Effects of vacuum level and milking duration on Guernseys and Holsteins differing with respect to lactation number and status of udder health. II. Milk yield, milking time, and rate of milk flow
Caruolo, E.V.; Dembiczak, C.M.; Mochrie, R.D.; Johnson, R.E.; Eaton, H.D.; Spielman, A.A.; Beall, G.
Jour Dairy Sci 38(11): 1283-1292
Forty-eight animals from a Streptococcus agalactiae-free herd, after a 4-week standardizing period immediately after calving, were assigned to be milked from the 5th to the 44 th week of lactation at either 10, 13.5, or 17 inches of vacuum and for a "normal" or "twice normal" duration. Of these animals, 24 were Guernseys and 24 Holsteins. Within each breed group, 12 were first-calf heifers and 12 had one or more previous lactations. Within each breed-lactation group of 12, 6 were selected for being "clean" of mastitis and 6 for being "infected." The following results were obtained: No appreciable differences in milk yield and fat corrected milk (FCM) were observed between vacuum levels. Milking time and time to reach peak rate of flow decreased in a linear manner and rate of milk flow increased. The least amount of time spent in stripping was at the 13.5 inches vacuum level, and the least amount of strippings, expressed as a percentage of the total yield, was at the 10 inches level. Leaving the milking machine on the udder for an extended duration (twice normal) resulted in slightly greater yields of FCM (1.0 lb./cow/day) and decreased stripping time. Mastitis-infected animals gave greater milk yields and had slower rates of milk flow than did the mastitis-clean animals. Differences between first-calf heifers and animals with one or more lactations and between Guernseys and Holsteins agreed in general with previously published studies.