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Reproductive and lactational responses of multiparous dairy cattle to short-term postpartum chromium supplementation during the summer months

Open AccessPublished:December 22, 2022DOI:https://doi.org/10.3168/jdsc.2022-0287

      Highlights

      • Multiparous Holstein dairy cows (n = 22) in early lactation were enrolled during seasonal heat stress.
      • Cows either received or did not receive a chromium (Cr) feed supplement during the treatment period.
      • Cr consumption did not affect milk yield, feed intake, blood glucose, or rectal temperatures.
      • Cr supplementation improved endometrial polymorphonuclear leukocyte percent.
      • Cr intake increased the size and number of small follicles and progesterone ratio.

      Abstract

      The objective of this work was to evaluate the potential benefits of short-duration, high-dose chromium (Cr) supplementation in early postpartum dairy cows during the summer months. Multiparous, early-lactation cows (20.95 ± 0.21 d in milk) were assigned to 1 of 2 treatment groups: (1) control diet (Con; n = 10) or (2) control diet + Cr propionate (CrPro; 12 mg/head per day Cr; n = 12). Measurements of ovarian structures, respiration rates (RR), rectal temperatures (RT), and blood glucose concentrations were recorded every 3 d. Blood was also collected for analysis of plasma progesterone concentrations. Every 6 d, in conjunction with ultrasonography, endometrial cytology samples were collected via cytobrush from each cow to determine the incidences of subclinical endometritis, as determined by polymorphonuclear leukocyte (PMNL)%. No differences were detected in RR, RT, blood glucose, feed intake, milk yield, or change in body weight. The supplementation did, however, improve some reproductive parameters. At cytology sample 6, the PMNL% increased in Con cows, and was greater than the PMNL% in the CrPro group. Chromium consumption did not affect the number or size of most follicles, with the exception being the 6 to 9 mm category where the CrPro group had a greater average diameter and tended to have greater numbers of follicles in this category. While corpus luteum numbers and size did not differ between treatments, the ratio of progesterone to average corpus luteum volume was greater in the CrPro group compared with the Con group. The results from this study indicate that, whereas the short-term, high-dose supplementation strategy did not affect feed intake or milk yield, this Cr supplementation strategy could benefit reproductive performance during periods of stress.

      Graphical Abstract

      Figure thumbnail fx1
      Graphical AbstractSummary: Twenty-two multiparous, lactating Holstein cows were enrolled in the experiment, spanning the summer months of June through September. Cows were housed in freestalls where they were individually fed using a Calan gate system. Cows were randomly assigned to the control (Con; no supplement; n = 10) or chromium propionate (CrPro; 12 mg/head per day chromium for 24 d; n = 12) treatment groups. Every 3 days, ovarian structures were counted and measured and blood samples, respiration rates, and rectal temperatures were collected. Every 6 days, a uterine swab was obtained for cytological evaluation to determine the incidences of subclinical endometritis, as determined by polymorphonuclear leukocyte percentage. Chromium supplementation benefited small ovarian follicles, polymorphonuclear leukocyte percentage, and the ratio of plasma progesterone to average corpus luteum volume.
      During periods of stress, such as summer heat exposure and the early postpartum period, individual physiological responses can reduce productivity, thereby decreasing economic profit for dairy producers. The severity of the responses to stress can be diminished with chromium (Cr) supplementation (
      • Mirzaei M.
      • Ghorbani G.R.
      • Khorvash M.
      • Rahmani H.R.
      • Nikkhah A.
      Chromium improves production and alters metabolism of early lactation cows in summer.
      ). Chromium is an essential trace mineral (
      • Soltan M.A.
      Effect of dietary chromium supplementation on productive and reproductive performance of early lactating dairy cows under heat stress.
      ) known for its ability to enhance insulin-mediated glucose uptake in dairy cattle, which, in practice, often results in an increase in milk production. The improvement in energetic status following Cr consumption can also positively affect reproductive performance, immune function, and responses to stressors (
      • Burton J.L.
      • Nonnecke B.J.
      • Dubeski P.L.
      • Elsasser T.H.
      • Mallard B.A.
      Effects of supplemental chromium on production of cytokines by mitogen-stimulated bovine peripheral blood mononuclear cells.
      ;
      • Mirzaei M.
