Tj Parkinson

Onset of puberty in pasture‐raised Thoroughbreds born in southern hemisphere spring and autumn

REASONS FOR PERFORMING STUDY There is little information on age, weight and time of year of puberty in Thoroughbred horses, and the interpretation of such data is difficult due to the wide variety of descriptions of the onset of puberty. OBJECTIVES To examine the age, bodyweight and date of onset of puberty in Thoroughbreds born in spring and autumn. METHODS Bodyweight data and blood samples were collected in 59 pasture-raised Thoroughbred horses. Five autumn-born and 18 spring-born colts and 3 autumn-born and 33 spring-born fillies were examined from birth to age 13 and 17 months. A testosterone concentration >2 s.d. above the baseline concentration was indicative of onset of puberty in colts; and progesterone concentration >2 ng/ml and at least 3 times greater than the previous progesterone concentration was indicative of a first ovulation in fillies. RESULTS Spring-born fillies and colts were older and heavier than autumn-born fillies and colts at puberty. The age at onset of puberty in spring- and autumn-born foals was 291-408 days and 212-270 days, respectively. The weight at puberty in spring-born foals was 302-409 kg, and in autumn-born foals was 277-344 kg. However, the mean date at onset of puberty was not significantly different between spring- and autumn-born horses, with puberty occurring in October (New Zealand spring). CONCLUSIONS AND POTENTIAL RELEVANCE Seasonal changes in photoperiod affect the timing of onset of puberty, provided a minimum threshold bodyweight has been reached. Spring-born horses reached this threshold weight during the winter months and remained reproductively inactive until after the stimulus of increasing day-length occurred. The autumn-born horses reached the threshold weight to support puberty at the same time as stimulatory photoperiod and, therefore, reached puberty significantly younger and lighter than the spring-born horses.

Bodyweights and growth rates of spring- and autumn-born Thoroughbred horses raised on pasture

Abstract AIM: To examine the growth of spring- and autumn-born Thoroughbred foals raised on pasture. METHODS: Bodyweight and growth rates were measured in pasture-raised Thoroughbred horses, born in either spring (n=56) or autumn (n=7), from birth to approximately 13 and 17 months of age. RESULTS: Birthweight tended to be lower in autumn- than spring-born foals (54.4, SD 7.92 kg vs 57.3, SD 5.90 kg; p=0.08). Between birth and 6 months of age, there was no difference in growth rate at equivalent ages between horses born in spring and autumn. Spring-born horses, which were weaned in the autumn, had lower post-weaning growth rates than autumn-born horses that were weaned in the spring. At time of the late yearling sales (March–April) in the Southern Hemisphere, unadjusted mean bodyweights of autumn-born horses (379.3, SD 24.8 kg) were lower (p=0.017) than those of the spring-born horses (437.2, SD 35.3 kg), although values in the autumn-born horses were all within two standard deviations (SD) of the mean of the spring-born animals. When adjusted for the covariates of birthweight and gender, the difference between spring- and autumn-born horses at that time was not significant (p=0.25). CONCLUSIONS AND CLINICAL RELEVANCE: Some autumn-born foals could be marketed for late yearling sales in the Southern Hemisphere, on the basis of bodyweight. Furthermore, they might also be competitive in the Northern Hemisphere industry (sales or racing), as they would be competing against horses of the same official age.

Causes of abortion on New Zealand dairy farms with a history of abortion associated with Neospora caninum

