Effect of dry period length on milk yield over multiple lactations

Shortening or omitting the dry period (DP) can improve the energy balance of dairy cows in early lactation through a decrease in milk yield after calving. Little is known about the effect of a short or no DP on milk yield over multiple lactations. Our objectives were (1) to assess the effect of DP length over multiple lactations on milk yield, and (2) to assess if the prediction of milk yield in response to DP length could be improved by including individual cow characteristics before calving. Lactation data (2007 to 2015) of 16 Dutch dairy farms that apply no or short DP were used to compute cumulative milk yield in the 60 d before calving (additional yield) and in the 305 d after calving (305-d yield), and the mean daily yield over the interval from 60 d before calving to 60 d before next calving (effective lactation yield). The DP categories were no (0 to 2 wk), short (3 to 5 wk), standard (6 to 8 wk), and long (9 to 12 wk). The effect of current DP and previous DP on yields was analyzed with mixed models (n = 1,420 lactations). The highest effective lactation yield of fat- and protein-corrected milk (FPCM) was observed for cows with a standard current DP (27.6 kg per day); a daily decrease was observed of 0.6 kg for a long DP, 1.0 kg for a short DP, and 2.0 kg for no DP. Previous DP did not significantly affect the effective lactation yield. Thus, cows can be managed with short or no DP over consecutive lactations without a change in quantity of milk losses. Cows that received no DP for consecutive lactations had a lower additional yield before calving (?172 kg of FPCM), but a higher 305-d yield (+560 kg of FPCM), compared with cows that received no DP for the first time. This could lessen the improvement of the energy balance in early lactation when no DP is applied a second time compared with the first time. For the second objective, a basic model was explored to predict effective lactation yield based on parity, DP length, and first-parity 305-d yield (n = 2,866 lactations). The basic model was subsequently extended with data about recent yield, days open, and somatic cell count. Extending the model reduced the error of individual predictions by only 6%. Therefore, the basic model seems sufficient to predict the effect of DP length on effective lactation yield. Other individual cow characteristics can still be relevant, however, to make a practical and tailored decision about DP length.     

Association of Herd Average Genetic and Environmental Milk Yield with Dairy Herd Improvement Variables

Two hundred fifteen Virginia Holstein herds were used to evaluate the relationship of genetic and environmental herd averages for mature equivalent milk yield with DHIA measures from 1976 to 1980. Herd breeding value was the average of twice the USDA Cow Index for individual cows. Means (±SD) were +243 kg (±107 kg) for genetic value and +685 kg (±757 kg) for environmental value. Herds progressed 31 kg/yr genetically and 122 kg/yr environmentally. Regressions of DHIA variables on genetic and environmental averages were within herd and year. Holding herd and year constant at +250 kg genetic milk, a 600 kg increase in environmental milk resulted in increases of 559 kg herd average milk, 19 kg fat, 13 kg genetic SD, and .08 services per conception and decreases of .64 d dry, 1.6 d open, .48 mo age at first lactation, and .05 mo calving interval. At +700 kg environmental milk, a 150 kg increase in genetic milk was associated with increases of 134 kg milk, 1.9 kg fat, and .05 services per conception; and decreases of .59 d dry, 4.8 d open, .65 mo age at first lactation, and .05 mo calving interval. Within herds, environmental improvement tended to be associated with improvement in reproductive measures, and genetic improvement was not detrimental to most measures of herd performance.     

Comparison of Culling Rates,Reasons for Disposal,and Yields for Registered and Grade Holstein Cattle

Survival of cows was investigated using data from the USDA files for daughters of 199 Holstein sires with at least 500 progeny each. Records included cows that first calved from 1965 to 1980 (n = 1,145,616). A smaller subset of data (n = 199,982) was summarized for age at first and last record, termination codes, Modified contemporary deviations of milk yield, and calving intervals. Grade cows leaving the herd were more likely sold for low production and less likely sold for dairy. Modified contemporary deviations in first lactation averaged 339 kg for grade cows and 331 kg for registered cows. Cows with only one record had lower yields in first lactation by 589 kg (grade) and 506 kg (registered). Compared with cows with more than two lactations, cows with two records had lower yields in first lactation by 199 kg (grade) and 259 kg (registered) and longer first calving intervals by 3.5 d (grade) and 5.0 d (registered). Grade and registered daughters of these sires left herds at different rates and for different reasons.     

