Farm-level nutritional factors associated with milk production and milking behavior on Canadian farms with automated milking systems.

The objective of this study was to describe nutritional strategies utilized on Canadian dairy farms with automated milking systems (AMS), both at the feed bunk and the concentrate offered at the AMS, as well as to determine what dietary components and nutrients, as formulated, were associated with milk production and milking behaviors on those farms. Formulated diets, including ingredients and nutrient content, and AMS data were collected from April 1, 2019, until September 30, 2020, on 160 AMS farms (Eastern Canada [East] = 8, Ontario [ON] = 76, Quebec [QC] = 22, and Western Canada [West] = 54). Both partial mixed ration (PMR) and AMS concentrate samples were collected from May 1 to September 30, 2019, on 169 farms (East = 12, ON = 63, QC = 42, West = 52). AMS milking data were collected for 154 herds. For each farm (n = 160), milk recording data were collected and summarized by farm to calculate average milk yield and components. Multivariable regression models were used to associate herd-level formulated nutrient composition and feeding management practices with milk production and milking behavior. Milk yield (37.0 ± 0.3 kg/d) was positively associated with the PMR ether extract (EE) concentration (PMR % EE; +0.97 kg/d per percentage point (p.p.) increase) and with farms that fed barley silage as their major forage source on farm (n = 16; +2.18 kg/d) compared with haylage (n = 42), while farms that fed corn silage (n = 96; +1.23 kg/d) tended to produce more milk than farms that fed haylage. Greater milk fat content (4.09 ± 0.28%) was associated with greater PMR-to-AMS concentrate ratio (+0.02 p.p. per unit increase) and total diet net energy for lactation (+0.046 p.p. per 0.1 Mcal/kg increase), but lesser % non-fiber carbohydrates (NFC) of the PMR (-0.016 p.p. per p.p. increase of % NFC). Milk protein content (3.38 ± 0.14%) was positively associated with forage % of the PMR (+0.003 p.p. per p.p. increase of % forage) and total diet % starch (+0.009 p.p. per p.p. increase of % starch), but negatively associated with farms feeding corn silage (-0.1 p.p. compared with haylage) as their major forage. Greater milking frequency (2.77 ± 0.40 milkings/d) was observed on farms with free-flow cow traffic systems (+0.62 milkings/d) and positively associated with feed push-up frequency (+0.013 milkings/d per additional feed push-up), while being negatively associated with PMR NFC content and % forage of the total ration (-0.017 milkings/d per p.p. increase of % forage). Lastly, greater milking refusal frequency (1.49 ± 0.82 refusals/d) was observed on farms with free-flow cow traffic systems (+0.84 refusals/d) and farms feeding barley silage (+0.58 refusals/d) than guided flow and farms feeding either corn silage or haylage, respectively. These data give insight into the ingredients, nutrient formulations and type of diets fed on AMS dairy farms across Canada and the association of those factors with milk production and milking behaviors.

Exploring herd-level perinatal calf mortality risk factors in eastern Canadian dairy farms.

This closed cohort study aimed to identify the associations between dairy calf management practices and herd-level perinatal calf mortality risk. From February 2020 to June 2021, predominantly Holstein dairy farms in Québec (n = 1832) and New Brunswick (n = 52), Canada, registered in the dairy herd improvement program, were visited once. A questionnaire covering all aspects of precalving, calving, and colostrum management was administered. Data regarding perinatal mortality were retrieved from the dairy herd improvement program database for each farm for 2021. Perinatal mortality was calculated for each farm as the proportion of calves dead at birth or dying within 24 h of life. A multivariable negative binomial model was used to assess herd-level factors associated with the risk of perinatal mortality. The final model included the lying surface in the calving area, the typical time to first colostrum intake, typical cow-calf contact time, the proportion of males born, the proportion of assisted calvings, and herd size. Herd-level perinatal mortality risk ranged from 0 to 38.1% (mean (SE) = 7.6% ± 0.1%). A greater proportion of males born, proportion of assisted calvings, and delayed colostrum feeding were associated with increased herd-level perinatal mortality. Factors associated with a decreased herd-level perinatal mortality risk were having a typical cow-calf contact time between 7 and 12 h after calving compared with reduced cow-calf contact time, soft lying surfaces in the calving area compared with concrete and mat-lying surfaces, and an increased number of calvings per year. Our results show that while some of the significant risk factors are not well understood (i.e., calving area lying surface, typical cow-calf contact time); Canadian farmers could focus on the factors under their control (i.e., time to first colostrum feeding, proportion of difficult calvings, males born, and calvings per year) to reduce the risk of perinatal mortality. Future work should focus on qualitative research to understand the dairy farmer motivations and limitations to implementing practices identified in this and other studies to reduce perinatal mortality.

Relationship between farm management strategies, reticuloruminal pH variations, and risks of subacute ruminal acidosis.

