Role of compensatory growth in lactation: a stair-step nutrient regimen modulates differentiation and lactation of bovine mammary gland.
Twenty Holstein heifers were assigned to either a control or test (stair-step compensatory; food restriction, followed by refeeding) growth group. The stair-step growth model was designed to induce distinctive compensatory allometric mammary development during three different hormonal states, coinciding with prepubertal, pubertal, and late gestational stages. Mammary tissues obtained by biopsy from pregnant and lactating cows were used for acini culture and chemical composition analysis. Test mammary tissues from late gestation heifers contained less (P = .067) fat than control counterparts (731 vs. 628 mg/g). DNA, RNA, and protein contents in test mammary tissue from late gestation cows were higher (P = .001 to .088) compared to control tissue. Milk protein secretion of test acini in culture was increased more than 20% over that of the control acini. Lactating mammary acinar cells in culture from test cows exhibited a 14% increase in amino acid uptake over that of the control. RNA dot-blot hybridization analysis revealed that alpha s1- and beta-casein mRNA accumulation in acini from test tissue was increased (P = .027 to .042) as much as 40-50%. During both food restriction and refeeding, concentrations of plasma growth hormone were elevated. Food restriction decreased levels of plasma insulin, whereas levels of insulin were elevated during refeeding. The long-term influence of compensatory growth upon subsequent lactation performance was also evaluated. Milk production data derived from previous two sequential growth trials showed that cows from test groups produced approximately 10% more (P = .001) milk compared to control counterparts. Results reinforce our postulation that compensatory growth induced by nutritional modulation regulates the differentiation and functional activity of the mammary gland.
Park
C S
CS
Department of Animal and Ranger Sciences, North Dakota State University, Fargo 58105.
Baik
M G
MG
Keller
W L
WL
Berg
I E
IE
Erickson
G M
GM
D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D002417:Cattle; D002454:Cell Differentiation; D004247:DNA / Q000032:analysis; D004032:Diet; D005260:Female; D006128:Growth; D013006:Growth Hormone / Q000097:blood; D007328:Insulin / Q000097:blood; D007774:Lactation / Q000502:physiology*; D008321:Mammary Glands, Animal / Q000032:analysis / Q000166:cytology / Q000187:drug effects / Q000502:physiology; D012313:RNA / Q000032:analysis
D007328:Insulin; D012313:RNA; D013006:Growth Hormone; D004247:DNA