Early life events associated with first lactation reproductive performance in southwest Victorian pasture-based dairy herds.

This was a prospective cohort study to determine how events from birth until first calving affect reproductive performance in the first lactation in pasture-based dairy herds in Victoria, Australia. Events during the preweaning (0 to 84 days), weaning to first breeding (85 to 473 days) and first breeding to first calving periods (474 to 804 days) were recorded and their association with reproductive performance during the first lactation was quantified. Reproductive performance outcomes included the number of days from first mating start date to first service (MSD-S1) and the number of days from first mating start date to first conception (MSD-CON). Predictors for reproductive performance included: passive transfer status as a calf; season of birth; age and breed of the dam; breed; the presence or absence of dystocia at the time of the heifer's birth; active feeding of colostrum versus being left on the dam for colostrum intake; presence of twinning; the presence or absence of preweaning diarrhoea; preweaning, prepubertal and postpubertal average daily gain; the presence or absence of periparturient disease at first calving; age at first calving; body condition score at first calving; sex of the first-born calf; the presence or absence of a stillborn calf at the first calving and requirement of assistance at first calving. Two Cox proportional hazards regression models were developed: the first for early life event variables associated with MSD-S1 and the second for early life events associated with MSD-CON. Heifers born in autumn and winter had 2.89 (95% CI 1.50 to 5.59, P = 0.002) times and 1.97 (95% CI 1.12 to 3.44, P = 0.018) times the daily hazard of being inseminated compared with heifers born in spring, respectively. For the MSD-S1 analyses heifers that gave birth to a live calf had 1.64 (95% CI 1.14 to 2.36, P = 0.008) times the daily hazard of being inseminated compared with heifers that had a stillborn calf. Increases in weight gain during the first breeding to first calving period by 0.1 kg/day increments increased the daily hazard of first insemination by a factor of 1.10 (95% CI 1.00 to 1.22, P = 0.043). Heifers that experienced periparturient disease had a significantly lower hazard of conception per day compared with heifers that did not experience periparturient disease at the first calving (HR 0.67, 95% CI 0.50 to 0.91, P = 0.009). Increases in weight gain during the first breeding to first calving period by 0.1 kg/day increased the daily hazard of conception by a factor of 1.10 (95% CI 1.01 to 1.21, P = 0.038). We conclude that of all the growth periods assessed in this study, events that occurred during the first breeding to first calving period (474 to 804 days) had the greatest association with reproductive performance in the first lactation. There should be a focus on increasing growth rates during this period and reducing the risk of stillbirth and periparturient disease to improve reproductive performance in the subsequent mating period after calving.

Reproductive performance of cows after fixed-time artificial insemination with ovulation synchronisation and re-synchrony in southern Australian dairy herds.

OBJECTIVE: To describe reproductive performance of lactating dairy cows after fixed-time artificial insemination (FTAI) with ovulation synchronisation and re-synchrony in Australian dairy herds, and to compare reproductive outcomes with those of conventional mating programs. METHODS: The study was conducted in two seasonally calving dairy herds in which lactating dairy cows (n = 675) were enrolled into three treatment groups: group 1, oestrus detection and AI for 34 days followed by a natural service period; group 2, FTAI on day 1 followed by re-synchrony of all cows prior to ultrasound pregnancy diagnosis at day 31 and FTAI of cows diagnosed not pregnant at day 34, then a natural service period; group 3, FTAI on day 1 followed by oestrus detection and AI for 34 days, then a natural service period. First-service conception rate (FSCR), 6-week in-calf (6WIC) rate and proportions pregnant at the end of mating were compared using logistic regression with farm fitted as a fixed effect. Times from mating start date to conception were described using survival analysis with Kaplan-Meier failure functions. RESULTS: FSCRs (45.3%, 49.1% and 45.6% for groups 1, 2 and 3, respectively) and proportions pregnant at the end of mating (77.6%, 76.0% and 76.8% for groups 1, 2 and 3, respectively) were similar for all groups. The 6WIC rate in group 2 was similar to that in group 3 (70.4% vs. 67.2%; P = 0.486), but tended to be higher than in group 1 (70.4% vs. 62.0%, P = 0.066). The median days to pregnancy for cows that conceived was 1 day in groups 2 and 3 and 10 days in group 1. CONCLUSION: Mating plans that use FTAI with ovulation synchronisation and re-synchrony during the AI period can achieve comparable reproductive performance to conventional mating programs in seasonally calving dairy herds.