Low reticuloruminal pH (rpH), often observed in subacute ruminal acidosis (SARA), may negatively affect rumen health and animal performance. To investigate the variability of rpH and the prevalence of SARA on commercial farms, we conducted an observational study on 110 early-lactation Holstein cows of different parities from 12 farms selected to cover a broad range of farm management strategies. The rpH of each cow was continuously monitored for 50 d using wireless boluses. To study the effects of animal and farm management characteristics on rpH, we used a multivariable mixed model analysis with the animal and farm as random effects. Automatic milking system and presence of corn silage in the ration were associated with a decrease in rpH of 0.37 and 0.20 pH units, respectively, whereas monensin supplementation was associated with an increase of 0.27 pH units. The rpH increased by 0.15 pH units during the first 60 d in milk. We defined a SARA-positive day as rpH below 5.8 (SARA5.8) or 6.0 (SARA6.0) for at least 300 min for 1 d. Using those definitions, during our study, a total of 38 (35%) and 65 (59%) cows experienced at least one episode of SARA5.8 and SARA6.0, respectively. The proportion of cows with at least one SARA-positive day varied among farms from 0 to 100%. Automatic milking system was associated with an increased risk of SARA5.8 (odds ratio: 10) and SARA6.0 (odds ratio: 11). The use of corn silage was associated with an increased risk of SARA5.8 (odds ratio: 21), whereas the use of monensin was associated with a decreased risk of SARA5.8 (odds ratio: 0.02). Our study shows that rpH is quite variable among farms, but also among animals on the same farm. We also show that multiple animal and farm characteristics are associated with rpH variability and the risk of SARA under commercial conditions.

Association of housing and management practices with milk yield, milk composition, and fatty acid profile, predicted using Fourier transform mid-infrared spectroscopy, in farms with automated milking systems.

Milk fatty acid (FA) profile can be divided into (1) de novo (C4-C14) that are synthesized in the mammary gland; (2) preformed (≥C18) that are absorbed from blood and originate from mobilized adipose tissues or dietary fat; and (3) mixed (C16), which have both origins. Our objectives were to describe the FA profile, as predicted using Fourier transform mid-infrared spectroscopy, of bulk tank milk from automated milking system (AMS) farms and to assess the association of management and housing factors with the bulk tank milk composition and FA profile of those AMS farms. The data used were collected from 124 commercial Canadian Holstein dairy farms with AMS, located in the provinces of Ontario (n = 68) and Quebec (n = 56). The farms were visited once from April to September 2019, and information were collected on barn design and herd management practices. Information regarding individual cow milk yield (kg/d), days in milk, parity, and the number of milking cows were automatically collected by the AMS units on each farm. These data were extracted for the entire period that the bulk tank milk samples were monitored, from April 2019 to April 2020 in Quebec and from August 2019 to May 2020 in Ontario. Across herds, milk yield averaged (mean ± standard error) 35.9 ± 0.4 kg/d, with 3.97 ± 0.01% fat and 3.09 ± 0.01% protein, whereas FA profile averaged 26.2 ± 0.1, 33.1 ± 0.1, and 40.7 ± 0.2 g/100 g of FA for de novo, mixed, and preformed, respectively. The FA yield averaged 0.34 ± 0.01, 0.44 ± 0.01, and 0.54 ± 0.01 kg/d for de novo, mixed, and preformed, respectively. Multivariable regression models were used to associate herd-level housing factors and management practices with milk production, composition, and FA profile. Milk yield was positively associated with using a robot feed pusher (+2.1 kg/d) and the use of deep bedding (+2.6 kg/d). The use of a robot feed pusher, deep bedding, and greater stall raking frequency were positively associated with greater yield (kg/d) of de novo, mixed, preformed, and de novo + mixed FA. Use of deep bedding was negatively associated with concentration of fat, de novo FA, mixed FA, and de novo + mixed FA, expressed in grams per 100 g (%) of milk. A wider lying alley width (≥305 cm) was associated with a greater concentration (g/100 g of milk) of de novo and de novo + mixed FA. Greater frequency of partial mixed ration delivery (>2×/d vs. 1 and 2×/d) was positively associated with a greater proportion (g/100 g of FA) of de novo, mixed, and de novo + mixed FA and negatively associated with the proportion of preformed FA. Overall, these associations indicated that bulk tank FA profile can be used as a tool to monitor and adjust management and housing in AMS farms.

Farm-level factors associated with lameness prevalence, productivity, and milk quality in farms with automated milking systems.

