Background: There is interest in using animal-mounted sensors to provide the detailed timeline of domesticated ruminant behaviour on rangelands. New method: Working with beef cattle, we evaluated the pedometer-like IceTag device (IceRobotics, Edinburgh, Scotland) that records step events, leg movement and body position (upright versus lying). We used partition analysis to compare behaviour as inferred from the device data with true behaviour as coded at high resolution from carefully synchronized video observations of 5-min duration. Results: Malfunctions reduced the target dataset by 7%. The correspondence between IceTag and video coded step counts was excellent (r(2) = 0.97), and the device's indications of upright or lying corresponded well (error rate = 1.4%) to the video-coded values. However, the proportion of steps that could be matched individually was relatively low (65% at a tolerance of 0.5 s), and the indicated start of a lying bout was often triggered by leg movements of an upright animal. Partition analysis of Grazing versus Not-Grazing yielded an overall error rate of 22%. In both three- and four-way classifications of behaviour (Graze, Rest, Travel; Graze, Stand, Lie, Travel) error rates were low for non-graze behaviours, but only 25% of Graze observations were correctly classified; the overall error rate was 22%. Comparison with existing method(s): The IceTag device performed well in mapping the diurnal patterns of animal position and step rate, but less well in separating grazing from upright resting. Conclusions: Our results suggest that pedometry is not the ideal method for classifying behaviour when grazing is of paramount interest. (C) 2017 Elsevier B.V. All rights reserved.

Thirty-five lactating dairy cows throughout weeks of lactation (WOL) 16 to 30 were used to determine optimal time needed for reliable measurement of performance variables, and to classify the cows into high-, medium-, and low-efficiency groups. Individual performance variables [body weight (BW), dry matter intake (DMI), and milk production] were measured daily with a computerized monitoring system. Body condition was visually scored weekly and used to calculate retained or depleted body energy as a result of fat content change (REF). Milk composition was analyzed weekly. Body weight, DMI, and total recovered energy (RE), which represents energy in milk production plus REF, were summarized weekly. Efficiency was calculated as RE/DMI and as residual feed intake (RFI; i.e., the difference between actual and expected DMI), which was calculated from multiple linear regression of DMI dependence on BW(0.75) and RE. Unexpectedly, it was found that BW did not affect DMI and RE/DMI. Changes and relative changes in phenotypic coefficient of variation and correlations among data from shortened tests ranging from 1 wk (WOL 16) to a sequence of 15-wk tests were used to determine optimal test period durations for 5 traits: BW, DMI, RE, RE/DMI, and RFI. Traits were fitted into a mixed model with repeated measures. For each week, the traits were summarized as a sequence of cumulative data, starting from WOL 16 and cumulated over periods that increased in 1-wk steps up to WOL 16 to 29. Weekly cumulations were compared with those for entire test period (WOL 16 to 30). Consistency of each cow's efficiency classification as high, medium, or low was tested by the total-agreement procedure; the kappa index P-value was used. Throughout WOL 16 to 30, the effects of increasing test period duration on between-animal coefficient of variation differed with respect to the various performance variables and RE/DMI: it tended to change with respect to BW, did not change with respect to DMI, and decreased with respect to RE and RE/DMI. In conclusion, compared with a 15-wk study, a 2-wk study can classify RFI and RE/DMI to 3 efficiency levels, with an individual correlation coefficient of 0.6. When the study was carried out over 3 wk or more, the lowest significant index of the classification was P<0.004, the lowest individual correlation coefficient was 0.65, and its lowest significance was P<0.01. The current study indicated that the insignificant effect of the BW of dairy lactating cows on their DMI should be validated in more studies.

