Serum bone biomarkers osteocalcin and pyridinoline in mares during pregnancy and lactation, and in foals during early post-natal life.

Breeding mares typically foal yearly. Little is known about the dynamics of maternal bone stores during gestation and lactation, the timing of any maternal bone mobilisation, re-accretion post-foaling, or the dynamics of bone metabolism in foals. We measured serum osteocalcin (OC) and serum pyridinoline (PYD) concentrations in 18 mares monthly from 6months gestation to foaling, and in both mares and foals for 4months after birth. From 6 to 11months of gestation, there was no change in mean monthly OC. Serum PYD increased between 7months gestation and foaling. After foaling, mean serum OC was low up to 14days, rising to peak at 1month. Serum PYD rose concomitantly during this period, but subsequently declined. The mare OC:PYD ratio fell to a nadir within 14days of birth, before rising to a peak at 2months. In foals, OC rose within the first 24h of birth to peak at 3months. PYD fell from birth levels by 1month of age. Maternal bone mobilisation occurs progressively from 8months of gestation until term, before increasing markedly in very early lactation. Net mobilisation switches to accretion by one to two months of foaling, suggesting that this is a period during which mares replenish their own bone stores. Changes in the ratio of OC to PYD indicate adaptation to the prevailing biological milieu. In foals, the increase in the OC:PYD ratio in early life reflects the dominance of bone accretion.

Natural exposure of horses to mosquito-borne flaviviruses in south-east Queensland, Australia.

In 2011 an unprecedented epidemic of equine encephalitis occurred in south-eastern (SE) Australia following heavy rainfall and severe flooding in the preceding 2-4 months. Less than 6% of the documented cases occurred in Queensland, prompting the question of pre-existing immunity in Queensland horses. A small-scale serological survey was conducted on horses residing in one of the severely flood-affected areas of SE-Queensland. Using a flavivirus-specific blocking-ELISA we found that 63% (39/62) of horses older than 3 years were positive for flavivirus antibodies, and of these 18% (7/38) had neutralizing antibodies to Murray Valley encephalitis virus (MVEV), Kunjin virus (WNV(KUN)) and/or Alfuy virus (ALFV). The remainder had serum-neutralizing antibodies to viruses in the Kokobera virus (KOKV) complex or antibodies to unknown/untested flaviviruses. Amongst eight yearlings one presented with clinical MVEV-encephalomyelitis, while another, clinically normal, had MVEV-neutralizing antibodies. The remaining six yearlings were flavivirus antibody negative. Of 19 foals born between August and November 2011 all were flavivirus antibody negative in January 2012. This suggests that horses in the area acquire over time active immunity to a range of flaviviruses. Nevertheless, the relatively infrequent seropositivity to MVEV, WNV(KUN) and ALFV (15%) suggests that factors other than pre-existing immunity may have contributed to the low incidence of arboviral disease in SE-Queensland horses during the 2011 epidemic.