EFFECTS OF TRANSCUTANEOUS THERMAL AND ELECTRICAL-STIMULATION OF THE TEAT ON PITUITARY LUTEINIZING-HORMONE, PROLACTIN AND OXYTOCIN SECRETION IN OVARIECTOMIZED, ESTRADIOL-TREATED BEEF-COWS FOLLOWING ACUTE WEANING

The objective of the study was to determine if chronic electrical or thermal stimulation of sensory neurons on the surface of the teat is able to activate pathways that suppress the weaning-induced increase in luteinizing hormone (LH) secretion in beef cows. Treatment groups (n = 5 per group) consisted of: 1) control suckled (CS); 2) weaned plus electrical stimulation of the teat (ESTT); 3) weaned plus electrical stimulation of the tail (ESTL); 4) weaned plus thermal stimulation of the teat (TTT); 5) weaned plus thermal stimulation of the tail (TTL) and 6) weaned (WN). Cows were ovariectomized on Day 5 post partum (PP) and were treated with estradiol-17-beta to maintain a constant tonic baseline. Beginning on Days 17 to 21 post partum, cows were suckled by their own calf (control), weaned or weaned and electrically or thermally stimulated for 10 minutes every 6 hours for 4 days. Chronic transcutaneous electrical and thermal stimulation of the teat or tail failed to impede the unambiguous rise (P < 0.001) in LH pulse frequency and amplitude following weaning. Positive and negative feedback of estradiol on LH secretion was not affected by treatments. Relatively consistent episodes of oxytocin and prolactin release were observed following control-suckling, but responses to electrical and thermal stimulation were inconsistent. Chronic electrical or thermal stimulation of teat-specific or nonspecific loci did not attenuate heightened secretion of LH after weaning. The results are further evidence against a role for mammary somatosensory neurons in the suckling-mediated inhibition of LH secretion.