Effect of modified dry period lengths and bovine somatotropin on yield and composition of milk from dairy cows

Dry periods of 40 to 60 d have been an industry standard because dry periods <40 d have resulted in reduced milk yields in the subsequent lactation by 10 to 30%. However, recent research has demonstrated no production losses for cows given a 30-d dry period. The current study evaluated milk production effects of shortened or omitted dry periods for cows at mature-equivalent production >12,000 kg of milk and treated with bovine somatotropin (bST). The study used 2 commercial dairies and one university dairy and included 4 treatments. Five multiparous and 5 primiparous cows from each farm were assigned to each treatment: 1) 60-d dry period, label use of bST (60DD); 2) 30-d dry period, label use of bST (30DD); 3) continuous milking, label use of bST (CMLST); and 4) continuous milking with continuous use of bST (CMCST). Per label, bST use started at 57 to 70 d in milk and ended 14 d before drying (60DD and 30DD) or expected calving date (CMLST). In primiparous cows, average milk yields during the first 17 wk of lactation were reduced for cows on treatments 30DD, CMLST, and CMCST vs. the 60DD treatment. (38.3, 35.1, and 37.5 vs. 44.1 +/- 1.3 kg/d, respectively). For multiparous cows, respective milk yields did not differ (46.6, 43.4, 46.5, and 47.7 +/- 2.1 kg/d). Shortened or omitted dry periods may impede mammary growth in primiparous cows, resulting in reduced milk yield in the subsequent lactation. In contrast, a shortened or omitted dry period with either bST protocol did not alter production in multiparous cows treated with bST. Quality aspects of prepartum milk and colostrum require additional characterization. For multiparous cows, milk income generated for short dry periods or for continuous milking might increase their profitability. At 17 wk of the subsequent lactation, estimates of the cumulative net margins of multiparous cows on the 30DD treatment and continuous milking treatments exceeded those of cows on the 60DD treatment by 40 dollars to 60 dollars per cow.     

Effect of lactation number, year, and season of initiation of lactation on milk yield of cows hormonally induced into lactation and treated with recombinant bovine somatotropin

Records representing data from 1,500 barren Holstein cows over an 8-yr period from a large commercial dairy farm in northern Mexico were analyzed to determine the effects of lactation number and season and year of initiation of lactation on milk production of cows induced hormonally into lactation and treated with recombinant bovine somatotropin (rbST) throughout lactation. Peak and 305-d milk yields were also assessed as predictors of total milk yield in cows induced into lactation. A significant quadratic relationship was found between 305-d milk yield and number of lactation [7,607 ± 145 and 9,548 ± 181 kg for first- and ≥6-lactation cows, respectively; mean ± standard error of the mean (SEM)] with the highest production occurring in the fifth lactation. Total milk yields of cows with ≤2 lactations were approximately 4,500 kg less than milk yields of adult cows (the overall average ± standard milk yield was 13,544 ± 5,491 kg per lactation and the average lactation length was 454 ± 154 d). Moreover, 305-d milk production was depressed in cows induced into lactation in spring (8,804 ± 153 kg; mean ± SEM) and summer (8,724 ± 163 kg) than in fall (9,079 ± 151 kg) and winter (9,085 ± 143 kg). Partial regression coefficients for 305-d milk yield and peak milk yield indicated an increment of 157 kg of milk per lactation per 1-kg increase in peak milk yield (r² = 0.69). Neither peak milk yield (r² = 0.18) nor 305-d milk yield (r² = 0.29) was accurate for predicting total milk yield per lactation. Year, parity, and season effects had significant influence on milk yield of cows induced into lactation and treated with rbST throughout lactation, and peak milk yield can assist in the prediction of 305-d milk yield but not total milk yield. This study also showed that hormonal induction of lactation in barren high-yielding cows is a reliable, practical, and affordable technique in countries where rbST treatment and prolonged steroid administration of dairy cows are legally permitted.     