The objectives of this study were to determine the differential incorporation of various omega-3 (n-3) fatty acids (FAs) supplemented to dairy cows into ovarian compartments and assess the effects on IVF. Forty-two 256-day pregnant cows were supplemented with encapsulated fats, in treatments designated as i) SFA - saturated fat at 240 and 560 g/day per cow, prepartum and post partum (PP) respectively; ii) FLX - flaxseed oil at 300 and 700 g/day per cow prepartum and PP respectively; and iii) FO - fish oil at 300 and 700 g/day per cow prepartum and PP respectively. Commencing at 60 days in lactation, ovum pickup (OPU) was performed twice weekly (20 sessions; five cows per group) and in vitro maturation and IVF were conducted. The proportion of α-linolenic acid (ALA) was greater in follicular fluid (FF), granulosa cells, and cumulus-oocyte complexes (COCs) of FLX cows than in other groups (P<0.001). The proportion of docosahexaenoic acid (DHA) was 6.7 times as great in FF of FO as in other groups (P<0.001); docosapentaenoic acid n-3 and DHA were detected in COCs of FO but not in others. The follicle number during OPU was higher in FLX and FO than in SFA (P<0.05), and the oocyte cleavage rate was higher in FLX and FO than in SFA (P<0.01). Also, the percentage of oocytes that developed to blastocysts tended to be higher in both n-3 groups than in SFA (P<0.1). In conclusion, both dietary n-3 FAs similarly improved folliculogenesis and IVF performance; therefore, ALA-rich botanical n-3 seems to be a satisfactory approach to improve oocyte quality.

Ruminal wall metabolism was studied in nonlactating heifers by altering the carbohydrate (CHO) digestion site between rumen and intestine. The CHO digestion site was estimated from in situ and total-tract digestibility of control (CONT) diets and diets supplemented with corn (CRN), barley (BARL), or soy hulls (SOYH). Ruminal epithelial metabolism regulating gene expression, morphology, and nutrient delivery was assessed from a combination of rumen volatile fatty acid (VFA) concentration, biopsies for papilla morphology, and expression of putative metabolic regulatory genes encoding enzymes that facilitate VFA utilization. Digestible dry matter and CHO intake were 25 and 45% higher, respectively, in the supplemented diets than in CONT diets. Fiber supplementation increased the intestinal and decreased ruminal CHO digestion. Ruminal nonfiber CHO digestibility was 10% lower in CRN than with the high rumen-degradable supplement. The CONT heifers had lowest total ruminal VFA and highest acetate concentration relative to the other treatments. Total VFA concentration in BARL and CRN diets tended to be higher than in SOYH. The SOYH diet tended to reduce papilla dimension relative to CRN and BARL. The CRN diet tended to increase papilla surface area relative to BARL and SOYH. Gene expression of propionyl-coenzyme A carboxylase was higher in CRN and BARL than in SOYH diets, and tended to be higher in CRN than in BARL and SOYH diets. Lactate dehydrogenase and butyryl coenzyme A synthase gene transcripts tended to be higher in CONT than in the supplemented treatments. Thus, rumen epithelial expression of genes involved in VFA metabolism and ruminal wall-structure development are influenced by other regulatory mechanism that is not directly affected by local signals. The in situ methods used are a useful tool for differentiating ruminal from extraruminal nutrient supply.

The aim of this work was to study the effects of mastitis induced by intramammary lipopolysaccharide (LPS) challenge on milk oxidative stability, as well as to understand the underlying biochemical processes that cause such changes. LPS challenge was associated with nitric oxide burst from the surrounding mammary epithelial cells and consequently induced nitrosative stress that was induced by the formation of NO2• from nitrite by lactoperoxidase. This response was associated with an ∼3-fold increased formation of hazardous compounds: nitrotyrosines, carbonyls and lipid peroxides. We sustained the involvement of xanthine oxidase as a major source of hydrogen peroxide. In consistent with previous findings, catalase has been shown to play a major role in modulating the nitrosative stress by oxidizing nitrite to nitrate. The current hygienic quality criteria cannot detect mixing of low-quality milk, such as milk with high somatic cells, and nitrite with high-quality milk. Thus, development of an improved quality control methodology may be important for the production of high-quality milk.

