BRAHMAN NEWS JUNE 2012 ISSUE #175
BY ALEX ASHWOOD
The causes of infertility are many and complex and often involve a combination of factors.
Cattle are categorised as infertile when they are unable to deliver viable eggs/sperm or complete a pregnancy, or sub fertile when their reproductive ability is less than optimal. These conditions can be temporary or permanent.
The common forms of infertility in females relate to inadequate follicle development and maturation, unsuccessful oestrus onset, ovulation and fertilisation and impaired development and delivery of the foetus.
Bulls also have a wide range of morphological and functional factors that affect their reproductive soundness including poor service capacity, genitalia disorders and poor quality semen.
Anything that interferes or disrupts the normal reproductive processes such as disease, poor nutrition, inadequate feed and herd management, genetic disorders, hormonal disturbances and adverse environments can impact negatively on fertility and reproductive performance.
Optimising rather than maximising fertility is more realistic
Improving herd fertility takes time. Depending on the seriousness and level of infertility it can take up to 3-5 years to totally resolve some herd fertility problems.
This article looks at some of the common morphological and functional causes of infertility that reduce breeding performance and profits.
PROBLEM COWS
CONGENITAL CAUSES OF INFERTILITY
These are frequently inherited and include developmental abnormalities of the ovaries, oviducts, uterus, cervix and vagina. Some of these have morphological significance whilst others are functionally significant.
Common morphological issues include ovarian hypoplasia (underdeveloped), anomalies of the genitalia, hermaphraditism, (ie some male and female genitalia), free martinism and double cervix.
Most abnormalities can be avoided by using animals with normally developed sexual organs, avoiding inbreeding and implementing rigorous culling programs for infertility.
3-10 per cent of the herd may be culled due to reproductive disorders
FUNCTIONAL CAUSES OF INFERTILITY
Functional infertility includes anoestrus (lack of visible heat), abnormal oestrus and early embryonic mortality resulting in repeat breeding and extended calving intervals.
Functional infertility is generally more common than infertility due to congenital causes.
CYSTIC OVARIES
A key cause of anoestrus is cystic and inactive ovaries.
Sometimes the corpus luteum (yellow body) persists beyond its usual life expectancy. If the “persistent” corpus luteum also has a fluid filled cavity it is referred to as a cystic corpus luteum. This is one form of the so called “cystic ovary” conditions.
Cystic ovaries contain one or more persistent fluid filled cavities. Ovarian cysts can be classified as follicular and luteal and range in size from a ripe grape to the size of an orange.
The effects of cystic ovaries vary according to their number and degree of lutenisation.
Follicular cysts are follicle like structures more than 2.5 cm in diameter and persist on the ovary for more than 10 days. They grow in a disorderly manner, fail to regress and accumulate with fluid. Since there is no ovulation such cows are infertile until the situation is corrected and normal
cycles resume.
Many unlutenised follicles tend to lead to extreme oestrus behaviour (nymphomania) with frequent irregular heats. Often the heat periods are extended and the cows mount others and stand for mounting showing extensive vulva oedema and copious amounts of mucous.
Often called ‘bullers’ because of persistent
homosexual tendencies
Follicular cysts may regress but should they persist it may be necessary to discuss therapeutic options with your veterinarian.
Luteal cysts are less frequent than follicular cysts and continuously produce progesterone rendering the cow anoestrus (no heats).
Cows with extensively lutenised cysts become infertile
Luteal cysts are difficult to differentiate from follicular cysts and is a further reason why it is necessary to seek proper diagnosis and treatment by your veterinarian.
Events in the hypothalamus, anterior pituitary and various target organs (eg ovaries) appear to be involved in the development of cystic ovaries. Generally there is an increase in the level of follicle stimulation hormone (FSH) and a reduction in lutenizing hormone (LH) which results in a failure to ovulate.
There is a reported genetic predisposition to cystic ovaries with estimates of heritability ranging from 0.05-0.43.
In some herds with the problem the occurrence of repeat breeders can range from 1-13 per cent.
The incidence of cystic ovaries tends to increase with age thus in low generation interval herds the likelihood of the problem increases.
Cows with endometritis and/or metritis (forms of uterine wall inflammation) and those with retained placentas have a higher incidence of cystic ovaries than healthy cows.
Other factors influencing the incidence of cystic ovaries include prolonged intervals from calving to first detected oestrus and the time period between oestrus and conception indicating the importance of good reproductive management.
Studies suggest that there may be a close association between cystic cows and certain herd mates which can increase “bulling” behaviour.
Herd & nutritional management can affect the incidence of cystic ovaries
NUTRITIONAL ANOESTRUS
Temperate (eg clovers) and subtropical-warm temperate legumes (eg lucerne) contain phytoestrogens that may reduce fertility. There is limited knowledge on the oestrogenic properties of tropical legumes.
Cows with normal ovaries can show anoestrus
Nutritional stress can be a major problem in some subtropical and tropical environments. Inadequate feed quality and quantity (or both) and low body condition pre and post calving frequently delay the onset of oestrus and normal ovulation.