Short communication: best prediction of 305-day lactation yields with regional and seasonal effects

In the United States, lactation yields are calculated using best prediction (BP), a method in which test-day (TD) data are compared with breed- and parity-specific herd lactation curves that do not account for differences among regions of the country or seasons of calving. Complete data from 538,090 lactations of 348,123 Holstein cows with lactation lengths between 250 and 500 d, records made in a single herd, at least 5 reported TD, and twice-daily milking were extracted from the national dairy database and used to construct regional and seasonal lactation curves. Herds were assigned to 1 of 7 regions of the country, individual lactations were assigned to 3-mo seasons of calving, and lactation curves for milk, fat, and protein yields were estimated by parity group for regions, seasons, and seasons within regions. Multiplicative pre-adjustment factors (MF) also were computed. The resulting lactation curves and MF were tested on a validation data set of 891,806 lactations from 400,000 Holstein cows sampled at random from the national dairy database. Mature-equivalent milk, fat, and protein yields were calculated using the standard and adjusted curves and MF, and differences between 305-d mature-equivalent yields were tested for significance. Yields calculated using 50-d intervals from 50 to 250 d in milk (DIM) and using all TD to 500 DIM allowed comparisons of predictions for records in progress (RIP). Differences in mature-equivalent milk ranged from 0 to 51 kg and were slightly larger for first-parity than for later parity cows. Milk and components yields did not differ significantly in any case. Correlations of yields for 50-d intervals with those using all TD were similar across analyses. Yields for RIP were slightly more accurate when adjusted for regional and seasonal differences.     

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.     

Intergenerational cycle of disease: Maternal mastitis is associated with poorer daughter performance in dairy cattle

Adverse prenatal environments, such as maternal stress and infections, can influence the health and performance of offspring. Mastitis is the most common disease in dairy cattle, yet the intergenerational effects have not been specifically investigated. Therefore, we examined the associations between the dam's mammary gland health and daughter performance using somatic cell score (SCS) as a proxy for mammary health. Using data obtained from Dairy Records Management Systems (Raleigh, NC), we linked daughter records with their dam's records for the lactation in which the daughter was conceived. Linear and quadratic relationships of dam mean SCS with the daughter's age at first calving (AFC; n = 15,992 daughters, 4,366 herds), first- (n = 15,119 daughters, 4,213 herds) and second-lactation SCS (n = 3,570 daughters, 1,554 herds), first- and second-lactation mature-equivalent 305-d milk yield, and milk component yields were assessed using mixed linear regression models. We uncovered a phenomenon similar to those found in human and mouse models examining prenatal inflammation effects, whereby daughters born from dams with elevated SCS had poorer performance. Dam mean SCS was positively associated with daughter's AFC and first- and second-lactation mean SCS. Furthermore, for every 1-unit increase in dam mean SCS, daughter's first- and second-lactation mature-equivalent fat yield declined by 0.34% and 0.91% (?1.6 ± 0.49 kg, ?4.0 ± 1.0 kg, respectively), although no effect was found on first- or second-lactation milk or milk protein yield. When accounting for genetics, daughter SCS, and AFC (first lactation only), dam mean SCS was associated with reduced second-lactation milk fat yield (?3.5 ± 1.8 kg/unit SCS), and a tendency was found for first-lactation milk fat yield (?1.9 ± 1.0 kg/unit SCS). Taken together, the association of greater dam mean SCS with lesser daughter milk fat yield is likely due to a few underlying mechanisms, in particular, a predisposition for mastitis and alterations in the epigenome controlling milk fat synthesis. As such, future studies should examine epigenetic mechanisms as a potential underpinning of this phenomenon.     

