Liability to diseases and their relation to dry matter intake and energy balance in German Holstein and Fleckvieh dairy cows

Dairy cow efficiency is increasingly important for future breeding decisions. The efficiency is determined mostly by dry matter intake (DMI). Reducing DMI seems to increase efficiency if milk yield remains the same, but resulting negative energy balance (EB) may cause health problems, especially in early lactation. Objectives of this study were to examine relationships between DMI and liability to diseases. Therefore, cow effects for DMI and EB were correlated with cow effects for 4 disease categories throughout lactation. Disease categories were mastitis, claw and leg diseases, metabolic diseases, and all diseases. In addition, this study presents relative percentages of diseased cows per days in milk (DIM), repeatability, and cow effect correlations for disease categories across DIM. A total of 1,370 German Holstein (GH) and 287 Fleckvieh (FV) primiparous and multiparous dairy cows from 12 dairy research farms in Germany were observed over a period of 2 yr. Farm staff and veterinarians recorded health data. We modeled health and production data with threshold random regression models and linear random regression models. From DIM 2 to 305 average daily DMI was 22.1 kg/d in GH and 20.2 kg/d in FV. Average weekly EB was 2.8 MJ of NE_L/d in GH and 0.6 MJ of NE_L/d in FV. Most diseases occurred in the first 20 DIM. Multiparous cows were more susceptible to diseases than primiparous cows. Relative percentages of diseased cows were highest for claw and leg diseases, followed by metabolic diseases and mastitis. Repeatability of disease categories and production traits was moderate to high. Cow effect correlations for disease categories were higher for adjacent lactation stages than for more distant lactation stages. Pearson correlation coefficients between cow effects for DMI, as well as EB, and disease categories were estimated from DIM 2 to 305. Almost all correlations were negative in GH, especially in early lactation. In FV, the course of correlations was similar to GH, but correlations were mostly more negative in early lactation. For the first 20 DIM, correlations ranged from ?0.31 to 0.00 in GH and from ?0.42 to ?0.01 in FV. The results illustrate that future breeding for dairy cow efficiency should focus on DMI and EB in early lactation to avoid health problems.     

Milk yield and milking station visits of primiparous versus multiparous cows on automatic milking system farms in the Upper Midwest United States

The objective of this study was to investigate milk yield and frequency of visits to the milking station of primiparous versus multiparous cows at different stages of lactation on farms with automatic milking systems (AMS) in the Upper Midwest United States. Forty farms were included in the study, and daily AMS software data were collected for 18 mo. For the investigation of milk yield and milking visits, stage of lactation was categorized into 14 periods, 7 d in length for the first 28 d in milk (DIM) and 30 d in length thereafter until 328 DIM. Cow traffic flow to the AMS (free or guided) was included in the model. For the evaluation of failures and refusals, stage of lactation was categorized into 6 periods, 7 d in length each for the first 28 DIM, and 2 periods of 150 d in length each thereafter until 328 DIM. Failures are milking station visits where a cow fails to be milked due to lack of machine attachment although it is time for the cow to be milked. Refusals are milking station visits before adequate time has passed since previous milking, thus the cow leaves the milking station without being milked. Data from lactation days beyond 328 DIM were excluded from the study. Primiparous cows in free-flow systems produced less milk than multiparous cows until the 11th stage of lactation and produced more milk from the 12th stage until the end of the study period. Primiparous cows in guided-flow systems produced less milk than multiparous cows all 14 stages of lactation, but were approaching the milk yield of multiparous cows at the end of the study period. This was a biologically normal lactation curve for primiparous cows. However, estimated peak ratio (primiparous vs. multiparous cows' peak milk yield) was lower than industry standards. Both traffic flow systems had fewer milking visits for primiparous cows compared with multiparous cows in early lactation. This lower milking frequency persisted until the 11th stage of lactation in free-flow systems. In guided-flow systems, primiparous cows were milked less frequently until the 5th stage of lactation, had similar milking frequency in the 6th stage of lactation, and were milked more frequently thereafter. Failures were greater for primiparous cows during all stages of lactation. However, the greatest differences were detected in the early stages of lactation. Primiparous cows had 0.067 more failures/cow per day on average than multiparous cows during wk 1 of lactation. For the remaining lactation stages, differences in failures ranged from 0.003 to 0.039. Refusals were less frequent (0.4 to 0.6/d) for primiparous cows during the first 2 wk of lactation, similar for wk 3 of lactation, and more frequent for the remaining lactation stages (0.10 to 0.14/d). Failures and refusals were only evaluated in free-flow systems. These findings appear to indicate a potential lagging performance for primiparous cows in early lactation as compared with multiparous cows. Additional investigation into improving the adaptation of primiparous cows to AMS in early lactation may be warranted.     

