Animal- and herd-level factors associated with onset of puberty in grazing dairy heifers.

AIMS: To explore animal- and herd-level risk factors influencing age at puberty in predominantly Holstein-Friesian dairy heifers managed in seasonal, pasture-based systems. METHODS: Heifers born in spring 2018 (n = 5,010) from 54 commercial dairy herds in New Zealand were visited on three occasions when the mean heifer age, within herd, was 10 (visit 1; V1), 11 (V2) and 12 (V3) months old. Blood samples were collected on each visit and liveweight, stature and anogenital distance (AGD) were measured at V2. Heifers were defined as having reached puberty at the first visit where blood progesterone was elevated (≥ 1 ng/mL). Animal-level response variables included pubertal status by V1, V2 and V3, and age at puberty (or age at V3 plus 31 days for those that had not attained puberty by V3). To explore herd-level management factors, farmers answered a questionnaire relating to animal location, land type, health, feeding, and management between weaning and mating. A partial least squares regression was undertaken to identify herd-level factors associated with the greatest influence on puberty rate within herd. RESULTS: The mean age at puberty was 352 (SD 34.9) days. Heavier animals at a greater proportion of expected mature liveweight based on their breeding value for liveweight, or animals with a higher breed proportion of Jersey and lower breed proportion of Holstein, were associated with earlier puberty. Herd puberty rates varied widely among enrolled herds, and averaged 20%, 39% and 56% by V1, V2 and V3, respectively. Liveweight, followed by breed and land type, had the greatest influence on the herd puberty rate. Heifer herds with a greater mean liveweight (absolute and proportion of expected mature weight) or greater Jersey proportion had more animals that reached puberty at any visit, whereas herds located on steep land or with greater Holstein breed proportions had lower puberty rates. Management-related factors such as vaccinations, provision of feed supplements, and weighing frequency were also herd-level risk factors of puberty but had less influence. CONCLUSIONS AND CLINICAL RELEVANCE: This study highlights the importance of having well-grown heifers for increasing the chances of earlier puberty onset and the effect of breed and youngstock management to achieve growth targets. These outcomes have important implications for the optimal management of heifers to achieve puberty before their maiden breeding and for the timing of measurements to potentially incorporate a puberty trait in genetic evaluations.

Prevalence and calf-level risk factors for failure of passive transfer in dairy calves in New Zealand.

AIM To determine the prevalence of failure of passive transfer (FPT) in dairy calves in New Zealand and to assess a range of potential calf-level risk factors for their association with FPT. METHOD Between July and September 2015, 107 dairy farms in nine regions across New Zealand were visited on three occasions: before 20% of cows had calved, when ∼50% of cows had calved, and when the last 10-20% of cows were calving. Farms were randomly selected from the client list of participating veterinary practices. On each farm, blood samples were collected from 10-20 calves between 24 hours and 8 days old and concentrations of total protein (TP) in serum determined. Calf identification, date of birth, dam's age and breed, details of colostrum feeding and the farmer's health assessment of the calf on arrival at the calf rearing facility were recorded. Concentrations of TP in serum ≤52 g/L were used to define FPT. RESULTS Of 3,819 calves sampled, 1,263 (33 (95% CI=31.6-34.6)%) were diagnosed with FPT, and the prevalence within farms ranged from 5-83%. Calf-level risk factors that were associated with increased odds of FPT were increasing age of dam (OR=1.12; 95% CI=1.08-1.16), calves recorded as unhealthy compared to healthy upon arrival at the calf rearing facility (OR=2.59; 95% CI=1.60-4.19), calves sampled on farms in Otago (OR=2.85; 95% CI=1.42-5.74) and Southland (OR 2.31; 95% CI=1.15-4.67) compared to the Far North, and calves sampled in the middle compared to the early calving period (OR=1.24; 95% CI=1.03-1.51). CONCLUSION On the farms visited FPT was diagnosed in one third of dairy calves. Calf-level risk factors for FPT included age of dam, health status of calf, region, and time of the calving period. Further investigations are required to establish why these are associated with increased odds of FPT. CLINICAL RELEVANCE These results provide a baseline for benchmarking, which, alongside the reported calf-level risk factors, can be used by veterinarians to improve colostrum management.