Effects of previous days open, previous days dry, and present days open on lactation yield

Influences of days open present lactation, days open previous lactation, and days dry previous lactation were fit simultaneously to determine their effects on measures of yield, which were fat-corrected milk, milk, and milk fat, all adjusted to a 305-d mature equivalent basis. Best linear unbiased estimates were obtained. Multiparity analyses were conducted using a model in which later parity records could be compared with more unselected first parity records. Additional parity information made little difference in the influence of previous days dry and previous and present days open on yield. As present days open increased from 20 to 300 d, lactation yields for FCM, milk, and milk fat increased approximately 1250, 1350, and 45 kg. As previous days open increased from 20 to 300 d, lactation yields for FCM, milk, and milk fat increased approximately 625, 650, and 25 kg. Cows dry 60 to 69 d gave the most milk the following lactation. Cows dry less than 40 d produced much less milk the next lactation. Heritability estimates for previous days dry were less than 7%. Multiplicative adjustment factors were developed to adjust lactation yield records for the largely environmental effects of days open and days dry.     

Long-term effects of postpartum clinical disease on milk production,reproduction, and culling of dairy cows

Two retrospective studies examining data of 7,500 lactating cows from a single herd were performed with the objective of evaluating the long-term effects of clinical disease during the early postpartum period on milk production, reproduction, and culling of dairy cows through 305 days in milk (DIM). In the first study, data regarding health, milk production, reproduction, and culling of 5,085 cows were summarized. Cows were classified according to incidence of clinical problem (metritis, mastitis, lameness, digestive problem, or respiratory problem) during the first 21 DIM (ClinD21). During 305 d of lactation, cows that had ClinD21 produced, on average, 410 kg less milk, 17 kg less fat, and 12 kg less protein compared with cows that did not have ClinD21 (NoClinD21). Although the interval to first breeding was not different between groups of interest, pregnancy rate through 305 DIM was lower in cows that had ClinD21 [adjusted hazard ratio (AHR) = 0.81]. When individual breedings were analyzed, cows that had ClinD21 presented lower rates of pregnancy per breeding for breedings performed before 150 DIM, reduced numbers of calving per breeding for breedings performed before 200 DIM, and greater number of pregnancy losses for all breedings performed through 305 DIM. The rate of culling from calving through 305 DIM was higher in cows that had a single ClinD21 (AHR = 1.79) and in cows that had multiple ClinD21 (AHR = 3.06), which resulted in a greater proportion of cows leaving the herd by 305 DIM (NoClinD21 = 22.6%; single ClinD21 = 35.7%; multiple ClinD21 = 53.8%). In the second study, data regarding postpartum health and 305-d yields of milk, fat, and protein were collected from 2,415 primiparous cows that had genomic testing information. Genomic estimated breeding values (EBV) were used to predict 305-d yields of milk, fat, and protein. Genomic EBV and predicted yields of milk, fat, and protein did not differ between cows that had ClinD21 and those that did not have ClinD21. In contrast, the observed 305-d yields of milk, fat, and protein were reduced by 345, 10, and 10 kg, respectively, in cows that had ClinD21 compared with cows that did not have ClinD21. We conclude that clinical disease diagnosed and treated during the first 21 DIM has long-term effects on lactation performance, reproduction, and culling of dairy cows, which contribute to detrimental consequences of health problems on sustainability of dairy herds. Replication of our studies in multiple herds will be important to confirm our findings in a larger population.     

Feeding and management of dairy heifers for optimal lifetime productivity

A total of 433 Holstein heifer calves were fed two different energy amounts from 6 wk of age to breeding weight to determine the effect of early nutrition and age at first calving on lifetime performance. A control group of 182 heifers was fed according to the Beltsville growth standard. A second group of 251 heifers was accelerated in growth by providing more energy during early development. Both groups of heifers were bred at a minimum weight of 340 kg. Average ages at first calving for control and accelerated heifers were 24.6 mo and 22.2 mo with corresponding 305-d first lactation unadjusted milk production values of 6985 and 6729 kg and unadjusted milk fat yields of 222 and 216 kg. Average 305-d milk production values through subsequent lactations for control and accelerated animals, were lactation 2, 7790, 7842 kg; lactation 3, 8200, 8330 kg; lactation 4, 9481, 9134 kg; lactation 5, 9865, 9588 kg; lactation 6, 9515, 10,108; lactation 7, 9661, 10,112. Average total milk yields over five lactations were 42,321 and 41,623 kg. Percentages of cows remaining in the herd after five lactations were 19 and 18 for control and accelerated animals. Reproductive problems, mastitis, and deaths accounted for 70% of cows leaving the herd and did not differ between treatment groups.     

