TMR versus grazing supplemented with TMR out or into the grazing plot: Productive response

Abstract Text: An experiment was carried out to study the effect of three contrasting feeding strategies involving TMR and grazing, during the first 60 days in milk of Holstein dairy cows. Thirty six multiparous dairy cows were blocked according to parity, expected calving date, body condition score (BCS; 2.9±0.37) and BW (641±49.2 kg) before calving, and were randomly allocated to follow one of three feeding treatments: TMR = total mix ratio (corn silage/concentrate mix 40/60; respectively), GR-one = one grazing session (AM: 0800 to 1400 h) supplemented with 50% of TMR out of the grazing plot and GR-two = two grazing sessions (AM: 0800 to 1400 h; PM: 1800 to 0400 h) supplemented with 50% of the TMR into the grazing plot. The three treatments were based on the same offer of energy (50 Mcal ENL/cow/d), differing in the source of feed (TMR vs grazing plus TMR) and the synchrony or not between the access to pasture and to TMR (GR-one vs GR-two). The cows were milked twice a day (04:30 and 15:00 h). Milk production was registered daily, milk composition weekly (samples from two consecutive milking) and BCS every two weeks (scale 1 to 5). A fresh daily strip of a fescue based pasture (3270±758 kgDM/ha) was open to each grazing treatment with an herbage allowance (above 4 cm) enough to reach 25 Mcal ENL per cow/d. A mix model was used (Glimmix procedure, SAS 9.2, 2010) to analyse the results with treatment, week and their interaction as fix effects and block as a random effect. A first order autoregressive heterogeneous (AR1) covariance structure was selected. TMR cows produced more milk, energy, protein and lactose (Table 1) than grazing cows. Daily fat production was not different between treatments, since TMR cows produced milk with less (p<0.05) or tendency for less (p<0.1) fat content than GR-two and GR-one treatments, respectively. Grazing treatments did not differ except on the tendency (p<0.1) for a higher milk fat content in GR-two than GR-one cows (Table 1). A reverse trend (p<0.1) was observed for BCS (2.9 vs 2.7 for GR-one and GR-two, respectively). The potential of GR-two cows to select a better mix of TMR and herbage than GR-one cows was not expressed in this trial. The long distance to the grazing plots (1.7 km) might have masked the potential benefits of GR-two feeding strategy.

Keywords: grazing, TMR, early lactation dairy cows, synchronizing