Effects of dietary supplementation of pioglitazone on metabolism,milk yield,and reproductive performance in transition dairy cows

The objective of this study was to investigate the effect of dietary supplementation of pioglitazone (PGT), a specific ligand for PPARγ, on metabolic dynamics, milk production, and reproductive performance of transition dairy cows. Eighty multiparous Holstein cows in their second or more lactations were blocked by the calving date and parity and assigned randomly to four dietary groups (n = 20 cow/treatment) including control (no PGT−/−), supplemented with PGT (6-mg PGT/kg body weight) from Day −14 to +21 relative to parturition (PGT+/+) or only during prepartum (PGT+/−) or postpartum periods (PGT−/+). Postpartum body condition score and body weight loss decreased (P < 0.05) in all PGT-supplemented groups. Milk yield was not affected by PGT supplementation (P > 0.05). Percentage of milk fat decreased (P < 0.05) in all PGT-treated groups; however, milk fat yield was lower (P < 0.05) in PGT (+/+) and PGT (+/−) groups compared with PGT (−/−). Peripartum (Day −7 to +7) concentrations of plasma nonesterified fatty acids and β-Hydroxybutyrate decreased in PGT (+/+) but not in the PGT (−/−) group (P < 0.05). During the postpartum period, PGT reduced (P > 0.05) plasma concentrations of nonesterified fatty acids in all PGT-treated groups but did not affect β-Hydroxybutyrate level. Plasma concentrations of triglycerides decreased in all PGT-supplemented groups. Supplementation of PGT increased the peripartum concentrations of plasma glucose in PGT (+/+) and PGT (+/−) groups compared with control. Plasma concentrations of insulin-like growth factor 1 were higher in PGT (+/+) compared with the control group during both the peripartum and postpartum periods. Plasma concentrations of growth hormone and insulin were not affected by PGT treatment (P > 0.05). Mean days to ovulation were lower in PGT (+/+) and PGT (-/+), and the proportion of cows ovulating by Day 14 postpartum was higher in PGT (+/+) compared with control. Days open were shorter in PGT (+/+), PGT (+/−), and PGT (−/+) groups compared with control. However, the proportion of pregnant cows at 120 days in milk were higher in all PGT-supplemented groups. The results showed positive effects of dietary supplementation of PGT, especially supplementation during both the prepartum and postpartum periods, on metabolic dynamics, ovarian function, and reproductive performance in transition dairy cows.     

Metabolic and endocrine responses to short-term nutrient imbalances in the feed ration of mid-lactation dairy cows

Short-term imbalances of dietary nutrients occur during natural fluctuations in roughage quality (e.g. on pasture) or temporal shortages of supplementary feed components. In contrast to a deficiency, macronutrients (i.e. carbohydrates, proteins, lipids) beyond the adequate supply with other nutrients may, for instance, alter milk composition, increase BW or result in a greater excretion of nitrogen. Especially dairy cows with a moderate performance, in mid- or late lactation, or in extensive farming systems may be exposed to imbalanced rations. A better understanding of metabolic and endocrine responses depending on macronutrient supply may help to precisely feed dairy cows. The present study investigated short-term metabolic and endocrine responses to different levels of concentrates formulated to particularly provide one major macronutrient source (carbohydrates, proteins or lipids). Based on parity number, lactational stage, milk yield and BW, nine mid-lactating cows (211 ± 19 days in milk) were grouped into three blocks of three animals each. Concentrates (aminogenic: rich in CP and nitrogen sources; glucogenic: high content of carbohydrates and glucogenic precursors; lipogenic: high lipid content) were fed in addition to hay in a factorial arrangement at increasing levels from 2.5 to 7.5 kg/d during 9 d. Milk yield, BW and feed intake were recorded daily. Blood and milk were sampled every 3 d at the end of each concentrate level. Milk fat, protein, lactose and urea contents were determined. In blood, concentrations of various metabolites, endocrine factors and enzyme activities (e.g. glucose, non-esterified fatty acids (NEFAs), β-hydroxybutyrate, urea, cholesterol, triglycerides, insulin, glucagon, aspartate aminotransferase (ASAT), gamma-glutamyltransferase (GGT) and glutamate dehydrogenase activity (GLDH)) were measured. Milk yield, milk composition and BW were not affected by type and level of concentrates. Feed intake increased in cows with greater amounts of the aminogenic and lipogenic concentrate compared with the glucogenic concentrate. Milk and plasma urea concentrations were elevated in the aminogenic and to a lesser extent in the lipogenic treatment compared with the glucogenic treatment. Glucose concentrations in plasma were not affected by treatments, whereas insulin and glucagon increased, and NEFA concentrations decreased only in cows fed 7.5 kg/d aminogenic concentrate compared with the glucogenic and lipogenic treatment. Activities of ASAT, GGT and GLDH as well as the total antioxidant capacity were not affected by diets. In conclusion, immediate metabolic and endocrine responses were observed due to the short-term dietary changes. Particularly, a surplus of nitrogen supply via the aminogenic diet affected metabolic responses and stimulated insulin and glucagon secretion.     