Health Care Requirements of Dairy Cattle. I. Response to Milk Yield Selection,

To measure direct response to single trait selection for milk yield and correlated response in health problems, two homologous base populations were formed by pairing 66 Holstein females by sire. Base populations and descendants were managed identically except for selection by milk yield. One base and lineage were mated with sires with highest predicted difference milk (selection group); other base and lineage were mated with average sires in 1964 (control group). Milk yield, supplemental labor, and veterinary and semen expense were recorded specific to each cow. Over 9 yr, 130 selection and 163 control cows were observed. Selection cows yielded more milk but with increase in labor and expense for health care. Estimates of labor for the selection group were greater for mammary, locomotion, and digestion categories and for expense in mammary, respiration, first insemination, and later insemination categories. Labor and expense for reproduction did not differ for genetic groups. Differences between groups in annual estimated labor and expense totaled $27.00. Extra income over feed cost more than compensated for greater health care and semen cost; however, the magnitude of the latter indicates a need for them to be considered when economically evaluating breeding programs where major emphasis is on milk yield.     

Responses of plasma glucose and nonesterified fatty acids to intravenous insulin tolerance tests in dairy cows during a 670-day lactation

The metabolic response of dairy cows undergoing an extended lactation to an insulin tolerance test (ITT) was investigated. Twelve multiparous Holstein-Friesian cows that calved in late winter in a pasture-based system were managed for a 670-d lactation by delaying rebreeding. Four 5-wk experimental periods commenced at approximately 73, 217, 422, and 520 d in milk (DIM). Cows were offered a diet of perennial ryegrass (73 and 422 DIM) or pasture hay and silage (217 and 520 DIM) supplemented with 1 kg dry matter (DM) of grain (control; CON) or 6 kg DM of grain (GRN). Daily energy intake was approximately 160 and 215 MJ of metabolizable energy/cow for CON and GRN, respectively. At all other times, cows were managed as a single herd and grazed pasture supplemented with grain to an estimated daily intake of 180 MJ of metabolizable energy/cow. Cows were fitted with a jugular catheter during the final week of each experimental period. An ITT using 0.12 IU of insulin/kg of body weight (BW) was conducted on each cow at approximately 100, 250, 460, and 560 DIM. Cows in the GRN treatment had greater milk yield, milk solids yield, and BW than cows in the CON treatment. Within treatment, individual cow responses to the ITT were highly variable. Plasma glucose and nonesterified fatty acid (NEFA) concentrations declined at all stages of lactation. The clearance rate of plasma glucose was slower before 300 DIM than after 300 DIM, which indicates greater inhibition of hepatic glucose synthesis and uptake of glucose by insulin-dependent tissues later in the lactation. The clearance rate, area under the curve, and recovery of plasma NEFA were greatest at 100 DIM, indicating greater responsiveness to the antilipolytic effect of insulin in early lactation, but also greater lipolytic responsiveness. The variation in response to the ITT was mostly a result of DIM rather than diet. However, the plasma NEFA response showed interactions between diet and DIM, indicating that energy intake may affect tissue responses to insulin. The responsiveness of peripheral tissues to insulin, primarily adipose tissue, changed throughout a 670-d lactation and contributed to a greater proportion of nutrients being partitioned to body reserves at the expense of milk yield as lactation progressed. Both stage of lactation and dietary intake have a role in the determination of whole-body and peripheral tissue responses to insulin; however, the exact mechanisms in control of this are unclear.     

Production performance of Holstein cows at 4 stages of lactation fed 4 dietary crude protein concentrations