Genetic evaluation of dairy cattle with test-day models with autoregressive covariance structures and with a 305-d model

This study compared genetic evaluations from 3 test-day (TD) models with different assumptions about the environmental covariance structure for TD records and genetic evaluations from 305-d lactation records for dairy cows. Estimates of genetic values of 12,071 first-lactation Holstein cows were obtained with the 3 TD models using 106,472 TD records. The compound symmetry (CS) model was a simple test-day repeatability animal model with compound symmetry covariance structure for TD environmental effects. The AR_s and AR_e models also used TD records but with a first-order autoregressive covariance structure among short-term environmental effects or residuals, respectively. Estimates of genetic values with the TD models were also compared with those from a model using 305-d lactation records. Animals were genetically evaluated for milk, fat, and protein yields, and somatic cell score (SCS). The largest average estimates of accuracy of predicted breeding values were obtained with the AR_s model and the smallest were with the 305-d model. The 305-d model resulted in smaller estimates of correlations between average predicted breeding values of the parents and lactation records of their daughters for milk and protein yields and SCS than did the CS and AR_e models. Predicted breeding values with the 3 TD models were highly correlated (0.98 to 1.00). Predicted breeding values with 305-d lactation records were moderately correlated with those with TD models (0.71 to 0.87 for sires and 0.80 to 0.87 for cows). More genetic improvement can be achieved by using TD models to select for animals for higher milk, fat, and protein yields, and lower SCS than by using models with 305-d lactation records.     

Agreement of predicted 305-day milk yields relative to actual 305-day milk weight yields

The objectives of this study were to compare the multiple trait prediction (MTP) model estimate of 305-d lactation yield with the 305-d daily milk yield data from on-farm automated meters and software and to examine the accuracy of electronic identification (ID). Twenty-four-hour milk and component yields are calculated by using milk weights and samples collected 8 to 10 times/yr by Dairy Herd Improvement (DHI) organizations. Daily milk weights were collected from cows on 20 Canadian farms that used parlor milking systems with electronic ID and that were enrolled in a regular DHI program. A total of 10,175 DHI test days from 1,103 cows with complete 305-d lactation yields were entered into the MTP model, and lactation yields were predicted. Test days were grouped into first, second, and third and greater lactations and within each lactation group, days in milk were categorized in 3 stages (5 to 60, 61 to 120, and 120 to 305 d in milk) for a total of 9 classes. Agreement analysis was used to compare the 305-d sum of daily milk to the MTP 305-d lactation yield predictions by using inputs from test days throughout the lactations. Results indicated that the MTP model overestimated lactation yields across all parity groups, ranging from 310 to 1,552 kg in parity 1, 640 to 2,000 kg in parity 2, and 567 to 1,476 kg in parity 3 and greater. A preliminary examination of electronic ID accuracy was conducted on 4 farms. Two electronic ID systems were examined for cow ID accuracy by verifying the ID number appearing in the parlor with the corresponding ear tag number. There were no ID errors on 3 of 4 farms tested and only a very small number of errors (3/80) on the fourth farm, indicating that the electronic ID systems used in milking parlors identify cows accurately.     

Season and lactation number effects on milk production and reproduction of dairy cattle in Arizona.