Impaired locomotion (lameness) may negatively affect the ability and desire of cows to milk voluntarily, which is a key factor in success of automated milking systems (AMS). The objective of this study was to identify factors associated with herd-level lameness prevalence and associations of lameness and other farm-level factors with milking activity, milk yield, and milk quality in herds with AMS. From April to September 2019, 75 herds with AMS in Ontario, Canada, were visited, and data on barn design and farm management practices were collected. Data from AMS were collected, along with milk recording data, for the 6-mo period before farm visits. Farms averaged 98 ± 71 lactating cows, 2.3 ± 1.5 robot units/farm, 43.6 ± 9.4 cows/robot, 36.4 ± 4.9 kg/d of milk, a milking frequency of 3.01 ± 0.33 milkings/d, and a herd average geometric mean SCC of 179.3 ± 74.6 (× 1,000) cells/mL. Thirty percent of cows/farm (minimum of 30 cows/farm) were scored for body condition (1 = underconditioned to 5 = over conditioned) and locomotion (1 = sound to 5 = lame; clinically lame ≥3 out of 5 = 28.3 ± 11.7%, and severely lame ≥4 out of 5 = 3.0 ± 3.2%). Clinical lameness (locomotion score ≥3) was less prevalent on farms with sand bedding, with increased feed bunk space per cow, and on farms with non-Holstein breeds versus Holsteins, and tended to be less prevalent with lesser proportion of underconditioned cows (with body condition score ≤2.5). Severe lameness occurrence (farms with any cows with locomotion score ≥4) was associated with a greater proportion of underconditioned cows and in farms with stalls with greater curb heights. Herd average milk yield/cow per day increased with lesser prevalence of clinical lameness (each 10-percentage-point decrease in clinical lameness prevalence was associated with 2.0 kg/cow per day greater milk yield) and greater milking visit frequency per day, and tended to be greater with increased feed push-up frequency. Lesser herd average somatic cell count was associated with lesser clinical lameness prevalence, herd average days in milk, and proportion of overconditioned cows, and somatic cell count tended to be lesser for farms with sand bedding versus those with organic bedding substrates. The results highlight the importance of minimizing lameness prevalence, using of sand bedding, ensuring adequate feed access and feed bunk space, and maintaining proper cow body condition to optimize herd-level productivity and milk quality in AMS herds.

Benchmarking of farms with automated milking systems in Canada and associations with milk production and quality.

The objective of this study was to benchmark the herd-level housing and management strategies of automated milking system (AMS) farms across Canada and assess the associations of these herd-level housing factors and management practices with milk production and quality. Canadian AMS farms (n = 197; Western Canada: n = 50, Ontario: n = 77, Quebec: n = 59, Atlantic Canada: n = 11) were each visited once from April to September 2019, and details were collected related to barn design and herd management practices. Milk-recording data for the 6 mo before farm visits were collected. Farms averaged (± standard deviation) 110 ± 102 lactating cows, 2.4 ± 1.9 AMS units/farm, 47.5 ± 14.9 cows/AMS, 36.7 ± 5.0 kg/d of milk, 4.13 ± 0.34% fat, 3.40 ± 0.16% protein, and a herd-average somatic cell count of 186,400 ± 80,800 cells/mL. Farms mainly used freestall housing systems (92.5%), organic bedding substrates (73.6%), and free flow cow traffic systems (87.8%); farms predominantly milked Holsteins (90.4%). Multivariable regression models were used to associate herd-level housing factors and management practices with milk production and quality. At the herd level, feed push-up frequency (mean = 12.8 ± 8.3 times per day) and feed bunk space (mean = 64 ± 21.5 cm/cow) were positively associated with milk yield. Greater milk yield was associated with herds using inorganic (sand) versus organic bedding, milking Holsteins versus non-Holsteins, and using a form of mechanical ventilation versus natural ventilation alone. Milk fat and milk protein content were only associated with breed. Herds with lower somatic cell counts had more frequent alley cleaning (mean = 12.1 ± 7.5 times per day), wider lying alleys (mean = 304.5 ± 40.0 cm), and sand bedding. The results highlight the importance of using sand bedding, using mechanical ventilation, keeping feed pushed up, ensuring alleys are clean, and ensuring adequate space at the feed bunk for maintaining herd-level productivity and milk quality in farms with AMS.

Short communication: Potential prediction of vitamin B12 concentration based on mid-infrared spectral data using Holstein Dairy Herd Improvement milk samples.

The purpose of this study was (1) to predict the quantitative concentration of vitamin B12 in milk using mid-infrared (MIR) spectrometry, and (2) to evaluate the potential of MIR spectra to discriminate different clusters of records based on their B12 concentration. Milk samples were collected from 4,340 Holstein cows between 3 and 592 d in milk and located in 100 herds. Samples were taken using in-line milk meters and divided into 2 aliquots: one for MIR spectrometry and the other for B12 concentration reference analyses by radioassay. Analyses were performed on 311 selected spectral wavelengths. A partial least squares regression model was built to quantify B12 concentration. Discriminant analysis was used to isolate B12 concentration clusters. A B12 concentration threshold was set at 442 ng/dL, because this represents the cutoff value for a 250-mL glass of milk to fulfill 46% of the daily vitamin B12 recommended dietary allowance for individuals 14 yr or older. For each analysis, records coming from two-thirds of herds were used to calibrate prediction equations, and the remaining records (one-third of herds for validation) were used to assess the prediction performance. In the case of discriminant analysis, validation sets were divided into evaluation sets (one-third of herds) to obtain alternate probability cutoffs and in test sets (two-thirds of herds) to validate equations. Spectral and B12 concentration outliers were identified by calculating standardized Mahalanobis distance and with a residual analysis, respectively (n = 3,154). Regarding quantitative B12 concentration, cross-validation and validation coefficients of determination averaged 0.51 and 0.46, respectively, which are relatively low, which would limit the potential use of the developed quantitative equations. In addition, root mean square errors of prediction of cross validation and validation sets averaged 88.9 and 94.7 ng/dL, respectively. Area under the receiver operating characteristic curve of test sets averaged 0.81 based on the 442 ng/dL threshold, which could be considered to represent good accuracy of classification. However, the false discovery rate averaged 36%. In summary, models predicting quantitative B12 concentration had low cross-validation and validation coefficients of determination, limiting their use, but the proposed discriminant models could be used to identify milk samples with naturally high B12.