Forage Growth and Performance of Grazing Dairy Cows Supplemented with Concentrate and Chopped or Long Hay

Holstein and Brown Swiss cows were in three groups of eight in a 3 × 3 Latin square design with 4-wk periods. Cows averaged 88 d in lactation at start of trial. All cows simultaneously grazed grass and clover pastures on a rotational basis. Supplement treatments were concentrate (A), concentrate with 10% added chopped hay (B), and concentrate plus 1 kg long hay/cow daily (C). Concentrate was offered at 1 kg/3 kg 4% fat-corrected milk to cows on A and C, and 1 kg/2.7 kg to those on B. Forage growth, amounts available for grazing, and average dry matter intake were measured by clipping subsamples prior to and after each grazing and by use of cages placed in the field.Milk yields and milk fat percentages were 27.1, 3.34; 27.9, 3.32; and 28.3, 3.20 for treatments A, B, and C, respectively. Differences between A and C were significant. Milk fat percentage decreased moderately when cows first went to pasture.There were no treatment differences in fat yield, milk protein percentage, yield of fat-corrected milk, rumen fluid composition, or body weight gain.Available forage per cow exceeded 22 kg dry matter/cow daily except during one 10-d period toward the end of the trial when it amounted to 16.6 kg. Intake of dry matter from pasturage, measured by the sward cutting technique, averaged 14.5 kg./cow daily over the 12 wk.     

Short communication: Metritis affects milk production and cull rate of Holstein multiparous and primiparous dairy cows differently

Metritis, a common transition disease in dairy cows, reduces milk production during the duration of the disease. To our knowledge, no work has investigated the short-term effects of metritis on feed intake and the long-term consequences on milk yield and risk of culling. The objectives were to determine the effect of metritis on 305-d lactation curves, dry matter intake (DMI), reproduction, and the probability of being culled. Identifying differences in response to metritis between primiparous and multiparous cows was of interest. Milk records were collected twice daily from Holstein cows diagnosed with puerperal metritis (11 primiparous and 16 multiparous) or classified as healthy (14 primiparous and 43 multiparous) during the first 3 wk after calving. Metritic cows were treated at the discretion of the herd veterinarian. Lactation curves of healthy and metritic cows were compared using a mixed model with a Wilmink function. Differences in DMI, days open, and the number of services per conception were assessed using mixed models. The probabilities that cows with and without metritis were not bred, were bred but never confirmed pregnant, or were culled were compared using Fisher's exact tests. Primiparous and multiparous animals were assessed separately. Multiparous cows with metritis produced less milk (35.1 ± 1.5 vs. 39.2 ± 1.0 kg/d), ate less during the 3 wk after calving (12.2 ± 1.2 vs.14.0 ± 0.8 kg/d), and were more likely to be culled (50.0%) than healthy cows (20.9%). The decision to cull was likely influenced by the lower milk yield in early lactation as a result of metritis; the decision to cull was made early, as 7 of the 8 culled metritic cows were not bred. No differences were found in any measurement between primiparous cows with and without metritis. These results indicate that metritis in early lactation has long-term effects on multiparous cows but not primiparous cows.     

Sodium salicylate treatment in early lactation increases whole-lactation milk and milk fat yield in mature dairy cows