Underdeveloped heifers is a key contributing factor to herd anoestrus. The ovaries may not be completely active and the reduction of oestrogen secretion may result in underdevelopment of other genital organs and the endocrine system.
POST PARTUM ANOESTRUS
Retention of foetal membranes and subsequent post partum metritis is a frequent cause of anoestrus and sub fertility. These conditions damage the endometrial lining of the uterus and reduce the secretion of luteolytic prostaglandin. The cyclic activity of the ovary is thus often interrupted and the cow or heifer may show anoestrus or return to service until the condition is corrected.
LACTATIONAL ANOESTRUS
Postpartum anoestrus is longer in high producing Bos indicus cows and heifers and is often associated with reduced feed intake and availability relative to milk production and condition score. This is a survival technique, so in times of low nutrition, the cow puts her resources into calf survival rather than a new pregnancy.
Depressed cycling and conception is due to suppressed growth of the follicle and restricted ovulation.
In the short term improved management (eg supplements) may not improve the situation in early lactation (up to 120 days) since the cow/heifer may produce more milk and not gain body condition until mid-late lactation. With stock with low condition score stock may not cycle until the calf is weaned.
Herd management strategies including early weaning, temporary weaning and restricted suckling are dependent on how economically the calves can be reared as well as the incorporation of efficient calf management programs to allow adequate growth.
Early weaning can be useful during periods of extreme feed shortage or when feed quality is exceptionally low. It allows the cow/heifer to recover body condition and reconceive. Early weaning at 3 months compared to 7 months has been shown to increase weight gain of the dam and reduce post partum anoestrus.
Temporary weaning at 40-50 days post partum has been shown to provide mixed results. Oestrus may or may not occur and sometimes the oestrus is short and pregnancy may not be obtained.
Partial suckling at 60 days encourages an earlier oestrus and conception. Table 1 shows the reproduction performance of restricted v’s continuous suckling of Bos indicus cows.
Whilst calves can be weaned at 8-12 weeks the stock generally require increased herd and feed management involving good yard facilities, high quality roughage and energy/protein supplements.
GENETIC FACTORS
Heritability rates for fertility, conception and calving are low (0.15-0.25) which demonstrates the importance of herd and feed management.
Outbreeding improves fertility rates whilst inbreeding reduces fertility rates. At an inbreeding coefficient (ibc) of 7 per cent there is only a small effect of inbreeding but at ibc levels of 12 per cent and above, calving intervals and are markedly longer and the number of services for conception higher.
TABLE 1 : effects of restricted v’s continuous suckling on post partum reproduction performance
| ONCE-A-DAY SUCKLING | CONTINUOUS SUCKLING | |
| Cows in oestrus by 60 days postpartum (%) (P<0.005) | 57 | 29 |
| Cows in oestrus by 90 days postpartum (%) | 74 | 63 |
| Conception rate (%) | ||
| At 60 days (P<0.005) | 31 | 12 |
| At 90 days | 61 | 44 |
| Anoestrous period (d) (P<0.05) | 57.1 + 4.19 | 72.24 ± 4.35 |
| Service period (d) (P<0.05) | 71.42 + 3.72 | 82.27 ± 3.80 |
SEASONAL FACTORS
Extended calving intervals due to delays to first service (days open) is frequently caused by low feed intake, poor feed management and difficult seasons.
Seasonal influences dramatically impact on fertility
Days open should not exceed 80-85 days if a calving interval of 12 months is to be achieved. This requires re-establishment of ovarian activity soon after calving and high conception rates. Days open is influenced by nutrition, season, milk yield, condition score, uterine involution and generally, a combination of these factors.
OTHER FACTORS
Studies indicate that fertility increases up to 8 year old cows then declines rapidly after 10-12 years.
The cause of age related fertility disorders and anoestrus include lactational stress, poor feed intake (reduced grazing activity) and a shutting down of the endocrine system (bovine menopause).
PROBLEM BULLS
The function of the bull is to produce viable sex cells (spermatazoa) and deliver them to the vagina to fertilise the ovum released from the ovary of the cow. The male reproductive organs are shown in Diag 1.
DIAGRAM 1: REPRODUCTIVE ORGANS OF THE BULL
The fertilising ability of the bull is critical to determining the reproductive performance of the herd. Subfertile and infertile conditions occur in bulls due to a variety of morphological and functional disorders. The most common of these are discussed in the following section.
TESTICLES
Defective testicle development (hypoplasia) occurs in 1.5-2.0 per cent of bulls, although with insufficient culling and inbreeding the incidence in some herds can be higher.
The condition may be unilateral or bilateral and in the latter case the bull is likely to be subfertile. These bulls should not be used for breeding since the condition is usually permanent and has a hereditary nature.
Cryporchidism is the failure of one or both testicles to descend into the scrotal sac during foetal development. Although testosterone is produced, spermatogenesis (sperm production) is inhibited and these bulls are sterile. If only one testis descends (unilateral cryptorchidism) sperm production is seriously reduced and these bulls should be culled because the condition can be inherited.