Short communication: Relationships among plasma and milk vitamin B12, plasma free fatty acids, and blood ß-hydroxybutyrate concentrations in early lactation dairy cows.

This study was undertaken to evaluate the relationship between plasma and milk concentrations of vitamin B12 as well as the relationship between plasma or milk concentrations of vitamin B12 and plasma concentration of free fatty acids (FFA) or blood concentration of ß-hydroxybutyrate (BHB) of early lactating Ayrshire (AY) and Holstein (HO) cows. A total of 44 dairy herds (7 AY and 37 HO herds) and 62 AY (21 in first, 19 in second, and 22 in third and more lactations) and 228 HO (51 in first, 74 in second, and 103 in third and more lactation) cows between 3 and 40 d in milk were involved in the study. Hand-stripped milk samples and blood samples were taken 6 h after the morning milking. Milk and plasma samples were analyzed for vitamin B12 concentration and plasma samples were analyzed for FFA concentration. A handheld device was used for blood BHB concentration determination. Thresholds for elevated plasma FFA concentration and hyperketonemia were set at ≥0.70 and ≥1.2 mmol/L, respectively. Vitamin B12 concentration in milk of AY primiparous cows [2,557 (1,995-3,276) pg/mL] was lower than in milk from HO primiparous cows [3,876 (3,356-4,478) pg/mL], whereas no difference was observed among other parities and breeds. Regardless of breeds, plasma concentration of vitamin B12 of first and second parities was lower than plasma concentration of third and more lactation cows. Milk vitamin B12 concentration was positively correlated with plasma vitamin B12 concentration, but the relationship was stronger for AY (ρ averaging 0.63) than for HO cows (ρ averaging 0.36). For AY and HO breeds, a significant relationship between milk or plasma vitamin B12 concentrations and plasma FFA concentration (ρ between 0.29 and 0.59) was observed. Moreover, cows with elevated plasma FFA concentration had greater milk and plasma vitamin B12 concentrations than cows with normal plasma FFA concentration. No relationship between vitamin B12 concentration in milk or plasma and blood BHB concentration and hyperketonemia was noted. In summary, milk is not well correlated with plasma vitamin B12 concentration for HO. It could be hypothesized that elevated plasma concentration of FFA could have a negative effect on the use of vitamin B12 by cow cells, which increases the concentration of the vitamin in plasma and its secretion in milk.

A randomized controlled trial on the effect of incomplete milking during early lactation on ketonemia and body condition loss in Holstein dairy cows.

Limiting milk production for a short period of time in early lactation could be a relevant strategy to prevent hyperketonemia (HYK). From December 2013 to March 2015, 838 multiparous Holstein cows from 13 herds were enrolled in a randomized controlled trial evaluating the effect of incomplete milking in early lactation on ketonemia and its effect on body condition score (BCS) loss. Cows were randomly assigned 4 wk before expected calving date to 1 of 2 treatment groups, (1) a conventional milking protocol (CON) for which cows were completely milked or (2) an incomplete milking protocol (INC) for which a maximum of 10 to 14 kg of milk/d were withdrawn during the first 5 d in milk (DIM). ß-Hydroxybutyrate (BHB) concentrations were measured from blood samples collected on each cow 3 times at weekly intervals. Hyperketonemia was defined as BHB ≥1.4 mmol/L. Body condition score variation in the postcalving period was calculated by subtracting BCS assessed at wk 7 from BCS assessed at first week after calving. Effect of treatment on ketonemia and prevalence of HYK were evaluated for 4 specific time periods: 1 to 3, 4 to 7, 8 to 17, and 18 to 26 DIM. Effect of treatment on ketonemia was investigated using linear mixed models with natural logarithm of BHB measurements as outcome and treatment groups as fixed effect. Generalized linear mixed models with HYK as outcome, using logit link, and treatment groups as fixed effect were used to investigate effect of treatment on odds of HYK. A logistic regression model with BCS loss (<0.75 or ≥0.75) as outcome and treatment groups and herd as fixed effects was used to study effect of INC on odds of having BCS loss ≥0.75. A total of 813 lactations had complete data and were used for statistical analysis of ketonemia and HYK. A total of 709 lactations had complete data and were used for analysis of BCS loss. Geometric means of blood BHB concentrations during the 1 to 3, 4 to 7, 8 to 17, and 18 to 26 DIM periods were, respectively, 0.72 (95% confidence interval = 0.66, 0.80), 0.66 (0.60, 0.73), 0.90 (0.80, 1.01), and 0.93 (0.83, 1.05) mmol/L for INC, and 0.65 (0.59, 0.72), 0.79 (0.72, 0.87), 0.94 (0.84, 1.06), and 0.92 (0.82, 1.04) mmol/L for CON. Cows in INC group had lower ketonemia during the 4 to 7 DIM period. Predicted prevalence of HYK during the 1 to 3, 4 to 7, 8 to 17, and 18 to 26 DIM periods were, respectively, 2.8 (3.2, 15.1), 4.6 (2.0, 10.0), 13.4 (8.4, 20.0), and 23.0% (17.4, 29.7) for INC and 2.6 (2.5, 13.8), 10.7 (5.6, 19.3), 19.4 (13.0, 27.9), and 21.3% (16.0, 27.8) for CON. The INC treatment reduced the prevalence of HYK during the 4 to 7 and 8 to 17 DIM periods. No association was observed between INC and BCS loss in the postcalving period. Overall, the incomplete milking protocol was effective for reducing ketonemia and prevalence of HYK during the early postpartum period.

