Metabolism of silage alcohols in lactating dairy cows

Dairy cows fed silage are subjected to various alcohols and low molecular weight esters. Four lactating Holstein cows fitted with ruminal cannulas and permanent indwelling catheters in the hepatic portal vein, hepatic vein, mesenteric vein, and mesenteric artery were used to study the absorption of alcohols into portal blood and the metabolism of feed alcohols in the rumen and splanchnic tissues. The cows were allocated to 4 experimental treatments in a Latin square design. All treatments were formulated as total mixed rations with the same overall nutrient composition, differing by the source of corn silage. Treatments were a control silage and 3 qualities of problematic corn silage (silage with Fusarium toxin, Penicillium-infected silage, and silage with a high propanol content). Feeding was followed by a decreasing ruminal pH, as well as decreasing molar proportions of ruminal acetate and isobutyrate. The ruminal concentrations of total VFA, ethanol, propanol, 2-butanol, ethyl acetate, propyl acetate, glucose, and l-lactate, and molar proportions of propionate, butyrate, isovalerate, valerate, and caproate increased after feeding. Treatments affected ruminal concentrations of propanol, propyl acetate, and butyrate and a strong correlation was observed between ruminal propyl acetate and the molar proportion of butyrate (r = −0.79). Arterial concentrations of ethanol, propanol, propanal, acetone (sum of acetone and acetoacetate), 3-hydroxybutyrate, l-lactate, glutamate, and glutamine increased, and the arterial concentration of glucose decreased after feeding, but no effects of treatment were observed for arterial variables. The postprandial increase in arterial ethanol was maintained for 5 h. The net portal release of ethanol tended to decrease with the treatment with the lowest ethanol content, and the net splanchnic release of ethanol increased after feeding, but overall, the net splanchnic flux of ethanol was not different from zero, in agreement with the liver being the major organ for alcohol metabolism. The net portal flux and net hepatic flux of propanol were affected by treatment. All dietary ethanol and propanol were accounted for by absorption of the respective alcohol into the portal blood. The hepatic extraction ratios of ethanol and propanol were, on average, 63 to 66%, and no indications of saturation of hepatic alcohol metabolism were observed at any time. We concluded that typical amounts of alcohols in corn silage do not interfere with splanchnic metabolism of any of the measured variables and do not saturate hepatic pathways for alcohol metabolism. However, even low concentrations of alcohols in feed might affect ruminal metabolism and are followed by hours of elevated peripheral blood concentrations of alcohols.     

Diurnal variations of progesterone,testosterone, and androsta-1,4-diene-3,17-dione in the rumen and in vitro progesterone transformation by mixed rumen microorganisms of lactating dairy cows

Five Holstein lactating dairy cows fed 5 total mixed rations (TMR) with different forage combinations were used in a 5 × 5 Latin square design to investigate diurnal variations of progesterone (P4), testosterone, and androsta-1,4-diene-3,17-dione (ADD) concentrations in the rumen. Meanwhile, different P4 inclusion levels [0 (control), 2, 20, 40, 80, and 100 ng/mL in culture fluids] were incubated in vitro for 6, 12, 24, 36, 48, and 72 h together with rumen mixed microorganisms grown on a maize-rich feed mixture (maize meal:Chinese ryegrass hay = :1) with an aim to determine microbial P4 transformation into testosterone and ADD. Ruminal P4, testosterone, and ADD concentrations of lactating dairy cows were greater in the TMR with forage combination of corn silage plus alfalfa hay or Chinese wild ryegrass hay than the TMR with the corn stover-based forage combination. The diurnal fluctuation pattern showed that P4, testosterone, and ADD concentrations in the rumen were greater at nighttime than daytime and peaked 6 h after feeding in the morning or afternoon. The in vitro batch cultures showed that the P4 elimination rate was highest at the P4 addition of 20 ng/mL and declined with the further increased addition of P4. The treatments after dosing P4 exhibited a shorter time than the control group until half of the initial P4 inclusion was eliminated (i.e., half time), and the lowest half time (1.46 h) occurred at the P4 addition of 20 ng/mL. In summary, the ruminal steroids concentration was affected by forage type and quality, and the rumen microorganisms exhibited great ability to transform P4 into testosterone and ADD, depending on incubation time and initial P4 addition level, suggesting that the host might affect the metabolism of its rumen microorganisms via the endogenous steroids.     

