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Department of Animal Sciences, University of Arizona, Tucson 85721
Corresponding author: Matthew J. VanBaale; e-mail: vanbaale{at}ag.arizona.edu.
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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2 = 0.49). Under the conditions of this commercial dairy herd in Arizona, increasing milking frequency to 6 times daily for 7 to 21 d at the start of lactation conditions did not increase milk yield nor improve lactation persistency.
Key Words: milking frequency • early lactation • somatotropin
Abbreviation key: 2x, 3x, 4x, 6x = milked 2, 3, 4, or 6 times daily, respectively, ECM = energy-corrected milk, IMF = increased milking frequency, PP = postpartum, rbST = recombinant bST
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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Somatotropin is secreted from the anterior pituitary gland and is found at higher concentrations in genetically superior cows (Kazmer et al., 1986). Recombinant bovine somatotropin (rbST) consistently increases milk yield by 10 to 15% per cow (Bauman and Vernon, 1993). Combining IMF and rbST simultaneously enhanced the production response compared with each treatment alone, indicating that the 2 galactopoietic tools are additive and probably increase milk synthesis via different mechanisms (Knight et al., 1992; Speicher et al., 1994). However, no studies have evaluated the affects of IMF (6x vs. 3x) during the first 7, 14, or 21 d PP, followed by rbST administration at 63 DIM on high-producing multiparous cows.
Study objectives were 1) to determine if cows milked 6x during early lactation would produce more milk during the IMF routine; 2) to evaluate the time necessary to milk cows 6x during early PP to have a positive impact on peak milk yield and lactation persistency, and 3) to determine if effects of IMF in early lactation and subsequent rbST administration during established lactation are additive.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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), and were housed in dry lot corrals (permitting 49.2 m2/cow) with shades (9.14 m wide by 3.96 m high; permitting 44.5 m2/cow). Cows milked 6x were housed in a separate pen from cows milked 3x (during the IMF routine; 
21 DIM) and both pens were located near (87 ± 36 m) the milking parlor (Table 2). Cows milked 6x for 7, 14, and 21 d were moved to the pen housing the 3x cows immediately after their 6x regimens had ended (d 8, 15, or 22), and all cows were commingled in a single pen at 29 DIM through the remainder of the 305-d trial. Use of animals in this investigation was approved by The University of Arizona Institute of Animal Care and Use Committee.
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Measurements
Daily milk weights were measured electronically by Boumatic Computer software (Madison, WI) for each animal milking throughout the 305-d lactation. Monthly milk composition analysis and SCC was conducted at Arizona DHIA (Tempe, AZ) using an infrared analyzer (model 2000 and model 500; Bentley Instruments, St. Paul, MN). Energy-corrected milk (ECM) was calculated from milk, protein, and fat volumes (0.327 x milk kg + 12.95 x fat kg + 7.2 x protein kg). Pen DMI was monitored and recorded using PROFEED2000 (DairyWorks, Tempe, AZ) feed management software. Cows were scored for body condition at freshening and at 28 ± 4-d intervals. Body condition scores were based on a 5-point scale (Wildman et al., 1982). Blood samples were collected from the coccygeal vein from a subset of cows (n = 15) from groups 1 and 4 at parturition and then on 7, 14, 21, and 28 ± 1 DIM, and the harvested plasma was immediately frozen at –20°C until analysis.
Plasma NEFA concentrations were determined enzymatically using commercially available kits validated for use in our laboratory (NEFA C kit; Wako Chemicals USA, Richmond, VA). These procedures were scaled down and conducted in 96-well microtiter plates (Rainin Instrument, LLC, Oakland, CA) and read using a microplate photometer (Multiskan Ascent, Thermo Electron Corporation, Vantaa, Finland) as previously described (Moore et al., 2004). The inter- and intraassay coefficients were 7.4 and 5.7%, respectively. Samples of TMR were obtained monthly, and wet chemistry analyses were conducted by the Dairy Nutritional Services Laboratory (Tempe, AZ).
