THE INDUCTION OF PARTURITION USING DEXAMETHASONE IN DAIRY CATTLE

Premature parturition was successfully induced with a preparation containing 2 dexamethasone esters in 709 out of 716 cows and heifers of gestational periods ranging from 3 to 8 months. A mortality rate of 38.5% was experienced among calves produced by induced cows, while only a 2.7% mortality rate occurred among 4,330 calves from normal parturitions. Approximately 50% of all treated cattle retained foetal membranes, but with apparently no ill-effect. The treatment apparently did not affect milk production, post-calving fertility, and the overall incidence of dystocias in cows and post-calving diseases. Three deaths occurred among induced cattle, but they could not be attributed to the treatment. It was concluded that the technique may prove to be of great value in dairy cattle, in seasonal milking areas.     

Embryo transfer for cows with reproductive problems

Surgical embryo recovery and transfer methods were applied to 25 cows and heifers with chronic reproductive problems. In 16 of the 25 animals, abnormalities could not be detected by palpation per rectum and, at laparotomy, the probable cause of low fertility was found to be oviductal obstructions or periovarian adhesions in 6 of them. Four pregnancies were obtained from 3 of these 6 animals. A definitive diagnosis was not obtained through laparotomy in the other 10 animals in this group; however, an abnormal uterine environment associated with senescence may have been responsible for low fertility in the older cows. Eighteen calves were obtained by embryo transfer from 8 of these 10 donor animals. The remaining 9 heifers and cows had lesions detectable by palpation per rectum. Chronic, purulent metritis was found in 2 cows, one of which produced 7 calves by embryo transfer. The other 7 had periovarian adhesions, and 8 calves were obtained from 2 of them. The adhesions in 6 of these 7 cows were attributable to cesarean section. Laparotomy was valuable for defining the extent of the adhesions and establishing a reliable prognosis in some cases.     

The influence of dietary selenium as selenium yeast or sodium selenite on the concentration of selenium in the milk of Suckler cows and on the selenium status of their calves

The aim of this trial was to determine whether the selenium status of suckling calves could be improved by supplementing their dams' diet with organic Se instead of sodium selenite. A herd of 103 Hereford cows, which were on grass paddocks all year round, was divided into two groups. Both groups had free access to a mineral supplement that contained 30 mg of Se/kg; for one group the source of the Se was a Se yeast product, and for the other group the source was sodium selenite. The basal feed contained .02 mg of Se/kg DM. During the trial, the mean daily consumption of the mineral supplement was approximately 110 g/cow. The calving season started in the middle of March and ended in the middle of May. Blood samples were taken from 11 cows and their calves in the yeast group and from nine in the selenite group at the end of April and again at the beginning of June, and milk samples were taken at the same times. At both samplings, the concentration of Se in whole blood and the activity of glutathione peroxidase (GSH-Px) in the erythrocytes of the cows and calves in the yeast group were higher than in the samples from the animals in the selenite group. The same pattern was seen for plasma, except for the cows at the first sampling. The mean concentrations of Se in whole blood from calves in the yeast and selenite groups were 130 and 84 microg/L, respectively, and plasma concentrations were 48 and 34 microg/ L, respectively. Mean Se concentration in the milk from the yeast group (17.3 microg/L) was higher than that in milk from the selenite group (12.7 microg/L). There were significant correlations (r = .59 to .68) between the concentrations of Se in the cow's milk or cow's whole blood compared with Se concentrations in the calves whole blood and plasma or with the erythrocyte GSH-Px activity of the calves. The Se status of the calves in the selenite group was considered to be marginal, but the status of the calves in the yeast group was considered to be adequate. Supplementation of the suckler cows' diet with organic Se in the form of Se yeast rather than sodium selenite improved the Se status of their calves when the Se was mixed into a mineral supplement containing 30 mg of Se/kg. In practice, such supplementation would probably eliminate the risk of nutritional muscular degeneration in suckling calves.     

Gastrointestinal nematode parasites in Saskatchewan cattle: egg count distributions in beef animals.

