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* Teagasc Moorepark, Dairy Production Research Centre, Fermoy, Co. Cork, Ireland
School of Agriculture, Food Science and Veterinary Medicine, College of Life Sciences, University College Dublin, Ireland
Department of Veterinary Basic Sciences, Royal Veterinary College, University of London, Hatfield, United Kingdom
1 Corresponding author: jmurphy{at}moorepark.teagasc.ie
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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Key Words: energy balance • milking frequency • reproduction
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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Increasing the proportion of dietary concentrate in early lactation has been shown to increase energy intake and improve energy balance (EB; Reist et al., 2003; Coffey et al., 2004). However, the proportion of concentrate in the diet is limited by the requirement for inclusion of structural fiber to maintain proper rumen function. In addition, cows of high genetic merit tend to partition additional ingested energy toward milk production, rather than reducing the extent of NEB (Veerkamp and Koenen, 1999). Given the difficulties associated with nutritional manipulation of EB in early lactation, interest in employing once-daily milking (1x) to restrict milk energy output and moderate NEB has emerged. The imposition of temporary 1x in early lactation reduces milk yield, and exerts a negative residual effect upon resumption of twice-daily milking, the extent of which becomes greater as the duration of the reduced milking frequency increases (Remond et al., 1999). Temporary 1x in early lactation does not affect DMI (McNamara, 2002; Remond et al., 2002). These studies reported that 1x cows had lower BCS and BW loss and a more positive EB than cows milked twice or 3 times daily. Pomies and Remond (2002) found that cows returned to positive EB much earlier, lost less BCS in early lactation, and maintained a higher BCS throughout lactation when milked once daily for the entire lactation compared with twice daily. The effects of 1x in early lactation on EB appear conducive to improved fertility. However, the direct effects on fertility have not been widely reported (McNamara, 2002). Increasing the energy density of the early lactation diet has produced variable responses regarding both EB and fertility. The objectives of this study were to investigate the effects of 1x and increased dietary energy density in early lactation on milk production, DMI, EB, BCS change, plasma metabolite concentrations, and subsequent reproductive function.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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The chemical composition of the silage and concentrates used over the duration of the trial is presented in Tables 1
and 2, respectively.
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A voluntary waiting period of 65 d was observed before first service. An estrus induction program began on d 65 postpartum in cows not previously detected in estrus using a controlled internal drug-releasing insert (CIDR; InterAg, Hamilton, New Zealand) containing 1.94 g of progesterone, and an injection of 2 mg of estradiol benzoate, (5 mg/mL; Intervet, Dublin, Ireland). The CIDR were removed on d 8 and an injection of PGF2
(2 mL of Estrumate; BP (Vet) Coopers, Berkhamsted, UK) was administered i.m. Cows received 1 mg of estradiol benzoate 24 h after CIDR removal. Semen from a single ejaculate was used to breed all cows. One AI technician performed all inseminations. The duration of the breeding season was 13 wk.
Samples and Animal Measurements
Milk yield (kg) was recorded daily at morning, evening, and night milkings using electronic milk meters (Dairy Master, Causeway, Co. Kerry, Ireland). Milk composition (fat, protein, and lactose) was determined twice weekly from successive morning, evening, and night milk samples during the treatment period and weekly thereafter by automated infrared absorption analysis using a Milkoscan 605 (Foss Electric, Hillerød, Denmark). Somatic cell count was determined once weekly by flow cytometry using a Bentley Somacount 300 (Bentley Instruments Inc., Chaska, MN).
Forage and concentrate intakes were recorded using the Griffith Elder feeding system. Samples of grass silage and corn silage offered were taken on Tuesdays and Fridays. Concentrate samples were taken once weekly. The DMI was calculated daily.
Cow BW (kg) was recorded once weekly before calving, immediately postcalving, and once weekly thereafter. The preparturient cows were weighed before feeding in the morning, and the lactating cows were weighed after morning milking, before feeding. The BCS (Lowman et al., 1976) of the cows was determined approximately 2 wk before calving to facilitate blocking, within 4 d after calving, and then once weekly until the end of the breeding season. Subcutaneous adipose tissue was recovered by biopsy (Robelin et al., 1986) on d 1 and 29 postpartum.