Atypical progesterone profiles and fertility in Swedish dairy cows

The incidence of normal and atypical progesterone profiles in Swedish dairy cows was studied. Data were collected from an experimental herd over 15 yr, and included 1,049 postpartum periods from 183 Swedish Holstein and 326 Swedish Red and White dairy cows. Milk progesterone samples were taken twice weekly until initiation of cyclical ovarian activity and less frequently thereafter. Progesterone profiles were 1) normal profile: first rise in milk progesterone above the threshold value before d 56 postpartum, followed by regular cyclical ovarian activity (70.4%); 2) delayed onset of cyclical ovarian activity: low milk progesterone the first 56 d postpartum (15.6%); 3) cessation of cyclical ovarian activity: ovarian activity resumed within 56 d postpartum, but ceased for a period of 14 d or more (6.6%); and 4) prolonged luteal phase: ovarian activity resumed within 56 d postpartum, but milk progesterone remained elevated in the nonpregnant cow for a period of 20 d or more (7.3%). Swedish Holsteins had 1.5 times higher risk of atypical profile than Swedish Red and Whites. Risk of atypical profiles was 0.5 and 0.7 times lower for older cows compared with first-parity cows; 2.3 times higher for cows in tie-stalls compared with those in loose housing; 2.6 times higher for cows calving during winter compared with summer; 0.5 times lower for cows in earlier (1994-1999) calving-year groups compared with the most recent (2000-2002); 2.5 times higher for cows with planned extended calving interval compared with conventional calving interval; and 2.2 times higher for an atypical profile in previous lactation compared with a normal profile. Cows with atypical profiles had a 15-d increase in interval from calving to first artificial insemination and an 18-d increase in interval from calving to conception. Progesterone samples taken within the first 60 d postpartum were used to calculate the percentage of samples above the threshold value of luteal activity. This measure had a significantly different mean in profiles and can be used to separate delayed onset of cyclical ovarian activity profiles and prolonged luteal phase profiles from normal. Thereby, it may be a more effective tool than measurements based only on the onset of ovarian cyclical activity in genetic evaluation of early postpartum fertility in dairy cows.     

Effects of the method of conservation of timothy on nitrogen metabolism in lactating dairy cows

Six ruminally and duodenally cannulated lactating primiparous Holstein cows were used to study the effects of different methods of conservation of timothy on N metabolism. Cows were assigned randomly to 2 replicated 3 × 3 Latin squares (35-d periods). Because of missing data from 2 cows, data were analyzed as a 3 × 4 Youden square. Diets contained a similar concentrate (44% of total ration on a dry matter basis) plus first-cut timothy conserved as hay, or as restrictively (formic) or extensively fermented silage (inoc). Crude protein contents were 10.4, 13.6, and 14.8% for hay, formic, and inoc, respectively. Hay and formic had a high soluble carbohydrate content (≥8.0% of dry matter) and formic and inoc had a high soluble protein content (≥8.0% of dry matter). Haying and restricting fermentation resulted in increased efficiency of partition to milk N (30.9, 28.2, 24.7% of N intake for hay, formic, and inoc, respectively). Despite a 14% lower N intake with hay, no effects of treatments were detected on microbial protein synthesis and apparent intestinal digestion of essential AA. Haying reduced feed protein degradation in the rumen, whereas this effect was not observed when restricting fermentation in the silage. Haying and restricting fermentation induced a lipogenic fermentation pattern in the rumen (4.55, 4.23, and 3.78 ratio of acetate to propionate for hay, formic, and inoc), but no effects on milk fat yield and plasma glucose were observed. Whole-body protein metabolism was unaffected by treatments.     

Alternatives to linear analysis of energy balance data from lactating dairy cows

The current energy requirements system used in the United Kingdom for lactating dairy cows utilizes key parameters such as metabolizable energy intake (MEI) at maintenance (MEm), the efficiency of utilization of MEI for 1) maintenance, 2) milk production (kl), 3) growth (kg), and the efficiency of utilization of body stores for milk production (kt). Traditionally, these have been determined using linear regression methods to analyze energy balance data from calorimetry experiments. Many studies have highlighted a number of concerns over current energy feeding systems particularly in relation to these key parameters, and the linear models used for analyzing. Therefore, a database containing 652 dairy cow observations was assembled from calorimetry studies in the United Kingdom. Five functions for analyzing energy balance data were considered: straight line, two diminishing returns functions, (the Mitscherlich and the rectangular hyperbola), and two sigmoidal functions (the logistic and the Gompertz). Meta-analysis of the data was conducted to estimate kg and kt. Values of 0.83 to 0.86 and 0.66 to 0.69 were obtained for kg and kt using all the functions (with standard errors of 0.028 and 0.027), respectively, which were considerably different from previous reports of 0.60 to 0.75 for kg and 0.82 to 0.84 for kt. Using the estimated values of kg and kt, the data were corrected to allow for body tissue changes. Based on the definition of kl as the derivative of the ratio of milk energy derived from MEI to MEI directed towards milk production, MEm and kl were determined. Meta-analysis of the pooled data showed that the average kl ranged from 0.50 to 0.58 and MEm ranged between 0.34 and 0.64 MJ/kg of BW0.75 per day. Although the constrained Mitscherlich fitted the data as good as the straight line, more observations at high energy intakes (above 2.4 MJ/kg of BW0.75 per day) are required to determine conclusively whether milk energy is related to MEI linearly or not.     

Effect of increasing amounts of supplemental progesterone in a timed artificial insemination protocol on fertility of lactating dairy cows

