Beef Cattle Reproduction and fertility of males and females

Introduction

Fertility is the most important economic trait in beef cattle. The recording and use of reproductive traits are of major importance in beef cattle breeding because they are directly connected with the birth of animals and the cycle in which animals are born. Environmental effects have a significant impact on reproductive performances, for example season of breeding and diseases. Fertility also can be influenced by management, for example, grouping of calvings and the ability of the breeder to detect oestrus and the system of production. Management treatments which increase the growth rate in growing animals or the production levels in high production cows can also greatly influence fertility.

Some reproductive traits are simple attributes of an individual animal (i.e. age at puberty, gametes production) and others are complex traits because they are related to reproductive peculiarities of the female, the male and the embryo or foetus (i.e. conception, production of a developing embryo).

Basically, most male and female reproduction traits are physiological traits recorded on the animal (sperm production in bulls and oestrus or pregnancy in females) and calculated traits from life history records as for instance dates and outcome of breeding. Calculated traits from recorded life history information provide ages at various stages of the reproductive cycle and facilitate the calculation of time intervals between various reproductive stages. This information also facilitates the calculation of conception rates.

Male reproduction

Male reproductive performances can be assessed by traits measured on the male itself (semen production and libido) or by the outcome of breeding recorded in mates (conception rate). Moreover, AI bulls also can be genetically evaluated for any sex-limited fertility traits recorded on their female’s relatives (e.g. age at calving, calving interval).

With AI bulls all that is required is a source of fertile sperm and with natural service bulls, libido and mating ability are most important.

Furthermore, some experiments show that male reproductive traits are genetically related to female reproduction and to body growth. For example, testis size is related to age at puberty and ovulation rate of female’s to body weight in the male.

Semen production

After collection, semen can be examined generally and microscopically and quantity and quality assessed by measuring or by scoring several criteria. These examinations include the volume of ejaculate, the spermatozoa concentration, the proportion of live spermatozoa, the sperm percent forward motility, the proportion of spermatozoa with morphological abnormalities and the semen freezeability. Procedures for semen evaluation have been developed by the Society of Theriogenology (www.therio.org). Semen examination can facilitate the calculation of age at puberty. After semen processing, the number of straws produced in a specified period can assess the bull’s fecundity.

Moreover, it has been established that total sperm cells production, testicular size and scrotal circumference (SC) are highly correlated in young bulls. Therefore, SC can be used as an indicator of the sperm producing capacity of a bull until about 5 years of age. SC varies with the bred, size and age of the bull. Yearling bulls of different breeds have SC of about 30-36 cm.

Recording Scrotal Circumference

1. Recorded Scrotal Circumference
2. The Scrotal Circumference (cm) should be taken at the largest diameter of the scrotum with a flexible tape placed around the scrotum after both testicles has been positioned beside each other in the scrotum.
3. Calculated yearling Scrotal Circumference Adjustment should be done by breed for age or weight. Adjusted 365 days SC = actual SC + (365 – days of age) x breed adjustment factor.

Sexual behaviour

The male reproductive behaviour is of particular importance in natural service, but the hereditary component of these traits should not be disregarded in AI.

1. Recorded behaviour traits
2. Libido or sex drive: defined as the “willingness and eagerness” of a bull to attempt to mount and service of a female. A libido score system has been developed to assess both sex drive and mating ability (Chenoweth, 1981)
3. Mating ability: the physical ability of bull to complete service
4. Serving capacity: a measure of the number of services achieved by a bull under stipulated conditions and thus includes aspects of both libido and mating ability (Blockey, 1976, 1981).

Calculated conception rates/breeding index

The conception rate and breeding index are calculated from the outcome of a single breeding, i.e. whether a female conceives (code=1) or not (code=0) or whether a zygote develops into an embryo or not. The outcome of a single breeding can be assessed at different times of the gestation cycle according to the methods of pregnancy diagnosis applied. When recorded on female mates, conception rate may be a practical measure of the fertilizing ability of the sperm cells and as such can be regarded as a fertility trait of the service bull.

To avoid dependencies or complications associated with successive inseminations (variation in cow fertility owing to the rank of oestrus, use of fertile bulls or natural mating for the second and latter mating, varying payment systems related to repeated AI services) only the first inseminations should be used as valid records.

