Stress Effects On Postpartum Reproduction In Dairy Cows

Stress effects on postpartum reproduction in dairy cows M. A. Crowe and E. J. Williams J ANIM SCI published online November 7, 2011

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Running head: Stress and reproduction in dairy cows

Stress effects on postpartum reproduction in dairy cows1,2

M. A. Crowe3, E. J. Williams

UCD School of Veterinary Medicine, University College Dublin, Belfield, Dublin 4, Ireland

1

Based on a presentation at the Triennial Lactation Symposium titled “LactationBiology Training for the Next Generation – a Tribute to Dr. H. Allen Tucker” at the Joint Annual Meeting, July 10-14, 2011, New Orleans, LA.

2

The authors acknowledge funding of their current research by Science Foundation Ireland (SFI; grant number 07/SRC/B1156).

3

Corresponding author: mark.crowe@ucd.ie 1
PublishedDownloaded from jas.fass.org at Canadian Agriculture Library on May 2,2012 Online First on November 7, 2011 as doi:10.2527/jas.2011-4674

ABSTRACT: The objective was to review the effects of production stressors on reproductive performance of dairy cows. It has been well documented that genetic selection for milk yield over the last 50 yr has been associated with reduced fertility. In addition to negative associations between yield and conception rate, there is alsoan association between milk production and expression of behavioral estrus. Stress caused by production diseases in high yielding dairy cows also contributes to the problems of poor fertility. Lameness results in reduced intensity of estrus, and can contribute to ovulation failure, which is largely due to reduced preovulatory estradiol secretion and failure of the LH surge. Mastitis has beenassociated with prolonged intervals to dominant follicle selection, and in animals with uterine infection the dominant follicle grows slower and produces less estradiol. In a recent study we identified that milk yield was associated with an increased incidence of uterine infection, which is known to contribute to reduced fertility and prolonged calving to conception intervals. The incidence of uterinedisease was 73% in high-yielding, compared with 45% in lowyielding cows. As well as effects at the ovary, various models of stress have also been shown to perturb endocrine secretion in the hypothalamus and anterior pituitary. In conclusion, the adverse effects on fertility associated with genetic selection for yield in dairy cows is in part associated with increased incidences of productiondisease induced stress but is also associated with high milk yield.

Key words: Dairy cows, estrus, fertility, lameness, production diseases, uterine infection

INTRODUCTION Fertility in dairy cows has decreased over the time period from the 1960s to the present day. This had been associated with a period of intense selection for cows having increased production of milk (Figure 1; Butler, 1998).The causes of this decline in fertility are multifactorial but revolve around the issue of supplying sufficient resources for milk production at the expense of other physiological processes including reproduction (Walsh et al., 2011). Conception rates to a single service for post partum dairy cows have decreased from about 65% to 38% over the last 40 yr (Figure 1; Butler, 1998). There is clearevidence that increased milk production is related to reduced fertility, which in part may be mediated by production effects on uterine health. 2
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In addition to the documented effects of increased milk yield on pregnancy rates there is evidence of reductions in the expression and duration of estrous behavior associated...