THE BLOOD LEVELS OF OXYTOCIN DURING SUCKLING AND HAND-MILKING IN THE GOAT WITH SOME OBSERVATIONS ON THE PATTERN OF HORMONE RELEASE

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Abstract
SUMMARY Thirty-six series of serial jugular blood samples were collected from 12 goats during suckling during the first 3 weeks of lactation and the transient appearance of oxytocin (5–86 μu./ml plasma) was detected in 24 of the series. Blood oxytocin was assayed on the lactating guinea-pig mammary gland. Forty series of serial blood samples were also collected from 12 goats during hand-milking over the first 6 weeks of lactation and the transient appearance of oxytocin (5–160 μu./ml plasma) was observed in 25 of these. The results indicated that: (1) oxytocin may be released at any time during the suckling or milking process; (2) in only 16% of experiments where oxytocin was released and 5·6% of all experiments investigated could a conditioned release of oxytocin be induced in goats before suckling and in no case before hand-milking despite a vigorous and prolonged conditioning period; (3) there is a large degree of variability in the pattern of oxytocin release between animals and between individual suckling and milking episodes in the same animal; (4) suckling and hand-milking are equally effective in causing the release of oxytocin; (5) stimuli arising during various stages of the suckling and hand-milking routines may be assigned a figure indicative of the relative effectiveness of these stimuli in terms of percentage probability in causing oxytocin release; (6) there is a greater probability of oxytocin release occurring before suckling than before hand-milking; (7) there is a very marked similarity in the pattern of oxytocin release both during and after teat stimulation in response to suckling and milking stimuli; (8) there is a greater probability of oxytocin being released in response to hand-milking during early lactation than during late lactation; (9) the milk-ejection reflex in the goat does not appear to be important for the achievement of normal milk yields during suckling or hand-milking.