Fecal samples were collected systematically in the spring from cows and yearlings entering, and in the fall from calves leaving, five community pastures in central Saskatchewan. Fecal samples were also collected systematically in the spring from cows entering, and in the fall from calves leaving, an experimental rotational grazing system. Samples were collected from 1398 animals and were examined by a quantitative fecal flotation technique with a sensitivity of ten eggs per gram. Distributions of nematode egg counts for 11 of the 12 cattle populations sampled were well described by a series of negative binomial distributions. A common value of k (a measure of aggregation) could be fitted to the counts from animals of all ages in four of the five community pastures, as well as to the counts from the cows from the fifth community pasture and from the rotational grazing system. A second value of k could be fitted to the counts from the calves from these two pasture. In addition, in three of the community pastures animals in the different age groups had the same mean count.     

Influence of restricted suckling and level of feed supplementation on postpartum reproductive performance of zebu and crossbred cattle in the semi-arid tropics.

This study was carried out in central Tanzania on a group of 45 Zebu and 37 crossbred cows which were 4 to 10 years old. At calving time, the animals were allocated to one of the 4 treatment groups. In addition to free access to grazing for all cows in the study, in group H:AR (n = 18), cows were fed a high level of concentrate supplementation (4kg/day) and calves were artificially reared; in group H:RS (n = 24), cows were fed a high level of concentrate supplementation (4kg/day) and calves were only allowed restricted suckling up until the weaning age of 6 months. In group L:AR (n = 23) cows were fed a low level of concentrate supplementation (2kg/day) and calves were artificially reared; and in group L:RS (n = 17) cows were fed a low level of concentrate supplementation (2kg/day) and calves were only allowed restricted suckling up until the weaning age of 6 months. Milk progesterone was used as a means of determining the postpartum resumption interval (PRI) and the interval from parturition to conception (PCI). The overall PRI was 47.4 +/- 0.4 days and was significantly affected by breed but not by calving season, with crossbred cows exhibiting a shorter PRI than Zebu cows. The effect of the treatments was significant, with cows in the group H:AR displaying a significantly shorter PRI than those in the other groups, while cows in group L:RS showed a significantly longer PRI than those in the other groups. The overall PCI was 149.5 +/- 3.7 days, and was not significantly affected by breed or calving season. The effect of the treatments was significant, with cows in the group H:AR having a significantly shorter PCI than cows in the other groups, while cows in group L:RS showed a significantly longer PCI than those in the other groups. Crossbred cows had higher live weights at calving (299.4 kg) than Zebu cows (272.6 kg), while all cows gained weight during the first 3 months after calving. The treatments had a significant effect on weight gain, with cows in the group H:AR gaining significantly more weight than those in the other groups. Cows which had high live weights at calving exhibited significantly shorter PRI and PCI than the lighter cows. Animals which had gained more than 5 kg during the first month after calving, or which had gained more than 8 kg during the first 3 months after calving, showed significantly shorter PRI and PCI than cows which had gained less weight. The results show that the calf rearing system and the level of feed supplementation interact with each other and can influence the postpartum anoestrous period in Zebu and Zebu crossbred cattle. Increasing the level of nutrition in restricted suckling cows tended to improve the postpartum anoestrous period, but the positive effects of supplementation could not completely compensate for the negative effects of suckling.     

Reduction in morbidity due to diarrhea in nursing beef calves by use of an inactivated oil-adjuvanted rotavirus-Escherichia coli vaccine in the dam.

An outbreak of neonatal diarrhea occurred among beef calves (2000 animals) from one large Argentinian farm in 1985. Rotavirus was detected in 78% (106/136) and enterotoxigenic Escherichia coli in 1.5% of the samples (2/136) obtained from sick calves. In comparison rotavirus was identified in only 1.6% (1/63) of the samples from clinically healthy calves. The rotavirus strain responsible for the outbreak was characterized as serotype 6 belonging to group A. In the following three years the protective capacity of a combined rotavirus-E. coli inactivated vaccine administered to the dams during the last third of the gestation period was evaluated on this farm by comparison of morbidity due to diarrhea in calves from vaccinated vs. placebo cows within the same year. The morbidity due to diarrhea among calves from dams in the vaccinated and placebo groups was 34% and 77%, respectively in 1986; 23% and 47% in 1987, and 15% and 34%, in 1988. In 1987 morbidity of diarrhea in calves born from vaccinated heifers was 54% and 74% in calves from placebo heifers. In 1988 morbidity from diarrhea was 41% and 54%, respectively among calves in these two groups. In all experiments, calves from heifers showed significantly greater morbidity than calves from cows. Differences in diarrhea morbidity between the vaccinated and placebo groups were statistically significant (P less than 0.05). Additional studies showed that the diarrhea had a significant influence (P less than 0.05) on the average live weight of the calves at weaning (5 to 7 months) with an average weight loss of 7.8 kg per calf among the calves affected with diarrhea.     