A randomized controlled trial on the effect of incomplete milking during the first 5 days in milk on culling hazard and on milk production and composition of dairy cows.

An incomplete milking in early lactation could help limit negative energy balance in dairy cattle, but its potential effects on culling hazard and on milk production and composition throughout the entire lactation are unknown. The objective of this study was to evaluate the effect of an incomplete milking during the first 5 d in milk on culling hazard, milk weight, milk fat and protein concentrations, and energy-corrected milk (ECM) yield during the whole lactation. A randomized controlled trial was conducted in 13 dairy farms near St-Hyacinthe, Quebec, Canada. Approximately 1 mo before expected calving, Holstein multiparous cows calving between December 2013 and March 2015 (n = 846 cow lactations) were randomly assigned to a control or a treatment group. Cows in the control group were milked conventionally, whereas cows in the treatment group were submitted to an incomplete milking protocol (maximum of 10, 12, and 14 L/d of milk was collected on days in milk 1-3, 4, and 5, respectively). All farms were registered on Dairy Herd Improvement Association, which was used to obtain records on culling, monthly milk yield, and milk fat and protein concentrations. In addition, daily milk yield records were available for 6 farms. A Cox proportional hazards model with a herd frailty term was fitted to the data to compare culling hazard among treatment groups. Regarding milk production and composition, 4 linear mixed models with herd as a fixed effect, cow as a random effect, and using an autoregressive covariance structure were used to study the effect of the incomplete milking on (1) milk weight, (2) milk fat concentration, (3) milk protein concentration, and (4) ECM yield. Culling hazard did not differ among treatment groups (hazard ratio = 1.0; 95% CI = 0.82, 1.3). We observed no differences in milk weight, milk fat, or protein concentration among treatment groups between weeks in milk (WIM) 2 and 44 (the studied period). We noted a difference in ECM between treatment groups for WIM 38, with incompletely milked cows producing less milk than conventionally milked cows (-2.7 kg/d; 95% CI = -0.02, -5.2 kg/d), but no differences were found for any of the other WIM. These results suggest that this strategy for controlling the negative energy balance has negligible effect on cow productivity.

Prevalence of elevated milk ß-hydroxybutyrate concentrations in Holstein cows measured by Fourier-transform infrared analysis in Dairy Herd Improvement milk samples and association with milk yield and components.

The purpose was to describe the prevalence and effect of elevated milk ß-hydroxybutyrate (BHB) as detected by routine Fourier-transform infrared analysis in Dairy Herd Improvement milk samples. Data collected over 4 yr included cow information as well as milk yield and composition from 498,310 samples from postparturient Holstein cows (5-35d in milk) from 4,242 herds. The following thresholds were used to classify cows based on their early lactation milk BHB concentration: <0.15mmol/L=negative; 0.15 to 0.19mmol/L=suspect; and ≥0.20mmol/L=positive. Overall prevalence (suspect + positive) was 22.6% and was higher for older cows (18.7, 19.5, and 27.6%, for cows in their first, second, and third or greater lactation, respectively). Distribution with regards to days in milk was different among parity groups, with first-lactation cows having highest prevalence (30%) in the first week after calving; cows in their second and third and greater parity had the highest prevalence in the second week after calving, at 25.8 and 34.6%, respectively. Season of calving affected the prevalence of elevated milk BHB, with cows calving in the fall and spring seasons showing higher prevalence. Distribution among herds was highly variable, as 45% of herds had a prevalence of 20% or less, 47% of herds had a prevalence between 21 and 40%, 6% of herds had a prevalence between 40 and 50%, and 2% of herds had a prevalence of 50% or above. Positive cows had lower milk yield, protein concentration and yield, and lower Transition Cow Index than negative cows, but also higher fat concentration and yield, as well as higher somatic cell count than negative cows. Suspect cows were generally intermediate. The present analysis highlights the opportunity for elevated milk BHB monitoring at the herd level through routine BHB testing in Dairy Herd Improvement milk samples.

Weight, height, and relative-reliability indicators as a management tool for reducing age at first breeding and calving of dairy heifers.

