Freemartins in Cattle
Australian Cattle Veterinarian, Spring 2013
Leo Cummins, “Ivanhoe” Bulart Bridge Road, Cavendish Vic.
Freemartinism in cattle is a condition which worries many beef producers when discussing twinning. In my opinion, the problem is overrated, since it can be dealt with relatively easily and should be more than compensated for by the extra productivity of a herd which is producing a significant proportion of twins.
Freemartins arise when vascular connections form between the placentae of developing heterosexual twin foeti, and the result is masculinisation of the female tract to varying degrees. Where mixed sex twins are born, then 90 to 95% of the females are likely to be freemartins. This does not reduce the total number of fertile replacement heifers available in the herd. 25% of the twin births will be 2 females, 25% will be 2 males and 50% will be 1 male and 1 female. The final result will be that a twinning herd has potentially the same number of replacement heifers available as a herd of single births.
In freemartin heifers, the ovaries fail to develop and remain small, typically about the size of a barley grain (0.2 – 0.4g) and are composed of both ovarian and testicular tissue, although most ovarian characteristics such as follicles are lacking. The rest of the genital tract including the vagina is markedly arrested in development. Seminal vesicles are often present. The vulva is usually fairly normal except for the occasional presence of a prominent clitoris and a large tuft of vulval hair. The absence of a cervix is a consistent finding in freemartins. Older freemartins will tend to have a small udder and teats and may develop slight secondary sex characteristics of males (eg a slightly thickened neck). Essentially, the vast majority of freemartins cannot be detected by normal external visual inspection. Rectal examination will reveal the underdeveloped reproductive tract. A fairly definitive simple test is to insert a smooth round ended rod into the vagina, the freemartins being half the length or less of normal heifers. A normal young female calf will have a vaginal length of 13 -15 cms and freemartins up to 30 days only 5 – 8 cms long, while normal yearlings are 25 – 35 cms and freemartins only 8 – 15 cms. When using a rod, make sure it is large enough so that it does not cannulate the urethra, as can sometimes happen when using an AI pipette to measure this.
Single born freemartins are considered to be quite rare, at least partly because the death of one twin in utero usually results in the loss of both foetuses because of the conjoined placentae. There are some reports of single born freemartins. In the “Ivanhoe” herd we have found several freemartin single born calves and a set of female twins which were freemartins (presumably due to a triplet conception with a male calf lost during pregnancy)
Freemartin heifers need to be removed from the breeding stream and placed in the slaughter stream. The absence of the anabolic and metabolic effects of the gonadal steroids on muscle and fat development is evident in the carcass of the freemartin. Increased marbling in the longissimus muscle resulted in a higher percentage of them grading USDA choice or above. Table 1 shows some data from USMARC twinning herd in Nebraska. In this, the steers from the twinning herd were also compared with MARC III composites mated to Simmentals (ie. 1/2 Simmental, 1/8 Hereford, 1/8 Angus, 1/8 Red Poll, 1/8 Pinzgauer cattle) as a reference group.
Table 1 (from Gregory et al 1996) Growth and Carcass information from the USMARC Twinner herd.
Note; wts are in Kg, ADG = average daily gain Kg/d, fat depth= cms at 12th rib, REA = longissimus muscle area cms, KPH = perirenal fat, Retail product =kg estimated retail product after removing all subcutaneous and accessible intramuscular fat and bone and adjusting to 20% fat. USMARC = US Meat Animal Research Center, Nebraska.
|150 d wt||184||199||192||190||164||168|
|200 d wt||240||259||249|
|365 d wt||365||335||340|
|Slaughter age d||439||439||439|
|ADG birth to slaughter||1.22||1.27||1.26||0.86||0.84||0.84|
|> USDA choice||65.3||75.6||75.3||80.2||76.6||90.6|
This shows that twins (including freemartins) are suitable for slaughter. In this US data, the adjusted daily gains from birth to slaughter for steers (single and twin) are not different, and similarly for heifers (single, normal twin and freemartin).The actual age of slaughter (at the same end weight) for twins is often 2 to 3 weeks later than singles because at USMARC they were 10% -20% lighter at weaning. In our experience (both research and commercial) at Hamilton, twin born calves were 20% lighter at weaning than singles but experienced some compensatory growth post weaning. Producers successfully producing twins will have weaning weights per cow of 160 – 170% compared to those weaning singles. Producers buying cattle to finish should not be penalised because the twins are slightly lighter at weaning, provided they take this into account in pricing. The higher percentage of USDA choice or better in the freemartins may be a significant bonus.
The vascular connections between the placentae of developing heterosexual twin foetae cause the development of XX/XY chimerism in both offspring, due to exchange of hemopoietic stem cells and the masculinisation of the reproductive system of the female twin foetus by hormones from the male foetus (androgens and anti-Mullerian hormone). New diagnostic methods based on the detection of Y-chromosome DNA segments by PCR may improve the sensitivity and efficiency of detection of freemartins. Chorionic vascular anastomoses start about day 35 and are reported to be well developed by day 39 of gestation. This is several days before sexual differentiation starts and which occurs earlier in the male than the female. Karyotyping of lymphocytes has frequently been used for the laboratory based diagnosis of freemartins. This chimerism results in the ability of these heterosexual twins to accept reciprocal skin grafts. In a study of bulls born co- twin with a freemartin (Dunn et al 1979), the proportion of XX cells in the blood varied from 5 to 95% and for each bull this proportion was stable over several years. In this study there was no association with the proportion of XX donor blood cells and the reproductive fitness of a chimaeric bull. Similarly the XX:XY blood lymphocyte ratio was not related to the degree of mascularisation of the freemartin heifer’s reproductive organs.
