North
Dakota State University Department of Animal and Range Sciences
Dairy Research
North
Dakota State University
Department
of Animal and Range Sciences
Dairy
Research
Current Projects
1. Stair-Step Nutrition and Growth Development of Replacement Heifers
The economic future of livestock operations depends largely on a sound rearing
program for replacement heifers. Successful replacement heifer regimens, in
turn, are determined by efficiency of heifer growth and, more importantly, their
subsequent lactation potential. The basic idea of our stair-step compensatory
nutrition regimen is to reduce energy levels when heifers are not as likely
to put it to good use and to push energy at times when the animal can make the
best use of supplemental energy.
1.1 Dairy and Beef Replacement Heifer Development System
The long-term goal of this research was to develop a nutrition regimen that
enhances lactation potential of heifers. Specifically, to determine the extent
of growth and lactation potential of beef heifers raised on a simplified stair-step
feeding program imposed during gestation.
Parallel studies were conducted using dairy and beef heifers. At 14 months of age, all heifers were bred and reared according to routine management practices at the respective research units. At approximately 18 months of age (ca. 3 months pregnant), heifers were assigned equally to one of two dietary treatments: (A) the control or (B) the stair-step compensatory nutrition regimen. The control heifers were fed diets meeting the National Research Council (NRC) standards. The stair-step heifers were subjected to a stair-step (3-3- month) feeding regimen, meeting NRC (Dairy and Beef) requirements except for energy content, by feeding an energy-restricted diet (70% of the energy requirements) for 3 months, followed by a high energy realimentation diet (130% of the energy requirements) for the last trimester of gestation. Heifers were housed and fed in individual pens at each research center. Upon completion of the stair-step nutrition regimen (i.e., calving), all heifers were fed diets that met NRC recommendations with seasonal adjustments for availability of roughage at each location and were managed as one group. After completion of the first lactation cycle, heifers were rebred and maintained according to the routine herd practices of the North Dakota State University Dairy and Beef research centers.
Dairy and beef heifers raised on a stair-step feeding regimen had general enhancement in the efficiency of growth, reproductive performance and transition health. Beef heifers on the stair-step regimen experienced fewer negative effects (high birth weight, dystocia, and(or) lactation suppression) that can occur when feeding energy in excess of requirements during late gestation. Indeed, beef heifers that were raised on a one-step feeding program had enhanced overall reproductive efficiency compared with conventionally reared animals. For dairy heifers, the one step compensatory nutrition regimen can be used to achieve similar growth and lactation potential as conventionally-reared primiparous Holstein cows. Further, a simplified single step compensatory growth regimen implemented during the last trimester of gestation positively affected transition health of Holstein heifers.
1.2 Stair-step Compensatory Growth Regimen in Dairy Heifers and its Effects on Transition Health
The objective of this experiment was to determine if compensatory growth has any effect on the immune system and transition health of heifers. The average weight of the heifers following the first 90 days of the trial were not statistically different between treatments; however, the stair-step group did weigh numerically less. By the conclusion of the trial, the heifer weights were similar between treatments. Colostrum samples were analyzed for the immunoglobulins IgG1, IgG2, IgM, IgA. Only IgG1 was lower in colostrum from the stair-step group. Further analysis of colostrum will be needed to explain this difference. Milk yield was not influenced by treatment, nor was milk fat or milk protein. Insulin was higher in the stair-step group and white blood cell count was similar for both treatments. T-cells were also analyzed (CD3, CD4, CD8, and gamma/delta). Preliminary data supports 1) the simplified one-step compensatory growth model did not negatively affect transition health of Holstein heifers; 2) the one-step model can be used to achieve similar growth and lactation potential of primiparous (first-calf) Holstein cows; 3) the simplified stair-step model did not alter milk production; and 4) the one-step stair-step model can be used to lower feed costs.
1.3 Compensatory Nutrition-mediated Proliferation and Gene Expression in HC11 Murine Mammary Cells
Our objective was to study the effect of energy restriction and realimentation upon proliferation and differentiation of HC11 murine mammary epithelial cells in culture. In two separate experiments, cells were grown in a humidified environment at 37oC and 5% CO2 in a medium consisting of RPMI 1640 with L-glutamine, 10% fetal bovine serum, 5 g/ml insulin, 10 ng/ml epidermal growth factor, and 50 g/ml gentamicin. Cells were then preincubated for 24 h without epidermal growth factor. The subsequent induction medium included the lactogenic hormones of 0.1 M dexamethasone and 5 g/ml prolactin. Control medium contained 2 mg/ml glucose, while restriction medium contained 0.5 mg/ml glucose, and realimentation medium contained 3 mg/ml glucose. When glucose was restricted during induction, proliferation of treatment cells was reduced 32%; after realimentation following energy restriction, treatment cells had 33% greater proliferation than control cells. Protein synthesis was not different after restriction, but was 6.5% greater in treatment cells following realimentation.
When glucose levels were modified during logarithmic growth, proliferation
and protein synthesis of treatment cells tended to be higher than that of the
control 48 h after induction. Cells in the compensatory nutrition regimen exhibited
a significant increase in the expression of poly(ADP-ribose) polymerase and
xanthine oxidoreductase during the first 48 h of induction. Results indicate
that a compensatory nutrition regimen stimulates mammary cell proliferation
and protein synthesis.