Serological study of a dairy herd with a recent history of Neospora abortion

HERD HISTORY: A cluster of 19 abortions occurred in April and May 1994 on a seasonal dairy farm of 277 cows in Taranaki. Lesions consistent with neosporosis were seen in several foetuses. The age of the aborting cows ranged from 2 to 12 years. Pregnant rising 2-year-old heifers had been grazed off the main farm on a run-off' until returning in May, when they were replaced on the run-off by the rising l-year-old calves. None of these pregnant heifers aborted. METHODS: Sera were obtained from all calves (n = 32), 32 of 33 pregnant heifers, 59 of 60 3-4 year-old cows and 101 of 150 older cows, plus all cows that had aborted. Sera were tested using an indirect fluorescent antibody assay. Non-aborting cattle sera were screened at 1:400, and further dilutions were tested from 15 aborted cows. RESULTS: The percentages of seropositive cattle were: 32% of the calves, 3% of the heifers, 31% of the younger cows and 27% of the older cows. The proportion of seropositive heifers was significantly lower (p< 0.01) than in the other age classes. There was no significant difference in the proportion of seropositive animals between these other age classes (p >0.05). Of the 15 cows that aborted, and for which further dilutions were tested, nine had titres of 1: 12,800, four had titres of 1:6400, one had a titre of 1: 1600 and one had a titre of 1:400. Twenty cows were the dams of pregnant heifers. Six of these cows were seropositive but all their offspring were seronegative. Fifteen aborting cows were held over to the following year when 13 became pregnant and calved normally. There were only two to three abortions in the whole herd in this following year. CONCLUSION: These results suggest that either a point-infection occurred sometime in early 1994 with an infective period short enough so that the heifers did not get infected when they returned to the main farm, or some factor precipitated a recrudescence of latent infection with a subsequent rise in titres in about 29% of the animals on. the main farm only. Although neither hypothesis can be proven or disproven in this observational study, the former hypothesis seems more likely.     

Influence of herd structure and type of virus introduction on the spread of bovine viral diarrhoea virus (BVDV) within a dairy herd

A herd is a population structured into groups not all equally in contact, which may influence within-herd spread of pathogens. Herd structure varies among cattle herds. However, published models of the spread of bovine viral diarrhoea virus (BVDV) assume no herd structure or a unique structure chosen as a representative. Our objective was to identify--for different index cases introduced into an initially BVDV--free dairy herd - risky (favourable) herd structures, which increased (decreased) BVDV spread and persistence compared to a reference structure. Classically, dairy herds are divided into calves, young heifers, bred heifers, lactating cows and dry cows. In the reference scenario, groups are all equally in contact. We evaluated the effect of isolating or merging groups. Three index cases were tested: an open persistently-infected (PI) heifer, an open transiently-infected heifer, an immune heifer carrying a PI foetus. Merging all groups and merging calves and lactating cows were risky scenarios. Isolating each group, isolating lactating cows from other groups, and merging calves and young heifers were favourable scenarios. In most structures, the most risky index cases were the following: first, the entry of a PI heifer; second, the birth of a PI calf; last, the entry of a transiently-infected heifer. Recommendations for dairy herds are to raise young animals together before breeding and to isolate lactating cows from others as much as possible. These recommendations will be less efficient if a PI adult enters into the herd.     