The effects on the fertility of a male of being born co-twin to a freemartin have been debated. One possibility considered was that XX cells might become established in the spermatogonia, hence resulting in the possibility of more female offspring from that bull. This appears not to be the case. The other possibility is the fertility of these bulls may be reduced. In one study where XX/XY chimerism was demonstrated on lymphocyte karyotypes, a higher proportion of chimeras were culled because of poor fertility than normal controls, however chimeras which were fertile were similar to the breed average in the AI centre. In a literature review, Long (1979) suggested that provided the semen is normal, there is no reason why a bull born co-twin to a freemartin should not be used for breeding. In the USMARC twin selection program, no difference has been observed in reproductive performance of young bulls born co-twins with freemartins and normal bulls.
One of the limitations of twinning in cattle is the fact that migration of embryos between the uterine horns is rare. However the placenta will grow and attach in the contralateral horn, thus with twins in cows, uterine overcrowding is only of minor concern, but this may be more important in heifers. When there were bilateral twin ovulations rather than unilateral, this decreased dystocia rate and increased calf survival. It is perhaps worth noting that obstetrical problems in cows with twins seemed a little lower in the MRC sponsored research at Hamilton and Grafton where twins were induced by supplementary embryo transfer to the contra-lateral horn (i.e. causing all bilateral pregnancies) than in the USMARC data. Bilateral pregnancy might also decrease the incidence of freemartinism slightly. The long term selection program at USMARC has increased the ovulation rate on both ovaries, but the right one still remains slightly more active. More interestingly, this selection has slightly increased the proportion of bilateral twin ovulations (now up to 55% of twin ovulations are bilateral). Understanding how further increases in bilateral twin ovulation could be achieved, while limiting triplet ovulations, should be beneficial.
While freemartinism in cattle is the norm, isolated cases have been reported in other species including sheep, goats and pigs. In sheep, its incidence may be increasing due to increasing fecundity. We reported an incidence of around 5% freemartinism in ewe replacements (actual litter distribution of these individuals unknown) from sheep flocks segregating for the Booroola gene where around 40% of the ovulations were triplet or more.
Summary: Twinning cattle need to be more carefully managed at birth than normal single bearing cattle as they may need calving assistance and/or mothering assistance for the first 1 -3 days. This means that pregnancy diagnosis of twinning is probably desirable and may need to be done between day 35 and days 80 – 90 by ultrasound. For intensive beef producers, the calving observations are similar to that required by many normal first calf heifers although the level of intervention may be higher. Thus, in many instances, in a herd where twins are expected, sex can be recorded at birth. Freemartinism is likely to affect 90 – 95% of the heifers born co-twin with a bull. Where birth records are not kept or a confirmation check is required, then simple measurement of vaginal length can be done at any age. Either of these 2 checks can be easily done by the farmer and should be sufficient to move the vast majority of freemartins into a slaughter category at a convenient age. There are more precise laboratory tests available, but these should not be required in twinner herds for beef production. Confirmation of potential reproductive status by rectal palpation can also be carried out, and for normal beef operations where the twinning rate is very low, this is all that is required. Freemartin heifers are very suitable slaughter animals for beef production. Bulls born co-twin to freemartin heifers should be suitable breeders provided they can pass a routine breeding soundness examination.References: This report has relied heavily on the twin selection work at USMARC, Nebraska and several other major reviews.
- Cummins (1994) “Beef Cattle Twinning” (ASAP contract) Proceedings of the Australian Society of Animal Production 20, 27-36.
- Cummins, Wright and Keiller (1997) “Observations on ovulation rates and the incidence of freemartins in a flock segregating for the booroola gene” Proceedings of 4th International Congress for Sheep Veterinarians, Armidale, pp 422-423.
- Cummins, Morris & Kirkpatrick (2008) “Developing twinning cattle for commercial production” Australian Journal of Experimental Agriculture 48, 930 – 934.
- Dunn, McEntee, Hall, Johnson and Stone (1979) “Cytogenetic and reproductive studies of bulls born co-twin with freemartins” Journal of Reproduction and Fertility 57, 21-30.
- Echternkamp (1999) “Freemartin” Encyclopedia of Reproduction (Knobil and Neill eds) Vol 2 Academic Press pp 406 – 417.
- Echternkamp and Gregory (2002) “Reproductive, growth, feedlot and carcass traits of single and twin births in cattle” Journal of Animal Science 80, 1 – 10.
- Long (1979) “The fertility of bulls born twin to freemartins” Veterinary Record 104, 211-213.
- Padula (2005) “The freemartin syndrome: an update” Animal Reproduction Science 87, 93-109.