Support of milk production in modern dairy cows demands a large proportion of its own metabolic resources, such as glucose, which might be required under stressful situations. The aim of the experiment was to test the hypothesis that acute immune stress shifts oxidative metabolism to glycolysis. Two mammary quarters in 6 Holstein cows were infused with lipopolysaccharide (LPS), whereas the 2 counter quarters served as controls to the treatment. An additional 6 cows were infused with saline and served as running controls. The LPS challenge induced dramatic transient increases in milk lactate (75-fold) and malate (11-fold) concentrations (both markers of glycolysis) at 24h posttreatment. No significant changes in lactate and malate concentrations were recorded in control quarters and control animals, indicating that the effect of LPS was restricted to the treated gland. The LPS challenge induced a dramatic transient decrease in milk yield, and lactose and citrate (a marker of mitochondrial metabolism) secretion at 24h posttreatment. The kinetics were inversely proportional to those of lactate and malate concentrations. Thus, our data suggest that LPS challenge induces acute conversion of epithelial cell metabolism from principally mitochondrial-oxidative to principally cytosolic (glycolytic), which allows the diversion of metabolic resources normally used to synthesize milk to support the immune system. An in vitro bacterial growth test showed that concentrations of lactate, malate, and lactose equivalent to those found in the in vivo experiment delayed and reduced the growth of a pathogenic Escherichia coli strain, suggesting that they play a role in diminution of bacterial multiplication in the mammary gland.

The objective of this study was to examine the incorporation of dietary n-3 fatty acids (FAs) into ovarian compartments and the effects on hormonal and behavioral patterns around estrus. Multiparous 256-day pregnant cows were fed either a standard diet both prepartum and postpartum (PP) (control; n=22) or supplemented with extruded flaxseed (E-FLAX) providing C18:3n-3 at 172.2 and 402.5 g/day per cow prepartum and PP respectively (n=22). The estrous cycle was synchronized, and at day 7 of the cycle, the cows were injected with prostaglandin F(2)(α) (PGF(2)(α)) and then subjected to 5 days of intensive examination. Compared with those in the control, in the E-FLAX group, the interval from PGF(2)(α) injection to behavioral estrus peak tended to be longer (3.6 h; P<0.1), that to estradiol (E(2)) peak was 6.5 h longer (P<0.03), and that to LH peak tended to be longer (5.3 h; P<0.07). The durations of behavioral estrus and E(2) surge were longer, and the area under the E(2) curve was greater in the E-FLAX cows. Afterward, 7-8 days following behavioral estrus, follicular fluids (FFs) from >7 mm follicles were aspirated. The proportions of n-3 FA increased in plasma, FF, and granulosa cells in the E-FLAX group. The concentrations of PGE(2) in the E(2)-active follicles tended to be lower in the E-FLAX cows (P<0.06). In conclusion, several modifications in hormonal and behavioral estrus patterns were demonstrated in cows fed n-3 FA, which might be attributed to alterations in membrane FA composition and partly mediated by lower PGE(2) synthesis.

The objectives were to examine the effect of high dietary crude protein on characteristics of preovulatory follicles in dairy heifers. Eight Israeli-Holstein heifers, 4 fitted with rumen fistula and 4 intact, were assigned to 1 of 3 treatments in a replicated (n=2) 4 × 3 incomplete Latin square design with 39-d periods. Treatments were: low (6.0%; LP), moderate (13.0%; MP), and high (20.0%; HP) crude-protein diets, containing 1.27 Mcal NE(L)/kg dry matter. Diets were based on approximately 66% wheat straw and various proportions of ground corn grain and soybean meal. The estrous cycles of the heifers were synchronized, and 14 d after behavioral estrus, heifers received PGF(2 α) injections. After a further 40 h, at d 39 of each period, follicular fluid (FF) was aspirated from follicles of diameter >7 mm. The intake of the LP diet was 9% lower than that of MP and HP diets. Rumen ammonia and plasma urea nitrogen concentrations were highest in the HP and lowest in the LP, with intermediate levels in MP diets. No differences were found between treatments in plasma and FF concentrations of glucose and nonesterified fatty acids. High-protein diets increased urea concentrations very similarly in preovulatory FF and in plasma. No differences were observed between diets, in preovulatory follicle diameters and concentrations of androstenedione. However, higher estradiol and progesterone concentrations in FF were observed under the HP than under the MP diet, with no difference between diets in estrogen to progesterone ratio. It can be concluded that high concentrations of urea in plasma, caused by high dietary crude protein, penetrated into preovulatory follicles, but did not impair preovulatory characteristics. This lack of detrimental effects might be attributed to the use in this study of nonlactating heifers, which have fewer nutritional and physiological constraints and eliminate negative effects of potential interactions with high urea on dairy cows' reproductive systems.