Recorded traits

1. Breeding index: number of matings / conception, gestation or calving.
2. It is of practical use only when the same (only one) bull is used to breed each cow and to obtain a conception, gestation or calving.
3. Conception rate after first breeding: proportion of cows, a bull had been mated to or inseminated with one bulls semen, which conceived or was pregnant at a defined stage of gestation or subsequently calved (calving rate).

Calculated non-return rates (NRR)

Non-return rate (NRR) is a particular expression of conception rate mainly used in AI industry. NRR is based on the observation that a bred/mated cow has not returned for another service within a defined number of days. In order to facilitate the understanding of the NRR and to facilitate the harmonization of calculations between countries, ICAR recommended a precise description for the expression of NRR. The real value of the non-return rates is to the artificial insemination industry since they can be calculated on a large number of inseminations.

In AI, non-return rates are usually calculated as an index of the fertility of the bulls and the efficiency of the inseminators. These indices are based on the assumption that a cow is pregnant to first insemination if she has not been submitted for a second insemination within a specified interval.

Non-return rate generally overestimate the calving rate due to loss of cows from the herd (sale, death), to embryonic or foetal loss, to failure to detect any subsequent heat and also returns to service that occur later than the specified interval. Furthermore, in some cases up to 10% of pregnant cows may show signs of behavioural oestrus.

Refer to Section 6 of the ICAR Guidelines for the expression on non-return rates for the purposes of AI organisations.

Non-return rate after first insemination (NRR) is the proportion of cows inseminated for the first time during a given period of time (such as a month) that have not been recorded as having returned for another service within a specified number of days, and so are presumed pregnant.

Only first inseminations should be considered. This means that first insemination to breed a heifer or first insemination to breed a cow after the end of each pregnancy should only be used

The interval within which the cows are observed for return after insemination should be specified (e.g. 56 day NRR).

The females with short returns only, can be considered either as non-returned females and are as such considered pregnant (included in the calculation) or alternatively as non-inseminated females (and excluded from the calculation).

As a recommendation, short returns, within 3 days after Ai, should be considered like non-inseminated females and both limits of the considered interval should be indicated (e.g. 3-56 day NRR) and these limits should be inclusive. Any other chosen option should be mentioned.

NNR Trait Details

1. The NRR related to the date of each AI Each of n cow inseminated for the first time within a specified period is observed for return during the same interval (3-24, 18-24) after the date of each AI.
   • Recommended ICAR NNR expression
   • Specified period’ (n=): ‘start of interval’-‘end of interval’ = day NRR
2. The 60 to 90-day NRR The cows inseminated for the first time within a specified month are observed for return during a 90 days interval from the first day of the month of insemination. In this case, the cows inseminated the first day of the month of insemination will have 90 days in which to be recorded for a subsequent service, while those inseminated the last day of the month of insemination will have only 60 days??
3. Additional information to record
   • The specific period in which cows have been inseminated.
   • The number of females inseminated for the first time, (n=).
   • The treatment of cows with short returns, either like non-returned and pregnant (included in the calculation) or like non-inseminated (excluded from the calculation).
   • The return interval this side of which a return is considered short return, the start of interval in the expressions given above.
   • The interval during which the returns for another service have been recorded after the first insemination.
   • Factors which NRR have been corrected for such as parity and season.

Additional information about the male

In order to identify the reproduction and the environmental effects, which have an impact on reproductive performances of both male and female, some additional information related to the male, should be recorded. Some additional information about the mate to which the mating is made may also be pertinent to the reproductive performances of the bull (see additional information about the female).

1. The mode of fertilisation (artificial insemination with frozen or fresh semen, natural ating).
2. In case of artificial insemination
   • Semen processing (e.g. dilution) in case of AI.
   • Date of semen collection, collection or ejaculate identification on straws.
   • AI by an inseminator or by Do It Yourself (DIY).
   • Identification of the inseminator.
   • AI day of the week.
   • Time interval from heat detection until AI completed.

