J. Dairy Sci. 2007. 90:2293-2301. doi:10.3168/jds.2005-881
© 2007 American Dairy Science Association ®
Prepartum Milking of Heifers Influences Future Production and Health
K. J. Daniels*,
,
S. S. Donkin*,
S. D. Eicher*,
,
E. A. Pajor* and
M. M. Schutz*,1
* Department of Animal Sciences, Purdue University, West Lafayette, IN 47907
ADM Animal Nutrition Research Center, Decatur, IN 46733
Livestock Behavior Research Unit, Agricultural Research Service, USDA, West Lafayette, IN 47907
1 Corresponding author: mschutz{at}purdue.edu
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ABSTRACT
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Transition heifers face multiple stressors during the periparturient period, including first exposure to milking, that may adversely impact dry matter intake (DMI), reduce milk production, compromise immune function, and increase susceptibility to disease. It was hypothesized that reducing the combined stressors experienced at calving would improve the periparturient performance, health, and well-being of heifers. The objective of this study was to determine the effect of initiating the milking procedure 3 wk before expected calving on production, DMI, body weight, energy balance, udder health, calving traits, and health status, as indicated by plasma acute phase protein concentrations. Twenty-two primigravid heifers, blocked by expected calving date, were assigned randomly either to a prepartum milking (PM) group or control group. The PM heifers were milked twice daily beginning at 21 d before expected calving, and control heifers were not milked until after calving. All heifers had access to the same precalving and post-calving diets. Results indicated that PM heifers produced more milk during the first 2 wk after calving and had greater DMI as a percentage of body weight during the first month after calving than did control heifers, although energy balance was more negative for PM heifers. The PM heifers had reduced somatic cell counts through the first month after calving and lower average somatic cell scores during lactation despite having more quarters with mastitis infection at calving. The PM heifers had less udder edema at the third milking postcalving, and had reduced concentrations of haptoglobin in blood sooner than did control heifers. These results indicate that prepartum milking is an alternative management practice that has beneficial effects on the production, health, and well-being of first-lactation cows.
Key Words: prepartum milking • heifer • well-being
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INTRODUCTION
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Parturition, dystocia, separation from the calf, changing diets, and exposure to mastitis-causing pathogens are some of the stressors encountered during the periparturient period, especially by primigravid heifers. At first parturition, stressors also include lactogenesis, possibly extreme udder edema, introduction to the milking process, and increased interaction with humans. In addition, heifers may be housed in groups with older cows soon after calving and experience associated social stressors (Albright and Arave, 1997). Although the terms "stress" and "stressor" often are not clearly defined and are used interchangeably (Hofer and East, 1998), we have defined a stressor as the change or state of the environment that induces a change in the internal state of a heifer. The action or reaction of the heifer to a stressor will be termed a stress response.
Many of the stressors encountered by heifers around calving are novel events, and novelty itself is considered a fear stressor (Grandin, 1997). Habituating animals by exposing them gradually to novel experiences decreases the stress response (Grandin, 1997). It has been shown that milking during early lactation may be stressful to some heifers, as judged by the inhibition of milk letdown, but that the rate of habituation in this regard varies among animals. On average, however, heifers become accustomed to the milking process by approximately 24 DIM (Van Reenen et al., 2002).
Prepartum milking of heifers may alleviate one or more of the stressors listed previously, thereby reducing their total stress response and leading to improved overall well-being. Some studies (Greene et al., 1988; Schutz and Eicher, 1999; Santos et al., 2004) have suggested that there may be benefits to the practice of prepartum milking. Milk production was increased for prepartum-milked heifers during the first 14 d (Schutz and Eicher, 1999), 100 d (Zeliger et al., 1972), or 130 d (Santos et al., 2004) postpartum.
