THE BREEDING SEASON

Fallow deer exhibit highly seasonal patterns of reproduction calibrated by photoperiod. They are short-day breeders, with the rut (peak of mating activity) occurring in October/November in the Northern Hemisphere (NH) and April/May in the Southern Hemisphere (SH). Breeding pattern within regions is highly synchronized in any one year, and reproductive management of this species on pastoral farms must therefore align feed supply with seasonal demands of late pregnancy and lactation. Patterns of reproduction also vary slightly at different latitudes, and local benchmarks for reproductive behavior and onset of the rut need to be established. Description of the estrous cycle, estrus, length of the breeding season, and gestation length are provided by Asher in Chapter 123.

REPRODUCTIVE BEHAVIOR

Bucks

The breeding season is enormously stressful for fallow bucks. Potential sire bucks should be clinically examined by a veterinarian well before the start of the rut for detection of abnormalities, because once the rut commences they become extremely aggressive toward other deer if confined in handling yards and injuries can occur. Bucks will fight vigorously during the pre-rut period to establish dominance, and in very large paddocks and in the wild will sometimes establish stands, which they mark by thrashing small trees and digging rutting scrapes. In confinement bucks will walk the boundary of their fence line incessantly, especially in small paddocks (1–3 hectares) and can cause deep erosions from this activity in wet conditions. In small enclosures bucks give the impression that they are herding does because there is no real opportunity for lekking to occur. Even when the herd of does is resting the dominant buck will be moving continually to defend the harem against competitor bucks or to check does for estrus.

If bucks are placed in adjoining paddocks they will fight vigorously through a fence and can make large holes in it. The fighting will also create holes in the top soil on either side of the fence, as the bucks attempt to hold ground during their pushing and shoving. This enormous energy expenditure leads to rapid weight loss, and adult bucks can lose 20 to 30 kg in a period of 6 to 8 weeks just prior to and during the rut. This equates to a change in body condition score from 3.5 to 1.5 (on a scale of 5) and leaves the buck vulnerable to winter death syndrome if low body condition is combined with poor quality feed and cold-snap weather conditions.⁷ Losses among sire bucks can be minimized by providing high-quality feed to sires immediately following the rut. This ensures protection of valuable genetics in preparation for subsequent breeding seasons.

Bucks are capable of breeding past the age of 15 years, but in the wild and on farms in competition with other bucks, they are unlikely to hold a harem beyond 7 to 8 years of age. Rapid turnover of breeding bucks on farms is desirable to reduce the intergeneration interval and maximize genetic gain through selection.

Does

Fallow does reach puberty weight prior to 16 months of age, but usually do not conceive until that age because of the acutely seasonal photoperiod effect that induces the onset of estrus. Occasionally precocious females will reach puberty weight by 8 months of age and conceive, but this should be avoided by careful management because of the impact of pregnancy on growth of the doe and the long-term impact on lifetime reproductive performance.

Estrous behavior in does appears quite passive compared with that of other livestock species.¹ It is rare for does in estrus to mount other does or be mounted, and the most obvious characteristic of fallow deer estrus is simply that a doe will stand to be mounted by the buck. A nonestrous doe will generally avoid close contact with the rutting buck and will run short distances if a buck approaches.

The onset of estrus can be very abrupt, although self-grooming, more activity than normal in the form of walking and fence-pacing, and reduced time spent feeding are indicative signs. Does can cycle for 3 to 6 months if not mated, at intervals of 21 to 25 days from early to later in the breeding season, respectively. Interest shown by both bucks and does in mating wanes remarkably after about the fourth estrous cycle of the breeding season, and it is uncertain whether this is due to weakening pheromonal signals associated with estrus or some other reason.

REPRODUCTIVE BIOLOGY

Fallow deer have a highly synchronized mating season. The does are polyestrous but most (∼95%) conceive in their first or second estrous cycle. Pregnancy testing using ultrasonography is 100% accurate from 50 days of gestation, and a high level of accuracy is achievable earlier than this by experienced operators. Rapid fetal growth takes place in the third trimester of pregnancy when daily energy requirements increase by 25%. Basic information on the reproductive biology of fallow deer is presented in Table 129-1.

Table 129-1 Fallow Deer Reproduction

Feature	Description
Onset of puberty	Does: 16 months (weight dependent, 35 to 40 kg)
Onset of puberty	Bucks: 14 months (motile sperm first detected)
Onset of breeding season	Mid-April Southern Hemisphere, mid-October Northern Hemisphere
Duration of breeding season	6 estrous cycles in adult does
Duration of breeding season	4–5 estrous cycles in younger does
Duration of rut	6 weeks (2–3 estrous cycles)
Length of estrous cycle	21 ± 0.6 days (1st cycle of breeding season)
Length of estrous cycle	25 ± 1.5 days (last cycle of breeding season)
Length of estrous	12 to 24 hours
Matings per estrous	Repeated mounting (16 ± 7) prior to final ejaculatory mount
Courtship	4 to 50 minutes (mean ± SD = 15 ± 10)
Gestation length	234 ± 2 days
Onset of fawning	Last week of spring
Duration of parturition	30–180 minutes from appearance of membranes
Fawning rate	88–92% of does joined
Male-female ratio at birth	1:1
Weaning rate	80–84% of does joined
Birth weight	Females: 4–4.2 kg
Birth weight	Males: 4.2–4.6 kg
Twinning rate	<1:200