Production performance and milk composition of dairy cows fed extruded canola seeds treated with or without lignosulfonate

Eight multiparous Holstein cows averaging 538 kg of body weight and 62 days in milk were used in a double 4 × 4 Latin square design with four 21-d experimental periods to determine the effects of feeding extruded versus non-extruded canola seed treated with, or without, 50 g/kg lignosulfonate on apparent whole tract digestibility, feed intake, milk production, milk composition, and milk fatty acid profile. Intake of dry matter (DM) and its components was similar among treatments. Extrusion had no effect on digestibility but decreased milk fat concentration. Lignosulfonate treatment of canola seeds decreased digestibility of DM and crude protein (CP). Milk production, milk concentrations of CP, lactose and total solids, and milk yields of CP and fat were similar among treatments. In general, there was no interaction between extrusion and lignosulfonate for milk fatty acid profile. Feeding extruded canola seeds increased milk fat concentration of trans11 18:1 to a greater extent without, than with, lignosulfonate treatment (150% versus 113%). Overall, it is clear that extrusion had more effects than lignosulfonate treatment on milk fatty acid profile, but changes were small and likely of little biological importance for human health.     

Prediction of first test day milk yield using historical records in dairy cows

The transition between two lactations remains one of the most critical periods during the productive life of dairy cows. In this study, we aimed to develop a model that predicts the milk yield of dairy cows from test day milk yield data collected in the previous lactation. In the past, data routinely collected in the context of herd improvement programmes on dairy farms have been used to provide insights in the health status of animals or for genetic evaluations. Typically, only data from the current lactation is used, comparing expected (i.e., unperturbed) with realised milk yields. This approach cannot be used to monitor the transition period due to the lack of unperturbed milk yields at the start of a lactation. For multiparous cows, an opportunity lies in the use of data from the previous lactation to predict the expected production of the next one. We developed a methodology to predict the first test day milk yield after calving using information from the previous lactation. To this end, three random forest models (nextMILK_FULL, nextMILK_PH, and nextMILK_P) were trained with three different feature sets to forecast the milk yield on the first test day of the next lactation. To evaluate the added value of using a machine-learning approach against simple models based on contemporary animals or production in the previous lactation, we compared the nextMILK models with four benchmark models. The nextMILK models had an RMSE ranging from 6.08 to 6.24 kg of milk. In conclusion, the nextMILK models had a better prediction performance compared to the benchmark models. Application-wise, the proposed methodology could be part of a monitoring tool tailored towards the transition period. Future research should focus on validation of the developed methodology within such tool.     

Evaluation of the genetic trend of milk yield in the multiple ovulation and embryo transfer populations of dairy cows, using stochastic simulation

Stochastic modeling of dairy cattle populations using multiple ovulation and embryo transfer (MOET) was used to compare 15-year genetic responses with an artificial insemination (AI) program. MOET and AI techniques were simulated in four populations, two with 100 breeding females each and two with 400 breeding females. The selection goal was to maximize genetic progress in milk yield. The reduction in genetic variation due to inbreeding and linkage disequilibrium was accounted for in the simulation process. All four MOET breeding schemes studied achieved larger genetic responses than the realized and theoretical genetic gains from the current AI progeny testing populations. Strict restriction against inbred matings slowed genetic progress significantly in the small population but would not be consequential in the larger population. However, allowing inbred matings in the smaller population caused a rapid accumulation of inbreeding. Linkage disequilibrium was as important as inbreeding in reducing genetic variation. Genetic drift variance was much smaller in the larger population.     

