Effects of calcareous marine algae on milk production, feed intake, energy balance, mineral status, and inflammatory markers in transition dairy cows.

The objective of this experiment was to compare the effects of calcareous marine algae (CMA; Acid Buf, Celtic Sea Minerals) with a limestone-based control on feed intake, milk production, energy balance, serum mineral metabolites, and inflammatory markers in transition dairy cows. Twenty-two multiparous and 10 primiparous cows were assigned to 2 treatments from 25 d before expected parturition until 42 d postpartum. Cows were assigned to treatment according to a randomized complete block design based on parity, pre-experimental body condition score, previous 305-d milk yield, and either fat + protein yield (for multiparous cows) or predicted transmitting ability for milk yield and fat + protein yield (for primiparous cows). Cows were fed a negative dietary cation-anion difference [-50 mEq/kg] total mixed ration (TMR) based on corn silage, grass silage, and straw during the prepartum period and a 50:50 forage:concentrate TMR based on grass silage, corn silage, and concentrate during the postpartum period. The 2 dietary treatments consisted of a control (CON), which contained limestone as the primary calcium source, and CMA, in which limestone was replaced by CMA at 0.42% and 0.47% of dry matter for the pre- and postpartum periods, respectively. The dietary treatments were fed as 2 different concentrate pellets added to the TMR. Cows fed the CMA diet had higher dry matter intake in both the prepartum (+1.08 kg) and postpartum (+0.94 kg) periods compared with cows fed the CON diet. Fat yield (+0.11 kg), fat concentration (+0.43%), and 4% fat-corrected milk (+1.56 kg) were higher in cows fed CMA than in cows fed CON. The concentration of plasma serum amyloid A was reduced and that of serum P was increased on the CMA treatment compared with the CON treatment. These findings demonstrate the benefits of supplementing CMA to dairy cows during the transition period compared with a CON treatment containing limestone as the primary Ca source.

Invited review: Effect of subacute ruminal acidosis on gut health of dairy cows.

Subacute ruminal acidosis (SARA) is assumed to be a common disease in high-yielding dairy cows. Despite this, the epidemiological evidence is limited by the lack of survey data. The prevalence of SARA has mainly been determined by measuring the pH of ruminal fluid collected using rumenocentesis. This may not be sufficiently accurate, because the symptoms of SARA are not solely due to ruminal pH depression, and ruminal pH varies among sites in the rumen, throughout a 24-h period, and among days. The impact of SARA has mainly been studied by conducting SARA challenges in cows, sheep, and goats based on a combination of feed restriction and high-grain feeding. The methodologies of these challenges vary considerably among studies. Variations include differences in the duration and amount of grain feeding, type of grain, amount and duration of feed restriction, number of experimental cows, and sensitivity of cows to SARA challenges. Grain-based SARA challenges affect gut health. These effects include depressing the pH in, and increasing the toxin content of, digesta. They also include altering the taxonomic composition of microbiota, reducing the functionality of the epithelia throughout the gastrointestinal tract (GIT), and a moderate inflammatory response. The effects on the epithelia include a reduction in its barrier function. Effects on microbiota include reductions in their richness and diversity, which may reduce their functionality and reflect dysbiosis. Changes in the taxonomic composition of gut microbiota throughout the GIT are evident at the phylum level, but less evident and more variable at the genus level. Effects at the phylum level include an increase in the Firmicutes to Bacteroidetes ratio. More studies on the effects of a SARA challenge on the functionality of gut microbiota are needed. The inflammatory response resulting from grain-based SARA challenges is innate and moderate and mainly consists of an acute phase response. This response is likely a combination of systemic inflammation and inflammation of the epithelia of the GIT. The systemic inflammation is assumed to be caused by translocation of immunogenic compounds, including bacterial endotoxins and bioamines, through the epithelia into the interior circulation. This translocation is increased by the increase in concentrations of toxins in digesta and a reduction of the barrier function of epithelia. Severe SARA can cause rumenitis, but moderate SARA may activate an immune response in the epithelia of the GIT. Cows grazing highly fermentable pastures with high sugar contents can also have a low ruminal pH indicative of SARA. This is not accompanied by an inflammatory response but may affect milk production and gut microbiota. Grain-based SARA affects several aspects of gut health, but SARA resulting from grazing high-digestible pastures and insufficient coarse fiber less so. We need to determine which method for inducing SARA is the most representative of on-farm conditions.

Effect of supplement crude protein concentration on milk production over the main grazing season and on nitrogen excretion in late-lactation grazing dairy cows.