Abstract AIM: To investigate the cause of abortion in cows from farms with a history of abortion associated with Neospora caninum. METHODS: Cows and primiparous heifers (n = 2,246) that were enrolled in a clinical trial of a vaccine for N. caninum, and 403 cows and heifers that conceived >6 weeks after the planned start of mating (PSM), were monitored for abortion on five dairy farms with a history of abortion associated with N. caninum. When abortion was detected the fetus and/or placenta were submitted for histopathological examination and maternal paired sera were collected for the detection of antibodies to N. caninum using the indirect fluorescent antibody test (IFAT), bovine viral diarrhoea virus (BVDV) using ELISA, and Leptospira spp. using the microscopic agglutination test (MAT). RESULTS: At the start of the clinical trial, 189/1,760 (10.7%) of cows and 61/486 (12.6%) of heifers had IFAT titres ≥1:200 for N. caninum. Abortions were detected in 111 (4.9%) enrolled and 37 (9.2%) non-enrolled cows and heifers. The relative risk of abortion was 4.21 (95% CI 2.92–6.08) times greater in enrolled animals that were seropositive to N. caninum than seronegative animals (p < 0.01). Among all animals, histopathological lesions suggestive of protozoal abortion were seen in nine, and of bacterial infection in 15, of the 40 cases where the fetus and/or placenta were recovered. IFAT titres for N. caninum ≥1:1,000 were detected in 66 cows at abortion, including 7/9 cases where there were fetal lesions indicative of N. caninum infection. In nine cows that aborted, there was evidence of seroconversion to BVDV and eight cows had MAT titres for Leptospira spp. ≥1:200. Histopathology revealed dual infectious aetiologies in two cases and, in another 17 cases, there was serological evidence of recent exposure to a second infectious agent capable of causing abortion in conjunction with N. caninum lesions in the fetus or fetal bacteraemia. CONCLUSIONS: Multiple infectious aetiologies occur at herd-level and in individual cows on farms with a history of abortion associated with N. caninum. A diagnosis of abortion due to N. caninum infection was made in 9/34 (26.5%) cases where fetal histopathology was undertaken. CLINICAL RELEVANCE: Thorough and ongoing diagnostic investigations should be undertaken in herds with higher than expected abortion losses to identify all causative agents as control measures could be implemented that may also reduce the risk of abortion in cows infected with N. caninum.

A case of bovine mastitis caused by Bacillus cereus

Abstract Although the cause of most bovine mastitis can be attributed to the major pathogens of the udder (Staphylococcus spp., Streptococcus spp. and Escherichia coli), occasional cases occur that are caused by more unusual organisms. The mastitis caused by a number of these organisms may be characterised by a very marked degree of tissue damage and, consequently, grossly abnormal mammary secretions. Notable amongst such organisms is Bacillus cereus, for which a number of cases have been reported from many countries with significant dairy industries (Scheifer et al., 1976; Jones and Turnbull, 1981). In a British survey, B. cereus mastitis accounted for 0.3% of cases (Johnson, 1986), whilst in the Sydney region of Australia, 119 cows were diagnosed with B. cereus mastitis between 1960 and 1985 (Johnson, 1986). However, no previous case reports have been found for cattle in New Zealand, although it is isolated from time to time in routine culture of milk from cows with inexplicably high somatic cell counts...

Claw lameness in dairy cattle: New Zealand-based research.

Abstract Extract Lameness in dairy cattle has significant welfare implications, and causes major losses to the dairy industry worldwide. The causes of lameness are multifactorial and contributing factors include environment, behaviour, management, nutrition, infection, and conformation or genetics.

Transcutaneous ultrasound over the right flank to diagnose mid- to late-pregnancy in the dairy cow

OBJECTIVE To investigate the practical application and image quality of transcutaneous ultrasonography across the right flank for the diagnosis of mid- to late-gestation in cattle. PROCEDURE Dairy cows of known pregnancy status were used to establish criteria for the identification of mid- to late-stage pregnancy by transcutaneous ultrasonography. Factors involved in the practical application of transcutaneous ultrasound for routine use in pregnancy diagnosis in dairy cattle were also examined. RESULTS Transcutaneous ultrasound, using a 3.5-MHz sector transducer applied over the caudodorsal right flank fold, allowed rapid and detailed visualisation of bovine pregnancy (i.e. fetus, fetal fluids, placentomes and/or fetal membranes) and could be used to establish criteria for the diagnosis of pregnancy. The commonly available cattle holding facilities of the herringbone dairy, rotary herringbone dairy, AI race or crush, and walk-through dairy all allow safe access to the right flank of a dairy or beef cow. However, transcutaneous scanning over the right flank is difficult in modern rotary turnstile dairies. CONCLUSION A 3.5-MHz sector transducer applied over the caudodorsal right flank fold allows detailed visualisation of the bovine fetus in most types of cattle-holding facilities. Further investigation of the sensitivity and specificity of this technique over the entire gestation period and its possible use in ageing of the bovine fetus is merited.