Improved udder health is a primary motive for considering prepartum milking of heifers. Santos et al. (2004) demonstrated that heifers initially milked 15 d before calving had lower SCC during the first 135 DIM than did control heifers milked only after calving. A significant reduction of udder edema also was reported for first-lactation cows milked before the expected calving date (Schutz and Eicher, 1999; Santos et al., 2004), and reduction of udder edema has been linked to decreased SCC (Santos et al., 2004). Less edema detected in prepartum-milked heifers may result from increased blood flow to the mammary tissue because of the induction of lactation (Al-Ani and Vestweber, 1986), although increased exercise from moving to and from the milking parlor may be beneficial too. Likewise, prepartum milking has been shown to decrease the rate of IMI during the first month postpartum (Greene et al., 1988). A reported (Santos et al., 2004) decrease occurred in the proportion of cows having positive bacterial growth in milk samples, as well as a decreased incidence of clinical mastitis during the first 135 DIM.
The acute phase response is the animal’s reaction to any tissue injury caused by infection, trauma, or stress response (Gruys et al., 1994). This response prevents further injury by isolating and destroying the infectious agent and initiating tissue repair processes (Baumann and Gauldie, 1994). One of the most reactive acute phase proteins in cattle is haptoglobin (HAP), which exhibits a large relative increase during the acute phase response (Hayes, 1994). It has been reported that heifers milked prepartum had earlier reduced blood concentrations of HAP during the first 2 wk postpartum, indicating a quicker recovery from the effects of calving (S. D. Eicher, Purdue, and S. T. Willard, Mississippi State Univ.; unpublished data).
Nutrient insufficiency, particularly energy, may be considered to be a calving-associated stress response because tissue energy demands exceed energy intake (NRC, 2001). The impact of prepartum milking in this regard is equivocal. In some instances, the plasma glucose and liver triglyceride content were unaffected by prepartum milking of cows (Grummer et al., 2000), whereas other studies reported decreased plasma glucose and increased NEFA, and a tendency for increased incidence of clinical ketosis associated with prepartum milking (Santos et al., 2004). The impact of prepartum milking of heifers on energy balance has not been investigated previously.
We hypothesized that reducing the combined stressors presented at calving would improve the periparturient performance, health, and well-being of heifers as they initiate lactation. The specific objective for this study was to determine the effect of prepartum milking on milk production, DMI, BW, energy balance, udder health, calving traits, and health status of treated heifers, as indicated by plasma acute phase protein concentrations.
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MATERIALS AND METHODS
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Experimental Treatments
This study was conducted at the Purdue University Dairy Research and Education Center, near Montmorenci, Indiana, from October 2001 through May 2002. Twelve blocks of 24 heifers approaching first calving were formed according to expected due date and were assigned randomly to either a prepartum milking (PM) or control group. One control heifer was removed from the study because of an undetermined illness, and the PM heifer in the same block was removed to balance blocks throughout the period. Beginning at 21 d before expected calving and continuing for the remainder of the study, PM heifers were milked twice daily at 0500 and 1600 h. The control heifers were not milked until after calving, when they followed the same milking schedule as the PM heifers. The PM heifers had milking units attached at each milking, and automatic detachers removed the unit when milk flow rate decreased to <0.45 kg/min for 30 s.
Housing
All heifers were housed in a geothermally temperature-moderated tie-stall facility (15.6 ± 10°C) beginning 28 d before expected calving to allow for acclimation to the environment before initiating the study. When calving was imminent, heifers were moved to maternity pens, were returned to tie stalls approximately 24 h after calving, and were housed there until after 56 DIM, when they were moved to a free-stall barn. Diets (consisting of corn silage, grass silage, grass hay, and additional supplementation) were formulated to meet or exceed NRC (2001) nutrient requirements for heifers before and after calving, based on typical DMI. Although the TMR was provided ad libitum, heifers in both groups received the same prepartum diet before calving and the same lactation diet thereafter. No attempt was made in this study to increase nutrient density of the diet to accommodate additional requirements potentially occurring because of prepartum milk production. All heifers were housed and managed in compliance with a protocol approved by the Purdue Animal Care and Use Committee.