The objectives of this study are to evaluate the effects of (1) a potential interaction between supplement crude protein (CP) concentration and differing cow genotypes on milk production, (2) differing cow genotypes on milk production, and (3) decreasing the supplement CP concentration on milk production and N excretion during the main grazing season within a spring-calving herd. A 2 × 2 factorial arrangement experiment, with 2 feeding strategies [14%; n = 30 (lower CP; LCP) and 18%; n = 28 (higher CP; HCP) CP concentrate supplements] offered at varying levels according to pasture availability and days in milk (DIM) was conducted over the main grazing season from April 3 to September 3, 2019, at University College Dublin Lyons Farm. Cows were also grouped into 2 genotype groups: lower milk genotype; n = 30 [LM; milk kg predicted transmitting ability (PTA): 45 ± 68.6 (mean ± SD); fat kg PTA: 10 ± 4.9; and protein kg PTA: 7 ± 2.3] and higher milk genotype; n = 28 [HM; milk kg PTA: 203 ± 55.0; fat kg PTA: 13 ± 3.8; and protein kg PTA: 10 ± 2.4]. A total of 46 multiparous and 12 primiparous (total; 58) Holstein Friesian dairy cows were blocked on parity and balanced on DIM, body condition score, and Economic Breeding Index. Cows were offered a basal diet of grazed perennial ryegrass pasture. The N partitioning study took place from August 25 to 30, 2019 (187 ± 15.2 DIM). No interactions were observed for any milk production or milk composition parameter. No effect of supplement CP concentration was observed for any total accumulated milk production, daily milk production, or milk composition parameter measured. The HM cows had increased daily milk yield (+1.9 kg), fat and protein (+0.15 kg), and energy-corrected milk (+1.7 kg), compared with the LM cows. Furthermore, HM cows had decreased milk protein concentration (-0.1%) compared with LM cows. For the N partitioning study, cows offered LCP had increased pasture dry matter intake (PDMI; +0.9 kg/d), dietary N intake (+0.022 kg/d), feces N excretion (+0.016 kg/d), and decreased N partitioning to milk (-2%), and N utilization efficiency (-2.3%). In conclusion, offering cows LCP had no negative influence on milk production or milk composition over the main grazing season where high pasture quality was maintained. However, any potential negative effects of offering LCP on milk production may have been offset by the increased PDMI. Furthermore, offering cows LCP decreased N utilization efficiency due to the higher PDMI and feed N intake associated with cows on this treatment in our study.

Effects of herd fertility on the economics of sexed semen in a high-producing, pasture-based dairy production system.

This study used a stochastic simulation model to estimate the potential economic benefit of using sexed semen in heifers only and in heifers and lactating cows in a high-producing, pasture-based system under 3 fertility scenarios. Three breeding strategies were modeled: (1) only heifers inseminated with sexed semen and cows inseminated with conventional unsexed semen (SSH); (2) both heifers and cows inseminated with sexed semen (SSHC); and (3) a reference scenario in which all females were inseminated with conventional, unsexed semen (CONV). Each scenario was evaluated under 3 herd fertility states: high (HF), medium (MF), and low (LF), which, under the reference scenario, corresponded to herd replacement rates of 21, 25, and 31%, respectively. The model estimated the economic profit, including the net present value of the genetic gain from selection intensity. The economic return from adoption of sexed semen strategies declined, with reduced levels of baseline herd fertility turning negative in the LF state. The mean (±SD) sexed semen advantage (SSA) per cow for HF-SSH, MF-SSH, and LF-SSH scenarios were €30.61 ± 8.98, €27.45 ± 7.19, and €14.69 ± 11.06, respectively. However, the SSA per cow for HF-SSHC, MF-SSHC, and LF-SSHC scenarios were €49.14 ± 15.43, €18.46 ± 30.08, and -€19.30 ± 57.11. The range in economic profit for SSA for SSH was most sensitive to calf prices in HF-SSH and the pregnancy rate of sexed semen as a percentage of conventional unsorted semen in MF-SSH and LF-SSH. The range in economic profit for SSA for SSHC scenarios was most sensitive to the pregnancy rate of sexed semen as a percentage of conventional unsorted semen in HF-SSHC, MF-SSHC, and LF-SSHC. This study highlights the effect of baseline herd fertility state on the financial advantage of adopting sexed semen in a pasture-based dairy production system.

A survey analysis of farmer practices and perceptions of zero-grazing on Irish dairy farms.

Zero-grazing (ZG; the mechanical harvesting and feeding of fresh grass) is increasingly used in grass-based milk production systems alongside conventional grazing. It allows farmers to supply fresh grass from land parcels that are outside of the main grazing block during seasonal shortages and periods when climatic conditions limit animal grazing opportunities. The objective of this study was to establish an understanding of current ZG practices on Irish dairy farms, to capture farmer perceptions on the implementation of this management practice, and to identify farmer knowledge requirements on ZG. An online survey was distributed and completed by 130 dairy farmers who use or have used ZG. Zero-grazing was used alongside conventional grazing by 92% of respondents. These farms were particularly fragmented, with between 1 and 14 separate land blocks. Respondents felt ZG helped them overcome fragmentation, increase grass use, and extend grass feeding in spring and autumn. However, extra cost and time input associated with ZG were recognized as key challenges. The majority of respondents rated current technical information available on ZG in the Republic of Ireland as "poor" or "very poor," and knowledge deficits were identified in the areas of cost analysis, grass management and productivity, cow productivity, cow health and nutrition, and soil fertility.

The effect of nutritional management in early lactation and dairy cow genotype on milk production, metabolic status, and uterine recovery in a pasture-based system.

High levels of milk production coupled with low feed intake cause negative energy balance in early lactation, especially in the first month postpartum (PP). Therefore, specific nutritional management at this time may improve nutritional and metabolic status with the possibility of contrasting genotypes responding differently. Thus, the objective of this study was to compare the effects of nutritional management strategies and dairy cow genotype on milk production, metabolic status, and some fertility parameters during early lactation in a pasture-based system. Sixty Holstein Friesian cows were blocked on parity and genotype [low-fertility high-milk (LFHM) and high-fertility low-milk (HFLM)] and were randomly assigned to 1 of 2 treatments in a 2 × 2 factorial arrangement, in a randomized complete block design based on calving date, previous 305-d milk yield, and precalving body condition score (BCS). The nutritional management treatments were: (1) ad libitum access to fresh pasture plus an allowance of 3 kg of concentrates per day (CTR, n = 30); and (2) ab libitum access to a tailored total mixed ration (TMR, n = 30). These diets were offered for the first 30 d PP. Following the first 30 d PP, cows fed TMR joined the CTR treatment and were managed similarly until 100 d PP. Blood samples were taken at d 7, 14, 21, and 28 PP to determine metabolic status. Milk samples for composition analysis were collected weekly and BCS assessed every 2 wk. Genotype had a significant effect on milk output, whereas LFHM had increased fat (+0.28 kg/d) and fat-plus-protein (+0.17 kg/d) yield in the first 30 d PP compared with HFLM cows. The LFHM group also exhibited higher protein and lactose yields over the first 100 d PP. Nutritional management did create significant differences in milk composition in the first 30 d: TMR cows had lower protein, milk urea nitrogen, and casein concentration and higher lactose concentration than CTR cows. Over the first 100 d PP, TMR cows had higher fat-plus-protein and lactose yields. Feeding TMR reduced concentrations of nonesterified fatty acids (-0.12 mmol/L) and ß-hydroxybutyric acid (-0.10 mmol/L) compared with the CTR group. Cows fed TMR had smaller BCS losses from calving to 60 d PP. There was no effect of any treatment on uterine recovery. Cows in the LFHM group demonstrated greater milk production in the first 30 and 100 d in milk. These results demonstrate that feeding cows a TMR for the first month of lactation has positive effects on milk output, metabolic status, and BCS profile.