Multiple lines of inquiry have suggested that a high degree of inflammation in early lactation cows is associated with low productivity and increased disease incidence. In addition, some small studies have suggested that milk production increases in response to antiinflammatory treatment in the first week of lactation. Our objective was to determine if administration of sodium salicylate (SS), a nonsteroidal antiinflammatory drug (NSAID), in the first week of lactation changes whole-lactation productivity and retention in the herd. At calving, 78 cows [n = 39 primiparous (1P); n = 24 second parity (2P); n = 15 third parity or greater (3P)] were alternately assigned to either control (CON) or SS treatments for 7 d postpartum. Sodium salicylate treatment was administered via individual water bowls at a concentration of 1.95 g/L, delivering a mean of 123.3 ± 5.5 g of salicylate/d during the 7-d treatment. For the first 21 d of lactation, dry matter intake, water intake, milk yield, and health were monitored daily, and milk samples were collected twice weekly for milk component analysis. Monthly milk yield and component testing through the rest of the lactation provided data to assess long-term responses, and the effects of treatment on the risk of leaving the herd and on 305-d milk, fat, and protein yields were assessed. During the first 21 d of lactation, we observed no differences in morbidity, except for increased risk of metritis in 3P SS cows. Treatment interacted with parity to influence both 305-d milk and milk fat yields, and a tendency for an interaction was detected for 305-d milk protein yield. Milk yield was 2,469 ± 646 kg greater over the lactation in 3P SS cows compared with 3P CON cows (21% increase) and tended to decrease by 8% in 1P cows treated with SS; no effects were detected in 2P cows. Furthermore, 3P SS cows produced 130 ± 23 kg more milk fat over the lactation (30% increase), with no effects detected for 1P or 2P. Treatment with SS tended to increase 305-d milk protein yield in 3P cows by 14%, with no effects in 1P or 2P cows. A tendency for a treatment × parity interaction was also observed for the risk of leaving the herd. First-parity cows treated with SS tended to have greater risk of leaving the herd than controls (30 vs. 6% risk); however, treatment did not alter herd retention in 2P or 3P groups, and SS had no effect on the risk of leaving the herd overall. Results indicate that SS has long-term effects on lactation of mature dairy cows, particularly on fat yield, but may have negative effects for primiparous cows.     

Relative Efficiency of Selection Methods for Profit in Dairy Cows

Selection singly on milk yield and calculated profitability traits, selection indexes, and regression indexes were compared for the relative gains in expected profit to 72 mo of age or life time profit. Indexes consisted of five traits of the first lactation: milk, fat percent, days in milk, number of breedings, and age at first calving. The study was on 1806 Holstein cows sired by 404 bulls in 38 California herds. Genetic gain in total profit was 13 to 14% greater when selection was on estimated profit to 41 mo than on milk yield to 305 days in the first lactation. Selection on traits of estimated profit on three bases, to 305 days in first lactation, to end of first lactation, and to 41 mo of age was 2 to 14% more efficient for genetic gain in total profit than selection on corresponding traits of milk yield or selection indexes. Regression indexes were 3 to 19% more efficient than selection indexes for predicting subsequent cumulative profit. In contrast, selection indexes were 6 to 20% more efficient than regression indexes for genetic gain in total profit. Heritabilities for estimated profit and traits of milk yield in the first lactation ranged from .26 to .49 for cows with two or more calvings. Heritabilities for profit to end of first lactation and to 41 mo of age exceeded comparable milk yield traits by 15 to 27%. The economic value of a 1-mo decrease in age at first calving was equivalent to an increase of 138 kg milk yield to the end of the first lactation for gain in total profit to 72 mo of age. Similarly, the genetic effects, or relative selection value, of a 1-mo decrease in age at first calving is valued at approximately 471 kg milk.     

Varying Protein Content and Nitrogen Solubility for Pluriparous,Lactating Holstein Cows: Lactation Performance and Profitability

Effects on total lactation performance of varying ration crude protein (15.3 vs. 13.6% of dry matter) and nitrogen solubility (35 vs. 45% of total nitrogen) in early lactation was studied using 57 pluriparous Holstein cows. Grain was fed according to production so as to minimize change in body weight throughout lactation. Forages high in nitrogen solubility, corn and grass silages, were fed free-choice. Percent concentrate in ration dry matter was highest (64%) 5 to 8 wk postpartum and lowest (3%) 33 to 44 wk postpartum. Protein and nitrogen solubility were varied by formulating four protein supplements fed as 10% of the grain allocation, so differences in treatments applied narrowed as lactation progressed. Cows fed the medium-protein diets produced 196 kg more milk than those receiving low-protein diets, but their peak daily milk yield was only .6 kg higher. Cows receiving rations with reduced nitrogen solubility produced 347 kg more milk than those fed the higher solubility diets, but their peak daily milk yield was 1.0 kg lower. Income above fed cost for the lactation was highest and postpartum loss in body weight was least for cows receiving medium-protein and low-solubility rations in early lactation, but no differences were significant. Both milk yield (38.3 to 40.6 kg) and total dry matter intake (3.74 to 3.91% body weight) means were maximum 6 to 7 wk postpartum, but lactation performance was not proportional to peak milk yield. When cows are fed to minimize body fat mobilization, response to increased protein in the diet is small. Reducing nitrogen solubility of silage-based diets increased milk produced per unit grain fed. There were no adverse effects of treatments on breeding efficiency or herd health.     