The objectives were to evaluate the effect of supplemental progesterone during a timed artificial insemination (TAI) protocol on pregnancy per insemination and pregnancy loss. Lactating dairy cows from 2 dairy herds were presynchronized with 2 injections of PGF_2α 14 d apart, and cows observed in estrus following the second PGF_2α injection were inseminated (n = 1,301). Cows not inseminated by 11 d after the end of the presynchronization were submitted to the TAI protocol (d 0 GnRH, d 7 PGF_2α, d 8 estradiol cypionate, and d 10 TAI). On the day of the GnRH of the TAI protocol (study d 0), cows were assigned randomly to receive no exogenous progesterone (control = 432), one controlled internal drug-release (CIDR) insert (CIDR1 = 440), or 2 CIDR inserts (CIDR2 = 440) containing 1.38 g of progesterone each from study d 0 to 7. Blood was sampled on study d 0 before insertion of CIDR for determination of progesterone concentration in plasma, and cows with concentration <1.0 ng/mL were classified as low progesterone (LP) and those with concentration ≥1.0 ng/mL were classified as high progesterone (HP). From a subgroup of 240 cows, blood was sampled on study d 3, 7, 17 and 24 and ovaries were examined by ultrasonography on study d 0 and 7. Pregnancy was diagnosed at 38 ± 3 and 66 ± 3 d after AI. Data were analyzed including only cows randomly assigned to treatments and excluding cows that were inseminated after the second PGF_2α injection. The proportion of cows classified as HP at the beginning of the TAI protocol was similar among treatments, but differed between herds. Concentrations of progesterone in plasma during the TAI protocol increased linearly with number of CIDR used, and the increment was 0.9 ng/mL per CIDR. The proportion of cows with plasma progesterone ≥1.0 ng/mL on study d 17 was not affected by treatment, but a greater proportion of control than CIDR-treated cows had asynchronous estrous cycles following the TAI protocol. Treatment with CIDR inserts, however, did not affect pregnancy at 38 ± 3 and 66 ± 3 d after AI or pregnancy loss.     

Reproduction in dairy cows following progesterone insert presynchronization and resynchronization protocols

The objectives of this study were to evaluate the effects of an intravaginal insert containing progesterone (CIDR, controlled internal drug releasing) administered in presynchronization and resynchronization protocols on cyclicity, detection of estrus, pregnancy rate, and pregnancy loss to first AI; reinsemination patterns; and pregnancy rates to second postpartum AI before and after the time of first-service pregnancy diagnosis in dairy cows. Holstein cows (n = 1,052) were blocked by parity and BCS at 3 ± 3 d in milk (study d 0 = day of calving) and assigned randomly to 1 of 3 presynchronization treatments. During the presynchronization programs, all cows received 2 injections of PGF_2α, on study d 35 and 49. Cows enrolled in the control presynchronization treatment received AI after detected estrus from study d 49 to 62. Cows enrolled in the CIDR estrus-detection (CED) presynchronization treatment received a CIDR insert from study d 42 to 49 and AI on detection of estrus from d 49 to 62. Cows enrolled in the CIDR timed AI (CTAI) presynchronization treatment received the same treatment as CED, but were subjected to timed AI on study d 72 after the Ovsynch (GnRH, 7 d PGF_2α, 2 d GnRH, 24 h timed AI) protocol. The control and CED cows not inseminated by study d 62 were enrolled in the Ovsynch protocol on the same day and received timed AI on study d 72. After first AI, cows were assigned to no resynchronization (RCON) or resynchronization with a CIDR insert (RCIDR) between 14 and 21 d after AI. Blood samples collected on study d 35, 49, and 62 were analyzed for concentrations of progesterone and cows were classified as anestrous when progesterone was <1.0 ng/mL in the first 2 samples. On study d 62, anestrous cows with progesterone ≥ 1.0 ng/mL were classified as having resumed cyclicity. Pregnancy was diagnosed at 31 and 60 d after first AI and at 42 d after second AI. A greater proportion of anestrous cows in CED and CTAI became cyclic by d 62 postpartum than control cows. Resynchronization with the CIDR insert increased the pregnancy rate at 31 d after first AI in CED and CTAI, and at 60 d after AI in all cows because of reduced pregnancy loss. These results indicate that presynchronization with the CIDR insert increased induction of cyclicity in anestrous cows and that resynchronization with the CIDR insert did not affect the reinsemination rate but did reduce pregnancy loss and increased the pregnancy rate at 60 d after first AI.     

Resynchronization strategies to improve fertility in lactating dairy cows utilizing a presynchronization injection of GnRH or supplemental progesterone: I. Pregnancy rates and ovarian responses

Objectives were to evaluate 3 resynchronization protocols for lactating dairy cows. At 32 ± 3 d after pre-enrollment artificial insemination (AI; study d −7), 1 wk before pregnancy diagnosis, cows from 2 farms were enrolled and randomly assigned to 1 of 3 resynchronization protocols after balancing for parity, days in milk, and number of previous AI. All cows were examined for pregnancy at 39 ± 3 d after pre-enrollment AI (study d 0). Cows enrolled as controls (n = 386) diagnosed not pregnant were submitted to a resynchronization protocol (d 0-GnRH, d 7-PGF_2α, and d 10-GnRH and AI) on the same day. Cows enrolled in the GGPG (GnRH-GnRH-PGF_2α-GnRH) treatment (n = 357) received a GnRH injection at enrollment (d −7) and if diagnosed not pregnant were submitted to the resynchronization protocol for control cows on d 0. Cows enrolled in CIDR treatment (n = 316) diagnosed not pregnant received the resynchronization protocol described for control cows with addition of a controlled internal drug release (CIDR) insert containing progesterone (P₄) from d 0 to 7. In a subgroup of cows, ovaries were scanned and blood was sampled for P₄ concentration on d 0 and 7. After resynchronized AI, cows were diagnosed for pregnancy at 39 ± 3 and 67 ± 3 d (California herds) or 120 ± 3 d (Arizona herds). Cows in the GGPG treatment had more corpora lutea than CIDR and control cows on d 0 (1.30 ± 0.11, 1.05 ± 0.11, and 1.05 ± 0.11, respectively) and d 7 (1.41 ± 0.14, 0.97 ± 0.13, and 1.03 ± 0.14, respectively). A greater percentage of GGPG cows ovulated to GnRH given on d 0 compared with CIDR and control cows (48.4, 29.6, and 36.6%, respectively), but CIDR and control did not differ. At 39 ± 3 d after resynchronized AI, pregnancy per AI (P/AI) was increased in GGPG (33.6%) and CIDR (31.3%) cows compared with control (24.6%) cows. At 67 or 120 ± 3 d after resynchronized AI, P/AI of GGPG and CIDR cows was increased compared with control cows (31.2, 29.5, and 22.1%, respectively). Presynchronizing the estrous cycle of lactating dairy cows with a GnRH 7 d before the start of the resynchronization protocol or use of a CIDR insert within the resynchronization protocol resulted in greater P/AI after resynchronized AI compared with control cows.     