The objectives were to determine the incorporation of dietary encapsulated fats differing in n-6:n-3 ratio into milk fat, plasma, and various ovarian compartments and to examine the effects on ovarian follicular status, preovulatory follicle characteristics, and oocyte quality. Twenty-four multiparous Israeli Holstein cows, averaging 114 d in milk, were assigned to 1 of 3 treatment groups: 1) control (n=7), in which cows were fed a lactating cow diet; 2) E-FLAX (n=8), in which cows were fed a lactating cow diet that consisted of 1kg/d of encapsulated fat (3.8% of dry matter) containing 40.8% flaxseed oil, providing 242.2g of C18:3n-3 (low n-6:n-3 ratio); or 3) E-SUN (n=9), in which cows were fed a lactating cow diet that consisted of 1kg/d of encapsulated fat (3.8% of dry matter) containing 40.8% sunflower oil, providing 260.0g of C18:2n-6 (high n-6:n-3 ratio). Ovaries were monitored by ultrasonography for follicular status, and after synchronization, follicles >7mm were aspirated and evaluated. Ovum pickup was performed (19 sessions for the control and E-FLAX groups and 11 for the E-SUN group), and in vitro maturation and oocyte fertilization were conducted. The E-FLAX treatment increased the proportions of C18:3n-3 (5.8 fold), C20:5n-3, and C22:5n-3 (approximately 4-fold) in milk fat as compared with the other 2 treatments. The proportion of C18:3n-3 fatty acid in plasma increased dramatically with the E-FLAX treatment, from 1.43 and 1.49% in the control and E-SUN groups, respectively, to 7.98% in the E-FLAX group. Consequently, the n-6:n-3 ratio in plasma was reduced from approximately 42 in the control and E-SUN groups to 6.74 in the E-FLAX group. Proportions of C18:3n-3 in follicular fluid and granulosa cells were approximately 5-fold higher in the E-FLAX group than in the other 2 groups. The percentage of C18:2n-6 in cumulus-oocyte complexes of cows in the E-SUN group was 54% higher than that in the E-FLAX group and was 2.4-fold higher than that in the control group; the proportion of C18:3n-3 in the E-FLAX group was 4.73% and was not detected in the other groups. The average numbers of 2- to 5-mm follicles on d 5 and 9 of the cycle were higher in the E-FLAX group than in the E-SUN group, whereas the average numbers of follicles > or =10mm on d 5, 9, and 13 were higher in the E-SUN group than in the other 2 groups. The estrous cycles of the cows were synchronized and PGF(2alpha) was injected on d 16 to 17 of the cycle. The interval from PGF(2alpha) injection to behavioral estrus was longer in the E-FLAX group than in the E-SUN group, and the beginning of the luteal phase of the subsequent cycle was delayed. Concentrations of estradiol in follicular fluid of the preovulatory follicles were higher in the E-SUN group than in the E-FLAX group. The number of follicles aspirated by ovum pickup was higher in the E-FLAX group than in the control group, and the cleavage rate in the E-FLAX group was higher than in the control group, but not the E-SUN group. In conclusion, dietary n-3 fatty acids influenced the follicular status and increased the cleavage rate of oocytes as compared with those of control cows. These findings could be related to modifications of the fatty acid composition in plasma and ovarian compartments in response to dietary supplementation.