Early-life events associated with first-lactation performance in pasture-based dairy herds.

This was a prospective cohort study to determine how events from birth until first calving affect performance during the first lactation in pasture-based dairy herds in Victoria, Australia. Events during the preweaning (0-84 d), prepubertal (85-473 d), and postpubertal (474-804 d) periods were recorded in 6 herds, and their association with first-lactation 100-d and 250-d total milk, fat, and protein yields was quantified. Predictors of first-lactation performance included passive transfer status as a calf; season of birth; age of dam; the presence or absence of dystocia at the time of the heifer's birth; the presence or absence of preweaning diarrhea; preweaning, prepubertal, and postpubertal average daily weight gain; age at first calving; the presence or absence of periparturient disease at first calving; sex of the first-born calf; the presence or absence of a stillborn calf at the first calving; and requirement of assistance at the first calving. Lactation performance was quantified using cumulative 100-d and 250-d milk, fat, and protein yields estimated from herd recording. A multivariable linear regression model was developed for each outcome: cumulative 100-d milk, fat, and protein yield and cumulative 250-d milk, fat, and protein yield. Heifers that experienced dystocia at the time of their birth produced 7.6 kg [95% confidence interval (CI): 1.8-13.3] less fat and 4.8 kg (95% CI: 0.6-8.9) less protein at 100 d in milk in the first lactation compared with heifers that were delivered without dystocia. Heifers born in the summer and autumn produced 20 L (95% CI: 0.8-40) more milk and 20 kg (95% CI: 5.9-33) more protein at 250 d in milk in the first lactation compared with heifers born in the spring. For 100 g/d increases in prepubertal average daily gain, heifers produced an additional 182 L (95% CI: 149-216) of milk, 4.1 kg (95% CI: 2.8-5.5) of fat, and 4.0 kg (95% CI 3.1-5.0) of protein at 100 d in milk and an additional 345 L (95% CI 264-425) of milk, 6.1 kg (95% CI 3.2-9.0) of fat, and 7.5 kg (95% CI 5.3-9.7) of protein at 250 d in milk. Postpubertal average daily gain was positively associated with 100-d milk yield and 250-d milk yield and protein production. We conclude that of all the growth periods assessed in this study, events that occurred during the prepubertal period (85-473 d of age) had the greatest effect on first-lactation performance.

Factors affecting colostrum quality in Australian pasture-based dairy herds.

OBJECTIVE: The aim of this study was to identify factors affecting colostrum quality in dairy cattle. METHODS: Colostrum samples were collected from lactating dairy cows (n = 990) from nine commercial dairy herds in south-west Victoria. Colostrum quality was measured using an optical Brix refractometer. Cow-level factors thought to influence colostrum quality included season of calving, dam breed and age, volume of first-milking colostrum produced and whether the dam leaked colostrum prior to calving. Multivariable logistic regression was used to quantify the association between each cow-level factor and whether or not colostrum was assessed to be of poor quality. RESULTS: Cows older than 5 years of age were less likely to have poor-quality colostrum compared with primiparous heifers (odds ratio (OR) 0.62, 95% confidence interval (CI) 0.11-0.89, P = 0.009). The odds of having poor-quality colostrum was increased in cows and primiparous heifers that leaked colostrum prior to calving (OR 2.06, 95% CI, 1.33-3.17, P = 0.001). Cows and primiparous heifers that produced ≥ 8.5 L of colostrum were 1.76 times as likely to have poor-quality colostrum as individuals that produced < 8.5 L (95% CI, 1.10-2.82, P = 0.018). Visual assessment of colostrum by the herd manager was moderately correlated with colostrum quality, with 69% of poor-quality samples being correctly classified. CONCLUSION: Although this study identified factors that increase the risk of poor-quality colostrum, we concluded that objective assessment using a Brix refractometer is a more reliable means of assessing colostrum quality.

