The Need for Stimulation in Various Bovine Breeds and Other Species

A review of the scientific literature on the stimulation requirements for milk ejection in bovines and other species is presented. Differences in cisternal capacity, lactation number, and stage of lactation are known to influence stimulation requirements. The role of calf suckling compared to other types of tactile stimulation in the milk ejection process is discussed for Bovines, buffalo, camels, swine and other species. The results of a field study of the effect of calf suckling on peak milk flow rates are presented. COMPARATIVE PHYSIOLOGY OF MILK REMOVAL A common mechanism of milk ejection through the release of oxytocin followed by contraction of myoepithelial cells and removal of the alveolar milk seems to apply to the majority of species studied. However, there are species differences in the need or degree of oxytocin release at milking (Akers, 2002). For instance, two animal models are used to explain the different patterns of the milk ejection reflex. In the rabbit model, initial suckling by the litter induces the release of a single pulse of 20-50 mμ oxytocin and milk removal is completed in 2-5 minutes. In the rat model, multiple pulses of 0.5 to 1.0 mμ of oxytocin are released at intervals of 5-15 min throughout suckling periods of 30-60 min. The sow’s milk ejection is similar to the rabbit model whereas human and ruminants’ milk ejection pattern is more similar to the rat model (Cross, 1977). There are large differences in the proportion of total milk stored within the cistern among ruminant dairy species. Specialized dairy cows store less than 30% of the total milk yield volume in the cistern after a normal milking interval (Ayadi et al., 2003). In contrast, the cisternal milk accounts for up to 75% in dairy goats (Marnet and McKusick, 2001), and in sheep it ranges from more than 50% for dairy breeds (McKusick et al., 2002) to less than 30% for meat breeds (Caja et al., 1999). It has been argued that milk ejection may not be essential for adequate milk removal in animals that store most of the milk in the gland cisterns (Cross, 1977; and Akers, 2002). However, Marnet and McKusick (2001) state that oxytocinmediated milk ejection is still of substantial importance in small ruminants for the UW-MRIL Proportion of Milk Stored in Cistern / Alveolus 0% 20% 40% 60% 80% 100%