Records representing 19,266 Holstein cows from Arizona DHIA data over a 5-yr period were analyzed to determine the effects of season and lactation number on milk production and reproduction. Seasons were winter (December, January, and February), spring (March, April, and May), summer (June, July, and August), and fall (September, October, and November). Traits analyzed by least squares ANOVA were 305-d FCM, complete lactation milk, calving interval, and services per conception. All sources of variation were significant except the interaction between lactation number and season of calving for complete lactation milk. Milk production was depressed for cows calving in summer and fall. First lactation cows had lowest milk production, and highest production occurred in either lactation 4 or 5. Cows calving in spring and summer had reduced reproductive performance, as measured by calving interval and services per conception. First lactation cows had lowest values for both reproductive traits. Previous days dry was negatively related to milk production for spring calvings but was positively related for all other seasons. Cows with higher milk production had reduced reproductive performance. Partial regression coefficients for calving interval and services per conception were 12 d and .25 services per conception per 1000 kg of 305-d FCM, respectively. Despite the negative effects of thermal stress, milk production and fertility in this study were not depressed as severely as in previous research reported from Arizona. Calving schedules may be adjusted to minimize the adverse effect of heat stress.     

Linear and curvilinear effects of inbreeding on production traits for walloon Holstein cows

The nonlinear effects of inbreeding were studied by comparing linear and curvilinear regression models of phenotypic performances on inbreeding coefficients for production traits (milk, fat, and protein yields) of Holstein cows in their first lactation. Three different regression models (linear, quadratic, and cubic) were introduced separately into a single-trait, single-lactation, random regression test-day model. The significance of the different regression coefficients was studied based on a t-test after estimation of error variances and covariances associated with the different regression coefficients. All of the tested regression coefficients were significantly different from 0. The traditional regression coefficients of milk, fat, and protein yields on inbreeding were, respectively, −22.10, −1.10, and −0.72 kg for Holstein cows in their first lactation. However, the estimates of 305-d production losses for various classes of animals based on inbreeding coefficients showed that the effect of inbreeding was not a linear function of the percentage of inbreeding. The 305-d milk yield loss profiles attributable to inbreeding, obtained by the various regression models, were different. However, for inbreeding coefficients between 0 and 10%, these differences were small.     

Relationships between early-life growth,intake, and birth season with first-lactation performance of Holstein dairy cows

The objective was to determine the relationships between early-life parameters [including average daily gain (ADG), body weight (BW), milk replacer intake, starter intake, and birth season] and the first-lactation performance of Holstein cows. We collected data from birth years 2004 to 2012 for 2,880 Holstein animals. Calves were received from 3 commercial dairy farms and enrolled in 37 different calf research trials at the University of Minnesota Southern Research and Outreach Center from 3 to 195 d. Upon trial completion, calves were returned to their respective farms. Milk replacer options included varying protein levels and amounts fed, but in the majority of studies, calves were fed a milk replacer containing 20% crude protein and 20% fat at 0.57 kg/calf daily. Most calves (93%) were weaned at 6 wk. Milk replacer dry matter intake, starter intake, ADG, and BW at 6 wk were 21.5 ± 2.2 kg, 17.3 ± 7.3 kg, 0.53 ± 0.13 kg/d, and 62.4 ± 6.8 kg, respectively. Average age at first calving and first-lactation 305-d milk yield were 715 ± 46.5 d and 10,959 ± 1,527 kg, respectively. We conducted separate mixed-model analyses using the REML model-fitting protocol of JMP (SAS Institute Inc., Cary, NC) to determine the effect of early-life BW or ADG, milk replacer and starter intake, and birth season on first-lactation 305-d milk, fat, and true protein yield. Greater BW and ADG at 6 wk resulted in increased first-lactation milk and milk component yields. Intake of calf starter at 8 wk had a significant positive relationship with first-lactation 305-d yield of milk and milk components. Milk replacer intake, which varied very little in this data set, had no effect on first-lactation 305-d yield of milk and milk components. Calves born in the fall and winter had greater starter intake, BW, and ADG at 8 wk. However, calves born in the summer had a higher 305-d milk yield during their first lactation than those born in the fall and winter. Improvements were modest, and variation was high, suggesting that additional factors not accounted for in these analyses affected first-lactation performance.     