Effects of fibre concentration of diets consisting of hay and slowly degradable concentrate on ruminal fermentation and digesta particle size in mid-lactation dairy cows

The objective of this study was to investigate the intestinal microbiota of growing kittens fed moderate- or high-protein diets using DNA-based qualitative and quantitative techniques. Kittens were weaned to a high-protein (HP; n = 7) or moderate-protein (MP; n = 10) diet at 8 weeks of age. Fresh faecal samples were collected at 8, 12, and 16 weeks of age. DNA was extracted and quantitative PCR used to quantify Bifidobacterium, Lactobacillus, Clostridium perfringens, and Escherichia coli concentrations. Denaturing gradient gel electrophoresis was performed to create a dendrogram and unrooted trees using Bionumerics 5.0 to identify similarity due to litter, age, or diet. Kittens fed HP had lower (p = 0.02) Bifidobacteria and Lactobacillus counts than MP-fed kittens. E. coli was lower (p = 0.02) in HP-fed kittens and tended to be affected by age (p = 0.09). Kittens were clustered by litter at 8 weeks of age, and then clustered by diet at 12 and 16 weeks of age. Our data suggest that faecal microbiota of growing kittens change after weaning and that dietary protein concentration affects E. coli, Bifidobacterium, and Lactobacillus populations. The relevance of these data in terms of intestinal health and disease remain to be determined and justifies further study.     

Effects of dietary crude protein concentration on animal performance and nitrogen utilisation efficiency at different stages of lactation in Holstein-Friesian dairy cows

Nitrogen (N) excretion from livestock production systems is of significant environmental concern; however, few studies have investigated the effect of dietary CP concentration on N utilisation efficiency at different stages of lactation, and the interaction between dietary CP levels and stages of lactation on N utilisation. Holstein-Friesian dairy cows (12 primiparous and 12 multiparous) used in the present study were selected from a larger group of cows involved in a whole-lactation study designed to examine the effect of dietary CP concentration on milk production and N excretion rates at different stages of lactation. The total diet CP concentrations evaluated were 114 (low CP), 144 (medium CP) and 173 (high CP) g/kg DM, with diets containing (g/kg DM) 550 concentrates, 270 grass silage and 180 maize silage. During early (70–80 days), mid- (150–160 days) and late (230–240 days) lactation, the same 24 animals were transferred from the main cow house to metabolism units for measurements of feed intake, milk production and faeces and urine outputs. Diet had no effect on BW, body condition score, or milk fat, protein or lactose concentration, but DM intake, milk yield and digestibilities of DM, energy and N increased with increasing diet CP concentration. The effect of diet on milk yield was largely due to differences between the low and medium CP diets. Increasing dietary CP concentration significantly increased urine N/N intake and urine N/manure N, and decreased faecal N/N intake, milk N/N intake and manure N/N intake. Although increasing dietary CP level significantly increased urine N/milk yield and manure N/milk yield, differences in these two variables between low and medium CP diets were not significant. There was no significant interaction between CP level and stage of lactation on any N utilisation variable, indicating that the effects of CP concentration on these variables were similar between stages of lactation. These results demonstrated that a decrease in dietary CP concentration from high (173 g/kg DM) to medium level (144 g/kg DM) may be appropriate for Holstein-Friesian dairy cow to maintain milk production efficiency, whilst reducing both urine N and manure N as a proportion of N intake or milk production.     

Effect of neonatal monosodium glutamate on the activities of glutamate dehydrogenase and aminotransferases in the circumventricular organs of rat brain

Summary Glutamate (Glu) the major amino acid in mammalian brain and most dietary proteins possesses neurotransmitter as well as neurotoxic properties. We administered monosodium glutamate (MSG) 4 mg/g bwt, sc on postnatal day (PND) 1 through 10 to rats on alternate days or daily and sacrificed them on PND 45 or PND 90 respectively. The activities of glutamate dehydrogenase and aminotransferases were evaluated in the circumventricular organs of brain. Results show that neonatal MSG produces alterations in glutamate metabolism in blood-brain-barrier deficient regions.     

Estimation of cold stress effect on dairy cows

Twelve crossbred heifers (Slovak Spotted x Holstein-Friesian) were housed in an open, uninsulated barn with straw bedding and a concrete-floored yard. Minimum temperatures inside the barn were as low as –19°C. The average milk yield decreased as the temperatures approached these minima. Compared with the temperate conditions, the feed intake and blood levels of glucose and free fatty acids increased. The level of sodium declined significantly during the second cold period. Correlations and regressions between milk yield and biochemical parameters were calculated, and the results indicate that the concentrations of free fatty acids, cholesterol, and triiodothyronine and the haematocrit values may serve to predict milk production during periods of cold stress, or in lactations of 305 days.     

