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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.
The effect of monensin on milk production was evaluated in 58 lactating Holstein cows (48 multiparous; 10 primiparous) grazing a mixed-alfalfa pasture and supplemented with a partial mixed ration in a completely randomized design with repeated measurements. Cows were paired by calving date, lactation number, previous lactation milk production, body weight, and body condition score and were assigned to one of 2 treatments: control or monensin. Cows on the monensin treatment received 2 monensin controlled-release capsules (335 mg/d for 90 d), one 30 d before the expecting calving date and the other 60 d after calving. Short-term (0 to 150 d in milk) and long-term (305-d adjusted lactation) effects of monensin were evaluated. Pasture (measured by difference between pre- and postgrazing pasture mass), supplements, and total dry matter intake did not differ between treatments and averaged 8.7, 14.1, and 22.9 kg/d, respectively. In the short-term, monensin increased milk production (27.7 vs. 26.6 kg/d) and milk protein yield (0.890 vs. 0.860 kg/d); milk fat yield was not affected (0.959 kg/d). Monensin decreased milk fat content (3.51 vs. 3.60%) with no changes in milk protein content (3.25%). In the long term, milk production and milk protein yield were also increased by monensin: 214 and 7 kg, respectively. Monensin reduced the loss of body condition score and increased percentage of pregnancy at first service (44.8 vs. 20.7%). Monensin improves production and reproduction performance of dairy cows grazing a mixed-alfalfa pasture and supplemented with a partial mixed ration.
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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