Milk, fat, protein, somatic cell score, and days open among Holstein, Brown Swiss, and their crosses

The objectives of this study were to compare Holstein (HO), Brown Swiss (BS), and their crosses for milk, fat, and protein yields, somatic cell score (SCS), days open (DO), and age at first calving (AFC), and to estimate the effects of heterosis and recombination. First through fifth lactation records were obtained from 19 herds milking crosses among BS and HO. The edited data set included 6,534 lactation records from 3,473 cows of the following breed combinations: 2,125 pure HO, 926 pure BS, 256 BS sire × HO dam (SH), 105 backcrosses to BS (SX), 18 HO sire × BS dam, and 43 backcrosses to HO. Least squares means for daily milk, fat, and protein yields, mature-equivalent milk, fat, and protein yields, SCS, DO, and AFC were calculated for breed combinations with a model that included fixed effects of age within parity (except for AFC), days in milk for daily yield and SCS, herd-year-season of calving, and breed combination. Cow and error were random effects. Breed combination was replaced with regressions on coefficients for heterosis and recombination in a second analysis. Last, data were analyzed with a 5-trait animal model that included a single pedigree file for both breeds and coefficients for heterosis and recombination. The least squares means for fat production were 1.21, 1.15, 1.27, and 1.16 kg for HO, BS, SH, and SX, respectively, which corresponds to a heterosis estimate of 7.30% and a recombination estimate of −3.76%. Heterosis and recombination estimates for protein production were 5.63% and −3.31%, respectively. Heterosis estimates increased for fat yield (10.38%) and protein yield (7.07%) when maternal grandsire identification from a known artificial insemination sire was required. Regression coefficients indicated an 11.44-d reduction in DO due to heterosis. Heterosis estimates for SCS were inconsistent. Regression on heterosis for SCS was significant and favorable (−0.22) when the breed of sire was BS, but nonsignificant and unfavorable when sire breed was HO (0.43). Heterosis estimates were favorable for all traits, whereas recombination effects tended to be unfavorable for yield traits. Reduced performance of future generations did not appear to be the result of inseminating crossbred cows with inferior sires. Results indicated that first-generation crosses among BS and HO compared favorably with HO. Yield in subsequent generations was somewhat below expectations, perhaps due to recombination loss in HO.     

Heritability of gross feed efficiency and associations with yield, intake, residual intake, body weight, and body condition score in 11 commercial Pennsylvania tie stalls

The objectives of this study were to calculate the heritability of feed efficiency and residual feed intake, and examine the relationships between feed efficiency and other traits of productive and economic importance. Intake and body measurement data were collected monthly on 970 cows in 11 tie-stall herds for 6 consecutive mo. Measures of efficiency for this study were: dry matter intake efficiency (DMIE), defined as 305-d fat-corrected milk (FCM)/305-d DMI, net energy for lactation efficiency (NE_LE), defined as 305-d FCM/05-d NE_L intake, and crude protein efficiency (CPE), defined as 305-d true protein yield/305-d CP intake. Residual feed intake (RFI) was calculated by regressing daily DMI on daily milk, fat, and protein yields, body weight (BW), daily body condition score (BCS) gain or loss, the interaction between BW and BCS gain or loss, and days in milk (DIM). Data were analyzed with 3- and 4-trait animal models and included 305-d FCM or protein yield, DM, NE_L, or CP intake, BW, BCS, BCS change between DIM 1 and 60, milk urea nitrogen, somatic cell score, RFI, or an alternative efficiency measure. Data were analyzed with and without significant covariates for BCS and BCS change between DIM 1 and 60. The average DMIE, NE_LE, and CPE were 1.61, 0.98, and 0.32, respectively. Heritability of gross feed efficiency was 0.14 for DMIE, 0.18 for NE_LE, and 0.21 for CPE, and heritability of RFI was 0.01. Body weight and BCS had high and negative correlations with the efficiency traits (−0.64 to −0.70), indicating that larger and fatter cows were less feed efficient than smaller and thinner cows. When BCS covariates were included in the model, cows identified as being highly efficient produced 2.3 kg/d less FCM in early lactation due to less early lactation loss of BCS. Results from this study suggest that selection for higher yield and lower BW will increase feed efficiency, and that body tissue mobilization should be considered.     