Genetic and non-genetic factors associated with milking order in lactating dairy cows

The ability to rapidly identify temporal deviations of an animal from its norm will be important in the management of individual cows in large herds. Furthermore, predictors of genetic merit for especially health traits are useful to augment the accuracy of selection, and thus genetic gain, in breeding programs. The objective of this study was to estimate the repeatability of milking order and to quantify the contribution of differences in additive genetic variation to phenotypic differences (i.e., heritability). The data used in this study included 9813 herd milk recording test-day records with time of milking from 85,532 cows in 1143 herds across an 8-year period. Milking order was available for both morning and evening milking for each cow with, on average, 3.33 milk test-day records (i.e., 6.66 milking events) per lactation, and on average 1.62 lactations per cow. Variance components for milking order were estimated using animal linear mixed models; covariance components between milking order and milk yield, milk composition and somatic cell score (i.e., logarithm₁₀ somatic cell count) were estimated also using animal linear mixed models. The heritability of milking order was 0.20 indicating partial genetic control of milking order. The repeatability of milking order within test-day, within lactation, and across lactations was 0.63, 0.51, and 0.47, respectively. Milking order was positively (P < 0.001), but weakly, phenotypically correlated with milk yield (r = 0.04), and milk fat concentration (r = 0.01) and negatively (P < 0.001), but weakly, correlated with milk protein concentration (r = −0.02) and somatic cell score (r = −0.05). Milking order was positively (P < 0.05), although weakly, genetically correlated with milk yield (r = 0.07) and negatively (P < 0.05), but also weakly, genetically correlated with somatic cell score (r = −0.08). This study is the first to show a contribution of additive genetics to milking order in dairy cattle but the genetic correlation between milking order and somatic cell score was weak.     

Effects of inclusion of neutral detergent soluble fibre sources in diets varying in forage particle size on feed intake, digestive processes, and performance of mid-lactation Holstein cows

The aim of this study was to evaluate effects of partial replacement of neutral detergent soluble fibre (NDSF) for starch in diets varying in particle size (PS) of alfalfa hay on chewing activities, ruminal fermentation, nutrient digestibility and performance in mid-lactation dairy cows. Eight multiparous Holstein cows (146 ± 6.0 d in milk; 36.7 ± 2.57 kg milk/d) were used in a replicated 4 × 4 Latin square design with four 21 d periods with the last 7 d for data collection. The experiment was a 2 × 2 factorial arrangement with 2 levels of NDSF (low = 85 g/kg or high = 130 g/kg diet dry matter) each combined with 2 PS (short = 20 mm or long = 40 mm) of alfalfa hay. Results show that forage PS alone, or in combination with NDSF inclusion, had no effect on dry matter (DM) intake. Although total chewing, eating and ruminating times were not affected by treatments, eating time per kg of neutral detergent fibre (NDF) ingested was higher in long versus short alfalfa hay-based diets (P<0.05). Feeding long forage PS increased sorting of the diet against particles >19 mm, and in favor of those <8 mm (P<0.05). Feeding diets high in NDSF lowered DM intake (P<0.05), but increased apparent digestibility of all nutrients including NDF (P<0.05) independent of forage PS. Ruminal pH and concentrations of total volatile fatty acids were unaffected by dietary treatments, however the proportion of butyrate was higher in ruminal fluid of cows fed high NDSF diets (P<0.05). Changes in milk composition included lower milk crude protein content in high NDSF diets and higher lactose content for short hay-based diets (P<0.05). That milk yield and milk energy output were similar in low versus high NDSF diets suggests that high NDSF-fed cows had higher energy efficiency due to lower DM intake. Results suggest that, independent of forage PS, NDSF sources can be successfully included to partly replace starchy grains in diets exceeding minimum fibre recommendations.     

Calculations of apparent ruminal synthesis and intestinal absorption of biotin in dairy cows as influenced by the extraction method

Abstract

Biotin is present in nature either free or as biocytin, which is only degraded under the action of a specific enzyme: biotinidase. This enzyme is not included in analytical assays generally used. A method for sample preparation using biotinidase was developed in our laboratory before analysis by ELISA. Three cows equipped with duodenal and ileal cannulae were used to compare the effects of methods of sample preparation on calculations of apparent ruminal synthesis and intestinal absorption of biotin. There was no apparent ruminal synthesis of biotin, no matter whether free or total biotin was measured (p = 0.84). Results also suggested that rumen microbes cannot utilize nor degrade biocytin present in the feed. Estimates of apparent intestinal absorption were influenced by the sample preparation method (p = 0.002). Analysis of free biotin caused an artefact, suggesting intestinal synthesis of this vitamin; whereas determination of total biotin concentrations showed that absorption was taking place in the small intestine.     