Dairy cow responses to dietary crude protein (CP) may depend on stage of lactation. The primary objective of this study was to evaluate the effects of 4 concentrations of dietary CP on dry matter intake (DMI), production performance, net energy for lactation (NE_L) output in milk, feed efficiency (FE: milk NE_L/DMI), and nitrogen use efficiency (100 × milk protein-N/N intake) when fed to cows grouped as early, mid-early, mid-late, and late lactation. Our secondary objective was to determine the range of CP concentration at which production responses were not negatively affected across days in milk (DIM). Multiparous Holstein cows (n = 64) were stratified by DIM [initial average ± standard deviation: 86 ± 14.9 (early), 119 ± 10.0 (mid-early), 167 ± 22.2 (mid-late), and 239 ± 11.1 (late)] and then randomly assigned within DIM group to receive 1 of 4 total mixed rations containing 13.6, 15.2, 16.7, and 18.3% CP (dry matter basis) according to a 4 × 4 factorial arrangement of treatments. Cows were individually fed a covariate diet for 14 d, followed by 56 d of treatment diets. Milk yield and DMI were recorded daily and milk components were analyzed weekly for 2 consecutive days at 3 daily milkings. Data were analyzed using a categorical mixed-effect model to evaluate the effects of CP concentration and DIM using linear, quadratic, and cubic contrasts, and their interactions. Additionally, a mixed-effect cubic regression model was fit with DIM, dietary CP concentration, and their interaction as continuous independent variables. Dietary CP concentration deemed optimal across DIM was determined as the range of CP for which the dependent responses did not differ from the predicted maximum. With advancing stage of lactation, DMI, milk NE_L output, and FE decreased linearly (from 30.4 to 28.4 kg/d for DMI, from 33.2 to 23.3 Mcal/d for NE_L output, and from 1.09 to 0.82 Mcal milk NE_L/kg DMI for FE for early and late lactation cows, respectively). Responses to dietary CP concentration were linear, quadratic, and cubic with the greatest values observed when cows were fed the 16.7% CP diet across DIM (30.8 kg/d, 31.0 Mcal/d, and 1.01 Mcal/kg for DMI, milk NE_L output, and FE, respectively). There was an interaction between dietary CP concentration and stage of lactation for DMI, milk NE_L output, milk component yield, and FE, which was due to the decline in response to additional CP as lactation progressed. Compared with the 16.7% CP diet, feeding the 18.3% CP diet decreased milk NE_L 0.81 and 5.3 Mcal/d for early and late lactation cows, respectively, indicating that feeding a higher CP concentration in late lactation had a negative effect on cow performance. Nitrogen use efficiency declined linearly with increasing CP concentration and DIM. Regression analysis suggested that dietary CP ranging from 16.3 to 17.4% maintained production in early and mid-early lactation. However, dietary CP could be reduced to between 15.7 and 17.1% in late lactation. This research suggested that there are distinct ranges of dietary CP concentrations that maintain cow performance at each stage of lactation.     

Economic and environmental impact of four levels of concentrate supplementation in grazing dairy herds.

Low-cost, pasture-based forage systems are a viable management alternative for small to moderately sized dairy farms in the Northeast United States. A whole farm analysis was conducted to evaluate the potential long-term environmental impact and economic benefit of varying the level of concentrate supplementation on seasonal grazing dairies. A representative dairy farm was simulated with various production strategies over 25 yr of historical Pennsylvania weather using the Dairy Forage System Model. A representative grazing farm (81 ha) was simulated with four levels of daily concentrate supplementation: 1) no supplement, 2) 3 kg of DM/cow in early lactation, 3) 6 kg of DM/cow in early lactation, and 4) 9 kg of DM/cow in early lactation fed daily to the lactating cows to meet annual milk production levels of 5000, 6068, 6968, and 7700 kg/cow, respectively. These farm systems were then compared to an alfalfa- and corn-based confinement system on the same land base where total mixed rations were fed to maintain an annual milk production level of 9000 kg/cow. The five systems were simulated for three scenarios. In the first, total milk sold per farm (625,000 kg) was similar across all systems. In the second, cow numbers were held constant across all systems (100 mature cows), and total milk sold per farm varied. In the third, stocking rate was set so that forage consumed equaled forage production on the farm. Profitability increased as supplementation level increased in the grazing systems, but at a decreasing rate with each successive level of supplementation. At higher levels of supplementation, the grazing dairy farms showed greater profitability than the confinement systems. Economic risk or year-to-year variation also decreased as concentrate supplementation level increased. The grazing systems showed an environmental benefit compared with the confinement systems by decreasing nitrogen leaching losses. Concentrate supplementation of grazing lactating dairy cows provided an increase in profitability and a mixed impact on nutrient balance of the farm.     