Comparative efficacy of three dry-cow antibiotic formulations in spring-calving New Zealand dairy cows.

Abstract Aim: To evaluate the efficacy of a dry-cow antibiotic preparation containing cloxacillin plus ampicillin in a formulation that gives a 10-week duration of action, in comparison to products containing cephalonium (10-week action) or cloxacillin alone (7-week action). Methods: A total of 493 cows were selected from 6 spring-calving dairy herds in the Manawatu region of New Zealand, according to the criteria of the SAMM plan, to receive intramammary antibiotic therapy at the end of lactation (drying off). Cows were randomly allocated to receive 1 of the 3 dry-cow antibiotic products under investigation. Cows were examined twice during the dry period and twice daily during the first 10 days of their subsequent lactation for the presence of mastitis. Milk samples were collected from individual quarters at the time of drying off and at 7 and 28-35 days after calving, for determination of milk somatic cell counts (SCC). Bacteriology was carried out on milk samples taken from cows that developed mastitis during the first 10 days after calving. Results: No cows developed mastitis during the dry period. Sixteen cows developed clinical mastitis within 10 days of calving; there was no difference in incidence between treatments. Streptococcus uberis was the most commonly isolated organism. Mean SCC on Day 7 were lower (p = 0.019) in cephalonium-treated quarters (189.9 ± 28.4 × 103 cells/ml) than in cloxacillin-treated quarters (388.7 ± 71.2 x 103 cells/ml); values in quarters receiving cloxacillin plus ampicillin were intermediate (252.0 ± 47.0 × 103 cells/ml). SCC were similar between treatment groups on Day 28–35. Conclusions: The use of a combination of cloxacillin plus ampicillin was effective for the prevention of mastitis during the dry- and peri-calving-periods in pastured dairy cattle.

Association between placentome size, measured using transrectal ultrasonography, and gestational age in cattle.

Abstract AIM: The aim of this study was to estimate whether fetal age could be accurately estimated using placentome size. METHODS: Fifty-eight cows with confirmed conception dates in two herds were used for the study. The length of the long axis and cross-sectional area of placentomes close to the cervix were measured once every 10 days between approximately 60–130 days of gestation and once every 15 days between 130–160 days of gestation. Four to six placentomes were measured using transrectal ultrasonography in each uterine horn. A linear mixed model was used to establish the factors that were significantly associated with log mean placentome length and to create an equation to predict gestational age from mean placentome length. Limits of agreement analysis was then used to evaluate whether the predictions were sufficiently accurate for mean placentome length to be used, in practice, as a method of determining gestational age. RESULTS: Only age of gestation (p<0.001) and uterine horn (p=0.048) were found to have a significant effect on log mean placentome length. From the three models used to predict gestational age the one that used log mean placentome length of all placentomes, adjusting for the effect of horn, had the smallest 95% limits of agreement; ±33 days. That is, predicted gestational age had a 95% chance of being between 33 days greater and 33.7 days less than actual age. This is approximately twice that reported in studies using measurement of fetal size. CONCLUSIONS: Measurement of placentomes near to the cervix using transrectal ultrasonography was easily achieved. There was a significant association between placentome size and gestational age, but between-cow variation in placentome size and growth resulted in poor agreement between placentome size and gestational age. CLINICAL RELEVANCE: Although placentomes can be easily visualised during diagnosis of pregnancy using transrectal ultrasonography, mean placentome size should not be used to estimate gestational age.

Postpartum gonadotropin secretion in Holstein-Friesian dairy cows differing genetically in liveweight

