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Even though supplementations of essential AA (EAA) are often related to increased lactose yields in dairy cows, underlying mechanisms connecting EAA availability to the mammary glands and lactose synthesis are poorly understood. The objective of this study was to examine the effects of branched-chain AA (BCAA) including Leu, Ile, and Val on (1) glucose transporter (GLUT1) abundance and glucose uptake, (2) the abundance of proteins regulating lactose synthesis pathway, and (3) fractional synthesis rates of lactose (FSR) using bovine mammary epithelial cells (BMEC) and mammary tissues slices (MTS). The BMEC (n = 4) were allocated randomly to regular Dulbecco's Modified Eagle Medium with Ham's F12 (DMEM/F12) medium (+EAA) or +EAA deficient (by 90%) in all EAA (− EAA), all BCAA (−BCAA), only Leu (−Leu), only Ile (−Ile) or only Val (−Val). Western immunoblotting analyses, depletion of glucose in media, and a proteomic analysis were performed to determine the abundance of GLUT1 in the cell membrane, net glucose uptake, and the abundance of enzymes involved in lactose synthesis pathway in BMEC, respectively. The MTS (n = 6) were allocated randomly to DMEM/F12 medium having all EAA and 13 C-glucose at concentrations similar to plasma concentrations of cows (+EAA p ), and +EAA p deprived of all BCAA (−BCAA p ) or only Leu (−Leu p ) for 3 h. The 13 C enrichments of free glucose pool in MTS (E Glu-free ) and the enrichments of glucose incorporated into lactose in MTS and media [E Lactose-bound (T&M) ] were determined and used in calculating FSR. In BMEC, −BCAA increased the fraction of total GLUT1 translocated to the cell membrane and the fraction that was potentially glycosylated compared with +EAA. Among individual BCAA, only −Leu was associated with a 63% increase in GLUT1 translocated to the cell membrane and a 40% increase in glucose uptake of BMEC. The −BCAA tended to be related to a 75% increase in the abundance of hexokinase in BMEC. Deprivation of Leu tended to increase glucose uptake of MTS but did not affect E Glu-free , E Lactose-bound (T&M) , or FSR relative to +EAA p . On the other hand, −BCAAp did not affect glucose uptake of MTS but was related to lower E Lactose-bound (T&M) , or FSR relative to +EAA p . Considering together, decreasing Leu supply to mammary tissues enhances GLUT1 and thus glucose uptake, which, however, does not affect lactose synthesis rates. Moreover, the deficiency of other BCAA, Ile, and Val alone or together with the deficiency of Leu seemed to decrease lactose synthesis rates without affecting glucose uptake. The data also emphasize the importance of addressing the effect of the supply of other nutrients to the mammary glands than the precursor supply in describing the synthesis of a milk component.

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Phytogenic feed additives that contain anti-inflammatory and antioxidant properties may have potential to reduce inflammation and oxidation observed during bouts of heat stress. The trial objective was to determine the effects of a phytogenic feed additive on markers of stress in heifers subjected to diurnal heat stress (dHS). Eighteen Holstein and four Jersey heifers (5–6 months of age; d1 BW=205±9 kg) were assigned to two dietary treatments (n = 11) based on breed and age; 1) a basal TMR diet (CTL), 2) CTL supplemented with 0.25 g/head/d of a proprietary blend of phytogenics (PFA; BIOMIN America, Inc., Overland Park, KS). Heifers were housed individually and fed their respective treatments for 14d prior to dHS (d-14-1), subjected dHS (d1-7), and followed through a recovery period (d8-11). Weights were collected at d1 (baseline), d7 (end of dHS), and d11 (end of recovery). The temperature set point was assigned at 33°C from 0900 to 2100 h and allowed to equilibrate with outside temperature during night (24°C) for a total of 7d dHS. Total DMI (tDMI) and DMI from 0900 to 2100 h (hsDMI) were recorded daily. Serum was collected at d1, 2, 7 and 11 to determine effect of treatment on markers of oxidation, inflammation, and stress. Treatment effects were analyzed using PROC MIXED in SAS with treatment and time as fixed effects and heifer as a random effect. Temperature humidity index during dHS was greater during the day (84.5) versus night (73.3). There were no treatment differences (P>0.05) in d 0–11 on ADG, ADFI, or GF between treatments. However, PFA numerically increased hsDMI, reduced (P< 0.05) haptoglobin and tended to reduce (P< 0.10) lipopolysaccharide binding protein compared with CTL. Overall, dietary PFA may be a potential strategy to mitigate the stresses that heifers experience during dHS.

The objective of this study was to examine the effects of a Zn-methionine complex in diet on milk yield, milk component yields, SCC, and milk Zn concentration of Holstein cows around peak lactation. After matching for parity and days in milk (DIM), 12 lactating Holstein cows (67 ± 2.5 DIM; 1385 ± 43 kg BW) were assigned to one of two dietary treatments: 1) control (CTL, n = 6), a TMR diet with 74 mg/kg added Zn in the form of zinc sulfate, n = 6) or 2) CTL supplemented with Zn-methionine complex (Zn-Met, n = 6) providing additional 20 mg of Zn/kg (512 mg/head/d). Dry matter intake (DMI) was lower by 0.8 kg/d for Zn-Met than CTL throughout the study (P = 0.05). Milk yield of Zn-Met decreased compared to CTL (40 vs 42 kg/d, P = 0.01) during the first 35 d but had similar milk yield during the last 35 d of the study. Milk protein and fat percentages, and fat yield were not different between treatments. Milk protein yield was similar between treatments during the first 35 d but tended to increase for Zn-Met (1.41 vs. 1.33 kg/d, P = 0.10) during rest of the study. Cows receiving Zn-methionine complex tended to have lower SCC (126 vs 328 ×10 3 cells/mL, P = 0.07) and greater concentration of Zn (4.48 vs 4.06 ppm, P = 0.05) in milk throughout the study. Overall, the present Znmethionine complex tended to improve milk protein yield and SCC more prominently as feeding progressed. However, it decreased DMI suggesting a negative impact on palatability of the diet.

The present study was conducted to examine how dairy heifer calves would respond to a heat stress bout in terms of growth relative to nutrient intake. Nine Holstein and 2 Jersey heifer calves (n = 11) were individually housed and enrolled in a study containing 3 experimental periods (P). Period 1 lasted 7 d during which baseline measurements were obtained. During period 2 (7 d), calves were subjected to diurnal heat stress (dHS) employed by maintaining barn temperature at 33°C (92°F) from 0900 to 2100 h and letting it be equilibrated with outside temperature [24°C (75°F)] during the night. Follow-up measurements were made over 4 d (P3) immediately after dHS. Calves consumed 25% less feed during the day but compensated for it consuming more feed (35%) in night during dHS. Despite DMI (kg/d) being similar between dHS and baseline, ADG and feed efficiency decreased significantly during dHS. These effects are likely consequence of nutrient repartitioning towards the activated immune system and away from productive processes (i.e., growth), as blood haptoglobin increased 3-fold during dHS. Nonetheless, calves exhibited compensatory growth concurrently with increased DMI and drinking water per unit of DMI immediately following dHS. Overall, dHS severely hampers growth and feed efficiency of dairy heifer calves despite unaltered DMI relative to baseline. Understanding nutrient partitioning in calves during and after heat stress could help mitigate the adverse effects and help calves effectively recover from heat stress.