Milk emission and udder health status in primiparous dairy cows during lactation Alberto Tamburini 1 *, Luciana Bava 1 , Renata Piccinini 2 , Alfonso Zecconi 2 , Maddalena Zucali 1 and Anna Sandrucci 1 1 Animal Science Department, Universita ` degli Studi di Milano, via Celoria 2, 20133 Milano, Italy 2 Veterinary Pathology, Hygiene and Public Health Department, Universita ` degli Studi di Milano, via Celoria 10, 20133 Milano, Italy Received 18 March 2009 ; accepted for publication 15 July 2009 ; first published online 29 September 2009 To investigate the relationships between milk flow traits and udder health status in primiparous cows, 74 primiparous Holstein cows were randomly selected in 5 herds and monitored monthly throughout the whole lactation. A total of 2902 quarter milk samples were collected for bacterio- logical analyses and the determination of lysozyme, N-acetyl-b-glucosaminidase (NAGase) and somatic cell count (SCC). Milk flow curves of the whole udder of each cow were registered with continuous electronic milk flow meters. Teat conditions and teat thickness changes during milking were assessed monthly. Quarters, udders and cows were classified as healthy, latent, inflamed and subclinical depending on SCC and the results of bacteriological analyses. Lyso- zyme in milk, teat apex score and teat thickness change did not vary with udder health status while NAGase in milk significantly increased as udder health status worsened (P <0 . 001). Milk production (P <0 . 001) and time of plateau phase (P <0 . 05) were significantly lower in subclinical cows in comparison with the others. Animals with a high frequency of bimodal curves in the first 100 days in milk showed the worst udder health status during the whole lactation (P <0 . 01). Moreover, cows classified as subclinical in the first 3 months of lactation had higher peak milk flow than healthy cows (3 . 81 v.3 . 48 kg/min ; P <0 . 05) and shorter duration of plateau phase, expressed both as minutes and as percentage of time of milk flow (pTPL; P <0 . 001). Multivariate logistic analysis showed udder health status to be associated with duration of plateau phase, time of milk flow, bimodality and duration of overmilking phase. With short time of plateau phase (pTPL < 25 %), short time of milk flow ( < 5 min), presence of bimodality and long over- milking phase (> 0 . 8 min) there was an increased risk of poor udder health status. These milk flow traits can be predictive indicators of udder health status; time of plateau phase, expressed as percentage of time of milk flow, can also be a useful parameter for animal selection. Keywords : Milk emission, dairy cows, udder health. Milking machine characteristics and milking procedures can affect udder health status, milk somatic cell count (SCC) and teat conditions (Barkema et al. 1999 ; Rasmussen et al. 2004; Zecconi & Hamann, 2006). Machine milking can promote new udder infections by affecting teat integrity, by transferring bacteria from the environment to the teat and by dispersing them within the udder (O’Shea et al. 1987; Hamann et al. 1993). Teat is the first line of defence against mastitis and during milking, and it represents the interface between mammary gland and milking machine (Weiss et al. 2004). As a consequence, milking machine and milking techniques applied by the milker have an influence on teat conditions and teat-end callosity (Rasmussen, 1993 ; Shearn & Hillerton, 1996 ; Neijenhuis et al. 2001). The shape and the parameters of the milk flow curve depend on various factors, such as cow genetic traits, teat anatomy, parity number and stage of lactation. However, milking conditions (i.e. machine characteristics, milking routine, milking interval) are probably the most import- ant external factors affecting milk emission patterns (Rasmussen et al. 1992; Bruckmaier, 2001; Tanc ˇin et al. 2006; Sandrucci et al. 2007). Moreover recent studies on milk flow traits showed an association with udder health or SCC (Mijic et al. 2005; Sandrucci et al. 2007; Tanc ˇin et al. 2007). A good example of the complex interrelations *For correspondence ; e-mail : alberto.tamburini@unimi.it Journal of Dairy Research (2010) 77 13–19. f Proprietors of Journal of Dairy Research 2009 13 doi:10.1017/S0022029909990240