Reproductive wastage

On most farms in NZ reproductive wastage is one of the biggest causes of lost revenue potential. The average weaning rate (i.e. calves weaned per 100 hinds mated) of adult hinds in NZ is about 84-86%. For first calvers (2 year-olds) it is about 70-75%. All up, about 18% of all hinds on NZ farms fail to produce a return each year. In 2012 there were 525,000 hinds farmed, of which approximately 94,500 failed to produce a live calf at weaning!

There will always be losses associated with reproduction but we can definitely reduce the scale of present wastage figures across our farms. However, each farm is different and it is important to identify the actual causes of reproductive wastage for each population of animals in order to effectively target the best strategy.

Wastage can occur at various stages of the hind’s annual reproductive cycle. Conception, pregnancy, birth, and lactation. In many cases it is assumed to occur at one point (e.g. high conception failure) when in fact it may be largely occurring elsewhere (e.g. post-natal calf mortality). It is important not to make assumptions but to closely monitor hinds throughout the annual cycle.

Early-pregnancy ultrasound scanning is one of the most important diagnostic tools to identify issues around conception rates (i.e. number of pregnancies per 100 hinds mated). Such scanning is normally conducted from mid-May to late June. Non-pregnancy rates of >5% in adult hinds and >10% in yearling hinds are cause for concern. Possible causal and corrective factors include:

1. Under-nutrition resulting in an average herd mating BCS of >3 in adult hinds will likely increase the proportion of hinds within the herd that fail to ovulate. Any hind at or less that BCS of 2 has a very high likelihood of ovulation failure. Lactation over the mating period will likely exacerbate the effects of low BCS.
   Corrective action: Improve level of nutrition to hinds over lactation (including supplementary feeding) and consider early pre-rut weaning to dry-off hinds prior to mating. Target an average BCS of 3.5+ by mating.
2. Low body weight of yearling (R2) hinds at first mating (16 months of age) is the principle cause of reproductive failure in young hinds. These animals fail to enter puberty (i.e. fail to ovulate).
   Corrective action: Set higher growth targets for young replacement hinds, taking into account their actual genotype and ultimate mature body size (see hind puberty)
3. Infertile, sub-fertile or low-libido stag.
   
   

Corrective action: Ensure that chaser stags are used within single-sire mating programmes. Replace stags that appear to show little interest in oestrous hinds during the mating period. Vet check sire stags before use to ensure that there are no physical abnormalities.

There is growing concern that foetal wastage (abortion) may be a significant issue amongst young (R2) hinds. Certainly, loss rates of up to 16% have been recorded on some farms recently. However, other farms have recorded minimal losses (0-1%). Research is underway to assess the incidence of abortion in both R2 and adult hinds. This involves ultrasound scanning in early pregnancy and again in late pregnancy, missing pregnancies at the second scan indicate foetal loss.

There is little doubt that peri-natal and post-natal calf death is one of the most significant sources of reproductive wastage across NZ deer farms. Current estimates suggest that about 8% of calves may be lost at or after birth. Possible causal and corrective factors include:

1. Starvation/dehydration of the calf due to abandonment by the hind. Typically calves die 1-3 days after birth. This is largely an issue of failure of dam:calf bonding within the first few hours of birth, an indicates a suboptimal calving environment and/or high levels of disturbance.
   Corrective action: Provide a better calving environment that contains low cover for birthing and the calf to hide in. Maintain hind stocking rates at <8 per ha over calving to reduce hind competition of calving sites. Minimise human disturbance around birthing. Ensure adequate nutrition for the hind leading up to and after calving.
2. Dystocia (difficult calving) typically causes to calf to die at or immediately after birth. This can account for 15-25% of all calf deaths. In the early days of deer farming it was thought that dystocia was caused by excessive feed during late pregnancy…but more recent evidence dispels that concept. The most likely causes relate to hind disturbances around the calving period that actually disrupt the birthing process.
   Corrective action: Again, provide a better calving environment that minimises disturbance and allows hinds to select an ideal calving site with minimal stress. Achieving the right hind stocking rate is very important, as research suggests that competition for birth sites is a major stressor on hinds.
3. Misadventure (accidental death) is a major cause of post-natal calf loss. Fences are the biggest cause of misadventure either through calves becoming entangled in them or simply migrating to other paddocks and becoming lost.
   Corrective action: Maintain the integrity of fences around calving paddocks (i.e. no holes for calves to crawl through). Reduce the incentive for calves to wander by providing adequate shelter within the paddock (but preferably away from the fence-lines). Where possible separate calving groups by at least one empty paddock, this reduces confusion for the calf.
4. Infectious agents (disease) can be problematic on some farms (refer to Health pages for more detailed information on specific diseases). The principle disease agents that have been seen to cause calf losses are Fusiformis, Cryptosporidia, E.coli, and Leptospira.
   Corrective action: It is difficult to predict outbreaks that might occur in some years and not others. If a problem is seen, veterinary advice should be sought immediately. In some cases it is possible to intervene during or just after calving. In other cases (e.g. Leptospirosis) it may be better to start a vaccination programme for hinds to prevent future outbreaks.

Puberty failure of young (R2) hinds is surprisingly common across NZ deer farms. Early-scan pregnancy rates amongst R2 hinds can range from >95% to <40%. For more information on yearling hind performance see Puberty in hinds.