Comparison of three diagnostic techniques for detection of rotavirus and coronavirus in calf faeces in Australia.

OBJECTIVE: Compare real-time reverse transcription polymerase chain reaction (qRT-PCR), a commercially available enzyme-linked immunosorbent assay (ELISA) and lateral flow immunochromatography assay (LAT) for the detection of rotavirus and coronavirus in faecal samples collected from diarrhoeic calves. DESIGN: Prospective survey. METHOD: Samples were tested at two separate facilities using a commercial ELISA and an in-house qRT-PCR. Simple logistic regression was performed to examine the relationship between the two tests. A subset of samples was screened using qRT-PCR, ELISA and a commercial LAT dipstick (132 faecal samples were tested for coronavirus and 122 samples for rotavirus). RESULTS: Of the 586 samples tested, 131 (22.39%) and 468 (79.86%) were positive for coronavirus and group A rotavirus, respectively, using qRT-PCR. The number of samples positive on ELISA for coronavirus and rotavirus was 73 (12.46%) and 225 (38.40%), respectively. Using LAT, 30 (22.73%) and 43 (35.35%) samples were positive for coronavirus and rotavirus, respectively. Simple linear regression revealed a statistically significant (P < 0.05) but weak (r(2) =-0.07 and -0.40) correlation between the rotavirus/coronavirus qRT-PCR and ELISA, respectively. There was also poor agreement between the LAT and qRT-PCR assays. CONCLUSION: The sensitivity and specificity of the commercial ELISA and LAT assays evaluated in this study were low compared with qRT-PCR. The low positive and negative predictive values of the assays suggests that they were of limited diagnostic benefit in the population sampled.

Prevalence of major enteric pathogens in Australian dairy calves with diarrhoea.

OBJECTIVE: Determine the prevalence of the major enteric pathogens in dairy and dairy beef calves with diarrhoea in Australia. DESIGN: Cross-sectional study. METHODS: Faecal samples from 84 Australian dairy and dairy beef properties (597 samples) were screened for rotavirus and coronavirus using real-time reverse transcription polymerase chain reaction, for Salmonella spp. using selective enrichment faecal culture, and for enterotoxigenic Escherichia coli (K99) and Cryptosporidium parvum using a commercial enzyme-linked immunosorbent assay. A logistic regression with random effects model was used to compare prevalence of pathogens in dairy and dairy beef operations. RESULTS: Enteric pathogens were isolated from 97.6% of outbreaks and 95.0% of samples. Rotavirus was the most common pathogen identified (477/597, 79.9%) followed by C. parvum (349/597, 58.5%), Salmonella spp. (142/597, 23.8%), coronavirus (129/597, 21.6%) and E. coli K99 (104/597, 17.4%). Multiple pathogens were identified on 96.4% of farms and from 71.0% of samples. Samples from dairy beef properties were more likely to have multiple pathogens than dairy properties (P < 0.05), whereas rotavirus and Salmonella spp. were more likely to be identified in samples collected from dairy beef than dairy properties (P < 0.05). CONCLUSION: Most outbreaks of calf diarrhoea in dairy and dairy beef operations involve multiple pathogens. Rotavirus and C. parvum were the most frequently identified pathogens across production systems. Salmonella spp. and rotavirus were more frequently identified in dairy beef operations.

Haemolytic anaemia in cattle in NSW associated with Theileria infections.

Several outbreaks of anaemia, jaundice, abortion and mortality in cattle in New South Wales were attributed to the intracellular parasite, Theileria buffeli. Disease occurred predominantly in periparturient animals that had been moved from inland to coastal areas. Diagnosis was made via exclusion of other causes of haemolytic anaemia and observation of the parasite in blood smears. Treatments included both registered and non-registered products. There is a possibility of a new strain of Theileria sp. in Australia and the possible vectors encountered in NSW are discussed.