Statistical Analyses
All performance data were analyzed for the first 9 wk PP and then from wk 10 to 44 to evaluate the effects of IMF during early lactation and the potential carryover effects after peak milk. Treatments 1, 2, 3, and 4 were analyzed to evaluate the impact of IMF, and treatments 4 and 5 were analyzed separately to determine the impact of 6x milking for 21 d PP with and without rbST administration beginning at 63 DIM. Data were analyzed using PROC MIXED procedures of SAS (SAS Institute, 1999). Previous 305-d mature equivalent milk yields were included as a covariate in the analysis. Daily milk yields were collapsed into weekly averages. Dependent variables tested were milk yield, calculated ECM, BCS, BW, SCC, fat and protein percentages, and yields. The independent variables for milk yield, calculated ECM, BCS, BW, SCC, fat, and protein percentages and yields included treatment, time, and the respective interactions. Time (week of study) was fit as a repeated measure and treatment means were separated using the PDIFF option for all. A 2 (General Association Cochran-Mantel-Hansen) analysis was done to test for associations of reproductive and herd health variables monitored.
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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and Table 3) and more (P < 0.01) ECM (45.0 vs. 42.6 and 41.6 ± 0.7 kg/d; Table 3) during the first 9 wk of lactation compared with cows milked 6x for 7 or 21 DIM, respectively. Milk yields did not differ among milking frequency treatments (38.3 ± 0.7 kg/d) after wk 9 (Table 3 and Figure 1). Yields of ECM were higher (P < 0.05) after wk 9 for cows milked 3x daily compared with 6x for 21 DIM (39.1 vs. 38.2 ± 0.4 kg/d). However, 3x cows had similar ECM yields as those milked 6x for 7 or 14 DIM, (38.8 kg/d; Table 3). Percentages of milk fat (3.80 ± 0.12) and protein (2.90 ± 0.06) did not differ among treatments during the first 9 wk after calving (Table 3). However, cows milked 3x daily had increased (P = 0.01) yields of fat compared with cows milked 6x for 7 or 21 DIM (1.68 vs. 1.55 ± 0.05 kg/d; Table 3). In addition, cows milked 3x or 6x for 7 or 14 DIM produced more (P < 0.01) protein compared with cows milked 6x for 21 DIM (1.25 vs.1.16 ± 0.03 kg/d). Somatic cell count (257 x 103 cells/mL) and BCS (3.60) did not differ between treatments during the first 9 wk after calving (Table 3). However, SCC were higher (P = 0.02) between wk 10 and 44 for cows milked 3x and 6x for 21 DIM compared with cows that were milked 6x for 14 DIM (595 and 526 vs. 294 x 103 ± 111 x 103 cells/mL; Table 3). Plasma NEFA concentrations (477 µEq/L) did not differ between the 3x and 6x 21-d treatments (Table 3).
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and Figure 2). Cows treated with rbST and milked 6x for 21 DIM produced more (P < 0.01) milk (38.8 vs. 34.2 ± 0.9 kg/d; Figure 2) and ECM (39.0 vs. 34.5 ± 0.4 kg/d) compared with cows milked 6x for 21 DIM and not provided rbST between wk 10 and 44 of lactation (Table 4). Neither milk fat (3.71) nor protein (2.86) percentages nor yields of fat (1.56 kg/d) differed during the first 9 wk after calving between the 2 treatment groups milked 6x for 21 DIM (Table 4). Average SCC (226 x 103 cells/mL) and BCS (3.58) were also similar between the 2 treatments during the first 9 wk after calving. Milk fat and protein content (3.62 and 2.91, respectively) were not affected by rbST administration; however, yields of milk fat (1.37 vs. 1.26 ± 0.03 kg/d) and protein (1.12 vs. 1.00 ± 0.03 kg/ d) were higher (P < 0.01) for cows administered rbST and milked 6x for 21 DIM compared with cows not receiving rbST (Table 4). Overall milk SCC (528 vs. 252 x 103 ± 102 x 103 cells/mL) were increased (P < 0.01) and BCS decreased (3.53 vs. 3.56 ± 0.01; P < 0.05) for cows administered rbST after being milked 6x for 21 DIM compared with cows milked 6x for 21 DIM and did not receive rbST at 63 DIM.
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2 = 0. 96; Table 5). The number of cows that were sent to the hospital pen during the 305-d trial for mastitis (97), digestive disorders (14), respiratory issues (9), lameness (22), or retained placenta (16), were not affected by milking frequency or somatotropin treatments (2 = 0.49).