Neglect of lactation stage leads to naive assessment of residual feed intake in dairy cattle

Residual feed intake (RFI) is a candidate trait for feed efficiency in dairy cattle. We investigated the influence of lactation stage on the effect of energy sinks in defining RFI and the genetic parameters for RFI across lactation stages for primiparous dairy cattle. Our analysis included 747 primiparous Holstein cows, each with recordings on dry matter intake (DMI), milk yield, milk composition, and body weight (BW) over 44 lactation weeks. For each individual cow, energy-corrected milk (ECM), metabolic BW (MBW), and change in BW (ΔBW) were calculated in each week of lactation and were taken as energy sinks when defining RFI. Two RFI models were considered in the analyses; RFI model [1] was a 1-step RFI model with constant partial regression coefficients of DMI on energy sinks (ECM, MBW, and ΔBW) over lactation. In RFI model [2], data from 44 lactation weeks were divided into 11 consecutive lactation periods of 4 wk in length. The RFI model [2] was identical to model [1] except that period-specific partial regressions of DMI on ECM, MBW, and ΔBW in each lactation period were allowed across lactation. We estimated genetic parameters for RFI across lactation by both models using a random regression method. Using RFI model [2], we estimated the period-specific effects of ECM, MBW, and ΔBW on DMI in all lactation periods. Based on results from RFI model [2], the partial regression coefficients of DMI on ECM, MBW, and ΔBW differed across lactation in RFI. Constant partial regression coefficients of DMI on energy sinks over lactation was not always sufficient to account for the effects across lactation and tended to give roughly average information from all period-specific effects. Heritability for RFI over 44 lactation weeks ranged from 0.10 to 0.29 in model [1] and from 0.10 to 0.23 in model [2]. Genetic variance and heritability estimates for RFI from model [2] tended to be slightly lower and more stable across lactation than those from model [1]. In both models, RFI was genetically different over lactation, especially between early and later lactation stages. Genetic correlation estimates for RFI between early and later lactation tended to be higher when using model [2] compared with model [1]. In conclusion, partial regression coefficients of DMI on energy sinks differed across lactation when modeling RFI. Neglect of lactation stage when defining RFI could affect the assessment of RFI and the estimation of genetic parameters for RFI across lactation.     

Associations among body condition score, body weight, somatic cell count, and clinical mastitis in seasonally calving dairy cattle

The objective of this study was to determine if an association existed among body condition score (BCS), body weight (BW), and udder health, as indicated by somatic cell score (SCS) and cases of clinical mastitis (CM). The data consisted of 2,635 lactations from Holstein-Friesian (n = 523) and Jersey (n = 374) cows in a seasonal calving pasture-based research herd between the years 1986 and 2000, inclusive. Increased BCS at calving was associated with reduced SCS in first- and second-parity cows, and greater SCS in cows of third parity or greater. This relationship persisted for most BCS traits throughout lactation. Body weight was positively associated with SCS, although the effect was greater in Jersey cows than in Holstein-Friesians. Increased BCS and BW loss in early lactation were associated with lower SCS and a reduced probability of a high test-day SCC. Body condition score was not significantly related to CM with the exception of a curvilinear relationship between the daily rate of BCS change to nadir and CM in early lactation. Several BW variables were positively associated with a greater likelihood of CM. Nevertheless, most associations with udder health lacked biological significance within the ranges of BCS and BW generally observed on-farm. Results are important in assuring the public that modern dairy systems, where cows are subjected to substantial amounts of BCS mobilization in early lactation, do not unduly compromise cow udder health.     

Modifying the lactation curve to improve lactation milk and persistency

Daily, stage and lactation estimated breeding values (EBV) and the shape of the lactation curve for each cow are controlled by a unique set of random (genetic) regression coefficients under a test day model, thus providing a basis for genetic improvement of these characteristics. Three selection procedures were developed for simultaneous improvement of total lactation milk and persistency: 1) index selection based on daily EBV, 2) index selection based on stage EBV, and 3) index selection based on random regression (RR) coefficients. A numerical example was given to demonstrate the computation of indexes based on stage EBV and based on RR coefficients. A conversion equation was derived to convert between genetic changes in EBV and RR coefficients. Index selection based on daily EBV would require the finding of 305 weighting factors for a lactation period of 305 d, making it impractical to determine the weighting factors on a daily basis. Alternatively, a lactation period was partitioned into a few stages to facilitate the construction of index selection based on stage EBV and index selection based on RR coefficients. These selection procedures make use of the annual genetic gains routinely computed in national genetic evaluations to restrict the genetic gains between different lactation stages to achieve the desired curve. When there is no prior knowledge of annual genetic gains, the proportional restriction of genetic gains between stages may be used. In summary, this study provides a simple means of modifying the lactation curve by manipulating genetic changes in different lactation stages at a pre-specified rate.     

