Fertility in females


There are a number of factors contributing to fertility in any female. Some may be modified by management and nutrition changes but others are out of the control of routine farm decision making. For completeness, I have listed all those issues which I believe may impact on puberty-onset and enhanced fertility in small ruminants. It is an attempt on my part to give a greater depth of understanding to all involved and thus enhance the quality of decision making with regard to those factors under our control when we consider undertaking an artificial reproduction programme.

GENETIC MAKE-UP – includes everything from genetically defective individuals (hermaphrodites, infantile reproductive tracts) through to strains known to be more fertile than others eg  Eastern red deer are usually regarded as earlier breeding than English deer, Poll Dorset sheep more prolific than     Merinos. Fortunately, genetic defects occur in a very small % of individuals. Some such as hermaphrodites can be culled out of the herd before breeding decisions are made. Others problems eg defective reproductive tracts will not be diagnosed until there is failure to breed. The reason females are presented for mating is usually because they carry genetic characteristics from their forebears which have commercial value eg heavy antler, multipointed antler, rapid growth rate, resistance to footrot.Their inherent fertility is not a primary selection criteria. In spite of addressing all areas of concern those strains or individuals with   lower fertility will still perform poorly compared to more fertile lines.

SEASONAL INFLUENCES – the onset of first oestrous within any season is related to daylength. Deer, sheep and goats all respond to shortening daylength (increased night time). With horses and cattle it is the opposite so that their breeding season is spring /summer compared to the deer’s autumn/winter breeding season. However, due to length of gestation offspring are all born in spring.

It is obvious that there will be other seasonal differences which may have some influence on this natural stimulus to the annual cycle. The level of influence will be hard to quantify and of course there is nothing we can do other than accept that this is another aspect on which to reflect.

Endeavouring to mate earlier in the season may be the more risky option. Looking to mid-season as optimum time to mate will alleviate any perceived risk from this factor. That is, the females should have settled into a regular cyclical pattern of oestrous by mid-season regardless of current weather conditions.

BODY WEIGHT AND CONDITION – all spp have a body weight below which they will not cycle. Puberty, the age at which a female first cycles occurs at around 70%  adult LW. It is important to achieve liveweights in excess of pubertal weight in ALL young females. To achieve only an average pubertal LW in a group of young females means that some will be underweight and so will not be cycling. Hence the simplistic advice “Feed ‘m”.

In mature females, body condition score (BCS) as opposed to body liveweight (LW) is the significant concern.  Lactation plays a major part in lowering body condition and hence the ability to cycle early in the season. In deer early weaning has as its main role that of enabling the hind to improve in condition so that she cycles early and thus has a greater chance of mating successfully. In inherently fertile lines of deer cycling with good fertility seems almost obligatory! With sheep and goats it is most likely that there will be at least a one to 2 month gap between weaning and mating so ample time to restore condition prior to mating. It would be prudent to aim at Condition Score 3 for reliable fertility. Certainly over fatness is not helpful and a rising plain of nutrition (and condition score) from weaning to mating is ideal (flushing).

NUTRITION- energy levels are the most basic and key factor in animal nutrition. Adequate levels of energy to achieve continuous growth of the foetus from conception to birth, then through suckling phase to weaning and puberty is critical to early fertility in all young stock. Once mature, maintenance of condition score(CS) above 2.5 at all times will go a long way to ensuring high levels of lifetime production. Please note this a minimum CS. What it means is that say a female is lactating and losing condition then management decisions must be made early to ensure that her condition is maintained above 2.5. Thus she will maintain constitution and respond with a rapid rise in body condition when offspring are weaned. Especially with hinds if allowed to drop lower than CS 2.5 then there will be a potential delay in onset of the first oestrus while the hind is making up for the rigours of lactation.

The other major feed input is protein. Without adequate protein in the diet, maintenance of milk production will be at expense of skeletal muscle and so the female’s constitution will be adversely affected. High-quality pasture as available on most NZ farms will provide adequate protein for maintenance of rumen microflora and ultimately their degradation and absorption as protein for the benefit of the hind.