Effects of continuous milking during the dry period or once daily milking in the first 4 weeks of lactation on metabolism and productivity of dairy cows

The objective was to compare the effects of 3 management systems in high-yielding dairy cows on metabolic profiles and milk production. Thirty-six multiparous Brown Swiss cows were randomly assigned to 1 of 3 treatment groups (n = 12 cows/group): the control (C) group, in which cows were dried off 56 d before calving and milked twice daily throughout next lactation (305 d); the once daily milking (ODM) group, in which cows were dried off 56 d before calving and milked once daily for the first 4 wk of lactation and twice daily for the remaining lactation; and the continuous milking (CM) group, in which cows were milked twice daily until calving and also during the subsequent lactation. Serum glucose concentrations decreased between wk 1 and 4 exclusively in C cows. Serum concentrations of NEFA and BHBA in the first 4 wk of lactation were highest in C cows compared with ODM and CM cows. Decreased backfat thickness during early lactation and reduction of body condition score were markedly more pronounced in C cows compared with ODM and CM cows. Mean lactational milk yield of C cows [11,310 ± 601 kg of energy-corrected milk (ECM)/305 d] was approximately 16% higher compared with ODM cows (9,531 ± 477 kg of ECM/305 d) and CM cows (9,447 ± 310 kg of ECM/305 d). The lactation curve of CM cows compared with C cows was characterized by a similar time of peak yield (wk 3), a reduced peak yield, and no obvious differences in persistency. Mean percentage of milk protein was significantly higher for CM cows (3.91%) compared with C cows (3.52%). In contrast, once daily milking was accompanied by a reduced and significantly delayed peak yield (wk 8) compared with the control treatment, whereas persistency was better and milk protein (3.79%) was higher in ODM cows than in C cows. In conclusion, continuous milking and once daily milking, targeting the interval before or after calving, respectively, substantially reduced the metabolic challenge of fresh cows and improved milk protein percentage. Continuous milking and once daily milking increased milk protein percentage markedly; furthermore, once daily milking during the first 4 wk of lactation improved the lactation curve.     

Temporary alterations to postpartum milking frequency affect whole-lactation milk production and the energy status of pasture-grazed dairy cows

This study investigated the immediate and long-term effects of temporary alterations to postpartum milking frequency (MF) on milk production, body condition score (BCS), and indicators of energy status in pasture-grazed cows supplemented with concentrates. Multiparous Holstein-Friesian cows (n = 150) were randomly assigned to 1 of 5 groups at calving: milked twice daily (2×) throughout lactation (control), or milked either once daily (1×) or 3 times daily (3×) for 3 or 6 wk immediately postpartum, and then 2× for the remainder of lactation. During wk 1 to 3 postpartum, cows milked 1× produced 15% less milk and 17% less energy-corrected milk (ECM) than cows milked 2×. This immediate production loss increased to 20% less milk and 22% less ECM during wk 4 to 6 postpartum for cows that remained on 1× milking; these animals also produced less than 1× cows switched to 2× milking after 3 wk. During wk 8 to 32, when all cows were milked 2×, those previously milked 1× had sustained reductions in milk (−6%) and ECM (−8%) yields, which were not affected by the duration of reduced postpartum MF. In contrast, cows milked 3× postpartum had 7% greater milk yields during wk 1 to 6 compared with 2× controls, irrespective of the duration of increased MF. Milk yields also remained numerically greater (+5%) during wk 8 to 32 in cows previously milked 3×. Nevertheless, yields of ECM were not increased by 3× milking, because of lower milk fat and protein contents that persisted for the rest of lactation. In addition, indicators of cow energy status reflected an increasing state of negative energy balance with increasing MF. Cows milked 1× postpartum had greater plasma glucose and lower plasma nonesterified fatty acid concentrations during the reduced MF, and plasma glucose remained lower for 2 wk after cows had switched to 2× milking. Moreover, BCS was improved relative to 2× controls from wk 5 to 6. In contrast, cows milked 3× had lower plasma glucose concentrations, greater plasma nonesterified fatty acid concentrations, and greater BCS loss during wk 1 to 3; however, greater body fat mobilization was not sustained, indicating that additional energy supplements may be required to achieve better milk production responses. In conclusion, temporary 1× milking had lactation-long negative effects on milk and milk component yields but improved cow energy status and BCS, whereas temporary 3× milking immediately increased milk yield but did not improve milk fat and protein yields in pasture-grazed cows.     

