Impact of a total mixed ration or pasture/pasture silage-based feeding strategy in the initial stages of lactation of spring-calving dairy cows on milk production, composition and selected milk processability parameters

The objective of this experiment was to investigate the effect of feeding strategy on milk production, composition and selected processability parameters in the initial stages of lactation. Twenty Holstein Friesian cows were allocated to one of two dietary treatments (n = 10; 7 multiparous and 3 primiparous) in a randomised complete block design for 21 d from day 10 to day 31 post-calving. Treatment 1 (pasture-based system [PBS]) was a pasture/pasture silage-based diet where cows were offered ad libitum grazed pasture or pasture silage (when weather did not permit grazing) plus 3 kg DM/d or 5 kg DM/d concentrate supplementation, respectively. On average, cows grazed pasture for 7.5 d and were fed pasture silage indoors for 13.5 d. Treatment 2 (TMR) was a total mixed ration (TMR) diet made up of concentrate, plus maize silage, pasture silage, beet pulp, soya bean meal and straw. Multiparous cows were blocked on calving date and balanced for parity and milk yield. Primiparous cows were balanced for live weight. Milk attributes pertinent to composition and functionality (e.g., fatty acids and rennet coagulation time [RCT]) were examined over a 21-d experimental period from day 10 to day 31 post-calving. Cows offered PBS tended to have a lower test day milk yield (PBS = 24.2 kg/cow vs. TMR = 26.8 kg/cow, P = 0.09) and a greater milk urea nitrogen (MUN) content compared to TMR (PBS = 0.030 g/100 g milk vs. TMR = 0.013 g/100 g milk, P < 0.001). Most notably, PBS-derived milks had a greater (P < 0.001) concentration of cis-9 trans-11 conjugated linoleic acid (CLA) compared to TMR. In conclusion, milk produced during early lactation from both feeding strategies was suitable for processing. Feeding a TMR compared with ad libitum pasture/pasture silage had no impact on average milk pH, casein concentration or RCT. Cows fed a pasture/pasture silage-based diet produced milk with a desirable RCT for milk processing, while the higher MUN content from cows offered PBS did not impact the processability of milk. Furthermore, milk from cows offered PBS had greater concentrations of cis-9 trans-11 CLA, which may offer human health benefits.