Bluetongue virus serotype 20: experimental infection of pregnant heifers

Three groups of 4 cows at 84 to 95 days, 100 to 160 days, and 170 to 180 days pregnant were inoculated both intradermally and subcutaneously with bluetongue virus serotype 20 (BTV20). Clinical observations and the viraemic and serological responses of the cows were followed for 9 to 17 weeks after inoculation. Viraemia developed in 9 of the 12 cows and was first detected 4 to 9 days after inoculation. Viraemia was detected for 4 to 21 days and in some animals only intermittently. The titre of the viraemia was obtained in 4 cows and ranged from detectable only, to 10(1) to 10(2.8) 50% tissue culture infecting doses per ml. Both serum neutralising and precipitating antibodies were detected in 11 of the 12 cows within 2 to 8 weeks after inoculation. No clinical responses were seen and one cow (516) did not develop a viraemia or produce detectable antibodies to the virus. The cows, calves and foetuses were necropsied following either parturition or slaughter between 200 and 270 days of pregnancy. No virus isolations were made from a wide range of tissues from the cows, calves or foetuses and no immunoglobulins or serum neutralising antibodies were detected in the serums of precolostral calves or foetuses at necropsy. No gross or histopathological lesions were seen in the cows, calves or foetuses, and there was no evidence that BTV20 crossed the bovine placenta or infected the foetus.     

Some Pharmacokinetic Parameters of R-(–)- and S-(+)-Ketoprofen: The Influence of Age and Differing Physiological Status in Dairy Cattle

The pharmacokinetic parameters of ketoprofen have previously been studied in cattle, but no studies have been performed on differing ages and metabolic situations in these animals. The aim of this work was to study the possible modifictions of the pharmacokinetics of ketoprofen enantiomers that may result from age, lactation or gestation in dairy cattle. Three groups of Holando Argentino cattle contained, respectively, 8 cows in early lactation, 8 pregnant cows and 8 newborn calves. Four animals from each group received the enantiomer R-(-)-ketoprofen, the other four animals received the S-(+) enantiomer, all by intravenous injection at a dose of 0.5 mg/kg. Significant differences between the three categories of animals were obtained in elimination half-life (t1/2) (1.52, 0.87 and 0.31 and 1.71, 0.69 and 0.26 in newborn calves, cows in early lactation and cows in gestation, respectively), mean residence time (MRT) (0.45, 1.25, 2.20 and 0.38, 0.99, 2.47 h, in cows in gestation, cows in early lactation and newborn calves, respectively) and area under the plasma concentration-time curve (AUC) (0.87, 2.93, 3.24, and 0.67, 2.78, 5.13 (microg/h)/ml in cows in gestation, cows in early lactation and newborn calves, respectively, for the R-(-) and S-(+) enantiomer, respectively. In calves, there was a significant difference in AUC (3.24 vs 5.13 (microg/h)/ml between R-(-)- and S-(+)-ketoprofen. In view of the differences between calves and adult cattle in the pharmacokinetic results for ketoprofen, the effects of age and physiological status (lactation, gestation) should be taken into account for therapeutic regimens.     

Breeding objectives for beef cattle used in different production systems: 2. Model application to production systems with the Charolais breed

A general bio-economic model for beef cattle production was used to define breeding objectives for Charolais cattle to be utilized in a variety of linked production systems. Economic weights were calculated for 16 traits (some with both direct and maternal components) in three production systems (pure-breeding and terminal crossing with beef or dairy cows) and two marketing strategies (sale or fattening of weaned surplus calves). Economic weights for the total breeding objective were calculated as weighted averages, where weights were numbers of cows expected to be mated with Charolais bulls in each production system and marketing strategy. Results suggest that the direct component of calving performance and cow longevity were of primary economic importance in all systems. Conception rate of cows and weaning weight reached about 50% of the standardized economic weight of calving performance in purebred systems with sale of weaned calves, whereas in purebred systems with fattening the economic importance of the direct component of cow conception rate, losses at calving, mature weight of cows, weaning weight, and fattening traits were of equal importance (each approximately about 20% that of calving performance). In terminal crossing systems, weaning weight was important when calves were sold at weaning, and fattening traits were important for systems selling fattened animals. The bio-economic model performed well under the conditions of this demonstration and could easily be customized for other applications.     

Survey of helminth infections in Maine dairy cattle.