Effects of a novel heat-treated protein and carbohydrate supplement on feed consumption, milk production, and cheese yield in early-lactation dairy cows.

Protein is an expensive component of the dairy cow diet, and overfeeding protein can have adverse economic and environmental impacts. Our objective was to maintain milk production and components while decreasing dietary crude protein (CP) through use of a heat-treated, rumen-resistant sugar amino acid complex (SAAC) as the Schiff base, as an addition to low-protein diets. Dietary treatments included a negative control [NC, 146 g of CP/kg of dry matter (DM)], a positive control (PC, 163 g of CP/kg of DM), and the NC supplemented with SAAC in lieu of some barley grain (SAAD, 151 g of CP/kg of DM). Diets were fed to 30 multiparous Holstein-Friesian dairy cows for the first 50 d postpartum. Dry matter intake (DMI) was determined daily. Milk yield and content of fat, protein, lactose, and casein were recorded weekly from wk 2 to 7 of lactation. The fixed effects of treatment, week, treatment × week, month of calving, and BCS at calving, and a random effect of cow, were analyzed using the MIXED procedure of SAS (SAS Institute Inc., Cary, NC). The SAAD treatment had greater energy-corrected milk yield than did NC. The PC treatment had greater DMI than did NC, and SAAD tended to have greater DMI than did NC. We found significant treatment effects for fat percentage and yield. The NC and SAAD treatments had higher fat percentages than did PC, and SAAD had a higher fat yield than did the NC and PC treatments. Treatment effects were found for casein yield and percentage. We discovered a treatment effect for protein percentage and yield. The PC treatment had higher protein percentage than did NC and SAAD. The PC treatment had a higher protein yield than did NC, and analysis revealed no difference in protein yield between PC and SAAD. The SAAD treatment had higher total milk solids than did the NC treatment. Lactose yield tended to be higher in PC than in NC, and no differences were found between PC and NC and SAAD treatments. The PC treatment had a higher casein percentage than did NC and SAAD; however, the SAAD and PC treatments had higher casein yields than did NC. The PC treatment had a higher casein:fat ratio than did the NC and SAAD treatments. The NC and SAAD treatments had higher Cheddar cheese yields than did PC. We found no treatment × week interactions for any parameter. Supplementing low-protein dairy cow diets with a heat-treated, rumen-resistant SAAC caused beneficial effects by improving milk components and increasing cheese yield to levels similar to those found when feeding expensive and environmentally damaging high-protein diets.

Herb species inclusion in grazing swards for dairy cows-A systematic review and meta-analysis.

A systematic review and meta-analysis were conducted to estimate the effect of herb species on milk production and urinary nitrogen (UN) excretion from grazing dairy cows. Grazing swards consisting of herb species grown with either a grass species or a grass and legume (multispecies swards) were compared with non-herb-containing swards consisting of a grass species grown as a monoculture or grass-legume swards (simple swards). A literature search was completed using the online databases CAB Direct, Web of Science, and Google Scholar, using the search strategy "dairy cow", "herb OR forb OR phorb", and "grazing". Milk production data, variance, and sample size were required for eligibility. In all, 116 studies were identified. Following eligibility screening, 11 papers from 6 journals, published between 2006 and 2018, were available for analysis. Studies were from New Zealand (N = 7), Australia (N = 3), and the United States (N = 1). The population was either Holstein Friesian or Holstein Friesian × Jersey dairy cows, with a range in mean daily milk yield (MY) from 12.1 kg to 34.7 kg (mean = 18.6 kg). A total of 25 comparisons were used for milk production analysis, with 324 and 284 cows included in multispecies and simple sward groups respectively. Data analysis was conducted in R using a random effects, robust variance estimation model (R Foundation for Statistical Computing, Vienna, Austria). Heterogeneity was reported using the I2 statistic. Milk production was significantly increased. Analysis of MY resulted in a weighted mean difference (WMD) of +1.20 kg/d (95% CI = 0.90, 1.49; I2 = 4%). Fat and protein kg were also significantly increased (WMD +0.06 kg/d; CI = 0.01, 0.11). Urinary nitrogen excretion was estimated from milk urea nitrogen when reported (n = 6). A WMD of -28.1 g of N/d (95% CI = -81.1, 24.9) was generated, with heterogeneity high among studies (I2 = 75%). This meta-analysis shows the potential benefits of multispecies swards. Although we saw no significant difference in UN excretion, an increase in milk production was found.

The effect of concentrate supplementation type on milk production, dry matter intake, rumen fermentation, and nitrogen excretion in late-lactation, spring-calving grazing dairy cows.