Blood samples were collected by jugular venipuncture 2 wk before expected calving date, twice weekly until d 28 postpartum, and once weekly from d 28 to d 70 postpartum. Sampling took place after morning milking and before feeding. Samples were collected into vials containing lithium heparin as an anticoagulant. The samples were immediately placed on ice packs, and were centrifuged at 2,000 x g for 10 min immediately after sampling. The plasma was decanted and stored at –20°C until analysis.
Follicular dynamics and the diameter of the ovulatory dominant follicle were determined for each cow via daily transrectal ovarian ultrasonography (7.5-MHz transducer; Aloka SSD-500, Aloka Ltd., Tokyo, Japan) from d 7 postpartum until first ovulation. The interval from calving to first ovulation was determined based on ultrasound examination. Pregnancy examinations were conducted using ultrasonography at 30 and 60 d after AI and 60 d after the end of the breeding season. Estrus detection was carried out using the Heatwatch system (DDx Inc., Denver, CO) in conjunction with 3 daily visual observations at 0700, 1500, and 1900 h, during and after the voluntary waiting period. Heatwatch transmitters were first applied 14 d postpartum. Milk samples for progesterone analysis were collected 3 times/wk during the morning milking from parturition until the start of the breeding season.
Laboratory Procedures and Analysis
The DM, NDF, crude fiber, and CP of the forage and concentrate samples were analyzed as described by McNamara et al. (2003). Determination of in vitro DM digestibility was carried out by near-infrared spectroscopy using a near infrared system 6500 spectrophotometer (Perstorp Analytical Inc., Silver Spring, MD). Silage pH on the juice pressed from the silage was measured using a glass electrode and a pH meter (pHM2 standard pH meter-radiometer, Radiometer, Copenhagen, Denmark).
Blood plasma was analyzed for glucose, triglycerides, NEFA, BHBA, urea, and cholesterol concentrations using appropriate kits and an ABX Mira auto analyzer (ABX Mira, Cedex 4, France). Insulin in plasma was assayed using a solid-phase radioimmunoassay (Coat-a-Count, Diagnostics Products Corp, Los Angeles, CA). The interassay coefficients of variation were 14.2 and 9.81% for samples with mean insulin concentrations of 6.4 and 13.1 µIU/mL, respectively, and the corresponding intraassay coefficients of variation were 9.85 and 3.88%. The minimum detectable concentration was 1.61 ± 0.03 µIU/mL.
The concentration of progesterone in milk was measured by enzyme immunoassay from representative un-extracted aliquots of whole milk as described by Sauer et al. (1986). The interassay coefficients of variation were 17.9, 12.0, and 12.2% for samples with mean progesterone concentrations of 2.34, 4.06, and 16.83 ng/ mL, respectively, and the corresponding intraassay coefficients of variation were 8.89, 3.27, and 5.11%. The minimum detectable concentration of the assay was 1.7 ± 0.52 ng/mL.
Plasma samples (100 µL without extraction) were assayed for growth hormone using a modified form of the double-antibody radioimmunoassay of Hart et al. (1975). The inter- and intraassay coefficients of variation were 12.2 and 7.6%, respectively. The minimum detectable concentration of the assay was 2.6 ng/mL.
Plasma IGF-I was measured using human OCTEIA IGF-I kits (IDS, Tyne and Wear, UK). Releasing reagent was added to dissociate IGF-I from binding proteins. The inter- and intraassay coefficients of variation were 8.7 and 2.1%, respectively, and the sensitivity was 1.9 ng/mL.
Subcutaneous adipose samples were processed as described by Robelin et al. (1986). Processed samples were photographed at 4x magnification using a standard light microscope and camera fitted with a C-mount adapter. Mean cell diameter was determined using Adobe Photoshop.