Effects of alfalfa silage storage structure and roasting corn on ruminal digestion and microbial CP synthesis in lactating dairy cows

The objective of this experiment was to quantify the effects of unroasted or roasted ground-shelled corn (GSC), when fed with alfalfa ensiled in bag, bunker, or O2-limiting tower silos on ruminal digestion and microbial CP synthesis in lactating dairy cows. The roasted corn was heat-treated in a propane-fired roasting system. Alfalfa was harvested as second cutting from fields with regrowth of the same maturity. A portion of each field was allotted to each silo. The diets with 3 × 2 factorial arrangement of treatments were fed to six multiparous rumen-cannulated Holstein cows in a cyclic change-over design with five 21-day periods. Experimental diets were comparable and averaged (on dry matter (DM) basis): 410 g/kg alfalfa silage (AS), 150 g/kg corn silage, 350 g/kg GSC, 50 g/kg soybean meal, 40 g/kg roasted soybeans, 177 g/kg CP, 264 g/kg NDF and 250 g/kg starch. Nutrient flow was quantified by the omasal sampling technique with use of three markers (Co, Yb and indigestible NDF). Continuous infusion of 10% atom excess (15NH4)2SO4 was used to label microbial CP. None of the interactions between storage structure of dietary AS and corn type were significant. DM intake was not different among dietary treatments, averaging 24.5 kg/day across diets. Means of ADF digested in the rumen for cows fed diets with AS from bag, bunker and O2-limiting tower silo were 2.1, 1.7 and 2.1 kg/day, respectively, and was lower in cows fed AS from the bunker silo. This response may partly be a reflection of the higher intake of ADF by cows fed AS ensiled in the O2-limiting tower silo compared with the bunker. There was a slightly greater supply of fermentable substrates for cows fed diets with roasted compared with unroasted GSC. The small increases in yield of milk protein and lactose observed in the previous production trial in cows fed diets containing roasted corn may have occurred because of greater supply of fermentable substrates.     

Effect of feeding Saccharomyces Cerevisiae on performance of dairy cows during summer heat stress

Effects of feeding a culture of Saccharomyces cerevisiae to lactating cows on their lactational performance during heat stress were determined. Multiparous Holstein cows (n = 723) calving during the summer months from two dairy farms were randomly assigned to a diet containing no yeast culture (control; n = 361) or 30 g/d of a S. cerevisiae yeast culture (YC; n = 362) fed from 20 to 140 d in milk (DIM). Cows were milked twice daily and the production of milk and milk components was measured every 2 weeks. Dry matter (DM) intakes from 6 pens were measured daily and pen temperature and humidity were evaluated hourly from June to November. Rectal temperature was measured in 88 cows (22/treatment/farm), once weekly, and blood was sampled from a subset of 120 cows at 58 and 100 DIM for measurements of plasma glucose, nonesterified fatty acids, 3-OH-butyrate, insulin, and urea N concentrations. Daily temperature, humidity and the temperature-humidity index in the study pens did not differ between treatments, and rectal temperature of cows in the control and YC treatments differed with days postpartum. Intake of DM was similar between diets, but cows fed YC produced 1.2 kg/d more milk, more milk true protein, solids-not-fat and lactose than that produced by control cows. However, energy-corrected milk yield, and concentrations of true protein, solids-not-fat and lactose did not differ between treatments. Feeding YC did not influence plasma metabolites, insulin, or body condition score of cows, but urea N concentrations were reduced. Feeding a yeast culture of S. cerevisiae improved yields of milk and milk components in heat-stressed multiparous Holstein cows.     

Effects of feeding supplemental palmitic acid (C16:0) on performance and milk fatty acid profile of lactating dairy cows under summer heat

