Effects of feed restriction on milk production and metabolism in mid-lactation dairy cows
Availability of glucose precursors and a proper interorgan coordination during the metabolic cascade of adaptations occurring during periods of lower DMI, are the vital importance to achieve a successful transition from late gestation to lactation. The aim of the study was to determine metabolic responses to a short-term period of negative energy balance induced by feed restriction (FR) and the effect of abomasal supplementation of different amino acids (AA) or glucose. Seven multiparous Holstein cows (93 ± 15 DIM) were randomly assigned to 7 treatments in a 7 × 4 incomplete Latin square design. In 6 treatments, daily DMI was restricted to provide 60% of energy requirements during 5 d; the 7th treatment consisted of ad libitum (AL) intake. Feed was provided once daily at 0900 h. Effects of FR (AL vs RC), day, time within day, and interactions were evaluated with ANOVA using the MIXED procedure of SAS. Evaluating the effect of FR, milk yield (P < 0.01), milk protein concentration (P = 0.03) and yield (P < 0.01), and lactose yield (P < 0.01) were lower for RC, whereas milk fat (P < 0.01) and urea N concentrations were higher (P < 0.01). Treatment RC induced lower plasma insulin (P = 0.01) and glucose (P = 0.04) concentrations, with quadratic (P < 0.01 for both) decreasing trends reaching nadir on d 3. Concentration of NEFA was higher (P < 0.01) and increased quadratically (P < 0.01) with its maximum on d 3 during FR. Serum BHBA increased linearly (P = 0.04) for RC (RC x d; P = 0.16) with its peak at d 4. Catabolism of amino acids (AA) increased early during FR as indicated by plasma urea N increasing (P < 0.01) quadratically (P < 0.01), with its peak on d 2 and decreasing afterward. Accounting for all the amino-N circulating in form of urea or eliminated in milk as MUN, the decrease in concentration of all the AA in circulation analyzed here was not sufficient for the amount of urea synthetized. Therefore, it seems probable that body tissue protein was rapidly mobilized, to produce the energy required to support the higher ECM especially through milk fat and lactose. Plasma 3-methylhistidine increased linearly (P < 0.01) denoting protein tissue mobilization of contractile fibers. A group of AA (Glu, Val, Leu, Tyr, Phe, Ser, His, Thr, Asn, Ala, Pro, Met) decreased in a quadratic manner with the nadir at d 2 and 3, while Asp, Trp and Ile decreased linearly. Concentrations of other AA increased (Gln, Gly, Cys) or did not vary (Lys, Arg) during FR. Plasma AA concentrations decreased after feed delivery in both diets, coinciding with the increase of insulin, except for Glu that increased in all treatments and Gln that increased after feeding only during FR. Metabolic adaptations to low insulin during FR seemed to select catabolism of AA as the first energy source before later relying more on fatty acids. Based on responses of plasma AA and insulin to feeding, protein synthesis in tissues likely remained sensitive to insulin within day.
University of Illinois - Urbana-Champaign
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University of Illinois at Urbana-Champaign