EFFECT OF CLINICAL MASTITIS ON PRODUCTION AND DAYS FROM FIRST
BREEDING TO CONCEPTION IN HOLSTEIN COWS USING SURVIVAL ANALYSIS
TEST
A. Heravi Moussavi and M. Danesh Mesgaran1
1-
Department of Animal Science and Center of Excellence for Animal Science, Ferdowsi
University of Mashhad ,Mashhad 91775-1163, Iran
Mastitis is one of the most common diseases affecting dairy cows and it causes major
economic losses to the dairy industry including reduction in milk production and reproductive
performance. Recently, survival analysis was used to assess the effects of diseases on
reproductive performance. Maizon et al. [1] showed that survival analysis allows for a more
appropriate management of censored data and time-dependent covariates, which are very
common in the study of variables such as days from first breeding to conception (DFBC).
The objective of this research was to study impact of clinical mastitis on DFBC and first 200
days cumulative milk production in Iranian Holstein dairy cows.
A data set of 13,000 lactations during 1996 to 2003 from five large dairy herds was
used for this study. Mastitis definitions included mastitis treated by systemic therapy or
mastitis treated by local therapy, acute mastitis or chronic mastitis, all cases of clinical
mastitis, treatment for mastitis, and clinical mastitis diagnosed by a veterinarian or a
technician. According to the parturition date, DFBC and mastitis data were analyzed by
survival analysis. Survival statistical analysis was performed using the statistical software
package JMP (SAS Institute Inc., NC, USA). Mastitis was considered if it occurred after
calving up to conception or until censoring. So, for the uncensored data, mastitis occurred
before first breeding or also during breeding but not after the conception. Conception was
defined by rectal palpation and subsequently confirmed by calving. The DFBC was defined
for an uncensored cow as the interval from first breeding to conception and for a censored
cow as the interval from first breeding to either culling or 350 d after calving, whichever
came first. The first 200 cumulative milk data were analyzed by Mixed models in SAS.
The results showed that DFBC (44.93 and 77.55 d, respectively in the healthy and
mastitic cows) was different among groups (P<0.001) and cows with clinical mastitis had a
prolonged interval compared with the healthy cows. The median DFBC almost in doubled in
the mastitic compared with the healthy cows (21 and 46 d, respectively). The Log-Rank and
Wilcoxon tests showed significant difference between the two groups (P<0.0001). The
cumulative 200 days milk production was less in cows with clinical mastitis (6021 and 5870
kg, respectively in the healthy and mastitic cows, p<0.001). This result is similar to finding of
Santos et al. [2]. The results demonstrated that clinical mastitis before first breeding or also
during breeding was one of the effective factors on milk production and reproductive
performance.
1- Maizon, D. O., P. A. Oltenacu, Y. T. Grohn, R. L. Strawderman, and U. Emanuelson.
2004. Effects of diseases on reproductive performance in Swedish Red and White dairy
cattle. Prev. Vet. Med. 66:113-126.
2- Santos, J. E., R. L. Cerri, M. A. Ballou, G. E. Higginbotham, and J. H. Kirk. 2004. Effect
of timing of first clinical mastitis occurrence on lactational and reproductive performance of
Holstein dairy cows. Anim Reprod. Sci. 80:31-45.