Milk production and somatic cell counts: a cow-level analysis

The objectives of this study were to quantify the relationship between 24-h milk loss and lactation milk loss due to mastitis at the cow level. For the year 2009, individual cow test-day production records from 2,835 Ontario dairy herds were examined. Each record consisted of 24-h milk and component yields, stage of lactation (days in milk, DIM), somatic cell count (SCC, ×10(3) cells/mL) and parity. The modeling was completed in 2 stages. In stage 1, for each animal in the study, the estimated slope from a linear regression of 24-h milk yield (kg), adjusted for DIM, the quadratic effect of DIM, and the 24-h fat yield (kg) on ln(SCC) was determined. In stage 2, the estimated slope were modeled using a mixed model with a random component due to herd. The fixed effects included season (warm: May to September, cool: October to April), milk quartile class [MQ, determined by the rank of the 24-h average milk yield (kg) over a lactation within the herd] and parity. The estimated slopes from the mixed model analysis were used to estimate 24-h milk loss (kg) by comparing to a referent healthy animal with an SCC value of 100 (×10(3) cells/mL) or less. Lactation milk loss (kg) was then estimated by using estimated 24-h milk loss within lactation by means of a test-day interval method. Lactation average milk loss (kg) and SCC were also estimated. Lastly, lactation milk loss (kg) was modeled on the log scale using a mixed model, which included the random effect of herd and fixed effects, parity, and the linear and quadratic effect of the number of 24-h test days within a lactation where SCC exceeded 100 (×10(3) cells/mL; S100). The effect of SCC was significant with respect to 24-h milk loss (kg), increasing across parity and MQ. In general, first-parity animals in the first MQ (lower milk yield animals) were estimated to have 45% less milk loss than later parity animals. Milk losses were estimated to be 33% less for animals in first parity and MQ 2 through 4 than later parity animals in comparable MQ. Therefore, the relative level of milk production was found to be a significant risk factor for milk loss due to mastitis. For animals with 24-h SCC, values of 200 (×10(3) cells/mL), 24-h milk loss ranged from 0.35 to 1.09 kg; with 24-h SCC values of 2,000 (×10(3) cells/mL), milk loss ranged from 1.49 to 4.70 kg. Lactation milk loss (kg) increased significantly as lactation average SCC increased, ranging from 165 to 919 kg. The linear and quadratic effect of S100 was a significant risk factor for lactation milk loss (kg), where greatest losses occurred in lactations with 5 or more 24-h test days where SCC exceeded 100 (×10(3) cells/mL).     

Effect of season and stage of lactation on plasma insulin and glucose following glucose injection in Holstein cattle

Changes in plasma glucose and insulin concentrations following glucose injection in dairy cows (six per stage of lactation per season) were characterized during early, middle, and late lactation in winter, spring, and summer. Blood samples were collected 60, 45, 30, 20, 15, 10, 5, and 0 min (period 1) before glucose injection (.1 g/kg body weight) and at 5, 10, 15, 20, 30, 45, and 60 min (period 2) after injection. Plasma insulin concentrations were affected by season, period, season by period interaction, and time within period. Plasma glucose was affected by period, time within period, and stage of lactation by period interaction. Insulin was lowest in summer. Magnitude of insulin response to glucose was highest in spring. Both plasma glucose and insulin increased significantly 5 min following glucose injection. Peak glucose concentrations increased with advancing lactation. Results indicate alterations in glucose metabolism as well as changes in insulin sensitivity to glucose in various seasons and stages of lactation.     

Heritability of electronically recorded daily body weight and correlations with yield, dry matter intake, and body condition score

The objectives of this study were to estimate heritability for daily body weight (BW) and genetic correlations of daily BW with daily milk yield (MY), body condition score (BCS), dry matter intake, fat yield, and protein yield. The Afiweigh cow body weighing system records BW of every cow exiting the milking parlor. The Afiweigh system was installed at the Pennsylvania State University dairy herd in August 2001 and in July 2004 at the Virginia Tech dairy herd. The edited data included 202,143 daily BW and 290,930 daily MY observations from 575 Pennsylvania State University and 120 Virginia Tech Holstein cows. Data were initially analyzed with a series of 4-trait animal models, followed by random regression models. The models included fixed effects for age within lactation group, week of lactation, and herd-date. Random effects included animal, permanent environment, and error. The order of the polynomials for random animal and permanent environmental effects with the random regression model for daily BW was 4 and 6, respectively. Heritability estimates for daily BW ranged from 0.48 to 0.57 and were largest between 200 and 230 and smallest at 305 d of lactation. Genetic correlations were large between BW and BCS (0.60). The genetic correlation between daily BW and MY was −0.14 but was positive (0.24) after adjusting for BCS. Electronically recorded daily BW is highly heritable, and genetic evaluations of daily BW and BW change across the lactation could be used to select for less early lactation BW loss.     

