Cloning cattle

Over the past six years, hundreds of apparently normal calves have been cloned worldwide from bovine somatic donor cells. However, these surviving animals represent less than 5% of all cloned embryos transferred into recipient cows. Most of the remaining 95% die at various stages of development from a predictable pattern of placental and fetal abnormalities, collectively referred to as the "cloning-syndrome." The low efficiency seriously limits commercial applicability and ethical acceptance of somatic cloning and enforces the development of improved cloning methods. In this paper, we describe our current standard operating procedure (SOP) for cattle cloning using zona-free nuclear transfer. Following this SOP, the output of viable and healthy calves at weaning is about 9% of embryos transferred. Better standardization of cloning protocols across and within research groups is needed to separate technical from biological factors underlying low cloning efficiency.     

Seasonality in cattle

Although cattle are basically not seasonal breeders, several physiological changes occur in response to two major climatic variables of season: ambient temperature and photoperiod. Ambient temperatures above 27°C lengthen the estrous cycle, decrease duration and intensity of estrus, decrease fertility and increase embryonic mortality. Some of these effects may be mediated via decreased secretion of luteinizing hormone and increased secretion of progesterone. Heat stress also suppresses growth rate, milk production and feed intake. In comparison with cattle exposed to less than 12 h of light per day, 14 to 16 h of light has relatively little effect on secretion of gonadotropins and fertility; however, growth rates, feed intake and milk yield are stimulated. Of all hormones measured in cattle, prolactin is the most responsive to changes in seasons, ambient temperature and photoperiod. Prolactin is greatest in summer when ambient temperatures are highest and photoperiods are longest.     

Significance of Neospora caninum in British dairy cattle determined by estimation of seroprevalence in normally calving cattle and aborting cattle

A case control study was conducted to evaluate the significance of Neospora caninum infections in cattle in England and Wales. The prevalence of N. caninum in normally calving cattle (the control group; n = 418) and aborting cattle (n = 633) was estimated using a commercial antibody-detection ELISA. Prevalence estimates for bovine virus diarrhoea virus, infectious bovine rhinotracheitis virus and Leptospira hardjo were also obtained by serology. The prevalence of N. caninum was significantly higher (P < 0.0001) in the aborting group (18%; 95% confidence interval: 15%, 21%) than in the control group (6%; 95% confidence interval: 4%, 8%); the latter is the first estimate, to date, of the national seroprevalence of N. caninum in dairy cattle in England and Wales. Prevalence estimates for bovine virus diarrhoea virus, infectious bovine rhinotracheitis virus and L. hardjo were not found to be higher in the aborting cattle than in the control group. With N. caninum, a strong association between seropositivity and abortion was found, with seropositive cows being 3.5-times more likely to abort than seronegative cows (odds ratio = 3.49; 95% confidence interval: 2.16, 5.69). Furthermore, 12.5% of abortions in dairy cattle in England and Wales may be attributable to N. caninum, as indicated by estimation of the population aetiological fraction.     

Superovulatory responses of cattle

Non-histological examination of superovulated ovaries of cows does not allow one to distinguish between corpora lutea and luteinized follicles. A better estimation of ovulation rate could, therefore, be made from the number of embryos recovered or from the levels of E₂-17β in the plasma 60 hours after PMSG.For comparison of different treatments, it is necessary to characterize activities of the stimulatory agents used. Administration of an FSH - LH preparation twice a day at decreasing doses gives the best mean responses, but no treatment has been found which can clearly decrease the large variation between individuals in their responses.Numerical, kinetic and endocrine ovarian factors can partly explain the variability of ovarian responses to PMSG in the heifer. Individual differences in follicular populations at the time of treatment, or in E₂-17β levels after stimulation, could be related to differences in responses in ovulation rate. Normal follicles >1.7 mm diameter before treatment would usually ovulate following PMSG injection, whereas early atretic follicles of the same size mostly luteinize.     

