Concurrent Lactation and Pregnancy: Pregnant Domestic Horse Mares Do Not Increase Mother-Offspring Conflict during Intensive Lactation

Abstract

Lactation is the most energy demanding part of parental care in mammals, so parent-offspring conflict arises over milk provided by the mother. In some species females commonly become pregnant shortly after parturition of previous young. This further intensifies mother-offspring conflict due to concurrent pregnancy and lactation. In equids it has been well established that pregnant females wean their foals earlier than non-pregnant ones. Intensified mother-offspring conflict was presumed to associate with pregnancy also during the period of intensive lactation, i.e., before the weaning process starts. We investigated the effect of pregnancy on suckling behaviour characteristics as indicators of mother-offspring conflict in domestic horses. Contrary to expectation, here we provide evidence of a decreased mother-offspring conflict related to pregnancy in lactating females during first two trimesters of pregnancy. Pregnant mares provided longer suckling bouts and did not reject or terminate suckling of their foals more often than non-pregnant mares. Our results suggest that pregnant mares cope with parallel investment into a nursed foal and a foetus through enhancing nursing behaviour in early stages of pregnancy before the initially low requirements of the foetus increase. They compensate their suckling foal with the perspective of its early weaning due to ongoing pregnancy.

Domestic Foal Weaning: Need for Re-Thinking Breeding Practices?

“…During most of the lactation period (i.e., from the first month to the seventh), foals terminate most suckling bouts (at least 50%). From the eighth month of lactation (as compared to earlier stages), termination of suckling bouts by dams increase and dams tend to exhibit more signs of rejection during their foals' suckling initiatives: thus, they may reject suckling attemps or terminate suckling bouts by moving away, blocking access to the nipple by flexing a hind leg, or more usually at that stage by displaying threats or other mild agonistic behaviors [37,38,40,48,49,51]. This increase in maternal rejection at the end of lactation has been considered an important step in the weaning process [38,40], although it has not been systematically observed [37,52] and could rather be affected by the nutritional status of the mare [38].…”

Behavioral Factors Affecting Reproduction in Domestic Horses: Sociobiological Approach

“…They are thus sensitive to intensive maternal investment due to concurrent pregnancy and lactation. Pregnant mares cope with parallel investment into a nursed foal and a fetus through enhancing nursing behavior in early stages of pregnancy before the initially low requirements of the fetus increase [53]. Nevertheless, lowering mare's investment for costly nursing allocated to non-filial offspring by killing it may significantly advance resources invested in stallion's own progeny.…”

Time spent suckling is affected by different social organization in three zebra species

“…Because suckling bout duration and frequency should not reflect energy intake, but the amount of maternal care in current offspring (Mendl & Paul, ; Cassinello, ; Therrien et al ., ; Pluháček et al ., 2010 a ; Bartošová et al ., ), we presume that they would be affected more by variability in social life of different species than by environmental adaptation. Therefore, we predicted that the time spent by suckling would increase with increasing intolerance towards foals in different zebra species, that is, foals of mountain zebras should spend the longest time by suckling, followed by foals of plains zebras and by foals of Grévy's zebras.…”

“…Previous studies on suckling behaviour of various equid species ( E. caballus , E. hemoinus , E. quagga , E. zebra ) reported that suckling bout duration and frequency could be affected highly by the age and the sex of the foal, the animal terminating the bout, parity of the mare and mother's pregnancy (Joubert, 1972 b ; Tyler, ; Rogalski, ; Rashek, ; Duncan et al ., ; Crowell‐Davis, ; Becker & Ginsberg, ; Smith‐Funk & Crowell‐Davis, ; Pluháček, Bartoš & Bartošová, 2010 a ; Bartošová et al ., ). Thus, we included these factors in our analyses, too.…”