Measurements
Milk yield was recorded at each milking. Composite milk samples were collected daily after calving until d 14, then weekly through d 56, and once every 2 mo thereafter during lactation. Samples were analyzed at Universal Lab Services, LLC (East Lansing, MI) for butter fat, protein, and SCC. Records from DHIA (Dairy Records Management Systems, Raleigh, NC) were used to obtain estimates of complete lactation milk, fat, and protein yields, as well as lactation average SCS, DIM, days open, persistency index, and 305-d mature equivalent production data.
Calf weight and gender were recorded at birth, as were gestation length, calving ease scores (standard 1 to 5 scoring system), incidence of stillbirths, and incidence of retained fetal membranes. Incidence of twins was recorded as a separate calf gender, and birth weight was the combined weight of the twins. Body weights and BCS were determined weekly throughout the study. Incidences of milk fever, ketosis, displaced abomasum, lameness, and other illnesses were recorded by the herd manager during the entire first lactation of each cow. When each disorder occurred, cows were treated according to the farm’s standard health protocols. Performance of the heifers did not seem to have been substantially affected by these disorders and so none were eliminated from the study analyses.
Daily DMI was calculated for each heifer using the amounts of feed delivered and refused. Energy balance was calculated by the difference from net energy consumed and predicted energy requirements for maintenance, growth, pregnancy, and lactation and used information from individual cows for calf birth weight, daily milk weight, and milk composition (Table 1
).
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Table 1. Calculations to approximate energy balance (EB) of control heifers and heifers milked prepartum beginning 3 wk before expected calving
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At the third milking postcalving, samples of secretions from each quarter were collected via aseptic methods, frozen, and analyzed at the Purdue University Animal Disease Diagnostic Laboratory (West Lafayette, IN) for the presence of common contagious and environmental mastitis-causing pathogens. An infection was defined as a positive culture for known mastitis-causing pathogens and excluded those samples that were identified as contaminated during bacteriological culturing.
Udder area was determined at the third milking postpartum as a measure of udder edema. The area of the parallelogram created by the 4 teats was measured by obtaining a blot of the teats on an absorbent pad immediately before and after milking. A decrease in the area from before and after milking served as a quantitative indicator of the extent of edema in the udder (Seykora and McDaniel, 1986).
Blood was collected by venipuncture of the coccygeal vein or artery into 10-mL heparinized Vacutainer tubes (Becton Dickinson, Franklin Lakes, NJ) on approximately (±3 d) d –28, –14, –7, –3, and –1 relative to expected calving date as well as d 1, 7, 14, 21, 28, and 56 relative to actual parturition. Concentration of HAP was determined by radial immunodiffusion assays (Saikin Kagaku Institute Co., Sendai, Japan). Immunoglobulin G2 concentration also was determined by radial immunodiffusion assays (VMRD, Pullman, WA). Concentrations of IgG2 were analyzed for d –28, –7, –3, –1, 1, 7, 14, 28, and 56 and HAP was analyzed for d –28, –14, –7, –1, 1, 7, 14, 21, and 28.
Statistical Analyses
Production traits were analyzed by using a mixed model procedure (PROC MIXED, SAS Institute, 2001) and included effects of treatment, day, block, and the interaction of treatment x day. The effect of block was not significant for any trait and was omitted in subsequent analyses. The models for milk, DMI, and energy balance were analyzed as repeated measures of the same trait. This methodology is analogous to a split plot in time, with heifer as the whole plot and day as the split plot. Thus, effects of treatment were tested by using the treatment within heifer (whole plot) error and effects of day and treatment x day interaction were tested by using (split plot) residual error. The autoregressive correlation structure among days was selected based on the lowest value for the Bayes information criterion of the correlation structures examined. Autoregressive correlation is appealing in that contiguous test days are more strongly correlated than test days more distant in time. The model for DMI as a percentage of BW was completed using the heterogeneous autoregressive estimation method. This varies slightly from the autoregressive method in that it allows for unequal variances for days, whereas the former assumes variances within day and that covariances across days are consistent.