Multiparous Israeli-Holstein cows (n = 42) averaging 158 d in milk and 621 kg of body weight were used to investigate the effects of energy source (fat or concentrate) on production, rumination time, energy balance, metabolic heat production, and efficiency under hot and humid conditions. Cows were assigned to 3 diet treatment groups: a lactating-cow ration (1.75 Mcal of net energy for lactation/kg of dry matter (DM; control); supplemented with 0.825 kg/d per cow of ground corn grain (2.7% of diet; HG); or supplemented with 0.300 kg/d per cow of calcium salts of fatty acids (1.5% of diet; HF). Milk production, body weight, and rumination time were recorded daily. Rectal temperature and respiratory rate (RR) were measured weekly. Mean daily maximum ambient temperature, relative humidity, and temperature-humidity index were 31.5 degrees C, 86.6%, and 76.8, respectively. Dry matter intake was lower in HF and HG cows than in controls. Average daily rumination time was lowest in the HG group: 393.0, 377.7, and 390.8 min/d for control, HG, and HF cows, respectively. Milk production was higher in the control group than in the HG group; milk fat content was 0.38 units higher and fat yield was 11% greater in HF cows than in HG cows. Fat-corrected milk yield was higher in HF cows than in HG cows, but not higher than in controls. Energy balance in HF cows was lower than in both other groups, and nonesterified fatty acid concentrations in plasma were increased by fat supplementation. Rectal temperature was highest in HF cows, and RR was higher in the HF cows than in the controls. Metabolic heat production was similar in HG and HF cows and lower than in controls. Body weight gain of the HG cows tended to be higher than that of the others. Efficiency of conversion of DM or energy intake to milk and fat-corrected milk was higher in HF cows than in both other groups; however, when taking the energy retention in body mass into account, no differences in energy utilization were observed between HF and HG groups. A principal component analysis revealed that rumination time played a pivotal role in the deleterious effect of heat stress in dairy cows. In conclusion, increasing the energy density in diets of heat-stressed mid-lactation cows over 1.75 Mcal/kg of DM was not effective in enhancing production. Both dietary treatments were effective in reducing metabolic heat production, but the changes were not reflected in rectal temperature and RR. Fat supplementation increased metabolic efficiency; however, whereas HF cows prioritized milk production, HG cows channeled energy for body mass deposition.

The objective was to study effects of cultivar, stage of maturity at harvest, wilting, and addition of lactic acid bacterial (LAB) inoculant at ensiling, and their interactions, on the aerobic stability of wheat silages. Wheat of two cultivars, harvested at the flowering or the milk stage of maturity were ensiled in mini-silos, either directly after cutting (DC) or after wilting (W). After 2–7 months of storage, silages were subjected to a 7-day aerobic stability test during which changes in chemical composition, dry matter (DM) and neutral detergent fiber (aNDF) digestibility, and temperature, as well as DM losses and CO2 production, were measured. Silages from wheat cultivar BH were relatively dry (DM between 287 and 430g/kg) and were mostly stable upon aerobic exposure. The flowering wheat of cultivar Galil was moister (DM of 199g/kg), and the DC silages were stable upon aerobic exposure. Silages of the wilted flowering wheat (DM of 370g/kg) spoiled and after 4 and 7 days, produced 15 and 76g/kg DM CO2, respectively. Silages from the milk stage of this cultivar, both DC and W were unstable, and a homofermentative LAB enhanced aerobic spoilage. Factorial analysis of variance was applied to the results with cultivar, stage of maturity, wilting and inoculant as main effects, as well as their interactions. Cultivar and LAB inoculant had effects on silage composition and aerobic stability, with stage of maturity having an effect on aerobic losses, whereas wilting did not have effects on aerobic spoilage indicators. The inoculant enhanced CO2 production in the silages prepared from the DC wheat of the flowering and milk stages, as compared with the respective non-inoculated control silages which contained high concentrations of VFA. However, in the wilted silages which contained less VFA, both control and inoculated silages deteriorated similarly with time of exposure to air.

