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1 Estación Experimental INTA Rafaela, Argentina 2300
2 University of California, Cooperative Extension, Merced, 95340
3 Facultad de Agronomía, Universidad de Buenos Aires, Argentina 1417
4 Elanco Animal Health, Eli Lilly Interamerica Inc., Buenos Aires, Argentina 1425
5 External Consultant Elanco Animal Health, Eli Lilly Interamerica Inc., Buenos Aires, Argentina 1425
Corresponding author: M. R. Gallardo; e-mail: mgallardo{at}rafaela.inta.gov.ar.
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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Key Words: monensin • dairy cow • mixed-alfalfa pasture • partial mixed ration
Abbreviation key: CRC = controlled-release capsule, PUN = plasma urea nitrogen
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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Monensin sodium is an ionophore approved for use in lactating dairy cows in several countries including Australia, Argentina, Brazil, New Zealand, South Africa, and recently the United States. A major benefit of feeding ionophores to lactating dairy cows is the shift in the acetate-to-propionate ratio toward more propionate and the associated decrease in methanogenesis (Russell and Houlihan, 2003). Based on the potential of ionophores to increase the supply of glucogenic precursors such as propionate, the administration of monensin to dairy cows may increase the hepatic synthesis of glucose and, therefore, improve the energy balance (Ipharraguerre and Clark, 2003). Benefits of feeding monensin to lactating dairy cows include increased milk production (McGuffey et al., 2001), antiketogenic effects, improved BCS (Sauer et al., 1989; Duffield et al., 1998), prevention of ruminal acidosis (McGuffey et al., 2001), and legume bloat control (Maas et al., 2002).
Most of the studies regarding the feeding of monensin to lactating dairy cows were conducted under nongrazing conditions with dairy cows fed TMR (Ipharraguerre and Clark, 2003), which may not be representative of grazing cows (Maas et al., 2002). Few studies were conducted with dairy cows grazing (Wilson et al., 1993; Hayes et al., 1996; van der Merwe et al., 2001) or consuming fresh pasture (Ruiz et al., 2001), and those studies had a short length of 2 (Ruiz et al., 2001) to 6 wk (van der Merwe et al., 2001). Most of those studies were conducted with low-producing dairy cows on pasture-only diets (Wilson et al., 1993; Hayes et al., 1996) and did not measure pasture DMI. None of the previous pasture studies included the use of pasture plus a partial mixed ration in a partial TMR feeding system. Information about the short- and long-term effects of monensin on production and reproduction performance is also needed (McGuffey et al., 2001). The objectives of our study were to evaluate short- and long-term effects of monensin controlled-released capsule (CRC; Rumensin, Elanco, Eli Lilly Interamerica Inc., Buenos Aires, Argentina) provided prepartum and in early lactation on milk production and composition, BCS, plasma metabolites, and reproduction variables of dairy cows grazing a mixed-alfalfa pasture and supplemented with partial mixed ration.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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Feeding and Grazing Management
During the 30 d prepartum and wk 1 postpartum, all cows were held in a dry lot pen and received a TMR with forage-to-concentrate ratio of 77:23 and 72:28, respectively (Table 1
). The amount of TMR was offered daily to ensure approximately 10% orts. Dry matter intake was measured by difference between offered and refused in all cows and averaged 13.6 (±1.3) and 16.8 (±2.0) kg/d for the 30 d prepartum and wk 1 postpartum TMR, respectively. Although that would have been an important period to measure individual DMI (Arieli et al., 2001; Vallimont et al., 2001), all cows were group-fed in one group; therefore, it was not possible to have statistically valid prepartum DMI measurements.
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DMI Measurements and Feed Sample Analyses
Dry matter intake was measured 3 times during the experiment in 5 groups per treatment (a total of 10 groups) of 5 to 6 cows each (a total of 58 cows). Each of the 3 DMI measurements was conducted for a 6-d period. The DMI measurements were conducted when cows averaged 60, 90, and 150 DIM. Because average calving date was March 10, DMI measurements corresponded in average to May 9, June 8, and July 8 (±6 d; Rafaela, Argentina, 31°11' South). Because all of the ingredients in the diets were group-fed to cows, the group or paddock of cows was used as an experimental unit.