The buck-doe ratio used by most fallow deer farmers is 1 : 40 for experienced adult bucks and 1 : 20 for rising 2- and 3-year-old bucks. Higher buck-doe ratios can lead to subfertility in males and prolong the breeding season. This may lead to the birth of late fawns (conceived in fourth or fifth estrous cycle), and these fawns will grow slower than their counterparts, be subject to winter conditions earlier in their development, and usually do not attain the adult body weights expected. Late fawns might not conceive at 16 months of age as expected, because their body weight will not be sufficiently high by then to support the onset of puberty, pregnancy, and then lactation. Fallow does are highly fertile and will continue to breed after 12 years of age, depending on conditions, although there is some evidence that they are most efficient between 3 and 8 years of age.¹⁰

Fallow does will usually miss one or more breeding seasons throughout their reproductive life even when environmental conditions seem favorable.¹⁰ Stress may play a role in inducing this reproductive spell, and may originate from the heavy demands of lactation in drought years or from feeding the rapidly growing male fawn through to weaning the previous year, from introducing deer to new surroundings at the start of the rut, or changed environmental conditions.

Fawn growth rates between 100 and 200 g/head/day are usually attained in the first 12 weeks of life, but slow to average between 50 and 100 g/head/day for the following 9 months up to yearling age. Growth profiles for female and male fawns up to 12 months of age are shown in the annual management calendar in Table 129-2. Castration of males at 6 months of age reduces growth rate by 10% compared with their male counterparts, but this is compensated for by increasing ease of management of slaughter animals during the following breeding season.

Table 129-2 Annual Management Calendar

Accurate records of reproductive performance and growth rates of progeny are essential for selection of high-producing animals and for sire comparisons in single-sire mating systems. Breeding does should be replaced at the rate of 20% per annum, and the intergeneration interval for breeding bucks should be as low as is feasible to maximize the genetic gains resulting from genetic selection.

WEANING

Weaning is a management procedure that separates breeding females from their progeny, and is usually carried out to (i) simplify management of doe mating groups over the rut, (ii) provide preferential feeding for juvenile animals during the winter, and (iii) allow easy access to young animals for animal health and welfare management once they are nutritionally independent of their dam, without disturbance to breeding herds.

Weaning can be carried out pre-rut or later in the breeding season in fallow deer, as lactation does not appear to inhibit ovulation and conception. However, the procedure should not be carried out without consideration of factors/stressors that can impact on behavioral and growth changes in weaned animals and their dams, such as unfavorable weather patterns (drought, wet, cold), body condition of dam or fawn, and introduction to unfamiliar surroundings of fawns, in particular after separation from their mother. If does become emaciated due to poor nutrition during lactation, it is probable that subsequent reproductive performance will be low if poor body condition is maintained throughout the rutting period, and pre-rut weaning is recommended under such conditions.¹ Studies have shown positive effects of pre-rut weaning on hind conception date and hind condition in red deer in New Zealand, but it was acknowledged that weaned calves grew more slowly.¹⁴

Weight loss occurs in fawns immediately after weaning and persists for 2 to 3 weeks whether the procedure occurs pre-rut or post-rut. Comparative evaluation of weight recovery in fallow deer weaned pre-rut compared with deer weaned post-rut has shown no difference between the groups by 12 to 14 months of age owing to compensatory weight gains that occurred during spring (9–12 months of age).¹¹ However, the availability of nutritious feed during this time is necessary to facilitate weight recovery. Minimization of weight loss at weaning is assisted by (i) weaning dams from their fawns so that fawns remain in familiar surroundings, (ii) adding two or three older animals of quiet temperament and who are used to human contact to the group of weaned deer, to assist in training of weaned deer to use of laneways, gates, and concentrate feeding points if required, and (iii) moving dams out of calling range of their fawns for 3 to 4 weeks. This may not be possible if deer are being weaned indoors, where appropriate strategies may need to be developed according to the size of the facility.

Controlled mating practices may require considerable pre-rut sorting and handling of breeding stock, and under these circumstances fawns are better removed from the breeding herd. The opportunity to preferentially feed weaned deer, and to carry out routine animal health management, without disturbance to breeding animals is facilitated by pre-rut weaning. In situations where concentrate feeding of deer is routinely practiced such as in-winter systems and indoors it is likely that young animals will not compete equally for feed with adult animals and their growth and development will not be optimal unless they are managed separately to adult stock. However, under extensive pastoral conditions where access to feed is not a limiting factor, where the mating policy involves joining a number of breeding bucks with the total breeding herd, and where reproductive performance data are not routinely recorded, separation of sub-yearling animals can take place in late winter/early spring without apparent production consequences.

There is little evidence in fallow deer to support the notion that either pre-rut weaning or post-rut weaning leads to improved reproductive management, if feed is available and disease or husbandry and management do not create stress that compromises growth and development in fawns or reproductive performance in does. Seasonal conditions and production targets should therefore dictate when weaning takes place under pastoral conditions.