In Ireland, milk is primarily produced using a spring-calving grass-based system, with the use of concentrate supplementation mainly when pasture availability and quality are reduced. In the autumn, when cows are in late lactation, reduced pasture productivity results in reduced milk yield and altered milk composition. Nitrogen utilization efficiency also reduces as lactation progresses. Concentrate supplementation has been found to increase milk production and reduce nitrogen (N) excretion, as high-N grass is usually replaced by a lower-N supplement; however, there is a paucity of information with regard to the optimum type of supplementation in late lactation. Therefore, the objective of this research is to investigate the effect of different concentrate supplementation types, based on barley or maize, on milk production, dry matter intake (DMI), rumen fermentation, and N excretion in late-lactation, spring-calving, grazing dairy cows. Thirty-six Holstein Friesian dairy cows were blocked on days in milk (185 DIM) and balanced for parity, pre-experimental milk yield, milk composition, and body condition score. Cows were randomly assigned to 1 of 3 dietary treatments in a randomized complete block design (n = 12). The 3 treatments consisted of a perennial ryegrass-based pasture-only (PO) treatment and pasture plus either of 2 supplementary concentrates, based on barley (PB) or maize (PM). The diets were fed for a 14-d acclimatization period and then for a further 63-d experimental period. Cows offered PO had a lower daily milk yield (15.1 kg) than PB (18.2 kg) or PM (16.8 kg). Similarly, PO had lower daily milk solids yield (1.46 kg) than PB or PM (1.68 and 1.53 kg, respectively). Cows offered PB had a greater milk yield and higher fat and protein yields than those offered PM. Offering PB increased total DMI (19.5 kg) compared with PO (17.7 kg), and milk response to concentrates was also greater for PB compared with PM (1.21 vs. 0.71 kg of milk per kg of concentrate). Cows offered PB had increased N in milk compared with PO. In conclusion, concentrate supplementation based on barley or maize resulted in increased milk and milk solids yield compared with offering PO. Cows offered barley had a greater response to concentrates and increased milk and milk solids yield in comparison to maize and showed increased N partitioning in milk compared with PO. A barley-based concentrate increased total DMI compared with PO.

The effects of cereal type and α-tocopherol level on milk production, milk composition, rumen fermentation, and nitrogen excretion of spring-calving dairy cows in late lactation.

Grass-based production systems use concentrate supplementation primarily when pasture quality and availability have declined. Barley is a common concentrate ingredient; however, oat grain grows well in Ireland, is a source of lipids and fiber, and may provide an alternative to barley. The antioxidant α-tocopherol (α-TOC) plays a role in cell membrane structure, and it has the potential to improve tight junction structures of the mammary gland that deteriorate in late lactation. The objective of this research was to investigate the effect of cereal type and α-TOC level on milk yield, milk composition, rumen fermentation, and N excretion in late-lactation dairy cows at pasture and when housed indoors on grass silage. Forty-eight Holstein Friesian dairy cows were blocked on days in milk (+185 d in milk) and balanced for parity, pre-experimental milk yield, milk composition, and body condition score and assigned to 1 of 4 dietary treatments in a randomized complete block design (n = 12). The dietary treatments were control (C) base diet; base diet + barley-based concentrate + low α-TOC (350 IU/kg) (B); base diet + oat-based concentrate + low α-TOC (350 IU/kg) (O); and base diet + oat-based concentrate + high α-TOC (1,050 IU/kg) (O+T). Following a 14-d acclimation period, diets were offered for a 49-d experimental period at pasture (P1) and a 21-d experimental period indoors (P2). The base diet was grazed grass in P1 and grass silage in P2. In P2, cows on C also received 2.65 kg (dry matter) of a standard concentrate. In P1, supplementation increased milk and milk solids yield (B: 20.7 kg/d, 1.74 kg/d; O: 20.6 kg/d, 1.81 kg/d; O+T: 20.5 kg/d, 1.77 kg/d, respectively) compared with C (17.8 kg/d, 1.60 kg/d). Cows offered B had a lower milk fat (4.60%) concentration than C (5.00%) and O (4.90%). In P2, cereal type and α-TOC level did not alter milk production. In conclusion, concentrate supplementation increased milk and milk solids yield and cows offered O had a higher milk fat concentration than cows offered B. Increasing the level of α-TOC had no major effect on production parameters measured in P1 or in P2.

The effect of calcareous marine algae, with or without marine magnesium oxide, and sodium bicarbonate on rumen pH and milk production in mid-lactation dairy cows.

