Mother-young relations and prolactin response to mammary stimulation in the cow: influence of milking and free or fettered suckling

Maternal behaviour and PRL response to mammary stimulation have been studied in three groups of 20 Friesian cows each, held according to three different systems of management. In the 1st group (group AL), the cows suckled 3 alien calves and were all kept in one pen after a fostering period of two weeks. In the second group (group AE), the cows suckled 3 alien calves twice a day when tethered. In this group, the fostering procedure was limited to 18 h. In the 3rd group (group T), the cows were separated from their calves just after birth and then milked twice a day. On day 45 after calving, mother-young relationships were observed in the three groups for one day, the animals all being kept with familiar or alien calves on this occasion. Then, on day 112 postpartum, the PRL response to suckling (groups AL and AE) or to milking (group T) was studied in 4 cows of each group. Group AL cows were maternal and selective. They preferentially suckled their foster calves rather than alien ones and suckling was carried out in parallel-inverse position. Group AE cows were also maternal but the relationships were not selective and suckling in parallel-inverse position was less frequent. Finally, most milked cows did not allow the calves to suck. A comparison of PRL response to mammary stimulation showed that the response of milked cows (group T) to milking was low whereas suckling by an alien calf in group AL did not lead to a PRL response; the presence of the 3 foster calves was needed to induce this response. These results indicate that breeding conditions after calving influence mother-young relationships and suggest that maternal behaviour is a modulating factor of PRL response to suckling.