MINERALS AND TRACE ELEMENTS – are an important part of nutrition to complement the energy and protein requirements necessary for good fertility. Certainly, under New Zealand conditions it is well known that failing to supplement with Selenium, in particular, may have significant effects on fertility. Failure of conception during the mating phase, reduced viability of the neonate and poor growth rates and death in the growing offspring have all been associated with inadequate Selenium levels. Trace element deficiencies must also be considered on a district by district basis. For example, while Selenium supplementation in deer is universally of concern in NZ, Copper supplementation may not be so important. Knowledge of variations in requirements of Copper, Cobalt, Iodine, Zinc and Selenium for differing locations is important in fine-tuning nutrition inputs for the herd. To supplement with an oral liquid drench of minerals (Copper, Selenium, Iodine, Cobalt and Zinc) at weaning and possibly repeat at CIDR insertion is a recommended procedure. However, it must be given with due consideration to any other supplementation which is part of the farm’s usual programme eg where Selenium prills are used then there could be the possibility of Selenium toxicity if mineral drench is given as well.

MANAGEMENT – any stress to the female stimulates high levels of cortisol which will negatively impact on cycling and subsequent fertility. As we are all aware stress can arise from a myriad of sources. Poor nutrition, rough herding, high stock densities, mixing of unrelated animals etc all can contribute to stress. Good stockmanship, attention to correct nutrition and being alert to the herd behaviour (settled or flighty) are all embodied in good management.

REPRODUCTIVE PHYSIOLOGY – it is a basic understanding of all reproductive work that where a fertile male and female are mated then the mating will be successful (offspring will result) 70% of the time. This is why most herd mating programmes are run for 3 cycles. Thus at first cycle (assuming all females are mated ), 70/100 become pregnant. At the second cycle 70% of the balance become pregnant (70% of 30 = 21) and at the last cycle 70% of the last 9 become pregnant. This gives us the theoretical 97% pregnancy rate which is the expected result.

This is an important concept to keep in mind as it explains the range of results we get in any AI or AI/ET programme eg the 30% losses alluded to above are a combination of genetic defects, embryo quality, uterine environment, health problems in hinds (including donors and recipients) etc. Of course, any instance of poor technique in embryo handling and donor/recipient surgery will compound above problems. Fortunately, the techniques of semen handling, embryo manipulation and surgical routines are well practiced and proven. It is expected that any AI technician and ET team will work to a high standard using proven techniques so that so far as is humanly possible losses are minimized through these procedures. In fact, with AI programmes in red deer, we find, with good management, an average of around 70% fertility to the timed AI which is effectively a 100% result when related to the success of one natural mating. Generally speaking, red deer AI projects are more successful than cattle projects so this is a very encouraging observation. On the other hand sheep and goats have the advantage of multiple ovulation. Thus if 60% of an AI group conceive but all have twins then we end up with 120% result. In practice, with sheep and goats, we usually suggest an outcome of an offspring /straw of semen. Finally, the major message to be well understood is that preparation of females prior to programming along with high level of stockmanship and feeding throughout programming, surgery and pregnancy all play a vital role in the success of any project.

Photo credit: Celeste Brown



From experience, we know that AI results of 60% and better are “successful” projects and hold rates of fresh embryo 60%+ and frozen/thawed embryo 50% + can also be regarded as successful. If results less than these are achieved then we can be confident that something has gone wrong with the basics. Of course, everybody is very pleased when better results are achieved. These “better” results are readily explained by having done all the basics well and also having the good fortune that all those aspects not under our control have been favourable during those better programmes.


From the above outline of factors affecting female fertility, an approach can be made to selection and management to optimize all factors which are perceived to influence the onset of puberty, cycling and enhanced fertility in any group of females. While these practices are important in any herd (stud or commercial) they are of particular relevance in the stud or commercial situation where AI and AI/ET programmes are planned. The reason for this is the concentration of activity on ONE cycle of the season for planned breeding programmes. In the case of deer, we are aiming for “100%” fertility at the FIRST cycle of the season whereas in natural mating situations the stag has 3cycles to achieve his expected 97% result. For sheep and goats, there is more flexibility due to the longer mating season and the longer rest period between weaning and mating which allows body condition to be adjusted. To address all manageable factors in the lead up to an AI or AI/ET project and thus do everything possible to enhance reproductive performance (offspring on the ground) there will be an inter-relationship of management, nutrition and supplements to consider. What is critical is that there is a pro-active approach from December onwards to ensure all females are presented in a healthy state for best reproductive performance by time programming commences. It is not appropriate to reflect on eg low Condition Score at programming time because of poor feed supply at weaning or failure to drench for parasites.



