Temporal variation in faecal n-alkane ratios and estimation of pasture intake in calves.
Bakker, ML; Alvarado, PI; Gonda, Horacio; Hidalgo, LG; Inza, MC; Wade, MH; Dalla Valle, DE; Otero, MJ; Yuño, MM
The temporal variation (between and within sampling days) in the faecal n-alkane ratios (C32/C31 and C32/C33), and the effect of AM or PM faecal sampling on the estimation of pasture intake, was studied in Holstein-Friesian calves in two independent trials. In Study 1, calves strip-grazed at different pasture allowances: Low or High (2.5 or 7.5 kg DM/100 kg LW/day). In Study 2, calves strip-grazed at different grazing time schedules but same total daily pasture allowance (4-h: one fresh grazing area/day for 4 h (11:00 AM to 3:00 PM) at a pasture allowance of 4.2 kg DM/100 kg LW, or 2x2-h: two fresh grazing areas/day, each one for 2 h (11:00 AM to 1:00 PM and 3:00 PM to 5:00 PM) at a pasture allowance of 2.1 kg DM/100 kg LW). In both trials, calves (LW range: 117-173 kg) were dosed orally with C32 embedded in paper stoppers twice a day. The variation between days in the faecal n-alkane ratios, estimated from the coefficient of variation (CV, %) over days 7 to 12 (Study 1) or 6 to 10 of dosing (Study 2), was not significantly different between pasture allowances (Low: 17%, High: 14%) or grazing time schedules (4-h: 16%, 2x2-h: 12%). In both studies, AM had significantly lower faecal n-alkane ratios than PM (p<0.01), therefore, significantly higher pasture intakes were estimated from AM compared with PM (Study 1: p<0.01, Study 2: p<0.001). The magnitude of the variation within sampling days in the faecal n-alkane ratios indicates that, in calves, more than one faecal sample per day should be taken to obtain a more reliable estimation of pasture intake under similar grazing conditions. In Study 1, the time required for the faecal concentration of C32 to reach stable levels was very short (day 2 of dosing), and suggests that the faecal sampling in calves might begin earlier than in present recommendations. Key words. n-alkanes, grazing, intake, calves.
Revista Argentina de Produccion Animal
2017, Volym: 37, nummer: 2, sidor: 1-9
Animal and Dairy Science
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