In Québec first calving occurs on average at 27 mo, whereas the target is 23 to 24.5 mo to maximize herd profitability. The aim of this study was to quantify current and future heifer growth using individual heifer random regressions and to generate indicators (such as heifer weight and height at 15 and 24 mo, average daily gain before and after 15 mo, age at which optimal weight for breeding is attained, i.e., 55% of mature weight, and reliability of the 15- and 24-mo weight predictions) that could be used as a practical on-farm tool. Dairy heifer weight estimated by heart girth circumference and height measured at the withers (from 0 to 27 mo) were obtained from the Valacta database (DHI agency, Ste-Anne-de-Bellevue, QC, Canada) from 1995 to 2012. Indicators were calculated based on the current situation of Holstein (HO), Ayrshire (AY), Jersey (JE), and Brown Swiss (BS) heifer growth in Québec. Heifers with less than 2 records were excluded from the analysis. Mature weights were determined by weight at calving of cows from third or greater lactation for a given breed and were 710 kg for HO, 625 kg for AY, 470 kg for JE, and 670 kg for BS. Estimated weights at 15 and 24 mo were 425 and 627, 334 and 482, 297 and 429, and 379 and 560 kg for HO, AY, JE, and BS, respectively, which are heavy enough for breeding and calving, except for AY. Relative reliabilities of the 15- and 24-mo weight predictions were on average 89 and 60%, respectively, based on measurements up to 15 mo. For HO, AY, JE, and BS, wither heights at 15 and 24 mo were 134 and 143, 125 and 134, 122 and 131, and 130 and 140 cm, respectively. Age at optimal breeding weight was 13.6, 15.5, 12.6, and 14.5 mo for HO, AY, JE, and BS, respectively. These data suggest that it is realistic to expect a first calving at 24 mo for HO, JE, and BS. A growth delay was observed for AY; average daily gain was 655 and 538 g/d before and after 15 mo, respectively. The average daily gain before and after 15 mo was 848 and 747 g/d for HO, 603 and 486 g/d for JE, and 775 and 662 g/d for BS, respectively. These indicators could be calculated for an individual heifer and on a herd-level basis and used on farm as a management tool for reducing age at first breeding and at first calving.

Short dry period management improves peripartum ruminal adaptation in dairy cows.

The present study aimed to determine whether the improvement in postpartum energy balance frequently reported in cows under short dry period management could be due to an improvement in ruminal function related to the reduction in the number of diet changes before calving. Six multiparous and 6 primiparous Holstein cows equipped with ruminal cannula were assigned to 6 blocks of 2 cows each according to parity, projected milk production at 305 d, and expected calving date. Within each block, cows were randomly assigned to either a conventional (CDP; 63.2 ± 2.0 d) or a short dry period (SDP; 35.2 ± 2.0 d) management in a randomized complete block design. The CDP cows were fed a far-off diet until 28 d before calving, followed by a prepartum diet, whereas SDP cows received only the prepartum diet. After calving, both groups were fed the same lactation diet. Milk yield and dry matter intake (DMI) were recorded daily and milk composition, weekly. Blood samples were taken twice a week during the first 4 wk postcalving and weekly otherwise. Omasal and ruminal samples were collected approximately 3 wk prior and 3 wk after calving. From 28 d before calving until calving, when the 2 groups of cows were fed the same prepartum diet, there was no effect of the dry period length management on DMI, plasma concentrations of ß-hydroxybutyrate, nonesterified fatty acids, and glucose and nutrient digestibility in the rumen. However, CDP cows tended to have lower ruminal pH and higher ruminal concentrations of total volatile fatty acids than SDP cows. From calving to 60 d in milk, daily DMI was higher for SDP than for CDP cows (22.3 ± 0.44 vs. 20.7 ± 0.30 kg), but milk production and milk concentrations and yields of fat, protein, and total solids were not affected by the dry period length management. After calving, body weight loss was reduced and body condition score tended to increase more rapidly for SDP than for CDP cows. Nutrient digestibility in the rumen, expressed in kilograms per day, was greater or tended to be greater for SDP cows, but differences were no longer significant when expressed per unit of nutrient ingested. The decrease in plasma nonesterified fatty acids and ß-hydroxybutyrate in SDP cows without effect on milk yield suggests an improved energy balance likely due to greater DMI. Results from the present study seem to indicate that reducing the number of diet changes before calving could facilitate ruminal adaptation to the lactation diet and improve energy balance postpartum.

Effects of folic acid and vitamin B12 supplementation on culling rate, diseases, and reproduction in commercial dairy herds.