Pre Programming Management Strategy – Every property is different so rather than give a specific recipe I have elected to simply list all the things you, as the manager, can do to best manage your mating group. It is then important to create a timeline prior to programming to ensure all is done in time and on time for a successful outcome. This is an area where discussion with your vet will be a valuable exercise as it will ensure that both you and your vet are actively involved in the programme outcome.

When to Programme – Generally it is best to take the date when most natural births take place and go back by the Gestation Period  (235 days for Rred Deer, 150 for sheep and goats) and that should be the optimum time for mating. Don’t use a programme to bring mating date forward. As 40% will fall pregnant to a backup sire ensure that your back up matings are not going to produce offspring which are too late born.

Mismatings – it is essential to have males securely fenced away from the females from well before programming commences. Ram lambs and buck kids can really stuff things up!

Selection of Females – here we are talking about genetics. What are your aims for the programme, what are the best genetic females to select to hopefully achieve your goals.  On the other hand, you will also need to consider things like age (is it first pregnancy eg) hogget, 2nd or mature, offspring previously reared successfully, udders good etc

Body Condition Score – must be addressed from 2-3 months in advance. Thus with hinds must Condition Score in January and closely monitor until weaning and supplement if necessary to maintain CS3. Similarly with ewes and goats. If ewes too heavy then restrict feed for a month to 6 weeks (be really hard on them) and this will enable a flushing effect at programming.

Parasite Control- internal and external – this needs to be sorted 4 -6 weeks prior to programming

Trace Element Supplementation – Selenium and Copper especially but also Iodine – again well in advance of programming with possible additional supplement at CIDR insertion eg Multimin inj.

Shearing and feet trimming – 4-6 weeks prior to programming

Vaccination Programmes – Clostridial – eg 5 in 1 or Covexin 10 – ensure booster is given prior to programming. – Leptospirosis – use if part of your farm programme – Toxovax and Campyvax – definitely consider these vaccinations in sheep and goats. Toxovax only has 5 day shelf life so order well in advance and administer at least 3 weeks before programming – Androvax – to boost twinning – timing of injection is important relative to breeding date. Just make sure your feed management and ewes can handle the extra demands.

 Monitoring Cycling Activity – note that when CIDR’s are used to control the reproductive cycle to permit timed AI they are recommended to be used in CYCLING  females. The use of teasers in ewe and goat programmes will enable selection of cycling females to recruit for the programme. It is deer industry practice to AI hinds from mid March – given that CIDRs are inserted 14 days prior to AI then it is my opinion that many hinds will NOT have had their first cycle of the season and so will not respond as well to the CIDR programme as in most cases early weaning is usually timed around 1st March.which is when CIDR’s are due to be inserted for early programmes.

Donors and Recipientseverything above applies to any AI or AI/ET project. However, some additional points with respect to ET projects is important. Recipient females (the ones which receive embryo from the donor) and donors are handled the same as females in an AI programme.


Compared with sheep projects, deer are more sensitive to changes and stress close to programming. Females which have previously been programmed successfully (either for AI or previously as recips) are the first choice to consider as recipients. Then consider females which have successfully reared one or more offspring so that you know they have good maternal ability. Donor selection should include known fertile mature females with a good breeding history as well as young females of apparently greater genetic merit but of unknown fertility. In this way the overall programme should give a result as all ET work is designed around average results. For this reason it is also better to programme several donors rather than one or two.

Hormones used in Programming – I mention this only to emphasise that the CIDRs and injectable hormones used in programming do not overcome poor management and nutrition problems. They also do not overcome poor fertility in the females in which they are used.

Source: McPhee BVSc, HDA, Centre Veterinarian

Xcell Breeding and Veterinary Services Ltd


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