The survey was done to determine the incidence and seasonal prevalence of the gastrointestinal helminths infecting Maine dairy cattle. Approximately equal groups of calves, heifers, and cows from 13 dairy farms, managerially and geographically representative of dairying in the state, were sampled at regular 2-month intervals over the period of a year. On the basis of fecal egg counts and identification of cultured larvae, the following results were obtained: Of the 94 adult cows, 78 heifers, and 91 calves sampled continuously in the course of the survey, 95.7%, 98.7%, and 96.7%, respectively, were strongylorid positive (infected with Ostertagia, Cooperia, Trichostrongylus, Haemonchus, and Oesophagostomun), with an overall incidence of 97%. Strongyloides papillosus eggs were in 64.6% of the cattle, Bunostomum in 40.3%, Nematodirus in 27.8%, Trichuris in 27.0%, Capillaria in 9.5%, Moniezia in 25.1%, and Dictyocaulus viviparus larvae in 2.7%. Worm burdens, as reflected by mean nematode egg production per gram of feces, varied. The greatest worm burdens were in the calves, followed by the heifers and the cows. A marked variation in egg production related to season was observed, particularly with the strongylorid worms. Peak strongylorid egg production was observed in the May-June sampling period. After the peak period, worm burdens decreased in all groups of cattle to their lowest point during the winter period of January-February. This pattern of egg production was similar to that reported by workers in other parts of the world. Farm management practices were shown to be related to the degree of parasitism existing in these herds. Those herds classed as poorly managed had significantly higher levels of parasitism in young animals than those classed as having fair or good management.     

Biologic quality of colostrum and calves from dairy cows injected with zinc during pregnancy]

The effects of an administration of the Zindep inj. preparation (Biotika) were evaluated in pregnant dairy cows as exerted on specific weight, total protein (TP) content, total immunoglobulin (IgC) and albumin (ALB) contents in colostrum. These parameters were also followed: calf's health, live weight, leucocyte (Lc) counts, T-lymphocyte (T-Ly) counts, contents of TPs, IgCs and ALBs in the blood serum of calves. Zinc concentrations were determined in colostrum, milk and calf blood serum. Our observations included 16 dairy cows in the seventh month of pregnancy in the second lactation and their calves in the winter feeding season. Eight experimental dairy cows were treated with the Zindep preparation in form of an injection to the neck muscles at a dose of 3 mg Zn/kg live weight in the mid-seventh month of pregnancy. Blood samples were taken from v. jugularis from all calves before their first drinking, on days 5, 15 and 30 of age. Colostrum, and/or milk samples were obtained by drawing of the colostrum or milk from the udder quarters within 60 minutes after parturition, on days 5 and 15 of lactation. Zn levels at birth were 16.48 +/- 2.67 mumol/l in experimental calves and 13.84 +/- 3.19 mumol/l in control calves. Zincaemia decreased slightly in both groups on days 5 and 15 of age, but it was insignificantly higher in calves coming from Zindep-treated dairy cows. Zn levels in the blood serum on the 30th day of age were 18.45 +/- 2.44 mumol/l in experimental animals and 15.73 +/- 3.11 mumol/l in control animals. Zn content in the colostrum of experimental cows was 2.40 +/- 0.42 mg/l and in the control it was 1088 +/- 0.52 mg/l (P < 0.05). On day 5 of lactation, Zn amounts in the milk of experimental dairy cows decreased to 0.95 +/- 0.12 mg/l and to 0.76 +/- 0.10 mg/l in the control (P < 0.01). Zn levels in the milk of experimental cows on day 15 of lactation were 0.95 +/- 0.13 mg/l and in the milk of control group they were 0.82 +/- 0.14 mg/l. Colostrum specific weight from zinc-treated cows was 1,067.86 +/- 0.75 g/cm3 and 1,056.8 +/- 13.53 g/cm3 in the control. TP and IgC concentrations were 137.81 +/- 38.11 g/l and 110.13 +/- 29.91 U ZST, respectively, in the colostrum of experimental group, and 105.98 +/- 32.02 g/l and 85.53 +/- 25.42 U ZST, resp., in control animals.(ABSTRACT TRUNCATED AT 400 WORDS)     

Use of serologic evaluation for antibodies against bovine viral diarrhea virus for detection of persistently infected calves in beef herds