Abstract AIM: To determine whether there are differences in postpartum gonadotrophic activity between strains of Holstein-Friesian dairy cows genetically selected on mature liveweight that might explain differences between the strains in fertility, and the interval between calving and the resumption of ovarian follicular activity. METHODS: Mixed-age Holstein-Friesian cows fed generous allowances of ryegrass/white clover pasture, and genetically selected for heavy (H) or light (L) mature liveweight, were given 10 µg buserelin on Days 21, 28, 35 and 42 (Experiment 1a;n=8/ group), or Days 7, 14, 21 and 28 (Experiment 1b; n=8/group) postpartum. The same dose of buserelin was also given to first-calved heifers from each strain (Experiment 1c; n=6/group) on Days 7, 14, 21, and 28 postpartum. Luteinising hormone (LH) concentrations were measured in serial blood samples that were taken for up to 240 min after administration of buserelin. In Experiment 2, serial blood samples were taken at 15-min intervals from H and L cows (n=7/group) over 8 h on Days 14, 21, 28 and 35 postpartum, to examine the endogenous secretion patterns of LH and follicle stimulating hormone (FSH). The time-course of the restoration of positive feedback between oestradiol and LH was examined by giving 1 mg oestradiol ben-zoate (ODB) 48 h after administration of 500 µg cloprostenol to mixed-age cows from each strain on Days 7 and 21 (n=8/group), or 14 and 28 (n=8/group) after calving (Experiment 3). Relationships between nutrition and the restoration of positive feedback were studied by giving 0.75 mg ODB/500 kg liveweight on Day 17 or 18 after calving to pure-bred Holstein (OSH) and New Zealand Friesian (NZF) cows that were fed either pasture (n= 12 OSH, 12 NZF) or a total mixed ration (TMR; n= 13 OSH, 12 NZF) (Experiment 4). Plasma LH and FSH concentrations were measured in samples collected for 42 h (Experiment 3) or 48 h (Experiment 4) after treatment with ODB. Milk progesterone concentrations were measured 3x weekly to define the reproductive status of animals in each experiment. Conception rates were recorded for animals in all of the experiments. RESULTS: First-service conception rates were lower (p<0.05) in H than L cows (46% vs 59%). In Experiments 1b and 1c, LH response to buserelin increased between Days 7 and 28 postpar-tum (both p<0.001), but did not differ between strains (p=0.77 and p=0.19, respectively). In Experiment 1a, LH responses to buserelin did not change between Days 21 and 42 postpar- tum, but overall mean peak concentrations were significantly (p<0.001) greater in L than H cows. In Experiment 2, anoestrous H cows had higher mean (p=0.004) and episodic (p=0.001) concentrations of LH than did L cows, but in cows that had active corpora lutea there were no such differences. There were no differences in FSH concentrations between strains. LH secretion in response to exogenous oestradiol (Experiment 3) increased between Days 7 and 28 postpartum (p<0.001), but there were no differences between strains. Responses were also similar in OSH and NZF cows on Day 17 or 18 postpartum, although there was a significant effect of ration upon the proportion of cows that exhibited an LH surge (20/24 cows on grass vs 12/25 on a TMR; p=0.005). CONCLUSION: These results confirm that H cows have poorer first-service conception rates than L cows, but do not support an hypothesis that there are major differences between these strains of Holstein-Friesian dairy cows in the rate of restoration in the hypothalamo-pituitary axis. However, in anoestrous cows, differences between strains in the endogenous release of LH may be related to an earlier onset of oestrous cycles in H animals.

A case of bovine placental mole associated with twin embryonic death and resorption

Abstract Extract Bovine embryonic or foetal death with persistence of the foetal membranes has been reported to occur uncommonly (Folger, 1937; Kennedy and Miller, 1993). Following death and resorption of the embryo, the membranes may persist as an empty cystic structure, which corresponds in size to that of the foetal membranes of a viable pregnancy at 3–4 months gestation. Such a structure is known as a cystic placental mole. In such cases, both the allantois and amnion may be present. Folger (1937) was the first to describe this condition and an unusual cystic placental mole the size of a 3–4 month-old pregnancy, that contained only clear gelatinous fluid and accompanied by retention of the corpus luteum, has also been described by McEntee (1970). Such structures may become infected and form a pyometra, or may undergo necrosis and be expelled. This condition should not be confused with hydatidiform mole, which appears as a cluster of grape-like translucent cysts or villi of the placenta that are expelled during third-stage labour (Gylstorff, 1985). The latter is the more common occurrence in humans (Hewani et al, 1999; Salehnia et al, 2000). An abnormal embryonic development, characterised by formation of an embryonic vesicle without an embryo, has also been reported in a mare (Vanderwall et al, 2000).