Milk Somatic Cells and Lactation in Small Ruminants

The milk somatic cell count (MSCC) is the basis for abnormal milk control programs. The current legal MSCC limit for bulk tank milk for goats and sheep in the United States is 1000 and 750 × 10³/ml, respectively. Milk somatic cell counts for goats are higher than MSCC for cows and sheep. The MSCC for goats free from intramammary infection (IMI) range from 270 to 2,000 × 10³/ml. Cell counts for sheep are similar to cows and range from 10 to 200 × 10³/ml. Neutro-phils comprise the major cell type in milk from uninfected goats and constitute 45 to 74% of the MSCC, compared with 2 to 28% for sheep and cows. The macrophage is the major cell type in milk from cows and sheep. Milk secretion in goats and sheep is largely apocrine in nature and cytoplasmic particles, similar in size to milk somatic cells, are normal constituents of their milk. Concentrations of cytoplasmic particles in sheep milk average 15 × 10³/ml, while goat milk averages 150 × 10³/ml. Therefore, to obtain accurate MSCC for goats, only cell counting procedures specific for DNA should be used. While IMI significantly increases MSCC for goats and sheep, noninfectious factors such as parity, stage of lactation, season and milk yield have been related to increased MSCC. An increase in MSCC for goats has been shown to decrease milk and fat yields. Intramammary infusion of antibiotics at dry-off and postmilking teat dipping in goats decreased the rate of new IMI and MSCC. Thus, mastitis control practices shown to be efficacious in cows are also effective in goats.     

Cow characteristics and their association with production performance with different dry period lengths

Shortening or omitting the dry period (DP) has been proposed as a management strategy to improve energy balance of dairy cows in early lactation. Both shortening and complete omission of the DP reduces milk production in the subsequent lactation compared with a conventional DP length of 60 d. Some cows have less milk production loss than other cows after applying no DP or a short DP. The aim of this study is to evaluate which cow characteristics are associated with the amount of milk production losses following no DP or a short DP (30 d). Daily production information from the lactation before and after the DP was available from 161 dairy cows (54 cows with a 0-d DP, 51 cows with a 30-d DP, and 56 cows with a 60-d DP) from a research herd. Daily production (milk, fat, and protein) until 305 d in milk was estimated for all cows. Subsequently, total fat- and protein-corrected milk yield from 60 d before the expected calving date until 305 d in the following lactation (FPCM_total) was estimated. A statistical analysis was performed to evaluate which cow characteristics were associated with limited or no production losses following no DP or a short DP, compared with a conventional DP length of 60 d. Average FPCM_total was 9,341, 10,499, and 10,795 kg for cows with no DP, a 30-d DP, and a 60-d DP, respectively. The cow characteristics parity, daily milk production at 12 wk before the expected calving date, and reduction in daily milk production between 16 and 12 wk before the expected calving date were associated with production loss due to a short (30 d) or no DP. Compared with 60 d DP, multiparous cows had less production loss (987 kg) following no DP than primiparous cows (2,132 kg). The difference in FPCM_total between the 3 DP groups was largest for cows with a low milk production (e.g., 10 kg/d) at 12 wk before the expected calving date. The greater the reduction in milk production between 16 and 12 wk before the expected calving date, the larger the difference in FPCM_total between the 3 DP groups. The difference in FPCM_total between cows with no DP and 60 d DP at a reduction in milk production between 16 and 12 wk of 10% was 665 kg, whereas this difference was 1,138 kg at a reduction of 70%. The cow characteristics found can be used to select cows for specific DP lengths in a decision-support model to support the farmer on the economic optimal DP length for each individual cow. Output of such a decision-support model can be, for instance, to advise a 30-d DP for multiparous cows with high milk production (e.g., 25 kg/d) at 12 wk before the expected calving date.     