Two experiments were carried out to evaluate different dietary buffers and their influence on (1) rumen pH in dairy cows and (2) milk production in dairy cows. The supplements included were calcareous marine algae (CMA; Lithothamnion calcareum), with or without marine magnesium oxide (MM; precipitated magnesia derived from seawater), and sodium bicarbonate (SB). Dietary treatments in experiment 1 consisted of the control [32.9% starch and sugar, and 19.9% neutral detergent fiber from forage per kg of dry matter (DM)] including no dietary buffer (CON); the control plus 0.45% DM CMA (CMA); the control plus 0.45% DM CMA and 0.11% DM MM (CMA+MM); the control plus 0.9% DM SB (SB). Diets were formulated to a dry matter intake (DMI) of 18 kg per cow/d. Dietary treatments in experiment 2 also consisted of CON (28.3% starch and sugar, and 23% neutral detergent fiber from forage per kg of DM), CMA, CMA+MM, and SB and were formulated to achieve identical intakes of experimental ingredients (80 g of CMA, 80 g of CMA plus 20 g MM, and 160 g of SB per cow/d) with a DMI of 22.6 kg per cow/d. Experiment 1 used 4 rumen-cannulated dairy cows in a 4 × 4 Latin square design. Rumen pH was measured over five 2-h periods, following feeding, using rumen pH probes. In experiment 2, 52 multiparous and 4 primiparous cows (62.7 ± 3.4 d in milk) were assigned to 4 experimental treatments for 80 d. Both CMA treatments maintained a greater mean rumen pH than the CON during 4 of the 5 periods following feeding and the CON had a greater number of hours below rumen pH 5.5 compared with all other treatments. Dry matter intakes tended to be higher on the SB compared with CON. The CMA treatment increased the production of milk fat and protein yield (kg/d) compared with all other treatments. Both CMA and CMA+MM increased milk fat yield compared with CON but were similar to each other and SB. Protein yield was highest in the CMA treatment compared with CON, CMA+MM, and SB. All 3 buffer treatments increased milk fat concentration compared with CON but did not differ from each other. The SB treatment reduced milk protein concentration and milk production efficiency, energy-corrected milk per kilogram of DMI. Results indicate that the addition of CMA can benefit milk fat and protein production when included in diets based on typical feedstuffs of the northern European region. The use of CMA when compared with SB, in such diets, can increase milk protein production and milk production efficiency.

A comparison of serum metabolic and production profiles of dairy cows that maintained or lost body condition 15 days before calving.

Body condition score (BCS) change is an indirect measure of energy balance. Energy balance before calving may affect production and health in the following lactation. It is likely that cows may experience BCS loss before calving due to negative energy balance. The objective of this study was to determine if loss of BCS 15d before calving affected milk production, BCS profile, and metabolic status during the transition period and early lactation. On d -15 to d 0 relative to calving, BCS was assessed (1=emaciated, 5=obese) for 98 Holstein-Friesian cows. The cows were divided into 2groups: those that did not lose BCS between d -15 and d 0 (maintained, BCS-M, n=55) and those that lost BCS from d -15 to d 0 (lost, BCS-L, n=43, average loss of 0.29±0.11 BCS). The fixed effects of BCS group, parity, week (day when analyzing milk production records), their interactions, and a random effect of cow were analyzed using PROC MIXED of SAS (SAS Institute Inc., Cary, NC). Before calving, BCS-L cows tended to have higher concentrations of nonesterified fatty acids than BCS-M cows (0.88 vs. 0.78mmol/L). After calving, BCS-L cows had higher nonesterified fatty acid concentrations in wk 1 (0.93 vs. 0.71mmol/L), wk 2 (0.84 vs. 0.69mmol/L), and wk 4 (0.81 vs. 0.63mmol/L) than BCS-M cows. The BCS-L cows had higher concentrations of ß-hydroxybutyrate (BHB) in wk 1 (0.72 vs. 0.57mmol/L), wk 2 (0.97 vs. 0.70mmol/L), and wk 4 (0.94 vs. 0.67mmol/L) compared with BCS-M cows. We detected significant reductions in insulin concentrations in BCS-L cows from wk -1 (2.23 vs. 1.37 µIU/mL) to wk 2 (1.68 vs. 0.89 µIU/mL) and wk 4 (2.21 vs 1.59 µIU/mL) compared with BCS-M cows. Prevalence of subclinical ketosis increased in BCS-L cows in wk 3 and 4 when BHB was ≥1.4mmol/L and in wk 1, 3, and 4 when BHB was ≥1.2mmol/L. In wk 1, BCS-L cows tended to have lower levels of calcium than BCS-M cows (2.33 vs. 2.27mmol/L). We found no differences between the groups of cows for milk yield and energy-corrected milk. The BCS-L cows had lower BCS up to 75d in lactation. Overall, BCS-L cows had higher somatic cell scores with an elevated somatic cell score on d 45, d 60, and d 75. There was an overall tendency for BCS-L cows to have higher fat yield and an overall significant increase in fat percentage. Overall, BCS-L cows had lower lactose percentage, with a reduction on d 60. This work shows that BCS loss before calving may have significant consequences for metabolic status, milk composition, somatic cell score, and BCS profile in dairy cows.

Concentrate supplementation of a diet based on medium-quality grass silage for 4 weeks prepartum: Effects on cow performance, health, metabolic status, and immune function.