OBJECTIVE: To determine whether use of serologic evaluation of a sentinel sample of calves or cows for antibodies against bovine viral diarrhea virus (BVDV) would accurately predict whether an animal persistently infected with BVDV could be detected in beef herds. SAMPLE POPULATION: 27 cow-calf herds in which the status of persistently infected calves was not known and 11 herds known to have persistently infected calves. Procedure-Detection of persistently infected calves was determined through immunohistochemical testing of tissue obtained at necropsy of all calves that died during calving season and skin (ear notch) specimens obtained from all young stock in the fall of 2002. Serum samples were collected from 30 spring-born calves and 10 mature cows. RESULTS: Optimum serologic test performance at time of weaning was detected when 10 calves were evaluated. At least 3 of 10 randomly selected calves were likely to have a titer > 1:1000 against BVDV type I or II in 53% of herds in which a persistently infected calf was detected during that year (sensitivity, 53%). However, at least 3 of 10 randomly selected calves were also likely to have a titer > 1:1000 in 20% of herds that did not have a persistently infected calf detected during that year (specificity, 80%). CONCLUSIONS AND CLINICAL RELEVANCE: Despite the use of a number of various cutoff values and sample sizes, serologic evaluation of a small number of calves or cows could not be used to accurately predict the presence of persistently infected cattle in a herd.     

In utero transmission of bovine leukemia virus

In an initial study, 18 calves born to cows persistently infected with bovine leukemia virus (BLV) were tested for infective virus and antibodies at birth, and no infected or seropositive animals were found. Four of these calves were maintained in quarters where infected animals were housed, and 3 of the 4 subsequently became infected. These were probably contact infections acquired during, or at some time after, birth. The remaining 14 calves were kept in isolation pens in a building housing no infected cattle. None of this group was found to be BLV infected during 1 year of observation. In further studies, 15 pregnant cows inoculated with BLV became infected. One abortion, considered to be unrelated to the BLV inoculation, occurred 38 days later. The remaining 14 cows gave birth to 1 dead and 14 live calves. The dead calf and its live twin were seropositive for BLV at birth, indicating that they had been infected in utero. The remaining 13 calves were negative for BLV antibodies at birth and remained so during 1 year of observation.     

Subclinical mastitis of beef cows

Two beef cow herds were investigated to determine the prevalence of subclinical mastitis and to determine whether it contributed to decreased weaning weight of calves nursed by affected cows. Quarter samples obtained about 30 days after calving were evaluated by the California mastitis test and by direct microscopic cell count. In 1 herd, a 92-cow confinement operation, 17 quarters of 12 cows were infected with Staphylococcus aureus, Streptococcus sp other than agalactiae, or Klebsiella sp. Mean 205-day adjusted weights were 203.9 kg and 218.2 kg for calves nursed by infected vs noninfected cows. In the other herd, a 75-cow range-pasture operation, 8 quarters of 8 cows were infected, all with S aureus. Mean 205-day adjusted weights were 162.5 kg and 174.6 kg for calves nursed by infected vs noninfected cows.     

Relationships between N'Dama cow body condition score and production performance under an extensive range management system in Southern Senegal: calf weight gain, milk production, probability of pregnancy, and juvenile mortality

This study aimed to determine the relationships between N'Dama cows body condition score (BCS) and (i) calf growth and the milk collected; and (ii) the probabilities of pregnancy and juvenile mortality. Animals from 10 herds ranging from 20 to 210 animals in herd size were followed monthly in an extensive range management system in Southern Senegal between 1993 and 1998. For daily weight gains and milk collected, linear mixed-effects models were fitted between calving and 6 months postpartum. Cow lactation was included as random effect, with an unstructured variance-covariance matrix. Calving season, parity, herd size, and calving BCS were the fixed effects. For the probabilities of pregnancy and juvenile mortality, survival models for grouped data were fitted on a monthly scale. The model selection was based on the Akaike information criteria. In large herds, calving BCS had little effect on milk production. In small herds, calves born to cows scoring ≥2.5 points at calving grew quicker and their dam were more milked. The relative difference in milk production between thin and fat cows averaged 23%. The relative gain was higher in the cool dry season than in the other seasons, and for primiparous than for multiparous cows. Except during the hot dry season, the probability of pregnancy was twice as high for cows scoring ≥2.5 points the two previous months than for other cows. The BCS had no effect on calf survival until 1 year of age in large herds. In small herds, calves born to thin cows at calving showed a survival at 1 year more than five points lower than calves born to fatter cows. The threshold of 2.5 points on a five-point scale is pertinent to describe the production performance of N'Dama cows in such a breeding context.     