      • Ghorbani G.R.
      • Khorvash M.
      • Rahmani H.R.
      • Nikkhah A.
      Chromium improves production and alters metabolism of early lactation cows in summer.
      ;
      • Negrón-Perez V.M.
      • Fausnacht D.W.
      • Rhoads M.L.
      Invited review: Management strategies capable of improving the reproductive performance of heat-stressed dairy cattle.
      ).
      The early postpartum period is a phase of production during which dairy cows are particularly susceptible to a variety of stress-related disorders. The transition in homeorhetic priority from maintaining pregnancy to producing substantial quantities of milk is a major physiological shift associated with a plenitude of maladies (
      • Esposito G.
      • Irons P.C.
      • Webb E.C.
      • Chapwanya A.
      Interactions between negative energy balance, metabolic diseases, uterine health and immune response in transition dairy cows.
      ). Dairy cows calving in the late spring or summer have the added physiological challenges associated with making this transition during heat stress (
      • Negrón-Perez V.M.
      • Fausnacht D.W.
      • Rhoads M.L.
      Invited review: Management strategies capable of improving the reproductive performance of heat-stressed dairy cattle.
      ). The physiological responses to elevated ambient temperatures are a major concern for the dairy industry, as they are associated with approximately $1.5 billion in economic losses each year for dairy operations in the United States. These losses result from combined effects of heat stress on milk yield, reproductive performance, disease incidence, and culling rates (
      • St-Pierre N.R.
      • Cobanov B.
      • Schnitkey G.
      Economic losses from heat stress by us livestock industries.
      ).
      The ability of Cr to improve postpartum energetic status and the physiological responses to stressors makes it an ideal candidate for supplementation to heat-stressed early-lactation dairy cows. Previous research, however, has typically relied on lengthy supplementation periods during which Cr treatment is initiated before calving (
      • Burton J.L.
      • Nonnecke B.J.
      • Dubeski P.L.
      • Elsasser T.H.
      • Mallard B.A.
      Effects of supplemental chromium on production of cytokines by mitogen-stimulated bovine peripheral blood mononuclear cells.
      ;
      • Soltan M.A.
      Effect of dietary chromium supplementation on productive and reproductive performance of early lactating dairy cows under heat stress.
      ;
      • Yasui T.
      • McArt J.A.
      • Ryan C.M.
      • Gilbert R.O.
      • Nydam D.V.
      • Valdez F.
      • Griswold K.E.
      • Overton T.R.
      Effects of chromium propionate supplementation during the periparturient period and early lactation on metabolism, performance, and cytological endometritis in dairy cows.
      ). We hypothesized that short-term, high-dose Cr supplementation initiated after calving (rather than during the dry period) would improve production parameters in early postpartum dairy cows during the summer months.
      All animal procedures were approved by the Virginia Tech Institutional Animal Care and Use Committee (IACUC). Twenty-two multiparous (2.86 ± 0.34 lactations), lactating Holstein cows (658.29 ± 13.61 kg of BW) were housed in one of two 12-stall pens within a freestall barn for the duration of the experiment, spanning the months of June through September. Milk production was recorded twice daily (0000 and 1200 h), and BW were collected after the second milking each day. Cows were individually fed once daily (1100 to 1400 h) using a Calan gate system (American Calan Inc.).
      Throughout the experiment, all cows were fed the same base TMR formulated to meet or exceed the nutrient requirements of early lactation (
      • National Academies of Sciences and Medicine
      Nutrient Requirements of Dairy Cattle.
      ). Cows were fed for ad libitum intake and feed refusals were collected and weighed daily. On d 0 (20.95 ± 0.21 DIM), each cow was randomly assigned to (and began) either the control (Con; n = 10) or Cr propionate (CrPro; n = 12) treatment group, based upon parity and average milk production over the 3 previous d. Cows assigned to the CrPro group, received 30 g of CrPro daily for 24 d (12 mg of Cr per head per day; KemTRACE chromium propionate; Kemin Industries Inc.). The supplement was administered by individually top-dressing and then hand-mixing into the top one-third of the TMR ration.
      In the morning of every third day from −6 to 24 d, transrectal ultrasonography was conducted (IBEX PRO portable ultrasound with a L7HDi linear transducer; E.I. Medical Imaging). Follicles were counted (all follicles), measured (all follicles > 5 mm), and categorized by size according to
      • Lucy M.C.