Udder edema, bacteriological quarter milk samples, complete lactation yields, and calving traits were analyzed using a generalized linear model (PROC GLM, SAS Institute, 2001). Bacteriological test results for milk quarter samples were analyzed as the incidence of positive cultures for specific pathogens and the number of infected quarters. Models for the change in udder area included treatment, block, and covariates for pre- and postmilking udder area. Block affected (P < 0.01) lactation persistency. Block was not significant, however, for any other trait and was omitted from final models for those traits. Because all 305-d mature equivalent data are already adjusted for lactation duration, DIM was not included in those models to account for differences in lactation stage. Further, the limited information made it infeasible to properly fit stage of lactation effects in this study. Models for calf birth weight, calving ease, and gestation length included treatment and calf gender. Health and disease incidences were not analyzed statistically because of insufficient data.
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RESULTS AND DISCUSSION
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Milk and Components
Udder secretions from PM heifers appeared normal and were measurable beginning approximately 15 d before actual calving, and gradually increased to 16.5 kg/d, on average, by day of calving. As expected, milk production was affected (P < 0.01) by DIM and by treatment x day interactions. At 1 d after calving, control heifers produced 7.2 kg of milk, whereas PM heifers produced 19.3 kg (Figure 1). The significant difference in production levels was apparent but decreased steadily until 14 DIM, after which treatment differences were no longer significant. Milk yield differed (P < 0.025) between treatments only during the first 14 DIM, but not during the first 28 DIM. These results confirm earlier reports (Schutz and Eicher, 1999; Kearney et al., 2000; Santos et al., 2004) in which PM heifers produced greater than 10 kg of milk/d at calving and maintained an advantage for approximately 14 d. In contrast, Greene et al. (1988) found no differences in the first and second monthly DHI milk weights for heifers milked prepartum beginning 14 d before expected calving. Use of monthly averages to estimate daily production during the first 2 wk postpartum is unlikely to be sufficiently robust to determine daily differences, as identified in the current study.
No treatment difference was detected for fat production because both groups produced about 1 kg/d of fat during the first month after calving (Figure 2). These findings agree in part with our earlier report (Schutz and Eicher, 1999) in which PM heifers produced more fat at calving and through approximately 4 DIM. Santos et al. (2004) reported differences in fat percentages, but not for fat yield during the first 135 DIM.
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Figure 2. Least squares means of fat, protein, and SCC by postpartum week for control heifers (open bars) and heifers milked prepartum beginning 3 wk before expected calving (solid bars). Standard errors of the means were 0.106 kg, 0.071 kg, and 189 cells/mL, respectively, for fat, protein, and SCC.
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The PM heifers produced 0.5 kg/d of protein immediately before calving. After calving, no treatment differences were detected (Figure 2
); however, control heifers averaged 0.77 kg of protein, whereas PM heifers averaged 0.66 kg of protein during the first month of lactation. Our results confirmed other findings (Schutz and Eicher, 1999; Santos et al., 2004) indicating that PM heifers produce more protein immediately after calving but do not maintain the additional production beyond that time.
Complete lactation information from DHIA records indicated no treatment differences in milk production for PM and control heifers (Table 2), although the PM heifers produced numerically more actual and mature equivalent milk. Heifers milked prepartum were in milk 75 more (P < 0.05) days after calving than control heifers. Both PM and control heifers produced, on average, 31.4 kg/d of milk during their entire lactations (Table 2). Effects of prepartum milking on total lactation yields and mature equivalent production observed in the present study were not different from the response observed in previous studies (Harmon and Hamilton, 1982; Greene et al., 1988; Schutz and Eicher, 1999). These data alleviate concerns that PM heifers simply peak earlier and are less persistent, leading to less overall lactation production. This conclusion is supported by the lack of treatment difference in the DHI persistency index (Table 2).