Because negative energy balance (EB) contributes to transition-period immune dysfunction in dairy cows, dietary management strategies should aim to minimize negative EB during this time. Prepartum diets that oversupply energy may exacerbate negative EB in early lactation, with detrimental effects on immune function. However, with lower body condition score (BCS) cows, it has been shown that offering concentrates in addition to a grass silage-based diet when confined during an 8-wk dry period resulted in increased neutrophil function in early lactation. The aim of this study was to examine if similar benefits occur when concentrate feeding was restricted to a 4-wk period prepartum. Twenty-six multiparous and 22 primiparous Holstein-Friesian cows were offered ad libitum access to medium-quality grass silage until 28 d before their predicted calving dates (actual mean of 32 d prepartum; standard deviation = 6.4). At this time multiparous cows had a mean BCS of 2.9 (standard deviation = 0.12) and primiparous cows a mean BCS of 3.0 (standard deviation = 0.14) on a 1 to 5 scale. Cows were then allocated in a balanced manner to 1 of 2 treatments (13 multiparous cows and 11 primiparous cows on each treatment): silage only (SO) or silage plus concentrates (S+C) until calving. Cows on SO were offered the same grass silage ad libitum. Cows on S+C were offered an ad libitum mixed ration of the same grass silage and additional concentrates in a 60:40 dry matter (DM) ratio, which provided a mean concentrate DM intake (DMI) of 4.5 kg/cow per d. After calving, all cows were offered a common mixed ration (grass silage and concentrates, 40:60 DM ratio) for 70 d postpartum. Offering concentrates in addition to grass silage during the 4 wk prepartum increased prepartum DMI (12.0 versus 10.1 kg/cow per d), EB (+40.0 versus +10.6 MJ/cow per d), and body weight (BW; 640 versus 628 kg), and tended to increase BCS (3.02 versus 2.97). However, postpartum DMI, milk yield, milk composition, BW change, BCS change, serum nonesterified fatty acid, and ß-hydroxybutryrate concentrations, health, and corpus luteum measures were unaffected by treatment. The in vitro assays of neutrophil phagocytosis, neutrophil oxidative burst, and interferon gamma production, conducted on blood samples obtained at d 14 prepartum and d 3, 7, 14, and 21 postpartum, were unaffected by treatment. Primiparous cows had higher phagocytic fluorescence intensity at d 14 prepartum and d 3 and 7 postpartum; a higher percentage of neutrophils undergoing oxidative burst at d 3, 7, and 21 postpartum; and a higher oxidative burst fluorescence intensity at d 14 prepartum and d 7, 14, and 21 postpartum compared with multiparous cows. This suggests that neutrophil function of primiparous cows was less sensitive to the changes occurring during the transition period than that of multiparous cows. In conclusion, offering concentrates during the 4-wk period prepartum had no effect on postpartum DMI, milk yield, body tissue mobilization, EB, measures of neutrophil or lymphocyte function, health, or corpus luteum activity.

Short communication: Effect of dietary manipulation of crude protein content and nonfibrous-to-fibrous-carbohydrate ratio on energy balance in early-lactation dairy cows.

Disparities between nutrient intake and demand often result in a state of negative energy balance (EB) in the early-lactation dairy cow. Reducing dietary crude protein (CP) content and providing glucogenic nutrients may overcome this issue. This study evaluates whether or not offering a diet lower in CP and higher in nonfiber carbohydrates (LP-NFC) can improve EB and the metabolic status of the early-lactation dairy cow compared with a diet higher in CP and fibrous carbohydrates (HP-FC). Twenty Holstein-Friesian dairy cows were assigned to 1 of 2 dietary treatments in a randomized block design. Diets were isoenergetic (6.57 MJ of net energy for lactation) and formulated to contain 15% CP and 6% starch (HP-FC), or 12% CP and 28% starch (LP-NFC) and were offered for the first 63 d of lactation. Intake and milk yield were determined daily, whereas milk and blood samples, weights, and body condition scores were collected weekly. Intakes (mean ± standard errors of the mean, SEM) of dry matter (17.4 ± 0.6 kg/d) and energy (113.0 ± 4.6 MJ of net energy for lactation) were not different between treatments. However, the HP-FC group had a higher milk yield (31.8 vs. 28.9 ± 1.4 kg/d) and a lower EB compared with the LP-NFC group. Blood urea N concentration (3.5 vs. 1.8 ± 0.2 mmol/L) was higher, whereas bilirubin (6.0 vs. 6.7 ± 0.2 mmol/L) and ß-hydroxybutyrate concentrations (0.7 vs. 0.8 ± 0.05 mmol/L) were lower in the HP-FC group compared with the LP-NFC group. These data suggest that EB can be improved during early lactation through the manipulation of milk output by offering a lower CP, higher NFC diet.

Effect of timing of post-partum introduction to pasture and supplementation with Saccharomyces cerevisiae on milk production, metabolic status, energy balance and some reproductive parameters in early lactation dairy cows.

Dietary change, an inconsistent nutrient intake and high levels of milk production make the early post-partum period (PP) a challenging time for the lactating dairy cow. This experiment investigates the effects of two early PP nutritional management strategies (NM): abrupt introduction to pasture (AP) or a total mixed ration (TMR) for 21 days followed by a gradual introduction to pasture over 7 days (GP), with (Y) or without (C) live yeast (YS) on milk production, energy balance (EB) and selected metabolic and reproductive variables. Forty multiparous dairy cows were assigned to one of four dietary treatments in a two (AP vs. GP) by two (Y vs. C) factorial, randomized block design. The experiment was conducted from days 1 to 70 PP. Blood samples were taken on day 1, day 5 and every 10 days until day 45 to determine metabolites, whilst intake (DMI), and EB were determined during week 6 PP. Milk was sampled weekly for fat, protein and lactose. Trans-rectal scanning for reproductive variables commenced on day 10 PP. Animals in the GP group had a higher DMI (p = 0.04), higher fat yield (p = 0.08) and fewer days to first ovulation (p = 0.09) vs. those in the AP group. EB (-3.5 ± 0.67 units of energy for milk production) and body condition score loss (0.70 ± 0.09) were not affected by NM. However, non-esterified fatty acids (NEFA) (p < 0.01) were higher, and glucose (p = 0.02) was lower in the AP vs. the GP group. Supplementary YS tended to improve EB (p = 0.09) and reduced NEFA (p < 0.01) vs. non-supplemented animals. These data suggest that offering animals a nutritionally balanced TMR during the first 3 weeks PP followed by a gradual introduction to pasture can improve DMI vs. pasture-based diets. Additionally, the blood metabolic profile suggests a more favourable energy status in the GP group or where YS was supplemented during the early PP period.

Comparison of milk and grass composition from grazing Irish dairy herds with and without milk fat depression.