      • Staples C.R.
      • Michel F.M.
      • Thatcher W.W.
      • Bolt D.J.
      Effect of feeding calcium soaps to early postpartum dairy cows on plasma prostaglandin f2 alpha, luteinizing hormone, and follicular growth.
      . Likewise, the number and average diameter of all luteal structures were evaluated. The volume of the corpus luteum (CL) was calculated from the measurements of diameter (
      • Ricci A.
      • Carvalho P.
      • Amundson M.C.
      • Fricke P.
      Characterization of luteal dynamics in lactating Holstein cows for 32 days after synchronization of ovulation and timed artificial insemination.
      ). Fluid-filled cavities within the CL were noted, but because the cavities were sometimes not spherical (as is frequently observed during routine ultrasound) and are not associated with reductions in circulating progesterone (
      • Kito S.
      • Okuda K.
      • Miyazawa K.
      • Sato K.
      Study on the appearance of the cavity in the corpus luteum of cows by using ultrasonic scanning.
      ;
      • Jaśkowski B.M.
      • Herudzińska M.
      • Gehrke M.
      • Niżański W.
      The impact of the cavitary corpus luteum on the blood progesterone concentration and pregnancy rate of embryo recipient heifers.
      ), they were not included in the calculation of CL volume (
      • Assey R.J.
      • Purwantara B.
      • Greve T.
      • Hyttel P.
      • Schmidt M.H.
      Corpus luteum size and plasma progesterone levels in cattle after cloprostenol-induced luteolysis.
      ).
      Rectal temperatures (RT), respiration rates (RR), and blood samples (coccygeal venipuncture; sodium heparin vacutainers; Becton, Dickinson and Company) were also collected every third day, before transrectal ultrasonography. Blood glucose concentrations were immediately determined using a handheld glucometer (Contour Next EZ; Ascensia Diabetes Care US Inc.). The remainder of each blood sample was placed on ice until plasma was collected following centrifugation at 3,000 × g and 4°C for 15 min.
      Every other procedure day (every 6 d), starting at −6 d, uterine cytology samples were also collected before transrectal ultrasonography as described in
      • Kasimanickam R.
      • Duffield T.F.
      • Foster R.A.
      • Gartley C.J.
      • Leslie K.E.
      • Walton J.S.
      • Johnson W.H.
      Endometrial cytology and ultrasonography for the detection of subclinical endometritis in postpartum dairy cows.
      . Samples were collected using a cytology brush (Cytobrush Plus GT; CooperSurgical Inc.) attached to the plunger of an AI rod that had been sterilized in a chlorhexidine solution. After collection, swabs were immediately rolled onto a glass slide and allowed to air dry. Each slide was sprayed with a fixative (CytoPrep Fixative; Electron Microscopy Sciences) and then stored until staining.
      After all slides were collected from all cows, they were stained with a modified Giemsa stain (Differential Quik Stain Kit; Electron Microscopy Sciences) with slight modifications to the manufacturer's recommended procedures. Briefly, each slide was first dipped for 10 s in a fixative solution, followed by 1 min in an eosin Y-based solution. The slides were then dipped 2× in the fixative solution, before being dipped 2× in a methylene blue trihydrate-based solution, then rinsed in distilled water and allowed to air dry. The slides were then dipped 10× each in 100% ethanol and xylene, before 2 drops of a toluene-based histological mounting medium (Permount Mounting Medium; Electron Microscopy Sciences) were placed on the sample for coverslip mounting. Coverslips were allowed to dry overnight. Two hundred cells were randomly counted by 2 observers blinded to the treatments, and the number of polymorphonuclear leukocytes (PMNL) within the 200 cells averaged to determine the PMNL%. Red blood cell (RBC) contamination was also assessed (scores averaged between 2 observers) as described in
      • Pascottini O.B.
      • Dini P.
      • Hostens M.
      • Ducatelle R.
      • Opsomer G.
      A novel cytologic sampling technique to diagnose subclinical endometritis and comparison of staining methods for endometrial cytology samples in dairy cows.
      .
      Progesterone concentrations in plasma samples were determined using an Immulite 2000 Progesterone solid-phase, competitive chemiluminescent enzyme immunoassay (Immulite 2000 XPi platform; Siemens Medical Solutions Inc., USA;
      • Podico G.