The objective was to determine performance and milk fatty acid changes of high producing dairy cows in early lactation, under summer heat, by adding a supplemental rumen inert fat in the form of a saturated free fatty acid (856 g/kg C16:0/kg of total fatty acids) to the total mixed ration (TMR). Early lactation multiparous Holstein cows in two similar pens of 99 and 115 cows were used in a 2 × 2 Latin Square design experiment with 35 d periods during a period when daily high and low temperatures averaged 34.3 and 15.9 °C, the relative humidity averaged 51% and there were no rain events. The TMR was the same for both groups, consisting of approximately 435 g/kg forage and 565 g/kg concentrate, except that the vitamin/mineral premix had no added fat (control, C) or added fat (C16:0) at a level designed to deliver approximately 450 g/cow/d of supplemental fat if cows consumed 26.5 kg/d of dry matter (DM). The two TMR averaged 905 g/kg organic matter (OM), 318 g/kg neutral detergent fiber (aNDF), and 186 g/kg crude protein (CP). The ‘C’ TMR had 58 g/kg total fatty acids with an estimated net energy for lactation (NE_l) of 7.3 MJ/kg (DM), while the C16:0 TMR had 72 g/kg total fatty acids and 7.5 MJ/kg NE_l (DM). Whole tract digestibility of DM, OM, aNDF and CP tended (P<0.10) to increase, and that of fatty acids increased substantially (P<0.01), with C16:0 feeding, whereas, DM intake was not affected. Milk fat content decreased (P<0.01) with C16:0 feeding (37.5 versus 36.0 g/kg), whereas, true protein content tended (P=0.09) to increase. There was a tendency (P=0.07) for increased milk yield (36.69 versus 38.04 kg/d), while milk protein yield increased (P=0.03) with C16:0 supplementation (1.08 versus 1.13 kg/d). Milk fat yield was unaffected by treatment. Concentrations of short and medium chain milk fatty acids (C6:0–C15:0), decreased, or tended to decrease, with C16:0 addition (C13:0 and C15:0, P<0.10; all others, P≤0.05). The concentration of C16:0 increased (P<0.001) in milk triglycerides from cows fed C16:0 (27.10 versus 31.57 g/kg), the longer chain saturated fatty acids C17:0 and C18:0 decreased (P≤0.05) and other long chain unsaturated fatty acids were unaffected. Benefits of C16:0 feeding on cow productivity must be balanced against negative effects on the nutritive value of the milk (i.e., increased C16:0 in milk fatty acids) produced for human consumption. However, relatively low amounts of supplemental C16:0 (27.10 versus 31.57 g/kg in milk triglycerides for C and C16:0 supplemented cows, respectively) were actually secreted in milk, in spite of them being essentially fully digested in the digestive tract. Strategies to divide cows into production groups based on milk yield and/or milk fat proportions could further limit C16:0 secretion in milk. Supplemental dietary C16:0 may have positive effects on milk production that outweigh the negative health effects of the increased C16:0 content in the milk fat.     

Effect of presynchronization strategy before Ovsynch on fertility at first service in lactating dairy cows

The aim of this study was to evaluate the effect of presynchronization with or without the detection of estrus on first service pregnancy per artificial insemination (P/AI) and on Ovsynch outcome in lactating dairy cows. A total of 511 cows were divided randomly but unevenly into 3 treatment groups at 44 to 50 days in milk (DIM). Ovsynch was started at the same time (69 to 75 DIM) in all three groups. Cows in the Ovsynch group (CON, N = 126) received no presynchronization before Ovsynch, and all cows were bred by timed AI (TAI). Cows in the presynchronization with estrus detection (PED) and the presynchronization with only TAI (PTAI) groups received two doses of prostaglandin F_2α (PGF) 14 days apart, starting at 44 to 50 DIM. Ovsynch was initiated 11 days after the second PGF treatment. Cows in the PED group (N = 267) received AI if estrus was detected after either PGF injection. Cows that were not determined to be in estrus after PGF injection received Ovsynch and TAI. Cows in the PTAI group (N = 118) were not inseminated to estrus, with all cows receiving TAI after Ovsynch. The ovulatory response to the first GnRH injection administered as part of Ovsynch differed (P = 0.002) among treatment groups (83.1% in PTAI, 72.6% in PED, and 62.7% in CON). However, the ovulatory response to the second injection of GnRH during Ovsynch did not differ among treatment groups. Of the 267 PED cows, a total of 132 (49.4%) exhibited estrus and were inseminated. The P/AI at the 31-day pregnancy diagnosis was similar between the cows in the PED group with AI after estrus detection (37.9%; 50/132) and those bred with TAI (34.1%; 46/135). The P/AI in the CON group (46.8%; 59/126) was greater (P < 0.05) than that in the PED group (36.0%; 96/267). In addition, the P/AI in the CON group was greater (P = 0.04) than that in the PED cows receiving TAI (34.1%; 46/135) but less than that in the PED cows bred to estrus (37.9%; 50/132) (P = 0.16). At the 31-day pregnancy diagnosis, the cows in the PTAI group had greater P/AI (55.9%; 66/118) than both those in the PED group (P < 0.01; either estrus or TAI) and those in the CON group (P = 0.08). Thus, presynchronization with PGF (PTAI) increased the ovulatory response to Ovsynch and improved P/AI in dairy cows. Interestingly, the breeding of cows to estrus during presynchronization reduced fertility to the TAI and overall fertility, including cows bred to estrus and TAI. These results indicate that maximal fertility is obtained when all cows receive TAI after the presynchronization protocol.     

