Understanding the Loss of Cattle Fertility and Reversing the Trend

Recent studies have revealed that there is an overall decrease in the fertility of cows in Europe. In order to combat this pattern producers can make changes to their feeding schedules which can have a dramatic impact on cyclicity and fertility in dairy and beef cows, writes Adam Anson, reporting for TheCattleSite.
calendar icon 30 September 2008
clock icon 3 minute read
The University of Nottingham

This growing trend of infertility has been attributed to modern intensive farming methods, which have revealed a negative correlation between milk production and fertility rates over the past 25 years.

According to Patrice Humblot from the French National Association for Animal Breeding, this trend is particularly prevalent in the United Kingdom and France.

Speaking at the 42nd University of Nottingham Feed Conference she said that negative energy balance (NEB) impacts on metabolic changes during the post partum period are affecting the "reproductive potential of both high yielding dairy cows and beef cows".

She says that in dairy cows, genetic selection for milk production and the induced changes in key metabolic hormones have been associated with a "reduction of reproductive potential including delayed resumption and increased irregularities of ovarian cyclicity and lower conception rates".

An In-depth Analysis

During the post partum period, changes in metabolism and alterations of growth hormone, IGF, insulin and leptin are associated with lipid mobilisation, as an attempt to maintain glucose homeostasis. This is associated with peripheral insulin resistance and major alterations of the insulin-like growth factor (IGF) system.

According to Mrs Humblot, there is evidence for both dairy and beef cows that Body Condition Score losses are associated with metabolic changes inducing impaired gonadotrophin secretion and subsequent alteration in follicular growth characteristics, leading to complete anoestrus in beef cows and to cyclic irregularities in dairy cows.

She says that in addition to these "central" impairments" of reproductive function, direct negative effects of NEB on reproductive function have been documented. Whole blood metabolic changes are found also in follicular fluid of NEB cows that may be detrimental to the quality of the oocyte and its surrounding cumulus cells.

"High NEFA and low glucose concentrations in the microenvironment of pre-ovulatory oocytes are associated with lower developmental competence/early embryonic development and reduced tolerance to cryopreservation."

Direct effects on embryo quality have also been observed at later stages of development following fertilisation. Similarly, high energy supply and more especially insulin status are also associated with the incidence and characteristics of ovarian cycles as it has been shown for example that increasing circulating insulin concentrations can enhance follicular growth together with detrimental effects on the developmental competence of the oocyte, she said.

This is very consistent with the metabolic changes and reproductive results observed (increased follicular growth and lower early embryonic development) following superovulation obtained with increased energy diets in dairy heifers expressing high growth rates.

Apart from direct effects on reproductive tissues, there is evidence that the alteration due to NEB of other functions such as the immune system may impair reproductive performance. These changes may contribute to a prolonged state of inflammation within the uterus making them more sensitive to uterine disease/incomplete involution.

Overcoming the Problem

According to Mrs Humblot these unfavorable changes to reproductive function have also revealed a clue as to how producers can overcome them by minimising NEB. This can be done with specific dietary and management regimes and a manipulation of the dry period.

Shortening of the dry period results in earlier post partum ovulation and higher pregnancy rates especially in multiparous cows, said Mrs Humblot. "However, in recent studies different regimes applied during the dry period did not induce a significant improvement of post partum reproductive efficiency."

However, she also revealed that there is new evidence that NEB is susceptible to modulation with subsequent positive effects on reproductive function, including post partum metabolic changes. "These approaches involve multiple mechanisms, that when taken together, may explain a large part of the lower reproductive performance observed in both high producing dairy cows and in beef cows", she said.

September 2008
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