Energy Balance
Energy balance was estimated as the difference between energy intake and the sum of energy for maintenance and milk production, as described by McNamara et al. (2003). The French NEL system was used, in which 1 unité fourragère lait (UFL) is the net energy for lactation equivalent of 1 kg of standard air-dry barley (Jarrige, 1989).
Statistical Analyses
Five cows from 3xST [displaced abomasum (2), retained placenta (2), physical injury] and 2 cows from 3xHE (displaced abomasum, retained placenta) were removed from the experiment. A smoothing spline was fit in Genstat 5 (1997; Lawes Agricultural Trust, IACR-Rothamstead, Harpenden, UK), to facilitate the estimation of daily BW records before analysis. Similarly, a smoothing spline was fit to calculate daily milk fat, protein, and lactose yields from which daily percentages were calculated. Somatic cell counts were transformed to logs before analysis.
Repeated measures of treatment effects on DMI, milk yield, milk constituent yield, milk composition, SCC, plasma analytes, and EB were carried out using the MIXED procedure of SAS (SAS Institute, 1991) with cow as a random effect nested within treatment. Treatment effects on BCS, adipocyte diameter, and BW change were analyzed using the GLM procedure. Treatment, time, and treatment x time interactions were tested. The reproduction data were analyzed using GLM (intervals to ovulation, service, and conception) and 
2 procedures (pregnancy rate to first and second services). Correlation coefficients between EB and some of the blood variables were obtained using the CORR procedure of SAS (SAS Institute, 1991).
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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and Figure 1). Milk yield on 1xST increased with commencement of twice-daily milking in wk 5, but remained approximately 2 kg/d lower than for 3xST throughout the first 20 wk of the lactation. This resulted in an 11.7% lower (P < 0.03) mean cumulative milk yield at wk 10 for 1xST. The cumulative reduction due to 1x was 11.3% (P < 0.05) at wk 20 of lactation compared with 3xST. Milk yield was increased by 17.0% (P < 0.01) with 3xHE compared with 3xST during the treatment period. The change to twice-daily milking and allocation of the ST diet in wk 5 resulted in a reduction in milk yield for 3xHE, and the milk yields of 3xST and 3xHE converged by wk 10 of lactation. The cumulative 10-wk milk yield was 10.2% greater (P < 0.05) for 3xHE compared with 3xST, but this had decreased to 5.9% (P > 0.05) by wk 20 of lactation. Total lactation yields were 6,198, 6,813, and 7,132 kg on treatments 1xST, 3xST, and 3xHE, respectively. This equated to a 615-kg (P < 0.05) difference due to milking frequency treatment, and a 319-kg (P > 0.05) difference due to dietary treatment.
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Milk protein concentration was increased both by 1 xST (P < 0.01) and 3xHE (P < 0.05) compared with 3xST. Daily protein yield was higher (P < 0.01) for 3xHE than 3xST, but reduced milk volume on 1xST resulted in lower (P < 0.05) daily protein yield compared with 3xST. Milk protein concentration declined across all treatments in the 2 wk posttreatment. However, protein concentration remained higher (P < 0.01) on 1xST compared with 3xST, and diet had no effect (P > 0.05).
Milk lactose concentration was not affected by milking frequency or diet (P > 0.05). Hence, the significant differences observed for daily lactose yield during the treatment period were largely due to milk volume differences.
Daily milk energy output was lower (P < 0.05) for 1 xST compared with 3xST, and higher (P < 0.01) for 3xHE compared with 3xST during the treatment period.
Somatic cell count was not affected by milking frequency, either during the trial period or in the post-treatment period (P > 0.05).
DMI, Net Energy Intake, and EB
Feeding the HE diet increased (P < 0.05) DMI during the treatment period, whereas milking frequency had no effect (P > 0.05; Figure 2). However, DMI was lower (P < 0.05) for 1xST than 3xST in wk 4. The DMI of the milking frequency groups converged upon commencement of twice-daily milking. There were no residual milking frequency or diet effects (P > 0.05) in the 2 wk posttreatment.