Effect of amount and composition of feed given over three lactations on the performance of the dairy cow

Eighty-nine autumn-calving first calf and adult Friesian cows participated in an experiment on the effect of feeding over three lactations on milk production and live weight change. Fixed daily allowances of digestible energy (DE) formed two of the treatments (h, H; moderate, M). Diets of similar composition were used for both treatments and rations were weighed daily for each cow. The cows within these treatments were re-randomized to H or M at second and again at third parturition on experiment. A further treatment (ALF), applied continuously over three lactations, consisted of the M allowance of compound feed, weighed daily for each cow, plus as lib. weighed, group-fed forages. The ALF animals were randomized for each lactation into two groups both of which received the same total compound feed allowance over the first 26 weeks of lactation. For one group (Flat) equal amounts were given daily whilst for the other group (Step) the daily amount was decreased monthly. After week 26 equal rations were fed. Hay, maize silage and grass silage formed the forages in winter. Grass, cut for the H and M groups but grazed for the ALF group, provided the summer forage. Energy intakes covered some 80-110% of requirements. Yields of milk and of milk solids responded similarly for both parties. In the first experimental lactation, treatment H led to greater yields compared with M. H also led to smaller losses of live weight in early lactation, equal gains in mid lactation, and smaller gains in late lactation and the dry period, compared with M. Extension of H into a second lactation increased the advantage in milk and solids yields observed in the first lactation on experiment. Recovery of body reserves on treatment M continued. Treatment H in a second lactation on experiment after M in the first lactation led to even greater compensatory gains in live weight at the expense of milk production. There was no effect in the third lactation of experiment of treatments applied in the first lactation. Treatments H and M applied factorially over lactations 2 and 3 gave the same pattern of treatment effects as in lactations 1 and 2. Treatment ALF broadly supported the same milk yield and live weight change as treatment H but improved fat, protein and lactose yields. Within treatment ALF, Flat and Step distribution of compound led to equal performance. Multiple lactation effects of ALF equalled those of H. The effects on milk composition of H compared with M treatment were variable. In general an advantage accrued to ALF over M but without long term effects.     

Trend analysis and prediction of seasonal changes in milk composition from a pasture-based dairy research herd

The composition of seasonal pasture-produced milk is influenced by stage of lactation, animal genetics, and nutrition, which affects milk nutritional profile and processing characteristics. The objective was to study the effect of lactation stage (early, mid, and late lactation) and diet on milk composition in an Irish spring calving dairy research herd from 2012 to 2020 using principal component and predictive analytics. Crude protein, casein, fat, and solids increased from 2012 to 2020, whereas lactose concentration peaked in 2017, then decreased. Based on seasonal data from 2013 to 2016, forecasting models were successfully created to predict milk composition for 2017 to 2020. The diet of cows in this study is dependent upon grass growth rates across the milk production season, which in turn, are influenced by weather patterns, whereby extreme weather conditions (rainfall and temperature) were correlated with decreasing grass growth and increasing nonprotein nitrogen levels in milk. The study demonstrates a significant change in milk composition since 2012 and highlights the effect that seasonal changes such as weather and grass growth have on milk composition of pasture-based systems. The potential to forecast milk composition at different stages of lactation benefits processers by facilitating the optimization of in-process and supply logistics of dairy products.     

The hidden cost of disease: I. Impact of the first incidence of mastitis on production and economic indicators of primiparous dairy cows