Female reproduction

The female reproductive performance refers not only to her capacity to produce developing embryos but also to her capacity to give birth to a live calf and to ensure a proper postnatal maternal environment for normal calf growth. Female reproductive traits include fertility traits calculated from life history dates and from the outcome of lifetime events such as breeding, pregnancy, parturition and weaning. Furthermore, sires breeding values can be predicted from most female reproductive traits recorded on relatives.

It should be recognised that some reproductive traits depend on the farmer’s arbitrary decisions such as breeding dates or culling decisions.

Oestrus / Breeding / Conception / Calving dates

The recording of reproductive life history dates in respect of each cow allows for the calculation of the ages at various reproductive events and time intervals between reproductive stages.

Important events include:

1. Date of heifer first oestrus (puberty).
2. Dates of first oestrus postpartum.
3. Breeding dates:
   • Date of first breeding in heifer or dates of first breeding postpartum in cow. This date is needed to calculate NRR.
   • Date(s) of subsequent or repeated AI.
   • Dates of observed natural mating.
   • Pasture natural mating exposure dates (start and end of breeding season).
4. Fertilizing breeding date, conception date. If several consecutive breeding or matings occurred, the last breeding date before calving is considered as the conception date. Moreover, the last breeding identifies the putative or assumed sire of the calf. The last breeding date should be compatible with the gestation length.
5. Calving date as a trait of the female.

Calculated ages at various reproductive events

Many ways of calculating ages and intervals as measures of reproductive performances are reported. In order therefore to provide a comprehensive picture of the trait, the details of the animals involved and of the elements included in the calculation are required.

1. Age at puberty.
2. Age at first breeding (in days or months).
3. Age at first successful breeding (in days or months).
4. Age at first calving (in days or months).
5. The first calving of the animal should be checked against normal biological criteria and with reported calving number.
6. Age at nth calving (in days or months).

Calculated interval between various reproductive events

1. Calving to first oestrus postpartum interval (days), measures the precocity of postpartum oestrus cycle resumption
2. Calving to first breeding interval (days)
3. Calving to conception interval (days open), can be computed for previous breeding cycles (days)
4. Interval between services, assessment of the current breeding efficiency (days)??
5. Calving interval, the calving numbers involved should be specified, it can be computed for previous breeding cycles (days). Calving events have to be consistent with calving number.
6. Average lifetime calving interval. This is the number of days between first and last calving divided by the number of calving (days). The number of the last calving should be specified.
7. Average days to calving = days from bull in to calving when pasture natural mating exposure is practised during a breeding season
8. Gestation length. The number of days between known conception date and subsequent calving date. In case of several consecutive breeding the last one is considered to be the conception date.

Pregnancy diagnosis, recording of the result of a breeding in female

The pregnancy diagnosis allows the determination of the outcome of a mating, its success or failure can be recorded as a binary trait (pregnant = yes not pregnant = no).

1. Methods of pregnancy diagnosis:
   • Observation of failure to return to oestrus in a specified return interval (e.g. between 18 and 24 days after breeding).
   • Palpation of ovaries, persistence of the corpus luteum (day 18-24).
   • Progesterone essay (at day 24).
   • Palpation of amniotic vesicle (from day 30-65).
   • Ultrasonic method to detect the embryo (from about day 20), (see Kastelic et al., 1988)
   • Calf birth.
2. The date of pregnancy diagnosis

Calculated conception rates or indices

Conception rate calculated from the outcome of a mating (whether a cow conceives or not), can be a measure of her capacity to ovulate and to produce a properly fertilizable ovum and her capacity to complete the implantation of the conceptus. As such, conception rate can be regarded as a fertility trait of the female. Moreover, conception is little if any influenced by the farmer because once he decided to breed a cow, success is always the desired outcome. As a female trait, conception rate can also be used to genetically evaluate sires.

Given hereafter are the basic definition of the main conception rates and indices used, but there are various ways of calculating such conception rates and indices. So it is important to define clearly the animals involved in numerator and denominator, the time or the interval at conception diagnostic from breeding date and the breeding number.

1. Female breeding index: number of matings / conception or gestation or calving. This measure of female fertility is often influenced by farmer’s decisions, for example elite cows may be bred more times than other ones that are likely to be culled earlier.
2. Number of calves produced per cow and per year at herd level

The outcome of a single breeding can be assessed at different times of the gestation according to the method of pregnancy diagnosis applied. So conception rate should be calculated at a defined day or interval from the date of breeding and could be calculated at the herd or progeny group level. The breeding ranks and parities also should be recorded.