Genetic relationship between culling, milk production, fertility, and health traits in Norwegian red cows

First-lactation records on 836,452 daughters of 3,064 Norwegian Red sires were used to examine associations between culling in first lactation and 305-d protein yield, susceptibility to clinical mastitis, lactation mean somatic cell score (SCS), nonreturn rate within 56 d in heifers and primiparous cows, and interval from calving to first insemination. A Bayesian multivariate threshold-linear model was used for analysis. Posterior mean of heritability of liability to culling of primiparous cows was 0.04. The posterior means of the genetic correlations between culling and the other traits were −0.41 to 305-d protein yield, 0.20 to lactation mean SCS, 0.36 to clinical mastitis, 0.15 to interval from calving to first insemination, −0.11 to 56-d nonreturn as heifer, and −0.04 to 56-d nonreturn as primiparous cow. As much as 66% of the genetic variation in culling was explained by genetic variation in protein yield, clinical mastitis, interval of calving to first insemination, and 56-d nonreturn in heifers, whereas contribution from the SCS and 56-d nonreturn as primiparous cow was negligible, after taking the other traits into account. This implies that for breeds selected for a broad breeding goal, including functional traits such as health and fertility, most of the genetic variation in culling will probably be covered by other traits in the breeding goal. However, in populations where data on health and fertility is scarce or not available at all, selection against early culling may be useful in indirect selection for improved health and fertility. Regression of average sire posterior mean on birth-year of the sire indicate a genetic change equivalent to an annual decrease of the probability of culling in first-lactation Norwegian Red cattle by 0.2 percentage units. This genetic improvement is most likely a result of simultaneous selection for improved milk yield, health, and fertility over the last decades.     

Effect of Feeding Frequency on Diurnal Dry Matter and Water Consumption,Liquid Dilution Rate,and Milk Yield in First Lactation

Four ruminally cannulated cows in first lactation (50 days postpartum) were assigned randomly to a 4 × 4 Latin square with the following feeding frequencies of the same total mixed ration: one, two, four, and eight times a day. Dry matter intake, water consumption, and ruminal pH were recorded hourly during 4-d collection (10-d adaptation between periods, Experiment 1). In Experiment 2, 30 animals were blocked by milk production on wk 4 postpartum and assigned to feeding one or four times a day through wk 19 postpartum. Individual feed consumption and milk production were recorded daily.Hourly consumption patterns of dry matter and water were variable over 24 h; once daily feeding tended to be more variable than other frequencies. Cows fed four times a day had higher ruminal liquid dilution rates than those fed eight times; feeding once and twice a day was not different from either. In Experiment 2, frequency of feeding total mixed ration had no significant influence on dry matter intake or milk yield; however, cows fed four times a day exhibited a consistent weekly tendency to be lower in dry matter intake and higher in milk yield than those fed once daily. Efficiency of fat-corrected milk production was slightly higher for cows fed four times than for those fed once daily.     