Mastitis is a highly prevalent disease, which negatively affects cow performance, profitability, welfare, and longevity. The objectives of this study were (1) to quantify the impact of the first instance of mastitis, at different stages of lactation, on production and economic performance, and (2) to further quantify the impact of the first instance of mastitis when only cows that remain in the herd for at least 100 d in milk (DIM) and those that remain for 305 DIM are included in the analysis. A retrospective longitudinal study was conducted using data from existing animal health record files and Dairy Herd Improvement records. After editing based on selected inclusion criteria and completeness of health records, data consisted of records from first-lactation Holstein cows, from 120 herds, that calved for the first time between 2003 and 2014, inclusive. Mastitic cows were assigned to 1 of 4 groups based on when in the lactation the first event of mastitis occurred: transition (1–21 DIM), early lactation (22–100 DIM), mid lactation (101–200 DIM), or late lactation (201+ DIM). Mid-lactation and late-lactation mastitic cows were also stratified by cumulative milk yield before the mastitis event. Healthy cows (i.e., no recorded mastitis event) were randomly assigned for each lactation stage, with mid-lactation healthy and late-lactation healthy cows similarly stratified. Production performance (cumulative milk, fat, and protein yield) and economic performance [milk value, margin over feed cost (MOFC), and gross profit] were analyzed using a mixed model with herd as a random effect. Significant losses in cumulative milk yield (?382 to ?989 kg) and correspondingly lower fat and protein yields were found in mastitic cows, with transition and late-lactation mastitic cows having the highest losses. Drops in production translated to significant reductions in cumulative milk value (?Can$287 to ?Can$591; ?US$228 to ?US$470), MOFC (?Can$243 to ?Can$540; ?US$193 to ?US$429), and gross profit (?Can$649 to ?Can$908; ?US$516 to ?US$722) for mastitic cows at all stages. Differences between mastitic and healthy cows in the early lactation and transition stages remained for all variables in the 100-DIM analysis, but, aside from gross profit, were nonsignificant in the 305-DIM analysis. Gross profit accounted for all costs associated with mastitis and thus continued to be lower for mastitic cows at all stages, even in the 305-DIM analysis in which culled cows were omitted (?Can$485 to ?Can$979; ?US$386 to ?US$779). The research reflects the performance implications of mastitis, providing more information upon which the producer can make informed culling decisions and maximize both herd profitability and cow longevity.     

Estimation of genetic parameters for test-day records of dairy traits in a seasonal calving system

Variance components for test-day milk yield were estimated for primiparous animals in a seasonal calving system where 80% of calvings occur within a 5-mo period in the spring. The objective was to investigate if the variance components of milk production were affected by seasonality via month in milk and test month (TM). These effects were, therefore, fitted for both the permanent environment effect and additive genetic effect. Estimates of heritability (0.14-0.27) were found to be lowest during early and late lactation for all calving months. The peak in heritability (0.22-0.27) occurred later in lactation for animals that calved toward the end of the spring calving season. Genetic variance of test day milk yield for all calving months was found to be highest at the beginning of the lactation (2.23-3.36kg(2)), with a plateau toward the middle of the lactation. Genetic variance was found to be highest (2.98-3.36kg(2)) for animals calving early in the season. Genetic correlations between corresponding stages of lactation were strongest (0.99-1.00) between consecutive calving months. Genetic correlations were slightly weaker when intervals between calving months increased; however, they remained above 0.96 in all cases. Akaike's information criterion values from models both inclusive and exclusive of TM, suggest that the model exclusive of TM is the preferred model. Estimated breeding values of lactation milk yield from bulls with 20 or more daughters, predicted for a full 305-d lactation, were used to compare the model with the standard test-day model (i.e., exclusive of TM), based on DIM. Correlations were higher than 0.995 for milk yield (and higher than 0.930 for persistency) between models inclusive and exclusive of TM, suggesting that given the straightforward approach taken in the current study, an apparent benefit for including seasonality in the evaluation of test-day milk yield was not found; however, there may be benefits of including it in the estimation of persistency.     

Estimating milk, fat, and protein lactation curves with a test day model.

Test day models were used to estimate lactation curves for milk, fat, protein, fat percentage, and protein percentage and to study the influence of age, season, and herd productivity on Holstein lactation curves. Random effects of lactation within herd and fixed effects of herd test date were absorbed. Fixed effects of cow's age on test day and either DIM (57 divisions) by parity (1, 2, greater than or equal to 3) class or season of calving (winter or summer) by DIM by parity class were estimated. Lactation curves for yield traits derived from DIM solutions were flatter for first versus later lactation, even without addition of age effects. Differences between lactation curves for the two seasons were slight, suggesting that most observed seasonal differences are caused by seasonal productivity accounted for by herd test date effects. At peak, winter calving cows yielded slightly more milk of similar fat percentage but of lower protein percentage than those calving in summer. Data were also partitioned into nine subsets based on rolling herd milk and fat percentage. Lactation curves for yield traits, but not percentage traits, varied with rolling herd milk. Lactation curves for fat yield and percentage varied with rolling herd fat percentage.     

