Dairy Health

DAIRY MANAGEMENT
Can Mastitis Have an Effect on Reproduction?

Dr. Allen Young
USU Extension Dairy Specialist

At the recent regional meetings of the National Mastitis Council an interesting presentation1 was given by researchers from the University of Tennessee on the relationship between mastitis and reproduction. I think you also will find their results interesting.

Mastitis is an inflammation of the mammary gland. Inflammation is the cow’s response to a bacterial infection. This is the most costly disease for dairy farmers in the United States. Mastitis is also one of the three major reasons why cows are removed from the herd. Low production and reproduction are the other major reasons. The first report of a possible link between mastitis and reproduction was in 1991. Since then other reports have shown similar relationships. Below is a brief summary of some of the work reported by the authors.

Milk samples, taken over an 11 year period from 758 Jersey cows from the University of Tennessee Dairy Experiment Station, were coded as clinical, subclinical, or uninfected based upon bacterial analysis and presence of mastitis. Reproductive data were also collected and correlated with the time that mastitis occurred. The results are summarized in Tables 1, 2, and 3. What they found was that:

Mastitis before 1st service delayed days to first service, increased days open and services per conception.
Mastitis after 1st service increased days open and doubled the services per conception.
Mastitis after pregnancy had no effect on reproduction. S
ubclinical or clinical mastitis both had the same deleterious effect on reproduction.
Different types of bacteria causing mastitis (gram positive or negative) had similar effects on decreasing reproductive performance.

These results are not unique. The message is that mastitis has an effect on decreasing reproductive performance. So what is the mechanism through which mastitis impairs reproduction? The simple answer is that currently we don’t know. The authors proposed a model, based upon other reproductive research, that might explain the relationship. The model suggestions three possible areas that might be affected:

Uterine-ovarian axis: Increased prostaglandin F2 alpha, body temperature, and/or immune response can decrease the length of the luteal cycle or embryonic development. This would also include a suggested negative effect from endotoxins produced by the bacteria.
Hypothalamus-Pituitary-Ovarian (brain to ovary) axis: Increased cortisol from mastitis inhibits LH and FSH secretion which decreases follicle development, maturation of the oocyte, or ovulation rate. The latter could lead to an increase in the number of cystic ovaries; something which has been documented.
Nutritional interactions: Decreased feed intake alters metabolites, thus changing the hormonal profile of the cow and inhibiting follicular development.

The increases in cortisol and prostaglandin F2 alpha seem to be the most reasonable explanations at this time. The net response is that pregnancy rate is decreased.

The message I think these data are suggesting is that we can no longer look at events on a dairy as being isolated from one another; all are interrelated. Udder health affects not only production and milk quality, it can also affect reproduction. When troubleshooting reproductive problems on a dairy, if obvious answers can’t be found, maybe it is time to start looking at other, less obvious reasons. Controlling mastitis may be one way to improve reproductive performance on your dairy.

Table 1. Effects of time of mastitis occurrence on reproductive performance.

	Days to First Service	Days Open	Serv per Conc
Before 1st Service	75.7^a	106.2^b	2.0^b
1st Service to Pregnancy	75.2^a,b	143.5^a	3.1^a
After Pregnancy or Uninfected	67.8^b	85.4^c	1.6^c

^a,b,cDifferent letters indicate significant differences between values within a column

Table 2. Effects of mastitis type before 1st service on reproductive performance.

	Days to First Service	Days Open	Serv per Conc
Control	67.8^b	85.4^b	1.6^b
Subclinical	74.8^a	107.7^a	2.1^a
Clinical	77.3^a,b	110^a	2.1^a,b
Changed from sub to clinical	75^b	100.9^a,b	1.8^a

^a,bDifferent letters indicate significant differences between values within a column.

Table 3. Effects of mastitis type during the breeding period on reproductive performance.

	Days to First Service	Days Open	Serv per Conc
Control	67.8^a	85.4^b	1.6^c
Subclinical	61.2^a	90.9^b	2.1^b,c
Clinical	70.6^a	143.6^a	3.0^a,b
Changed from sub to clinical	93.9^b	196^a	4.3^a

^a,b,cDifferent letters indicate significant differences between values within a column.

¹Olive, S.P., F.N. Schrick, M.E. Hockett, and H.H. Dowlen. 2000. Clinical and subclinical mastitis during early lactation impairs reproductive performance of dairy cows. National Mastitis Council 2000 Regional Meeting, Cleveland, OH, August 24, 2000, p. 34.