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BW, BCS, and Adipocyte Diameter
Neither milking frequency (P > 0.05) nor dietary treatment (P > 0.05) affected the degree of BW change during the treatment period (Table 4). However, cows on 1xST began to gain weight earlier postpartum. Consequently, they lost less (P < 0.01) weight than cows on 3xST by d 60 of lactation. There was no residual dietary treatment effect on BW loss.
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). The BCS loss for all groups during the treatment period was approximately 0.25 units. By the start of the breeding season the mean BCS loss was approximately 0.5 units for all groups (P > 0.05). Change in mean adipocyte diameter over the treatment period tended to be lower (P = 0.07) for 1xST compared with 3 xST. Change in mean adipocyte diameter over the treatment period was not different (P > 0.05) between the 3xHE and 3xST groups (Table 4).
Plasma Analytes
Plasma glucose concentration was higher (P < 0.01) during wk 2 for 1xST compared with 3xST (Figure 3). Plasma NEFA was lower (P < 0.05) for 1xST compared with 3xST over the treatment period. Similarly, plasma BHBA was lower (P < 0.05) for 1xST compared with 3xST at this time. Daily EB was positively correlated with plasma concentrations of cholesterol (r = 0.34; P < 0.01), and negatively correlated with plasma concentrations of BHBA (r = –0.18; P < 0.01) and NEFA (r = –0.45; P < 0.01). Plasma concentrations of urea and triglyceride were not affected by milking frequency treatment (P > 0.05; Table 5). Dietary treatment had no effects on any of the plasma metabolites measured (P > 0.05). Plasma insulin concentration during the treatment period was higher (P < 0.05, Figure 4) for 1 xST than 3xST (2.25 vs. 1.27 µIU/mL; SED = 0.48). No differences in plasma insulin were evident in the first week of lactation (P > 0.05), but 1x increased (P < 0.01) plasma insulin during wk 2 to 4. No residual effects of milking frequency on plasma insulin were apparent after wk 5 of lactation (P > 0.05). Plasma insulin concentration was not affected by diet over the treatment period or in the posttreatment period (P > 0.05).
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). There were no posttreatment effects on IGF-I. No difference in growth hormone concentration was observed between the milking frequency treatments (P > 0.05).
Fertility Measurements
The interval to first ovulation, as measured by ultrasound scanning, was shorter (P < 0.01) for 1xST compared with 3xST (Table 6), with a higher proportion (P < 0.05) of 1xST cows ovulating the first postpartum dominant follicle. Dietary treatment did not affect interval to first ovulation or the proportion of cows ovulating the first postpartum dominant follicle (P > 0.05). The onset of luteal activity, as measured by milk progesterone, was earliest for 1xST (P < 0.05) compared with 3xST, with no difference (P > 0.05) due to dietary treatment. There were no treatment effects on interovulatory interval (P > 0.05) or the duration of the luteal phase (P > 0.05). Neither milking frequency nor diet had any effects on intervals to conception, conception rates to first or second service, or overall pregnancy rate (P > 0.05).
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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As expected, increasing the proportion of concentrate and including corn silage in the diet increased DMI (Phipps et al., 1995; Ferris et al., 2001). However, daily DMI over the treatment period was not affected by milking frequency. The lower DMI of 1xST in wk 4 suggests that an effect was beginning to emerge, but commencement of twice daily milking for both groups in wk 5 resulted in the convergence of DMI. The results indicate that continuation of 1x over a more prolonged period would lead to lower daily DMI, as has been observed where cows were milked once daily over a full lactation (Pomies and Remond, 2002).
Once-daily milking resulted in a more positive EB during the first 3 wk of lactation. This difference was not apparent in wk 4, presumably due to the lower DMI of 1xST at that time. The improvement in EB of approximately 1 UFL/d over the treatment period was less marked than previously documented (Remond et al., 1999, 2002; McNamara, 2002). These authors reported that cows milked once daily were approaching positive EB by the third week of lactation. In contrast, the mean daily EB of the 1x cows in the current study did not become positive at any time during the first 6 wk of lactation.