      • Canisso I.F.
      • Ellerbrock R.E.
      • Dias N.W.
      • Mercadante V.R.G.
      • Lima F.S.
      Assessment of peripheral markers and ultrasonographic parameters in pregnant mares receiving intramuscular or intrauterine cloprostenol.
      ). All samples were run in a single assay with an intraassay coefficient of variation of 1.99%.
      Climatic data were obtained (National Oceanic and Atmospheric Administration) and included dry bulb temperature (Tdry bulb) and dew point temperature (Tdew point) observed at 15-min intervals for the full duration of the study. Temperature-humidity index (THI) values were calculated from hourly mean Tdry bulb and Tdew point as described in
      • Brown B.M.
      • Stallings J.W.
      • Clay J.S.
      • Rhoads M.L.
      Periconceptional heat stress of Holstein dams is associated with differences in daughter milk production during their first lactation.
      .
      One cow was removed from the experiment for reasons unrelated to the treatment. Data were analyzed using the MIXED procedure of SAS (SAS Institute Inc.). Independent variables were treatment (Con or CrPro), day of experiment, and their interaction. Cow was included in the model as the subject from which repeated measurements were taken. When day of experiment or the interaction between treatment and day of experiment were not significant, they were removed from the model. For analysis of PMNL%, RBC score was included as a covariate. The ratio of plasma progesterone to CL volume was calculated and analyzed using 2 separate approaches for each cow on each sample day: (1) plasma progesterone concentration/average CL volume, and (2) plasma progesterone/total CL volume. For each analysis, 8 covariance structures were tested and the most appropriate was selected based upon Akaike's information criterion, Akaike's information criterion with correction, and Bayesian information criterion values. Pairwise comparisons were conducted using Tukey's procedure. The probabilities of the presence of a CL or subclinical endometritis (SCE) at the time of sample collection was analyzed using the FREQ procedure of SAS as well as mixed-effect logistic regression. Results are reported as least squares means ± standard errors of the means. Statistical significance was declared at P ≤ 0.05 and tendencies at 0.05 ≤ P ≤ 0.10.
      Previous studies have reported changes in milk production when Cr supplementation levels were as low as 6 mg per head per day and initiated during the dry period (
      • Soltan M.A.
      Effect of dietary chromium supplementation on productive and reproductive performance of early lactating dairy cows under heat stress.
      ). In contrast, the current study was designed to determine whether initiating supplementation approximately 3 wk postcalving (thus, short-term) could benefit early-lactation dairy cows experiencing thermal stress as they approach the end of the voluntary waiting period. Since the duration of supplementation was short in comparison to most previous experiments, the amount of Cr administered in this study was greater than most previous experiments (thus, high-dose), yet still within the manufacturer's recommended dose range (
      • Soltan M.A.
      Effect of dietary chromium supplementation on productive and reproductive performance of early lactating dairy cows under heat stress.
      ;
      • Kafilzadeh F.
      • Shabankareh H.K.
      • Targhibi M.R.
      Effect of chromium supplementation on productive and reproductive performances and some metabolic parameters in late gestation and early lactation of dairy cows.
      ;
      • Yasui T.
      • McArt J.A.
      • Ryan C.M.
      • Gilbert R.O.
      • Nydam D.V.
      • Valdez F.
      • Griswold K.E.
      • Overton T.R.
      Effects of chromium propionate supplementation during the periparturient period and early lactation on metabolism, performance, and cytological endometritis in dairy cows.
      ).
      Pre-treatment feed intake, milk yield, and the feed intake to milk yield ratio were all similar between cows that were ultimately assigned to Con and CrPro treatments. Initial BW did tend to differ (642.1 ± 19.4 kg and 688.3 ± 17.7 kg of BW for Con and CrPro, respectively; P = 0.09) and this tendency was maintained throughout the experiment (632.1 ± 19.2 kg and 675.7 ± 17.5 kg of BW during treatment for Con and CrPro, respectively; P = 0.11). As such, the change in BW (d 0 BW to d 24 BW) was also evaluated and did not differ between treatment groups (Table 1). Likewise, feed intake, milk yield, and the feed intake to milk yield ratio were unaffected by treatment (Table 1). While these results differ from many previous experiments (
      • Soltan M.A.