Pasture DMI was estimated in five 400-m2 pasture paddocks per treatment by difference between pre- and postgrazing pasture mass according to the method described by Meijs et al. (1982). Pasture DMI measurement by difference between pre- and postgrazing pasture mass has been recently compared with other techniques and validated by Macoon et al. (2003). Within each pasture paddock, 6 pre- and 6 postgrazing 0.25-m2 pasture mass samples were taken by cutting to ground level with manual scissors. For the entire trial, pre-and postgrazing pasture mass averaged 2105 (±234) and 553 (±109) kg/ha of DM, respectively. The amount of pasture offered on a daily basis or pasture allowance ranged from 14.7 to 16.8 kg/d of DM per cow. The DMI of concentrate and TMR were daily measured by difference between the amount of concentrate or TMR offered minus the amount of concentrate or TMR refused during each 6-d period in the 5 groups of cows per treatment.
For each of the 3 pasture DMI measurements, chemical composition of the pasture consumed by cows was estimated indirectly by difference as described by Meijs et al. (1982). Pre- and postgrazing pasture mass samples were used to provide subsamples for chemical analysis. Each nutrient quantity removed during grazing was calculated and expressed as a percentage of DM using the following equation:
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where X = concentration of nutrient in pasture consumed, Y = pregrazing nutrient (kg/ha), Yf = postgrazing nutrient (kg/ha), M = pregrazing DM (kg/ha), and Mf = postgrazing DM (kg/ha).
Concentrate and TMR samples were also taken for chemical composition analysis during the same 6 d that pre- and postgrazing pasture mass samples were taken.
Pasture, concentrate, and TMR samples were dried at 55°C for 48 h in a forced-air oven and ground through a 1-mm screen (Wiley Mill, Thomas Scientific, Philadelphia, PA) and then analyzed for DM, CP, ash, fat (AOAC, 1990), NDF, ADF, and lignin (Van Soest et al., 1991). Energy concentration (NEL/kg of DM) of the diets was calculated according to The Ohio State University model (Weiss et al., 1992).
Chemical composition of the mixed-alfalfa pasture consumed (Meijs et al., 1982) when cows averaged 60, 90, and 150 DIM is shown in Table 2 to show changes in pasture composition over each pasture DMI measurement. It should be noted, however, that pasture composition might well have changed more than is represented by Table 2. On average, mixed-alfalfa pasture consumed by cows had high CP (>25%) and low DM (<20%), NDF (<35%), and NFC (<25%). The corn-based concentrate had 16% of CP and 56% of NFC (Table 2). The TMR supplemented had low CP (11%) to compensate for the high CP of the mixed-alfalfa pasture (Table 2).
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Body condition of the cows was scored by 3 experienced independent observers using the 5-point BCS scale (1 = thin to 5 = fat; Wildman et al., 1982) on d 30 before the expected calving date, at calving, and every 3 wk during the following 150 DIM. Blood samples were taken immediately after the a.m. milking from the coccygeal vessels into one 20-mL evacuated tube containing anticoagulant (heparin and sodium fluoride) and one 20-mL evacuated tube without anticoagulant on d 21 before the expected calving date, at parturition, and on d 10 and 21 postpartum. Blood was immediately placed on ice and transported to the laboratory. Samples were centrifuged at 3000 x g for 15 min at 4°C. Plasma was analyzed for glucose and urea nitrogen (Wiener Laboratory, Rosario, Argentina) and for NEFA (Randox Laboratories Ltd., UK). Reproductive performance was evaluated by the percentage of pregnancy at first insemination, at 6 wk, and at 12 wk from the start mating date.
Statistical Analysis
Data were analyzed as a completely randomized design with repeated measurements using the PROC MIXED procedure of SAS (1999). For DMI data, the groups of cows were used as experimental unit. For milk production and composition, BCS, plasma metabolites, and reproduction performance data, the individual cows were used as experimental units. For the milk production data, the previous lactation milk production of multiparous cows and the BW of primiparous cows were used as covariates. Differences were declared significant at P < 0.05.
During the study, 4 multiparous cows were eliminated because of mastitis (Staphylococcus aureus) after the reproductive performance data collection was completed. Thus, 58 cows were used for the statistical analysis of plasma metabolites and reproductive performance data, and 54 cows were used for the statistical analysis of milk production and composition and BCS. No interactions (P > 0.05) between treatment and week of lactation were observed; therefore, only treatment effects are presented and discussed.
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RESULTS AND DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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0.27; Table 3). Values of total DMI found in our study were high and consistent with the high milk production from calving to wk 20 of lactation (>27 kg/d; NRC, 2001). Mixed-alfalfa pasture, TMR, and concentrate DMI did not differ between treatments and averaged 8.7, 9.1, and 5.0 kg/d, respectively (P 0.36; Table 3). Lack of effect of monensin on DMI is in agreement with a recent review by Ipharraguerre and Clark (2003). In 8 of 12 studies with lactating dairy cows, no significant effects of monensin on DMI were observed. None of the studies reviewed in which cows grazed pasture reported DMI (Ipharraguerre and Clark, 2003). Ruiz et al. (2001) reported no effects of monensin on fresh forage and concentrate DMI fed to dairy cows in confinement. Phipps et al. (2000) found a small nonsignificant reduction in DMI from 19.4 to 18.9 kg/d in dairy cows fed a TMR as the dose of monensin increased from 0 to 450 mg/d.