Induced abortion in cattle

Several procedures were used to abort cattle during the second and third trimesters of gestation. The treatment to abortion interval was better (P<0.05) when dexamethasone trimethyiacetate (DTMA) injections repeated at either 6 or 4 day intervals than when a single injection of DTMA was followed 6 days later by the administration of stilboestrol. The treatment to abortion interval was not significantly shorter when DTMA was repeated after 4 days rather than 5 days (0.10<P>0.05). Prostaglandin F_2α produced abortion 1 to 4 days following direct administration into the foetai fluids.Peripheral plasma progesterone concentration had a tendency to rise immediately following the second injection of DTMA given at a 6 day interval. This was followed by a decline. Two injections of DTMA given at 4 day intervals resuited in a decline in progesterone concentration. Abortion occurred when plasma progesterone concentrations were about 1 ng/ml in cows treated with DTMA. In cows treated with prostagiandin F_2α the plasma progesterone concentration fell rapidly within one day of administration to approximately 2 ng/ml, at which concentration abortion took place.     

Serum antigens of cattle

We have produced an alloimmune serum that detects a new cattle immunoglobulin light chain allotype. Genetic analysis involving more than 600 offspring showed that this allotype is controlled by an autosomal codominant allele [Ig(L)b ²], of theIg(L)b ¹ gene previously reported from this laboratory. This system also contains a recessive allele for which no product can now be detected. The frequencies of the three alleles in 5 dairy breeds are reported. The Ig(L)B1 and Ig(L)B2 allotypes are expressed as complexes of 2 or 3 precipitin bands in double diffusion gels containing polyethylene glycol-6000. The complexes are transmitted as genetic units.     

Differences in cattle globins

1. Comparisons have been made between electrophoretic mobilities of the cattle haemoglobins, HbA, HbB, HbC, HbD and HbF, at pH8.9. The fastest was HbB, then came in decreasing order HbF, HbC, HbA and HbD. 2. Globins were prepared from the main fractions of the five haemoglobins by CM-cellulose chromatography and investigated by starch-gel electrophoresis in four different buffer systems. In three of these (pH2.0 and 11.8) the globins appeared as two bands on stained starch gels. The slowest bands, the alpha-chains, showed the same rate of migration in all five globins. The faster bands, the non-alpha-chains, differed, that of HbF being the fastest and that from HbC the slowest. The other three were intermediate with, however, very small difference between the non-alpha-chains from HbA and HbD. 3. At pH1.8 in an acetate-phosphate-hydrochloric acid-urea buffer three bands appeared in all five globins of which the two slowest were indistinguishable in rates of migration, whereas the rates of migration of the third and fastest bands differed. Explanations for the occurrence of three bands are discussed.     

Chromosome markers in cattle

Summary Giemsa banding in cattle chromosomes enables the demarcation of both centromeric areas as pale regions and banding patterns along the chromosome arms. These are valuable in identifying all the chromosomes of a given karyotype. A high degree of intra- and inter-individual variation in the size of the centromeres was observed. This variation is useful for the identification of each individual and provides a broad base of chromosome markers for cattle breeding.     

Haemoglobin variants in cattle

From a comparative survey of reports on cattle Hb variants it is concluded that prior to the present communication the occurrence of at least seven different adult Hb molecules have been reported.
In addition comes the finding of a new Hb variant called HbG which is reported in this study. This was found in three animals among 101 East African Zebu cattle. It migrated more slowly than any cattle Hb variant previously reported and made up 20% of total Hb.
The gene frequencies of the East African Zebu population were: Hb^A = 0.52, Hb^B = 0.32, Hb^c = 0.14 and Hb^G = 0.01.     

Maternal behavior in cattle

We provide a critical summary of the literature on maternal behavior in cattle. The studies we review increase our basic understanding of this behavior and provide insights into practical problems in cattle production. When domesticated cattle are permitted to rear their young, the behaviors associated with maternal care are for the most part similar to those observed in wild ungulates. These behaviors allow the cow to bond with her calf, protect and provide it with nourishment and ultimately break down this bond at weaning. Different commercial production systems have emphasized different maternal behaviors, some being viewed as advantageous while others are considered a hindrance. Extensive production systems (most beef cattle production) place the responsibility of rearing the newborn largely on the cow and risk factors that affect the maternal bonding process (e.g. cross licking) remain important practical challenges. Most dairy cattle production discourages all aspects of maternal behavior with the exception of milk production, but changing consumer demand (e.g. increases in organic production) will make an understanding of maternal behavior in this system a priority in years to come.