      Effect of dietary chromium supplementation on productive and reproductive performance of early lactating dairy cows under heat stress.
      ;
      • Mirzaei M.
      • Ghorbani G.R.
      • Khorvash M.
      • Rahmani H.R.
      • Nikkhah A.
      Chromium improves production and alters metabolism of early lactation cows in summer.
      ), they are consistent with others (
      • Yang W.Z.
      • Mowat D.N.
      • Subiyatno A.
      • Liptrap R.M.
      Effects of chromium supplementation on early lactation performance of Holstein cows.
      ;
      • Yasui T.
      • McArt J.A.
      • Ryan C.M.
      • Gilbert R.O.
      • Nydam D.V.
      • Valdez F.
      • Griswold K.E.
      • Overton T.R.
      Effects of chromium propionate supplementation during the periparturient period and early lactation on metabolism, performance, and cytological endometritis in dairy cows.
      ), indicating that Cr-specific effects on feed intake and milk yield can vary with supplementation strategy and other undetermined variables.
      Table 1Mean physiological parameters (LSM ± SEM) of early-lactation dairy cows that did (CrPro) or did not (Con) receive chromium supplementation
      Control (Con; n = 10); chromium supplementation (CrPro; 12 mg/head per day Cr; n = 12).
      Parameter
      CL = corpus luteum; SCE = subclinical endometritis.
      ConCrProP-value
      Feed intake (kg)44.66 ± 1.7842.33 ± 1.630.35
      Milk yield (kg)57.75 ± 2.2857.12 ± 2.090.84
      Feed intake:milk yield (kg)0.79 ± 0.030.75 ± 0.030.39
      Change in BW (kg)−1.18 ± 4.56−0.63 ± 4.560.93
      Respiration rate (bpm)66.97 ± 1.4068.19 ± 1.310.52
      Rectal temperature (C°)39.20 ± 0.0439.16 ± 0.040.46
      Blood glucose (mg/dL)58.96 ± 0.5258.41 ± 0.490.44
      Number of CL1.27 ± 0.081.38 ± 0.080.34
      CL diameter (mm)15.37 ± 0.7215.65 ± 0.670.78
      Number of follicles <5 mm5.18 ± 0.475.56 ± 0.450.56
      Number of follicles 6–9 mm1.88 ± 0.172.26 ± 0.160.09
      Diameter of 6–9 mm follicles (mm)6.95 ± 0.097.21 ± 0.080.04
      Number of follicles 10–15 mm0.87 ± 0.090.95 ± 0.080.52
      Diameter of 10–15 mm follicles (mm)11.85 ± 0.1711.54 ± 0.160.18
      Number of follicles >15 mm0.35 ± 0.060.24 ± 0.060.17
      Diameter of 15 mm follicles (mm)16.46 ± 0.4216.61 ± 0.430.79
      Incidence of SCE (%)17.5013.720.54
      1 Control (Con; n = 10); chromium supplementation (CrPro; 12 mg/head per day Cr; n = 12).
      2 CL = corpus luteum; SCE = subclinical endometritis.
      Calculated THI values indicated that cows enrolled in this study were exposed to stressful thermal conditions (THI levels of 68 or greater;
      • Zimbelman R.
      • Rhoads R.
      • Rhoads M.
      • Duff G.
      • Baumgard L.
      • Collier R.
      A re-evaluation of the impact of temperature humidity index (THI) and black globe humidity index (BGHI) on milk production in high producing dairy cows.
      ) for 14 h per day (data not shown). Because of scheduling constraints, RR and RT were only collected in the mornings (between 0600 and 1100 h) in conjunction with transrectal ultrasound. Even though these measurements were collected in the morning hours following the overnight THI nadir, they were greater than would be expected during thermoneutral conditions and consistent with morning measurements of lactating dairy cattle exposed to controlled heat stress (Table 1;
      • Rhoads M.L.
      • Rhoads R.P.
      • VanBaale M.J.
      • Collier R.J.
      • Sanders S.R.
      • Weber W.J.
      • Crooker B.A.
      • Baumgard L.H.
      Effects of heat stress and plane of nutrition on lactating Holstein cows: I. Production, metabolism, and aspects of circulating somatotropin.