Comparison of test interval and best prediction methods for estimation of lactation yield from monthly, a.m.-p.m., and trimonthly testing

A method with best prediction properties that condenses information from all test days into measures of lactation yield and persistency has been proposed as a possible replacement for the test interval method and projection factors. The proposed method uses previously established correlations between individual test days and includes inversion of a matrix for each lactation. Milk weights that were representative of monthly, a.m.-p.m., and trimonthly test plans were examined to compare the accuracy of best prediction and test interval methods for estimating lactation yield. Individual milk weights or daily yields of 658 Canadian cows in 17 herds were selected to correspond to test intervals for 100,000 US cows. For a.m.-p.m. testing, the initial milk weight that was credited was selected randomly from the a.m. or p.m. milking and was alternated thereafter. Trimonthly credits were from one of the first three designated test day weights, selected randomly, and each third designated test weight thereafter. Correlations between 305-d actual lactation yield and lactation estimates by the test interval method were 0.97, 0.96, and 0.93 for monthly, a.m.-p.m., and trimonthly testing, respectively. Corresponding correlations for the best prediction method were 0.97, 0.97, and 0.93. Standard deviations of differences between estimated and 305-d actual yields for monthly, a.m.-p.m., and trimonthly testing were 373, 400, and 546 kg, respectively, for best prediction regressed on herd mean, which was a reduction in estimation error of 4, 6, and 10% over the test interval method. The advantage of best prediction was moderate if two milk weights were recorded monthly and was larger if testing was less frequent. Advantages also were found for fat and protein yields estimated by multitrait best prediction for records with reduced component sampling.     

Predicting Milk Yield of Holstein Cows from 306 to 395 Days in Milk

Prediction equations were determined to estimate daily milk yield from 306 to 395 d in milk for forecasting herd milk sales from Holstein cows in lactation >305 d. Data were test day milk weights for 65,322 primiparous and 119,220 pluriparous lactations of > 305 d from the Southern US. A forecast model was developed using same lactation 305 d milk yield (in classes of 500 kg increments) that gave similar predicted daily yields as models utilizing last sample milk weight information. This model has the advantage of early forecasting of later milk using projected 305-d yields.Reduced forecast models ignoring days pregnant, yield class, or both accounted for 95, 68, and 59%, and 91, 67, and 56% as much variation in daily milk as the full model for the primiparous and pluriparous cows. Percentage of 305-d milk yielded in mo 11, 12, and 13, depending on 305-d yield class, ranged from 7.1 to 7.0%, 6.2 to 6.0%, and 5.4 to 5.0%, and 5.4 to 5.0%, 4.3 to 3.9%, and 3.3 to 3.0% for first parity and pluriparous cows calving in winter and 125 d open. Cows not calving in winter or with more than 125 d open yielded more milk in extended lactation. These percentages are larger than generally assumed in studies of days open, thus indicating that cost of days open may have been overestimated.     