Inverse age resistance to experimental Babesia divergens infection in cattle

Two groups of calves, 1.5-2 and 7-11 months old respectively, and dairy cows were inoculated i.v. with 3 x 10(7) erythrocytes infected with Babesia divergens. High parasitaemia, fever and other clinical signs of babesiosis occurred among adult animals. A very low parasitaemia and a slightly increased body temperature but no other symptoms occurred in calves. these findings substantiate the conclusion that there exists an inverse age resistance against Babesia divergens. The kinetics of B. divergens IgG antibody formation were similar in all age groups. Consequently this antibody response was not the factor determining the development of the primary parasitaemia and thus the inverse age resistance phenomenon. However, age is not necessarily the only factor involved in the clinical expression of babesiosis. The kinetics of antibody formation was not associated with the intensity of the parasitaemia. In fact only about half the animals had a demonstrable parasitaemia although the antibody responses were similar in all age groups.     

Reproductive Performance and Reconception of Nellore Cows According to Their Pure‐ or Cross‐Bred Calves

The objective of the present research was to evaluate the effect of a calf's genetic group on the productive and reproductive efficiency of its Nellore dam. Fixed‐time artificial insemination was applied to 800 cows using semen extracted from Nellore, Simmental and Angus Red bulls. Four hundred eleven cows calved, producing 119 Nellore, 103 ½Simmental–½Nellore and 189 ½Nellore–½Angus Red calves. The second mating period, which paired Nellore cows with Simmental bulls, was initiated 10 days after parturitions began and lasted for 5 months. Based on the two successive parturitions, the cumulative parturition rate for calving periods of 3, 4 and 5 months was calculated. Although no significant difference was observed for birth weight among the genetic groups, cross‐bred calves weighed, on average, 10% more than did pure‐bred calves at the age of 205 days. Nellore dams experienced a gestation period that was 7 days longer than did the cross‐bred dams, and the former showed a higher parturition rate at 90 and 120 days of the calving season, but not at 150 days (calving rates of 80.6, 76.4 and 76.2% for mothers of Nellore, ½Nellore–½Angus Red and ½Nellore–½Simmental, respectively, p > 0.05). At 90 and 120 days, Nellore dams produced more kg of calf per mated dam. In conclusion, in a short breeding season, Nellore dams nursing pure‐bred Nellore calves were found to have a higher biological efficiency compared with Nellore dams nursing cross‐bred calves.     

Poor inheritance of low attractiveness for Amblyomma variegatum in cattle

Because of the high variability of cattle infestation, selective breeding has been proposed to control three-host ticks in Africa in the same way as it has been implemented to control the one-host tick Boophilus microplus in Australia. Interbreeding (divergent selection experiment) between Gudali zebu cattle was performed at the Wakwa Research Centre, Adamawa, Cameroon to assess the feasibility and impact of such a selective breeding programme. Fifty cows (chosen out of 129) and 2 bulls (chosen out of 10) were selected according to their greater or lesser attractiveness for the tick Amblyomma variegatum, assessed by their infestation degree (ID, ratio between individual animal infestation and mean herd infestation). Half of the animals displayed a high ID (H) and the remainder a low ID (L). The presence of a suckling calf had a significant effect on the infestation of its dam, the udder of lactating cows being significantly less infested (P<0.001) because of a tick removal effect by the calves. Observed infestation data were therefore corrected to allow comparison between lactating and non-lactating cows. The ID of the cows was assessed on five occasions from 1992 to 1994: the consistency of the infestation hierarchy was good overall (P<0.001) despite high variability seen in some animals which would complicate the selection of cattle with low infestation. Four breeding groups were set up (LxL, LxH, HxL, HxH) and 40 calves were born in 1993 and 1994. There was a correlation (P<0.02-0.001) between liveweight (or age) and ID when the younger calves of the groups were 6 months old, but the correlation disappeared by the time the calves were all older than 1 year. There was no difference between the average ID of the calves from the four breeding groups, and no correlation was observed between dam ID and calf ID. The average ID of the 10 calves born of the dams with the lowest ID was however significantly lower than that of the 10 calves born of the dams with the highest ID (0.82 versus 1.15, P=0.03), but the difference was much less than that observed between the dams (0.35 versus 2.30, P=7x10(-9)). A positive correlation between dam ID and calf ID was found when only these 20 cows were taken into consideration (r=0.57, P<0.01). These results indicate that selective breeding of Gudali zebu cattle to produce animals with low infestation by the tick A. variegatum would be uncertain but that a more drastic selection of the breeders than that implemented in the present study may perhaps have some positive impact.