      ). Some previous studies have found that when livestock were subjected to heat stress, Cr supplementation reduced RR and RT, particularly during the hottest hours of the day (
      • Liu F.
      • Cottrell J.J.
      • Wijesiriwardana U.
      • Kelly F.W.
      • Chauhan S.S.
      • Pustovit R.V.
      • Gonzales-Rivas P.A.
      • DiGiacomo K.
      • Leury B.J.
      • Celi P.
      • Dunshea F.R.
      Effects of chromium supplementation on physiology, feed intake, and insulin related metabolism in growing pigs subjected to heat stress.
      ;
      • Hung A.T.
      • Leury B.J.
      • Sabin M.A.
      • Fahri F.
      • DiGiacomo K.
      • Lien T.F.
      • Dunshea F.R.
      Dietary nano chromium picolinate can ameliorate some of the impacts of heat stress in cross-bred sheep.
      ). Dietary supplementation of Cr, however, did not improve RR or RT in the current experiment. The lack of difference in either parameter during Cr supplementation is likely the result of the time of day at which RR and RT measurements were conducted (not during maximum THI). Other heat-stress studies have also failed to detect an improvement in RR or RT during Cr supplementation (
      • Mirzaei M.
      • Ghorbani G.R.
      • Khorvash M.
      • Rahmani H.R.
      • Nikkhah A.
      Chromium improves production and alters metabolism of early lactation cows in summer.
      ;
      • Mayorga E.J.
      • Kvidera S.K.
      • Seibert J.T.
      • Horst E.A.
      • Abuajamieh M.
      • Al-Qaisi M.
      • Lei S.
      • Ross J.W.
      • Johnson C.D.
      • Kremer B.
      • Ochoa L.
      • Rhoads R.P.
      • Baumgard L.H.
      Effects of dietary chromium propionate on growth performance, metabolism, and immune biomarkers in heat-stressed finishing pigs1.
      ).
      Chromium is a potent regulator of insulin-mediated glucose uptake, which typically causes circulating glucose concentrations to be lesser in Cr-supplemented animals (
      • Mowat D.N.
      • Chang X.
      • Yang W.Z.
      Chelated chromium for stressed feeder calves.
      ;
      • Depew C.L.
      • Bunting L.D.
      • Fernandez J.M.
      • Thompson Jr., D.L.
      • Adkinson R.W.
      Performance and metabolic responses of young dairy calves fed diets supplemented with chromium tripicolinate.
      ;
      • Stahlhut H.S.
      • Whisnant C.S.
      • Lloyd K.E.
      • Baird E.J.
      • Legleiter L.R.
      • Hansen S.L.
      • Spears J.W.
      Effect of chromium supplementation and copper status on glucose and lipid metabolism in Angus and Simmental beef cows.
      ). This is not always the case, however, particularly for those studies involving heat stress (
      • Soltan M.A.
      Effect of dietary chromium supplementation on productive and reproductive performance of early lactating dairy cows under heat stress.
      ;
      • Mirzaei M.
      • Ghorbani G.R.
      • Khorvash M.
      • Rahmani H.R.
      • Nikkhah A.
      Chromium improves production and alters metabolism of early lactation cows in summer.
      ;
      • Mayorga E.J.
      • Kvidera S.K.
      • Seibert J.T.
      • Horst E.A.
      • Abuajamieh M.
      • Al-Qaisi M.
      • Lei S.
      • Ross J.W.
      • Johnson C.D.
      • Kremer B.
      • Ochoa L.
      • Rhoads R.P.
      • Baumgard L.H.
      Effects of dietary chromium propionate on growth performance, metabolism, and immune biomarkers in heat-stressed finishing pigs1.
      ). Likewise, blood glucose concentrations in the current experiment did not differ between treatment groups (Table 1). Previous work from our laboratory and others suggests that insulin-stimulated glucose uptake is already maximized in heat-stressed dairy cattle (
      • Rhoads M.L.
      • Rhoads R.P.
      • VanBaale M.J.
      • Collier R.J.
      • Sanders S.R.
      • Weber W.J.
      • Crooker B.A.
      • Baumgard L.H.
      Effects of heat stress and plane of nutrition on lactating Holstein cows: I. Production, metabolism, and aspects of circulating somatotropin.
      ;
      • Xie G.
      • Cole L.C.
