Submitted to: British Journal of Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 24, 2011
Publication Date: June 23, 2011
Citation: Waterman, R.C., Roberts, A.J., Geary, T.W., Grings, E.E., Alexander, L.J., MacNeil, M.D. 2011. Effect of reduced heifer nutrition during in utero and post-weaning development on glucose and acetate kinetics. British Journal of Nutrition. 106:1702-1712. Interpretive Summary: One of the major production expenses for beef cow/calf enterprises is associated with the development of replacement heifers and their related feed inputs. The present constraints (industry standard) are such that heifers need to obtain a certain body weight (60 to 65% of mature weight) and be pubertal by 14 months of age in order achieve the goal of heifers having their first calf as a 2-year-old. It is thought, for cow/calf producers in the Northern Great Plains this requires providing additional feed resources above that provided by native rangelands from weaning to breeding. Proper development of replacement heifers is crucial in order to obtain puberty and promote lifetime productivity and optimal milking ability. Low levels of nutrition following weaning can delay the onset of puberty while high levels of nutrition following weaning may reduce lifetime productivity, longevity in a cow herd, and limit milking ability of heifers. Researchers concluded that producers have many options to develop heifers as long as necessary weight is achieved by breeding (14 months of age). Therefore, producers encounter the challenge of obtaining reproductive competency (i.e., puberty) in heifers while minimizing input (i.e., harvested feedstuffs) costs. However, over the last few decades it is evident that mature cow size has increased which makes it even more difficult to economically feed heifers to achieve the standard BW by breeding. Recent research provides evidence that harvested feed inputs can be reduced without sacrificing reproductive performance or by targeting a lesser BW (% of mature BW) for replacement females. Therefore, producers encounter the challenge of obtaining reproductive competency (i.e., puberty) in heifers while minimizing input (i.e., harvested feedstuffs) costs. To evaluate the metabolic influence of reduced harvested feedstuffs, during the heifer development period, an evaluation of the efficiency of tissue nutrient uptake of specific energetic metabolites can be evaluated (i.e., glucose and acetate). Evaluation of these metabolites will provide a greater understanding of how nutrient between restricted fed heifers and heifers fed all they can consume differ. An important outcome from this study was that heifers receiving a 20% reduction in feed had the same tissue uptake of glucose and acetate as heifers that were fed to appetite both at the termination of a 140-d development period and again approximately 17 months later when heifers were pregnant with their second calf. Thus, allowing for a reduction in the amount of feed required and input costs with no detrimental effects on uptake of glucose and acetate.
Technical Abstract: Energetic efficiency was evaluated in composite heifers born from dams receiving one of two levels of winter supplementation and then at weaning randomly assigned to their own nutritional treatment of either control (CON; fed to appetite; n = 8/yr) or restricted (RES; fed 80% of that fed to controls adjusted to a common BW: n = 8/yr) in a two year study. A glucose tolerance test (GTT) and acetate clearance test (ACT) administered on heifers at the termination of a 140-d development period when heifers were approximately 403 d of age and consuming silage based diets. Heifers were subjected to an additional GTT and ACT at 940 d of age when pregnant with their second calf and grazing dormant forage. No differences were measured (P > 0.10) for heifer treatment for baseline serum metabolites or measures in GTT and ACT. However, changes in baseline serum concentrations (P > 0.05) were different between metabolic challenges which occurred at different stages of development. Time to reach peak acetate concentration following infusion occurred sooner at the second metabolic challenge, but acetate disappearance (P = 0.22) and a half-life (P = 0.74) were similar to the first metabolic challenge. A trend for glucose half-life to be shorter in heifers from dams receiving in utero winter treatments that support marginal growth was observed (P = 0.083). Heifers developed with lower total dry matter intake during a140 d development period had similar glucose and acetate incorporation rates as ad libitum fed heifers throughout different production stages.