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Table 2. Entire lactation measures from DHI production and reproduction traits of control heifers and heifers milked prepartum beginning 3 wk before expected calving1
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BW, DMI, and Energy Balance
Neither treatment nor treatment x day relative to calving influenced the BW of heifers. As expected, however, day relative to calving affected (P < 0.01) the BW of heifers as they progressed through parturition. Body weights increased in all heifers until calving, when they decreased dramatically and then continued to decrease slowly until 28 DIM.
For DMI as a percentage of heifer BW (DMI%BW), no differences were detected for treatment or day relative to calving (Figure 3). At calving, control heifers consumed less (P < 0.05; treatment x day relative to calving) DM (1% of their BW) compared with PM heifers (1.9% of BW). This difference was maintained for all but 9 d until 28 DIM. For all DIM, PM heifers had a numeric advantage in DMI%BW. The PM heifers may have had greater DMI to compensate for increased nutrient needs resulting from milk production during the first 14 DIM. Prepartum milking seemed to have affected DMI during the entire first month of lactation, although differences in DMI before calving were not different for PM or control heifers. The numeric advantage for DMI combined with decreased BW for PM heifers led to more visible differences in DMI%BW. These data indicate the need to account for variations in size when analyzing intakes in first-lactation cows.
Prepartum milking shifted the onset of negative energy balance (NEB) around calving to the prepartum period (Figure 4). Differences (P < 0.01) in energy balance occurred in response to treatment and the week relative to calving and their interaction. The PM heifers had a much greater deficit before calving (–20.9 Mcal/d), whereas control heifers were deficient by only –6.3 Mcal/d. This large difference decreased after calving, when PM heifers had an energy deficit similar to control heifers after wk 2. Both treatments maintained a deficit of approximately 5 Mcal/d throughout the first month of lactation. Before calving, heifers utilize dietary energy for maintenance, growth, and pregnancy. Initiating milking 3 wk before calving increased prepartum nutrient insufficiency for PM heifers. The PM heifers did not increase DMI or net energy intake before calving when milk production began, which underscores the increased necessity for body tissue mobilization to support the pre-calving milk production for this group. In addition, the PM heifers produced more milk through d 14 and therefore remained in a more severe state of NEB postcalving, despite having a greater DMI immediately postcalving. Greater NEB for PM heifers is supported by a greater BW loss for this group during the study. Nevertheless, any adverse impacts of NEB did not seem to inhibit the lactation milk yield of PM heifers relative to control heifers. Similarly, Santos et al. (2004) found that greater energy needs before calving of PM heifers were compensated for by increased mobilization of body reserves of energy and were supported by decreased concentrations of plasma glucose and increased NEFA.
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Figure 4. Least squares means of energy balance (±SE) for control heifers (open bars) and heifers milked prepartum beginning 3 wk before expected calving (solid bars) during the week before calving (–1 wk) and 1, 2, and 4 wk after calving. Standard error of the mean was 1.65 Mcal/d.
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Udder Health
The PM heifers averaged 110,000 SCC, whereas control heifers averaged 569,000 SCC during the month after calving (Figure 2). The SCC in control heifers decreased steadily from 965,000 during the week after calving to 319,000 during the fourth month of lactation, whereas the PM heifers maintained approximately 110,000 during all weeks analyzed. These results are similar to those reported by others (Schutz and Eicher, 1999; Santos et al., 2004), indicating that PM heifers had smaller SCS during the first 2 wk and the first 135 DIM, respectively. Likewise, lactation average SCS were smaller (P < 0.05) for PM than for control heifers (Table 2) and indicated improved udder health that was maintained during the course of lactation for those heifers milked prepartum. Differences between groups represent more than a doubling of SCS in the control heifers. Santos et al. (2004) showed that PM heifers had SCS that were 0.84 units less than controls for the first 135 DIM. Removal of milk from the udder and through the streak canal before calving and dilution of bacteria in a larger volume of milk immediately after calving are possible explanations for these benefits of prepartum milking. Further, with milk samples being analyzed only once every 2 mo after 56 DIM in this study, the previous SCS may have had a larger effect on the lactation average SCS calculated for heifers using data from the entire lactation estimated by DHIA.