Effect of dietary level of rumen-degraded protein on production and nitrogen metabolism in lactating dairy cows

Twenty-eight (8 with ruminal cannulas) lactating Holstein cows were assigned to 4 × 4 Latin squares and fed diets with different levels of rumen-degraded protein (RDP) to study the effect of RDP on production and N metabolism. Diets contained [dry matter (DM) basis] 37% corn silage, 13% alfalfa silage, and 50% concentrate. The concentrate contained solvent and lignosulfonate-treated soybean meal and urea, and was adjusted to provide RDP at: 13.2, 12.3, 11.7, and 10.6% of DM in diets A to D, respectively. Intake of DM and yield of milk, fat-corrected milk, and fat were not affected by treatments. Dietary RDP had positive linear effects on milk true protein content and microbial non-ammonia N (NAN) flow at the omasal canal, and a quadratic effect on true protein yield, with maximal protein production at 12.3% RDP. However, dietary RDP had a positive linear effect on total N excretion, with urinary N accounting for most of the increase, and a negative linear effect on environmental N efficiency (kg of milk produced per kg of N excreted). Therefore, a compromise between profitability and environmental quality was achieved at a dietary RDP level of 11.7% of DM. Observed microbial NAN flow and RDP supply were higher and RUP flow was lower than those predicted by the NRC (2001) model. The NRC (2001) model overpredicted production responses to RUP compared with the results in this study. Replacing default NRC degradation rates for protein supplements with rates measured in vivo resulted in similar observed and predicted values, suggesting that in situ degradation rates used by the NRC are slower than apparent rates in this study.     

Whole-body glucose metabolism and mammary energetic nutrient metabolism in lactating dairy cows receiving digestive infusions of casein and propionic acid

This study analyzed the effect of propionate (C3) and casein (CN) on whole-body and mammary metabolism of energetic nutrients. Three multiparous Holstein cows fitted with both duodenal and ruminal cannulas were used in 2 replicated Youden squares with 14-d periods. Effects of CN (743 g/d in the duodenum) and C3 (1,042 g/d in the rumen) infusions, either separately or in combination as supplements to a grass silage diet, were tested in a factorial arrangement. The control diet provided 97% of energy and protein requirements. Within each period, blood samples were taken (d 11) from the carotid artery and the right mammary vein to determine net uptake of energetic nutrients. Plasma blood flow was calculated using the Fick principle (based on Phe and Tyr). On d 13, [6,6-²H₂]glucose was infused in the jugular vein to determine whole-body glucose rate of appearance (Ra) based on enrichments in arterial plasma. Both C3 and CN treatments increased whole-body Ra (17% and 13%, respectively) but only CN increased milk (18%) and lactose (14%) yields, suggesting no direct link between whole-body Ra and milk yield. When CN was infused alone, the apparent ratio of conversion of CN carbon into glucose carbon was 0.31 but, when allowance was made for the CN required to support the extra milk protein output, the ratio increased to 0.40, closer to the theoretical ratio (0.48). This may relate to the observed increases in arterial glucagon concentrations for CN alone. Conversely, the apparent conversion of infused C3 carbon alone to glucose was low (0.31). With C3, mammary plasma flow increased as did uptakes of lactate, Ala, and Glu whereas the uptake for β-hydroxybutyrate (BHBA) decreased. Mammary net carbon balance suggested an increase with C3 treatment in glucose, lactate, Ala, and Glu oxidation within the mammary gland. Mammary glucose uptake did not increase with CN treatment, despite an increase in glucose arteriovenous difference and extraction rate, because plasma flow decreased (−17%). Whereas CN, alone or in combination with C3, increased both lactose and protein yields, only mammary AA (and BHBA in CN alone) uptake increased because plasma flow decreased (−17%). These data suggest that the observed variations of milk lactose yield (and other milk components) are linked to metabolic interchanges between several energetic nutrients at both the whole-body and mammary levels and are not explained by increases in whole-body glucose availability.     