BACKGROUND: This study investigated the factors relating to pasture chemical and fatty acid (FA) composition that influence the milk fat percentage of spring calving, grazing dairy cows. The relationship between milk fat percentage and FA composition of the milk in these herds was also investigated. RESULTS: Milk protein percentage, milk casein percentage and cheddar cheese yield were increased in milk from HMF herds. Cows from LMF herds did not have negatively altered milk processability including rennet coagulation time (RCT), pH and ethanol stability. Crude protein, NDF, ADF, ether extract and total FA content of pasture was not different between LMF and HMF herds. Milk fat concentration of conjugated linoleic acid (CLA) t10, c12 was not different between HMF and LMF herds. Pre-grazing herbage mass and pasture content of crude protein, neutral detergent fibre (NDF) and total FA were similar between HMF and LMF herds. Pasture offered to LMF herds had a higher concentration of monounsaturated fatty acids (MUFA). A strong negative relationship (r = -0.40) was evident between milk fat percentage and pasture crude protein content for MMF herds (3.31-3.94% milk fat). CONCLUSIONS: This research reports improved milk protein percentage, milk casein percentage and cheddar cheese yield from HMF herds compared to LMF herds. Milk processability was not impacted by low milk fat percentage. Pasture NDF and total fatty acid content was similar in HMF herds and LMF herds. Milk fat percentage had a strong negative association (r = -0.40) with pasture crude protein content in MMF herds (MF 3.31-3.94%). Correlation values between pasture chemical and FA composition and milk fat percentage in LMF herds and HMF herds were low, indicating that diet is not the only causative factor for variation in milk fat of grazing dairy cows. Comparison of milk fatty acid composition from herds with and without milk fat depression suggests that there may be other fatty acids apart from CLA t10, c12 that contribute to the inhibition of milk fat synthesis during milk fat depression in grazing herds.

Effect of the metabolic environment at key stages of follicle development in cattle: focus on steroid biosynthesis.

Cellular mechanisms that contribute to low estradiol concentrations produced by the preovulatory ovarian follicle in cattle with a compromised metabolic status are largely unknown. To gain insight into the main metabolic mechanisms affecting preovulatory follicle function, two different animal models were used. Experiment 1 compared Holstein-Friesian nonlactating heifers (n = 17) and lactating cows (n = 16) at three stages of preovulatory follicle development: 1) newly selected dominant follicle in the luteal phase (Selection), 2) follicular phase before the LH surge (Differentiation), and 3) preovulatory phase after the LH surge (Luteinization). Experiment 2 compared newly selected dominant follicles in the luteal phase in beef heifers fed a diet of 1.2 times maintenance (M, n = 8) or 0.4 M (n = 11). Lactating cows and 0.4 M beef heifers had higher concentrations of ß-hydroxybutyrate, and lower concentrations of glucose, insulin, and IGF-I compared with dairy heifers and 1.2 M beef heifers, respectively. In lactating cows this altered metabolic environment was associated with reduced dominant follicle estradiol and progesterone synthesis during Differentiation and Luteinization, respectively, and in 0.4 M beef heifers with reduced dominant follicle estradiol synthesis. Using a combination of RNA sequencing, Ingenuity Pathway Analysis, and qRT-PCR validation, we identified several important molecular markers involved in steroid biosynthesis, such as the expression of steroidogenic acute regulatory protein (STAR) within developing dominant follicles, to be downregulated by the catabolic state. Based on this, we propose that the adverse metabolic environment caused by lactation or nutritional restriction decreases preovulatory follicle function mainly by affecting cholesterol transport into the mitochondria to initiate steroidogenesis.

Effect of supplemental concentrate type on milk production and metabolic status in early-lactation dairy cows grazing perennial ryegrass-based pasture.

Forty-four early-lactation dairy cows of mixed parity were used to examine the effect of 4 supplemental concentrate types (n=11) on milk production and metabolic status. Animals were blocked by parity and calving date, and blocks were balanced for previous milk yield and milk protein yield. Cows received grazed pasture plus 5.17 kg of DM/d of 1 of the following isoenergetic (1.1 units of energy for lactation) concentrates: 1) high crude protein (CP) with rolled barley (HP, 19% CP); b) low CP with rolled barley (LP, 15% CP); c) low CP with barley and a supplemental methionine hydroxy analog (HMBi; LP + HMBi, 15% CP); and d) low CP with ground corn (LP-corn, 15% CP). Milk yield was recorded from d 1 to 100 postpartum, with weekly milk sampling, body weight, and body condition score (BCS) measurements. Blood and rumen sampling were conducted weekly from wk 2 to 6 postpartum. Milk yield was lower for cows in the LP treatment compared with those offered other concentrate types (25.2 vs. 27.5 ± 0.39 kg/d). Animals in the HP group had a higher milk yield than those in the LP + HMBi group (28.2 vs. 26.8 ± 0.39 kg/d). Milk fat yield was lower from animals in the LP-corn group compared with those in the LP + HMBi group (0.94 vs. 1.03 ± 0.03 kg/d). Milk protein yield was lower in the LP group compared with those in the HP group (0.88 vs. 0.97 ± 0.02 kg/d). Animal body weight, BCS, and BCS loss were not affected by concentrate type. However, nonesterified fatty acids were higher from animals in the HP group than for those in the LP + HMBi group (0.41 vs. 0.33 ± 0.03 mmol/L), and ß-hydroxy butyric acid was higher from animals in the HP group than for those in the other treatments (0.71 vs. 0.59 ± 0.03 mmol/L). Glucose was higher from animals in the LP-corn group than for those in the HP and LP groups (3.3 vs. 3.2 ± 0.05 mmol/L). Blood urea-N was higher from animals offered HP compared with those offered the other treatments (5.49.6 vs. 4.21 ± 0.44 mmol/L). However, rumen NH(3)-N and volatile fatty acid concentration in the rumen were not affected by supplemental concentrate type. Reducing supplemental concentrate CP reduced milk yield. However, milk fat production and energy-corrected milk were not different, reducing the likelihood of an improved energy balance or a more favorable blood metabolic profile in early-lactation dairy cows grazing perennial ryegrass. Offering HMBi with low-CP concentrates or replacing rolled barley with ground maize improves milk production relative to low-CP concentrates and metabolic status relative to high-CP concentrates.