1. Conception rate: proportion of cows bred in a herd or in a progeny group, which conceived or was pregnant at a defined stage of gestation (day or interval) or which calved (calving rate).
2. Non return rate at a given interval (see guidelines from ICAR for calculations NRR in male reproduction section).

Number of calves per gestation, prolificacy

The number of calves per gestation is important in so far as it may affect calving mode, birth weight, weaning weight and growth during pre-weaning period. Moreover, in the case of suckling of both twins by the mother pre-weaning growth and maternal ability assessment also are influenced.

1. Code for number of calves: (1) single calf, (2) twins, (3) triplets or more.
2. Additional information: suckling of both twins by the mother or fostering of one calf or artificial rearing of one or both. When prolificacy is a trait of interest, the number of embryos, foetuses or calves could be an indicator of the ovulation rate for one oestrus cycle but dizygotic twins should only be considered. Blood groups or DNA polymorphism can assess the zygotic status. Dizygotic twins are considered full sibs.

Additional information about the female

To define at best the management of reproduction and the environmental effects, which have an impact on reproductive performances of both male and female, some additional information related to the female, should be recorded. Some additional information about the male is also pertinent to the reproductive performances of the cow (see additional information about the male).

1. Time of service with respect to the onset of oestrus.
2. Mode of oestrus detection (visual, devices, teaser bulls).
3. The hormonal treatments of the dam if any (induction of oestrus).
4. The previous calving mode of the dam.
5. The postpartum pathology of the dam (metritis, retained placenta).
6. Fertility problems in the dam (anoestrus, anovulation, ovarian cysts).
7. Cow disposal for infertility / sterility in case of unsuccessful breeding.
8. Type of calf rearing (suckling calf or fostering of the calf or artificial rearing), which may affect the moment of the resumption of oestrus cycles postpartum. Suckling delays the onset of postpartum oestrus.
9. Abortion.

Mothering aptitude (see temperament/behaviour)

The maternal behaviour may affect the viability of the calf and can require fostering.

1. Production trait, the milk yield the cow produces to allow pre-weaning growth of the calf, usually assessed by the weaning weight.
2. Behavioural trait of the mother towards her calves, i.e. the way the mother takes care of her calves after birth.

Embryo transfer and ovum pickup

In some breeds, Multiple Ovulation and Egg Transfer (MOET) is used as a breeding technique or/and in selection program. Ovum Pick Up technique (OPU) is an alternative source of cattle embryos that required in vitro maturation of oocytes and their in vitro fecundation and culture to the stage of blastocyst before egg transfer.

In order to fulfil the standard data for an animal and to properly use records, the following information should be recorded:

1. Identification of the embryo and of its genetic parents.
2. Date of transfer.
3. Coding of the calves produced by egg transfer.
4. Identification of the recipient cow.
5. Coding of donor and recipient dams to identify cows which did not raise a natural calf.

To specifically analyse the efficiency of the multiple ovulation technique, the traits to be recorded are:

1. Number of unfertilised oocytes/flushing.
2. Number of degenerate embryos/flushing.
3. Number of transferable embryos/flushing. Moreover some environmental factors may influence the results and particular information should be recorded in the donor cow including the multiple ovulation treatment used and date, the dates of AI and of flushing and the identification of the technician. As for the result of the egg transfer, the following information should be recorded:
   1. The date of eggs transfer.
   2. The mode of transfer as fresh or thawed embryos.
   3. The type of oestrus of the recipients as natural or by hormone treatment and
   4. The identification of the technician.

   Calving ease or difficulty, calving mode

   Difficult calvings lead to increased calf and cow mortality and could impair the health of the calf, the health of the dam, her subsequent fertility and her production performances.

   Dystocia can be of maternal or foetal origin.

   Maternal factors are:

   1. Anatomical or pathological defects in the pelvic canal (variation in pelvic opening area, pelvis immaturity, and fibrosis of the reproductive tract).
   2. Insufficient preparation for parturition or expulsive contractions.