Effect of Business and Dairy Herd Management Practices on the Variable Cost of Producing Milk

A Cobb-Douglas-type function was used to study the effect of several business and dairy herd factors on the variable cost of production per 45.4 kg milk in 410 New York State dairy herds. The model used was a recursive system of equations with milk sold per cow per year and total variable cost associated with milk production as endogenous variables. Solutions were obtained using the two-stage least squares procedure. Relationships were essentially linear between variable production cost per 45.4 kg of milk and average age of the herd, percent days in milk, average age at first calving, average body weight, average days dry, fat test, and kilograms of concentrates fed. For average days open, herd size, number of cows per worker, tillable acres per cow, percent cows leaving the herd, and capital investment per cow, relationships were curvilinear. A lower variable production cost was associated with those herds having fewer days open, younger age at first calving, higher percent days in milk, lower percent cows leaving the herd, and heavier cows. Average body weight of all cows, average days dry, cows per worker, and tillable acres per cow had very little relationship with the variable production cost.     

Cow-level factors associated with subclinical hypocalcemia at calving in multiparous Jersey cows

The objective of our study was to identify cow-level factors associated with subclinical hypocalcemia at calving (SCH) in multiparous Jersey cows. A total of 598 Jersey and 218 Jersey × Holstein crossbreed cows from 2 commercial dairy herds were enrolled in a retrospective cohort study. Blood samples to determine total Ca concentration were collected from the coccygeal vessels at 3 h 19 min (±2 h 33 min) after calving. We used 2 serum Ca concentration thresholds to define SCH: <2.00 mmol/L (SCH-2.00) and <2.12 mmol/L (SCH-2.12). We evaluated the association of cow-level factors with SCH with multivariable Poisson regression models. Variables evaluated for association with SCH were herd; parity (2, 3, and ≥4); breed; previous lactation length and 305-d mature-equivalent milk yield; previous lactation first test milk yield and last test somatic cell count; lengths of calving interval, gestation, dry, and close-up periods; body condition and locomotion scores at calving; calving ease; and calf sex for singletons. We categorized continuous variables into quartiles (≤25th percentile, interquartile range and ≥75th percentile). The prevalence of SCH among Jersey cows was 40 (SCH-2.00) and 64% (SCH-2.12). Jersey cows of higher parity had greater risk of SCH-2.00 and SCH-2.12. The risk of SCH-2.12 was higher after birthing male calves. We also found a tendency for previous lactation length and previous lactation 305-d mature-equivalent milk yield effect to affect risk of SCH-2.12. The risk of SCH-2.12 was lower for cows that had a previous lactation length shorter than the 25th percentile compared with cows that had a previous lactation length within the interquartile range. The risk of SCH-2.12 was higher for cows that had a previous lactation 305-d mature-equivalent milk yield below the 25th percentile compared with cows that had a previous lactation 305-d mature-equivalent milk yield above the 75th percentile. Also, Jersey × Holstein crossbreed was associated with increased risk of SCH-2.00. In the multivariable analysis, we observed no association between SCH and previous lactation first test milk yield; last test somatic cell count; lengths of calving interval, gestation, dry, and close-up periods; body condition and locomotion scores at calving; and calving ease. Our study identified parity, breed, calf sex, previous lactation length, and previous lactation 305-d mature-equivalent milk yield as cow-level factors associated with SCH in multiparous Jersey cows.     

Effect of days to conception in the previous lactation on the risk of death and live culling around calving

The objective was to quantify the effect of days to conception (days open) in the previous parity on the risk of death and live culling (excluding the disposal reasons “dairy purposes” and “death”) in the proximity of a subsequent calving in Holstein cows enrolled in the Dairy Herd Improvement program. After edits, 2,075,834 observations of cows calving between 2001 and 2007 in herds located in 36 US states primarily east of the Mississippi river were available. The period at risk included the time between 14 d before expected calving to 60 d after calving. Days open were categorized in 6 periods: 0 to 45 d, 46 to 90 d, 91 to 150 d, 151 to 210 d, 211 to 300 d, and 301 to 600 d after calving in the previous parity. Other variables of interest included parity, length of the dry period before calving, relative last test-day milk yield before dry off before calving, season of calving, and the cow's relative 305-d mature equivalent (305ME) milk yield before calving. Control variables were calving year, herd size, and relative herd 305ME milk yield. All variables were categorized. Generalized mixed models were used and included herd as random effect. Interactions between days open and the variables of interest were included in the models. Least squares means for the risk of death between −14 and 60 d after calving were 2.5, 2.5, 2.9, 3.6, 4.4, and 5.8% for increasing categories of days open. Similarly, for the same categories, least squares means for the risk of live culling were 4.5, 5.0, 5.4, 6.1, 6.9, and 8.1%. The effect of days open on the risk of death was slightly greater for third-parity cows, for long dry periods, for cows with low test-day milk yield before dry off before calving, for spring calvings, and for intermediate relative 305ME milk yield before calving. Similar trends for these interactions were found for the risk of live culling, except for relative 305ME milk yield before calving, where the effect of days open was more pronounced for high-producing cows. In conclusion, increased days open in the previous parity were associated with a greater risk of death and live culling around calving.     

