BODY-TEMPERATURE AND ENDOCRINE INTERACTIONS BEFORE AND AFTER CALVING IN BEEF-COWS

Multiparous beef cows (n = 7) were used to evaluate peripartum changes and interactions among body temperature (BT) and circulating progeste rone (P-4), estradiol-17 beta (E-2), triiodothyronine (T-3), cortisol, thyroxine(T-4), and 13,14-dihydro-15-keto-prostaglandin F-2 alpha (PG FM) concentrations. Electronic temperature monitors were placed under the obliquus abdominis internus muscle of the left flank, and BT was m easured using radiotelemetry every 3 min for 10-s periods from 144 h b efore to 24 h after calving. Environmental temperatures (ET) were reco rded hourly. Body and environmental temperatures were averaged, separa tely, within 8-h periods. Blood samples were collected every 8 h, and hormone concentrations were measured. Time of day affected BT(P < .01) , at 0300 cows had the lowest BT, at 1900 the highest, and at 1100 val ues were intermediate. Body temperature remained relatively constant ( P > .10) from 144 to 56 h before calving and from 8 to 24 h after calv ing but decreased (P < .01) from 48 to 8 h before calving. Precalving BT was affected (P < .01) by ET, but hour-before-calving (time) had th e greatest effect on BT during the 48 to 8 h immediately preceding par turition (b' = .41, P < .01) and was independent of ET effects. Before the BT decrease, cows gestating heifers had lower (P < .01) BT than c ows gestating bulls. Plasma E-2, PGFM, T-3, and T-4 concentrations bef ore the precalving decrease in body temperature were greater (P < .03) in cows gestating bull rather than heifer calves. Approximately 30% o f the variation (R-2) during the temperature decrease was explained by plasma hormone concentrations; PGFM (b' = -.30, P < .05) and T-3 (b' = -.22, P < .10) had the most significant effects. In conclusion, BT o f the cow before the precalving decrease was affected by ET and sex of calf. However, the prepartum BT decrease was independent of these var iables, and seemed partially endocrine-induced.