Effects of equine chorionic gonadotropin and type of ovulatory stimulus in a timed-AI protocol on reproductive responses in dairy cows

The objectives were to evaluate the effects of equine chorionic gonadotropin (eCG) supplementation (with or without eCG) and type of ovulatory stimulus (GnRH or ECP) on ovarian follicular dynamics, luteal function, and pregnancies per AI (P/AI) in Holstein cows receiving timed artificial insemination (TAI). On Day 0, 742 cows in a total of 782 breedings, received 2 mg of estradiol benzoate (EB) and one intravaginal progesterone (P4) insert (CIDR). On Day 8, the CIDR was removed, and all cows were given PGF2α and assigned to one of four treatments in a 2 × 2 factorial arrangement: (1) CG: GnRH 48 h later; (2) CE: ECP; (3) EG: eCG + GnRH 48 h later; (4) EE: eCG + ECP. There were significant interactions for eCG × ovulatory stimulus and eCG × BCS. Cows in the CG group were less likely (28.9% vs. 33.8%; P < 0.05) to become pregnant compared with those in the EG group (odds ratio [OR] = 0.28). There were no differences in P/AI between CE and EE cows (30.9% vs. 29.1%; OR = 0.85; P = 0.56), respectively. Thinner cows not receiving eCG had lower P/AI than thinner cows receiving eCG (15.2% vs. 38.0%; OR = 0.20; P < 0.01). Treatment with eCG tended to increase serum progestesterone concentrations during the diestrus following synchronized ovulation (P < 0.10). However, the treatment used to induce ovulation did not affect CL volume or serum progesterone concentrations. In conclusion, both ECP and GnRH yielded comparable P/AI. However, eCG treatment at CIDR removal increased pregnancy rate in cows induced to ovulate with GnRH and in cows with lower BCS.     

Effects of rumen-protected choline supplementation on milk production and choline supply of periparturient dairy cows

The objective of the present study was to determine the effects of rumen-protected choline (RPC) supplementation on body condition, milk production and milk choline content during the periparturient period. Thirty-two Holstein cows were allocated into two groups (RPC group - with RPC supplementation, and control group - without RPC supplementation) 28 days before the expected calving. Cows were fed the experimental diet from 21 days before expected calving until 60 days of lactation. The daily diet of the RPC group contained 100 g of RPC from 21 days before calving until calving and 200 g RPC after calving for 60 days of lactation, which provided 25 g and 50 g per day choline, respectively. Body condition was scored on days -21, 7, 35 and 60 relative to calving. Milk production was measured at every milking; milk fat, protein and choline content were determined on days 7, 35 and 60 of lactation. Body condition was not affected by RPC supplementation. Milk yield was 4.4 kg higher for the group of cows receiving supplementary choline during the 60 days experimental period and 4% fat-corrected milk production was also increased by 2.5 kg/day. Milk fat content was not altered by treatment, but fat yield was increased by 0.10 kg/day as a consequence of higher milk yield in the RPC-treated group. Milk protein content tended to increase by RPC supplementation and a 0.18 kg/day significant improvement of protein yield was detected. Milk choline content increased in both groups after calving as the lactating period advanced. However, milk choline content and choline yield were significantly higher in the RPC group than in the control group. The improved milk choline and choline yield provide evidence that some of the applied RPC escaped ruminal degradation, was absorbed from the small intestine and improved the choline supply of the cows and contributed to the changes of production variables.     