Long-acting insulins alter milk composition and metabolism of lactating dairy cows

This study investigated the effect of 2 different types of long-acting insulin on milk production, milk composition, and metabolism in lactating dairy cows. Multiparous cows (n = 30) averaging 88 d in milk were assigned to one of 3 treatments in a completely randomized design. Treatments consisted of control (C), Humulin-N (H; Eli Lilly and Company, Indianapolis, IN), and insulin glargine (L). The H and L treatments were administered twice daily at 12-h intervals via subcutaneous injection for 10 d. Cows were milked twice daily, and milk composition was determined every other day. Mammary biopsies were conducted on d 11, and mammary proteins extracted from the biopsies were analyzed by Western blot for components of insulin and mammalian target of rapamycin signaling pathways. Treatment had no effect on dry matter intake or milk yield. Treatment with both forms of long-acting insulin increased milk protein content and tended to increase milk protein yield over the 10-d treatment period. Analysis of milk N fractions from samples collected on d 10 of treatment suggested that cows administered L tended to have higher yields of milk protein fractions than cows administered H. Milk fat content and yield tended to be increased for cows administered long-acting insulins. Lactose content and yields were decreased by treatment with long-acting insulins. Administration of long-acting insulins, particularly L, tended to shift milk fatty acid composition toward increased short- and medium-chain fatty acids and decreased long-chain fatty acids. Plasma concentrations of glucose and urea N were lower for cows administered long-acting insulins; interactions of treatment and sampling time were indicative of more pronounced effects of L than H on these metabolites. Concentrations of nonesterified fatty acids and insulin were increased in cows administered long-acting insulins. Decreased concentrations of urea N in both plasma and milk suggested more efficient use of N in cows administered long-acting insulins. Western blot analysis of mammary tissue collected by biopsy indicated that the ratios of phosphorylated protein kinase b (Akt) to total Akt and phosphorylated ribosomal protein S6 (rpS6) to total rpS6 were not affected by long-acting insulins. Modestly elevating insulin activity in lactating dairy cows using long-acting insulins altered milk composition and metabolism. Future research should explore mechanisms by which either insulin concentrations or insulin signaling pathways in the mammary gland can be altered to enhance milk fat and protein production.     

Pregnancy in dairy cows after synchronized ovulation regimens with or without presynchronization and progesterone

Two experiments examined pregnancy after synchronized ovulation (Ovsynch) with or without progesterone (P4) administered via controlled internal drug release (CIDR) intravaginal inserts. In experiment 1, 262 lactating cows in one herd were in 3 treatments: Ovsynch (n = 91), Ovsynch + CIDR (n = 91), and control (n = 80). The Ovsynch protocol included injections of GnRH 7 d before and 48 h after an injection of PGF20. Timed artificial insemination (TAI; 57 to 77 d postpartum) was 16 to 20 h after the second GnRH injection. Cows in the Ovsynch + CIDR group also received a CIDR (1.9 g of P4) insert for 7 d starting at first GnRH injection. Control cows received A-I when estrus was detected using an electronic estrus detection system. Based on serum P4, 44.1% of cows were cyclic before Ovsynch. Pregnancy rates at 29 d (59.3 vs. 36.3%) and 57 d (45.1 vs. 19.8%) after TAI and embryo survival (75.9 vs. 54.5%) from 29 to 57 d were greater for Ovsynch + CIDR than for Ovsynch alone. In experiment 2, 630 cows in 2 herds received TAI at 59 to 79 d postpartum after 6 treatments. Estrous cycles were either presynchronized (2 injections of PGF2alpha 14 d apart; n = 318) or not presynchronized (n = 312). Within those groups, Ovsynch was initiated 12 d after second presynchronization PGF2alpha, and used alone (n = 318) or with CIDR inserts for 7 d (1.38 g of P4/insert, n = 124 or 1.9 g of P4/insert, n = 188). Before Ovsynch, 80% of cows were cyclic. Presynchronization increased pregnancy (46.8 vs. 37.5%) at 29 d after TAI, but CIDR inserts had no effect on pregnancy in experiment 2. Overall embryonic survival between 29 and 57 d in experiment 2 was 57.7%. Use of CIDR inserts with Ovsynch improved conception and embryo survival in experiment 1 but not in experiment 2, in part due to differing proportions of cyclic cows at the outset. Presynchronization before Ovsynch enhanced pregnancy rate.     

Ruminal and intermediary metabolism of propylene glycol in lactating Holstein cows

Four lactating Holstein cows fitted with ruminal cannulas and permanent indwelling catheters in the mesenteric artery, mesenteric vein, hepatic portal vein, and hepatic vein were used in a cross-over design to study the metabolism of propylene glycol (PG). Each cow received 2 treatments: control (no infusion) and infusion of 650 g of PG into the rumen at the time of the morning feeding. Propylene glycol was infused on the day of sampling only. Samples of arterial, portal, and hepatic blood as well as ruminal fluid were obtained at 0.5 h before feeding and at 0.5, 1.5, 2.5, 3.5, 5, 7, 9, and 11 h after feeding. Infusion of PG did not affect ruminal pH or the total concentration of ruminal volatile fatty acids, but did decrease the molar proportion of ruminal acetate. The ruminal concentrations of PG, propanol, and propanal as well as the molar proportion of propionate increased with PG infusion. The plasma concentrations of PG, ethanol, propanol, propanal, glucose, l-lactate, propionate, and insulin increased with PG and the plasma concentrations of acetate and β-hydroxybutyrate decreased. The net portal flux of PG, propanol, and propanal increased with PG. The hepatic uptake of PG was equivalent to 19% of the intraruminal dose. When cows were dosed with PG, the hepatic extraction of PG was between 0 and 10% depending on the plasma concentration of PG, explaining the slow decrease in arterial PG. The increased net hepatic flux of l-lactate with PG could account for the entire hepatic uptake of PG, which suggests that the primary hepatic pathway for PG is oxidation to l-lactate. The hepatic uptake of propanol increased with PG, but no effects of PG on the net hepatic and net splanchnic flux of glucose were observed. Despite no effect of PG on net portal flux and net hepatic flux of propionate, the net splanchnic flux of propionate increased and the data suggest that propionate produced from hepatic metabolism of propanol is partly released to the blood. The data suggest that PG affects metabolism of the cows by 2 modes of action: 1) increased supply of l-lactate and propionate to gluconeogenesis and 2) insulin resistance of peripheral tissues induced by increased concentrations of PG and propanol as well as a decreased ratio of ketogenic to glucogenic metabolites in arterial blood plasma.     

