Effect of gradual or abrupt cessation of milking at dry off on milk yield and somatic cell score in the subsequent lactation.

The dry period is a crucial time in the lactation cycle for mastitis prevention and control. Research results show that over 60% of new within udder infections detected in early lactation are contracted during the dry period. The periods directly following dry off and before calving are associated with an increased susceptibility to new infections. These periods allow farmers to use antimicrobial dry cow therapy, without needing to discard the milk due to antibiotic residues. However, many factors influence susceptibility to within udder infections as well as the efficacy of antimicrobial dry cow therapy products in prevention of new and elimination of existing infections. Thus, use of dry cow therapy does not guarantee that the udder will be free from infections at calving. In this context then the objective of the study of Dr P.N. Gott and colleagues was to assess the effect of milk cessation method (abrupt or gradual) at dry off on milk yield and somatic cell score (SCS) up to 120 days in milk during the subsequent lactation. Their study was published in the Journal of Dairy Science, Volume 100 of 2017, page 2080 to 2089, with the title: Effect of gradual or abrupt cessation of milking at dry off on milk yield and somatic cell score in the subsequent lactation. 

Data from 428 cows from eight dairy herds in were analyzed. With abrupt cessation, the  regular milking schedule (2 or 3 times) on the farm was maintained through dry off and with  gradual cessation cows were milked once daily for the final week of lactation. Milk yield and SCS data were collected from the test-day records of the relevant Dairy Herd Improvement Association. Aseptic quarter milk samples were collected approximately one week before dry off, at dry off and within one week after calving for bacterial culture to determine the presence of within udder infections.

Overall, the milk cessation method was not significantly associated with either milk yield or SCS in early lactation; however, interaction between the milk cessation method and herd was highly significant. Cows producing greater amounts of milk around dry off had significantly higher SCS in the following lactation. Shorter dry periods were significantly associated with decreased milk yield in the following lactation, especially among abruptly dried off cows. Additionally, as expected, several other factors, such as parity of cows and stage of lactation, were significantly associated with both outcomes. In general, the results showed that higher milk yield at dry off was associated with higher SCS in the following lactation, even though milk cessation method at the end of lactation had a varying effect on test-day milk yield and SCS in different herds during the first 120 day in milk of the following lactation. The latter result suggests that other factors in different herds are more important than method of dry off.