   Foetal factors are:

   1. Oversize (relative, absolute or pathological).
   2. Faulty position.
   3. Dead calf.
   4. Twinning.

   For breeding purposes, the most relevant causes of dystocia are oversized calf and narrow pelvic area in relation with dam’s age. The presence of a veterinarian at calving is not necessarily associated with these causes, but may have been requested for any of the other causes of dystocia. So the description of a calving mode class by the veterinary assistance is meaningless in so far as breeding is concerned.

   Recommended codes for calving mode or ease

   1. Easy calving without assistance
   2. Easy calving with some assistance
   3. Difficult calving (hard pulling, assistance by 2 or more persons, mechanical assistance)
   4. Caesarean section
   5. Embryotomy

   Other additional information to be recorded: calving date, parity and age of the dam, sex of calf, calf presentation at parturition, twinning, breed of dam and ID of dam.

   Birth weight

   The most common cause of dystocia is foetal oversize and the most interesting cause in connection with the breeding ability of the sire for calving ease is the birth weight.

   Pelvic opening

   Most calving difficulty or dystocia occurs in first-calf heifers. Research indicates that disproportion between calf size (birth weight) and size of the female pelvic inlet (pelvic area) is a major contributor to calving difficulty. As a result, the yearling pelvic measurements can be used as a culling tool to reduce the potential incidence and severity of calving difficulty among first-calf heifers.

   1. Pelvic measurements:
      • Sacropubic (vertical) diameter (cm).
      • Transilial (horizontal) diameter (cm).
   2. Calculated pelvic area (cm2) Estimated pelvic area is the product of vertical and horizontal measurements
   3. Yearling calculated pelvic area Pelvic measurements should be taken between 320 and 410 days of age and adjusted to 365 days of age to accurately evaluate yearling bulls and heifers. BIF proposed formulas for male and female (see annex calculated traits definition), but the adjustment should be breed specific.

   Mortality from birth

   The time of death can be recorded as date or/and code. Generally, the codes are connected to live history events (birth, weaning, post-weaning) or to time period from such events which should be specified. The usual times of death are given hereafter.

   1. Date of death
   2. Code for time of death:
      • Stillbirth, still-born: dead-born full term.
      • Death during parturition.
      • Perinatal death generally defined as death within first 48H.
      • Death within a specified time from birth.
      • Death in any specified interval.
      • Death after weaning.

   From those records, various mortality or viability rates can be calculated, so the animals involved in numerator and denominator and the time or the interval from lifetime event considered should be clearly defined. These rates also could be calculated at herd or sire levels and separated according to different causes of mortality that should be specified.

   1. Calculated calf mortality rate Dead calves, within a time period or towards a defined event, as a % of cows exposed, pregnancies, calvings or calves born alive
   2. Calculated viability rate Alive calves, within a time period or towards a defined event, as a % of cows exposed, pregnancies, calvings or calves born alive
   3. Weaning rate: proportion of calves weaned for a specified denominator
   4. Causes of mortality:
      • Congenital defects.
      • Dystocic calving.
      • Accident.
      • Disease (respiratory, digestive, infectious, metabolic….).
      • Other.

   Disposal from birth

   The time of disposal can be recorded as date or/and code. Generally, the codes are connected to live history events or time period from such events that should be specified.

   1. Date of disposal.
   2. Code for time of disposal.
      • Postnatal, preweaning, postweaning, other.
   3. Causes of disposal. There are numerous causes of disposal, which can vary from one production system to another. So, an exhaustive list of causes is difficult to establish. Moreover breeders may decide upon an animal‘s disposal based on more than one reason. On can generally classify these causes into voluntary and involuntary decision of the breeder.
      • Voluntary: sale for fattening, sale for breeding, sale for slaughtering.
      • Involuntary: culling for defects, diseases, infertility, sterility, production deficiency, mothering ability, temperament, other.
   4. Calculated age at disposal, at culling. From those records, various disposal statistics or rates can be calculated, The animals involved in numerator and denominator, the time or the interval from lifetime events should be clearly defined. These rates also could be calculated at herd or sire levels and separated according to different causes of disposal that should be specified.
   5. Calculated rates of disposal, for a specified type of animals at a specified age or event or within specified period.