Supplemental progesterone and timing of resynchronization on pregnancy outcomes in lactating dairy cows

The objective was to determine the effect of exogenous progesterone (P₄) in a timed artificial insemination (TAI) protocol initiated at 2 different times post-AI on pregnancies per AI (P/AI) in lactating dairy cows. Cows (n = 1,982) in 5 dairy herds were assigned randomly at a nonpregnancy diagnosis 32 ± 3 d post-AI to 1 of 4 resynchronization (RES) treatments arranged in a 2 × 2 factorial design using the Ovsynch-56 (GnRH, 7 d later PGF_2α, 56 h later GnRH, 16 h later TAI) protocol. Treatments were as follows: cows initiating RES 32 ± 3 d after AI with no supplemental P₄ (d 32 RES-CON; n = 516); same as d 32 RES-CON plus a controlled internal drug release (CIDR) insert containing P₄ at the onset of Ovsynch-56 (d 32 RES-CIDR; n = 503); cows initiating RES 39 ± 3 d after AI (d 39 RES-CON; n = 494); and same as d 39 RES-CON plus a CIDR (d 39 RES-CIDR; n = 491). Cows were inseminated if observed in estrus before TAI. The P/AI was determined 32 and 60 d after TAI. In a subgroup of cows (n = 1,152), blood samples were collected and ovarian structures examined by ultrasonography on the days of the first GnRH (G1) and PGF_2α of Ovsynch-56. Percentage of cows with a corpus luteum (CL) at G1 was unaffected by timing of treatments, but percentage of cows with a CL at PGF_2α was greater for d 32 than for d 39 cows (87.9 vs. 79.4%). In addition, percentage of cows with P₄ ≥1 ng/mL at G1 was unaffected by timing of treatments, but was increased for d 32 compared with d 39 RES cows on the day of the PGF_2α of the RES protocols (86.5 vs. 74.3%). Treatment did not affect ovulation to G1 or P/AI 32 d after RES TAI (d 32 RES-CON = 30.1%, d 32 RES-CIDR = 28.8%, d 39 RES-CON = 27.5%, d 39 RES-CIDR = 30.5%). A greater percentage of d 39 RES cows underwent premature luteolysis during the RES protocol compared with d 32 RES cows. An interaction was detected between day of RES initiation and CIDR treatment, in which the CIDR increased P/AI 60 d after TAI for d 39 (CON = 23.7% vs. CIDR = 28.0%), but not for d 32 (CON = 26.9% and CIDR = 24.2%) cows. Pregnancy loss was unaffected by treatment. In addition, cows had improved P/AI 60 d after TAI when they received a CIDR and did not have a CL (CON-CL = 28.2%, CON-No CL = 19.2%, CIDR-CL = 27.0%, and CIDR-No CL = 26.5%) or had P₄ <1 ng/mL (CON-High P₄ = 27.8%, CON-Low P₄ = 15.0%, CIDR-High P₄ = 25.0%, and CIDR-Low P₄ = 29.4%) at G1, but not if a CL was present or P₄ was ≥1 ng/mL at G1. In conclusion, addition of a CIDR insert to supplement P₄ during the RES protocol increased P/AI for cows initiating RES 39 ± 3 d after AI but not 32 ± 3 d after AI.     

Treatment of cycling and noncycling lactating dairy cows with progesterone during Ovsynch

Our objective was to determine whether progesterone (P4) supplementation during an Ovsynch protocol would enhance fertility in lactating dairy cows. Lactating dairy cows (n = 634) at 6 locations were assigned randomly within lactation number and stage of lactation to receive the Ovsynch protocol [OVS; synchronization of ovulation by injecting GnRH 7 d before and 48 h after PGF_2α, followed by one fixed-time AI (TAI) 16 to 20 h after the second GnRH injection] or Ovsynch plus a controlled internal drug release (CIDR) P4-releasing insert for 7 d, beginning at the first GnRH injection (OVS + CIDR). Blood was sampled to quantify P4 10 d before the first GnRH injection, immediately before the first GnRH injection, at the time of CIDR removal, before the PGF_2α injection (1 to 2 h after CIDR insert removal), and 48 h after the PGF_2α injection to determine cyclicity status before initiation of treatment, luteal status at the PGF_2α injection, and incidence of luteal regression. Overall, conception rates at 28 (40 vs. 50%) and 56 d (33 vs. 38%) after TAI differed between OVS and OVS + CIDR, respectively; but a treatment × location interaction was detected. Compared with OVS, pregnancy outcomes were more positive for OVS + CIDR cows at 4 of 6 locations 28 d after TAI and at 3 of 6 locations 56 d after TAI. An interaction of luteal status (high vs. low) before CIDR insert removal and PGF_2α injection with pretreatment cycling status indicated that cows having low P4 at PGF_2α injection benefited most from P4 supplementation (OVS + CIDR = 36% vs. OVS = 18%), regardless of pretreatment cycling status. Pregnancy loss between 28 and 56 d after TAI was greater for noncycling cows (31%) compared with cycling cows (16%). Pregnancy loss for cows receiving P4 (21%) did not differ from that for cows not receiving P4 (21%). Supplementation of P4, pretreatment cycling status, and luteal status before PGF_2α injection altered follicular diameters at the time of the second GnRH injection, but were unrelated to pregnancy outcomes. Incidence of multiple ovulation was greater in noncycling than in cycling cows. Further, cows having multiple ovulations had improved pregnancy outcomes at 28 and 56 d after TAI. In summary, a CIDR insert during the Ovsynch protocol increased fertility in lactating cows having low serum P4 before PGF_2α injection. Improved pregnancy outcomes were observed at some, but not all locations.     