      • Zhao L.D.
      • Skrzypek M.V.
      • Sanders S.R.
      • Rhoads M.L.
      • Baumgard L.H.
      • Rhoads R.P.
      Skeletal muscle and hepatic insulin signaling is maintained in heat-stressed lactating Holstein cows.
      ;
      • Stewart J.W.
      • Arneson A.G.
      • Byrd M.K.H.
      • Negron-Perez V.M.
      • Newberne H.M.
      • White R.R.
      • El-Kadi S.W.
      • Ealy A.D.
      • Rhoads R.P.
      • Rhoads M.L.
      Comparison of production-related responses to hyperinsulinemia and hypoglycemia induced by clamp procedures or heat stress of lactating dairy cattle.
      ). Consequently, it is likely that Cr is unable to further increase glucose uptake under these conditions.
      Studies have shown that both heat stress and energetic status can affect circulating progesterone concentrations and the length of the luteal phase (
      • De Rensis F.
      • Scaramuzzi R.J.
      Heat stress and seasonal effects on reproduction in the dairy cow–A review.
      ). If disruptions are severe enough, estrous cyclicity or the establishment of pregnancy (or both) will be detrimentally affected (
      • Bishop C.V.
      • Selvaraj V.
      • Townson D.H.
      • Pate J.L.
      • Wiltbank M.C.
      History, insights, and future perspectives on studies into luteal function in cattle.
      ). In the current study, neither the number of CL nor their average diameter were affected by Cr supplementation (Table 1). Maximum plasma progesterone concentrations could not be determined because blood samples were not collected frequently enough (samples were collected every 3 d). Instead, the ratios of progesterone concentration to CL volume were determined using 2 separate approaches. The analysis utilizing total CL volume yielded no differences between the Con and CrPro groups (0.54 ± 0.06 and 0.59 ± 0.06 ng/cm3, respectively; P = 0.56). Interestingly, even though there were no differences in CL number between treatments, the analysis using the average CL volume as the denominator demonstrated that the cows consuming the CrPro produced more progesterone per average unit of CL volume than the Con group (Figure 1). Because the size of the CL is roughly related to its age (
      • Kayacik V.
      Evaluation of the corpus luteum size throughout the cycle by ultrasonography and progesterone assay in cows.
      ;
      • Ricci A.
      • Carvalho P.
      • Amundson M.C.
      • Fricke P.
      Characterization of luteal dynamics in lactating Holstein cows for 32 days after synchronization of ovulation and timed artificial insemination.
      ), this analysis suggests that if blood samples had been collected more frequently (i.e., if peak progesterone values could have been determined), the maximum plasma progesterone concentrations may have been greater in the CrPro treatment group than in Con. Additional research is needed to confirm this speculation. Ultimately, however, greater circulating progesterone concentrations could increase the likelihood of pregnancy recognition and subsequent establishment of pregnancy.
      Figure thumbnail gr1
      Figure 1Mean (LSM ± SEM) ratios of progesterone (P4; ng/mL) to average corpus luteum (CL) volume (cm3) differed between the control (Con) and chromium propionate (CrPro) treatment groups. *P = 0.03.
      Follicle development during the early postpartum period is linked with subsequent fertility in lactating dairy cows (
      • Furukawa E.
      • Masaki T.
      • Sakaguchi K.
      • Bo M.
      • Yanagawa Y.
      • Ueda K.
      • Nagano M.
      Relationship between the timing of the first postpartum ovulation and antral follicle counts in Holstein cows.
      ;
      • Sood P.
      • Sarma H.D.
      • Kadwad V.B.
      • Kumar S.
      Effect of ovarian follicular wave pattern and endocrine characteristics on pregnancy outcome in cows.
      ) and can be detrimentally affected by heat stress (
      • De Rensis F.
      • Scaramuzzi R.J.
      Heat stress and seasonal effects on reproduction in the dairy cow–A review.
      ). Chromium supplementation in the current study affected 2 follicular measurements (Table 1). The CrPro treatment increased the average diameter of the follicles in the small category and tended to increase the number of small follicles (6–9 mm in size). This increase in number and size of the recruited follicles was not sustained, however, as the numbers and diameters of larger follicle categories did not differ between treatments (Table 1).