Variation in EB is largely explained by variation in energy intake, and to a lesser extent by milk yield (Villa-Godoy et al., 1988). Where improvements in EB due to 1x have been observed (McNamara, 2002; Remond et al., 2002), the quality of diet offered and DMI achieved were higher than in the current study. The effect of 1x on EB may therefore be dependent on plane of nutrition.
Increasing the energy density of the diet in early lactation did not improve EB, as milk energy output of cows offered the HE diet increased by a similar magnitude to net energy intake. Other studies have demonstrated a positive relationship between proportion of concentrate in the lactating diet and EB (Reist et al., 2003; Coffey et al., 2004). The 4-wk duration of the HE diet was shorter than for the studies cited above, and it coincided with the stage of lactation when maximal partitioning of available energy to milk production was occurring (Bell, 1995).
Cows milked once daily began to gain BW sooner than 3x cows, resulting in lower cumulative BW loss at d 60 of lactation. The earlier resumption of weight gain in 1xST cows may be due to an improved EB, brought about by the negative residual effect on daily milk yield.
Subcutaneous adipocyte diameter is positively related to body fat content (Robelin et al., 1986). Despite the similarity in BCS profiles of the treatment groups, the 1xST cows had a smaller reduction in subcutaneous adipocyte diameter compared with that of the 3xST and 3xHE cows. This indicates that the improvement in EB due to 1x was sufficient to reduce body fat mobilization, despite being undetected by body condition scoring. Furthermore, the lower plasma NEFA concentration of the 1xST cows compared with the 3xST and 3xHE groups is consistent with a lesser degree of body fat mobilization.
Plasma insulin increases in response to elevated blood glucose concentration, and is positively associated with EB in the early postpartum period (Diskin et al., 2003). Numerous studies have shown that cows in a more positive EB have greater circulating concentrations of IGF-I (Spicer et al., 1990; Beam and Butler, 1999), contrary to the current study. Once-daily milking reduced plasma NEFA concentration, indicating a positive effect on EB (Diskin et al., 2003). In addition, 1xST increased plasma insulin concentrations in line with the positive effects observed on energy status and metabolite profiles.
Daily ultrasound scanning and milk progesterone profiling showed that 1xST cows resumed cyclicity 10 d earlier than 3xST and 3xHE cows, due to a higher proportion of cows having ovulated the dominant follicle of the first follicular wave. Daily EB during wk 2 and 3 was less negative for the 1xST group, coincident with the mean day of first postpartum ovulation. Beam and Butler (1999) reported that cows with a shorter interval to EB nadir and a more positive EB during the first 3 wk of lactation had a reduced interval to first ovulation.
Plasma insulin and glucose concentrations were higher for 1xST around the time of first ovulation. Glucose is an important metabolic factor regulating the onset of cyclicity; increased plasma glucose promotes LH release through its effects on GnRH secretion (Diskin et al., 2003). Insulin has been identified as having stimulatory effects on granulosa cell proliferation, estradiol production by granulosa cells, as well as androgen production by thecal cells (Spicer and Echternkamp, 1995). In summary, the effects of once daily milking on early postpartum metabolic status were conducive to enhanced follicular development and earlier onset of cyclicity.
Early reestablishment of ovarian activity allows for the completion of multiple ovulatory cycles preceding insemination, which has been linked to improved conception rates (Darwash et al., 1997). However, this factor becomes important only when intervals to first ovulation exceed about 40 d. In this study the majority (87%) of cows had resumed cyclicity by 40 d, and conception rate and final pregnancy rate did not differ due to milking frequency, despite the earlier onset of cyclicity for the 1xST group.
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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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Received for publication September 13, 2005. Accepted for publication November 14, 2005.
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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) = once a day milking for the first 4 wk of lactation on standard diet; 3xST (
) = 3 times a day milking for the first 4 wk of lactation on standard diet; 3xHE (•) = 3 times a day milking for the first 4 wk of lactation on a high-energy diet.
