The effects of dry period length on udder health, metabolic status and lactation persistency

The effects of dry period length on post-partum udder health are still ambiguous possibly partly because in many studies dry period (DP) length and the use of dry cow antibiotics were confounded. Recently, the preventive use of antimicrobials in the EU has been restricted. To our knowledge, no study had evaluated the effects of DP length without the use of dry cow antibiotics on udder health. Furthermore, we hypothesized that prepartum cow characteristics could determine postpartum udder health after different DP lengths.

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Text: Renny van Hoeij

To identify cow characteristics that determine postpartum udder health and to evaluate the effects of DP length without the use of dry cow antibiotics, two large experiments were conducted. In the first experiment, cows had a 0, 30 or 60 days DP, and cows with a 30 or 60 days DP were treated with dry cow antibiotics. In the second experiment, cows had a 0 or 30 days DP, and cows with a 30 days DP were not treated with dry cow antibiotics.

In the first experiment, cows with a 0-days (d) DP had a greater occurrence of chronic intra-mammary infections (IMI) and a lower occurrence of cured IMI across the DP than cows with a 30-d or 60-d DP treated with dry cow antibiotics. Postpartum average somatic cell count (SCC) for the lactation was greater in cows with a 0-d DP than in cows with a 30-d or 60-d DP, although the incidence of elevations of SCC (SCC ≥ 200,000 cells/mL) or clinical mastitis were not different among cows with different DP lengths. Postpartum SCC, elevations of SCC or clinical mastitis were determined by parity, elevations of SCC in the previous lactation, last fat and protein corrected milk before a 60-d DP, average SCC between 150 to 37 days prepartum, average SCC for the previous lactation, or last SCC before the DP.

In the second experiment, the occurrence of chronic or new IMI across the DP was not different between cows with a 0-d or 30-d DP. During week 1 to 44 of lactation, cows with a 0-d DP had a greater SCC than cows with a 30-d DP, but not when SCC was corrected for milk yield. During week 1 to 44 of lactation, the occurrence of at least one elevation of SCC (≥200,000 cells/mL) and clinical mastitis were not different between DP lengths, although cows with a 0-d DP had a numerically greater occurrence of clinical mastitis and tended to have a greater hazard for clinical mastitis than cows with a 30-d DP.

Comparing experiment 1 and 2, a 0-d DP seems to decrease udder health, compared with a 30-d or 60-d DP with dry cow antibiotics. However, when none of the cows were treated with dry cow antibiotics, cows with a 0-d DP did not differ from cows with a 30-d DP for all assessed udder health variables across the DP and for most of the assessed udder health variables in the subsequent lactation. The effects of DP length on clinical mastitis in the subsequent lactation should be evaluated further in larger field studies.

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Renny van Hoeij graduated as a veterinarian from Utrecht University in 2013. Subsequently she started her PhD degree on the effects of dry period length on udder health, metabolic status and lactation persistency at Wageningen University & Research under the supervision of Bas Kemp, Theo Lam, Jan Dijkstra, and Ariëtte van Knegsel. On December 20th 2017 she defended her thesis successfully. Renny is currently working as a ruminant’s researcher at Agrifirm Feed B.V. in the Netherlands

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