Genetic evaluation of lactation persistency for five breeds of dairy cattle

Cows with high lactation persistency tend to produce less milk than expected at the beginning of lactation and more than expected at the end. Best prediction of lactation persistency is calculated as a function of trait-specific standard lactation curves and linear regressions of test-day deviations on days in milk. Because regression coefficients are deviations from a tipping point selected to make yield and lactation persistency phenotypically uncorrelated it should be possible to use 305-d actual yield and lactation persistency to predict yield for lactations with later endpoints. The objectives of this study were to calculate (co)variance components and breeding values for best predictions of lactation persistency of milk (PM), fat (PF), protein (PP), and somatic cell score (PSCS) in breeds other than Holstein, and to demonstrate the calculation of prediction equations for 400-d actual milk yield. Data included lactations from Ayrshire, Brown Swiss, Guernsey (GU), Jersey (JE), and Milking Shorthorn (MS) cows calving since 1997. The number of sires evaluated ranged from 86 (MS) to 3,192 (JE), and mean sire estimated breeding value for PM ranged from 0.001 (Ayrshire) to 0.10 (Brown Swiss); mean estimated breeding value for PSCS ranged from −0.01 (MS) to −0.043 (JE). Heritabilities were generally highest for PM (0.09 to 0.15) and lowest for PSCS (0.03 to 0.06), with PF and PP having intermediate values (0.07 to 0.13). Repeatabilities varied considerably between breeds, ranging from 0.08 (PSCS in GU, JE, and MS) to 0.28 (PM in GU). Genetic correlations of PM, PF, and PP with PSCS were moderate and favorable (negative), indicating that increasing lactation persistency of yield traits is associated with decreases in lactation persistency of SCS, as expected. Genetic correlations among yield and lactation persistency were low to moderate and ranged from −0.55 (PP in GU) to 0.40 (PP in MS). Prediction equations for 400-d milk yield were calculated for each breed by regression of both 305-d yield and 305-d yield and lactation persistency on 400-d yield. Goodness-of-fit was very good for both models, but the addition of lactation persistency to the model significantly improved fit in all cases. Routine genetic evaluations for lactation persistency, as well as the development of prediction equations for several lactation end-points, may provide producers with tools to better manage their herds.     

Effects of length of dry period on yields of milk fat and protein, fertility and milk somatic cell score in the subsequent lactation of dairy cows

The objective was to utilize data from modern US dairy cattle to determine the effect of days dry on fat and protein yield, fat and protein percentages, days open, and somatic cell score in the subsequent lactation. Field data collected through the dairy herd improvement association from January 1997 to December 2003 and extracted from the Animal Improvement Programs Laboratory national database were used for analysis. Actual lactation records calculated from test-day yields using the test-interval method were used in this study. The model for analyses included herd-year of calving, year-state-month of calving, previous lactation record, age at calving, and days dry as a categorical variable. Fat and protein yield was maximized in the subsequent lactation with a 60-d dry period. Dry periods of 20 d or less resulted in substantial losses in fat and protein yield in the subsequent lactation. In contrast to yields, a short dry period was beneficial for fat and protein percentages. Short dry periods also resulted in fewer days open in the subsequent lactation; however, this was entirely due to the lower milk yield associated with shortened dry period. When adjusted for milk yield, short dry periods actually resulted in poorer fertility in the subsequent lactation. Long days dry improved somatic cell score in the subsequent lactation. Herds with mastitis problems should be cautious in shortening days dry because short dry periods led to higher cell scores in the subsequent lactation compared with 60-d dry.     

Investigating the effect of temporal,geographic, and management factors on US Holstein lactation curve parameters

We fit the Wood's lactation model to an extensive database of test-day milk production records of US Holstein cows to obtain lactation-specific parameter estimates and investigated the effects of temporal, spatial, and management factors on lactation curve parameters and 305-d milk yield. Our approach included 2 steps as follows: (1) individual animal-parity parameter estimation with nonlinear least-squares optimization of the Wood's lactation curve parameters, and (2) mixed-effects model analysis of 8,595,413 sets of parameter estimates from individual lactation curves. Further, we conducted an analysis that included all parities and a separate analysis for first lactation heifers. Results showed that parity had the most significant effect on the scale (parameter a), the rate of decay (parameter c), and the 305-d milk yield. The month of calving had the largest effect on the rate of increase (parameter b) for models fit with data from all lactations. The calving month had the most significant effect on all lactation curve parameters for first lactation models. However, age at first calving, year, and milking frequency accounted for a higher proportion of the variance than month for first lactation 305-d milk yield. All parameter estimates and 305-d milk yield increased as parity increased; parameter a and 305-d milk yield rose, and parameters b and c decreased as year and milking frequency increased. Calving month estimates parameters a, b, c, and 305-d milk yield were the lowest values for September, May, June, and July, respectively. The results also indicated the random effects of herd and cow improved model fit. Lactation curve parameter estimates from the mixed-model analysis of individual lactation curve fits describe well US Holstein lactation curves according to temporal, spatial, and management factors.