Udder edema, measured as the change in area of the udder between teats from measurements obtained before and after milking, was affected by treatment (Table 3). An increased change in area is associated with less edema, because an edematous udder will change less in shape during milk out. Change in area was greater (P < 0.01) for PM heifers, at 50.0 cm2 vs. 18.2 cm2 for control heifers. This change in area was not influenced by the area between teats, either before or after milking, when area between the teats was fit in models as covariates. The larger change in udder area for the PM heifers corresponded to a smaller udder postmilking. Greene et al. (1988) found no difference in udder edema in response to prepartum milking using a visual assignment of edema score methodology, whereas Zeliger et al. (1972) reported a slight reduction in udder edema for heifers milked before calving. Other research (Schutz and Eicher, 1999; Santos et al., 2004) indicated a large decrease in udder edema for heifers milked prepartum, using the same method as in the current study. Other measures of udder edema, such as digital pressure of the udder skin, indicate a reduction in edema during both the pre- and postpartum intervals for heifers subjected to initial milking during the prepartum interval (Santos et al., 2004). Removing milk from the mammary gland twice daily before calving and associated increased blood flow may contribute to reduced udder edema. Likewise, increasing the activity associated with moving heifers to and from the parlor also may play a role.
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Table 3. Udder edema traits of control heifers and heifers milked prepartum beginning 3 wk before expected calving1
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Bacteriological analysis of milk samples from individual quarters indicated that PM heifers had increased incidence of Streptococcus uberis infection, with approximately 0.7 more infected quarters per heifer (P < 0.01) during the observation periods. No other pathogen-specific infections were affected by treatment (Table 4). This suggests that PM heifers were more susceptible to environmental pathogen infections than control heifers, because there was not a significant difference in incidence of Staphylococcus aureus, the only contagious pathogen detected. This effect may be related to the total time exposed to the parlor, which for PM heifers was approximately 21 d longer than for control heifers. The PM heifers had teat ends exposed to the milking units twice daily during this period, whereas control heifers did not. Results reported in other studies contradict these data, finding no difference in the rate of infections or infected quarters for PM animals (Zeliger et al., 1972; Schutz and Eicher, 1999). Santos et al. (2004) reported a 16.4% decrease in positively cultured quarters for heifers milked before calving; however, this difference was not significant when samples collected at 28 DIM were analyzed. This indicates that the extent of exposure to the milking parlor and the milking process may explain the level of mastitis pathogen colonization more fully than treatment. In addition to the SCC results, Santos et al. (2004) concluded that many of the infectious pathogens were environmental and of short duration. A relationship between increased udder edema and elevated SCS, which was also true in our study, was noted by Santos et al. (2004), but seemingly contradicts the increased presence of bacteriological pathogens in PM heifers.
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Table 4. Incidence of infected quarters, measured as positive cultures for specific pathogens, for control heifers and heifers milked prepartum beginning 3 wk before expected calving
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Udder health in the PM heifers seems to have improved during lactation, which may indicate that the PM heifers recovered quickly from mastitis caused by environmental pathogens. Combining a distinct reduction of edema in the udder with decreased SCC, the slight increase in positive cultures per quarter may not be an indicator of overall or long-term decreased udder health, but only of increased exposure to opportunistic pathogens.
Calving, Health, and Reproduction
No differences were detected between treatments for gestation length, birth weight, calf gender, or occurrence of stillbirths (Table 5). Calving ease scores tended (P < 0.10) to be smaller for PM heifers, indicating that they required less assistance at calving, corresponding to a numerically nonsignificant advantage in lighter calf birth weight. These results do not confirm an earlier report (Greene et al., 1988) in which a tendency was detected for PM heifers to be assisted at calving more often than control heifers. However, Schutz and Eicher (1999) found that PM heifers tended to need less assistance at calving. It is possible in the field study reported by Greene et al. (1988) that heifers milked before calving were observed more and therefore assisted more (as subjectively recorded) than the control heifers, and that was not true in this study.