Effect of pregnancy on milk production and bodyweight from identical twin study

The energy requirements of the fetus through pregnancy have been previously investigated in several slaughter experiments, and many studies have attempted to estimate the effect of pregnancy on milk production. Data from 154 pasture-based dairy cows (77 twin pairs) were subjected to a retrospective analysis to determine the effect of pregnancy on milk production and body weight. A decline in milk yield from 126 d of pregnancy was observed in twins that were pregnant, but the decline was small and insignificant until 147 d of gestation (at 33 wk of lactation), after which pregnant cows produced less milk (0.8 kg/cow per day). Protein and fat concentration increased in pregnant cows from 77 and 133 d of gestation, respectively. The yield of milk fat and protein was not affected by pregnancy until 168 d of gestation, after which pregnant cows produced less milk fat (0.06 kg/cow per day) and milk protein (0.04 kg/cow per day) compared with their nonpregnant twins. Body weight was higher in pregnant twin cows after 90 d of gestation and continued to increase until the end of lactation (182 d of pregnancy). Fitted splines showed higher milk protein concentrations in pregnant cows throughout lactation, and milk protein yield was higher (20 g/cow per day) during the breeding season (between 12 to 17 wk of lactation) in pregnant twins. Higher milk yield and energy secreted in milk (net energy for lactation) were also found in the pregnant twins during the breeding season. Although pregnancy-related reductions in yields of milk, milk fat, and milk protein occurred after midgestation, overall effects of pregnancy on milk production in this pasture-based, seasonal calving system were small.     

Factors associated with milk processing characteristics predicted by mid-infrared spectroscopy in a large database of dairy cows

Despite milk processing characteristics being important quality traits, little is known about the factors underlying their variability, due primarily to the resources required to measure these characteristics in a sufficiently large population. Cow milk coagulation properties (rennet coagulation time, curd-firming time, curd firmness 30 and 60 min after rennet addition), heat coagulation time, casein micelle size, and pH were generated from available mid-infrared spectroscopy prediction models. The prediction models were applied to 136,807 spectra collected from 9,824 Irish dairy cows from research and commercial herds. Sources of variation were investigated using linear mixed models that included the fixed effects of calendar month of test; milking time in the day; linear regressions on the proportion of Friesian, Jersey, Montbéliarde, Norwegian Red, and “other” breeds in the cow; coefficients of heterosis and of recombination loss; parity; stage of lactation; and the 2-way interaction parity × stage of lactation. Within- and across-parity cow effects, contemporary group, and a residual term were also included as random effects in the model. Supplementary analyses considered the inclusion of either test-day milk yield or milk protein concentration as fixed-effects covariates in the multiple regression models. Milk coagulation properties were most favorable (i.e., short rennet coagulation time and strong curd firmness) for cheese manufacturing in early lactation, concurrent with the lowest values of both pH and casein micelle size. Milk coagulation properties and pH deteriorated in mid lactation but improved toward the end of lactation. In direct contrast, heat coagulation time was more favorable in mid lactation and less suitable (i.e., shorter) for high temperature treatments in both early and late lactation. Relative to multiparous cows, primiparous cows, on average, yielded milk with shorter rennet coagulation time and longer heat coagulation time. Milk from the evening milking session had shorter rennet coagulation time and greater curd firmness, as well as lower heat coagulation time and lower pH compared with milk from the morning session. Jersey cows, on average, yielded milk more suitable for cheese production rather than for milk powder production. When protein concentration was included in the model, the improvement of milk coagulation properties toward the end of lactation was no longer apparent. Results from the present study may aid in decision-making for milk manufacturing, especially in countries characterized by a seasonal supply of fresh milk.     

Cow characteristics associated with the variation in number of contacts between dairy cows

In modern freestall barns where large groups of cows are housed together, the behavior displayed by herd mates can influence the welfare and production of other individuals. Therefore, understanding social interactions in groups of dairy cows is important to enhance herd management and optimize the outcomes of both animal health and welfare in the future. Many factors can affect the number of social contacts in a group. This study aimed to identify which characteristics of a cow are associated with the number of contacts it has with other group members in 2 different functional areas (feeding and resting area) to increase our understanding of the social behavior of dairy cows. Inside 2 herds housed in freestall barns with around 200 lactating cows each, cow positions were recorded with an ultra-wideband real-time location system collecting all cows' positions every second over 2 wk. Using the positioning data of the cows, we quantified the number of contacts between them, assuming that cows spending time in proximity to one another (within a distance of 2.5 m for at least 10 min per day) were interacting socially. We documented in which barn areas these interactions occurred and used linear mixed models to investigate if lactation stage, parity, breed, pregnancy status, estrus, udder health, and claw health affect the number of contacts. We found variation in the number of contacts a cow had between individuals in both functional areas. Cows in later lactation had more contacts in the feeding area than cows in early lactation. Furthermore, in one herd, higher parity cows had fewer contacts in the feeding area than first parity cows, and in the other herd, cows in third parity or higher had more contacts in the resting area. This study indicates that cow characteristics such as parity and days in milk are associated with the number of contacts a cow has daily to its herd mates and provides useful information for further research on social interactions of dairy cows.