This study was undertaken to determine the effect of a combined folic acid and vitamin B12 supplement given in early lactation on culling rate, metabolic disorders and other diseases, and reproduction in commercial dairy herds. A total of 805 cows (271 primiparous and 534 multiparous cows) in 15 commercial dairy herds were involved. Every 2mo from February to December 2010 and within each herd, cows were assigned according to parity, previous 305-d milk production, and calving interval to 5mL of either (1) saline 0.9% NaCl (control group) or (2) 320mg of folic acid + 10mg of vitamin B12 (vitamin group). Treatments were administered weekly by intramuscular injections starting 3wk before the expected calving date until 8wk after parturition. A total of 221 cows were culled before the next dry period. Culling rate was not affected by treatment and was 27.5%; culling rate was greater for multiparous (32.2%) than for primiparous cows (18.8%). Within the first 60d in milk (DIM), 47 cows were culled, representing 21.3% of total culling, and no treatment effect was noted. Ketosis incidence based on a threshold ≥100µmol/L of ß-hydroxybutyrate in milk was 38.3±2.9% for the vitamin group and 41.8±3.0% for the control group and was not affected by treatment. The combined supplement of folic acid and vitamin B12 did not decrease incidence of retained placenta, displaced abomasum, milk fever, metritis, or mastitis. However, the incidence of dystocia decreased by 50% in multiparous cows receiving the vitamin supplement, although no effect was observed in primiparous cows. The first breeding postpartum for multiparous cows occurred 3.8d earlier with the vitamin supplement compared with controls, whereas no treatment effect was seen for primiparous cows. Days open, first- and second-breeding conception rates, number of breedings per conception, and percentage of cows pregnant at 150 DIM were not affected by treatment. The reduced percentage of dystocia combined with the earlier DIM at first breeding for multiparous cows receiving the combined supplementation in folic acid and vitamin B12 indicates that the vitamin supplement had a positive effect in older cows.

Economic effect of short (35-d) compared with conventional (60-d) dry period management in commercial Canadian Holstein herds.

The Canadian dairy industry operates under a supply management system with production quotas (expressed in kilograms of butterfat per day) owned by dairy producers. Any management strategy influencing production responses must, therefore, be evaluated to estimate its effects on quota needed to sell the milk produced. In the present study, half of the cows from 13 commercial herds (850 cows, average of 70 cows per herd) were assigned to be managed for a short dry period (SDP; 35 d dry) and the other half was managed for a conventional dry period (CDP; 60 d dry) to evaluate the economic impact of a steady state involving either CDP or SDP. Economic variables included in the partial budget were: variations in revenues from milk and components as well as animals sold; costs related to feeding, reproduction, replacement, housing, and treatments. All variables were first estimated on a cow basis for each herd individually, and average results were used to calculate the partial budget for an average herd. Yearly milk and component yields per cow increased, which implies that fewer cows are required to produce the same amount of quota. Accordingly, 2 scenarios were investigated: in the first one, available quota was kept constant, and herd size was adjusted to avoid over-quota production. Consequently, the partial budget was calculated considering that 5 fewer cows were present in the herd. In this situation, switching to an SDP management increased net annual income for the farm by $2,677 (Can$), which represents $41.38 per cow. In the second scenario, the number of cows was kept constant, but additional quota (5.5 kg/d, $25,000/kg) was bought to allow selling all of the milk produced. In this case, net farm income was increased by $17,132 annually with SDP, which represents $245.18 per cow. This budget includes interest on the purchase of quota. A comparison of partial budgets for individual herds involved in the study revealed considerable variation among herds. Switching from a CDP to a SDP management would be beneficial for average dairy herds in eastern Canada.

Incidence of metabolic disorders and reproductive performance following a short (35-d) or conventional (60-d) dry period management in commercial Holstein herds.

A total of 850 Holstein cows from 13 commercial dairy herds were involved in the present study to compare the effects of 2 different dry period (DP) management strategies on health and reproductive parameters. Cows were assigned to either a short (SDP; 35-d) or a conventional (CDP; 60-d) DP management within each herd, based on previous 305-d milk yield, parity (414 primiparous and 436 multiparous), and estimated calving interval. Cows assigned to CDP were fed a dry cow ration from dry-off until 21 d prepartum, and were then switched to a precalving ration. Cows assigned to SDP were fed the precalving ration throughout their DP. Rations were specific to each herd. A significant treatment × parity interaction was found for culling rate. Dry period management did not affect culling rate for second-lactation cows but a significantly higher culling rate occurred in multiparous CDP cows compared with SDP (42.6 vs. 31.6% ± 3.7 for CDP and SDP, respectively). Management used in the DP did not affect incidence of severe ketosis, displaced abomasum, milk fever, and mastitis, although incidence of these metabolic disorders were lower in second-lactation than third- or greater-lactation cows. The incidence of mild ketosis (evaluated by milk ketone concentration) was lower following SDP, probably as a result of better energy balance. On the other hand, the incidence of retained placenta was higher in multiparous cows assigned to SDP, but the reason for this increase remains unclear. Nevertheless, this did not lead to increased incidence of metritis. Moreover, DP management did not influence reproductive measures, including days in milk at first breeding, number of breedings per conception, as well as conception rates at first and second services. Regarding days open, overall, all 13 herds were not significantly affected by treatment, but 1 herd clearly showed opposite results to the 12 others. Our results indicate that a short DP management strategy could facilitate transition from one lactation to the next by decreasing the incidence of mild ketosis, with no major negative effects on other health parameters and reproduction. The variation in results observed among herds suggests that other management practices influence the response observed following a short or conventional DP, emphasizing the need for other field studies.

