Lactational performance and milk fatty acid profile of Holstein cows in response to dietary fat supplements and forage:Concentrate ratio

Objective of this experiment was to investigate the lactation performance of dairy cows fed hydrogenated palm oil and yellow grease. Eight lactating multiparous Holstein cows, 55±9 d in milk (DIM), were used in a replicated 4×4 Latin square design during four 3-week periods to evaluate responses to diets with a lower (34:66) forage (alfalfa hay) to concentrate ratio (F:C) supplemented (on a DM basis) with no added fat (Control), 2% hydrogenated palm oil (HPO), 2% yellow grease (YG), and/or with a higher (45:55) F:C ratio supplemented with 2% yellow grease (YGHF). Data were collected during the last week of each period. Feeding fat and higher F:C ratio had no effect on milk yield but compared to HPO, YG increased milk yield (P<0.05), 4% fat-corrected milk (P<0.02), and energy-corrected milk (P<0.01). Fat supplementation tended (P<0.06) to increase milk fat content and yield but these were not affected by increasing F:C ratio. Milk fat content was not influenced by fat source but YG increased its yield compared to HPO. Changing F:C ratio from 34:66 to 45:55 decreased milk protein content (P<0.003) and yield (P<0.03). Also, YG tended to increase milk protein content and increased milk protein yield compared to HPO. Increasing F:C ratio from 34:66 to 45:55 increased (P<0.01) milk short-chain FA without affecting total milk fat conjugated linoleic acid, although feeding fat, especially YG compared to HPO, affected their concentrations substantially. Including fat and also YG compared to HPO tended (P<0.07) to increase and increased (P<0.01) total milk fat conjugated linoleic acid without affecting desaturase indices, respectively. Feeding fat decreased milk short-chain FA and increased long-chain FA (LCFA) with significant changes in C18:0 and cis-9 C18:1 concentration. Furthermore, YG decreased medium-chain FA and increased LCFA and total unsaturated FA of milk fat relative to HPO. Total-tract digestibility of dry- and organic-matter were greater in the YG diet than HPO (P<0.05 and P<0.04, respectively), however, it was not affected by fat compared to control or F:C ratio. Ruminal pH and volatile FA concentrations were similar among treatments, except for butyrate that was lower in cows fed HPO. In general, feeding yellow grease with low F:C ratio in alfalfa hay-based diets had no detrimental effects on nutrient digestibility but increased production responses and improved milk FA profile without inducing milk fat depression.