Acute phase proteins were used as indicators of acute and chronic stress. There were no significant differences between treatments for IgG2 concentrations, indicating a lack of extraordinary immune challenge for the PM group (Mallard et al., 1997). No differences were detected between treatments for HAP concentrations before calving (Figure 5). Increased HAP concentrations indicate an acute phase response to either tissue injury or other stressors (Gruys et al., 1994). All heifers had increased concentrations from d –28 to calving, indicating a response to an environmental or management stressor. Concentrations then spiked to peak during the first 7 d after calving and returned to precalving levels by 14 DIM. At d 7 after calving, PM heifers had lower (P < 0.05) concentrations than control heifers, but this difference was not apparent at the other time periods. These data indicate an earlier adaptation to the stressors encountered near calving for PM heifers and is similar to the response to PM milking observed previously (S. D. Eicher, Purdue, and S. T. Willard, Mississippi State Univ.; unpublished data).
Although health occurrences were monitored and recorded throughout the study, the number of heifers and incidences precluded statistical analysis. Displaced abomasum, ketosis, lameness, mastitis, metritis, retained fetal membranes, and other disorders, such as pneumonia, were each evaluated separately (Table 6). Only ketosis and metritis had a difference of more than 1 occurrence between treatments, with more incidences of ketosis (2 vs. 0) for the PM heifers and more occurrences of metritis (3 vs. 1) for the control group. Greene et al. (1988) found no statistical differences in health disorders caused by prepartum milking of cows and heifers, except in the occurrence of milk fever, for which PM cows tended to have an increased chance of being positively diagnosed. Santos et al. (2004) reported a tendency for heifers milked before calving to be diagnosed with clinical ketosis, but the difference was not large (0 vs. 2) in the current study. Schutz and Eicher (1999) found that PM heifers tended to have fewer displaced abomasa. Taken together, these studies suggest a beneficial effect of PM on health incidence; however, greater numbers of heifers need to be evaluated.
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Table 6. Incidences of health disorders of control heifers and heifers milked prepartum beginning 3 wk before expected calving
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Total DIM were approximately 75 d greater for PM heifers (Table 2). If DIM before calving were included, this difference would increase to approximately 90 d more for the first lactation for PM heifers. The source of these differences is not apparent because neither this study nor a previous report (Schutz and Eicher, 1999) indicated that prepartum milking led to an increase in time to first insemination.
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CONCLUSIONS
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Milking heifers before calving had no long-lasting negative consequences on milk production or composition. When daily milking was initiated at 21 d before expected calving, heifers produced more milk during the first 2 wk after calving and displayed a peak production and persistency that was similar to conventionally managed heifers. The increase in energy demands to support prepartum lactation did not seem to be offset by increased DMI before calving, although energy balance returned to levels similar to control heifers after about 2 wk.
Prepartum milking also lowered SCC through the first month after calving and reduced average SCS during the course of the lactation, despite an increase in infected quarters at calving. Prepartum milking reduced the incidence of udder edema and increased systemic HAP. Together these changes indicate a beneficial response to protracting the period of time during which heifers encounter stressors around parturition.
The present study supports previous experimental evidence that indicates several beneficial effects of prepartum milking. Additional and earlier onset of the NEB that accompanied prepartum milking and increased numbers of IMI is cause for caution. Additional modifications to prepartum management, such as increased diet energy density, may be necessary to fully realize the potential of prepartum milking.
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ACKNOWLEDGEMENTS
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The authors wish to thank 2 anonymous reviewers for their assistance in strengthening the manuscript.
Received for publication December 18, 2005.
Accepted for publication January 5, 2007.
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ABSTRACT
INTRODUCTION
) and for heifers milked prepartum beginning 3 wk before expected calving (
).