Complete-lactation milk and component yields following a short (35-d) or a conventional (60-d) dry period management strategy in commercial Holstein herds.

A total of 850 cows distributed among 13 commercial Holstein herds were involved in this study to compare the effects of 2 different dry period (DP) management strategies on milk and component yields as well as body condition score (BCS) over complete lactations. Within each herd and every 2 mo, cows were assigned to a short (35 d dry; SDP) or conventional (60 d dry; CDP) DP management based on previous lactation 305-d milk yield, predicted calving interval, and parity: primiparous (n=414) and multiparous (n=436). Cows assigned to CDP were fed a far-off dry cow ration from dry-off until 21 d prepartum, and were then switched to a precalving ration. Cows assigned to SDP were fed the precalving ration throughout their DP. Rations were different across herds, but the late-lactation, precalving, and early lactation rations were identical for both treatment groups within each herd. Additional milk was obtained at the end of lactation from cows assigned to SDP due to the extended lactation. Average daily milk yield in the following lactation was not different between treatments for third- or greater-lactation cows, but was significantly decreased in second-lactation SDP cows. However, when expressed as energy-corrected milk, this difference was not significant. Although lower for primiparous than multiparous cows, body weight and BCS were not affected by DP management strategy. Milk production and BCS responses to treatments varied among herds. Results from the present study suggest that a short DP management strategy could be more appropriate for today's dairy cows, although not suitable for all cows or all herds.

Apparent ruminal synthesis and intestinal disappearance of vitamin B12 and its analogs in dairy cows.

The aim of the project was to calculate the apparent synthesis or destruction of cobalamin (vitamin B(12)) and its analogs in the rumen as well as their apparent intestinal disappearance in dairy cows. Four lactating cows were fed a diet supplemented with cobalt alone (0.76 mg/kg of DM; control) or with cobalt and vitamin B(12) (cyanocobalamin, 500 mg/d; treated). In addition to cobalamin, the only biologically active molecule for the cow, 7 analogs were identified in duodenal and ileal digesta: cobinamide, which lacks the base, ribose, and phosphate groups; and 6 other molecules in which the base, 5,6-dimethylbenzimidazole, is replaced by cresol, 2-CH(3)-adenine, adenine, 2-CH(3)-S-adenine, or 5-OH-benzimidazole, or an unidentified cobamine. Small amounts of cobalamin and cobinamide were detected in the total mixed ration, but apparent synthesis of all forms took place in rumen. During the control period, cobalamin represented 38% of the total amounts of corrinoids produced in rumen. Approximately 11% of the average daily intake of cobalt was used for apparent ruminal synthesis of corrinoids, of which only 4% was incorporated into cobalamin. Only 20% of the supplement of cyanocobalamin was recovered at the duodenal level; cobinamide appeared to be the major product of degradation of supplementary cyanocobalamin in the rumen. During the control and treatment periods, there was an apparent intestinal disappearance of cobalamin and 5-OH-benzimidazole cobamide only; only the apparent intestinal disappearance of cobalamin differed between the 2 periods. Although cobalamin was not the major form synthesized by ruminal microflora and, even if supplementary cyanocobalamin was extensively destroyed by ruminal microflora, based on calculations of apparent intestinal disappearance, cobalamin seems to be the major form absorbed in the small intestine.

Fate of supplementary B-vitamins in the gastrointestinal tract of dairy cows.

Four lactating Holstein cows equipped with ruminal, duodenal, and ileal cannulas were used in 2 studies to evaluate the disappearance of supplementary B-vitamins before and from the small intestine. The cows were fed a total mixed ration with chromic oxide in 12 daily meals. Each study consisted of a control (no vitamin supplementation) and a treatment period (with vitamin supplementation). Amounts of vitamins (mg/d) supplemented in studies 1 and 2, respectively, were: thiamin: 300 and 10; riboflavin: 1600 and 2.0; niacin: 12,000 and 600; vitamin B6: 800 and 34; biotin: 20 and 0.02; folic acid: 2600 and 111; vitamin B12: 500 and 0.4. In study 1, vitamins were added to the feed 5 d before and during the 4-d collection period. In study 2, vitamins were infused postruminally 1 d before and during the 4-d collection period. Substantial disappearance before the duodenal cannula was noted in study 1 (67.8% thiamin, 99.3% riboflavin, 98.5% nicotinamide, 41.0% pyridoxine, 45.2% biotin, 97.0% folic acid, and 62.9% vitamin B12). Except for nicotinamide and folate, there was almost no disappearance of postruminally infused vitamins before the duodenal cannula (study 2), suggesting extensive ruminal destruction or use. Apparent intestinal absorption values differed greatly among vitamins, but the proportion of vitamins disappearing from the small intestine was not negatively influenced by supplementation. Except for riboflavin and niacin, absolute amounts disappearing from the small intestine were greater during the treatment than the control periods, suggesting that B-vitamin supply in dairy cows is increased by supplementation, although losses in the rumen are extensive.