EQUUS - - Medicalfro­nt -

A new study from France sug­gests that abrupt wean­ing can be so stress­ful that it al­ters a young horse’s per­son­al­ity.

Re­searchers at the French Horse and Riding In­sti­tute and the Na­tional In­sti­tute for Agri­cul­tural Re­search Val de Loire Cen­tre in Nouzilly se­lected 34 Welsh Pony mares and their foals for the study. The horses lived to­gether in large herds or pairs un­til the foals were about 8 months old, when wean­ing com­menced.

For the ex­per­i­ment, 16 of the mares and foals un­der­went a “tra­di­tional” wean­ing process: With­out any prepa­ra­tion or trial sep­a­ra­tions, the mares were sim­ply moved to a dif­fer­ent farm on wean­ing day.

The re­main­ing 18 mares and foals were handled dif­fer­ently: The pairs were sep­a­rated grad­u­ally over a five­week pe­riod, start­ing with 15 min­utes spent on op­po­site sides of a steel fence each day. The sep­a­ra­tion time was in­creased in­cre­men­tally--by two min­utes per day the first week, five min­utes per day the sec­ond week, 20 min­utes per day the third week and 30 min­utes per day the fourth week---un­til the pe­ri­ods lasted six hours. The mares and foals could see, hear and touch each other through the fence, but the foals could not nurse. On wean­ing day, the mares were taken to a dif­fer­ent farm dur­ing the sep­a­ra­tion pe­riod.

To quan­tify be­hav­ioral dif­fer­ences be­tween the

groups, the re­searchers ob­served the foals through­out the wean­ing process and doc­u­mented vo­cal­iza­tions, so­cial interactio­ns with other foals and stress-re­lated be­hav­iors, such as be­ing ex­tremely alert. The re­searchers also gave each foal a per­son­al­ity test im­me­di­ately af­ter wean­ing and again three months later. The test was de­signed to mea­sure re­ac­tiv­ity to hu­mans, gre­gar­i­ous­ness, fear­ful­ness, curiosity and ac­tiv­ity.

In ad­di­tion, the re­searchers checked sev­eral phys­i­o­log­i­cal pa­ram­e­ters to eval­u­ate each foal’s level of stress. These in­cluded blood con­cen­tra­tion of the stress hor­mone cor­ti­sol, the length of telom­eres---the pro­tec­tive “caps” on the ends of DNA strands that can be re­duced by stress in early life---and the ex­pres­sion of par­tic­u­lar genes. “In a pre­vi­ous ex­per­i­ment, we had al­ready found some dif­fer­ences in the ex­pres­sion of some genes in horses that live alone in in­di­vid­ual boxes com­pared to horses that live in an en­riched en­vi­ron­ment,” says Léa Lansade, PhD.

The data showed that foals who were weaned grad­u­ally vo­cal­ized and trot­ted less on the day of sep­a­ra­tion than did the young­sters re­moved from their dams abruptly. The pro­gres­sively weaned foals also had lower cor­ti­sol lev­els, and the per­son­al­ity tests showed that they were more cu­ri­ous, less fear­ful, less gre­gar­i­ous and less re­ac­tive to hu­mans than were their peers who were abruptly weaned.

What’s more, the dif­fer­ence be­tween the two groups of wean­lings were still ev­i­dent at least three months later. Lansade says these per­son­al­ity changes could be long-lasting or even per­ma­nent. “It is pos­si­ble, be­cause sudden wean­ing is a real trauma oc­cur­ring dur­ing the de­vel­op­ment of the young when per­son­al­ity is not fixed.

”The gene anal­y­sis showed that while fear, re­ac­tiv­ity and gre­gar­i­ous­ness cor­re­lated with high cor­ti­sol lev­els, curiosity was as­so­ci­ated with an in­creased telom­ere length and higher ex­pres­sion of genes in­volved in mi­to­chon­drial func­tions. “That shows that wean­ing mod­i­fies deeply the phys­i­ol­ogy of the an­i­mal, and that leads to a spe­cific tran­scrip­tomic fin­ger­print,” says Lansade. “These analy­ses are more ac­cu­rate to eval­u­ate the im­pact of chronic stress com­pared to be­hav­ior or cor­ti­sol lev­els. We are lucky to have the op­por­tu­nity to use these new tools in horses.”

Lansade says the du­ra­tion of the wean­ing pe­riod is prob­a­bly less im­por­tant than how the sep­a­ra­tion is car­ried out. “We do not know ex­actly how long a wean­ing pe­riod should be. But, I think that it is im­por­tant to ha­bit­u­ate the foal to be sep­a­rated very pro­gres­sively, only a few min­utes at the be­gin­ning, to avoid any stress. Peo­ple have to ob­serve their an­i­mals dur­ing the pro­gres­sive sep­a­ra­tions. In that way, they can adjust the length of the pro­ce­dure in func­tion of the re­ac­tions of the mare and the foals.”

Ref­er­ence: “Pro­gres­sive ha­bit­u­a­tion to sep­a­ra­tion al­le­vi­ates the neg­a­tive ef­fects of wean­ing in the mother and foal,” Psy­choneu­roen­docrinol­ogy, Novem­ber 2018

Foals weaned grad­u­ally were less fear­ful, less gre­gar­i­ous and less re­ac­tive to hu­mans than were their peers who were weaned more abruptly.

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