      Heat stress and the early postpartum period are both associated with an increased risk for metritis in dairy cattle. The incidence of endometritis within some dairy herds exceeds 50% (
      • Cheong S.H.
      • Nydam D.V.
      • Galvão K.N.
      • Crosier B.M.
      • Gilbert R.O.
      Cow-level and herd-level risk factors for subclinical endometritis in lactating Holstein cows.
      ). Endometritis is problematic for several reasons, but is perhaps best known for its effect on postpartum fertility, as indicated by reduced first service pregnancy rates, increased services per conception, and greater median days open (
      • Sheldon I.M.
      • Molinari P.C.C.
      • Ormsby T.J.R.
      • Bromfield J.J.
      Preventing postpartum uterine disease in dairy cattle depends on avoiding, tolerating and resisting pathogenic bacteria.
      ). In this study, individual cows did occasionally meet or exceed the thresholds for SCE diagnosis (
      • Gilbert R.O.
      • Shin S.T.
      • Guard C.L.
      • Erb H.N.
      • Frajblat M.
      Prevalence of endometritis and its effects on reproductive performance of dairy cows.
      ). At no point, however, did mean PMNL% for either treatment group exceed the threshold for SCE diagnosis (Figure 2). The incidences of SCE also did not differ between treatments (Table 1).
      Figure thumbnail gr2
      Figure 2Mean (LSM ± SEM) percentage of polymorphonuclear leukocytes (PMNL) counted in the endometrial cytology samples differed between control (Con; circles) and chromium propionate (CrPro; squares) treatments (P = 0.01). (a, b) denotes significance (P = 0.01) between treatment groups; (y, z) denotes significance (P = 0.02) within the Con group.
      Within the Con group, the PMNL% increased between samples 5 and 6 (P = 0.02; Figure 2). This increase in PMNL% at the end of the sampling period could be indicative of a resurgence in endometrial inflammation. Although we cannot rule out the possibility that this was the result of repeated endometrial swabs (the swabs may partly explain the Con group PMNL%), it is important to note that the cows in the CrPro treatment were subjected to the same number (and timing) of procedures and did not exhibit an increase in PMNL%. Thus, the uterine PMNL% was greater in the Con group compared with the CrPro group at sample time point 6 (P = 0.01; Figure 2). The difference in PMNL% between Con and CrPro-treated cows is supported by previous work where the incidence of SCE at 40 to 60 d postpartum was reduced by CrPro supplementation (
      • Yasui T.
      • McArt J.A.
      • Ryan C.M.
      • Gilbert R.O.
      • Nydam D.V.
      • Valdez F.
      • Griswold K.E.
      • Overton T.R.
      Effects of chromium propionate supplementation during the periparturient period and early lactation on metabolism, performance, and cytological endometritis in dairy cows.
      ). Together, these results indicate that Cr supplementation may aid in improving the uterine environment in postpartum dairy cows. Any strategy capable of improving the uterine environment also has the potential to increase fertility. In the current study, however, there were not enough cows enrolled to evaluate pregnancy rates following supplementation.
      Overall, the short-duration, high-dose CrPro supplementation strategy implemented in this study did not affect blood glucose concentrations, RR, RT, feed intake, and milk yield. Although these variables were not affected by CrPro supplementation, it did improve reproductive parameters, including the ratio of progesterone to average CL volume, PMNL%, and characteristics of small ovarian follicles. These results indicate that CrPro supplementation could act to improve subsequent pregnancy recognition, lower SCE rates, and ultimately improve fertility. Additional research following cows through AI and pregnancy detection is needed to confirm these assertions. Ultimately, the short-duration, high-dose CrPro supplementation strategy benefited aspects of reproductive performance of early-lactation dairy cattle during the summer months.

      Notes

      This work was primarily funded by the Virginia Agricultural Council (grant no. 769; Richmond, VA), with additional funding provided by the Virginia Agricultural Experiment Station and the Hatch Program of the National Institute of Food and Agriculture, U.S. Department of Agriculture (Washington, DC).
      The authors express their gratitude to Natalie Glunz and Kemin Industries Inc. (Des Moines, IA) for donating the KemTRACE Chromium supplement used in this research. The authors also thank the undergraduate volunteers and the Virginia Tech Kentland Dairy Complex staff.
      The authors have not stated any conflicts of interest.

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