The objective of this study was to determine the effects of feeding an increased amount of extruded flaxseed with high proportions of n-3 fatty acids (FA) to transition dairy cows on performance, energy balance, and FA composition in plasma, adipose tissue, and milk fat. Multiparous Israeli-Holstein dry cows (n = 44) at 256 d of pregnancy were assigned to 2 treatments: (1) control cows were fed prepartum a dry-cow diet and postpartum a lactating-cow diet that consisted of 5.8% ether extracts; and (2) extruded flaxseed (EF) cows were supplemented prepartum with 1 kg of extruded flaxseed (7.9% dry matter)/cow per d, and postpartum were fed a diet containing 9.2% of the same supplement. The EF supplement was fed until 100 d in milk. On average, each pre- and postpartum EF cow consumed 160.9 and 376.2g of C18:3n-3/d, respectively. Postpartum dry matter intake was 3.8% higher in the EF cows. Milk production was 6.4% higher and fat content was 0.4% U lower in the EF group than in the controls, with no differences in fat and protein yields. Energy balance in the EF cows was more positive than in the controls; however, no differences were observed in concentrations of nonesterified fatty acids and glucose in plasma. Compared with controls, EF cows had greater proportions of C18:3n-3 in plasma and adipose tissue. The proportion of n-3 FA in milk fat was 3.7-fold higher in the EF cows, and the n-6:n-3 ratio was decreased from 8.3 in controls to 2.3 in the EF cows. Within-group tests revealed that the C18:3n-3 content in milk fat in the EF cows was negatively correlated with milk fat percentage (r = -0.91) and yield (r = -0.89). However, no decrease in de novo synthesis of less than 16-carbon FA was found in the EF group, whereas C16:0 yields were markedly decreased. It appears that the enrichment of C18:3n-3 in milk fat was limited to approximately 2%, and the potential for increasing this n-3 FA in milk is higher for cows with lower milk fat contents. In conclusion, feeding increased amounts of C18:3n-3 during the transition period enhanced dry matter intake postpartum, increased milk production, decreased milk fat content, and improved energy balance. Increased amounts of EF considerably influenced the FA profile of plasma, adipose tissue, and milk fat. However, the extent of C18:3n-3 enrichment in milk fat was limited and was negatively correlated with milk fat content and yield.

Recent data have shown that bovine fatty liver is associated with inflammation, but a causative role of inflammatory mediators has not been demonstrated. To determine whether inflammation can induce fatty liver, recombinant bovine tumor necrosis factor alpha (TNF) was administered to late-lactation Holstein cows in a randomized complete block design. Cows (n = 5 per treatment) were blocked by feed intake and milk production and randomly assigned within block to control (saline), TNF at 2 μg/kg per d, or pair-fed control (saline, intake matched) treatments. Treatments were delivered once daily by subcutaneous injection for 7 d. Plasma samples were collected daily for analysis of glucose and non-esterified fatty acids (NEFA) and a liver biopsy was collected on d 7 for triglyceride (TG) and quantitative real-time PCR analyses. Data were analyzed with mixed models using treatment contrasts to assess effects of TNF administration and decreased feed intake. By d 7, feed intake and milk production decreased by 15% and 12%, respectively, for both TNF and pair-fed cows compared to controls. TNF administration significantly increased hepatic TNF mRNA and protein abundance and increased liver TG content by 103% (P < 0.05) without affecting plasma NEFA concentration. TNF tended to decrease hepatic carnitine palmitoyltransferase 1 and increase fatty acid translocase (CD36) and 1-acyl-glycerol-3-phosphate acyltransferase transcript abundance (all P < 0.10), effects which are consistent with increased NEFA uptake and storage as TG. TNF also decreased transcript abundance for glucose6-phosphatase (P = 0.02) and phosphoenolpyruvate carboxykinase 1 (P = 0.09), genes important for gluconeogenesis. Plasma glucose concentration was not affected by treatment. These findings indicate that TNF promotes liver TG accumulation and suggest that inflammatory pathways may also be responsible for decreased glucose production in cows with fatty liver.