Providing bulls are properly fed, total sperm production is correlated with the weight of the testes and the bull, thus mature bulls produce more sperm than young bulls.
The testes secrete testosterone which maintains the function of the male reproductive tract, male characteristics and sex drive.
Studies suggest that Bos taurus and Bos indicus bulls with a scrotal circumference of less than 30 cm and 28 cm respectively produce inferior semen especially if they have soft testicles.
Poor fertility from bulls with inferior sized testicles is mostly due to insufficient quantities of semen to service 40-50 cows.
The minimum size for Bos indicus bulls testicles
is 33 cm at 24 months
Because testis size is highly related to sperm production it is generally assumed that bulls with large testicles can be joined to more cows (Table 2). Whilst scrotal size is related to testes size, other factors such as feeding can affect scrotal size (eg highly fed bulls can increase scrotal circumference by 3-6 cm without increasing testicle size, fertility and service capacity).
Bulls that are underfed at puberty have low rates of testes growth and smaller testicles at maturity and lower fertility.
Within reason and taking into consideration the age/growth/condition of the bull, scrotal circumference can provide a guideline to mating loads to avoid low-marginal fertility rates (Table 2).
TABLE 2: the mating potential of bulls
| NO. OF FEMALES | SCROTAL CIRCUMFERENCE (CM) |
| 40 | 33 |
| 60 | 35 |
| 80 | 36+ |
Note:
- Other factors also need to be considered (eg age, libido, condition score, correct leg structure and structural unsoundness, size of paddocks, level of nutrition).
- Bulls with satisfactory to excellent semen quality provide similar levels of herd fertility.
- Bulls with adequately sized and positioned testicles which are firm and not “hard” or soft generally provide suitable levels of reproductive performance.
- Key semen quality factors include suitable morphology and motility scores.
- Servicing capacity should also take into consideration the elongation of testicles of Bos indicus bulls.
- Bulls should be in good not fat condition.
SPERMATAZOA
A variety of morphological abnormalities of sperm occur which can be associated with infertility eg detached sperm heads, coiled tails, immature sperm. Lack of use or overfed bulls frequently leads to abnormal sperm which is corrected by exercise, more frequent use and proper feeding.
It is not simply a matter of the number & motility of sperm produced
Recent studies indicate that overfed bulls even with apparently satisfactory crushside semen evaluations can have significantly lower successful matings. It is suggested that the semen of overfat bulls undergoes oxidative stress and DNA damage and is less likely to fertilise an egg.
Sperm DNA of overfed bulls
is packaged differently
PENIS AND PREPUCE
Prolapse of the prepuce is often due to congenital hypoplasia of the retractor muscles of the sheath (a condition more common in polled bulls) and often results in erosion and inflammation of the mucous membrane lining the prepuce and sheath.
Deviation of the penis may take a variety of forms (eg lateral, ventral and spiral deviations). Persistent frenulum which is the attachment of the penis inside of the sheath results in the deflection of the penis at erection and in serious cases the penis cannot be extruded or not enter the vagina properly. Although the problem can be rectified surgically these bulls should not be used for breeding purposes due to the possible hereditary nature of the condition.
Various conditions can make the extrusion of the penis painful and difficult, eg virus induced benign tumours and trauma induced ruptures of the tough membrane surrounding the penile tissue causing fibrous adhesions.
EPIDIDYMIS
This is a highly convulated sperm storage tube which is more than 30 metres long. It comprises of a head, body and tail which lie close to the testis (Diag 1).
During passage through the epididymis, the sperm mature. The time interval from this head to the tail is about 8 weeks. Thus, factors that adversely affect spermatogenesis usually become evident 2 months later. Sperm are not motile in the epididymis but become motile after ejaculation (an energy conservation mechanism)
BOTTOM LINE
Reproductive performance is crucial in determining the efficiency of a cattle enterprise. Unfortunately, it is quite common that herds are well below optimal levels due to slow and repeat breeders. The problem often takes some time to become evident, therefore early detection is critical in order to reduce losses.
Repeat breeders are those females that require several services to conceive and have extended calving intervals reducing calving and weaning rates. The problem is often caused by a number of factors which can quite often be complex and interrelated.
It is important that heifers and cows are well grown and in appropriate condition at mating, are appropriately vaccinated and are adequately managed (herd and feed).
Fertility in cattle is affected by genetic, environmental, disease and management factors. These factors influence the efficiency of reproduction processes at follicular development, ovulation, fertilisation implantation, gestation and parturition in females. The quantity and quality of semen and reproductive soundness in bulls is affected by the same factors.
Unless producers constantly monitor the fertility indicators of the herd, reproduction problems can be responsible for production losses through poor breeding performance and reduced calving rates.
Possible indicators of poor fertility include heifer growth and size, cow and bull condition and health, heat observations, returns to service, low pregnancy, calving or weaning rates and long calving intervals.
Proper diagnosis and treatment of herd infertility require good records and careful assessment