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. Monensin increased milk production 4% (27.7 vs. 26.6 kg/d) during the first 150 DIM (P = 0.001; Table 4; Figure 1); however, it did not affect 3.5% FCM (27.5 kg/d; P = 0.341; Table 4). Milk production levels are similar to those reported for high-producing dairy cows consuming a similar diet to the one used in our study that included <50% pasture, TMR, and concentrate (Bargo et al., 2002). Response in milk production to monensin obtained in our experiment is in agreement with recent reviews (McGuffey et al., 2001; Ipharraguerre and Clark, 2003). Cows receiving monensin had a milk response that averaged 1.3 kg/d or 5% in 11 monensin premix experiments (McGuffey et al., 2001), 1.1 kg/d or 7% in 4 monensin CRC experiments (McGuffey et al., 2001), and 1.5 kg/d or 7% in 14 experiments (Ipharraguerre and Clark, 2003) compared with the 1.1 kg/d or 4% response of our study. Ipharraguerre and Clark (2003) reported that in 5 of 7 studies conducted with cows consuming pasture, milk response to monensin averaged 1.1 kg/d with a range of 0.4 (Hayes et al., 1996) to 1.85 kg/d (Ruiz et al., 2001). However, in most of these studies, cows were fed only pasture diets, and none of them included pasture supplementation with a partial mixed ration.
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Milk fat content was reduced 2.5% (3.51 vs. 3.60%; P = 0.038) by monensin, but no differences were observed in content of total protein (3.25%; P = 0.672; Table 4). Milk fat and protein content results were in agreement with the reviews of McGuffey et al. (2001) and Ipharraguerre and Clark (2003) that described that monensin decreased milk fat content with no effects on milk protein content. In over 30 studies, the administration of monensin to dairy cows reduced, numerically in 20 studies and significantly in 10 studies, the milk fat content (Ipharraguerre and Clark, 2003). In many of the studies where monensin reduced milk fat content, an increase in milk production was also observed; therefore, a dilution effect could be part of this result (Ipharraguerre and Clark, 2003). This is in agreement with the similar milk fat yield between treatments found in our study (Table 4). Ruiz et al. (2001), however, did not find differences in milk fat content of dairy cows fed fresh forage with or without monensin. No differences in milk fat and protein content were reported by van der Merwe et al. (2001) for dairy cows grazing kikuyu and clover pastures. Ipharraguerre and Clark (2003) reported that only in 3 of 24 studies, milk protein content was reduced by the administration of monensin. Milk total protein yield increased with monensin (0.890 vs. 0.860 kg/d; P = 0.001; Table 4). No differences in milk protein yield were reported for grazing dairy cows (Hayes et al., 1996). Monensin increased MUN concentration (10.3 vs. 9.7 mg/dL; P = 0.071; Table 4). However, other studies did not find differences in MUN content with dairy cows fed fresh temperate pastures (Ruiz et al., 2001). van der Merwe et al. (2001) reported lower MUN concentration for grazing dairy cows receiving monensin.
Long-term effects of monensin on milk production and composition are presented in Table 5. Most of the studies published have evaluated monensin effects only in the short term (McGuffey et al., 2001). Total lactation milk production adjusted to 305 d was 3% greater (P = 0.001) when cows received monensin with an averaged response of 0.7 kg/d or 214 kg per lactation compared with the control. Monensin did not affect 3.5% FCM production that averaged 24.2 kg/d (P = 0.532; Table 5). Monensin reduced milk fat content in the complete lactation (3.47 vs. 3.56%; P = 0.018), without affecting milk total protein content (3.27%; P = 0.356; Table 5). No differences were observed in milk fat yield (0.90 kg/d; P = 0.479); however, monensin increased milk total protein yield in the entire lactation 2.8% (0.850 vs. 0.827 kg/d; P = 0.001; 259 vs. 252 kg per lactation).