Effects of Bacillus subtilis natto on milk production,rumen fermentation and ruminal microbiome of dairy cows

Two experiments were conducted to evaluate the effects of Bacillus subtilis natto, which was initially isolated from fermented soybeans on milk production, rumen fermentation and ruminal microbiome in dairy cows. In Experiment 1, 36 early lactation Chinese Holstein dairy cows (56 ± 23 days in milk) were randomly assigned to three groups: Control, cows were fed total mixed ration (TMR); BSNLOW, TMR plus 0.5 × 10¹¹ colony-forming units (cfu) of B. subtilis natto/cow per day; and BSNHIGH, TMR plus 1.0 × 10¹¹ cfu of B. subtilis natto/cow per day. During the 70-day treatment period, daily milk production and daily milk composition were determined in individual cows. The results showed that supplementing dairy cows with 0.5 × 10¹¹ and 1.0 × 10¹¹ cfu of B. subtilis natto linearly increased (P < 0.01) milk production (25.2 and 26.4 kg/day v. 23.0 kg/day), 4% fat-corrected milk (27.3 and 28.1 kg/day v. 24.2 kg/day), energy-corrected milk (27.3 and 28.2 kg/day v. 24.2 kg/day), as well as milk fat (1.01 and 1.03 kg/day v. 0.88 kg/day), protein (0.77 and 0.82 kg/day v. 0.69 kg/day) and lactose yield (1.16 and 1.22 kg/day v. 1.06 kg/day) but decreased milk somatic cell counts (SCC) by 3.4% to 5.5% (P < 0.01) in BSNLOW and BSNHIGH treatments compared with Control. In Experiment 2, four rumen-cannulated dairy cows were fed the basal diet from 1 to 7 days (pre-trial period) and rumen samples were collected on days 6 and 7; the same cows then were fed 1.0 × 10¹¹ cfu/day B. subtilis natto from days 8 to 21 (trial period) and rumen samples were collected on days 20 and 21. B. subtilis natto was discontinued from days 22 to 28 (post-trial period) and rumen samples were collected on days 27 and 28. Compared with the pre- and post-periods, ruminal pH decreased by 2.7% to 3.0% during the trial period (P < 0.01), whereas ammonia nitrogen (NH₃-N), total volatile fatty acids and molar proportion of propionate (P < 0.01) and valerate (P < 0.05) increased. Molar proportion of acetate decreased and the acetate to propionate ratio was lower (P < 0.01) during the trial period. However, no differences for 24-h in sacco dry matter digestibility were detected among different periods (treatments) though NDF digestibility was reduced in the trial and post-trial periods (P < 0.01). Compared with pre-trial period, total ruminal bacteria, proteolytic and amylolytic bacteria in rumen enumerated by culture methods increased by 15.0%, 16.2% and 11.7%, respectively (P < 0.01) but protozoa decreased to 5.35 log₁₀ cfu/ml (P < 0.01) during the trial period. These results demonstrate that B. subtilis natto improves milk production and milk components yield, decreases SCC and promotes the growth of total ruminal bacteria, proteolytic and amylolytic bacteria, which indicate that B. subtilis natto has potential to be applied as a probiotic for dairy cows.     

Effects of a ruminally protected B-vitamin supplement on milk yield and composition of lactating dairy cows

It is not clear if B vitamins supplied to the small intestine of dairy cows from dietary and rumen microbial sources are provided in sufficient quantity to maximize animal performance. Our objective was to determine effects of adding a ruminally protected B vitamin blend supplement, containing biotin, folic acid, pantothenic acid and pyridoxine, to the diet of high producing dairy cows on their productivity. Two dairy facilities located in California (USA) were used, one with mid lactation Holstein cows (Experiment 1) and the other with early lactation Holstein cows (Experiment 2). In each Experiment, cows were randomly assigned to treatment in a 2 × 2 crossover design with 28 d (Experiment 1) or 35 d (Experiment 2) experimental periods. In Experiment 1, milk and milk fat yield were unaffected by treatment, although milk fat proportion was lower (37.1 versus 36.3 g/kg; P<0.01), but milk protein yield was higher (1.21 versus 1.24 kg/d; P=0.02) in cows fed B vitamins. In Experiment 2, milk (39.60 versus 40.46 kg/d; P=0.02), milk fat (1.40 versus 1.47 kg/d; P<0.01) and milk protein yield (1.10 versus 1.16 kg/d; P<0.01), as well as milk energy output (113.2 versus 117.8 MJ/d; P<0.01) were all higher with B vitamin feeding. Body condition score (BCS) increased more with B vitamin feeding in Experiment 2, but was unaffected in Experiment 1. Body locomotion score (BLS) increased with B vitamin feeding in both experiments (P=0.01 and < 0.01, respectively), possibly an indication of reduced locomotory ability. Overall, productivity of high producing lactating dairy cows responded positively to feeding a mixture of ruminally protected B vitamins, although differences in the extent of the positive responses between experiments perhaps suggests that early lactation cows, with lower DM intake to milk yield ratios, may be more responsive to ruminally protected B vitamins than mid lactation cows, with higher DM intake to milk yield ratios.