The object of this study was to evaluate the impact of monensin administration on the early lactation performance of cows maintained on a high-energy diet, and on health traits during the transition period. Cows (n = 168; parity 3.3 +/- 1.4, initial body condition score 3.1 +/- 0.08, and milk yield of 34.3 kg/d +/- 0.9 for multiparous cows in the preceding lactation) were divided into control and monensin treatment groups. A controlled-release capsule supplying 335 mg of monensin/d for 95 d was inserted into the rumen of monensin-treated cows 30 d before the expected calving. Blood samples were obtained 2 h after feeding on d 14 prepartum and on d 7, 14, and 50 postpartum. Plasma glucose concentration was 3% higher (58 +/- 0.5 vs. 56.4 +/- 0.5 mg/dL) and beta-hydroxybutyric acid was 17% (6.7 +/- 0.3 vs. 8.0 +/- 0.3 mg/dL) lower in monensin-treated than control cows. Plasma glucose was 10% higher (60.0 +/- 0.6 vs. 54.5 +/- 0.3 mg/dL) and beta-hydroxybutyric acid was 16% lower (6.8 +/- 0.3 vs. 7.9 +/- 0.2 mg/dL) in primiparous than multiparous cows. Plasma nonesterified fatty acid concentration (measured only in primiparous cows) was 17% lower (287 +/- 15 vs. 336 +/- 17 muEq/L) in treated than in control cows. Rate of ketosis incidence was 60% lower (8 vs. 21%) in monensin-treated than in control cows, and the proportion of control cows that required a supply of glucogenic precursors was 3-fold higher than in monensin-treated cows. The body condition score was 3.1 +/- 0.05, 2.7 +/- 0.05, and 2.4 +/- 0.05 on d 60 prepartum and d 7 and 50 postpartum, respectively, and was not affected by treatment. During the first 5 mo of lactation, milk yield was 7% higher (37.6 +/- 0.6 vs. 35.2 +/- 0.6 kg/d) in monensin-treated cows than in control cows. Our results showed that monensin administration, as a controlled-release capsule in prepartum cows, can be beneficial, even if these cows are maintained on a high-energy diet during the subsequent lactation.

Dietary unsaturated fatty acids (UFAs) have been implicated in several reproductive processes in dairy cows through a variety of mechanisms. This study examined the effects of periparturient supplementation of rumen bypass fats low or high in proportion of UFAs (oleic and linoleic) on preovulatory follicle characteristics. Forty-two 256-day pregnant dairy cows were divided into three groups and were fed a control diet (n=14) or supplemented with fats either low (LUFA; n=14) or high (HUFA; n=14) in UFAs. At 14-15 days following behavior estrus, the cows received a prostaglandin F(2)(alpha) injection and 48 h later >7 mm follicles were aspirated. Progesterone (P(4)), androstenedione (A(4)), and estradiol (E(2)) were determined in the follicular fluid. Out of 75 follicles, 37 follicles that were aspirated between 55 and 70 days post partum were regarded as E(2)-active follicles (E(2)/P(4) ratio >1) and subjected for further analysis. The diameter of preovulatory follicles was greater in cows fed HUFA than in those fed control or LUFA. The concentrations and content of A(4) and E(2) in follicles and E(2)/P(4) ratio were higher in the HUFA group than in the other two groups. The P450 aromatase mRNA expression in granulosa cells that were collected from the aspirated preovulatory follicles was also higher in the HUFA cows than in the other groups. A significant correlation was observed between E(2) concentrations in preovulatory follicles and E(2) concentrations in plasma at aspiration. In conclusion, dietary UFA increased the size of and elevated steroid hormones in preovulatory follicles, which may be beneficial to consequent ovarian function.

The steroidogenic capacity of several tissues has been shown to be regulated by lipoproteins. However, the ability of the various lipoprotein classes to affect steroid production in general and estradiol-synthesis in particular has not been established in bovine ovarian cells. In previous studies, we described alterations in the lipoprotein profiles in follicles of different sizes and corresponding changes in lipoprotein-receptor gene expression. In the present study, the effect of low-density lipoprotein (LDL)-enriched medium on aromatization competence of whole ovarian follicles was determined in vitro. Gene expression of aromatase increased and that of selective-uptake receptors decreased in the presence of LDL. These results suggest a role for LDL availability in folliculogenesis.