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. The use of monensin in the diet of grazing dairy cows supplemented with partial mixed ration resulted in greater mean BCS (2.92 vs. 2.82; P = 0.009; Table 6). Thirty days before the expected calving date, BCS was similar between treatments and averaged 3.46 (Figure 2). Monensin cows had greater BCS at calving (3.21 vs. 2.96; P = 0.009), at 21 DIM (2.89 vs. 2.73; P = 0.129), and at 105 DIM (2.82 vs. 2.66; P = 0.112; Figure 2). Change of BCS was also affected by monensin (Table 6). Cows on the control treatment lost more BCS between 30 d before parturition and calving date (–0.49 vs. –0.26; P = 0.010) and between 30 d before parturition and 21 DIM (–0.71 vs. –0.60; P = 0.311), respectively. Between 21 and 147 DIM, both treatment maintained BCS with an average change of –0.02 (P = 0.434). Similar results on BCS after calving were reported by Duffield et al. (1998) and Ramanzin et al. (1997). These results could be related to a better energy balance in favor of the monensin treatment, probably because of a lower mobilization of body reserves.
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). Monensin also decreased concentration of NEFA at 10 DIM (470 vs. 590 µeq/L; P = 0.078; Table 6). Other researchers have reported similar results (Ramanzin et al., 1997; Sauer et al., 1989; Duffield et al., 2003). On the other hand, previous grazing studies with low-producing dairy cows (Hayes et al., 1996; Maas et al., 2002) reported no differences in NEFA concentrations. Lack of agreement between previous grazing studies and our study might have been related to the earlier stage of lactation, greater milk production (Table 4), and type of diet (pasture supplemented with concentrate and TMR).
Plasma glucose concentration did not differ between treatments and averaged 60.2 mg/dL (P = 0.222; Table 6). This agrees with the results of Hayes et al. (1996), who reported no differences in plasma glucose concentration of grazing dairy cows. Vallimont et al. (2001) reported similar plasma glucose concentration in dairy cows fed TMR and receiving monensin prepartum. In a field study involving 251 Holstein cows (Duffield et al., 2003), plasma glucose concentration was not affected by monensin CRC administered 3 wk precalving. In other studies (Duffield et al., 1998; Green et al., 1999; Phipps et al., 2000), however, greater plasma glucose concentrations were observed when monensin was added to the diet, including a grazing study (Maas et al., 2002). Increased plasma glucose concentration is probably related to the action of this ionophore on propionic acid production in the rumen and gluconeogenesis in the liver (Ipharraguerre and Clark, 2003). In over 13 studies where monensin was administered to lactating dairy cows, plasma glucose was significantly increased in only 4 studies and in all of them in a small proportion (5.9%; Ipharraguerre and Clark, 2003). The lack of response on plasma glucose concentration to monensin does not deny the glucogenic effect of this ionophore, which was demonstrated by Arieli et al. (2001) using a tracer dose of U-13C-labeled glucose. That study found that monensin increased the distribution space and pool size of glucose without affecting its mean plasma concentration (Arieli et al., 2001).
Plasma urea nitrogen (PUN) was greater with the inclusion of monensin (P = 0.030; Table 6), in agreement with the greater MUN previously reported (Table 4). This agrees with previous studies that reported greater PUN in dairy cows receiving monensin (Green et al., 1999; Duffield et al., 2003), including a grazing study (Hayes et al., 1996). The increase in PUN can be related to the monensin capacity of decreasing ruminal degradation of proteins and peptides enhancing the absorption of amino acids and nitrogen at the small intestine (McGuffey et al., 2001; Ruiz et al., 2001). Others reported no differences in PUN when pasture- (Maas et al., 2002) or TMR-fed (Vallimont et al., 2001) cows received monensin.
Percentage of pregnancy was improved at first AI (44.8 vs. 20.7%; P = 0.049) and at wk 12 (75.9 vs. 55.2%; P = 0.101; Table 6). The greater mean BCS and lower mean NEFA concentration (Table 6) on the monensin treatment, resulting in an improvement in energy balance, could have influenced reproductive performance. It is well documented that negative energy balance during early lactation is associated with reduced fertility (Butler and Smith, 1989). In our study, a lesser negative energy balance in early lactation might have occurred even with a similar 3.5% FCM production (Table 4), which could indicate similar total milk energy. Our results suggest that monensin could play a significant role in improving the fertility of supplemented grazing dairy cows. Lean et al. (1993) proposed that monensin might improve reproductive performance if its administration is early enough to remove the negative effects of reduced DMI in early lactation. Other grazing studies (Hayes et al., 1996), however, reported no improvement of reproductive performance (measured by first AI, second AI, and cumulative pregnancy rates) when using monensin. More grazing studies with larger number of animals should be done to confirm our observations.
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CONCLUSIONS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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ACKNOWLEDGEMENTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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Received for publication July 5, 2004. Accepted for publication October 15, 2004.
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REFERENCES |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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