Effect of supplementary concentrate type on nitrogen partitioning in early lactation dairy cows offered perennial ryegrass-based pasture.

Forty-four early lactation (64 ± 20 d in milk) dairy cows of mixed parity were used to assess the effect of 4 supplementary concentrate types (n=11) on N partitioning. Animals were blocked on parity and calving date, and blocks were balanced for previous milk yield and milk protein yield. Cows received grazed pasture plus 5.17 kg of dry matter (DM)/d of one of the following isoenergetic concentrates: high crude protein (CP) with rolled barley (HP, 19% CP); low CP with rolled barley (LP, 15% CP); low CP with barley and supplementary 2-hydroxy-4-methylthio butanoic acid (HMBi; LP+HMBi, 15% CP); and low CP with ground corn (LP Corn, 15% CP). Nitrogen partitioning studies were conducted at wk 6 and 10 postpartum by using the n-alkane technique to determine pasture dry matter intake (DMI). Pasture DMI (13.3kg of DM/d) and dietary digestibility of DM were not affected by concentrate type. Milk yield was lower for LP compared with other concentrate types (25.4 vs. 28.3 kg/d). Yields of milk protein and milk casein were not affected by concentrate type. However, milk solid yield and milk fat yield were higher for LP+HMBi (1.97 and 0.92 kg/d) compared with LP (1.72 and 0.87 kg/d). Concentrations of fat, protein, lactose, and casein were not affected by concentrate type. Dietary N intake was higher for HP compared with other treatments (0.545 vs. 0.482 kg/d, HP vs. average of the 3 LP treatments). Dietary N intakes were not different among low CP concentrates. Fecal N excretion was not affected by concentrate type. However, urinary N excretion was related to N intake and was higher for HP compared with other treatments (0.261 vs. 0.195 kg/d, HP vs. average of the 3 LP treatments). Urinary N excretion was not different among low CP concentrates. Milk N output was higher for HP (0.139 kg/d) compared with LP (0.12 kg/d) but not LP+HMBi (0.137 kg/d) or LP Corn (0.138 kg/d). The portion of feed N excreted as feces N was lower for HP compared with other treatments (0.272 vs. 0.327, HP vs. average of the 3 LP treatmentsHowever, the portion of feed N excreted as urine N was higher for HP (0.466) compared with LP+HMBi (0.408) and LP Corn (0.366) but not compared with LP. The portion of feed N excreted as milk N was higher for LP Corn (0.282) compared with HP (0.257) but not LP+HMBi or LP. Dietary reformulation to reduce N excretion in pasture-based dairy production systems is possible. However, maintenance of milk yield and milk N when concentrate CP was reduced (19 vs. 15%) required the use of either protected AA (HMBi) or ground corn.

Effect of forage source and a supplementary methionine hydroxy analog on nitrogen balance in lactating dairy cows offered a low crude protein diet.

Four primiparous and 4 multiparous midlactation dairy cows were stratified by pre-experimental milk yield (23.5 ± 2.3 kg/d), protein yield (0.75 ± 0.066 kg/d), parity, and days in lactation (121 ± 10 d) into 4 groups of 2 in a 2 × 2 factorial, Latin square design (n = 8) to assess the effect of forage source and a supplementary methionine hydroxy analog on nitrogen (N) balance where low crude protein (CP) diets (13.3%) are offered. Diets contained either predominantly grass silage [GS (G- and G+)] or corn silage [CS (C- and C+)] as the forage source and were offered with (G+ and C+) or without (G- and C-) the isopropyl ester of 2-hydroxy-4 methylthio butanoic acid (HMBi). The G- and G+ contained 46% GS and 10% CS in the dry matter (DM), whereas C- and C+ contained 12% GS and 52% CS in the DM. Supplementary HMBi was included at a rate of 0.2% of DM in G+ and C+ diets. Diets were isonitrogenous (9.8 ± 0.4% protein truly digested in the small intestine) and isoenergetic (0.96 ± 0.01 units of energy for lactation; kg/DM). Each of the 4 experimental periods lasted 24 d: 14 d for dietary adaptation, followed by 10 d of housing in individual metabolism stalls; N balance was conducted on the last 5 d of each experimental period. Intake of DM was higher for CS-based vs. GS-based diets (20.23 vs. 18.41 kg/d). No effect of dietary treatment was found on milk yield or yields of milk fat, protein, and lactose. Supplementing with HMBi tended to improve milk solids yield (1.69 vs. 1.59 kg/d), casein yield (0.59 vs. 0.55 kg/d), and concentrations of casein (2.89 vs. 2.73%) and protein (3.58 vs. 3.49%) in the milk. Dietary N intake was higher for CS-based vs. GS-based diets (0.460 vs. 0.422 kg/d). However, forage source or supplementary HMBi had no effect on N excretion in the feces, urine, or milk. Excretion of urinary urea was positively related to N intake. Concentrations of urea N in the plasma (2.34 vs. 1.72 mmol/L), milk (2.54 vs. 2.24 mmol/L), and urine (123.32 vs. 88.79 mmol/L), and total excretion of urinary urea N (40.23 vs. 35.09 g/d) were higher for animals offered CS-based vs. GS-based diets. Corn silage improved N intake through improved DM intake. However, neither forage source nor HMBi supplementation affects N output in the feces, urine, or milk.