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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), it was not surprising that we did not detect an IMF effect on lactation persistency (Figure 1). Milk fat and protein are typically reduced as milking frequency increases as both Smith et al. (2002) and Erdman and Varner, (1995) report decreased milk protein and fat percentages when cows were milked 3x vs. 2x. In addition, Hale et al. (2003) indicated that IMF in early lactation decreased milk fat and the decrease persisted for the entire lactation. In our study, monthly milk fat (3.8) and protein (2.9) percentages were not affected by IMF during the first 9 wk PP or from wk 10 to 44, which agrees with Bar-Peled et al. (1995) and Sanders et al. (2000). The reported differences in milk fat between the aforementioned studies may be explained by the fact that we did not observe an increase in milk yield or by differences in milk sampling strategies. In our study and others (Bar-Peled et al., 1995; Sanders et al., 2000), milk samples were analyzed monthly (therefore the range in DIM at sampling was ± 28 d) and there were no differences observed in milk composition, whereas Hale et al. (2003) sampled weekly and detected differences.
Smith et al. (2002) compiled performance records representing approximately 10,600 cows/yr (1998 to 2000) and observed an overall decrease in SCC when cows were milked 3x vs. 2x. However, in our study, milk SCC were not affected by IMF during the first 9 wk PP, which agrees with other IMF trials (Bar-Peled et al., 1995; Sanders et al., 2000; Hale et al., 2003). In contrast to early lactation, during wk 10 to 44 of lactation, cows previously milked 6x for 7 or 14 DIM did have reduced milk SCC compared with 3x or 6x for 21 DIM (Table 3); however the biological significance (if any) is difficult to interpret.
Reasons why our IMF milk production data do not agree with others (Bar-Peled et al., 1995; Sanders et al., 2000; Hale et al., 2003; Dahl et al., 2004) are not clear, but facility logistics may have contributed to the discrepancies. Unlike previous reports, where cows were housed in a tie-stall environment or individual pens, or where the influence of facility is not reported, cows used in our study were not individually penned. Instead, they were housed in a dry-lot facility located 87 ± 36 m from the milking parlor (Table 2). Thus, cows in the 6x milking regimen walked to and from the parlor 6 times daily (1044 ± 432 m/d) and spent, on average, 6.5 h/d outside their pen. Consequently, they were physically away from feed and water longer than were control animals. This study was carried out under conditions typical to large western commercial dairies, where it is likely that IMF will alter available time for feed and water consumption. Although increased walking may have affected estimated maintenance requirements, the calculated increase was small (1.12 vs. 0.80 Mcal/d; NRC, 2001), and compared with typical large commercial dairies, the total walking distance was nominal even for cows being milked 6x daily.
Although cows milked 6x were away from feed longer, average pen DMI per cow during the IMF regimen did not differ (19.3 kg/d). In contrast, Bar-Peled et al. (1995) reported an increase in DMI (16.8 vs. 19.4 kg/d, from 0 to 42 DIM; and 20.1 vs. 22.4 kg/d from 49 to 70 DIM) for cows milked 3x compared with 6x. Despite the increase in DMI in cows milked 6x (Bar-Peled et al., 1995), both BW and BCS were reduced by 6x milking. Not surprisingly (because we did not detect milk yield or DMI differences), IMF had little or no effect on early or late-lactation BCS (Table 3). In agreement with our BCS data, IMF had no effect on early-lactation plasma NEFA concentrations (Table 3), a metabolic proxy for adipose mobilization. Incidentally, DMI (for all IMF treatments) immediately postpartum (0 to 21 DIM) in our study was similar to that reported for the cows milked 6x in Bar-Peled et al. (1995) in later lactation (i.e., ~40 DIM). In contrast to Bar-Peled et al. (1995), our cows consumed similar amounts of feed while experiencing differing IMF regimens. Cows milked 3x in the current study produced more milk than cows milked 6x in the Bar-Peled et al. (1995) study, suggesting that perhaps the 3x milking under conditions used in this experiment maximized the potential for changes in milking frequency to enhance production during early lactation.
