title: Litter size determines circadian periodicity of nursing in rabbits.
abstract: Nursing in rabbits occurs inside the nest with circadian periodicity. To determine the contribution of suckling stimulation in regulating such periodicity, we varied the size of the litters provided (1, 2, 4, or 6-8 pups). Nursing does, kept under a 14:10 (L:D) photoperiod, were continuously videotaped from parturition into lactation day 15. Although parturitions occurred throughout the day, a significant negative linear correlation (p < 0.0001; r = -0.68) was evident between time of delivery and time of nursing on lactation day 1, regardless of newborn number: longer intervals between these two events were seen in does delivering in the early morning than in those that gave birth late in the day. In rabbits suckling 6-8 pups, a Rayleigh analysis revealed that the population vector best describing their nursing pattern (across lactation days 1-15) had a phase angle = 58° (corresponding to solar time 0352 h and rho = 0.78; p < 0.001). In contrast, the nursing pattern of does nursing litters smaller than 6 pups did not show circadian periodicity; rather, mothers showed multiple entrances into the nest box throughout the day. Cluster analysis revealed that the main equilibrium point of intervals between suckling bouts shifted from 24 h (6-8 pups) to 6 h (4 and 2 pups) and to as low as 4 h with 1 pup. In the groups nursing 2, 4, or 6-8 pups, most nursing episodes were followed by food and water intake. Those mothers also showed self-grooming of the ventrum and nipples after nursing. The incidence of these behaviors was lower in does nursing 1 pup. In conclusion, nursing in rabbits spontaneously occurs with circadian periodicity, but it is largely modulated by a threshold of suckling stimulation.
authors.affiliation: Centro de Investigación en Reproducción Animal, CINVESTAV-Universidad Autónoma de Tlaxcala, Tlaxcala, México. gabygmm@gmail.com
authors.forename: Gabriela
authors.initials: G
authors.lastname: González-Mariscal
authors.forename: Ana Celia
authors.initials: AC
authors.lastname: Lemus
authors.forename: Arturo
authors.initials: A
authors.lastname: Vega-Gonzalez
authors.forename: Raúl
authors.initials: R
authors.lastname: Aguilar-Roblero
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D000833:Animals, Suckling / Q000502:physiology*; D001522:Behavior, Animal; D002940:Circadian Rhythm / Q000502:physiology*; D016000:Cluster Analysis; D005260:Female; D007774:Lactation; D008098:Litter Size; D010507:Periodicity; D017440:Photoperiod; D011817:Rabbits; D013997:Time Factors