Broodmares are often sent long distances to be bred or foaled. Transport is a stress that can, in some instances, create problems such as embryonic loss or hormonal upsets that can interfere with normal cycling and breeding. Because of stresses associated with transport, a number of studies have been done in the last dozen years, to determine how travel affects the horse's physiological processes, especially those that sustain pregnancy.
Short hauls usually have no adverse effects, according to studies done at West Texas University Utah tate University, Colorado State University and Kansas State University. Researchers at Colorado found no significant difference in embryo loss among mares transported for nine hours and a control group that were not hauled. There were hormonal changes indicative of stress in the transported mares (changes which could cause abortion) but those mares had no higher embryo loss than the stay-at-homemares.
The 54 pregnant mares in the study were divided into three groups (the control group which stayed
home: mares that were transported at 16 to 22 days of pregnancy: and mares transported at 32 to 38 days of pregnancy). Blood samples were taken before, during and immediately after their trip, as well as 12, 24, 48 and 72 hours later. The tests showed stress induced hormone changes, and four of the 30 ransported mares aborted. But the pregnancy loss rate was not much different from the stay-at-home ares to which three out of 24 mares also aborted.
Most mares have no problems with transport during pregnancy, but the Colorado Study found that
mares, whose progesterone levels tend to be low, stand a greater chance of aborting when subjected to tressful travel situations during early pregnancy. Stress can cause a decline in progesterone (a
hormone which is necessary to maintaining the pregnancy).
n a normal mare, the stress of transport, especially short hauls, is temporary and not enough to cause roblems. But if the mare is already low on progesterone, there is more risk. If this type of mare must e transported, the horse owner should work with a vet to monitor and supplement progesterone levels o avoid embryonic loss. The researchers speculated that vulnerability to stress may be greatest at about 5 to 45 days after conception when the embryo is attaching itself to the placenta.
RANSPORT POSITION AFFECTS STRESS LEVEL
Researchers at Texas A & M University conducted studies in 1986 and 1987 to measure the stresses
associated with travel position - whether the horses are positioned frontward or backward during
transport, since there had been previous indications that horses facing backward during transport suffer less stress. In the Texas study, the behavior of the horses (facing backward or forward) was noted, Tounting the number of foot movements, the times the horse hit the sides (and the front or back of their restraints), the times they lost balance and the number of shifts in position taken to maintain balance.
The horses were also hooked up to a portable recorder to continuously monitor heart rates. To measure stress hormones, blood samples were taken before they were loaded, in the van or trailer before it started moving, and during the trip. The horses facing backward fared much better than the horses facing the front.
