Puberty in hinds

The ‘body weight threshold’ is the critical live-weight a hind must achieve in order to become reproductively capable in her second autumn. Such weight thresholds apply to nearly all mammals. For red deer we often refer to this as the ‘70% Rule’ for a given genotype.

Hinds must attain at least 70% of their genotype’s average mature live-weight in order to attain puberty. This is a very general concept but is remarkably relevant for all the subspecies of red deer (including wapiti).

For example, in the Probability graph below for Scottish (Western) red deer – the smallest of the red deer subspecies and the original base stock for NZ deer farms – the expected mature weight of hinds is about 95kg. The body weight threshold for puberty is 65kg at 16 months. If the average weight of the R2 hinds at 16 months is 65kg, then we would expect 50% of the hinds in the herd to attain puberty while the remaining 50% would fail to do so indicated by the blue line.

This is a very high failure rate. Therefore, the ‘live-weight target’ for this genotype should be considerably higher than 65kg. In the example, if the average weight of the R2 hinds at 16 months is 80kg, then we would expect 90% of the hinds in the herd to reach puberty indicated by the green line.

In order to achieve a 95% pregnancy rate, the live-weight target needs to be set at 85kg for this breed. It is important to set 16-month live-weight targets well above threshold weights. The higher the target relative to your herd, the more likely you are to achieve a good conception rate.

When considering live-weight targets to ensure good reproductive success in young hinds, farmers need to be aware of the genotype of their hinds. There is little value in setting targets based on information about Scottish (Western) red deer when in fact the herd is made up of Eastern red deer or wapiti, or composites with all these subspecies. The expected mature hind/cow weight for these genotypes is considerably larger. The graph below indicates the relationship between genotype and the body weight threshold for puberty at 16 months.

Again, when setting 16-month live-weight targets it is important that they are considerably higher than the puberty thresholds for the breed (see Table below).

Recent evidence suggests that poor growth performance of hinds in their first 3-4 months of life (during lactation period) can influence puberty threshold weights later in life, to achieve good reproductive performance of R2 hinds, growth must be optimised from birth onwards. Where hind growth is compromised early in life through poor lactation or poor milk intake, it is even more important to set high target liveweights at 16 months of age.

There is growing evidence of high (>8%) incidences of foetal loss from R2 hinds on some farms. The evidence for this is based on repeated ultrasound scanning of hinds over the gestating period. Disappearance of a foetus seen on earlier scans indicates abortion. The incidence of foetal wastage across NZ farms has yet to be assessed and the causal factors are still being investigated (see Reproductive wastage).

There is no evidence that calf mortality for first calvers is greatly different from that of adult hinds. However, calf mortality is a significant source of reproductive wastage within NZ deer herds irrespective of hind age (see Reproductive wastage).

To calculate expected conception rates of R2 Hinds based on body weight, and to plot growth curves against requirements use the Deer Growth Curve. Available to view here >>