title: [Milk yield and environmental factors: Multiple regression analysis of the association between milk yield and udder health, fertility data and replacement rate].
abstract: OBJECTIVE
  The relationship between milk yield and both fertility and general animal health in dairy herds is discussed from opposing viewpoints. The hypothesis (1) that raising the herd milk yield would decrease fertility results, the number of milk cells as an indicator for udder health and the replacement rate as a global indicator for animal health as well as increasing the occurrence of specific diseases as a herd problem was compared to the opposing hypotheses that there is no relationship (2) or that there is a differentiated and changing relationship (3).
  
  
  METHODS
  A total of 743 herd examinations, considered independent, were performed in 489 herds between 1995 and 2010. The milk yield, fertility rate, milk cell count, replacement rate, categorized herd problems and management information were recorded. The relationship between the milk yield and both the fertility data and animal health was evaluated using simple and multiple regression analyses.
  
  
  RESULTS
  The period between calving and the first service displayed no significant relationship to the herd milk yield. Simple regression analysis showed that the period between calving and gestation, the calving interval and the insemination number were significantly positively associated with the herd milk yield. This positive correlation was lost in multiple regression analysis. The milk cell count and replacement rate using both the simple and multiple regression analyses displayed a significant negative relationship to the milk yield.
  
  
  CONCLUSIONS
  The alternative hypothesis (3) was confirmed. A higher milk yield has no negative influence on the milk cell count and the replacement rate in terms of the udder and general health. When parameterizing the fertility, the herd milk yield should be considered. Extending the resting time may increase the milk yield while preventing a decline in the insemination index.
authors.affiliation: Dr. Carol Fölsche, Dammstraße 1, 15910 Schlepzig, E-Mail: carol@martin-foelsche.de.
authors.forename: C
authors.initials: C
authors.lastname: Fölsche
authors.forename: R
authors.initials: R
authors.lastname: Staufenbiel
mesh_terms: D000818:Animals; D001947:Breeding; D002417:Cattle / Q000502:physiology*; D003612:Dairying; D005260:Female; D005298:Fertility / Q000502:physiology; D007774:Lactation / Q000502:physiology*; D008321:Mammary Glands, Animal / Q000502:physiology*; D008892:Milk; D012044:Regression Analysis
keywords: Dairy cow; period between calving; period between conception; period of first service; replacement policy; services per conception; somatic cell count