Puberty in hinds

Puberty in hinds

When does puberty occur in hinds?
Red deer and wapiti cows on NZ deer farms normally attain puberty (first ovulation) at 16 months of age during their second autumn. Hinds that attain puberty at 16 months are highly likely to conceive and calve at about 24 months of age. However, in order to do so R2 hinds must reach 70% of their adult body weight by their second autumn.  Failure to do so will delay puberty by at least a year.

What are ‘body weight thresholds’ and ‘live-weight targets’ for puberty?
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. One way of interpreting this is…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 (see blue line).

However, that is a very high failure rate. Therefore, the ‘live-weight target’ for this genotype should be considerably higher than 65kg. In the above 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 (see 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 is set relative to your herd, the more likely you are to achieve a good conception rate.

 

What is the effect of genetics on thresholds and targets?
When considering live-weight targets for ensure good reproductive success in young hinds, farmers need to be aware of the actual 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…because the expected mature hind/cow weight for these genotypes is considerably larger. The ‘probability’ graph below shows 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).

 Breed

Puberty threshold weight (kg)

 Liveweight target for a 95% scan rate (kg)

100% Western (W)

 65

 85

 50:50% W x E

 75

 95

 100% Eastern (E)

 85

 110

 30% wapiti

 89

 115

 50% wapiti

 108

 135

 100% wapiti

 150

 190

What other factors can affect thresholds and targets?
There is recent evidence that poor growth performance of hinds in their first 3-4 months of life (i.e. while on their mums) can influence puberty threshold weights later in life,effectively forcing hinds to reach a higher weight threshold in order to breed at 16 months. The simple message is.to achieve optimal reproductive performance of R2 hinds, optimise growth from birth onwards.  If 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.

What about foetal wastage (abortions)?
Over the last 2-3 years 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).

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

Growth Curve for Replacement Hinds

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 download here:

 hind conception graph

Show me the science

Asher, G. W., Scott, I.C., Archer, J.A., Ward, J.F., Littlejohn, R.P. (2010) Seasonal luteal cyclicity of pubertal and adult red deer (Cervus elaphus)

Asher, G.W., Archer, J.A., Scott, I.C., O’Neill, K.T., Ward, J.F., Littlejohn, R.P. (2005) Reproductive performance of pubertal red deer (Cervus elaphus) hinds: Effects of genetic introgression of wapiti subspecies on pregnancy rates at 18 months of age. Animal Reproduction Science 90: 287-306.

Asher, G.W., Archer, J.A., Ward, J.F., Scott, I.C., Littlejohn, R.P. (2011) Effect of exogenous melatonin implants on the incidence and timing of puberty in female red deer (Cervus elaphus). Animal Reproduction Science 123: 202-209.