L. Gallo et al., EFFECT OF SLOW-RELEASE SOMATOTROPIN ON THE PATTERN OF MILK-YIELD BETWEEN AND WITHIN INJECTION INTERVALS, Journal of dairy science, 80(1), 1997, pp. 46-51
Thirty-six Alpine goats (10 primiparous and 26 multiparous) were used
to study the milk yield response induced by recombinant bST administer
ed in a sustained-delivery vehicle. Eighteen goats were injected with
recombinant bST at 4-wk intervals from about 7 wk postpartum for 12 wk
. Patterns of milk yield were highly affected by injection of recombin
ant bST. Milk yield of treated goats increased from day of injection,
peaked between d 3 to 5 after treatment, and then decreased progressiv
ely. This pattern of response was-well fitted by a curve containing ta
o exponential terms: Y-i = A x [exp(-k(1)d(i) - exp(-k(2)d(i))], where
Y-i = daily relative response of treated goats to recombinant bST, co
mputed as a deviation of least squares means of milk yield at day i (i
= 0, ..., 26) of the treatment interval from least squares means of m
ilk yield at d 27 of the treatment interval; A constant; k(1) and k(2)
= response rate parameters; and d(i) = day from treatment (i = 0, ...
, 27). Administration of recombinant bST also improved persistency of
lactation, and the overall milk yield response to exogenous hormone wa
s 300 g/d (13.9%) higher than the yield of untreated goats. This respo
nse was due to both the short-term response immediately after injectio
n (53%) and the medium-term effect on lactation persistency.