Effect of lactation therapy on Staphylococcus aureus transmission dynamics in two commercial dairy herds

BMC Veterinary Research

Table 1 Production, SCC, infection status, and Staphylococcus aureus isolation events for treatment and control group

Herd	Pen	Monthly average number lactating cows	Monthly average milk production (kg)	Monthly average SCC (cells/ml x 1000)	Total Quarter Days at risk for new IMI¹	Total Quarter Days Infected²	Number S. aureus isolates (# quarters/# cows)
							IMI associated isolates³	incidental isolates³
1	treatment	95	31.4	419	129984	1335	80(21/20)	15(13/11)
	control	98	32.7	401	130254	2479	137(25/21)	22(20/17)
	whole herd⁴	319	32.7	404			221(50/45)	37(33/28)
2	treatment	91	42.3	292	125241	1345	58(11/9)	2(2/2)
	control	89	41.4	296	116295	14	1(1/1)	0
	whole herd	346	35.0	298			68(21/16)	4(4/4)

¹ Sum of individual quarter days uninfected at risk for new intramammary infection (IMI).
² Sum of individual quarter days infected based on midpoint estimates of IMI start and stop dates [17].
³ IMI status based on definitions of Zadoks et al. [12]; incidental isolates are those not meeting IMI criteria.
⁴ Whole herd totals include all lactating cows during study period, (cows that entered treatment and control groups, plus cows never housed with these groups); number of isolates obtained from whole herd exceeds sum of treatment and control pens as 13 IMI isolates and 2 incidental isolates were obtained from milk samples collected from cows sampled at the start of a lactation and either the IMI cured prior to entry into a study pen or the cow did not enter a study pen during the course of the trial.

ISSN: 1746-6148