There are a variety of reasons why hinds may fail to breed. The principal cause of failure is undoubtedly poor nutrition and low body condition score (BCS) (see Mating management of adults). However, there are a number of other reproductive disorders than can afflict individuals, but these only account for a small proportion of losses.
Any disease that causes body wastage (i.e. reduces BCS) will seriously reduce reproductive potential in the herd. For example, chronic Johne’s disease in hinds is often associated with emaciation and, invariably, reproductive collapse.
However, some disease pathogens can exert a direct effect on reproduction through preventing fertilization (e.g. uterine inflammation) or causing foetal wastage (abortion). Such diseases are not well studied in deer, but in other domestic ruminant species include Brucella, Leptospira, Campylobacter, Toxoplasma to name a few.
True cases of infertility (ovarian failure) are occasionally recorded in deer but in most cases would be overlooked.
However, red deer and wapiti are relatively long-lived ruminants (up to 20+ years), and it is not uncommon for cases of reproductive senescence (old age) to occur. This is analogous to menopause in humans, whereby hinds outlive their supply of eggs within the ovary. This normally occurs at 15-17 years of age in red deer hinds.
Occasionally hinds undergoing a very difficult birthing are unable to resorb or eject the dead foetus/calf, and the encysted remains become lodged within the reproductive tract. This condition compromises the hind's ability to again become pregnant through fertilisation failure or inability of an embryo to implant in the uterus.
Freemartinism occurs in cattle and red deer when a male/female set of twins is produced. The female offspring has a high probability of lifelong infertility through foetal androgenisation from her male sibling in utero. This is due to the placentation system in these species (which do not normally twin) whereby the twin foetuses share a common blood supply. The male foetus produces androgen hormones that enter the female foetus and disrupt development of the reproductive organs. There can also be exchange of male and female cells leading to offspring with mixed male:female cell lines (‘chimeras’).
Although natural twinning in red deer is quite rare, the increasing adoption of oestrous synchronisation and AI technologies has been associated with increased rates of twinning. As such, the incidence of sterile freemartin hinds is likely to have also increased. Freemartin hinds may appear normal but often have incomplete or abnormal development of their reproductive tract. Some freemartin hinds actually grow velvet antler.
The detection of reproductively abnormal hinds is often based on records on actual performance over one or two year. Hinds that repeatedly fail to rear a calf should be culled from the herd. While they do not contribute to the genetic make-up of the herd, they do eat a lot of feed for no financial return.
Stewart-Scott, I.A., Pearce, P.D., Moore, G.H., Fennessy, P.F. (1990) Freemartinism in red deer (Cervus elaphus L.). Cytogenetics and Cell Genetics 54: 58-59.
Information on A successful pregnancy: Preventing foetal losses is available in a convenient DINZ Deer Fact sheet (August 2017). Download your own copy here >>