The Milk Producer - January 2009 - (Page 33)

Jan AppSc,33-35:New Template 12/18/2008 10:55 AM Page 1 APPLIEDSCIENCE By By Herman Barkema and Richard Olde Riekerink Timing is everything Somatic cell count data could provide misleading results if you take milk samples any time other than before milking F or researchers and veterinarians, sample collection during milking may not always be feasible. Moreover, increased use of portable somatic cell counters means you or one of your dairy farm’s advisors are more likely to take milk samples between milkings. However, collecting milk samples any time other than immediately before or during milking could have consequences for interpreting somatic cell count (SCC) data as an indicator of bacterial udder infections. These infections are the most important cause of increased SCC. Other factors affecting SCC include a cow’s age, lactation stage, season, stress, management and variation during the day, but these are considered less important. The most recent study on SCC variation during the day dates from 1967, and milk production has more than doubled since then. With decreasing average individual cow SCC and increased milk production per cow, SCC may decrease faster after milking nowadays, and taking samples indicating intramammary infection could possibly be taken sooner after milking. Our study determined how sampling time affects SCC as an indicator of an udder’s infection status. The 60 study cows were on six Prince Edward Island tie-stall dairy farms that milked twice daily. All cows had four milk-producing quarters, no clinical mastitis, and production of more than 10 kilograms per SCC starts rising after morning milking regardless of infection. day. Quarter samples were collected immediately before the morning and evening milkings, half-way through the morning milking, immediately after the morning milking and every 60 minutes after detachment of the milking unit. We classified quarters in three categories, based on infection status: not infected; infected with minor udder pathogens (coagulasenegative staphylococci or Corynebacterium bovis); infection with major udder pathogens (Staphylococcus aureus or Streptococcus uberis). In total, 17 quarters, or 7.1 per cent, were infected with major pathogens: • 11 Staph. aureus; • one mixed infection with Staph. aureus and Strep. dysgalactiae; • one Strep. uberis; • three Streptococcus spp. other than Strep. agalactiae, Strep. uberis or Strep. dysgalactiae; • one E. coli. Thirty-one quarters, or 12 per cent, were infected with minor udder pathogens: • 12 coagulase-negative staphylococci; • 19 Corynebacterium bovis. Average SCC of all 240 quarters was 101,000 cells per millilitre. They ranged from 5,000 to 7,677,000 before morning milking. Average SCC increased sharply after the morning milking to a maximum of 322,000 one hour after milking, ranging from 15,000 to 8,136,000 (see Figure 1). Compared with the average SCC before the morning milking, the level of post-milking samples was higher until seven hours after milking. SCC in high-producing cows increased more after milking, but declined faster. The difference between SCC before morning milking and SCC between milkings was smaller in quarters of early-lactation cows than in later lactation animals. The average SCC of quarters infected with a major pathogen, as expected, was higher than the average for quarters with a minor pathogen infection or no infection, and did not increase much after the morning milking (Figure 1). SCC of quarters with a minor pathogen infection differed only slightly from quarters with no infection. For quarters with no infection, SCC before the morning milking increased to 220,000 cells per mL from 75,000 just after milking. Halfway milking SCC was similar to the level from before morning milking. MilkPRODUCER | January 2009 | 33

Table of Contents for the Digital Edition of The Milk Producer - January 2009

The Milk Producer - January 2009
Contents
Editor's Notes
DFO Chair's Message
Dairy Update
DFC Promotion
Processor Spotlight
Farm Finance
Take Steps to Reduce Feed Costs
Research
Feed Management
Applied Science
Markets
New'n'Noted
Back Forty

The Milk Producer - January 2009