Relationship between somatic cell count and milk yield in different stages of lactation

The association between somatic cell count (SCC) and daily milk yield in different stages of lactation was investigated in cows free of clinical mastitis (CM). Data were recorded between 1989 and 2004 in a research herd, and consisted of weekly test-day (TD) records from 1,155 lactations of Swedish Holstein and Swedish Red cows. The main data set (data set A) containing 36,117 records excluded TD affected by CM. In this data set, the geometric mean SCC was 55,000 and 95,000 cells/mL in primiparous and multiparous cows, respectively. A subset of data set A (data set B), containing 27,753 records excluding all TD sampled in lactations affected by CM, was created to investigate the effect of subclinical mastitis (SCM) in lactations free of CM. Daily milk yields were analyzed using a mixed linear model with lactation stage; linear, quadratic and cubic regressions of log₂-transformed and centered SCC nested within lactation stage; weeks in lactation; TD season; parity; breed; pregnancy status; year-season of calving; calving, reproductive, metabolic and claw disorders; and housing system as fixed effects. A random regression was included to further improve the modeling of the lactation curve. Primiparous and multiparous cows were analyzed separately. The magnitude of daily milk loss associated with increased SCC depended on stage of lactation and parity, and was most extensive in late lactation irrespective of parity. In data set A, daily milk loss at an SCC of 500,000 cells/mL ranged from 0.7 to 2.0 kg (3 to 9%) in primiparous cows, depending on stage of lactation. In multiparous cows, corresponding loss was 1.1 to 3.7 kg (4 to 18%). Regression coefficients of primiparous cows estimated from data set B were consistent with those obtained from data set A, whereas data set B generated more negative regression coefficients of multiparous cows suggesting a higher milk loss associated with increased SCC in lactations in which the cow did not develop CM. The 305-d milk loss in the average lactation affected with SCM was 155 kg of milk (2%) in primiparous cows and 445 kg of milk (5%) in multiparous cows. It was concluded that multiparous cows in late lactation can be expected to be responsible for the majority of the herd-level production loss caused by SCM, and that preventive measures need to focus on reducing the incidence of SCM in such cows.     

Effect of Ration Protein Content and Solubility on Milk Production of Primiparous Holstein Heifers

Twenty-eight primiparous heifers were blocked at calving and assigned to four dietary treatments in a 2 × 2 factorial arrangement of two crude protein concentrations (15.4 and 20.7%) and two protein solubilities (22.8 and 53% of protein). Heat-treated soybeans replaced raw soybeans in low solubility rations. Rations were offered for the first 10 wk of lactation divided into two 5-wk periods. Feed was offered ad libitum in period 1 and restricted in period 2. Digestibility and N balance were measured at completion of the lactation study. Body weight change, DM intake, milk yield, milk protein percentage, rumen pH, and total VFA were not affected by treatments. Milk fat percentage was increased by higher CP content during period 1, resulting in a 16.2% increase in 4% FCM. Plasma urea N and rumen NH₃ were elevated by higher CP content. Reducing protein solubility depressed rumen NH₃. A protein × solubility interaction for the acetate to propionate ratio suggests that protein and solubility combinations that optimized plasma urea N and rumen NH₃ provided a more favorable rumen environment and supported highest milk production. Nitrogen digestibility was influenced most by ration CP; however, lower solubility improved DM and N digestibilities. Both dietary CP content and solubility must be considered to maintain optimum rumen environment.