The effect of feed intake and growth hormone-releasing factor on lactating dairy cows.
Twenty-four lactating dairy cows, averaging 30.0 kg/d of milk and 159 d of lactation, were used to study the effect of feed intake and growth hormone-releasing factor in a 2 x 2 factorial arrangement. For the first 10-d period, cows had free access to a TMR and received a fixed amount of high moisture corn, protein supplement, and hay. In the second 10-d period, 12 cows were maintained on this high intake, and 12 cows received 70% of their previous intake (low intake). During the following 10-d period, each intake group was divided, and each of two subgroups (n = 6) received twice daily s.c. injections of saline or growth hormone-releasing factor (10 micrograms/kg of BW per injection). Feed restriction decreased milk production by 24%. Milk production increase was not different following growth hormone-releasing factor treatment for cows maintained at high intake (4.6 kg/d) or low intake (3.4 kg/d). Feed restriction increased concentration of growth hormone but did not affect IGF-I concentration. Growth hormone-releasing factor increased IGF-I concentration similarly for both intake groups but increased concentrations of insulin and IGF-binding proteins-1 and -3 only in the high intake group. Low intake did not affect growth hormone, IGF-I, or milk responses to growth hormone-releasing factor, but suppressed the increase in concentrations of insulin and IGF-binding proteins-1 and -3 following treatment with growth hormone-releasing factor for cows on high intake.
Lapierre
H
H
Agriculture Canada, Lennoxville, QC.
Pelletier
G
G
Abribat
T
T
Fournier
K
K
Gaudreau
P
P
Brazeau
P
P
Petitclerc
D
D
D000821:Animal Feed; D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism; D002417:Cattle / Q000502:physiology*; D004032:Diet; D004044:Dietary Proteins / Q000008:administration & dosage; D005260:Female; D005508:Food Deprivation; D013007:Growth Hormone-Releasing Hormone / Q000494:pharmacology*; D007328:Insulin / Q000097:blood; D018970:Insulin-Like Growth Factor Binding Protein 1; D018969:Insulin-Like Growth Factor Binding Proteins; D007334:Insulin-Like Growth Factor I / Q000378:metabolism; D007774:Lactation / Q000187:drug effects*; D003313:Zea mays
D002352:Carrier Proteins; D004044:Dietary Proteins; D007328:Insulin; D018970:Insulin-Like Growth Factor Binding Protein 1; D018969:Insulin-Like Growth Factor Binding Proteins; D007334:Insulin-Like Growth Factor I; D013007:Growth Hormone-Releasing Hormone