Investigating the effect of fatty acid supplementation on milk fat production and animal performance in genetically diverse grazing dairy cows during early to mid-lactation

The objective of this experiment was to investigate the effect of fatty acid (FA) supplementation on milk fat production and animal performance in genetically diverse grazing dairy cows during the high-risk period for reduced milk fat synthesis. Forty-five primiparous (mean ± SD; 58 ± 18 DIM and 415 ± 59 kg of BW) and 135 multiparous (45 ± 18 DIM and 497 ± 74 kg of BW) spring-calving dairy cows were blocked based on breed, Economic Breeding Index, parity, pre-experimental milk solids production, and BW and were then randomly assigned to 1 of 3 dietary treatments. The 3 dietary treatments were pasture supplemented with 3.6 kg of DM/cow per day of concentrate containing no supplemental fat (CON); pasture supplemented with 3.6 kg of DM/cow per day of concentrate containing a calcium salt of FA with a FA composition of 58% palmitic acid and 28% oleic acid (MIX); and pasture supplemented with 3.6 kg of DM/cow per day of concentrate containing a fat prill of FA with a FA composition of 97% palmitic acid (PA). The dietary treatments were offered during an 11-wk experimental period, which was then followed by a 6-wk carryover period. During the carryover period, cows received a common diet of pasture and 0.89 kg of DM/cow per day of a dairy concentrate supplement. Each dietary treatment group was comprised of 3 animal genetic groups (AG). Cows fed MIX tended to have greater milk yield, ECM yield, 3.5% FCM yield, fat yield and milk solids yield when compared with cows fed CON, but were similar to cows fed PA. Cows fed PA had greater milk fat concentration when compared with cows fed CON and MIX. Fatty acid supplementation affected the composition of milk fat produced, with cows fed MIX and PA having lower concentrations of de novo FA when compared with cows fed CON. Cows fed PA had greater concentrations of mixed FA when compared with cows fed MIX and CON, whereas cows fed MIX had greater concentrations of preformed FA when compared with cows fed CON and PA. Cows fed CON and PA had similar milk protein concentration but were both greater than cows fed MIX. There was no effect of FA supplementation during the carryover period on the majority of milk production outcomes. Milk fat production was affected by AG; however, there were no major interactions observed between FA supplementation and AG. Fatty acid supplementation of grazing dairy cows can increase milk fat concentration during the high-risk period for reduced milk fat synthesis but it is dependent on the FA composition of the supplemental ingredient. Overall, careful consideration is required when determining the economic sustainability of offering FA supplements to cows consuming high nutritive value pasture.