Effects of supplemental progesterone after artificial insemination on expression of interferon-stimulated genes and fertility in dairy cows

The objectives of the current study were to evaluate the effects of supplemental progesterone after artificial insemination (AI) on expression of IFN-stimulated genes (ISG) in blood leukocytes and fertility in lactating dairy cows. Weekly cohorts of Holstein cows were blocked by parity (575 primiparous and 923 multiparous) and method of insemination (timed AI or AI on estrus) and allocated randomly within each block to untreated controls, a controlled internal drug release (CIDR) containing 1.38 g of progesterone from d 4 to 18 after AI (CIDR4), or a CIDR on d 4 and another on d 7 after AI and both removed on d 18 (CIDR4+7). Blood was sampled to quantify progesterone concentrations in plasma and mRNA expression in leukocytes for the ubiquitin-like IFN-stimulated gene 15-kDa protein (ISG15) and receptor transporter protein-4 (RTP4) genes. Pregnancy was diagnosed on d 34 ± 3 and 62 ± 3 after AI. Treatment increased progesterone concentrations between d 5 and 18 after AI in a dose-dependent manner (control = 3.42, CIDR4 = 4.97, and CIDR4+7 = 5.46 ng/mL). Cows supplemented with progesterone tended to have increased luteolysis by d 19 after AI (control = 17.2; CIDR4 = 29.1; CIDR4+7 = 30.2%), which resulted in a shorter AI interval for those reinseminated after study d 18. Pregnancy upregulated expression of ISG in leukocytes on d 19 of gestation, but supplementing progesterone did not increase mRNA abundance for ISG15 and RTP4 on d 16 after insemination and tended to reduce mRNA expression on d 19 after AI. For RTP4 on d 19, the negative effect of supplemental progesterone was observed only in the nonpregnant cows. No overall effect of treatment was observed on pregnancy per AI on d 62 after insemination and averaged 28.6, 32.7, and 29.5% for control, CIDR4, and CIDR4+7, respectively. Interestingly, an interaction between level of supplemental progesterone and method of AI was observed for pregnancy per AI. For cows receiving exogenous progesterone, the lower supplementation with CIDR4 increased pregnancy per AI on d 62 in cows inseminated following timed AI (CIDR4 = 39.2; CIDR4+7 = 27.5%); in those inseminated following detection of estrus, however, the use of a second insert on d 7 resulted in greater pregnancy per AI (CIDR4 = 26.9; CIDR4+7 = 31.5%). Pregnancy loss did not differ among treatments. Supplemental progesterone post-AI using a single intravaginal insert on d 4 was beneficial to pregnancy in cows inseminated following timed AI, but incremental progesterone with a second insert on d 7 did not improve fertility of dairy cows.     

Effect of uncouplers of oxidative phosphorylation on metabolism of propionate in liver explants from dairy cows

Our objective was to determine the effects of uncouplers of oxidative phosphorylation on the metabolism of propionate in liver tissue of dairy cows in the postpartum period. A total of 8 primiparous dairy cows were biopsied for liver tissue explants in 2 block-design experiments. Cows were 5.9 ± 2.8 (mean ± SD) days in milk, and the 2 experiments were run concurrently. Treatments for experiment 1 were 10 μM 2,4-dinitrophenol methyl ether (DNPME) or propylene carbonate (vehicle control). Treatments for experiment 2 were 5 mM sodium salicylate (SAL) or no treatment (control). Explants were incubated in 2.5 mM [¹³C₃]propionate with treatments and terminated after 0.5, 15, and 60 min of exposure to tracer. Treatment with DNPME had no effects on measured metabolites compared with control. Treatment with SAL increased total ¹³C% enrichment of succinate (3.03 vs. 2.45%), but tended to decrease total ¹³C% enrichment of fumarate (2.86 vs. 3.10%) and decreased total ¹³C% enrichment of malate (3.96 vs. 4.58%) compared with the control. Treatment with DNPME appeared to have no effects on hepatic propionate metabolism, and treatment with SAL may impair the succinate dehydrogenase reaction.     