Again, the exact reasons why our milking frequency data do not agree with others (Bar-Peled et al., 1995; Sanders et al., 2000; Dahl et al., 2004) are unclear. Inadequate nutritional status is not likely as cows across treatments averaged over 13,000 kg of 3.5% FCM throughout lactation. Furthermore, the nutritional status was likely sufficient as cows had an average BCS of 3.65 and 3.60 at calving and in wk 9 of lactation, respectively. In addition, nutritional status was certainly sufficient during established lactation as exogenous rbST increased (12%) milk yield consistently throughout lactation (Figure 2). Furthermore, environmental factors such as heat stress were not an issue as the majority of the trial was conducted during the winter (November through March) months and ambient temperature (12 ± –10°C) and humidity (50 ± 25%) were low. An explanation may be that cows in all treatments had an average milk production of 35.8 kg/d during the first 21 DIM and this is difficult to compare because other studies (Bar-Peled et al., 1995; Sanders et al., 2000) that administered a 6x milking regimen milked cows 6x daily through 42 DIM. Consequently, high-producing cows, especially high producers that have a steep slope of milk yield increase, may not be as responsive to increased milking frequency immediately after calving (21 DIM). Although Hale et al. (2003) demonstrated an increase in as few as 21 d after calving, their cows were milked 4x vs. 2x, not 6x vs. 3x.
Exogenous bovine somatotropin consistently increases milk yield by 10 to 15%/cow (Bauman and Vernon, 1993). In our study, 2 groups of cows were milked 6x for 21 DIM, and then 1 group received rbST beginning at 63 DIM. Although milking cows 6x during early lactation and subsequently administering rbST at 63 DIM has not previously been evaluated, combining IMF and rbST in established lactation additively enhances milk yield (Knight et al., 1992). This supports the concept that the 2 galactopoietic tools are additive and probably increase milk synthesis via different mechanisms (Knight et al., 1992; Speicher et al., 1994). We did not see a milk response to IMF, although cows milked 6x and treated with rbST (wk 10 to 44) produced more milk (12%) and more ECM (12%) than cows that did not receive rbST.
Percentages of milk fat (3.62) and protein (2.91) were not affected by rbST administration; however, yields of fat (1.37 vs. 1.26 kg/d) and protein (1.12 vs. 1.00 kg/d) were higher for cows provided rbST and milked 6x for 21 DIM compared with cows not receiving rbST. Milk somatic cells (5.28 vs. 2.52 x 103 cells/mL) were increased and BCS was slightly decreased (3.53 vs. 3.56) for cows given rbST after being milked 6x for 21 DIM compared with cows not receiving rbST and milked 6x for 21 DIM. It has been demonstrated that somatotropin does not alter the normal relationship between milk yield and mastitis (White et al., 1994). In the current study, mastitis was the most common reason for cows visiting the hospital pen in all treatments; however, there was no difference in clinical mastitis incidence between cows given rbST and those not given rbST. As previously reported (White et al., 1994) with respect to mastitis, the performance and health of cows administered rbST appears to be similar to that of cows not administered rbST but yielding similar amounts of milk.
Reproductive variables (cows pregnant within 65 d of the voluntary waiting period, average DIM at pregnancy, and average service per conception) and the number of cows that were sent to the hospital pen (for mastitis, digestive disorders, respiratory issues, lameness, or retained placenta) were not affected by IMF or by use of somatotropin during our 305-d trial. This suggests that IMF with or without rbST had no influence on animal health and reproductive performance. Therefore, the decision to implement a 6x milking regimen for 7, 14, or 21 d PP in an attempt to immediately increase milk synthesis or enhance lactation persistency does not appear to be warranted under the management conditions of the current study.
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CONCLUSIONS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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ACKNOWLEDGEMENTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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FOOTNOTES |
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Received for publication February 7, 2005. Accepted for publication July 5, 2005.
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REFERENCES |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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= 3x milking, 
= 6x milking for 7 d postpartum, 
= 6x milking for 14 d postpartum, x = 6x milking for 21 d postpartum. All cows were milked 3x daily except for experimental periods in the first 3 wk.
= 6x milking for 21 DIM going to receive rbST beginning at wk 9, 
= 6x milking for 21 DIM not going to receive rbST throughout the 44-wk trial.