The first study evaluated herd-level associations between milk somatic cell count (SCC), milk yield, and various farm characteristics, with an emphasis on antibiotic usage at dry-off. The second study investigated whether the herd-level DCT practice was associated with cow-level udder health in early lactation. The third study determined cow-level milk yield and SCC differences within the first half of lactation between selectively DCT-treated and -untreated cows.

Results show that herd-level selective-DCT strategy, even with a very moderate proportion of medicated cows, is no hindrance to maintenance of low herd-average SCC and good milk yield. Regardless of the farm’s DCT practice, average milk yield increased over time, while average SCC remained rather constant. However, the large variation between farms in average yield and SCC over DCT practices suggests the need for farm-specific protocols. The practice of treating all cows in a herd was associated with lower test-day SCC within early lactation compared with the selective-DCT practice. Moreover, a DCT-treated cow on a selective-DCT farm had lower SCC after calving than did an untreated cow. This indicates that DCT continues to be an effective mastitis control practice. Most selective-DCT farms administered DCT to only one-third of their cows, or less. The DCT effect on milk yield differed depending on late-lactation SCC, so that a higher SCC near dry-off led to an increased difference in yield between treated and untreated cows within the first half of lactation. A missed DCT for a high-SCC cow thus had an adverse effect on subsequent lactation milk yield and on SCC, highlighting the need for accurate selection of cows to be treated. Risk factors associated with higher post-calving SCC included high late-lactation SCC, lactational mastitis treatment, high parity, high preceding-lactation average SCC, and high milk yield near dry-off.

Rising awareness of the selective-DCT approach currently is emerging in those countries where it is common to treat all cows at the end of lactation. The successful implementation of selective DCT on Finnish farms will hopefully encourage these countries to gradually reduce antibiotic use in dairy livestock. Such a development would perhaps have a positive effect on consumer confidence in the dairy industry. On Finnish dairy farms, rapid structural change in agriculture continues, and therefore maintaining the current low consumption of antibiotics requires optimal farm management, professional advice, and active monitoring.
  • Rajala-Schultz, Päivi Johanna, Handledare
  • Hovinen, Mari, Handledare
Tilldelningsdatum21 sep. 2022
Tryckta ISBN978-951-51-8218-0
Elektroniska ISBN978-951-51-8219-7
StatusPublicerad - 17 juni 2022
MoE-publikationstypG5 Doktorsavhandling (artikel)


  • 413 Veterinärvetenskap

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