Intravaginal progesterone insert to synchronize return to estrus of previously inseminated dairy cows

An intravaginal progesterone insert (CIDR insert; 1.38 g of progesterone) was evaluated for synchronization of returns to estrus (SR), conception rate (CR), and pregnancy rate (PR) in dairy cows previously artificially inseminated (AI). Healthy, nonpregnant, lactating Holstein cows, > or = 40 and < or = 150 d postpartum at eight commercial farms were used. Cows detected in estrus and receiving AI 2, 3, or 4 d after one injection of PGF2alpha (25 mg) were assigned as either controls (n = 945), or to receive a CIDR insert (n = 948) for 7 d (14 to 21 +/- 1 d after AI). Cows were observed for returns to estrus from 18 to 26 +/- 1 d after initial AI (resynchrony period) and were reinseminated if in estrus. Vaginal mucus on CIDR inserts (97.3% retention) at removal was scored: 1 = no mucus; 2 = clear; 3 = cloudy; 4 = yellow; and 5 = red or brown. Percentage of cows in estrus (SR) during the 3 d after CIDR insert removal was contrasted to the highest 3-d cumulative percentage in estrus for controls. Cows conceiving to initial AI were omitted in calculations of SR, CR, and PR during resynchrony. Mucous scores of 3 or 4 (mild irritation) were observed in 65% of cows and a score of 5 (more severe irritation) was observed in 2%; otherwise, health was unaffected. The PR to initial AI was lower for cows subsequently receiving CIDR inserts than for controls (32.7 vs. 36.7%). The CIDR insert increased SR (34.1 vs. 19.3% in 3 d) and overall estrus detection (43% in 4 d vs. 36% in 9 d) compared with controls. For the 9-d resynchrony period, CR and PR for CIDR-treated (26.7, 12.2%) and control (30.9, 11.1%) cows did not differ significantly. The CIDR inserts improved synchrony of returns to estrus, slightly reduced PR to initial AI, but did not affect CR or PR to AI during the resynchrony period.     

Concentrations of progesterone in milk of cows administered an intravaginal progesterone insert

Milk from pregnant cows contains concentrations of progesterone (P4) considered safe for human consumption. The objective of this study was to determine if concentrations of P4 in milk during administration of an intravaginal progesterone insert (CIDR insert) are less than concentrations of P4 in milk associated with pregnancy. Results have implications for human use of milk from cows receiving CIDR inserts. Holstein cows (N = 64; > 40 and < 150 d after calving) were administered 25 mg of PGF2alpha i.m. (study d 0) and 20 cows detected in estrus from 2 to 4 d later were assigned randomly to either control (N = 10; no further treatment) or CIDR insert (N = 10; 1.38 g of P4) inserted on study d 17 (14 +/- 1 d after estrus) and removed 7 d later. Composite milk samples were collected contemporaneously from each of the 20 estrous cycling cows and from 10 pregnant cows (> or = 60 and < or = 220 d of gestation) twice daily from study d 17 to 27. Concentrations of P4 in defatted milk samples were quantified using a validated radioimmunoassay. Mean logs of areas under the curve of concentrations of P4 from the afternoon on study d 17 through the afternoon on study d 27 were 3.05 ng day/ml for control, 3.33 ng day/ml for CIDR insert, and 3.81 ng day/ml for pregnant cows. Therefore, increased P4 due to pregnancy was 0.76 ng day/ml (3.81-3.05), whereas the increase in P4 due to CIDR insert was only 0.28 ng day/ml (3.33-3.05). Applying a 95% confidence interval to 0.28 ng day/ml provided an upper value of 0.70 ng day/ml, lower than the increase due to pregnancy. Because milk from pregnant cows is considered safe for human consumption, it follows that milk from cows administered CIDR inserts should also be considered safe, based on concentrations of P4.     

Abomasal protein infusion in postpartum transition dairy cows: Effect on performance and mammary metabolism

The effect of increasing the postpartum metabolizable protein (MP) supply on performance and mammary metabolism was studied using 8 Holstein cows in a complete randomized design. At parturition, cows were assigned to abomasal infusion of water (CTRL) or casein (CAS). Arterial and epigastric venous blood samples were taken 14 d before expected parturition and at 4, 15, and 29 d in milk (DIM). To compensate previously estimated deficiency of essential AA and to avoid oversupply, casein protein infusion was graduated with 696 ± 1, 490 ± 9, and 212 ± 10 g/d at 4, 15 and 29 DIM, respectively. Dry matter intake was unaffected by CAS. Compared with CTRL, MP supply was greater at 4 DIM with CAS but did not differ by 29 DIM. Milk yield was greater with CAS (+7.2 ± 1.3 kg/d from 1 to 29 DIM). Milk protein yield was greater with CAS at 4 DIM and averaged 1,664 ± 39 g/d compared with 1,212 ± 86 g/d for CTRL, but did not differ at 29 DIM (1,383 ± 48 g/d). The ratio of MP total supply to requirement was numerically greater at 4 DIM for CAS compared with CTRL, indicating less postpartum protein deficiency. In contrast, a greater net energy deficiency tended to be induced with CAS, but the greater milk yield allowed a large part of mobilized fat to be secreted in milk. Arterial concentration of total essential AA increased sharply after parturition for CAS compared with slight decreases for CTRL. The patterns of arterial concentrations combined with arterial-mammary venous concentration differences indicated that Lys, Leu, and Tyr were the first-limiting AA at 4 DIM with CTRL. Mammary plasma flow was unaffected by treatment, indicating similar perfusion of mammary tissue. The greater milk yield with CAS was associated with greater mammary uptake of individual essential AA, tendencies to greater uptake of glucose, lactate, and β-hydroxybutyrate, whereas uptakes of volatile fatty acids were unaffected. Despite similar MP supply by 29 DIM, milk and lactose yields were greater with CAS indicating a persistent response to increased postpartum MP supply. In conclusion, the postpartum MP deficiency can have a substantial negative effect in dairy cows as the major outcome of increasing the postpartum MP supply was increased milk, milk protein, and lactose yield, as well as an enhanced MP balance. Potential positive effects for other body functions than milk synthesis are discussed. Future investigations are needed to delineate how to transfer the effect into practical feeding strategies.